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WO2019037769A1 - Process - Google Patents

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Publication number
WO2019037769A1
WO2019037769A1 PCT/CN2018/102144 CN2018102144W WO2019037769A1 WO 2019037769 A1 WO2019037769 A1 WO 2019037769A1 CN 2018102144 W CN2018102144 W CN 2018102144W WO 2019037769 A1 WO2019037769 A1 WO 2019037769A1
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WO
WIPO (PCT)
Prior art keywords
formula
promoter
methanol
zeolite
process according
Prior art date
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PCT/CN2018/102144
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French (fr)
Inventor
Benjamin James DENNIS-SMITHER
John Glenn Sunley
Zhiqiang Yang
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BP China Holdings Ltd
BP PLC
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BP China Holdings Ltd
BP PLC
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Publication of WO2019037769A1 publication Critical patent/WO2019037769A1/en
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
    • C07C41/01—Preparation of ethers
    • C07C41/09—Preparation of ethers by dehydration of compounds containing hydroxy groups
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
    • B01J29/7038—MWW-type, e.g. MCM-22, ERB-1, ITQ-1, PSH-3 or SSZ-25

Definitions

  • This invention relates in general to a dehydration process and in particular to a process for the dehydration of methanol in the presence of a zeolite catalyst and a promoter compound.
  • WO 2004/074228 describes a process for preparing dimethyl ether in high yield by employing a dual-catalyst system.
  • Methanol is initially dehydrated over a hydrophilic solid acid catalyst such as gamma-alumina; unreacted methanol is then dehydrated over a second solid acid catalyst, a hydrophobic zeolite such as ZSM-5.
  • EP-A-1396483 and WO 2004/074228 exemplify the use of high reaction temperatures, typically 250 °C and higher. Whilst the use of such high reaction temperatures may be desirable to achieve acceptable reaction rates, a disadvantage is that at temperatures, typically in excess of 250 °C, hydrocarbons are co-produced with the dimethyl ether product and this typically leads to a reduction in catalytic performance.
  • WO 2011/027105 describes a process for the simultaneous dehydration of methanol and hydrolysis of methyl acetate.
  • the process can be conducted at reaction temperatures below 250 °C by employing a zeolite having a 2-dimensional framework structure comprising at least one channel having a 10-membered ring.
  • zeolites are zeolites of framework type FER typified by ferrierite and HEU typified by clinoptilolite.
  • the present invention provides a process for dehydrating methanol to dimethyl ether product in the presence of a catalyst and promoter, wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and the promoter is:
  • the promoters of the present invention allow productivity to dimethyl ether product to be improved in dehydration reactions of methanol which are carried out in the presence of 2-dimensional framework aluminosilicate zeolites having a maximum free sphere diameter of greater than 4.70 Angstroms.
  • a method of improving the productivity to dimethyl ether product in a process for dehydrating methanol in the presence of a catalyst and a promoter wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and the promoter is :
  • a promoter in a process for the catalytic dehydration of methanol to dimethyl ether to improve productivity to dimethyl ether product
  • the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms
  • the promoter is:
  • a further aspect of the present invention provides a process for dehydrating methanol to dimethyl ether product in the presence of a catalyst, wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and wherein prior to using the catalyst in the dehydration process, the catalyst has been impregnated with a promoter selected from:
  • the catalytic dehydration reaction of methanol can be represented by the following equation : 2 methanol dimethyl ether + water.
  • the catalyst belongs to the class of aluminosilicate zeolites.
  • Aluminosilicate zeolites are crystalline microporous materials which have framework structures constructed from tetrahedra of SiO 4 and AlO 4 that share vertices. Such tetrahedral species are generally referred to as TO 4 species wherein the T atom is silicon or aluminium.
  • Aluminium ‘T’ atoms can be partially or wholly replaced by one or more gallium, boron or iron atoms.
  • gallium, boron or iron modified zeolites are considered to fall within the definition of the term ‘aluminosilicate zeolites’ .
  • Silicoaluminophosphate structures containing PO 4 tetrahedra are not considered to be aluminosilicate materials and consequently, such silicoaluminophosphates, for example SAPO-type materials, are not within the scope of the present invention.
  • a zeolite framework topology contains a regular array of pores, channels and/or pockets that vary in size, shape and dimensionality. These framework topologies or structure types of zeolites are assigned three-letter structure codes by the Structure Commission of the International Zeolite Association, under the authority of IUPAC.
  • Zeolites may also be classified according to the size of their pores. Zeolites with pore openings limited by 8 T atoms in tetrahedral co-ordination are defined as “small pore zeolites” (8-membered rings) . Zeolites with pore openings limited by 10 T atoms in tetrahedral co-ordination are defined as “medium pore zeolites” (10-membered rings) . Zeolites with pore openings limited by 12 T atoms in tetrahedral co-ordination are defined as “large pore zeolites” (12-membered rings) .
  • a free diameter of the pore size is also used. This free diameter identifies the maximum size of the molecules that can enter a particular channel aperture. These dimensions will vary depending on the particular structure of the zeolite in question.
  • the extent to which the dehydration reaction is promoted may vary depending on factors such as the structure of the zeolite and nature of the promoter employed in the reaction. Desirably, to promote increased productivity to dimethyl ether, the channels of a zeolite must be of a size such that a promoter is able to diffuse freely through the zeolite channels.
  • maximum free sphere diameter is meant the diameter of the largest-free-sphere that can diffuse along the ‘a’ axis, ‘b’ axis or ‘c’ axis of a zeolite.
  • a zeolite has a maximum free sphere diameter of greater than 3.67 Angstroms.
  • Maximum sphere diameters can be calculated by Delaunay triangulation and details of the calculations can be found in Foster et al “A geometric solution to the largest-free-sphere problem in zeolite frameworks” Micropor. Mesopor. Mat. vol. 90, pgs 32-38, 2006. Calculated maximum sphere diameters are also provided in the above-mentioned International Zeolite Association (IZA) website.
  • IZA International Zeolite Association
  • Table A Maximum free sphere diameters of some typical zeolites are shown in Table A. The diameters provided are in respect of the ‘c’ axis except for the framework types MTT and MWW where the maximum free sphere diameters are in respect of the ‘a’ axis.
  • Table A 1-D, 2-D, 3-D indicate whether the zeolite has a 1-dimensional, 2-dimensional or 3-dimensional framework structure.
  • zeolites of framework codes HEU and FER such as clinoptilolite and ferrierite respectively do not have a maximum free sphere diameter of greater than 4.70 Angstroms and are not desirable for use in the present invention.
  • the zeolite has a maximum free sphere diameter of greater than or equal to 4.75 Angstroms, more preferably greater than 4.75 Angstroms.
  • the zeolite is a medium or large pore zeolite.
  • the zeolite is a large pore zeolite.
  • large pore zeolites are those of framework types, EON, IWV, SEW and USI.
  • the zeolite is a medium pore zeolite.
  • medium pore zeolites include those of the framework types MFS, MWW and TER.
  • Zeolite crystals contain pore or channel systems of molecular dimensions with fixed geometry and size and can be classified according to the number of channels running in different directions within the zeolite framework structure.
  • a zeolite is described as 1- dimensional, 2-dimensional or 3-dimensional if the zeolite has one, two or three channels in different directions, respectively.
  • Zeolites for use in the present invention possess a 2-dimensional framework structure.
  • Non-limiting examples of such 2-dimensional zeolites are those of framework types EON, IWV, SEW, USI, MFS, MWW and TER.
  • the zeolite has the framework type MWW, for example the zeolites PSH-3 and MCM-22.
  • zeolites are synthesised from synthesis mixtures comprising a silica source, an alumina source, alkali metal hydroxide and water in desired proportions.
  • the synthesis mixture is maintained, with or without agitation, under temperature, pressure and time conditions sufficient to form a crystalline aluminosilicate zeolite.
  • the resulting zeolite contains alkali metal as a cation.
  • Such cations may be replaced by known ion-exchange techniques.
  • the zeolite may be contacted with aqueous solutions of ammonium salts to substitute ammonium ions for the alkali metal cations.
  • Ammonium-form zeolites are also available commercially.
  • zeolites in their ammonium-form can be catalytically active, for use in the present invention it is preferred to utilise a zeolite in its hydrogen-form (H-form) .
  • H-form zeolites are commercially available.
  • an ammonium-form zeolite can be converted to the H-form by known techniques, for example by calcining the ammonium-form zeolite, in air or inert gas, at high temperature.
  • the zeolite is a hydrogen-form (H-form) zeolite.
  • a zeolite may be composited with at least one binder material.
  • the binder material may be a refactory inorganic oxide, such as silicas, aluminas, alumina-silicates, magnesium silicates, magnesium aluminium silicates, titanias and zirconias.
  • the relative proportions of zeolite and binder material in the composite may vary widely.
  • the binder material can be present in an amount of from 10%to 90%by weight of the composite.
  • the silica to alumina molar ratio of a zeolite may vary widely but suitably is in the range 10 to 300, for example in the range 20 to 280, such as in the range 20 to 100.
  • esters of Formula I and di-esters of Formula II may also be used in the present invention.
  • an alkyl carboxylate ester of Formula I may be a straight alkyl chain carboxylate ester or a branched alkyl chain carboxylate ester.
  • straight alkyl chain carboxylate esters of Formula I suitable for use in the present invention are methyl acetate, methyl propionate, methyl n-butyrate, methyl n-pentanoate, methyl n-hexanoate, methyl n-heptanoate and methyl n-octanoate.
  • the di-ester compound of Formula II is selected from at least one of dimethyl succinate, dimethyl glutarate and dimethyl adipate.
  • a promoter may be added as a component of the feed to the dehydration process.
  • a promoter may be generated in-situ by the addition to the process of any compound (a precursor compound) from which an alkyl carboxylate ester of Formula I or di-ester compound of Formula II can be generated in-situ.
  • the molar ratio of promoter to methanol is maintained throughout the dehydration reaction at less than 1. In some or all embodiments of the present invention the molar ratio of promoter to methanol is maintained in the range 0.000001 : 1 to less than 0.5 : 1, preferably in the range of 0.00005 : 1 to less than 0.5 : 1. In some or all embodiments of the present invention, the molar ratio of promoter to methanol is maintained in the range of 0.00001 : 1 to less than 0.5 : 1, for example 0.00005 : 1 to 0.2 : 1, such as 0.0001 : 1 to 0.2 : 1.
  • the molar ratio of promoter to methanol is maintained in the range of 0.01 : 1 to less than 0.5 : 1, for example 0.01 : 1 to 0.2 : 1, such as 0.02 : 1 to 0.2 : 1.
  • the total amount of promoter relative to the total amount of methanol is maintained throughout the dehydration reaction in an amount of at least 1 ppm.
  • the total amount of promoter relative to the total amount of methanol is maintained throughout the dehydration reaction in an amount of at least 0.001 mol%, for example in an amount of 0.001 mol%to less than 50 mol%, such as 0.001 mol%to 20 mol%, for instance 0.005 mol%to 20 mol%.
  • the total amount of promoter relative to the total amount of methanol is maintained throughout the dehydration reaction in an amount of at least 0.01 mol%, for example in an amount of 0.01 mol%to less than 50 mol%, such as 0.01 mol%to 20 mol%, for instance 0.05 to 20 mol%. In some or all embodiments of the present invention, the total amount of promoter relative to the total amount of methanol is maintained throughout the dehydration reaction in an amount of at least 1 mol%, for example in an amount of 1 mol%to less than 50 mol%, such as 1 mol%to 20 mol%, for instance 2 to 20 mol%.
  • the zeolite may have a silica to alumina molar ratio in the range 20 to 280, suitably in the range 20 to 100.
  • the promoter is di-ester compound of Formula II is selected from at least one of dimethyl succinate, dimethyl glutarate and dimethyl adipate and suitably the concentration of promoter relative to methanol is maintained in an amount of 0.01 to 20 mol%, for example 2 to 20 mol%
  • the zeolite is a medium pore zeolite, suitably of framework type MWW, for example the zeolites PSH-3 or MCM-22.
  • the zeolite may have a silica to alumina molar ratio in the range 20 to 280, suitably in the range 20 to 100.
  • the catalyst may be impregnated with the promoter prior to being used in the dehydration process.
  • the method of impregnation is not limited and any technique known in the art may be used, for example, incipient wetness technique or excess solution technique.
  • the incipient wetness technique is so-called because it requires that the volume of impregnating solution be predetermined so as to provide the minimum volume of solution necessary to just wet the entire surface of the support, with no excess liquid.
  • the excess solution technique as the name implies, requires an excess of the impregnating solution, the solvent being thereafter removed, usually by evaporation.
  • the promoter may be used as the impregnation solution directly, or a dilute solution of the promoter may be used.
  • the solvent for the impregnation solution may suitably be an aqueous solution, an organic solution, or a mixture of aqueous and organic solvent (s) , depending upon the solubility of the promoter being used; non-limiting examples of suitable solvents include water, alcohols, for example methanol, ethers, and mixtures thereof, such as aqueous alcoholic solutions, for example an aqueous methanol solution.
  • the dehydration process may be carried out as a standalone process.
  • the dehydration reaction is not, for example carried out as part of a co-production process, such as co-production processes for the production of acetic acid and dimethyl ether by dehydration of methanol and hydrolysis of a methyl acetate co-feed.
  • the feed components to the process are methanol and at least one promoter compound of Formula I or Formula II or a precursor compound thereof.
  • the product stream of the methanol dehydration reaction will comprise dimethyl ether, water, unconverted methanol and one or more compounds selected from promoter compounds of Formula I or Formula II and the precursor compounds of promoter compounds of Formula I or Formula II.
  • one or more components of the product stream of the dehydration process are recycled as feed to the process. In such instances one or both of dimethyl ether and water are additional feed components to the dehydration process.
  • the feed components to the dehydration process are methanol, at least one promoter selected from Formula I or Formula II and one or both of dimethyl ether and water.
  • the feed components to the process may be methanol and at least one precursor compound of the promoters of Formula or Formula II.
  • the feed components to the dehydration process are methanol, one or both of (i) at least one promoter compound of Formula I or Formula II and (ii) at least one precursor compound of a promoter compound of Formula I or Formula II; and one or both of dimethyl ether and water.
  • the feed components to the process may be supplied to the process in one or more feed streams.
  • methyl acetate is not a component of the feed to the process.
  • the dehydration process is carried out as a heterogeneous process, either as a vapour phase heterogeneous process or as a liquid phase heterogeneous process.
  • the type of reactor used for the dehydration process is not limited, and it may be suitably carried out in any type of reactor within which a vapour phase heterogeneous process or a liquid phase heterogeneous process may be performed.
  • Non-limiting types of reactors with which the dehydration reaction may be performed include tank reactors, multi-tubular reactors, plug-flow reactors, loop reactors, fluidized bed reactors, and reactive distillation columns.
  • the dehydration process may be carried out at a temperature of from 100 to 300 °C. In some or all embodiments of the present invention, the dehydration process is carried out at a temperature of from 140 to 250 °C, for example from 150 to 250 °C.
  • the dehydration process may be carried out at atmospheric pressure or at elevated pressure.
  • the dehydration process is carried out at a total pressure of atmospheric pressure to 3000kPa. Where the process is conducted in the liquid phase, higher total pressures, such as 4000kPa to 10,000kPa, may be required to maintain the dimethyl ether product in solution.
  • the dehydration process is carried out as a heterogeneous vapour phase process at a total pressure of atmospheric pressure to 3000kPa.
  • the temperature may be from 100 to 300 °C, such as from 140 to 250 °C, for example from 150 to 250 °C.
  • the process may be carried out at a total gas hourly space velocity (GHSV) in the range 500 to 40,000 h -1 .
  • GHSV total gas hourly space velocity
  • the process may be carried out at a total liquid hourly space velocity (LHSV) in the range 0.2 to 20 h -1 .
  • LHSV liquid hourly space velocity
  • the dehydration process may be carried out using one or more beds of zeolite catalyst, suitably selected from fixed bed, fluidised bed, and moving beds of catalyst.
  • the dehydration process may be operated as either a continuous or a batch process, preferably as a continuous process.
  • the dehydration process generates a crude reaction product comprising dimethyl ether and water as reaction products, unreacted methanol and one or more promoter or precursor compounds.
  • One or more components of the crude reaction product may be recycled as feed to the process.
  • Dimethyl ether may be recovered from the crude reaction product by any suitable method, for example by distillation methods.
  • the productivity of catalysts will typically decrease over time on stream; in industrially applied catalytic processes, one of the ways by which the decrease in productivity may be compensated for is by increasing the reaction temperature to maintain a consistent productivity.
  • a disadvantage of increasing the temperature of the reaction is that this may lead to an increase in undesirable by-products or may result in a decrease in selectivity; another disadvantage of increasing the temperature of the reaction is that such an increase in temperature may accelerate the rate of catalyst deactivation.
  • decreases in productivity of the catalyst may be at least in part compensated for by increasing the relative concentration of the promoter in the methanol feed, and thus may reduce or eliminate the need for an increase in temperature to compensate for any reduction in productivity which may occur with time on stream; similarly, decreases in productivity of the catalyst may be at least in part compensated for by changing the promoter used or by adding a second or further additional promoter compound to the methanol feed as the time on stream increases.
  • promoters as described herein may result in an increase in the stability of the catalyst and may make the catalyst more resistant to deactivation by impurities present in the methanol feed.
  • a catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and wherein prior to using the catalyst in the dehydration process, the catalyst has been impregnated with a promoter selected from:
  • the feed to the dehydration process comprises methanol and may optionally comprise other components, for example dimethyl ether, water, or at least one compound which is a promoter compound of Formula I or Formula II or a precursor compound thereof.
  • SAR indicates the silica : alumina molar ratio of a zeolite
  • 2-D indicates a 2-dimensional framework structure.
  • the zeolites (except MCM-22) were obtained in ammonium-form from Zeolyst International. MCM-22 can be prepared using methods reported in the literature and can also be purchased commercially.
  • the zeolites were utilised in the methanol dehydration reactions in the H-form by calcination of the ammonium form of the zeolite in air at 500 °C.
  • the methyl ester compounds were essentially pure compounds (a total organic nitrogen content of about 0.1 ppm, expressed as nitrogen on a ppm by weight basis) and were obtained from Sigma-Aldrich or Brenntag UK Limited.
  • the diester compounds were obtained from Alfa Aesar or Acros Organics.
  • This Example demonstrates the effect of various alkyl carboxylate ester promoter compounds on the dehydration of methanol employing 2-dimensional zeolite catalysts.
  • the reactions were conducted in a 16-channel parallel fixed-bed stainless steel reactor system. Each reactor (2 mm internal diameter) was heated to maintain a temperature of 150 °C. Each reactor housed a 25 mg bed of catalyst (having particle size fraction of 100 to 200 microns diameter) loaded on top of a 6cm deep bed of an inert material (carborundum) . The reactor volume above the catalyst was also packed with carborundum.
  • Each reactor was maintained at a temperature of 150 °C and at a total pressure of 1100kPa throughout the reactions.
  • a gaseous feed comprising 10 mol%methanol and inert gas was introduced into the reactor and allowed to flow through the catalyst bed for a period of 48 hours at which point a promoter compound was added to the feed to achieve a gaseous feed comprising 10 mol%methanol and 5 mol%promoter compound (relative to methanol) .
  • This gaseous feed comprising the promoter compound was introduced into the reactor for a period of 24 hours at a constant flow rate of methanol of 13 mmol h -1 and a constant promoter flow rate of 0.7 mmol h -1 .
  • the effluent stream from each reactor was diluted with inert gas (nitrogen) and was periodically analysed by online gas chromatography to determine the yield of dimethyl ether product.
  • the observed space time yields to dimethyl ether product are also provided in Table 2.
  • This Example demonstrates the effect of a di-ester compound on the dehydration of methanol employing 2-dimensional zeolite catalysts.
  • the methanol dehydration reaction was carried out using the catalysts and di-ester compound specified in Table 3 below.
  • the dehydration reaction was carried out using a 16-channel parallel fixed-bed stainless steel reactor system.
  • Each reactor (10 mm internal diameter) housed a catalyst bed of 0.168 g catalyst diluted with 0.337 g silica.
  • the particle size of the catalyst and silica were in the range 450 to 900 microns in diameter.
  • the catalyst bed was loaded on top of a 6.5 cm deep bed of an inert material (quartz sand) .
  • the reactor volume above the catalyst bed was also packed with quartz sand.
  • Each reactor was maintained at a temperature of 150 °C and at a total pressure of 1100kPa throughout the reactions.
  • a gaseous feed comprising 10 mol%methanol and inert gas was introduced into the reactor and allowed to flow through the catalyst bed for a period of 48 hours at which point a promoter compound was added to the feed to achieve a gaseous feed comprising 10 mol%methanol and 5 mol%promoter compound (relative to methanol) .
  • This gaseous feed comprising the promoter compound was introduced into the reactor for a period of 24 hours at a constant flow rate of methanol of 45 mmol h -1 and a constant promoter flow rate of 2.3 mmol h -1 .
  • This Example demonstrates the effect of different concentrations of various alkyl carboxylate ester and di-ester compounds on the catalytic dehydration of methanol in the presence of the zeolite PSH-3.
  • the reactions were conducted in a 16-channel parallel fixed-bed stainless steel reactor system. Each reactor (2 mm internal diameter) was heated to maintain a temperature of 150 °C. Each reactor housed a 25 mg bed of catalyst (having particle size fraction of 100 to 200 microns diameter) loaded on top of a 6cm deep bed of an inert material (carborundum) . The reactor volume above the catalyst was also packed with carborundum.
  • Each reactor was maintained at a temperature of 150 °C and at a total pressure of 1100kPa throughout the reactions.
  • a gaseous feed comprising 10 mol%methanol and inert gas was introduced into the reactor and allowed to flow through the catalyst bed for a period of 48 hours at which point a promoter compound was added to the feed to achieve a gaseous feed comprising 10 mol%methanol and 0.001, 0.01 or 0.1 mol%promoter compound (relative to methanol) .
  • This gaseous feed comprising the promoter compound was introduced into the reactor for a period of 24 hours at a constant flow rate of methanol of 13 mmol h -1 and a constant promoter flow rate of 0.00013, 0.0013 or 0.013 mmol h -1 .
  • the effluent stream from each reactor was diluted with inert gas (nitrogen) and was periodically analysed by online gas chromatography to determine the yield of dimethyl ether product.
  • the observed space time yields to dimethyl ether product are provided in Table 4.

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Abstract

L'invention concerne un procédé de déshydratation de méthanol en éther diméthylique en présence d'une zéolite d'aluminosilicate bidimensionnelle ayant un diamètre de sphère libre maximal supérieur à 4,70 Angströms, et un promoteur de formule I CnH(2n+1)CO2CH3 dans laquelle n = 1 à 11 ou formule II CmH2m(CO2CH3)2 dans laquelle m = 2 à 7 et le rapport molaire du promoteur au méthanol est maintenu à moins de 1.The invention relates to a process for the dehydration of methanol to dimethyl ether in the presence of a two-dimensional aluminosilicate zeolite having a maximum free sphere diameter greater than 4.70 Angstroms, and a promoter of formula IC n H (2n + 1) CO 2 CH 3 wherein n = 1 to 11 or formula II C m H 2m (CO 2 CH 3) 2 wherein m = 2-7 and the molar ratio of methanol to promoter is maintained at less than 1.

Description

PROCESS
This invention relates in general to a dehydration process and in particular to a process for the dehydration of methanol in the presence of a zeolite catalyst and a promoter compound.
Industrial processes for the dehydration of methanol to dimethyl ether using non-zeolitic catalysts such as alumina are known. Such processes employing alumina catalysts are described, for example in EP-A-1396483.
Processes for the dehydration of alcohols such as methanol employing zeolite catalysts are known and described, for example in WO 2004/074228.
WO 2004/074228 describes a process for preparing dimethyl ether in high yield by employing a dual-catalyst system. Methanol is initially dehydrated over a hydrophilic solid acid catalyst such as gamma-alumina; unreacted methanol is then dehydrated over a second solid acid catalyst, a hydrophobic zeolite such as ZSM-5.
EP-A-1396483 and WO 2004/074228 exemplify the use of high reaction temperatures, typically 250 ℃ and higher. Whilst the use of such high reaction temperatures may be desirable to achieve acceptable reaction rates, a disadvantage is that at temperatures, typically in excess of 250 ℃, hydrocarbons are co-produced with the dimethyl ether product and this typically leads to a reduction in catalytic performance.
WO 2011/027105 describes a process for the simultaneous dehydration of methanol and hydrolysis of methyl acetate. The process can be conducted at reaction temperatures below 250 ℃ by employing a zeolite having a 2-dimensional framework structure comprising at least one channel having a 10-membered ring. Examples of such zeolites are zeolites of framework type FER typified by ferrierite and HEU typified by clinoptilolite.
Processes for the co-production of acetic acid and dimethyl ether by the dehydration of methanol and hydrolysis of methyl acetate in the presence of zeolites having a 2-dimensional framework structure are also described, for example in WO 2013/124404 and WO 2013/124423.
Processes in which methanol-containing streams are dehydrated over solid acid catalysts such as heteropolyacids, gamma-aluminas or zeolites are described, for example in WO 2015/193186 and WO 2015/193188.
Applicant has now found that compounds which are (i) alkyl carboxylate esters of Formula I C nH  (2n+1) CO 2CH 3 or (ii) di-ester compounds of Formula II C mH 2m (CO 2CH 3)  2 in which Formulae n = 1 to 11 and m = 2 to 7, have a beneficial effect on the rate of dehydration of methanol reactions carried out in the presence of aluminosilicate zeolites which have a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms.
Accordingly, the present invention provides a process for dehydrating methanol to dimethyl ether product in the presence of a catalyst and promoter, wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and the promoter is:
(i) at least one an alkyl carboxylate ester, C nH  (2n+1) CO 2CH 3 (Formula I) ; or
(ii) at least one di-ester compound, C mH 2m (CO 2CH 3)  2 (Formula II) , wherein in Formula I, n = 1 to 11; and in Formula II, m = 2 to 7 and wherein and the molar ratio of promoter to methanol is maintained at less than 1.
Advantageously, the promoters of the present invention allow productivity to dimethyl ether product to be improved in dehydration reactions of methanol which are carried out in the presence of 2-dimensional framework aluminosilicate zeolites having a maximum free sphere diameter of greater than 4.70 Angstroms.
Also, according to the present invention there is provided a method of improving the productivity to dimethyl ether product in a process for dehydrating methanol in the presence of a catalyst and a promoter, wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and the promoter is :
(i) at least one an alkyl carboxylate ester, C nH  (2n+1) CO 2CH 3 (Formula I) ; or
(ii) at least one di-ester compound, C mH 2m (CO 2CH 3)  2 (Formula II) , wherein in Formula I, n = 1 to 11; and in Formula II, m = 2 to 7 and wherein and the molar ratio of promoter to methanol is maintained at less than 1.
Yet further according to the present invention there is provided the use of a promoter in a process for the catalytic dehydration of methanol to dimethyl ether to improve productivity to dimethyl ether product wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and the promoter is:
(i) at least one an alkyl carboxylate ester, C nH  (2n+1) CO 2CH 3 (Formula I) ; or
(ii) at least one di-ester compound, C mH 2m (CO 2CH 3)  2 (Formula II) , wherein in Formula I, n = 1 to 11; and in Formula II, m = 2 to 7 and wherein and the molar ratio of promoter to methanol is maintained at less than 1.
A further aspect of the present invention provides a process for dehydrating methanol to dimethyl ether product in the presence of a catalyst, wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and wherein prior to using the catalyst in the dehydration process, the catalyst has been impregnated with a promoter selected from:
(i) at least one an alkyl carboxylate ester, C nH  (2n+1) CO 2CH 3 (Formula I) ; or
(ii) at least one di-ester compound, C mH 2m (CO 2CH 3)  2 (Formula II) , wherein in Formula I, n = 1 to 11; and in Formula II, m = 2 to 7.
The catalytic dehydration reaction of methanol can be represented by the following equation : 2 methanol
Figure PCTCN2018102144-appb-000001
dimethyl ether + water.
For use in the present invention, the catalyst belongs to the class of aluminosilicate zeolites. Aluminosilicate zeolites are crystalline microporous materials which have framework structures constructed from tetrahedra of SiO 4 and AlO 4 that share vertices. Such tetrahedral species are generally referred to as TO 4 species wherein the T atom is silicon or aluminium. Aluminium ‘T’ atoms can be partially or wholly replaced by one or more gallium, boron or iron atoms. For the purposes of the present invention, such gallium, boron or iron modified zeolites are considered to fall within the definition of the term ‘aluminosilicate zeolites’ .
Silicoaluminophosphate structures containing PO 4 tetrahedra are not considered to be aluminosilicate materials and consequently, such silicoaluminophosphates, for example SAPO-type materials, are not within the scope of the present invention.
A zeolite framework topology contains a regular array of pores, channels and/or pockets that vary in size, shape and dimensionality. These framework topologies or structure types of zeolites are assigned three-letter structure codes by the Structure Commission of the International Zeolite Association, under the authority of IUPAC.
A description of zeolites, their framework codes, structure, dimensionality, properties and methods of synthesis can be found in The Atlas of Zeolite Framework Types (C.  Baerlocher, W.M. Meier, D.H. Olson, 5 th Ed. Elsevier, Amsterdam, 2001) in conjunction with the web-based version ( http: //www. iza-structure. org/databases/) .
Zeolites may also be classified according to the size of their pores. Zeolites with pore openings limited by 8 T atoms in tetrahedral co-ordination are defined as “small pore zeolites” (8-membered rings) . Zeolites with pore openings limited by 10 T atoms in tetrahedral co-ordination are defined as “medium pore zeolites” (10-membered rings) . Zeolites with pore openings limited by 12 T atoms in tetrahedral co-ordination are defined as “large pore zeolites” (12-membered rings) .
In addition to the topological description of zeolite pore size, a free diameter of the pore size is also used. This free diameter identifies the maximum size of the molecules that can enter a particular channel aperture. These dimensions will vary depending on the particular structure of the zeolite in question.
The extent to which the dehydration reaction is promoted may vary depending on factors such as the structure of the zeolite and nature of the promoter employed in the reaction. Desirably, to promote increased productivity to dimethyl ether, the channels of a zeolite must be of a size such that a promoter is able to diffuse freely through the zeolite channels.
In the present specification and claims, by “maximum free sphere diameter” is meant the diameter of the largest-free-sphere that can diffuse along the ‘a’ axis, ‘b’ axis or ‘c’ axis of a zeolite. In the present invention, a zeolite has a maximum free sphere diameter of greater than 3.67 Angstroms. Maximum sphere diameters can be calculated by Delaunay triangulation and details of the calculations can be found in Foster et al “A geometric solution to the largest-free-sphere problem in zeolite frameworks” Micropor. Mesopor. Mat. vol. 90, pgs 32-38, 2006. Calculated maximum sphere diameters are also provided in the above-mentioned International Zeolite Association (IZA) website.
Maximum free sphere diameters of some typical zeolites are shown in Table A. The diameters provided are in respect of the ‘c’ axis except for the framework types MTT and MWW where the maximum free sphere diameters are in respect of the ‘a’ axis. In Table A, 1-D, 2-D, 3-D indicate whether the zeolite has a 1-dimensional, 2-dimensional or 3-dimensional framework structure.
Table A
Figure PCTCN2018102144-appb-000002
As is shown in Table A, zeolites of framework codes HEU and FER, such as clinoptilolite and ferrierite respectively do not have a maximum free sphere diameter of greater than 4.70 Angstroms and are not desirable for use in the present invention.
In some or all embodiments of the present invention, the zeolite has a maximum free sphere diameter of greater than or equal to 4.75 Angstroms, more preferably greater than 4.75 Angstroms.
In some or all embodiments of the present invention, the zeolite is a medium or large pore zeolite.
In some or all embodiments of the present invention, the zeolite is a large pore zeolite. Non-limiting examples of large pore zeolites are those of framework types, EON, IWV, SEW and USI.
In some or all embodiments of the present invention, the zeolite is a medium pore zeolite. Non-limiting examples of medium pore zeolites include those of the framework types MFS, MWW and TER.
Zeolite crystals contain pore or channel systems of molecular dimensions with fixed geometry and size and can be classified according to the number of channels running in different directions within the zeolite framework structure. A zeolite is described as 1- dimensional, 2-dimensional or 3-dimensional if the zeolite has one, two or three channels in different directions, respectively. Zeolites for use in the present invention possess a 2-dimensional framework structure. Non-limiting examples of such 2-dimensional zeolites are those of framework types EON, IWV, SEW, USI, MFS, MWW and TER.
In some or all embodiments of the present invention, the zeolite has the framework type MWW, for example the zeolites PSH-3 and MCM-22.
Typically, zeolites are synthesised from synthesis mixtures comprising a silica source, an alumina source, alkali metal hydroxide and water in desired proportions. The synthesis mixture is maintained, with or without agitation, under temperature, pressure and time conditions sufficient to form a crystalline aluminosilicate zeolite. The resulting zeolite contains alkali metal as a cation. Such cations may be replaced by known ion-exchange techniques. For example, the zeolite may be contacted with aqueous solutions of ammonium salts to substitute ammonium ions for the alkali metal cations. Ammonium-form zeolites are also available commercially.
Whilst zeolites in their ammonium-form can be catalytically active, for use in the present invention it is preferred to utilise a zeolite in its hydrogen-form (H-form) . H-form zeolites are commercially available. Alternatively, an ammonium-form zeolite can be converted to the H-form by known techniques, for example by calcining the ammonium-form zeolite, in air or inert gas, at high temperature.
In some or all embodiments of the present invention, the zeolite is a hydrogen-form (H-form) zeolite.
For use in the present invention, a zeolite may be composited with at least one binder material. The binder material may be a refactory inorganic oxide, such as silicas, aluminas, alumina-silicates, magnesium silicates, magnesium aluminium silicates, titanias and zirconias.
For use in the present invention the relative proportions of zeolite and binder material in the composite may vary widely. Suitably, the binder material can be present in an amount of from 10%to 90%by weight of the composite.
For use in the present invention, the silica to alumina molar ratio of a zeolite may vary widely but suitably is in the range 10 to 300, for example in the range 20 to 280, such as in the range 20 to 100.
Promoter compounds for use in the present invention are (i) at least one alkyl carboxylate ester of Formula I, C nH  (2n+1) CO 2CH 3 wherein n = 1 to 11 or (ii) at least one di-ester compound of Formula II, C mH 2m (CO 2CH 3)  2 wherein m = 2 to 7.
Mixtures of esters of Formula I and di-esters of Formula II may also be used in the present invention.
In some or all embodiments of the present invention, the alkyl carboxylate ester of Formula I is an alkyl carboxylate ester wherein n = 1 to 9, such as n = 2 to 7, for example wherein n = 3 to 7.
In the present invention, an alkyl carboxylate ester of Formula I may be a straight alkyl chain carboxylate ester or a branched alkyl chain carboxylate ester.
In some or all embodiments of the present invention, the alkyl carboxylate ester of Formula I is a straight alkyl chain carboxylate ester wherein n = 1 to 9.
In some or all embodiments of the present invention, the alkyl carboxylate ester of Formula I is a straight alkyl chain carboxylate ester wherein n = 2 to 7.
Specific non-limiting examples of straight alkyl chain carboxylate esters of Formula I suitable for use in the present invention are methyl acetate, methyl propionate, methyl n-butyrate, methyl n-pentanoate, methyl n-hexanoate, methyl n-heptanoate and methyl n-octanoate.
In some or all embodiments of the present invention, the di-ester compound of Formula II is a di-ester wherein m = 2 to 4.
In some or all embodiments of the present invention, the di-ester compound of Formula II is selected from at least one of dimethyl succinate, dimethyl glutarate and dimethyl adipate.
In the present invention, a promoter may be added as a component of the feed to the dehydration process. Alternatively and/or additionally, a promoter may be generated in-situ by the addition to the process of any compound (a precursor compound) from which an alkyl carboxylate ester of Formula I or di-ester compound of Formula II can be generated in-situ.
Precursor compounds which can be used for the in-situ generation of the alkyl carboxylate esters promoters of Formula I, C nH  (2n+1) CO 2CH 3, wherein n = 1 to 11, include compounds of formula C pH  (2p+1) CO 2X wherein the value of p corresponds to that of n in  Formula I and X is selected from hydrogen, a C 2 or higher alkyl group, halogen, such as chlorine, and a -C (=O) -R 1 group wherein R 1 is hydrogen or an alkyl group.
Precursor compounds which can be used for the in-situ generation of the di-ester promoter compounds of Formula II, C mH 2m (CO 2CH 3)  2 wherein m = 2 to 7, include compounds of formula C dH  (2d) (CO 2X)  2 wherein the value of d corresponds to that of m in Formula II and each X may be the same or different and is selected from hydrogen, a C 2 or higher alkyl group, halogen, such as chlorine, and a -C (=O) -R 1 group wherein R 1 is hydrogen or an alkyl group.
In the present invention the molar ratio of promoter to methanol is maintained throughout the dehydration reaction at less than 1. In some or all embodiments of the present invention the molar ratio of promoter to methanol is maintained in the range 0.000001 : 1 to less than 0.5 : 1, preferably in the range of 0.00005 : 1 to less than 0.5 : 1. In some or all embodiments of the present invention, the molar ratio of promoter to methanol is maintained in the range of 0.00001 : 1 to less than 0.5 : 1, for example 0.00005 : 1 to 0.2 : 1, such as 0.0001 : 1 to 0.2 : 1. In some or all embodiments of the present invention, the molar ratio of promoter to methanol is maintained in the range of 0.01 : 1 to less than 0.5 : 1, for example 0.01 : 1 to 0.2 : 1, such as 0.02 : 1 to 0.2 : 1.
Suitably, in the present invention the total amount of promoter relative to the total amount of methanol is maintained throughout the dehydration reaction in an amount of at least 1 ppm. In some or all embodiments of the present invention, the total amount of promoter relative to the total amount of methanol is maintained throughout the dehydration reaction in an amount of at least 0.001 mol%, for example in an amount of 0.001 mol%to less than 50 mol%, such as 0.001 mol%to 20 mol%, for instance 0.005 mol%to 20 mol%. In some or all embodiments of the present invention, the total amount of promoter relative to the total amount of methanol is maintained throughout the dehydration reaction in an amount of at least 0.01 mol%, for example in an amount of 0.01 mol%to less than 50 mol%, such as 0.01 mol%to 20 mol%, for instance 0.05 to 20 mol%. In some or all embodiments of the present invention, the total amount of promoter relative to the total amount of methanol is maintained throughout the dehydration reaction in an amount of at least 1 mol%, for example in an amount of 1 mol%to less than 50 mol%, such as 1 mol%to 20 mol%, for instance 2 to 20 mol%.
In some or all embodiments of the present invention, the promoter is an alkyl carboxylate ester of Formula I, suitably an alkyl carboxylate ester of Formula I which is a straight alkyl chain carboxylate ester wherein n = 1 to 9, preferably n = 2 to 7, for example wherein n = 3 to 7, and suitably the concentration of promoter relative to methanol is maintained in an amount of 0.01 to 20 mol%, for example 2 to 20 mol%, and the zeolite is a medium pore zeolite, suitably selected from zeolites of framework type MWW, such as MCM-22 or PSH-3. In these embodiments, the zeolite may have a silica to alumina molar ratio in the range 20 to 280, suitably in the range 20 to 100.
In some or all embodiments of the present invention, the promoter is di-ester compound of Formula II is selected from at least one of dimethyl succinate, dimethyl glutarate and dimethyl adipate and suitably the concentration of promoter relative to methanol is maintained in an amount of 0.01 to 20 mol%, for example 2 to 20 mol%, and the zeolite is a medium pore zeolite, suitably of framework type MWW, for example the zeolites PSH-3 or MCM-22. In these embodiments, the zeolite may have a silica to alumina molar ratio in the range 20 to 280, suitably in the range 20 to 100.
In some or all embodiments of the present invention, the catalyst may be impregnated with the promoter prior to being used in the dehydration process. The method of impregnation is not limited and any technique known in the art may be used, for example, incipient wetness technique or excess solution technique. The incipient wetness technique is so-called because it requires that the volume of impregnating solution be predetermined so as to provide the minimum volume of solution necessary to just wet the entire surface of the support, with no excess liquid. The excess solution technique as the name implies, requires an excess of the impregnating solution, the solvent being thereafter removed, usually by evaporation. The promoter may be used as the impregnation solution directly, or a dilute solution of the promoter may be used. When a dilute solution of promoter is used, the solvent for the impregnation solution may suitably be an aqueous solution, an organic solution, or a mixture of aqueous and organic solvent (s) , depending upon the solubility of the promoter being used; non-limiting examples of suitable solvents include water, alcohols, for example methanol, ethers, and mixtures thereof, such as aqueous alcoholic solutions, for example an aqueous methanol solution.
Suitably, in the present invention, the dehydration process may be carried out as a standalone process. In such cases the dehydration reaction is not, for example carried out  as part of a co-production process, such as co-production processes for the production of acetic acid and dimethyl ether by dehydration of methanol and hydrolysis of a methyl acetate co-feed. Thus, suitably, in the present invention, the feed components to the process are methanol and at least one promoter compound of Formula I or Formula II or a precursor compound thereof.
However, typically, the product stream of the methanol dehydration reaction will comprise dimethyl ether, water, unconverted methanol and one or more compounds selected from promoter compounds of Formula I or Formula II and the precursor compounds of promoter compounds of Formula I or Formula II. Thus, in some or all embodiments of the present invention, one or more components of the product stream of the dehydration process are recycled as feed to the process. In such instances one or both of dimethyl ether and water are additional feed components to the dehydration process.
Thus, in some or all embodiments of the present invention the feed components to the dehydration process are methanol, at least one promoter selected from Formula I or Formula II and one or both of dimethyl ether and water.
In instances where it is desired to generate the promoter in situ in the dehydration process the feed components to the process may be methanol and at least one precursor compound of the promoters of Formula or Formula II.
Thus, in some or all embodiments of the present invention the feed components to the dehydration process are methanol, one or both of (i) at least one promoter compound of Formula I or Formula II and (ii) at least one precursor compound of a promoter compound of Formula I or Formula II; and one or both of dimethyl ether and water.
The feed components to the process may be supplied to the process in one or more feed streams.
Preferably, methyl acetate is not a component of the feed to the process.
The dehydration process is carried out as a heterogeneous process, either as a vapour phase heterogeneous process or as a liquid phase heterogeneous process.
The type of reactor used for the dehydration process is not limited, and it may be suitably carried out in any type of reactor within which a vapour phase heterogeneous process or a liquid phase heterogeneous process may be performed. Non-limiting types of reactors with which the dehydration reaction may be performed include tank reactors,  multi-tubular reactors, plug-flow reactors, loop reactors, fluidized bed reactors, and reactive distillation columns.
The dehydration process may be carried out at a temperature of from 100 to 300 ℃. In some or all embodiments of the present invention, the dehydration process is carried out at a temperature of from 140 to 250 ℃, for example from 150 to 250 ℃.
Suitably, the dehydration process may be carried out at atmospheric pressure or at elevated pressure.
In some or all embodiments of the present invention, the dehydration process is carried out at a total pressure of atmospheric pressure to 3000kPa. Where the process is conducted in the liquid phase, higher total pressures, such as 4000kPa to 10,000kPa, may be required to maintain the dimethyl ether product in solution.
In some or all embodiments of the present invention, the dehydration process is carried out as a heterogeneous vapour phase process at a total pressure of atmospheric pressure to 3000kPa. In these embodiments, the temperature may be from 100 to 300 ℃, such as from 140 to 250 ℃, for example from 150 to 250 ℃.
For vapour phase processes, the process may be carried out at a total gas hourly space velocity (GHSV) in the range 500 to 40,000 h -1.
For liquid phase processes, the process may be carried out at a total liquid hourly space velocity (LHSV) in the range 0.2 to 20 h -1.
The dehydration process may be carried out using one or more beds of zeolite catalyst, suitably selected from fixed bed, fluidised bed, and moving beds of catalyst.
The dehydration process may be operated as either a continuous or a batch process, preferably as a continuous process.
The dehydration process generates a crude reaction product comprising dimethyl ether and water as reaction products, unreacted methanol and one or more promoter or precursor compounds. One or more components of the crude reaction product may be recycled as feed to the process.
Dimethyl ether may be recovered from the crude reaction product by any suitable method, for example by distillation methods.
Without being bound by theory, the productivity of catalysts will typically decrease over time on stream; in industrially applied catalytic processes, one of the ways by which the decrease in productivity may be compensated for is by increasing the reaction  temperature to maintain a consistent productivity. A disadvantage of increasing the temperature of the reaction is that this may lead to an increase in undesirable by-products or may result in a decrease in selectivity; another disadvantage of increasing the temperature of the reaction is that such an increase in temperature may accelerate the rate of catalyst deactivation. However, without wishing to be bound by theory, it is believed that in the present invention, decreases in productivity of the catalyst may be at least in part compensated for by increasing the relative concentration of the promoter in the methanol feed, and thus may reduce or eliminate the need for an increase in temperature to compensate for any reduction in productivity which may occur with time on stream; similarly, decreases in productivity of the catalyst may be at least in part compensated for by changing the promoter used or by adding a second or further additional promoter compound to the methanol feed as the time on stream increases.
In addition to the beneficial effect on the rate of dehydration of methanol reactions carried out in the presence of the catalyst, it is believed that the use of promoters as described herein may result in an increase in the stability of the catalyst and may make the catalyst more resistant to deactivation by impurities present in the methanol feed.
In a further aspect of the present invention provides a process for dehydrating methanol to dimethyl ether product in the presence of a catalyst, wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and wherein prior to using the catalyst in the dehydration process, the catalyst has been impregnated with a promoter selected from:
(i) at least one an alkyl carboxylate ester, C nH  (2n+1) CO 2CH 3 (Formula I) ; or
(ii) at least one di-ester compound, C mH 2m (CO 2CH 3)  2 (Formula II) , wherein in Formula I, n = 1 to 11; and in Formula II, m = 2 to 7.
In this further aspect of the invention, the feed to the dehydration process comprises methanol and may optionally comprise other components, for example dimethyl ether, water, or at least one compound which is a promoter compound of Formula I or Formula II or a precursor compound thereof.
The invention is now illustrated with reference to the following non-limiting Examples.
Examples
Details of the catalysts used in the Examples are provided in Table 1 below. In Table 1, only ring sizes of 8 T atoms or greater are given. Smaller ring sizes have been omitted.
Table 1
Figure PCTCN2018102144-appb-000003
SAR indicates the silica : alumina molar ratio of a zeolite
2-D indicates a 2-dimensional framework structure.
Catalysts used in the Examples
The zeolites (except MCM-22) were obtained in ammonium-form from Zeolyst International. MCM-22 can be prepared using methods reported in the literature and can also be purchased commercially.
The zeolites were utilised in the methanol dehydration reactions in the H-form by calcination of the ammonium form of the zeolite in air at 500 ℃.
Ester and di-ester compounds used in the Examples
The methyl ester compounds were essentially pure compounds (a total organic nitrogen content of about 0.1 ppm, expressed as nitrogen on a ppm by weight basis) and were obtained from Sigma-Aldrich or Brenntag UK Limited. The diester compounds were obtained from Alfa Aesar or Acros Organics.
Example 1
This Example demonstrates the effect of various alkyl carboxylate ester promoter compounds on the dehydration of methanol employing 2-dimensional zeolite catalysts.
The methanol dehydration reactions were carried out using the catalysts and promoter compounds specified in Table 2 below.
The reactions were conducted in a 16-channel parallel fixed-bed stainless steel reactor system. Each reactor (2 mm internal diameter) was heated to maintain a  temperature of 150 ℃. Each reactor housed a 25 mg bed of catalyst (having particle size fraction of 100 to 200 microns diameter) loaded on top of a 6cm deep bed of an inert material (carborundum) . The reactor volume above the catalyst was also packed with carborundum.
Each reactor was maintained at a temperature of 150 ℃ and at a total pressure of 1100kPa throughout the reactions. A gaseous feed comprising 10 mol%methanol and inert gas was introduced into the reactor and allowed to flow through the catalyst bed for a period of 48 hours at which point a promoter compound was added to the feed to achieve a gaseous feed comprising 10 mol%methanol and 5 mol%promoter compound (relative to methanol) . This gaseous feed comprising the promoter compound was introduced into the reactor for a period of 24 hours at a constant flow rate of methanol of 13 mmol h -1 and a constant promoter flow rate of 0.7 mmol h -1.
The effluent stream from each reactor was diluted with inert gas (nitrogen) and was periodically analysed by online gas chromatography to determine the yield of dimethyl ether product. The observed space time yields to dimethyl ether product are also provided in Table 2.
Table 2
Figure PCTCN2018102144-appb-000004
As Table 2 shows, taking account of experimental error, the use of the alkyl carboxylate ester compounds provided improved space time yields to dimethyl ether where the 2-dimensional zeolite had a maximum free sphere diameter of greater than 4.70 Angstroms but no increase in dimethyl ether productivity was observed where the zeolite had a maximum free sphere diameter of less than 4.70 Angstroms.
Example 2
This Example demonstrates the effect of a di-ester compound on the dehydration of methanol employing 2-dimensional zeolite catalysts.
The methanol dehydration reaction was carried out using the catalysts and di-ester compound specified in Table 3 below.
The dehydration reaction was carried out using a 16-channel parallel fixed-bed stainless steel reactor system. Each reactor (10 mm internal diameter) housed a catalyst bed of 0.168 g catalyst diluted with 0.337 g silica. The particle size of the catalyst and silica were in the range 450 to 900 microns in diameter. The catalyst bed was loaded on top of a 6.5 cm deep bed of an inert material (quartz sand) . The reactor volume above the catalyst bed was also packed with quartz sand.
Each reactor was maintained at a temperature of 150 ℃ and at a total pressure of 1100kPa throughout the reactions. A gaseous feed comprising 10 mol%methanol and inert gas was introduced into the reactor and allowed to flow through the catalyst bed for a period of 48 hours at which point a promoter compound was added to the feed to achieve a gaseous feed comprising 10 mol%methanol and 5 mol%promoter compound (relative to methanol) . This gaseous feed comprising the promoter compound was introduced into the reactor for a period of 24 hours at a constant flow rate of methanol of 45 mmol h -1 and a constant promoter flow rate of 2.3 mmol h -1.
The effluent stream from each reactor was cooled to 5 ℃ in a condenser and the gas phase from the condenser was periodically analysed by online gas chromatography to determine the yield of dimethyl ether product. The observed space time yields to dimethyl ether product are given in Table 3 below.
Table 3
Figure PCTCN2018102144-appb-000005
Example 3
This Example demonstrates the effect of different concentrations of various alkyl carboxylate ester and di-ester compounds on the catalytic dehydration of methanol in the presence of the zeolite PSH-3.
The reactions were conducted in a 16-channel parallel fixed-bed stainless steel reactor system. Each reactor (2 mm internal diameter) was heated to maintain a temperature of 150 ℃. Each reactor housed a 25 mg bed of catalyst (having particle size fraction of 100 to 200 microns diameter) loaded on top of a 6cm deep bed of an inert  material (carborundum) . The reactor volume above the catalyst was also packed with carborundum.
Each reactor was maintained at a temperature of 150 ℃ and at a total pressure of 1100kPa throughout the reactions. A gaseous feed comprising 10 mol%methanol and inert gas was introduced into the reactor and allowed to flow through the catalyst bed for a period of 48 hours at which point a promoter compound was added to the feed to achieve a gaseous feed comprising 10 mol%methanol and 0.001, 0.01 or 0.1 mol%promoter compound (relative to methanol) . This gaseous feed comprising the promoter compound was introduced into the reactor for a period of 24 hours at a constant flow rate of methanol of 13 mmol h -1 and a constant promoter flow rate of 0.00013, 0.0013 or 0.013 mmol h -1.
The effluent stream from each reactor was diluted with inert gas (nitrogen) and was periodically analysed by online gas chromatography to determine the yield of dimethyl ether product. The observed space time yields to dimethyl ether product are provided in Table 4.
Table 4
Figure PCTCN2018102144-appb-000006
As the results in Table 4 shows, in the presence of the alkyl carboxylate ester compounds the productivities to dimethyl ether increased at promoter range of concentrations.

Claims (18)

  1. A process for dehydrating methanol to dimethyl ether product in the presence of a catalyst and a promoter, wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and the promoter is:
    (i) at least one an alkyl carboxylate ester, C nH  (2n+1) CO 2CH 3 (Formula I) ; or
    (ii) at least one di-ester compound, C mH 2m (CO 2CH 3)  2 (Formula II) , wherein in Formula I, n = 1 to 11; and in Formula II, m = 2 to 7 and wherein and the molar ratio of promoter to methanol is maintained at less than 1.
  2. A process according to claim 1 wherein the alkyl carboxylate ester of Formula I is a straight chain alkyl carboxylate ester.
  3. A process according to claim 1 or claim 2 wherein in Formula I, n= 2 to 9, preferably n= 2 to 7.
  4. A process according to any one of the preceding claims wherein the total amount of promoter relative to methanol is maintained in an amount of at least 1 ppm.
  5. A process according to any one of the preceding claims wherein the molar ratio of promoter to methanol is maintained in the range 0.00001: 1 to 0.2: 1
  6. A process according to any one of the preceding claims wherein the promoter is added to the dehydration process.
  7. A process according to any one of the preceding claims wherein the promoter is generated in-situ in the dehydration process.
  8. A process according to any one of the preceding claims in which process the feed components to the process are methanol, one or both of (i) at least one promoter compound of Formula I or Formula II and (ii) at least one precursor compound of a promoter compound of Formula I or Formula II; and one or both of dimethyl ether and water.
  9. A process according to any one of the preceding claims wherein the zeolite is a H-form zeolite.
  10. A process according to any one of the preceding claims wherein the zeolite is selected from framework type MWW.
  11. A process according to claim 10 wherein the zeolite of framework code MWW is a zeolite selected from PSH-3 or MCM-22.
  12. A process according to claim 1 wherein the zeolite is a medium or large pore zeolite.
  13. A process according to any one of the preceding claims wherein the zeolite is composited with a binder material.
  14. A process according to any one of the preceding claims wherein the process is carried out at a temperature of from 100 ℃ to 300 ℃.
  15. A process according to any one of the preceding claims wherein the process is carried out as a heterogeneous vapour phase process.
  16. A process according to any one of the preceding claims wherein methyl acetate is not a component of the feed to the process.
  17. Use of a promoter in a process for the catalytic dehydration of methanol to dimethyl ether to improve productivity to dimethyl ether product wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and the promoter is:
    (i) at least one an alkyl carboxylate ester, C nH  (2n+1) CO 2CH 3 (Formula I) ; or
    (ii) at least one di-ester compound, C mH 2m (CO 2CH 3)  2 (Formula II) , wherein in Formula I, n = 1 to 11; and in Formula II, m = 2 to 7 and wherein and the molar ratio of promoter to methanol is maintained at less than 1.
  18. A method of improving the productivity to dimethyl ether product in a process for dehydrating methanol in the presence of a catalyst and a promoter, wherein the catalyst is at least one aluminosilicate zeolite which has a 2-dimensional framework structure and a maximum free sphere diameter of greater than 4.70 Angstroms, and the promoter is:
    (i) at least one an alkyl carboxylate ester, C nH  (2n+1) CO 2CH 3 (Formula I) ; or
    (ii) at least one di-ester compound, C mH 2m (CO 2CH 3)  2 (Formula II) , wherein in Formula I, n = 1 to 11; and in Formula II, m = 2 to 7 and wherein and the molar ratio of promoter to methanol is maintained at less than 1.
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WO2011027105A1 (en) * 2009-09-03 2011-03-10 Bp Chemicals Limited Process for producing acetic acid and dimethyl ether using a zeolite catalyst
US20120220804A1 (en) * 2009-11-17 2012-08-30 Lurgi Gmbh Manufacture of dimethyl ether from crude methanol
WO2013124404A1 (en) * 2012-02-23 2013-08-29 Bp Chemicals Limited Catalyst and process for the production of acetic acid and dimetyhl ether
WO2013124423A1 (en) * 2012-02-23 2013-08-29 Bp Chemicals Limited Process for the production of acetic acid and diemthyl ether
CN104341279A (en) * 2013-08-05 2015-02-11 华东理工大学 A kind of method of preparing polyoxymethylene dimethyl ether by methanol and formaldehyde
WO2015193183A1 (en) * 2014-06-20 2015-12-23 Bp Chemicals Limited Process for the co-production of acetic acid and dimethyl ether
WO2015193188A1 (en) * 2014-06-20 2015-12-23 Bp Chemicals Limited Process for the co-production of acetic acid and dimethyl ether

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WO2011027105A1 (en) * 2009-09-03 2011-03-10 Bp Chemicals Limited Process for producing acetic acid and dimethyl ether using a zeolite catalyst
US20120220804A1 (en) * 2009-11-17 2012-08-30 Lurgi Gmbh Manufacture of dimethyl ether from crude methanol
WO2013124404A1 (en) * 2012-02-23 2013-08-29 Bp Chemicals Limited Catalyst and process for the production of acetic acid and dimetyhl ether
WO2013124423A1 (en) * 2012-02-23 2013-08-29 Bp Chemicals Limited Process for the production of acetic acid and diemthyl ether
CN104341279A (en) * 2013-08-05 2015-02-11 华东理工大学 A kind of method of preparing polyoxymethylene dimethyl ether by methanol and formaldehyde
WO2015193183A1 (en) * 2014-06-20 2015-12-23 Bp Chemicals Limited Process for the co-production of acetic acid and dimethyl ether
WO2015193188A1 (en) * 2014-06-20 2015-12-23 Bp Chemicals Limited Process for the co-production of acetic acid and dimethyl ether

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