WO2023156764A1

WO2023156764A1 - Process

Info

Publication number: WO2023156764A1
Application number: PCT/GB2023/050321
Authority: WO
Inventors: Paul Gordon; Javad Tabatabaei
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 2022-02-15
Filing date: 2023-02-13
Publication date: 2023-08-24
Anticipated expiration: 2024-08-15
Also published as: TW202342653A; CN118541342A; GB202201979D0

Abstract

A process for producing a feedstock chemical. The process comprising hydrogenolysis of a glycolate compound in one or more reactors in the presence of a ruthenium catalyst, wherein the hydrogenolysis is carried out at a glycolate conversion of less than 100%. The process finds use in the production of monoethylene glycolate.

Description

Process Field of the Invention The present invention relates to a process for producing a feedstock chemical. More specifically, the present invention relates to a process for producing monoethylene glycol from a glycolate compound. Background of the Invention Monoethylene glycol is an important feedstock chemical used in the production of polymeric materials such as polyester and polyethylene terephthalate (PET). Monoethylene glycol also finds use as an anti-freeze material and a heat transfer medium. Monoethylene glycol may be produced by the hydrogenolysis of glycolate compounds such as alkyl glycolates (e.g. methyl glycolate) and/or glycolic acid in the presence of high pressures of hydrogen gas and a catalyst. The catalyst employed is typically a homogeneous catalyst. A typical hydrogenolysis process for producing monoethylene glycol may take place in one or more reactors, such as in one or more continuously stirred tank reactors. These reactors may be arranged in series to improve the efficiency of the process. It was considered beneficial to the process to maximise the conversion of feedstock to monoethylene glycol in these reactors as this minimises the amount of unconverted feedstock which has to be recycled. It was also believed that maximising conversion minimised the amount of partially hydrogenated by-products which are formed and which can be difficult to separate from the monoethylene glycol product. US7709689B2 describes a process for the hydrogenation of carboxylic acids and derivatives thereof. Over time the catalyst used in the hydrogenolysis process can become deactivated necessitating its removal and replacement with fresh catalyst. A process purge, which forms a purge stream, may therefore be provided from the hydrogenolysis process. The purge stream comprises a mixture of feedstock reagents, monoethylene glycol product, organic by- products of the hydrogenolysis reaction, water, and active and deactivated catalyst. The purge stream may undergo onsite treatment to concentrate the mixture of active and deactivated catalyst prior to recovery of the catalyst However after the concentration process a residual aqueous waste stream will remain which will contain a mixture of organic compounds, including the monoethylene glycol product. This aqueous stream therefore represents a loss of product and catalyst from the process and presents an increased demand upon effluent treatment facilities. Consequently, there remains a need for improved processes for producing monoethylene glycol which reduce the rate of degradation of the catalyst and thereby reduce the rate of catalyst purges and the amount of catalyst lost to recovery processes. Summary of the Invention Accordingly, the present invention provides a process which minimises catalyst deactivation and by-product formation whilst maintaining good process economics. In a first aspect of the invention there is provided a process for producing monoethylene glycol, the process comprising hydrogenolysis of a glycolate compound in one or more reactors in the presence of a ruthenium catalyst; obtaining a crude product stream from the one or more reactors; feeding the crude product stream to a separation zone wherein a catalyst stream is separated from an intermediate product stream; and recycling the catalyst stream to the one or more reactors, wherein the hydrogenolysis is carried out at a glycolate conversion of less than 100%. It has surprisingly been found that when the hydrogenolysis is carried out at a glycolate conversion of less than 100% that the rate of ruthenium catalyst deactivation is minimised as compared to when a glycolate conversion of 100% is used. Operating at a glycolate conversion of less than 100% allows the purge rate of the process to be reduced and hence the loss of catalyst from the system to be reduced. It has surprisingly been found that management of the ruthenium catalyst to minimise its deactivation is key to maintaining the stable operation and the economics of commercial hydrogenolysis processes for producing monoethylene glycol. For instance, in a commercial plant up to 90% of the catalyst cost may be accounted for by the cost of the ruthenium metal. This represents a significant contribution to the working capital of a plant. Whilst the process for recovering the ruthenium metal is typically very efficient, complete (i.e. 100%) recovery of the ruthenium will not be achieved. Consequently, the more ruthenium metal which is sent for recovery the higher the absolute losses of this expensive metal from the process. Moreover, higher catalyst purge rates necessitate holding a larger inventory of fresh catalyst or catalyst precursor on site to replace the deactivated catalyst sent for recovery. Without being bound by any sort of theory it is believed that once the ruthenium catalyst has converted the glycolate compounds into monoethylene glycol it may undergo side reactions forming species which have lower or no catalytic activity, and which are not readily converted back to active catalytic species. Furthermore, it has surprisingly been found that operating at a glycolate conversion of less than 100% reduces the amount of 2-methoxyethanol produced in the hydrogenolysis process.2-methoxyethanol is associated with significant toxicity issues and it must be separated from wastewater before the water can be discharged safely. It is therefore desirable to minimise the amount of this compound which forms during hydrogenolysis. The process of the first aspect of the invention therefore provides an optimum balance between catalyst deactivation (hence the requirement to remove the catalyst through a process purge) and process operability. Brief Description of the Drawings Figure 1 shows a block flow diagram of an example process of the invention. Figure 2 shows a plot of hydrogen consumption over time for freshly prepared catalysts. Figure 3 shows a plot of hydrogen consumption over time for catalysts previously taken to 100% and 90% glycolate conversion. Figure 4 shows a ³¹P NMR spectrum of the solution resulting from the hydrogenolysis of Feed Solution 1940-29 Figure 5 shows a ³¹P NMR spectrum of the solution resulting from the hydrogenolysis of Feed Solution 1940-33 Figure 6 shows a ³¹P NMR spectrum of the solution resulting from the hydrogenolysis of Feed Solution 1940-31 Figure 7 shows a ³¹P NMR spectrum of the solution resulting from the hydrogenolysis of Feed Solution 1940-30 Figure 8 shows a ³¹P NMR spectrum of the solution resulting from the hydrogenolysis of Feed Solution 194034 Figure 9 shows a ³¹P NMR spectrum of the solution resulting from the hydrogenolysis of Feed Solution 1940-32 Detailed Description Preferred and/or optional features of the invention will now be set out. Any aspect of the invention may be combined with any other aspect of the invention unless the context demands otherwise. Any of the preferred and/or optional features of any aspect may be combined, either singly or in combination, with any aspect of the invention unless the context demands otherwise. The present invention provides a process for producing monoethylene glycol, the process comprising hydrogenolysis of a glycolate compound in one or more reactors in the presence of a ruthenium catalyst, wherein the hydrogenolysis is carried out at a glycolate conversion of less than 100%. The process of the invention comprises hydrogenolysis of a glycolate compound. The glycolate compound as used in the present invention is not particularly limited and may comprise any organic compound containing a glycolate group which can be converted to monoethylene glycol, either directly or indirectly, by a hydrogenolysis reaction. A glycolate group is shown in Scheme 1, below.

The glycolate compound may comprise an alkyl glycolate (e.g. methyl glycolate, ethyl glycolate, propyl glycolate, or butyl glycolate, preferably methyl glycolate), glycolic acid, monoethylene glycol glycolate, diethylene glycol glycolate, dimethyl diglycolate, glycolate esters, and mixtures thereof. In preferred processes of the invention the glycolate compound may comprise an alkyl glycolate (e.g. methyl glycolate, ethyl glycolate, propyl glycolate, or butyl glycolate, preferably methyl glycolate) and/or glycolic acid. In preferred processes of the invention the glycolate compound may comprise methyl glycolate and/or glycolic acid. The glycolate compound may be produced by any suitable method. It may be preferred that the glycolate compound is prepared by reacting formaldehyde with carbon monoxide and water in a carbonylation reactor in the presence of a catalyst, for example a sulphur catalyst. This reaction will be understood to be synonymously referred to as the carbonylation of formaldehyde. Such a process is described in US10640443B2. The hydrogenolysis process of the invention is carried out in one or more reactors. It may be preferred that the one or more reactors are continuously stirrer tank reactors. It may be preferred that the hydrogenolysis process is carried out in two or more reactors, three or more reactors, or four or more reactors. It may be preferred that the hydrogenolysis process is carried out in two or more reactors, three or more reactors, or four or more reactors, wherein the reactors are continuously stirred tank reactors. It will be understood that the hydrogenolysis process of the invention may be carried out in a continuous fashion, as distinct from a batch or “one pot” synthesis. The hydrogenolysis is carried out at a glycolate conversion of less than 100%, preferably less than or equal to 99%, more preferably less than or equal to 98% or less than or equal to 97%, most preferably less than or equal to 96%. The hydrogenolysis may be carried out at a glycolate conversion of greater than or equal to 90%, preferably greater than or equal to 92%, more preferably greater than or equal to 94%, most preferably greater than or equal to 95%. It may be preferred that hydrogenolysis is carried out at a glycolate conversion of from greater than 90% to less than 100%, preferably from greater than or equal to 92% to less than or equal to 98%, more preferably from greater than or equal to 94% to less than or equal to 97%, most preferably from greater than or equal to 95% to less than or equal to 96%. It has surprisingly been found that when the hydrogenolysis is carried out at a glycolate conversion of less than 100%, as above, that the rate of ruthenium catalyst deactivation is reduced as compared to when a glycolate conversion of 100% is used. Operating at a glycolate conversion of less than 100% allows the purge rate of the process to be reduced and hence the loss of the ruthenium catalyst from the system to be reduced. Furthermore, when the hydrogenolysis is carried out at a glycolate conversion of greater than or equal to 90%, but less than 100%, an optimum balance is achieved between ruthenium catalyst deactivation and the impact on operability caused by unreacted glycolate compound being present in an output stream (for example a crude product stream) from the one or more reactors. Furthermore, it has surprisingly been found that operating at a glycolate conversion of less than 100% reduces the amount of 2-methoxyethanol produced in the hydrogenolysis process.2-methoxyethanol is associated with significant toxicity issues and it must be separated from wastewater before the water can be discharged safely It is therefore desirable to minimise the amount of this compound which forms during hydrogenolysis. This benefit is particularly important when the glycolate compounds undergoing hydrogenolysis comprise methylmethoxyacetate and/or methoxyacetic acid contaminants. These contaminants may be formed as by-products in the reaction to produce the glycolate compound, such as in the carbonylation of formaldehyde. The process of the invention is therefore particularly suited to hydrogenolysis processes which use glycolate compounds produced by the carbonylation of formaldehyde. For the avoidance of doubt, by “glycolate conversion” as used herein it is meant the amount of glycolate compound(s) converted to monoethylene glycol expressed as a percentage in a first pass of the one or more reactors. For the avoidance of doubt, the glycolate conversion of the process is the glycolate conversion across all of the one or more reactors. The glycolate conversion may be monitored by suitable methods known in the art. For example, the glycolate conversion may be measured using spectroscopic methods such as near infra-red spectroscopy, and/or by “ex-situ” methods such as gas chromatography. The hydrogenolysis of the glycolate compound is typically carried out at elevated temperature and/or elevated pressure. The hydrogenolysis of the glycolate compound may be carried out at a temperature of greater than 170 °C, greater than 175 °C, or greater than 180 °C. The hydrogenolysis of the glycolate compound may be carried out a temperature of less than 220 °C, less than 210 °C, or less than 200 °C. Typically, the hydrogenolysis of the glycolate compound is carried out a temperature of from 170 °C to 220 °C, from 175 °C to 210 °C, or from 180 °C to 200 °C. The hydrogenolysis of the glycolate compound may be carried out at a pressure of greater than 70 bara, greater than 75 bara, or greater than 80 bara. The hydrogenolysis of the glycolate compound may be carried out a pressure of less than 105 bara, less than 100 bara, or less than 95 bara. Typically, the hydrogenolysis of the glycolate compound is carried out a pressure of from 70 bara to 105 bara, 75 bara to 100 bara, or from 80 bara to 95 bara. As will be understood, the hydrogenolysis of the glycolate compound is carried out in the presence of a partial pressure of hydrogen gas. Typically, the partial pressure of hydrogen is less than or equal to the total pressure in the one or more reactors For example the partial pressure of hydrogen in the one or more reactors may be greater than 70% of the total pressure of the one or more reactors, greater than 75% of the total pressure of the one or more reactors, greater than 78% of the total pressure of the one or more reactors, or greater than 80% of the total pressure of the one or more reactors. For example, the partial pressure of hydrogen in the one or more reactors may be less than 95% of the total pressure of the one or more reactors, less than 90% of the total pressure of the one or more reactors, less than 87% of the total pressure of the one or more reactors, or less than 85% of the total pressure of the one or more reactors. Typically, the partial pressure of hydrogen in the one or more reactors is from 70% to 95% of the total pressure of the one more reactors, 75% to 90% of the total pressure of the one more reactors, 78% to 87% of the total pressure of the one more reactors, or 80% to 85% of the total pressure of the one more reactors. As used herein, it will be understood that by the term “catalyst pre-cursor” is meant a compound which may form an active catalyst. For example, the catalyst pre-cursor may form the active catalyst in-situ in the hydrogenolysis reaction. The process of the invention comprises a ruthenium catalyst. In preferred processes of the invention the ruthenium catalyst is a ruthenium phosphine complex. As will be understood by the skilled person a ruthenium phosphine complex comprises one or more phosphine ligands coordinated to a ruthenium atom. In preferred processes of the invention the ruthenium catalyst is a ruthenium triphos complex comprising one or more ruthenium triphos moieties, where the terms “triphos” and “ruthenium triphos moiety” are as defined below. In particularly preferred processes of the invention the ruthenium catalyst is a compound of general formula [Ru(“triphos”)H₂(solv)]. It will be understood that “solv” represents a molecule, such as a solvent molecule, which may be coordinated to the ruthenium metal. Without limitation, “solv” may be a molecule present in the hydrogenolysis process, such as an alkyl glycolate (e.g. methyl glycolate, ethyl glycolate, propyl glycolate, and butyl glycolate), glycolic acid, glycolate, monoethylene glycol, hydroxide, methanol, or water. It may be preferred that solv is methyl glycolate. As used herein ruthenium triphos moiety refers to a triphos ligand coordinated to a ruthenium metal atom, as illustrated in Scheme 2 below.

The term “triphos” is used to refer to a ligand of Formula (I):

In the ligand of Formula (I), R₁, R₂, R₃, R₄, R₅, and R₆ may be the same or different. In the ligand of Formula (I), R₁, R₂, R₃, R₄, R₅, and R₆ are typically the same. In the ligand of Formula (I), R₁, R₂, R₃, R₄, R₅, and R₆ may be independently selected from the group consisting of unsubstituted C_1-20-alkyl, substituted C_1-20-alkyl, unsubstituted C_3-20-cycloalkyl, substituted C_3-20-cycloalkyl, unsubstituted C_1-20-alkoxy, substituted C_1-20-alkoxy, unsubstituted C_6-20-aryl, substituted C_6-20-aryl, unsubstituted C_1-20-heteroalkyl, substituted C_1-20-heteroalkyl, unsubstituted C_2-20-heterocycloalkyl, substituted C_2-20-heterocycloalkyl, unsubstituted C_4-20- heteroaryl and substituted C_4-20-heteroaryl. In the ligand of Formula (I), R₁, R₂, R₃, R₄, R₅, and R₆ may be independently selected from: i) substituted or unsubstituted branched- or straight-chain alkyl groups such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl or stearyl; ii) cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or adamantyl; or iii) aryl groups such as phenyl, naphthyl or anthracyl. Preferably, R₁, R₂, R₃, R₄, R₅, and R₆ are aryl groups which are the same, more preferably R₁, R₂, R₃, R₄, R₅, and R₆ are each a substituted or non-substituted aryl group such as a substituted or unsubstituted phenyl group, most preferably R₁, R₂, R₃, R₄, R₅, and R₆ are phenyl groups. In particularly preferred embodiments the triphos ligand is 1,1,1- tris(diphenylphosphinomethyl)ethane. The ruthenium catalyst may be a ruthenium triphos complex comprising one or more ruthenium triphos moieties. For example, the ruthenium triphos complex may comprise one ruthenium triphos moiety, or two ruthenium triphos moieties which may be bonded together via one or more bridging ligands to form a bridged complex. Said bridging ligand may be, for example, chloride ligands (typically referred to as µ-chloride), hydroxide ligands (typically referred to as µ-OH, or µ-hydroxide), hydride ligands (typically referred to as µ-H or µ- hydride), or oxide ligands (typically referred to as µ-O, or µ-oxide). Such bridging ligands are well known in the art. The ruthenium catalyst may comprise a ruthenium triphos moiety comprising additional ligands. Additional ligands may be one or more selected from the list comprising dihydrogen, hydride, carbonate, carbonyl, alkyl glycolates (e.g. methyl glycolate, ethyl glycolate, propyl glycolate, and butyl glycolate), glycolic acid, glycolate, monoethylene glycol, hydroxide, methanol, or water. The additional ligands may be coordinated in a monodentate, bidentate, or multidentate fashion to the ruthenium atom. Typically, the additional ligands are coordinated in a monodentate, a bidentate, or tridentate fashion to the ruthenium atom. In particularly preferred embodiments, the ruthenium catalyst is a catalyst of formula [Ru(“triphos”)H₂(solv)]. In particularly preferred embodiments, the ruthenium catalyst is [Ru(1,1,1-tris(diphenylphosphinomethyl)ethane)H₂(solv)]. It has surprisingly been found that in the process of the invention, where the hydrogenolysis is carried out at a glycolate conversion of less than 100%, and the catalyst is a ruthenium catalyst, in particular a ruthenium triphos catalyst (for example [Ru(“triphos”)H₂(solv)]), that the rate of process purges can be reduced. Without being bound by any sort of theory it is believed that ruthenium catalysts, in particular ruthenium triphos catalysts (for example [Ru(“triphos”)H₂(solv)]), show enhanced stability and resistance to degradation when the hydrogenolysis is carried out at a glycolate conversion of less than 100%. Without being bound by any sort of theory it is believed that the ruthenium triphos catalysts may form stable dimeric species comprising two ruthenium triphos moieties when the hydrogenolysis is carried out at a glycolate conversion of 100%, these dimeric species are thought to have reduced activity or be inactive for catalysing the hydrogenolysis of glycolate compounds to monoethylene glycol. The ruthenium catalyst may have a concentration in the one or more reactors of the process of greater than 100 ppm, greater than 150 ppm, greater than 200 ppm, or greater than 250 ppm on a ruthenium metal weight basis. There is no particular upper limit at which the ruthenium catalyst may be present. For instance, the ruthenium catalyst may have a concentration in the one or more reactors of the process of less than 20,000 ppm, or less than 10,000 ppm on a ruthenium metal weight basis. Typically, however, the ruthenium catalyst may have a concentration in the one or more reactors of the process of less than 2500 ppm, greater than 2000 ppm, greater than 1800 ppm, or greater than 1500 ppm on a ruthenium metal weight basis. For example, the ruthenium catalyst may have a concentration in the one or more reactors of from 100 ppm to 2500 ppm, from 150 ppm to 2000 ppm, from 200 ppm to 1800 ppm, or from 250 ppm to 1500 ppm on a ruthenium metal basis. The concentration of the ruthenium catalyst (measured on a ruthenium metal basis) may be determined by ICP-OES using methods known in the art. The process of the invention produces monoethylene glycol. The process of the invention comprises the step of obtaining a crude product stream from the one or more reactors. The crude product stream comprises monoethylene glycol and unreacted glycolate compounds. The crude product stream may comprise one or more of water, alkyl glycolate (e.g. methyl glycolate, ethyl glycolate, propyl glycolate, butyl glycolate, preferably methyl glycolate), glycolic acid, methanol, diethylene glycol, 2-methoxyethanol, methoxyacetic acid, methyl methoxyacetate, ethylene glycol glycolate, and/or butane-1,2,3,4-tetrol. Unreacted glycolate compounds include glycolate compounds which have not been converted to monoethylene glycol in the one or more reactors and are therefore present in the crude product stream. For example, unreacted glycolate compounds may comprise alkyl glycolates such as methyl glycolate. Whilst the unreacted glycolate compound may need to be separated from the crude product stream, the benefits of reduced ruthenium catalyst degradation and/or reduced 2- methoxyethanol production in the hydrogenolysis process offsets allowing this slip of unconverted glycolate compound from the one or more reactors. The process of the invention comprises the step of feeding the crude product stream to a separation zone wherein a catalyst stream is separated from an intermediate product stream. Typically, the catalyst stream is separated as a heavy fraction and the intermediate product stream is separated as a light fraction. Typically, the separation zone comprises a vaporiser, such as a falling film evaporator, which places the crude product stream under a vacuum, optionally in one or more stages. Typically, the crude product stream is placed under a vacuum of less than 1 bara, less than 0.8 bara, less than 0.6 bara, or less than 0.4 bara. Typically, the crude product stream is placed under a vacuum of greater than 0 bara, greater than 0.1 bara, greater than 0.2 bara, or greater than 0.3 bara. The catalyst stream may comprise substantially the same compounds as the crude product stream, however, the quantities of each compound present will be different. For example, the proportion of volatile light compounds (e.g. alkyl glycolates such as methyl glycolate) will be reduced in the catalyst stream relative to the crude product stream, whilst the proportion of heavy compounds (e.g. ethylene glycol glycolate) may be increased in the catalyst stream relative to the crude product stream. The catalyst stream may comprise monoethylene glycol, water, alkyl glycolate (e.g. methyl glycolate, ethyl glycolate, propyl glycolate, butyl glycolate), glycolic acid, methanol, diethylene glycol, 2-methoxyethanol methoxyacetic acid, methyl methoxyacetate, ethylene glycol glycolate, and butane-1,2,3,4-tetrol. The catalyst stream is recycled to the one or more reactors. Accordingly, the process of the invention comprises the step of recycling the catalyst stream to the one or more reactors. It may be beneficial to take a purge stream from the catalyst stream to prevent the build-up of heavy organic compounds and/or deactivated catalyst. The purge stream may have the same composition as the catalyst stream. Accordingly, the process of the invention may comprise the step of taking a purge stream from the catalyst stream. The purge stream may be sent to a waste treatment zone and/or catalyst recovery zone. The intermediate product stream may comprise monoethylene glycol, water, alkyl glycolate (eg methyl glycolate ethyl glycolate propyl glycolate butyl glycolate preferably methyl glycolate), glycolic acid, methanol, diethylene glycol, 2-methoxyethanol, methoxyacetic acid, methyl methoxyacetate, ethylene glycol glycolate, and butane-1,2,3,4-tetrol. The intermediate product stream may be passed to a refining zone where a pure monoethylene glycol stream may be separated from an unreacted glycolate compound stream and one or more heavy compound streams. In addition to those methods described hereinbelow, the skilled person is aware of methods to separate compounds from one another and obtain a pure monoethylene glycol product. Typically, the refining zone may comprise one or more distillation columns configured to separate the pure monoethylene glycol stream from the unreacted glycolate compound stream and the one or more heavy compound streams. The one or more distillation columns of the refining zone may be configured to separate the pure monoethylene glycol stream as a side-draw, the unreacted glycolate compound as a light fraction from at or near the top of the one or more distillation columns, and the one or more heavy compound stream as heavy fractions from at or near the bottom of the one or more distillation columns. The pure monoethylene glycol stream comprises monoethylene glycol. Preferably the pure monoethylene glycol stream comprises monoethylene glycol which is pure, or substantially pure. For example, the monoethylene glycol in the pure monoethylene glycol stream may have a purity of 99% or more, 99.5% or more, 99.9% or more, or 99.95% or more. The unreacted glycolate compound stream comprises unreacted glycolate compounds. Unreacted glycolate compounds has the meaning as described hereinabove. The unreacted glycolate compound stream may be recycled back to the one or more reactors. Accordingly, the process of the invention may comprise the step of recycling the glycolate compound stream to the one or more reactors. By recycling the glycolate compound stream to the one or more reactors the overall efficiency of the process may be optimised and unreacted glycolate compounds may be converted to monoethylene glycol and/or diethylene glycol in subsequent reaction in the one or more reactors. The step of recycling the glycolate compound stream to the one or more reactors therefore increases the overall efficiency of the process. The one or more heavy compound streams may comprise a diethylene glycol stream. The diethylene glycol stream comprises diethylene glycol The diethylene glycol stream may comprise pure, or substantially pure, diethylene glycol. It is advantageous to separate diethylene glycol in the diethylene glycol stream as diethylene glycol is a valuable feedstock chemical. The one or more heavy compound streams may comprise a heavy by-products stream. The heavy by-products stream may comprise by-products from the hydrogenolysis process for producing monoethylene glycol of the invention. For instance, the heavy by-products stream may comprise compounds such as ethylene glycol glycolate, ethylene glycol diglycolate, diethylene glycol glycolate, methyl diglycolate, diethylene glycol diglycolate, triethylene glycol, and butane-1,2,3,4-tetrol. The heavy by-products stream may be recycled to the one or more reactors. Alternatively, or additionally, the heavy by-products stream may be purged as a waste liquid fuel stream. Accordingly, the process may comprise the step of recycling the heavy by-products stream to the one or more reactors and/or purging the heavy by- products stream as a waste liquid fuel stream. Non-limiting embodiments of the invention will now be described with reference to the Figures. Figure 1 shows an example process according to the invention. To one or more hydrogenolysis reactors, 1, is fed a stream comprising a glycolate compound, 12. A catalyst makeup stream, 11, is also provided to the one or more hydrogenolysis reactors, 1, to replace deactivated catalysts. A crude product stream, 13, is obtained from the one or more hydrogenolysis reactors, 1, which is fed to a separation zone, 2. In the separation zone, 2, the pressure is dropped to around 0.4 bara. From the separation zone, 2, is obtained a catalyst stream, 21, and an intermediate product stream, 24. The catalyst stream, 21, is split to return a catalyst containing feed, 23, to the one or more hydrogenolysis reactors. A purge stream, 22, may also be taken where deactivated catalyst and by-product compounds may be removed from the process. The intermediate product stream, 24, is fed to a recovery zone, 3. In the recovery zone, 3, by-product compounds are separated as a heavy fraction, 31, from at or near the bottom of a distillation column. Said heavy fraction, 31, may be recycled to the hydrogenolysis reactors, 1, or purged as a waste liquid fuel stream. Other heavy organic compounds such as diethylene glycol are also removed as a heavy compound stream, 32, and retained as a saleable product. Monoethylene glycol is removed as a pure monoethylene glycol stream, 33. An unreacted glycolate compound stream, 34, is obtained at or near the top of the distillation column. The unreacted glycolate compound stream, 34, is fed back to the one or more hydrogenolysis reactors, 1. Examples Methyl glycolate, glycolic acid, 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos), and methanol can be obtained commercially from Sigma Aldrich.2-methoxy-2-oxoethyl 2- hydroxyacetate was prepared by esterification of glycolic acid and methanol. [Ru(acac)₃] was prepared according to the method described in Gupta, A. (2000). "Improved synthesis and reactivity of tris(acetylacetonato)ruthenium(III)", Indian Journal of Chemistry, Section A. 39A (4): 457. NMR Spectroscopy NMR spectra were acquired at a static magnetic field strength of 9.4 T (ν₀(¹H) = 400.23 MHz) on a Bruker NEO console using TopSpin 4.0 software. A standard bore Bruker 5 mm BBO BBF-H-D probe was used, appropriately tuned and referenced. For ³¹P NMR spectroscopy, the probe was tuned to 161.8 MHz and referenced to an external standard of 85% H₃PO₄ at 0 ppm. Samples were dissolved in d⁶-acetone obtained from Sigma Aldrich and the acquisitions were run ¹H decoupled at 22°C and spun at 12 Hz. Preparation of a Feed Solution Feed Solution was prepared by mixing water (2.85 wt%), methanol (6.61 wt%), methyl glycolate (71.99 wt%), glycolic acid (5.04 wt%) and 2-methoxy-2-oxoethyl 2-hydroxyacetate (12.35 wt%) and trace impurities. Experiment 1 Three hydrogenolysis reactions were carried out using a Feed Solution, prepared as described above. To the Feed Solution (200 g) was added Ru(acac)3 (0.484g) and 1,1,1- tris(diphenylphosphinomethyl)ethane (triphos)(0.925g, 1.2 mol equivalents relative to ruthenium) resulting in a ruthenium concentration of 609 ppmwt. The autoclave containing the Feed Solution, Ru(acac)3, and triphos was purged with N2, leak tested, then purged with H₂. The autoclave was pressurised to approximately 250 psig with H₂ and stirred at 265 rpm. The temperature was rapidly increased to 180°C, with stirring increased to 1000 rpm once the internal temperature reached 160°C. Once stable at 180°C the pressure was stabilised at 750 psig and a controlled and measured flow of H₂ was added to maintain system pressure. The rate and degree of reaction was determined by following the rate of H₂ consumption. Two reactions were taken to 100% glycolate conversion and a third reaction to 90% glycolate conversion as judged by H₂ consumption.100% glycolate conversion equated to the consumption of 87 litres of H₂. Where the reactions were taken to 100% glycolate conversion a hold at elevated temperature for 0.5 hours or 1.5 hours was carried out after H₂ consumption ceased. The reactors were then rapidly cooled to room temperature and discharged. The reactions are summarised in Table 1 below:

Table 1 The hydrogen consumption over time is shown in Figure 2. This Figure shows that the hydrogen consumption, hence activity, of each freshly prepared catalyst was substantially identical. Experiment 2 The solutions resulting from Experiment 1 were each collected and individually diluted with further Feed Solution to afford three Diluted Feed Solutions (1940-30, 1940-34, 1940-32) containing 300 ppmwt ruthenium. These Diluted Feed Solutions (200g) were each charged to a 300 mL PARR autoclave and the hydrogenolysis reaction repeated. The autoclave containing the Diluted Feed Solutions from Experiment 1 was purged with N₂, leak tested, then purged with H₂. The autoclave was pressurised to approximately 250 psig with H₂ and stirred at 265 rpm. The temperature was rapidly increased to 180°C, with stirring increased to 1000 rpm once the internal temperature reached 160°C. Once stable at 180°C the pressure was stabilised at 750 psig and a controlled and measured flow of H₂ was added to maintain system pressure. The rate and degree of reaction was determined by following the rate of H₂ consumption. The rate of hydrogen consumption in normal litres per hour (NLPH) was determined by analysing the slope of the plot of hydrogen consumption versus time between 1-2 hours reaction time. These reactions are summarised in Table 2 below:

Table 2 A comparison of the activity of the catalysts prepared and operated at 90% conversion (1940-31) and 100% conversion (1940-29 and 1940-33) can be seen in Figure 3. It is evident that the environment seen by the catalyst is critical to maintaining its activity, with the catalyst from the reaction taken to 90% conversion (1940-32) affording a significantly higher rate of H₂ consumption and hence activity, compared to the activity of the catalyst from solutions taken to 100% conversion (1940-30 and 1940–34). It is further clear that catalysts which are taken to 100% conversion continue to deactivate the longer they are held at 100% glycolate conversion. Without being bound by any sort of theory it is believed that once the catalyst has consumed all glycolate containing reagents it undergoes deactivating reactions and may form species which cannot be converted back to the active catalyst. Example 3 The solutions resulting from the hydrogenolysis reactions of Example 1 and Example 2 were analysed by ³¹P NMR spectroscopy. The ³¹P NMR spectra showed peaks which were assigned to either an active catalyst or species believed to be inactive/less active in catalysis. Without being bound by theory it is believed that the broad peak having a chemical shift of 40 ppm may be assigned to the active catalyst, which is thought to be [Ru(triphos)H₂(solv)]. Here it is believed that the active catalyst is predominantly present as [Ru(triphos)H₂(methyl glycolate)] (i.e. solv is methyl glycolate). Peaks at lower shifts were assigned to species having lower or no catalytic activity for the hydrogenolysis of glycolate compounds to monoethylene glycol. The peak at 43 ppm was assigned to the dimeric species [Ru(triphos) μ-H]₂ which is believed to be a stable deactivation product of the active catalyst. Comparing the ³¹P NMR spectra of solutions produced in Example 1 (Figures 4, 5, and 6), it can be seen that when a glycolate conversion of 90% is used the catalyst is present predominantly as the active [Ru(triphos)H₂(solv)], judged by the broad peak at 40 ppm in Figure 6. Comparatively, as seen in the spectra of Figure 4 and Figure 5, the active catalyst species is present to a much lesser extent when a glycolate conversion of 100% is used. Further, the peak assigned to the dimeric species [Ru(triphos) μ-H]₂ at 43 ppm is seen to increase as a function of hold time following 100% glycolate conversion, and is essentially absent when a glycolate conversion of 90% was used. Furthermore, as the post reaction hold time is increased from 0.5 hours to 1.5 hours, additional, species were observed to have formed. Comparing the ³¹P NMR spectra of solutions produced in Example 2 (Figure 7, 8, and 9), it can be seen that fewer species are present in the solution taken from the 90% glycolate conversion of Example 1 compared with those taken to 100% glycolate conversion in Example 1. Furthermore, it can be seen that increasing the hold time following 100% glycolate conversion in Example 1 not only produces more species but that these species do not readily convert back to the active catalytic species in the subsequent hydrogenolysis of Example 2. In particular, it can be seen that the peak assigned to the dimeric species [Ru(triphos) μ-H]₂ at 43 ppm persists in the second hydrogenolysis of Example 2 (i.e. This species may be seen in Figures 4 and 5 and in Figures 7 and 8). As a consequence, these additional, newly formed, species would need to be purged from a hydrogenolysis process to prevent the accumulation of less active species and the reduction in the amount of active catalyst present in the system.

Claims

Claims 1. A process for producing monoethylene glycol, the process comprising hydrogenolysis of a glycolate compound in one or more reactors in the presence of a ruthenium catalyst; obtaining a crude product stream from the one or more reactors; feeding the crude product stream to a separation zone wherein a catalyst stream is separated from an intermediate product stream; and recycling the catalyst stream to the one or more reactors, wherein the hydrogenolysis is carried out at a glycolate conversion of less than 100%.

2. A process according to claim 1, wherein the ruthenium catalyst is a ruthenium phosphine complex.

3. A process according to claim 1 or claim 2, wherein the ruthenium catalyst is a ruthenium triphos complex comprising one or more ruthenium triphos moieties, preferably [Ru(triphos)H₂(solv)].

4. A process according to claim 3, wherein triphos has Formula (I):

wherein R₁, R₂, R₃, R₄, R₅, and R₆ are the same or different; and R₁, R₂, R₃, R₄, R₅, and R₆ are independently selected from the group consisting of unsubstituted C_1-20-alkyl, substituted C_1-20-alkyl, unsubstituted C_3-20-cycloalkyl, substituted C_3-20-cycloalkyl, unsubstituted C_1-20-alkoxy, substituted C_1-20-alkoxy, unsubstituted C_6-20-aryl, substituted C_6-20-aryl, unsubstituted C_1-20-heteroalkyl, substituted C_1-20-heteroalkyl, unsubstituted C_2-20-heterocycloalkyl, substituted C_2-20-heterocycloalkyl, unsubstituted C_4-20- heteroaryl and substituted C_4-20-heteroaryl.

5. A process according to claim 3 or claim 4, wherein triphos is 1,1,1- tris(diphenylphosphinomethyl)ethane.

6. A process according to any one of the preceding claims, wherein the ruthenium catalyst is [Ru(1,1,1-tris(diphenylphosphinomethyl)ethane)H₂(solv)].

7. A process according to any one of the preceding claims, wherein the glycolate compound comprises an alkyl glycolate, methyl glycolate, glycolic acid, monoethylene glycol glycolate, diethylene glycol glycolate, dimethyl diglycolate, glycolate esters, or mixtures thereof.

8. A process according to any one of the preceding claims, wherein glycolate conversion of from greater than 90% to less than 100%, preferably from greater than or equal to 92% to less than or equal to 98%, more preferably from greater than or equal to 94% to less than or equal to 97%, most preferably from greater than or equal to 95% to less than or equal to 96%.

9. A process according to any one of the preceding claims, wherein the glycolate compound is prepared by the carbonylation of formaldehyde.

10. A process according to any one of the preceding claims, wherein the process comprises the step of taking a purge stream from the catalyst stream, and optionally sending the purge stream to a waste treatment zone and/or catalyst recovery zone.

11. A process according to any one of the preceding claims, wherein the process further comprises the step of passing the intermediate product stream to a refining zone where a pure monoethylene glycol stream is separated from an unreacted glycolate compound stream and one or more heavy compound streams.

12. A process according to any one of the preceding claims, wherein the one or more heavy compound streams comprise a diethylene glycol stream and/or a heavy by-products stream.

13. A process according to claim 11 or claim 12, wherein the unreacted glycolate compound stream is recycled to the one or more reactors.

14. A process according to claim 12 or claim 13, wherein the process further comprises the step of recycling the heavy by-products stream to the one or more reactors and/or purging the heavy by-products stream as a waste liquid fuel stream.

15. A process according to any one of claims 11 to 14, wherein the monoethylene glycol in the pure monoethylene glycol stream has a purity of 99% or more, 99.5% or more, 99.9% or more, or 99.95% or more.

16. A process according to any one of the preceding claims, wherein the one or more reactors are continuously stirrer tank reactors.

17. A process according to any one of the preceding claims, wherein the process is a continuous process for producing monoethylene glycol.