WO2016026676A1

WO2016026676A1 - Manufacture of purified alcohols

Info

Publication number: WO2016026676A1
Application number: PCT/EP2015/067688
Authority: WO
Inventors: Eddy Van Driessche; Stephen Beadle; Carl Beck; Michael Player; Byron SEVIN; Bee YAP
Original assignee: Exxonmobil Chemical Patents Inc.
Priority date: 2014-08-22
Filing date: 2015-07-31
Publication date: 2016-02-25

Abstract

A process for production and treatment of synthetic alcohol results in the substantial removal of carbonyl-containing impurities from the alcohol, while preventing, detecting, and if necessary,removing the presence of unsafe levels of residual hydrogen in the finished alcohol product. The process includes catalytically hydrogenating an aldehyde containing stream to produce a crude alcohol mixture containing at most 2 wt% aldehyde and at least 50wt% alcohol based on the weight of the total mixture; distilling the crude alcohol mixture to produce a distilled alcohol;treating the distilled alcohol with sodium borohydride to produce a treated alcohol; performing periodic measurement of carbonyl number of the treated alcohol; and stopping the sodium borohydride treatment when the measured carbonyl number reaches a value in the range of 0.05 –0.20 mg KOH/g. to produce a finished alcohol product.

Description

MANUFACTURE OF PURIFIED ALCOHOLS

FIELD OF THE INVENTION

[0001] The invention relates to the manufacture of purified alcohols by the hydro formylation (oxonation) reaction, in particular to the purification of Oxo alcohols produced by the hydrogenation of aldehydes.

BACKGROUND OF THE INVENTION

[0002] Hydro formylation is a well-known process in which an olefin is reacted with carbon monoxide and hydrogen in the presence of a catalyst to form aldehydes and/or alcohols containing one carbon atom more than the feed olefin. It is also known as the Oxo process, or as the oxonation process. The commercially important Oxo process produces such alcohols, which find uses in plastics, soaps, lubricants, and other products. Thus, hydro formylation of ethylene yields propionaldehyde and propylene yields a mixture of n- and iso-butyraldehyde (with the n- isomer usually predominating), followed by catalytic hydrogenation to the corresponding alcohols, e.g., n-propanol and n-butanol. Synthetic alcohols, particularly those in the range of about 8 to 13 carbon atoms (C8-C13), are used as plasticizers for poly(vinyl chloride) and the like. By way of example, the important plasticizer alcohol, 2-ethylhexanol, is made by alkali-catalyzed condensation of n-butyraldehyde to yield the unsaturated aldehyde, 2-ethyl-hex-2-enal, which is then hydrogenated to yield the desired 2-ethylhexanol.

[0003] The Oxo process and variations thereon are the subject of numerous patents and patent applications, recent examples of which are U.S. Pat. Nos. 8,288,595; 8,049,043; and 8,022,256.

[0004] Synthetic alcohols are typically plagued with the problem of undesirable residual carbonyl impurities, e.g., aldehydes and ketones that can create performance and color issues in product alcohol usage and in downstream derivatives of the alcohols. Many methods have been tried to mitigate the problem, for example, treatment with reducing agents, such as hydrogen in the presence of a catalyst such as zinc and copper catalyst, Raney nickel catalyst, zirconium promoted nickel-kieselguhr catalyst, or the like, treatment with borohydrides such as sodium borohydride, and also ozone treatments. See, for instance, U.S. Patent Nos. 3,642,915 and 3,232,848.

[0005] As an example of a commercial process, the crude alcohol product from the hydrogenation section of the Oxo is subjected to heart-cut distillation to remove both light impurities and heavy impurities. The distilled alcohol product however still contains trace carbonyl impurities, and is thus, passed through a finishing section, where it is treated with sodium borohydride. The reactivity of sodium borohydride towards aldehydes and ketones (if present) is much greater than the reactivity of sodium borohydride with the active hydrogen of the alcohol or the ester carbonyl. Sodium borohydride reduces aldehydes and ketones to the corresponding alcohols.

[0006] However, treatment with sodium borohydride can cause a safety hazard by leaving free hydrogen and potentially hydrogen-releasing impurities in the final alcohol product. Over time such impurities release free hydrogen from solution which can form a flammable vapor space during storage and transport. Over-treatment with sodium borohydride can also lead to the formation of particulates in the product alcohol. Over- treatment can also slow down the reaction to form plasticizers in the next production step. Over-treatment may also lead to a decrease in resistivity in products used for wire and cable insulation.

[0007] Therefore, there is a need for a well-controlled method of sodium borohydride treatment to remove undesirable carbonyl impurities from Oxo alcohol that results in reduced hydrogen content in the finished alcohol product in order to ensure safe handling, transit, and storage.

SUMMARY OF THE INVENTION

[0008] The present inventors have developed processes and systems to produce a purified alcohol product, particularly synthetic Oxo alcohols, which removes substantially all carbonyl-containing impurities from an alcohol product and reduces residual hydrogen levels in the finished product to safe levels. The inventive process embodies the inventors surprising discovery that during hydro finishing treatment, residual hydrogen is only substantially created in the finished alcohol after all carbonyl-containing species have been converted into alcohols, and that by stopping the treatment process at a specific point, the creation of residual hydrogen can be substantially avoided. Thus, the inventive process for producing purified alcohols may include catalytically hydrogenating an aldehyde containing stream to produce a crude alcohol mixture containing at most 2 wt% aldehyde and at least 50 wt% alcohol based on the weight of the total mixture; distilling the crude alcohol mixture to produce a distilled alcohol; treating the distilled alcohol with sodium borohydride to produce a treated alcohol; performing periodic measurement of carbonyl number of the treated alcohol; and stopping the sodium borohydride treatment when the measured carbonyl number reaches a value in the range of 0.05 - 0.20 mg KOH/g, or alternatively a value in the range of 0.08 - 0.15 mg KOH/g, to produce a finished alcohol product. [0009] The inventors also discovered that any trace amounts of dissolved hydrogen created through the hydro finishing treatment may be effectively and safely removed from the alcohol product with little additional expense through a dispersion step. Thus, the process may further include dispersing the treated alcohol through an inert vapor environment. Such dispersion may be accomplished by introducing the treated alcohol into one or more vessels through one or more dispersion inlets, e.g., spray nozzles.

[0010] Additionally, the process may include testing the amount of residual hydrogen in the treated alcohol, such testing comprising (i) collecting a liquid-only sample of the treated alcohol with a pressure-cylinder apparatus; (ii) forming a head space of air in the pressure- cylinder apparatus by draining a portion of the liquid from the cylinder; (iii) chemically treating the alcohol sample in the cylinder with an agent to release hydrogen from dissolved unstable impurities; (iv) agitating the sample until hydrogen is equilibrated between the liquid phase and vapor phase; and (v) measuring the head space for hydrogen content by gas chromatography. [0011] The present invention also encompasses an alcohol purification system which includes a hydro finishing system downstream of a distillation unit, the hydro finishing system including the following fluidly connected components: an on-line carbonyl content analyzer configured to measure carbonyl content of an alcohol mixture as the alcohol mixture flows through the hydro finishing system; a treatment vessel containing sodium borohydride effective for hydrogenating residual carbonyl-containing compounds in the alcohol mixture; and one or more dispersion vessels, each dispersion vessel comprising a dispersion inlet and a substantially inert or non-flammable vapor space.

[0012] The inventive alcohol purification system may additionally include an automatic closed-loop control system configured to prohibit flow of the alcohol mixture to the treatment vessel when the on-line carbonyl content analyzer measures a carbonyl number at or below a target value, of for example, 0.10 mg KOH/g or 0.15 mg KOH/g.

[0013] It is an object of this invention to provide a simple and effective process for production and treatment of synthetic alcohol resulting in the substantial removal of carbonyl- containing impurities from the alcohol, while preventing the presence of unsafe levels of residual hydrogen in the finished alcohol product.

[0014] The embodiments listed above are not mutually exclusive and may be combined. These and other embodiments, objects, features, and advantages will become apparent as reference is made to the following drawings, detailed description, examples, and appended claims.

BRIEF DESCRIPTION OF THE FIGURES

[0015] Figure 1 schematically illustrates a hydro finishing treatment system according to an aspect of the invention.

[0016] Figure 2 charts carbonyl number over time during sodium borohydride treatment of a CIO alcohol sample.

[0017] Figures 3 and 4 chart carbonyl number over time during sodium borohydride treatment of C13 alcohol samples.

[0018] Figure 5 charts carbonyl number and hydrogen formation during treatment of C13 alcohol using 200% of a stoichiometric amount of sodium borohydride relative to the starting carbonyl content of the sample.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Described herein are systems and methods for the manufacture of purified alcohols, particularly Oxo alcohols formed by hydrogenation of aldehydes. Various specific aspects of the invention will now be described, including definitions that are adopted herein for purposes of understanding the claimed invention. While the following detailed description illustrates specific aspects, those skilled in the art will appreciate that the invention can be practiced in other ways. For purposes of determining infringement, the scope of the invention will refer to any one or more of the appended claims, including their equivalents, and elements or limitations that are equivalent to those that are recited. Any reference to the "invention" may refer to one or more, but not necessarily all, of the inventions defined by the claims.

[0020] The invention is in part directed to a process of producing an alcohol including catalytically hydrogenating an aldehyde containing stream to produce a crude alcohol mixture containing at most 2 wt% aldehyde and at least 50 wt% alcohol based on the weight of the total mixture; distilling the crude alcohol mixture to produce a distilled alcohol; treating the distilled alcohol with sodium borohydride to produce a treated alcohol; performing periodic measurement of carbonyl number of the treated alcohol; and stopping the sodium borohydride treatment when the measured carbonyl number reaches a value in the range of 0.05 - 0.20 mg KOH/g to produce a finished alcohol product.

[0021] The alcohol product may contain alcohols with 6 to 15 carbon atoms, including single species or mixtures within that range, such as from 7 to 11 or from 8 to 10, such as 9 carbon atoms. The alcohol product may be an alcohol mixture, and this mixture may have an average carbon number of from 6 to 15 carbon atoms, such as an average carbon number between 8 to 13, such as between 8.5 and 10.5 or between 8.5 and 9.5.

[0022] Referring to Figure 1, an aspect of the inventive process includes catalytically hydro genating aldehyde-rich stream 5 in one or more hydro genation reactors 10, forming a crude alcohol stream 15 comprising at most 2 wt% aldehyde and at least 50 wt% alcohol based on the weight of the total mixture.

[0023] Hydrogenation may employ a heterogeneous catalyst. Many catalyst are suitable for use in this hydrogenation service such as catalysts based on copper, chrome, cobalt, nickel, molybdenum, aluminum oxide, and combinations thereof, for examples cuprous chrome catalysts, sulphided cobalt/molybdenum catalyst, or reduced nickel-molybdenum catalysts, e.g., carried on alumina support, that are disclosed in X. Wang et al, "Characterization of Active Sites over Reduced N1-M0/AI2O3 Catalysts for Hydrogenation of

Linear Aldehydes", J. Phys. Chem. B 2005, 109, pp. 1882-1890. These catalysts may contain no, or only small amounts of phosphorus, such as 0-1.0 %wt P, or 0-0.5 %wt P, as disclosed in U..S. Patent No. 5,382,715. Alternatively, they are substantially free of phosphorus, as disclosed in U.S. Patent No. 5,399,793.

[0024] Liquid phase processes for hydrogenating the C3 to C5 aldehydes produced by low pressure rhodium based hydro formylation processes, or for hydrogenating the C6 to CIO enals or enal mixtures produced by aldolisation of one or more of said C3 to C5 aldehydes, are disclosed in U.S. Pat. No. 4,960,960 or U.S. Pat. No. 5,093,535. These processes include the operation of reactors in series, either as a series of catalyst beds in the same reactor vessel, or as catalyst beds in separate reactor vessels. Many types of fixed bed reactors are suitable for hydrogenation services. Tubular reactors are particularly suitable because of their temperature control advantages, but adiabatic chamber reactors may also be used.

[0025] The hydrogenation reactors may be vertical tubes, provided with a jacket for temperature control and heat removal. They may be operated in upflow or in downflow mode. In the jacket, water or another suitable cooling medium such as an alkanol, or methanol may be circulated using a pumparound system from which hot cooling medium may be withdrawn, and to which cold cooling medium may be supplied. Each reactor may be provided with a so- called conditioner, which is a heat exchanger one side of which is part of the cooling medium circulation, and which on the other side is for conditioning the reactor feed to the appropriate temperature before it passes to the reactor itself. Conditioning of the reactor feed is especially important when a reactor that is not a lead reactor contains relatively fresh and active catalyst, and therefore needs to be operated at start-of-run conditions, this typically requires a lower temperature. The upstream reactor on the other hand, may contain partially deactivated catalyst and therefore needs to be operating at mid-of-run or end-of-run conditions which require a higher temperature. Feed conditioning can therefore avoid a reactor feed that is too hot for an active catalyst to handle, and can therefore reduce the risk for temperature runaway.

[0026] The reactors may be of several known types, or a combination of types, depending on the method of removing the reaction heat and controlling the temperature. The reaction may be carried out in a bundle of tubes containing catalyst where the heat is removed through the tube walls into circulating coolant which may generate steam in-situ, or externally, or with the hot coolant discarded and replaced with cooler water or cooling medium. The temperature profile in such a reactor is controlled to a desired operating window by virtue of the high heat transfer surface compared to the reactor volume.

[0027] The series of hydrogenation reactors may be vertical vessels containing one or more fixed beds of catalyst and are equipped with facilities to distribute the gas and liquid over the catalyst to ensure good contact among the catalyst, liquid and gas phases. The reactors are equipped with facilities to remove the heat of reaction and to control the temperature within the desired range over the life of the catalyst. The reactor dimensions are selected to provide the desired velocity over the beds to give sufficient contacting and to provide adequate residence time to reach the desired conversion of all the components in the feed. Clearly the reactor system will be equipped with that equipment required for startup and shutdown and continuous safety monitoring and response, which need not be described here.

[0028] Any of these reactor types are sufficient and may be used uniformly or mixed considering the differences in efficiency, controllability, safety, and initial investment.

[0029] Referring again to Figure 1, an aspect of the inventive process includes distilling crude alcohol stream 15 in distillation unit 20 to produce distilled alcohol stream 25.

[0030] The crude alcohol product of hydrogenation following the separation of the excess hydrogen comprises a mixture of the desired alcohols, olefins and paraffins, alcohol dimers, acetals and traces of aldehydes, acids and formates together with dissolved carbon dioxide and carbon monoxide, and dissolved hydrogen and water. The crude alcohol may then be cooled and purified further, firstly through a coalescer to remove free water, followed by fractional distillation to separate the desired alcohol from the lower boiling fraction of the mixture and a second distillation step, optionally at a different pressure, to separate the desired alcohol from the higher boiling fraction. Water and any methanol or other lower alcohols typically will be separated with the lower boiling fraction, and may settle out as a separate phase in the tower overhead system, from where they can be discarded or taken for further use. Such a distillation unit may comprise one or more distillation columns, lined up in a 2-tower heart cut formation where the distilled alcohol is taken as overhead of the second tower.

[0031] Carbonyl-containing impurities may be created during distillation when air enters the distillation system through leaks. In the presence of air and distillation temperatures, the crude alcohol product of the hydrogenation step may react back into aldehydes. The inventors have found that the creation of aldehydes during distillation may be minimized under certain conditions. It is known to be advantageous to reduce the acidity of a hydrogenation product stream by treating it with a dilute alkaline solution before it is sent to distillation, preferably by dilute sodium hydroxide or caustic, as disclosed in U.S. Patent No. 8,247,618. However, the creation of carbonyl-containing species during distillation may be reduced or eliminated by limiting the amount of sodium hydroxide or caustic present in the distillation feed. For example, an alcohol product distilled from a crude alcohol distillation feed that has not been treated with NaOH may have more than 4 times less carbonyl-containing species than an alcohol product distilled from a caustic-treated crude alcohol, assuming identical distillation conditions. Therefore, the amount of NaOH present in the distillation feed may be zero. Second, the creation of carbonyl-containing species during distillation may be minimized by controlling the distillation temperatures. Typically, distillation may be accomplished at bottoms temperatures of 200°C to 280°C, such as 240°C. By operating one or more of the distillation columns at a lower temperature, for example at 200°C, the amount of carbonyl- containing species present in the distilled alcohol product may be reduced by over half. Therefore, in an aspect of the invention, the distillation unit comprises one or more distillation columns and the distillation columns are operated at a depressed temperature in the range of 200°C to 240°C.

[0032] Referring to Figure 1, an aspect of the inventive process includes treating distilled alcohol stream 25 until it has a carbonyl number within the range 0.05 - 0.20 mg KOH/g to produce a treated alcohol stream 35.

[0033] The distilled alcohol may contain trace aldehydes and other carbonyl-containing impurities that are not hydrogenated during the hydrogenation step and/or carbonyl- containing impurities that are products of side reactions occurring during distillation. The inventive process thus provides a hydro finishing step, or treatment step to convert the carbonyl-containing impurities remaining in the distilled alcohol. This step may comprise treating the distilled alcohol with an alkali metal borohydride compound such as sodium borohydride. [0034] The amount of residual aldehydes and ketones may be expressed as a carbonyl number. The theoretical carbonyl number (TCBN) of a material is traditionally reported in mg KOH per gram of sample. This originated from the fact that historically KOH was used to titrate the HCL liberated when the carbonyl compound reacted with hydroxylamine hydrochloride. The theoretical value for a pure carbonyl compound is expressed by the following formula:

TCBN = (FWKOH/FWCARBONYL COMPOUND) X (NCARBONYL COMPOUND) X 1000 mg/ g

where FW is the formula weight of the species specified in the equation. N is the number of active carbonyl groups in the carbonyl compound. The TCBN for pure 2-octanone, typically used as a calibration standard, is 438. The carbonyl number (CBN) for a standard is expressed by the following formula:

CBN=(W x TCBN x P)/T

where W is the weight of carbonyl compound; P is the percent purity of carbonyl compound; T is the total weight of standard. The CBN for 98% pure 2-octanone is 429 (W/T=l). The units for both TCBN and CBN are mg KOH/g, which are typically omitted in reporting the respective numbers.

[0035] Referring again to Figure 1, in an aspect of the invention, distilled alcohol stream 25 is treated in treatment vessel 30 which contains tablets of alkali metal borohydride, including, without limitation, sodium borohydride. Distilled alcohol stream 25 is treated at a temperature of 50°C to 100°C, or alternatively about 70°C. It has been found that the treatment effect is faster with increasing temperature. For example, whereas it may take 90 minutes of treatment to reduce the carbonyl number of an alcohol mixture from about 1.0 to 0.1 at 100°C, it may take 210 minutes of treatment to reduce the same alcohol mixture from about 1.0 to 0.1 at 80°C. It has also been found that the treatment effect is faster with lower molecular weight aldehydes, and with offering a higher accessible tablet surface to the liquid. Thus, alternatively to tablets, the alkali metal borohydride may take the form of a powder or solution. Such a solution may comprise water or ethanol and may additionally contain some amount of caustic NaOH. The alcohol may be recycled by pump 40 through on-line analyzer 50 and heat exchanger 60 back to treatment vessel 30 if needed to reach the target carbonyl number.

[0036] Before treatment, the distilled alcohol may have a carbonyl number in the range of 0.2 - 2.0 mg KOH/g. In an aspect of the invention, 95-200%, or alternatively 97-100% of a stoichiometric amount of sodium borohydride is used to treat the distilled alcohol, based on the number of moles of carbonyl compounds present in the distilled alcohol. In another aspect of the invention, the distilled alcohol is treated to remove carbonyl-containing compounds until the treated alcohol has a carbonyl number within the range of 0.05- 0.20 mg KOH/g to produce a treated alcohol. Or the distilled alcohol may be treated until it has a carbonyl number within the range of 0.08 - 0.15 mg KOH/g. The inventors have found that if the sodium borohydride (NaBH₄) treatment is ceased while the treated alcohol has a carbonyl number over this threshold, then an unacceptable amount of impurities may remain in the finished alcohol. However, NaBH₄ treatment below this carbonyl number may result in compounds dissolved in the treated alcohol that can decompose slowly, releasing detrimental quantities of hydrogen into the treated alcohol. Moreover, the inventors have found that that the potential hydrogen released from over-treated product alcohol cannot be fully controlled using typical flashing and/or stripping techniques alone. However, it has been found that heating over-treated product alcohol and holding it at elevated temperature, for example at 60°C to 90°C, for an extended period of time, for example for 24 hours to 72 hours, is effective in reducing measured hydrogen content.

[0037] It is thus important to accurately measure the carbonyl number of the alcohol product during the treatment process. Measurement may be accomplished by wet chemical analysis either manually, as described in U.S. Patent App. Pub. 2006/0105464, or through online analysis, as described in co-pending US patent application No. 62/040,815. Using a manual process, measurement may be done on samples taken during the treatment process at a frequency depending on the alcohol grade. Analysis of the treated alcohol is required every 30 minutes to one hour when treating begins, then every 15 to 20 minutes as the target carbonyl number, for example 0.15 mg KOH/g, is closely approached.

[0038] An on-line analysis method, as described in co-pending US patent application No. 62/040,815, may be utilized to measure carbonyl number in real time with minimal operator intervention and automatic control integration. On-line measurement of carbonyl number of the distilled alcohol may be performed while treating the distilled alcohol with sodium borohydride and the sodium borohydride treatment may be stopped when the measured carbonyl number reaches a value in the range of 0.05 - 0.20 mg KOH/g, or when the measured carbonyl number reaches a value in the range of 0.08 - 0.15 mg KOH/g, or alternatively when the measured carbonyl number reaches a target value such as 0.10 mg KOH/g or 0.15 mg KOH/g. The on-line analyzer may feed real time data to an automatic closed-loop control system configured to prohibit flow of the alcohol mixture to the treatment vessel when the on-line analyzer measures a carbonyl number in the target range or at the target value. [0039] In an aspect of the invention, the alcohol stream is dispersed through an inert or non-flammable environment after or in conjunction with sodium borohydride treatment. With reference to Figure 1, the alcohol stream may thus be directed through or stored in one or more dispersion vessels 70. Dispersion vessel 70 may contain an internal vapor space that comprises an inert gas, e.g., nitrogen from inert gas source 45, or is otherwise non-flammable. The alcohol stream is introduced into dispersion vessel 70 in a manner that physically disperses the alcohol liquid to create mass transfer that closely equilibrates hydrogen between the liquid phase and the vapor phase. In an aspect of the invention, the alcohol stream is thus "splash loaded" into dispersion vessel 70, e.g., introduced into the vapor space of dispersion vessel 70 through one or more dispersion inlets 80. Dispersion inlets may comprise spray nozzles. The alcohol stream may be pumped to the top of dispersion vessel 70 and introduced through dispersion inlets 80 located vertically above the liquid level in the dispersion vessel, rather than following the conventional method of filling a tank from the bottom.

[0040] This dispersion step urges residual hydrogen out of solution from the treated alcohol. This is enabled by the fact that Oxo alcohols are non-static accumulators. Further, the inert atmosphere in the dispersion vessel, e.g., due to the inclusion of nitrogen, prevents the formation of a flammable vapor space. If the sodium borohydride treatment is monitored in real time and closely controlled as described, it has been found that 1 or 2 splash loading steps is sufficient to remove residual hydrogen to render the product alcohol safe for all potential downstream handling and transport.

[0041] The inventive process may also include testing the amount of residual hydrogen in the treated alcohol. Overtreatment with sodium borohydride may leave compounds in the product alcohol that slowly decompose into free hydrogen. Because the hydrogen is not immediately present as free hydrogen, instead being slowly released over time through the decomposition of hydrogen-containing impurities, direct measurements of hydrogen in gas phase after treatment do not give an accurate indication of the long term safety of a finished alcohol product. The inventors have found that the residual hydrogen level of a sodium borohydride-treated Oxo alcohol can be tested through several steps comprising an aspect of the invention.

[0042] First, a sample of treated alcohol is collected using a pressure-cylinder apparatus. Such pressure-cylinder apparatuses may be constructed from components available from Swagelok Company. Assembled cylinders are commercially available from suppliers such as Sampling Systems, a division of PMMI, Inc. With a pressure-cylinder apparatus, a liquid-only sample may be captured. Alternatively, any method of capturing a liquid-only sample can be used. Next, a head space of air is created in the cylinder. This can be accomplished for example by draining some of the sample, typically 20%, and allowing air ingress into the cylinder. The hydrogen-containing impurities then may be decomposed, causing the release of the chemically captured hydrogen. In one aspect of the invention, the cylinder-contained sample is chemically treated with an agent to release hydrogen from dissolved unstable impurities. The agent may be any compound or mixture, such as, without limitation, acetic acid, that can decompose excess sodium borohydride and other hydrogen-containing impurities. Enough agent is added to ensure that substantially all hydrogen-containing impurities are decomposed. The cylinder then may be agitated, e.g. shaken, in order to generate the equilibrium of hydrogen between the liquid phase and gas phase. After the decomposed sample reaches equilibrium, the vapor in the headspace may be tested by gas chromatography or other known methods to determine the quantity of hydrogen present.

[0043] Importantly, this method results in an accurate assessment of the maximum amount of hydrogen that would be released from an alcohol product over time after its hydrogen-containing impurities would have decomposed during transport and storage. Thus this measurement can be an indicator of long term safety of the alcohol product in terms of free hydrogen and expected hydrogen release. The measured hydrogen content of the sample can be used to calculate the maximum potential hydrogen remaining in the alcohol product by using standard vapor-liquid equilibrium calculations, well known by those skilled in the art. Based on these calculations and the lower explosive limit of hydrogen, a target maximum for sample hydrogen content may be determined. After conservatively accounting for the most extreme downstream handling and storage possibilities and building in a sufficient safety factor, it has been found that a measured hydrogen content of 0.6 vol% or less, based on the volume of the sample head space, is safe for all downstream handling. Additional dispersion steps in series may be utilized if necessary to reduce hydrogen content to safe levels before downstream handling and storage. Thus, in another aspect of the invention, if the hydrogen in the vapor phase of the agitated sample cylinder is above 0.6 vol%, then the dispersion step is repeated for the treated alcohol stream in order to further reduce the hydrogen content of the final alcohol product.

[0044] An additional testing step may be taken to detect the presence of peroxides in the alcohol product. Peroxides may be formed in the alcohol stream due to air ingress during distillation. Peroxides present in the alcohol product may or may not be indicated in carbonyl number measurements. Some methods of carbonyl number measurement may indicate the presence of peroxides in addition to aldehydes or ketones. Specifically, it has been found that testing for carbonyl number using a free hydroxylamine method yields higher results for alcohol containing peroxide than for alcohol where all peroxides have been decomposed with triphenylphosphine (TPP). A quick test can be performed to detect the presence of peroxide by dipping a peroxide test strip into a sample of the alcohol product. Typical commercially available peroxide test strips register peroxide content by color. After dipping the peroxide test strip into the alcohol sample, the test zone of the strip is compared against a color scale that indicates peroxide content. It has been found that the use of such strips can constitute a semi-quantitative measurement of peroxides in alcohol, as such strip tests correlate well with peroxide titration. This information can be useful in troubleshooting the origin of a carbonyl number measurement, e.g., identifying the presence of air ingress in the alcohol distillation unit.

[0045] The inventive process can be used to produce alcohol product substantially free of carbonyl-containing compounds and residual hydrogen. This is the case even when it is necessary to treat the hydro formylation product with alkali metal salt, the presence of which has been found to increase aldehyde creation during alcohol distillation. Thus, it is an aspect of the invention that the crude alcohol mixture contains an alkaline compound prior to distillation.

[0046] The techniques of the present invention may be used in connection with the cobalt catalyzed hydro formylation reactions as described in WO 2005/058787. The products of such a cobalt catalyzed reaction include aldehydes, alcohols, formate esters, acetals, ethers, ether- alcohols, as well as unreacted olefins and paraffins.

[0047] The olefinic material that is hydroformylated may be short or long chained compounds containing olefinic unsaturation, depending on the final product desired. Most organic compounds possessing at least one non-aromatic carbon-carbon double bond may be reacted by this method. Generally the compound will have at least five carbon atoms. Thus, straight and branched-chain olefins such as pentenes, hexenes, heptenes, octenes, nonenes, decenes, undecenes, dodecenes, tridecenes and tetradecenes, styrene, olefin oligomers such as di- and tri-isobutylene and hexene and heptene dimers, olefinic fractions from the hydrocarbon synthesis process, thermal or catalytic cracking operations, and other sources of hydrocarbon fractions containing olefins, and mixtures of all of these, may be used as starting material, depending upon the nature of the final product desired. The feed may include a mixture of isomers, both skeletal and in double bond location or it may be isomerically pure (or nearly so) skeletally and/or in double bond location. The feed may comprise LAOs and/or LIOs (linear alpha olefins and linear internal olefins, respectively), which terms are well- known in the art, as olefinic material.

[0048] The olefmic material may be a mixture of olefins having a carbon number of from C5 to Ci g, or alternatively Cg to C15. It will be recognized that the olefin feed may not consist of 100% olefins, nor of 100% olefins within the specified carbon number range, but may be a distribution of olefins having different carbon chain lengths. At least 50 wt%, or 70 wt%, or 80 wt%, or alternatively, 90 wt% of olefins are in the specified carbon number range. In certain cases it may be preferable to use a feed of 100 wt% (or nearly so) of the specified carbon number or carbon number range.

[0049] The olefinic material may be the olefinic reaction product of the acid catalyzed oligomerisation of lower olefins, including without limitation propylene and/or butenes, which may also optionally also include pentenes. Ethylene may be present in minor quantities during oligomerisation, as well as trace quantities of dienes or acetylenes such as butadiene, methyl acetylene, propadiene or pentadienes. Heavier olefins may be added to the feed, selectively separated and recycled from the oligomerisation product, to selectively increase the production of selected carbon number products. The olefinic material may also be the olefinic reaction product of the oligomerisation of various lower olefins and compounds having olefinic unsaturation, using regular or surface deactivated zeolite catalysts, or siliceous monodimensional acidic zeolites.

[0050] By "lower olefins" or "lower olefinic material" as used herein is simply meant that the starting material to be oligomerised over the zeolite has lower carbon numbers than the final product. The oligomers may be dimers, trimers, tetramers or higher oligomers, or mixtures thereof. The starting material may be a C3 or greater olefin (or mixtures thereof), and the olefinic material may be supplied to the oxonation reactor(s) according to the present invention derived from the oligomerisation of C3 and/or C4 olefins using the aforementioned modified zeolites. A feed may comprise butenes (including without limitation n-butene) and propylene in the ratio of about 1 :0.01 to 1 :0.049 wt%. Conveniently, paraffins are also present in the feed to act as a heat sink in the reaction. The amount of paraffins to use to provide a desired heat sink function can be readily determined by one of ordinary skill in the art.

[0051] Other olefinic materials that may be used as a feed into the oxonation or hydro formylation reactors include oligomers produced by the Octol® process or the Dimersol® process. See, for instance, the previously mentioned U.S. Patent No. 6,015,928. Octol® and Dimersol® are registered trademarks owned respectively by Degussa and Institut Francais du Petrole (IFP). Other olefinic materials may be made using the process as described in U.S. Patent No. 6,437,170. Yet other olefinic materials include oligomers produced using solid phosphoric acid (SPA) catalysts and those produced using ZSM-5, ZSM-57 and/or SAPO-11 catalysts, procedures which are known in the art. Other olefinic materials may be produced using oligomerisation processes as disclosed in WO 2006/133908, WO 2006/133967 or WO 2007/006398.

[0052] Typical hydro formylation reaction conditions include a temperature of about 125°C to about 200°C and/or a pressure of about 100 bar to about 350 bar, and/or a catalyst to olefin ratio of about 1 : 10000 to about 1 : 1. The molar ratio of hydrogen to carbon monoxide is conveniently in the range of about 0.5 to about 10. The process may also be carried out in the presence of an inert solvent such as a ketone, e.g., acetone, or an aromatic compound such as benzene, toluene or xylenes.

[0053] Any type of hydro formylation reactor may be operated in combination with the present invention. Suitable hydro formylation reaction systems are described e.g., in U.S. Patent Nos. 3,830,846; 6,444,856; 6,642,420; 6,723,884; 4,320,237; 6,720,457; and 6,015,928.

[0054] The high purity alcohols produced from the invention may then be used for example in the production of plasticiser esters and synthetic lubricants through esterification with an acid or anhydride. The acid or anhydride may be selected from the group consisting of benzoic acid, phthalic acid, adipic acid, trimellitic acid, cyclohexanoic acid, cyclohexanoic dibasic acid, pyromellitic acid and their anhydrides. Particularly the phthalate esters are of significant commercial importance. Suitable esterification reactions are described in WO 2005/021482, WO 2008/110305 and U.S. Patent No. 8,344,174 respectively. If the alcohol is a polyol, a polyol ester is typically produced. Optionally, not all of the hydroxyl functions are esterified, and free alcohol functions may remain present in the polyol ester, such as from 5 to 35% relative to the starting alcohol functions in the polyol. These polyol esters may also find use as synthetic lubricants. Further esters of commercial interest may be made by esterification of the high purity alcohols made according to the invention with an acid or anhydride. The acid or anhydride may be selected from the group consisting of adipic acid, benzoic acid, cyclohexanoic acid, phthalic acid, cyclohexanoic dicarboxylic acid, trimellitic acid, or any of their anhydrides, or mixtures thereof.

[0055] The ester molecules produced using the process of the invention may comprise aromatic rings, such as alkyl benzoates, di-alkyl phthalates or tri-alkyl trimellitates. The aromatic rings in these ester molecules may be hydrogenated to produce the corresponding cyclohexane equivalents, such as mono-alkyl, di-alkyl or tri-alkyl cyclohexanoates. In particular, di-isononyl phthalate (DINP) may be further hydrogenated to form di-isononyl cyclohexanoate. The process of the invention may therefore be for the production of a phthalate di-ester, in particular DINP, and further comprise the hydrogenation of the phthalate di-ester to the corresponding cyclohexanoate, in particular di-isononyl cyclohexanoate. Suitable hydrogenation processes are disclosed in EP Patent No. 1,042. 273, and U.S. Pat. Nos. 7,683,204; 7,875,742; and 8,203,017.

[0056] A further aspect of the invention is directed to an alcohol purification system including a hydro finishing system downstream of a distillation unit. The distillation unit may comprise one or more distillation columns as described. The hydro finishing system may include the following fluidly connected components: an on-line carbonyl content analyzer configured to measure carbonyl content of an alcohol mixture as the alcohol mixture flows through the hydro finishing system; a treatment vessel containing sodium borohydride effective for hydrogenating residual carbonyl-containing compounds in the alcohol mixture; one or more dispersion vessels, each dispersion vessel comprising a dispersion inlet and a substantially inert or non-flammable vapor space. Each dispersion inlet may comprise a spray nozzle located vertically above the liquid level in the corresponding dispersion vessel. The inventive alcohol purification system may also include an automatic closed-loop control system configured to prohibit flow of the alcohol mixture to the treatment vessel when the on- line carbonyl content analyzer measures a carbonyl number in the range of 0.05 - 0.20 mg KOH/g, or a carbonyl number in the range of 0.08 - 0.15 mg KOH/g, or alternatively a target value such as 0.10 mg KOH/g or 0.15 mg KOH/g.

Examples

[0057] The advantages of the systems and methods described herein will now be further illustrated with reference to the following non-limiting Examples.

Example 1

[0058] An isodecyl alcohol mixture was treated with sodium borohydride in a treatment vessel to lower the carbonyl compound content. The alcohol mixture was introduced at 75°C into the treatment vessel containing sodium borohydride in tablet form. The alcohol mixture was then circulated through the treating system as necessary to reduce the carbonyl number to the target value. The carbonyl number of the alcohol mixture was measured before beginning treatment and at frequent intervals during treatment according to the method disclosed in co-pending US patent application No. 62/040,815 ("Method 1"). Using Method 1, a sample of the alcohol mixture was taken and then mixed with a solution of 2,4-dinitrophenylhydrazine (DNPH) and sulfuric acid. A portion of the resulting reaction mixture was then mixed with an aqueous NaOH solution and a denatured alcohol solution. This final mixture was then analyzed in a Hunter colorimeter.

[0059] Carbonyl number was also measured according to the alternative procedure disclosed in U.S. Patent Publication No. 2006/0105465 ("Method 2"). Using Method 2, a sample of the alcohol mixture was taken and then mixed with a solution of 2,4-dinitrophenylhydrazine (DNPH) and sulfuric acid. A portion of the resulting reaction mixture was then mixed with a solution of KOH and denatured alcohol. This mixture was filtered, and then analyzed in a Hunter colorimeter. The treatment was continued until a measurement indicated that the alcohol had reached a target carbonyl number of 0.1-0.2, after which, the alcohol was routed away from the treatment vessel.

[0060] The results of the carbonyl measurement during treatment of the isodecyl alcohol mixture for Example 1 are shown in Figure 2. The final carbonyl number as measured by Method 2 was 0.144 mg KOH/g.

[0061] After treatment, the alcohol mixture was tested for hydrogen content. Using a sampling cylinder, available from Sampling Systems of Sweeny, TX, a liquid-only sample of the treated alcohol was collected. 120 ml of alcohol was drained from the cylinder and air ingress into the cylinder was allowed. 20 ml of 10% acetic acid was then injected into the cylinder and the cylinder was mechanically shaken for 10 minutes. The cylinder was then allowed to rest for 1 minute. 1 ml of gas from the cylinder head space was then taken and measured using gas chromatography for hydrogen content. The hydrogen content was found to be 2.61 vol%.

[0062] The results of Example 1 show that closely monitored and targeted sodium borohydride treatment can result in advantageously low carbonyl content in a final Oxo alcohol product. This alcohol product may then subsequently be splash loaded according to the invention until the measured hydrogen content is reduced to a safe amount, such as at or below 0.6 vol%.

Examples 2 and 3

[0063] Tridecyl alcohol mixture was treated and tested using the same procedure as Example 1 above, except treatment was performed at 85°C. Examples 2 and 3 were performed using different vessels and vary in total treatment time and final carbonyl number. The carbonyl measurement results of Example 2 appear in Figure 3 and the results of Example 3 appear in Figure 4. For Example 2, the final carbonyl number as measured by Method 2 was 0.05 mg KOH/g and the hydrogen content was 6.42 vol%. For Example 3, the final carbonyl number as measured by Method 2 was 0.02 mg KOH/g and the hydrogen content was 9.56 vol%.

[0064] The results of Examples 2 and 3 show that as Oxo alcohol is over-treated to a carbonyl number below about 0.05 mg KOH/g, the residual hydrogen level increases. The high amount of hydrogen in these treated alcohols may require several subsequent splash steps in series to reduce hydrogen to safe levels in the alcohol product.

Example 4

[0065] Distilled tridecyl alcohol mixture was treated in a laboratory with sodium borohydride at 200% of a stoichiometric amount, based on the number of moles of carbonyl compounds present in the distilled alcohol. The carbonyl number of the alcohol mixture and the amount of free hydrogen formed during treatment were measured periodically. Figure 5 shows the results of this test, with carbonyl number and hydrogen formation charted vs. treatment time.

[0066] The results of Example 4 show that most hydrogen formation during treatment occurs after the carbonyl number of the alcohol mixture drops below about 0.05 mg KOH/g. Thus, by avoiding over-treatment below 0.05 mg KOH/g, free hydrogen formation can largely be avoided.

Example 5

[0067] Oxo alcohols treated with sodium borohydride were captured in Vessel 1 containing a nitrogen-filled vapor space. The alcohol was then tested for hydrogen content using the method of Example 1. After testing, the alcohol was pumped to Vessel 2, where it was injected into a nitrogen-inerted vapor space using a spray nozzle. Hydrogen content testing was then repeated using the method of Example 1. This procedure was performed for isononyl alcohol and separately using isotridecyl alcohol. The results of each hydrogen measurement appear in Table 1.

Table 1

[0068] The results of Example 5 show that a dispersion step can reduce the unstable hydrogen content in a finished alcohol product.

[0069] The embodiments and examples set forth herein are presented to best explain the present invention and its practical application and to thereby enable those skilled in the art to make and use the invention. However, those skilled in the art will recognize that the foregoing description have been presented for the purpose of illustration and example only. The description set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching without departing from the spirit and scope of the claims.

Claims

CLAIMS What is claimed is:

1. A process for producing purified alcohols comprising:

catalytically hydrogenating an aldehyde containing stream to produce a crude alcohol mixture containing at most 2 wt% aldehyde and at least 50 wt% alcohol based on the weight of the total mixture;

distilling the crude alcohol mixture to produce a distilled alcohol;

treating the distilled alcohol with sodium borohydride to produce a treated alcohol; performing periodic measurement of carbonyl number of the treated alcohol; and stopping the sodium borohydride treatment when the measured carbonyl number reaches a value in the range of 0.05 - 0.20 mg KOH/g.

2. The process of claim 1, wherein the sodium borohydride treatment is stopped when the measured carbonyl number reaches a value in the range of 0.08 - 0.15 mg KOH/g.

3. The process of any of the preceding claims, wherein the periodic measurement is performed by on-line analysis.

4. The process of any of the preceding claims, wherein 97-100% of a stoichiometric amount of sodium borohydride is used to treat the distilled alcohol, based on the number of moles of carbonyl compounds present in the distilled alcohol.

5. The process of any of the preceding claims, further comprising dispersing the treated alcohol through an inert vapor environment.

6. The process of claim 5, wherein the treated alcohol is dispersed by introducing the treated alcohol into one or more vessels through one or more spray nozzles.

7. The process of any of the preceding claims, wherein the crude alcohol mixture contains an alkaline compound prior to distillation.

8. The process of any of the preceding claims, wherein the crude alcohol is treated with an alkaline solution before it is sent to distillation

9. The process of any of claims 5 or 6 further comprising:

testing the amount of residual hydrogen in the treated alcohol, such testing comprising:

(i) collecting a liquid-only sample of the treated alcohol with a pressure- cylinder apparatus;

(ii) forming a head space of air in the pressure-cylinder apparatus by draining a portion of the liquid from the cylinder;

(iii) chemically treating the alcohol sample in the cylinder with an agent to release hydrogen from dissolved unstable impurities;

(iv) agitating the sample until hydrogen is equilibrated between the liquid phase and vapor phase; and

(v) measuring the head space for hydrogen content by gas chromatography.

10. The process of claim 9, wherein the agent is acetic acid.

11. The process of claims 9 or 10, further comprising:

repeating the dispersion step of claim 5 for the treated alcohol if the hydrogen content in the vapor phase of the agitated sample cylinder is above 0.6 vol%.

12. An alcoho 1 purification system comprising :

a distillation unit comprising one or more distillation columns downstream of a hydro genation reactor; and

a hydro finishing system downstream of the distillation unit comprising the following fluidly connected components:

an on-line carbonyl content analyzer configured to measure carbonyl content of an alcohol mixture as the alcohol mixture flows through the hydro finishing system; a treatment vessel containing sodium borohydride effective for hydrogenating residual carbonyl-containing compounds in the alcohol mixture;

one or more dispersion vessels, each dispersion vessel comprising a dispersion inlet and a substantially inert or non-flammable vapor space.

13. The system of claim 12, wherein the dispersion inlet comprises a spray nozzle located vertically above the liquid level in the dispersion vessel.

14. The system of claims 12 or 13, further comprising:

an automatic closed-loop control system configured to prohibit flow of the alcohol mixture to the sodium borohydride treatment vessel when the on-line carbonyl content analyzer measures a carbonyl number in the range of 0.05 - 0.20 mg KOH/g.

15. The system of any of claims 12-14, wherein the automatic closed-loop control system is configured to prohibit flow of the alcohol mixture to the treatment vessel when the on-line carbonyl content analyzer measures a carbonyl number in the range of 0.08 - 0.15 mg KOH/g.