A continuous process for the conversion of carbohydrates to ethylene glycol.

Abstract

The process of the present invention provides for the conversion of carbohydrates to ethylene glycol by retro-aldol catalysis and sequential hydrogenation using a controlled method having at least one of acetol (hydroxyacetone) and a tracer as inputs.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. §119(e) of U.S. Application No. 62 / 905,068, filed September 24, 2019, and entitled "METHODS FOR OPERATING CONTINUOUS, UNMODULATED, MULTIPLE CATALYTIC STEP PROCESSES," which is incorporated by reference in its entirety for all purposes.

[0002] Technical Field This invention relates to a process for the catalytic conversion of carbohydrates to ethylene glycol via a retro-aldol / hydrogenation route. [Background technology]

[0003]

[0003] Ethylene glycol is a useful commodity chemical with widespread applications both as a building block for other materials such as polyethylene terephthalate (PET) as well as for its inherent properties, for example, in antifreeze. The demand for ethylene glycol is substantial, making it one of the most highly produced organic chemicals in the world. Currently, ethylene glycol is made by a multi-step process that begins with ethylene from a hydrocarbon feedstock.

[0004]

[0004] Proposals have been made to produce ethylene glycol from renewable resources such as carbohydrates. These alternative processes include catalytic routes, such as hydrogenolysis of sugars, and catalytic processes using retro-aldol catalysts to generate intermediates from sugars that are hydrogenated over a hydrogenation catalyst to produce ethylene glycol and propylene glycol.

[0005] In the retro-aldol pathway, carbohydrates are converted to intermediates over a retro-aldol catalyst, and the intermediates are then catalytically converted to ethylene glycol and / or propylene glycol over a hydrogenation catalyst in an unmodulated reaction zone. As used herein, the term unmodulated means that the process is carried out in a single pot, or in the case of multiple vessels or zones, intermediates are not removed between vessels or zones. The required initial retro-aldol reaction is endothermic and requires high temperatures, e.g., often above 230°C, to provide sufficient reaction rates to preferentially select for the conversion of the carbohydrate to the intermediate. Isomerization of sugars may be carried out under conditions favorable for retro-aldol conversion. For example, aldoses such as glucose can be isomerized to fructose. Under retro-aldol conditions, aldoses such as glucose provide intermediates containing two carbon atoms, e.g., glycolaldehyde, which can be hydrogenated to ethylene glycol. Under retro-aldol conditions, fructose is converted to intermediates containing three carbon atoms, among others, which under hydrogenation conditions provide propylene glycol and glycerol. In addition, retro-aldol intermediates such as glycolaldehyde may react to provide by-products such as 1,2-butanediol. Furthermore, hydrogenation may cause decomposition of ethylene glycol and propylene glycol. Because hydrogen is required, mass transfer of hydrogen to the catalytic sites may be insufficient to sustain hydrogenation, and this hydrogen deficiency may cause the production of by-products such as organic acids. Therefore, to optimize the production of ethylene glycol in an unregulated reaction zone, the retro-aldol conversion conditions and the hydroconversion conditions need to be balanced. Summary of the Invention [Problem to be solved by the invention]

[0006]

[0006] There is therefore a need to provide a method for controlling a retro-aldol / hydrogenation process using an unregulated reaction zone. Moreover, it is desirable for such a method to use input parameters that can be reasonably obtained from the process, particularly input parameters that can be ascertained relatively quickly to provide real-time data regarding the operation of the process. [Means for solving the problem]

[0007]

[0007] The present invention provides a process for the conversion of carbohydrates to ethylene glycol by retro-aldol catalysis and sequential hydrogenation using a control method having at least one acetol (hydroxyacetone) as an input and at least one tracer. The tracer precursor is one or more ketones having 3-6, preferably 4-6 carbons, and the tracer is one or more of the unreacted tracer precursor and hydrogenation products of the ketone, such as alcohol, in the raw product resulting from feeding the ketone to the reaction zone. The acetol concentration in the raw product reflects both the relative amount of aldose isomerization and information on hydrogenation, since acetol is a three-carbon compound obtained from retro-aldol catalysis of fructose. The tracer reflects the hydrogenation intensity, since the carbonyl of the ketone does not undergo retro-aldol transformation. Since the conversion of carbohydrates does not result in the co-production of hydrocarbons with only internal carbonyls or internal hydroxyls, inputs based on one or more tracers are not confounded as by-products. A control system useful for the retro-aldol / hydrogenation conversion of carbohydrates to ethylene glycol may employ one or more of a number of other inputs, such as pressure, temperature, residence time, pH, raw product composition, feed composition and rate. Acetol and / or tracers provide information not readily available otherwise regarding the conditions of the process, and thus their use as inputs to the control system can provide more robust and useful process control. An increase in acetol concentration in the raw product has been found by this invention to be a precursor to an observable decrease in selectivity to ethylene glycol. Thus, process changes can be implemented in a timely manner to maintain conversion and selectivity to ethylene glycol. Similarly, tracers specifically target hydrogenation activity, helping to avoid confusion as to whether changes in by-products or product production are due to problems with retro-aldol catalyst activity or hydrogenation catalyst activity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Any suitable process control system may be used, and a more scalable control system for the present process may be used, which may be a design space system (DSC) or a model predictive control system (MPC), both of which are well known in the art and are often preferred. In DSC, boundary conditions or windows are pre-determined and operation within the window is considered to be under control. In MPC, dynamic process models are often created empirically and take into account future effects on the process in addition to the current control status. Control effects in MPC may be based on predictive models that look ahead to future events. However, the disclosed process using either or both of acetol and tracers in the raw product enhances the ability to control the process, regardless of whether the control is manual or based on a sophisticated control system.

[0009]

[0009] One broad aspect relates to a continuous process having a control system for controlling one or more operating parameters based on one or more inputs for catalytic conversion of at least aldose- or ketose-producing carbohydrate feeds to at least one of lower glycols, ethylene glycol and propylene glycol, in an unmodulated reaction zone, by sequential retro-aldol catalytic conversion to intermediates under retro-aldol conditions, including the presence of a retro-aldol catalyst providing retro-aldol catalytic activity in a liquid medium, in the unmodulated reaction zone, and catalytic hydrogenation of the intermediates to lower glycols under hydrogenation conditions, including the presence of hydrogen and a hydrogenation catalyst providing hydrogenation catalytic activity in the unmodulated reaction zone, and continuously or intermittently withdrawing a raw product from the unmodulated reaction zone, the process comprising controlling at least one operating parameter of the process using the concentration of acetol in at least the raw product as an input to the control system for the process. Preferably, the carbohydrates include aldoses and the lower glycols include ethylene glycol.

[0010]

[0010] Acetol is derived from fructose, and therefore its concentration depends on the fructose produced, so changes in the concentration of fructose must be taken into account. In a preferred process for making ethylene glycol, in response to an increase in acetol concentration, even without evidence of a decrease in retro-aldol catalytic activity, at least one of (i) increasing hydrogenation catalytic activity and (ii) decreasing at least one of the rate of feeding the carbohydrate feed and the concentration of the carbohydrate in the feed is performed. For example, if there is evidence of a decrease in retro-aldol catalytic activity with an increase in mannitol or glycerol, and the increase in acetol is greater than expected from the decrease in retro-aldol catalytic activity, it would suggest decreasing at least one of the rate of feeding the carbohydrate feed and the concentration of the carbohydrate in the feed until retro-aldol catalytic activity is restored.

[0011] Another broad aspect relates to a continuous process having a control system for controlling one or more operating parameters based on inputs for catalytic conversion of an aldose- or ketose-producing carbohydrate feed to at least one of lower glycols, ethylene glycol and propylene glycol, in an unregulated reaction zone, said catalytic conversion comprising sequential retro-aldol catalytic conversion to intermediates under retro-aldol conditions comprising the presence of a retro-aldol catalyst providing retro-aldol catalytic activity in a liquid medium in the unregulated reaction zone, catalytic hydrogenation of the intermediates to lower glycols under hydrogenation conditions comprising the presence of hydrogen and a hydrogenation catalyst providing hydrogenation catalytic activity in the unregulated reaction zone, feeding a ketone having 3 to 6, preferably 4 to 6 carbons, to a reaction zone in which a tracer is produced under conditions of the reaction zone, and continuously or intermittently withdrawing a raw product from the unregulated reaction zone, said process comprising controlling at least one operating parameter of the process using at least the concentration of at least one component of the tracer in the raw product as an input to a control system for the process.

[0012]

[0012] If the tracer indicates a change in the hydrogenation of the ketone, then preferably at least one of (i) and (ii) is adjusted: (i) the absolute amount of catalytically active species and the relative amounts of retro-aldol catalytic activity and hydrogenation catalytic activity, respectively, and (ii) at least one of the feed rate and carbohydrate concentration to the reaction zone. If more ketone is hydrogenated, often at least the feed rate to the reaction zone is increased or the hydrogenation catalytic activity is decreased. If less ketone is hydrogenated, preferably either or both of (i) the hydrogenation catalytic activity in the reaction zone is increased and / or (ii) at least one of the feed rate and concentration of carbohydrate to the reaction zone is decreased.

[0013] In many instances, the retro-aldol catalyst is homogeneous and the hydrogenation catalyst is heterogeneous. The desired process objective is often selectivity of conversion to ethylene glycol, and in some cases, the selectivity to all of ethylene glycol and propylene glycol ("total lower glycols") is greater than about 75 weight percent based on the weight of the feed. In some cases, the concentration of at least one component of acetol or tracer can be compared to the concentration of at least one of isitol, 1,2-butanediol, pH, and in the case of acetol, the tracer, if used, in the raw product for process control purposes, and to acetol, if a tracer is used. The reaction process can be a cascade process or a single pot process. When making ethylene glycol, the acetol concentration is often compared to the concentration of at least one of sorbitol, 1,2-butanediol, and glycerol. When making ethylene glycol, the tracer concentration is often compared to the concentration of at least one of sorbitol and glycerol.

[0014]

[0014] The use of the tracer precursor may be continuous or intermittent. For example, the tracer precursor may be used intermittently to ensure that the process is running on demand, or to help troubleshoot problems in the operation of the process, and to bring the process back into line with the desired operation. The disclosed process may also be used in laboratory or pilot scale operations, for example, to evaluate hydrogenation catalysts and hydrogenation catalyst activity for research, development or qualitative purposes, or to evaluate ex-situ samples of catalysts and hydrogenation catalyst activity that are used or will be used in larger, e.g., commercial scale, processes. The ex-situ evaluation may be used as a parameter for use in a control system for the process.

[0015]

[0015] While multiple embodiments are disclosed, still other embodiments of the present disclosure will be apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the present invention. As will be understood, the present disclosure is capable of modification in various obvious respects without departing from the spirit and scope of the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.

[0016] Detailed Description

[0016] All patents, published patent applications and articles referenced herein are hereby incorporated by reference in their entirety.

[0017] definition

[0017] As used herein, the following terms have the meanings set forth below unless otherwise specified or clear from the context of their use.

[0018]

[0018] When ranges are used herein, only the endpoints of the range are stated to avoid the need to lengthily set out and list each and every value included in the range. Any suitable intermediate values ​​and ranges between the recited endpoints can be selected. As an example, if a range of 0.1 to 1.0 is recited, all intermediate values ​​(e.g., 0.2, 0.3, 0.63, 0.815, etc.) are included, as are all intermediate ranges (e.g., 0.2 to 0.5, 0.54 to 0.913, etc.).

[0019]

[0019] Use of the terms "a" and "an" is intended to include one or more of the described components.

[0020] Mixing or mixed refers to the formation of a physical combination of two or more elements, where such a combination may have a homogeneous or non-homogeneous composition throughout, examples of which include, but are not limited to, solid mixtures, solutions, and suspensions.

[0020]

[0021] Biologically derived carbohydrate feedstock means a product containing carbohydrates that is sourced, derived, or synthesized in whole or in substantial part from biological materials or renewable agricultural materials (such as, but not limited to, plants, animals, and marine materials) or forestry materials.

[0021]

[0022] By-products are accidental or secondary products that occur in the production of the desired product, including accidental or secondary products and intermediates to these products, as well as reaction products from the desired product. By-products do not include intermediates to the desired product. As an example, in the catalytic conversion of glucose to ethylene glycol, any unreacted glycolaldehyde is not considered to be a by-product, and hydroxyacetone is considered to be a by-product, even though both glycolaldehyde and hydroxyacetone may be capable of further reaction under the conditions of the reaction. Other by-products include, but are not limited to, mannitol, sorbitol, glycerol, 1,2-butanediol, erythritol, threitol, organic acids, and gases.

[0022]

[0023] Catalyst means heterogeneous or homogeneous catalyst. For the purposes described herein, a catalyst that behaves when dissolved in a medium, for example as a colloidal suspension, is considered to be a homogeneous catalyst, regardless of whether the catalyst is dissolved or not. The catalyst may contain one or more catalytic metals and, in the case of heterogeneous catalysts, may include supports, binders and other adjuvants. A catalytic metal is a metal in its elemental state or bound by ionic or covalent bonds. The term catalytic metal refers to a metal that is not necessarily in a catalytically active state, but has the potential to become catalytically active when not in a catalytically active state. A catalytic metal can provide catalytic activity or modify catalytic activity, such as a promoter, selectivity regulator, etc.

[0023]

[0024] The activity or performance of a catalyst refers to the activity of the catalyst outside the reaction zone. Thus, factors that affect catalyst activity include the condition of the catalyst itself, but also its placement in the reaction zone. For example, if a portion of the catalyst is physically confined in the reaction zone, it is relatively unavailable to carry out the desired catalytic conversion, even though the catalyst itself may be active. Thus, mixing or other means of redistribution to make the catalyst surface more accessible is expected to improve the external catalyst activity.

[0024]

[0025] Changes in catalytic activity can be due to changes in the catalyst itself, such as chemical changes, physical deterioration, redistribution of components on the catalyst, loss of catalytically active species from the catalyst, or poisoning, or other effects from components that become deposited or react during the course of the reaction. Changes in catalytic activity can also be caused by the environment around the catalyst, for example, through steric effects or reactions, or through complexing with components that become transformed by the catalyst, in which case the catalyst itself may be relatively unchanged. Thus, an increase or decrease in catalytic activity can be, but is not necessarily, due to an increase or decrease in the mass of the catalyst per unit volume.

[0025]

[0026] Entering into contact means that a fluid begins to come into contact with a component, such as a medium containing a homogeneous or heterogeneous catalyst, but does not require that every molecule of the fluid come into contact with the catalyst.

[0026]

[0027] Conversion efficiency is the mass percent of the feedstock that is converted to chemical products in the process.

[0028] Hydraulic distribution refers to the distribution of the aqueous solution in the vessel, including contact with any catalyst contained therein.

[0027]

[0029] Intermediate means a compound that can be further reacted to a desired product under the conditions of the reaction zone. As defined herein, an intermediate to a by-product is itself considered a by-product.

[0028]

[0030] Intermittent means from time to time, which may be at regular or irregular time intervals.

[0031] An input value refers to input information from a process for a control method. An input may be an operational input, sometimes referred to as an independent variable, meaning that a reported value, such as temperature, is subject to control. An input may be a process parameter, sometimes referred to as a dependent variable, meaning that the determined value is derived from multiple operational variables in the process. For example, the concentration of an intermediate, by-product, or chemical product is the result of a combination of a set of process conditions. An input value may be from one or two or more operational inputs and process parameter inputs, and may require calculation. For example, conversion efficiency can be determined from the raw material concentration in the feed and the feed rate to the reaction zone, and from the concentration of the chemical product in the effluent from the reaction zone and the flow rate of the effluent.

[0029]

[0032] Itol is a polyhydric alcohol in which each carbon has a hydroxyl group, e.g., a sugar alcohol.

[0033] Liquid medium refers to the liquid in the reactor. The liquid is a solvent for the carbohydrates, intermediates and products, as well as for the homogeneous tungsten-containing retro-aldol catalyst. Typically, such liquids preferably contain at least a certain amount of water, and are therefore referred to as aqueous media.

[0030]

[0034] Operating parameters, or process parameters, for a process are those parameters that can be controlled, examples of which include, but are not limited to, temperature, pressure, feed rates and concentrations of reactants, residence time, adjuvants, pH, and hydrogenation and retro-aldol catalyst activity.

[0031]

[0035] Hydrogenable organics ("HOCs") are oxygen-containing hydrocarbons that can be hydrogenated under process conditions to one or more products. HOCs include, but are not limited to, sugars and other ketones and aldehydes, hydroxyl-containing hydrocarbons such as alcohols, diols, and itols.

[0032]

[0036] The pH of an aqueous solution is determined at ambient pressure and temperature. For example, in determining the pH of an aqueous hydrogenation medium or product solution, the liquid is cooled and allowed to stand at ambient pressure and temperature for 2 hours prior to pH determination. If the solution for which a pH measurement is sought contains less than about 50 weight percent water, water is added to the solution to provide more than 50 weight percent water. For consistency purposes, dilutions of the solution are made to provide the same weight percent water.

[0033]

[0037] pH control agent means one or more of a buffer and an acid or a base.

[0038] The term raw material is used to indicate one or more reactants that are added to a reaction zone during a process and is not intended to reflect the need for purity or purification. A raw material may be a product from another chemical or biochemical process. Since reactants include intermediates, the term raw material provides ease of understanding.

[0034]

[0039] The reaction zone is the volume containing the first and second catalysts and may be a single vessel or multiple vessels, or a reactor.

[0040] The reactor may be one or more vessels in series or parallel, and the vessel may contain one or more zones. The reactor may have any design suitable for continuous operation, such as, but not limited to, tank and pipe or tube type reactors, and may have the ability to mix fluids as needed. Reactor types include, but are not limited to, laminar flow reactors, fixed bed reactors, slurry reactors, fluidized bed reactors, moving bed reactors, simulated moving bed reactors, trickle bed reactors, bubble columns, and loop reactors.

[0035] Discussion

[0041] The process for converting carbohydrates containing aldohexose-bearing or ketose-bearing carbohydrates in a reaction zone to at least one of ethylene glycol and propylene glycol (lower glycols) is carried out by subjecting the sugars to catalytic retro-aldol conditions to produce intermediates that are hydrogenated under catalytic hydrogenation conditions. See, for example, published U.S. Patent Applications Nos. 2017 / 0349513 and 2018 / 0086681 and U.S. Patent Nos. 9,399,610 and 9,783,472, which are incorporated herein by reference in their entireties.

[0036]

[0042] The raw material contains carbohydrates, which are most often pentoses and / or hexoses or compounds that yield pentoses or hexoses. Examples of pentoses and hexoses include xylose, lyxose, ribose, arabinose, xylulose, ribulose, glucose, mannose, galactose, allose, altrose, idose, talose, and gulose, fructose, psicose, sorbose, and tagatose. Most carbohydrate feedstocks of biological origin yield glucose when hydrolyzed. Glucose precursors include, but are not limited to, maltose, trehalose, cellobiose, kojibiose, nigerose, nigerose, isomaltose, β,β-trehalose, α,β-trehalose, sophorose, laminaribiose, gentiobiose, and mannobiose. Carbohydrate polymers and oligomers can be used, such as hemicellulose, partially hydrolyzed forms of hemicellulose, and disaccharides such as sucrose, lactulose, lactose, turanose, maltulose, palatinose, gentiobiulose, melibiose, and melibiulose, or combinations thereof.

[0037]

[0043] The carbohydrate feed may be a solid or, preferably, in the form of a liquid suspension or may be dissolved in a solvent such as water. When the carbohydrate feed is in a non-aqueous environment, it is preferred that the carbohydrate is at least partially hydrated. Non-aqueous solvents include alkanols, diols and polyols, ethers, or other suitable carbon compounds of 1 to 6 carbon atoms. Solvents include hybrid solvents, particularly hybrid solvents containing water and one of the non-aqueous solvents mentioned above. Certain hybrid solvents are capable of dissolving higher concentrations of hydrogen under the conditions of the hydrogenation reaction, thus reducing the possibility of hydrogen starvation. Preferred non-aqueous solvents are those that can be hydrogen donors, such as isopropanol. Often these hydrogen donor solvents have hydroxyl groups that are converted to carbonyls upon donation of a hydrogen atom, which can be reduced under the conditions in the reaction zone. Most preferably, the carbohydrate feed is provided in an aqueous solution. In either case, the volume of the feed and the volume of the withdrawn raw product must be balanced to provide a continuous process.

[0038]

[0044] An additional consideration in providing carbohydrate to the reaction zone is minimizing energy and capital costs. For example, in steady state operation, the solvent contained in the feed exits the reaction zone with the raw products and requires separation to recover the desired glycol product.

[0039]

[0045] Preferably, the feed is introduced into the reaction zone in a manner that avoids undesirable concentrations of HOCs that could cause hydrogen starvation. The more multiple arrangements for carbohydrate feeding per unit volume of reaction zone are used, the more concentrated the carbohydrates in the feed can be. In general, the mass ratio of water to carbohydrate in the carbohydrate feed is preferably in the range of 4:1 to 1:4. Aqueous solutions containing 600 grams or more of certain carbohydrates, such as dextrose and sucrose, per liter are sometimes commercially available.

[0040]

[0046] The carbohydrate contained in the carbohydrate feed is provided at a rate of at least 50 or 100 grams, preferably about 150 to 500 grams, per liter of reactor volume per hour. Optionally, a separate reaction zone containing a retro-aldol catalyst and substantially free of hydrogenation catalyst may be used.

[0041]

[0047] In these processes, a liquid medium containing the carbohydrate is contacted with a retro-aldol catalyst under retro-aldol reaction conditions. Contacting may begin prior to or upon introduction of the liquid medium into the portion of the reaction zone containing the hydrogenation catalyst. Preferred temperatures for the retro-aldol reaction are typically from about 230° C. to 300° C., more preferably from about 240° C. to 280° C., although the retro-aldol reaction may be carried out at lower temperatures, for example at 90° C. or as low as 150° C. Pressures (absolute) are typically in the range of about 15-200 bar (1500-20,000 kPa), for example in the range of about 25-150 bar (2500-15000 kPa).

[0042]

[0048] The retro-aldol reaction conditions include the presence of a retro-aldol catalyst. A retro-aldol catalyst is a catalyst that catalyzes the retro-aldol reaction. Examples of compounds that can provide a retro-aldol catalyst include heterogeneous and homogeneous catalysts such as catalysts supported on a carrier, including, but not limited to, tungsten and its oxides, sulfates, phosphides, nitrides, carbides, halides, acids, and the like. Also included are tungsten carbide, soluble phosphotungsten, and tungsten oxide supported on zirconia, alumina, and alumina-silica. A preferred catalyst is provided by a soluble tungsten compound and a mixture of tungsten compounds. Soluble tungstates include, but are not limited to, ammonium tungstate and alkali metal salts of tungstic acid, such as sodium tungstate and potassium tungstate, paratungstic acid, partially neutralized tungstic acid, ammonium and alkali metal metatungstate, and ammonium and alkali metal tungstate. The presence of ammonium cations often results in the production of undesirable amine by-products in the lower glycol products. Without wishing to be limited by theory, the species exhibiting catalytic activity may or may not be the same as the soluble tungsten compound introduced as the catalyst. Instead, the catalytically active species may be formed as a result of exposure to retro-aldol reaction conditions. Tungsten-containing complexes are typically pH-dependent. For example, a solution containing sodium tungstate at a pH greater than 7 will produce sodium metatungstate at lower pH. The form of the complexed tungstate anion is generally pH-dependent. The rate at which the complexed anion formed from the condensation of the tungstate anion is formed is influenced by the concentration of the tungsten-containing anion. Preferred retro-aldol catalysts include ammonium or alkali metal tungstate that become partially neutralized with an acid, preferably a 1-6 carbon organic acid, such as, but not limited to, formic acid, acetic acid, glycolic acid, and lactic acid.Partial neutralization is often about 25-75%, i.e., on average 25-75% of the cations of the tungstic acid become acid sites. Partial neutralization can occur prior to introducing the tungsten-containing compound into the reactor or with the acid contained in the reactor.

[0043]

[0049] The concentration of the retro aldol catalyst used can vary widely and is expected to depend on the activity of the catalyst as well as other conditions of the retro aldol reaction, such as acidity, temperature and carbohydrate concentration. Typically, the retro aldol catalyst is provided in an amount that provides about 0.01 or 0.05 to 100 grams, for example, about 0.02 or 0.1 to 50 grams of tungsten, calculated as elemental metal per liter of aqueous hydrogenation medium. The retro aldol catalyst can be added as a mixture with all or a portion of the carbohydrate feed, or as a separate feed to the aqueous hydrogenation medium, or by recycling the liquid medium, or any combination thereof. In some cases, a homogeneous tungsten-containing retro aldol catalyst can deposit tungsten-containing compounds or complexes on the hydrogenation catalyst, adversely affecting the activity of the hydrogenation catalyst. Continuous or intermittent cycling of the catalyst containing a given amount of tungsten can lead to removal of at least a portion of the deposited tungsten compounds or complexes. Thus, the disclosed method contemplates that controlling the absolute amount of catalytically active species and the relative amount of each of the first and second catalysts includes operations where the objective of the process is catalyst reactivation. The disclosed method also contemplates that controlling the absolute amount of catalytically active species and the relative amount of each of the first and second catalysts includes operations where the objective of the process is reduction of the catalytic activity of one of the first or second catalysts. The reduction in catalytic activity can be achieved by any suitable means, such as, but not limited to, one or more of reducing the catalyst concentration in the liquid medium, selective poisoning of the catalytically active species of the catalyst, and providing an additive or modifier that reduces the catalytic activity without necessarily reducing the catalytically active species.

[0044]

[0050] In many cases, the carbohydrate feed is subjected to retro-aldol conditions in a reaction zone containing a hydrogenation catalyst before being introduced into the aqueous hydrogenation medium. Preferably, the introduction into the aqueous hydrogenation medium occurs in less than one minute, and in most cases in less than 10 seconds, from the time the carbohydrate feed is subjected to retro-aldol conditions. Some or all of the retro-aldol reaction can be carried out in a reaction zone containing a hydrogenation catalyst. In any case, the most preferred process, when isomerization of glucose to fructose is not desired, has a short period between retro-aldol conversion and hydrogenation.

[0045]

[0051] Hydrogenation, i.e., the addition of hydrogen atoms to organic compounds without breaking carbon-carbon bonds, can be carried out at temperatures ranging from about 100°C or 120°C to 300°C or higher. Typically, the aqueous hydrogenation medium is maintained at a temperature of at least about 230°C until substantially all of the carbohydrates have reacted and the carbon-carbon bonds of the carbohydrates are broken in a retro-aldol reaction, thereby enhancing selectivity to ethylene glycol and propylene glycol. Thereafter, if necessary, the temperature of the aqueous hydrogenation medium may be reduced. However, hydrogenation proceeds rapidly at these higher temperatures. Thus, temperatures for hydrogenation reactions are often about 230°C to 300°C, e.g., 240°C to 280°C. Pressures are typically in the range of about 15 to 200 bar, e.g., about 25 to 150 bar. The hydrogenation reaction requires the presence of hydrogen, plus a hydrogenation catalyst. Hydrogen has low solubility in aqueous solutions. The concentration of hydrogen in the aqueous hydrogenation medium increases as the hydrogen partial pressure in the reaction zone increases. The pH of the aqueous hydrogenation medium is often at least about 3, such as from about 3 or 3.5 to 8, and in some cases from about 3.2 or 4 to 7.5.

[0046]

[0052] The hydrogenation is carried out in the presence of a hydrogenation catalyst. In many cases, the hydrogenation catalyst is a heterogeneous catalyst. It may be arranged in any suitable manner, including, but not limited to, fixed bed, fluidized bed, trickle bed, moving bed, slurry bed, and structured bed. Among the more widely used reduction metal catalysts are nickel, ruthenium, palladium, and platinum. However, it is expected that many reduction catalysts will work in this application. The reduction catalyst can be selected from a wide variety of supported transition metal catalysts. Nickel, Pt, Pd, and ruthenium as the primary reduction metal component are well known for their ability to reduce carbonyls. One particularly preferred catalyst for the reduction catalyst in this process is a supported Ni-Re catalyst. Similar versions of Ni / Re or Ni / Ir can be used with excellent selectivity for the conversion of the formed glycolaldehyde to ethylene glycol. Nickel-rhenium is the preferred reduction metal catalyst, which may be supported on alumina, alumina-silica, silica, or other supports. Supported Ni-Re catalysts with B as a promoter are useful. Typically, in a slurry reactor, the supported hydrogenation catalyst is provided in an amount of less than 10, sometimes less than about 5, e.g., about 0.1 or 0.5 to 3 grams of nickel (calculated as elemental nickel) per liter of liquid medium in the reactor. As noted above, not all of the nickel in the catalyst is in the zero valence state, nor is all of the nickel in the zero valence state readily available to glycolaldehyde or hydrogen. Thus, for a particular hydrogenation catalyst, the optimum mass of nickel per liter of liquid medium is expected to vary. For example, Raney nickel catalysts are expected to provide fairly high nickel concentrations per liter of liquid medium. Often, in a slurry reactor, the hydrogenation catalyst is provided in an amount of at least about 5 or 10, more often about 10 to 70 or 100 grams per liter of aqueous hydrogenation medium, and in a packed bed reactor, the hydrogenation catalyst comprises about 20 to 80 volume percent of the reactor.In some cases, the weight hourly space velocity is about 0.01 or 0.05 to 1 / hour based on the total carbohydrate in the feed. Preferably, the residence time is sufficient for glycolaldehyde and glucose to be less than 0.1 weight percent of the reaction product, and most preferably less than 0.001 weight percent of the reaction product.

[0047]

[0053] In the disclosed processes, the combination of reaction conditions (e.g., temperature, hydrogen partial pressure, catalyst concentration, hydraulic distribution, and residence time) are sufficient to convert at least about 95 mass percent, often at least about 98 mass percent, and sometimes substantially all, of the carbohydrates to yield aldoses or ketoses. It is well within the skill of one of ordinary skill in the art having the benefit of the disclosure herein to determine the set of condition or conditions that will provide the desired carbohydrate conversion.

[0048]

[0054] Optimizing the retro-aldol process to produce ethylene glycol involves optimizing the retro-aldol conversion, which is primarily a kinetics limitation, and optimizing the hydrogenation reaction, which is primarily a mass transfer limitation. Mass transfer limitations include the supply of hydrogen to the hydrogenation catalyst sites, and hydrogen starvation can occur when localized regions with high hydrogenation catalyst activity exist. Hydrogen starvation can occur, by way of example and not limitation, due to uneven distribution of hydrogenation catalyst within the reaction zone, and localized regions with higher feed concentration in the reaction zone. Hydrogen starvation can thus lead to the formation of organic acids, which can become by-products in the drawn medium. For process control purposes, pH determinations can often be used as a proxy for organic acid concentration. In some cases, reducing the rate of feed can attenuate acid production, but manipulation of either or both the absolute and relative amounts of retro-aldol catalyst and hydrogenation catalyst may also be necessary.

[0049]

[0055] Acetol or tracers are often used in conjunction with other parameter observations. Particularly when acetol is used, acetol is a precursor of observable reduction in conversion and selectivity to ethylene glycol, and changes in acetol can be used to trigger review of changes in other parameters to confirm changes in the process and prevent significant process collapse, preferably to avoid loss of material in conversion and selectivity to ethylene glycol. In one embodiment, when acetol increases, it triggers the addition of tracer precursor to evaluate catalytic hydrogenation activity, or triggers removal of a portion of hydrogenation catalyst for ex situ evaluation.

[0050]

[0056] An additional process parameter input for process control is often the concentration in the withdrawn medium of at least one of itol and 1,2-butanediol. Itol contained in the withdrawn medium results from reactions with carbohydrate feeds. For example, glucose can be hydrogenated to sorbitol. In the retro-aldol process, glucose can provide glycolaldehyde and erythrose and threose. These four-carbon sugars, when hydrogenated, produce erythritol and threitol. Glucose can also undergo isomerization to fructose, which, when hydrogenated, can produce mannitol under retro-aldol conditions. Fructose can also be a compound with three carbons, thus producing glycerol. Due to the production of itol, insight into the process can be gained from the type of itol and the production rate.

[0051]

[0057] As a general matter, increasing the butyrol concentration will indicate that, all other things remaining substantially constant, the retro-aldol catalyst activity will be affected, and one example of an operational input would be to adjust at least one of: (I) the absolute and relative amounts of retro-aldol catalyst activity and hydrogenation catalyst activity, respectively, by increasing the retro-aldol catalyst activity or decreasing the hydrogenation catalyst activity, and (II) reducing the rate of feed of raw materials to the reaction zone.

[0052]

[0058] When 1,2-butanediol concentration is used as a process parameter input, 1,2-butanediol may result from a reaction between two glycolaldehyde molecules or from the dehydration of tetrose. In the former, the general rule is that, all other things remaining substantially the same, an increase in 1,2-butanediol concentration reflects a loss of hydrogenation catalyst activity in the reaction zone. In this case, examples of operational input adjustments would be made to at least one of (I) the absolute and relative amounts of retro-aldol catalyst and hydrogenation catalyst, respectively, by increasing the catalytic activity of the hydrogenation catalyst or decreasing the catalytic activity of the retro-aldol catalyst, and (II) reducing the rate of feed of raw materials to the reaction zone. In the latter, retro-aldol conversion activity may be insufficient, and at least one of (I) increasing the activity of the retro-aldol catalyst and (II) reducing the rate and concentration of feed of raw materials to the reaction zone is expected to be the responsive action. Therefore, it may be useful to have another parameter that is indicative of whether the concentration of 1,2-butanediol is changing. For example, since the isomerization reaction predominates over the retro-aldol conversion, whether an increase in 1,2-butanediol is accompanied by an increase in glycerol produced from fructose from the isomerization of glucose would be an indication of reduced retro-aldol activity, all else remaining equal.

[0053]

[0059] Acetol is usually present in the withdrawn medium at a very low concentration.However, it has been found that the increase in acetol is a sensitive indicator of the decrease in activity of hydrogenation catalyst, especially when the concentration of fructose is not substantially changed.Under these circumstances, the increase in acetol concentration can be addressed by increasing the catalytic activity of hydrogenation catalyst and / or reducing the rate or concentration of raw material feed to reaction zone.In some cases, the acetol concentration in the withdrawn medium is less than 0.15 mass percent, preferably less than 0.10 mass percent.

[0054]

[0060] Tracers can be used similarly to acetol. Ketones, such as methyl ethyl ketone, are useful in providing tracers for the retro-aldol / hydrogenation process because the internal carbonyl is resistant to hydrogenation compared to the carbonyl of the aldehyde. The extent of hydrogenation of the ketone is therefore an indicator of hydrogenation activity in the reaction zone. It is expected that the concentration of the ketone can vary widely and will depend, for example, on the ability to analytically detect the concentration of the tracer in the withdrawn medium. Often the concentration of the tracer is in the range of about 1 ppm (parts per million) to 1 mass percent based on the mass of the medium.

[0055]

[0061] The control system and control system hardware used are not critical to the broad process of this invention, and any suitable control system, including manual operation, can be used. Design space and model predictive control are well known, multivariate, and preferred. The former is based on a model, where operational input values ​​are maintained up to a window of acceptable operation. When operational inputs are correlated, the design space control system can be designed using a predictive model, such that adjustments in one operational input are consistent with adjustments in one or more other operational inputs. The latter considers not only the instantaneous state of the process, but also the future state of the process. The model can be developed, for example, with a linear or quadratic model. These models may be derived from experimental data and the performance of the process with respect to process objectives. With model predictive control, data from the process can be used to refine the interpretation of the model's future predictions. The control system can be open loop or closed loop, and in the case of closed loop, the loop can be the entire plant or a portion thereof.

[0056]

[0062] Although the present disclosure has been described with reference to various embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the disclosure.

Claims

1. 1. A continuous process having a control system for controlling one or more operating parameters based on one or more inputs for the catalytic conversion of a carbohydrate feed containing at least aldose-producing carbohydrates or ketose-producing carbohydrates to at least one of ethylene glycol and propylene glycol lower glycols in an unregulated reaction zone by sequential retro-aldol catalytic conversion to intermediates under retro-aldol conditions comprising the presence of a retro-aldol catalyst providing retro-aldol catalytic activity in a liquid medium in an unregulated reaction zone, and catalytic hydrogenation of the intermediates to lower glycols under hydrogenation conditions comprising the presence of hydrogen and a hydrogenation catalyst providing hydrogenation catalytic activity in said unregulated reaction zone, and continuously or intermittently withdrawing a raw product from said unregulated reaction zone, said process comprising controlling at least one operating parameter of said process using the concentration of acetol in at least said raw product as an input to said control system for said process.

2. 2. The process of claim 1, wherein the carbohydrate comprises an aldose and the lower glycol comprises ethylene glycol.

3. 3. The process of claim 2, wherein in response to an increase in acetol concentration, at least one of: (i) increasing the hydrogenation catalyst activity; and (ii) decreasing at least one of the rate of supply of the carbohydrate feed and the concentration of the carbohydrate in the feed.

4. 3. The process of claim 2, wherein the retro-aldol catalyst is homogeneous and the hydrogenation catalyst is heterogeneous.

5. 3. The process of claim 2, wherein the concentration of acetol is compared to the concentration of at least one of isitol, 1,2-butanediol, and pH in the raw product for process control purposes.

6. 6. The process of claim 5, wherein the retro-aldol catalytic activity is increased in response to an increase in acetol concentration and an increase in the concentration of at least one of sorbitol, 1,2-butanediol, and glycerol in the raw product.

7. 3. The process of claim 2, wherein the hydroxyacetone concentration is maintained at less than about 0.15 weight percent of the raw product.

8. 3. The process of claim 2, wherein in response to an increase in acetol with an increase in at least one of mannitol and glycerol, at least one of the rate of feeding of the carbohydrate feed and the concentration of the carbohydrate in the feed is decreased until retro-aldol catalytic activity increases.

9. 2. The process of claim 1, wherein the reaction zone is a cascade reaction zone.

10. 1. A continuous process having a control system for controlling one or more operating parameters based on inputs for catalytic conversion of a carbohydrate feed containing at least an aldose-producing carbohydrate or a ketose-producing carbohydrate to at least one of lower glycols, ethylene glycol and propylene glycol, in an unregulated reaction zone, said catalytic conversion comprising sequential retro-aldol catalytic conversion to intermediates under retro-aldol conditions comprising the presence of a retro-aldol catalyst providing retro-aldol catalytic activity in a liquid medium in the unregulated reaction zone, and a hydrogenation catalytic activity in the unregulated reaction zone.

16. The process of claim 15, further comprising: catalytically hydrogenating the intermediate to a lower glycol under hydrogenation conditions comprising the presence of hydrogen and a hydrogenation catalyst provided therein; supplying a tracer precursor comprising a 3-6 carbon ketone to a reaction zone to produce at least one tracer from said reaction zone under conditions in said reaction zone; and continuously or intermittently withdrawing a raw product from said unregulated reaction zone, said process comprising controlling at least one operating parameter of said process using at least the concentration of at least one component of said tracer in said raw product as an input to said control system for said process.

11. 11. The process of claim 10, wherein the tracer in the raw product indicates a change in the portion of hydrogenated tracer precursor and then adjusts at least one of: (i) the absolute amount of catalytically active species and the relative amounts of the retro-aldol catalytic activity and the hydrogenation catalytic activity, respectively; and (ii) at least one of the carbohydrate feed rate and concentration in the feed to the reaction zone.

12. 12. The process of claim 11, wherein the concentration of the tracer in the raw product indicates that a greater portion of the tracer precursor is being hydrogenated, and either or both of the feed rate to the reaction zone is increased or the hydrogenation catalyst activity in the reaction zone is decreased.

13. 12. The process of claim 11, wherein the concentration of the tracer in the raw product indicates that a lesser portion of the tracer precursor is being hydrogenated, and either or both of: (i) increasing the hydrogenation catalyst activity in the reaction zone; or (ii) decreasing at least one of the carbohydrate feed rate and concentration in the feed to the reaction zone.

14. 11. The process of claim 10, wherein the retro-aldol catalyst is homogeneous and the hydrogenation catalyst is heterogeneous.

15. 11. The process of claim 10, wherein the carbohydrate comprises an aldose and the lower glycol comprises ethylene glycol, and the concentration of at least one component of the tracer is compared to the concentration of at least one of isitol, 1,2-butanediol, acetol, and pH in the raw product for process control purposes.

16. 16. The process of claim 15, wherein the tracer in the raw product indicates that the portion of the tracer precursor that is hydrogenated is substantially constant and that the concentration of at least one of sorbitol and glycerol in the raw product is increased, increasing the retro-aldol catalyst activity.

17. 16. The process of claim 15, wherein the tracer in the raw product indicates a decrease in the portion of the tracer precursor that is hydrogenated and the concentration of at least one of sorbitol, 1,2-butanediol, and glycerol is not increased, and wherein the process comprises either or both of: (i) increasing the hydrogenation catalyst activity; and (ii) decreasing at least one of the feed rate and concentration of the carbohydrate in the feed.

18. 11. The process of claim 10, wherein hydrogenation catalyst withdrawn from or intended for use in a larger reaction zone is used to evaluate the hydrogenation catalyst activity.

19. 11. The process of claim 10, wherein the tracer precursor is added to troubleshoot the process.

20. 11. The process of claim 10, wherein the tracer precursor comprises methyl ethyl ketone and the tracer comprises methyl ethyl ketone and isobutanol.