Methods for operating continuous, unmodulated, multiple catalytic step processes

Abstract

To provide methods for controlling continuous, unmodulated, multiple catalytic conversion step processes in order to accommodate changes in the performance of each catalyst during the course of the process when operating chemical conversion processes using two or more sequential catalytic conversions.SOLUTION: In this method, certain process parameters are used in a manner that is indicative of changes in catalyst performance, and this control method provides for adjustment of at least one of: the absolute amount of catalytically active species, the relative amounts of each of a first catalyst and a second catalyst, and at least one of the rate of feed or concentration of raw material to a reaction zone.SELECTED DRAWING: None

Description

Technical Field

[0001] Cross - Reference to Related Applications

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

[0002] Technical Field

[0002] This invention relates to methods for operating chemical conversion processes using two or more sequential catalytic conversions, particularly processes where the flow between catalytic conversions is unmodulated. The methods of this invention include, but are not limited to, predictive control methods and design space methods.

Background Art

[0003]

[0003] Catalytic processes are used in commercial applications for the production of chemicals, pharmaceuticals, fuels, polymers, etc. In some of these processes, feedstocks or raw materials must undergo two or more catalytic reactions or multi - step processes to provide the desired product. The raw material is first converted to an intermediate, and then one or more conversion steps are performed to provide the target product.

[0004]

[0004] Conventionally, these multi-step processes proceed in separate steps. That is, the raw materials are subjected to the catalyst conditions for producing the intermediate to recover the intermediate, and then subjected to a second catalytic step to produce the chemical product. For the purposes described herein, this is referred to as a modulated cascade process. Thus, each step of the modulated cascade process can be controlled to reflect from among a number of desirable process conditions to achieve conversion efficiency and selectivity.

[0005]

[0005] Most catalysts suffer from performance changes due to inactivation, degradation, or physical loss. Also, in some cases, the production of by-products and other losses of raw materials or intermediates are directly or indirectly affected by the catalyst conditions in some cases. For a single catalytic conversion process or a modulated cascade process, the optimization of conditions can take into account the conditions of the catalyst used in a single conversion. Thus, when adjusting the temperature, pressure, feed rate, residence time, adjuvant, pH, and other controllable process variables of the reactants, the operator has reasonable confidence regarding the effect of the changes. Thus, a multi-step process provides the benefit of controlling the overall process step by step and avoiding confusing the control of one catalytic process with the control of another catalytic process.

[0006]

[0006] Controlling each step of the modulated cascade process, particularly control using the recovery of the intermediate between steps, increases the production cost. Operating a multi-step process as an unmodulated cascade process can provide an economic benefit, especially when multiple steps are under an integrated control system. An unmodulated cascade process means that there are separate reaction zones, and a liquid stream containing the intermediate from the first reaction zone passes through subsequent reaction zones, where the liquid stream is reacted without removing the intermediate. The subsequent reaction zone may be the next reaction zone or a later reaction zone in the flow order.

[0007] In addition to the regulated cascade process, a multi-step process carried out in a single reaction zone ("single pot") has been proposed. In these single pot processes, it is often inevitable that the intermediate may react to produce unwanted by-products. Therefore, in order to achieve an acceptable economy, the intermediate is quickly subjected to the next catalytic reaction in order to reduce the production of by-products. One such process is the conversion of sugars to ethylene glycol and propylene glycol by sequential retro-aldol and hydrogenation steps. The retro-aldol step produces, for example, glycolaldehyde, which, when hydrogenated, yields ethylene glycol. On the other hand, since glycolaldehyde has high reactivity, it may also react to produce by-products, such as 1,2-butanediol, even in the absence of a catalyst. In these latter multi-step processes, it has been proposed to carry out the multiple reactions either in a single vessel or in sequential vessels such that the first vessel contains the first catalyst and substantially no second catalyst.

[0008]

[0008] Typical process control focuses on the conversion to and selectivity of the desired product, and thus one or more manipulative inputs, such as feed rate, concentration of raw materials in the feed, temperature, pressure, residence time, pH, and concentration of adjuvants, are inputs to the process control, and one or more of the manipulative inputs are adjusted such that an operation that satisfies the objectives of the process is provided. Changes in the catalytic performance and relative performance of the catalyst are confounding factors in process control, and thus adjustments that are thought to improve the conversion and selectivity made in response to manipulative inputs may destabilize the operation due to the performance of the catalyst. In addition, even when the manipulative input indicates that there are no operational problems, one or more of the performances of the catalyst may deteriorate to the point where destabilization occurs.

Summary of the Invention

Problems to be Solved by the Invention

[0009]

[0009] Therefore, there is a need to provide a method for controlling a plurality of catalytic conversion process steps that are continuous but not regulated in order to accept changes in the performance of each catalyst and in the relative performance of the catalysts. Further, such a method desirably uses input parameters that can be reasonably obtained from the process, in particular input parameters that can be relatively quickly identified and that can provide real-time data regarding the management of the process.

Means for Solving the Problem

[0010]

[0010] According to the present invention, there is provided a control method for carrying out a plurality of catalytic conversion process steps that are continuous but not continuously regulated, using at least two catalysts, i.e., a first catalyst and a second catalyst, that accept changes in the performance of each catalyst and in the relative performance of the catalysts. The process converts at least one raw material into a desired chemical product in a medium, comprising contacting a first of the raw materials with a catalyst to provide an intermediate, and then contacting the intermediate with a second catalyst to provide a chemical product. Although the discussion herein refers to two catalysts, this is for purposes of clarity. The method of the invention is equally applicable to processes in which three or more sequential catalytic reactions are used. The method of the invention also encompasses processes in which one or more non-catalytic reactions are carried out before, between, or after the two catalytic reactions. For example, a first catalytic reaction can provide an intermediate that reacts with another chemical substance contained in the reaction system to non-catalytically form a second intermediate, which can then become the desired chemical product by a catalytic reaction. In this method, specific process parameters are used to indicate catalyst performance, and the control method provides at least one adjustment of the absolute amount of the catalytically active species and the relative amounts of each of the first and second catalysts, as well as the rate and concentration of the feed of the raw material to the reaction zone.

[0011]

[0011] The method of this invention involves determining, from the effluent from a second catalyst (“withdrawn medium”), (I) the conversion efficiency of the process to the desired product using the rate and concentration of the raw materials in the feed to the process, and (II) determining at least one of the concentration of at least one by-product in the withdrawn medium, the concentration of the intermediate in the withdrawn medium, and, if used, the concentration of at least one tracer. Both (I) and (II) may rely on conventional analysis of samples of the raw material feed to the plurality of catalytic conversion process steps and product streams from the plurality of catalytic conversion process steps. Generally, the analytical instruments for determining the concentration of the described elements can provide near real-time data, for example within 30 minutes from sampling, often within 10 or 5 minutes.

[0012] Although not wishing to be limited by theory, it is believed that the concentration of at least one of the by-products, intermediates, and tracers selectively indicates a change in the performance of one of the catalysts. In some cases, the by-product or tracer is more sensitive to the reaction conditions than the product itself. For example, in the reverse aldol / hydrogenation conversion of glucose to ethylene glycol, an increase in hydroxyacetone is a precursor to an observable decrease in selectivity to ethylene glycol. The term "absolute amount of catalytically active species in the reaction zone" is used herein to refer to the effectiveness of the catalyst in that reaction zone and is not necessarily related to the mass of the catalyst. The absolute amount of catalytically active species may be based on the performance of the catalyst or may be a relative relationship. Thus, the absolute amount of catalytically active species may be changed, for example, by deactivation, conversion to inactive or relatively low-activity molecules, addition of a promoter, or poisoning, without changing the mass of the catalyst. Alternatively, the absolute amount of catalytically active species can be changed by addition or removal of the catalyst from the reaction zone. The adjustment may be made to balance the performance of one of the catalysts without making it one of the catalysts, or the feed rate may be reduced to accept the effective capacity of the deteriorated catalyst. Adjustments to the catalyst include, but are not limited to, addition of more catalyst to the reaction zone and chemical modification of the catalyst. Chemical modifications include, but are not limited to, addition of a promoter or poison to the reaction zone to selectively affect the activity of one of the catalysts. It is understood that reaction parameters can also affect the performance of the catalyst. For example, a change in temperature can affect the kinetics of the catalytic reaction. Although the catalyst is more or less active after changing the parameters, for the purposes described herein, such a change in parameters is not considered to change the absolute amount of catalytically active species. When one of the catalysts is a homogeneous catalyst or a finely dispersed heterogeneous catalyst present throughout the reaction zone, such addition or removal of the catalyst can be carried out using the medium added to the reaction zone or withdrawn from the reaction zone to provide the desired activity in the reaction zone.

[0013]

[0013] The control method of this invention can be incorporated into a more extensible control system for this process as needed, and this system may be a design space system (DSC) or a model predictive control system (MPC), both of which are well-known in the art. In DSC, the boundary conditions or windows are predetermined, and operations within the window are considered to be under control. In MPC, a dynamic process model is often created empirically, and in addition to the current control status, the future impact of the current control status on the process is taken into account. Anticipating future events, control actions can be taken based on the prediction model.

[0014]

[0014] One broad form of this invention is a predictive control method for managing a continuous, unregulated, sequential, multiple catalytic reaction process, each catalyst undergoes changes in performance during the process, and the process related to the method of this invention (i) introducing at least one raw material and optionally a tracer precursor continuously or intermittently into a reaction zone containing a medium at a feed rate and concentration, (ii) maintaining the reaction zone under catalytic conversion conditions suitable for a first catalytic conversion to produce a medium containing an intermediate, said conditions including temperature, pressure, residence time, concentration of the first catalyst, and optionally pH and adjuvant, (iii) contacting the medium containing the intermediate with a second catalyst under conditions suitable for another conversion to produce a chemical product, said conditions including temperature, pressure, residence time, concentration of the second catalyst, and optionally pH and adjuvant, and (iv) continuously or intermittently withdrawing the medium containing the chemical product from the contact with the second catalyst at a rate providing a continuous process including, Here, at least one by-product is produced, and the catalytic activity of at least one of the first catalyst and the second catalyst undergoes a change in performance during continuous operation. The control method comprises: (a) Continuously or intermittently inputting predetermined process parameters from the operation of the process into a model predictive controller having a control model; (b) Optionally, adjusting the operative input to the process so as to meet the desired process objectives; and optionally, (c) Adjusting the control model including: (A) In component (a), the input predetermined process parameters are, in order to be reflected in the data of the control model regarding the performance of the catalyst, (I) the rate and concentration of the feed of the raw material in step (i), and the conversion efficiency of the raw material into chemical products, and (II): the concentration of at least one by-product in the withdrawn medium, the concentration of the intermediate in the withdrawn medium, and the concentration of at least one tracer in the withdrawn medium at least one of including; (B) Optionally, in order to meet the desired process objectives, at least one of (I) at least one of the absolute amount of the catalytically active species and the relative amounts of the first catalyst and the second catalyst respectively, and (II) as the operative input, at least one of the rate and concentration of the feed of the raw material to the reaction zone is adjusted, relating to the above method.

[0015]

[0015] In a preferred embodiment of this first broad form of the invention, the reaction process involves a sequential retro-aldol catalytic conversion to an intermediate (first catalyst), and a catalytic hydrogenation of the intermediate to at least one of ethylene glycol and propylene glycol (the "lower glycols") (second catalyst), which includes the catalytic conversion of sugar to at least one of ethylene glycol and propylene glycol. In many examples, the retro-aldol catalyst is homogeneous and the hydrogenation catalyst is heterogeneous. This process is complex and subject to many catalytic and non-catalytic reactions. For example, the sugar can isomerize and the intermediate can react with by-products, all of which have an adverse effect on the selectivity to the desired lower glycol. The goal of the desired process is often the selectivity of the conversion to either ethylene glycol or propylene glycol, and in some cases, the selectivity to all of ethylene glycol and propylene glycol (the "total lower glycols") is greater than about 75 weight percent based on the mass of the feed. By-products of this method include one or more of 1,2-butanediol, hydroxyacetone, one or more itols, and pH. When used, the preferred tracer precursor is one or more ketones having 3 to 6 carbons, preferably 4 to 6 carbons, and the tracer is the unreacted ketone or the reaction product of the ketone. The predictive control model preferably determines the pH of the effluent, and the pH is input into the model. Since acid can be a by-product of this process, the pH can be a useful input. The reaction process may be a cascade process or a single-pot process.

[0016]

[0016] A second broad form of this invention is a design space method for managing a continuous, unregulated, sequential, multiple catalytic reaction process, where each catalyst undergoes a change in performance during the process of the process, and this method adjusts the operating input to provide an output within a predetermined range, relating to the above method. The process related to the method of this invention is (i) At least one raw material and optionally a tracer precursor are introduced continuously or intermittently, at a feed rate and concentration, into a reaction zone containing a liquid medium; (ii) Maintaining the reaction zone under catalytic conversion conditions suitable for a first catalytic conversion to produce a liquid medium containing an intermediate, said conditions including the temperature, pressure, residence time, concentration of a first catalyst, and optionally pH and adjuvants; (iii) Contacting the liquid medium containing the intermediate with a second catalyst under conditions suitable for another conversion to produce a chemical product, said conditions including the temperature, pressure, residence time, concentration of the second catalyst, and optionally pH and adjuvants; and (iv) Withdrawing continuously or intermittently the liquid medium containing the chemical product from the contact with the second catalyst, at a rate providing a continuous process comprising wherein at least one by - product is produced and the catalytic activity of at least one of the first catalyst and the second catalyst undergoes a change in performance during continuous operation.

[0017]

[0017] The method comprises (a) continuously or intermittently comparing predetermined process parameters from the operation of the process with a predetermined window for such operation; and (b) adjusting the operational input to the process, if necessary, to meet the desired process objectives comprising In component (a), the input predetermined process parameters include (I) the rate and concentration of the feed of the raw material in step (i), and the conversion efficiency of the raw material to the chemical product, and (II) the concentration of at least one by - product in the withdrawn liquid medium, the concentration of the intermediate in the withdrawn liquid medium, and the concentration of at least one tracer in the withdrawn liquid medium at least one of comprising Here, in component (b), the adjustment is made to at least one of (I) the absolute amount of the catalytically active species and the relative amounts of the first and second catalysts, and (II) as an operational input, at least one of the rate and the concentration of the feed of the raw material to the reaction zone.

[0018]

[0018] In a preferred embodiment of this first broad form of the present invention, the reaction process involves a sequential retro-aldol catalytic conversion to an intermediate (first catalyst), and a catalytic hydrogenation of the intermediate to at least one of ethylene glycol and propylene glycol ( "lower glycols") (second catalyst), including the catalytic conversion of sugar to at least one of ethylene glycol and propylene glycol. In many examples, the retro-aldol catalyst is homogeneous and the hydrogenation catalyst is heterogeneous. This process is complex and is subject to many catalytic and non-catalytic reactions. For example, the sugar can isomerize, and the intermediate can react with by-products, all of which have an adverse effect on the selectivity to the desired lower glycol. The goal of the desired process is often the selectivity of the conversion to either ethylene glycol or propylene 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 mass of the feed. By-products of this method include one or more of 1,2-butanediol, hydroxyacetone, one or more itols, and pH. When used, the preferred tracer precursor is one or more ketones having 3 to 6, preferably 4 to 6, carbons, and the tracer is an unreacted ketone or a reaction product of the ketone. The predictive control model preferably determines the pH of the effluent, and the pH is input into the model. Since an acid can be a by-product of this process, the pH can be a useful input. The reaction process may be a cascade process or a single-pot process.

Embodiments for Carrying Out the Invention

[0019] Although multiple embodiments are disclosed, further additional embodiments of the present disclosure will be apparent to those skilled in the art from the following detailed description that illustrates and describes exemplary embodiments of the invention. As would be expected and understood, the present disclosure is capable of modification in various distinct aspects without departing from the essence and scope of the present disclosure. Accordingly, the drawings and the detailed description are to be regarded as being substantially exemplary and not limiting.

[0020] Detailed Description All patents, published patent applications, and papers referenced herein are hereby incorporated by reference in their entirety.

[0021] Definitions The following terms, as used herein, have the meanings set forth below unless otherwise specified or apparent from the context of their use.

[0022] When ranges are used herein, only the endpoints of the range are recited to avoid having to set forth and describe every possible value included within the range. Any appropriate intermediate values and ranges between the recited endpoints can be selected. As an example, when 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.).

[0023] The use of the terms "a" and "an" is intended to include one or more of the recited elements.

[0024] To mix or mixed means the formation of a physical combination of two or more elements, such a combination may have a composition that is homogeneous or non - homogeneous throughout, examples of which include, but are not limited to, solid mixtures, solutions, and suspensions.

[0024]

[0025] Biological origin carbohydrate feedstocks mean products that are wholly or substantially supplied from, derived from, or synthesized from biological substances or renewable agricultural materials (but not limited to these, such as plant, animal, and marine materials, etc.) or forest materials, and contain carbohydrates thus supplied, derived, or synthesized therefrom.

[0025]

[0026] By-products are accidental or secondary products that occur in the production of the desired product, examples of which include accidental or secondary products and intermediates to these products, and further reaction products from the target product. By-products do not include intermediates to the target product. As an example, in the catalytic conversion of glucose to ethylene glycol, glycolaldehyde and hydroxyacetone may be capable of further reacting under the conditions of this reaction, but any unreacted glycolaldehyde is not considered a by-product, and hydroxyacetone is considered a by-product. Other by-products include, but are not limited to, mannitol, sorbitol, glycerin, 1,2-butanediol, erythritol, threitol, organic acids, and gases.

[0026]

[0027] Catalyst means a heterogeneous or homogeneous catalyst. For the purposes described herein, a catalyst that exhibits behavior as, for example, a colloidal suspension when dissolved in a medium is considered a homogeneous catalyst regardless of whether the catalyst is dissolved. The catalyst may be enzyme-based or an inorganic substance, contain one or more catalytic metals, and in the case of a heterogeneous catalyst, may contain a support, binder, and other adjuvants. The catalytic metal is the metal in the elemental state or is bonded by ionic or covalent bonds. The term catalytic metal does not necessarily have to be in the catalytically active state, but when not in the catalytically active state, refers to a metal that has the potential to become catalytically active. The catalytic metal can provide catalytic activity or modify catalytic activity, such as a promoter or selectivity regulator.

[0027]

[0028] The activity or performance of a catalyst refers to the extrinsic activity of the catalyst in the reaction zone. Thus, factors that affect catalyst activity include the state of the catalyst itself, but also its placement in the reaction zone. For example, if part of the catalyst is physically blocked in the reaction zone, it may be relatively unavailable for performing the required catalyst conversion even if the catalyst itself is active. Thus, means of mixing or other redistribution to make the catalyst surface more accessible are expected to improve the extrinsic catalyst activity.

[0028]

[0029] Changes in catalyst activity can be due to changes in the catalyst itself, such as chemical changes, physical degradation, redistribution of components on the catalyst, loss of catalytically active species from the catalyst, or poisoning, or other effects from components that deposit or become reactive during the course of the reaction. Changes in catalyst activity can also be caused by the environment around the catalyst, for example, via steric effects or reactions, or via complexation with components that are to be converted by the catalyst, in which case the catalyst itself may remain relatively unchanged. Therefore, an increase or decrease in catalyst activity may, but not necessarily, be due to an increase or decrease in the mass of catalyst per unit volume.

[0029]

[0030] A chemical product is a chemical substance or mixture of chemical substances in the effluent from contact with a second catalyst in the reaction zone. This may be a marketable product or a feedstock for further reactions. Thus, the term chemical product is used to designate the composition located in the process of the present invention.

[0030]

[0031] Initiating contact means that a fluid begins to contact a medium containing a component, such as a homogeneous or heterogeneous catalyst, but it is not necessary for all molecules of the fluid to contact the catalyst.

[0031]

[0032] The conversion efficiency is the mass percentage of the raw material that is converted to chemical product in the present process.

[0033] The first catalyst and the second catalyst mean two different catalysts, and this term is not intended to exclude the presence of other catalysts, which may be intermediates in the reaction process to the first and second catalysts, or may be present before the first catalyst or after the second catalyst during the reaction process. The importance of the second catalyst lies in the case where specific input values for the control system are determined. For example, the feed can first be contacted with the first catalyst to provide an intermediate, and then the intermediate can be contacted with another catalyst that can convert it to a further intermediate. This further intermediate can be converted to a chemical product on the second catalyst.

[0032]

[0034] Hydrodynamic distribution means the distribution of the aqueous solution in the vessel including contact with any catalyst contained therein.

[0035] Intermediate means a compound that can further react to the desired product under the conditions in the reaction zone. As defined herein, an intermediate to a by-product is considered a by-product itself.

[0033]

[0036] Intermittent means sometimes and can be at regular or irregular time intervals.

[0037] Input value means the input information from the process for the control method. The input may be an operative input, which is sometimes referred to as an independent variable, meaning that a reported value such as temperature is provided for control. The input may also be a process parameter, which is sometimes referred to as a dependent variable, meaning that the determined value is obtained from a plurality of operative variables in the process. For example, the concentration of an intermediate, by-product or chemical product is the result of a combination of a series of process conditions. The input value may be from one or two or more operative inputs and process parameter inputs and may require calculation. For example, the conversion efficiency can be determined from the concentration of the raw material in the feed and the feed rate to the reaction zone, and can also be determined from the concentration of the chemical product in the effluent from the reaction zone and the flow rate of the effluent.

[0034]

[0038] Itol is a polyhydric alcohol in which each carbon has a hydroxyl group, for example, a sugar alcohol.

[0039] The medium is a gas, liquid, supercritical or mixed-phase fluid containing raw materials, intermediates, by-products and chemical products passing through the reaction zone. The medium may be formed using an inert medium, for example, a solvent or suspension medium for a liquid medium, or the raw materials, intermediates, by-products and chemical products may constitute all or part of the medium. The medium may contain other components such as buffers and other adjuvants.

[0035]

[0040] The pH controller means one or more of a buffer and an acid or a base.

[0041] The purpose of the process may be one or more of the objectives required for the operation of the process. For example, the purpose of the process may be to maximize the conversion efficiency to a chemical product, or to maximize the production rate of the chemical product. The objective may be primary or secondary, for example, to maximize the production rate under the influence of maintaining the concentration of the by-product below a specific level.

[0036]

[0042] The term "raw material" is used to denote one or more reactants added to the reaction zone during the process and is not intended to imply a 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" is used to facilitate understanding.

[0037]

[0043] The reaction zone is a volume containing the first and second catalysts and may be a single vessel or multiple vessels, or a reactor. The reaction zone contains both the first and second catalysts, but may have a region containing one of the catalysts or a region rich in one of the catalysts.

[0038]

[0044] The reactor may be one or more vessels in series or in 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, tanks and pipe or tube reactors, and may have the ability to mix fluids as required. Examples of 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.

[0039]

[0045] The tracer precursor is a chemical substance that can be catalytically converted only by the first or second catalyst. The tracer is a compound derived from the tracer precursor contained in the withdrawn liquid medium. The tracer may be an unreacted tracer precursor or a reaction product of the tracer precursor.

[0040] Discussion

[0046] A method for operating a continuous, unregulated, sequential, plurality of catalytic reaction processes of the present invention addresses changes in the catalytic activity of the catalyst and its relative performance during the course of the process. The method involves using specific process parameters in a control system and then adjusting at least one of the following (I) and (II) to meet the process objectives: (I) at least one of the absolute amount of the catalytically active species and the relative amounts of each of the first and second catalysts, and (II) as an operational input, at least one of the rate and concentration of the feed of raw materials to the reaction zone. The control system hardware used is not critical to the method of the present disclosure, and individual operational input adjustments to setpoints, design space control systems, model predictive control systems, etc. can be used.

[0041]

[0047] Design space and model predictive control are well-known and multivariable. The former is model-based, and the operational input values are maintained within an acceptable operating window. When the operational inputs are correlated, the design space control system can be designed using a predictive model such that an adjustment in one operational input is consistent with adjustments in one or more other operational inputs. The latter takes into account not only the instantaneous state of the process but also the future state of the process. This model can be developed, for example, as a linear model or a quadratic model. These models may be derived from experimental data and the performance of the process with respect to the process objectives. With regard to model predictive control, data from the process can be used to refine the interpretation of future predictions of the model. The control system may be open-loop or closed-loop, and in the case of a closed-loop, the loop may be the entire plant or a portion thereof. Since the present disclosure relates to unregulated sequential catalytic conversion, the control system is at least one that addresses the reaction zone.

[0042]

[0048] Using any process control system, the important issues are the selection of the inputs used and how to reflect those inputs in process control. What constitutes this invention is the selection and the resulting control. Once the invention is understood, it will be apparent to a control engineer with ordinary skill in the art that it will be possible to implement the invention in a control system.

[0043]

[0049] The method disclosed herein is generally applicable to chemical processes that use a plurality of catalytic reactions that are continuous, unregulated, sequential, and in which the catalyst undergoes a change in performance during the process. This process can be said to have a single reaction zone in which at least two catalytic conversions occur. The catalytic conversions can occur in different or the same regions of the reaction zone, and the reaction zone may contain one or more vessels in parallel or in series, provided that the flow is substantially unregulated.

[0044]

[0050] The first and second catalysts may be homogeneous or heterogeneous catalysts, or one may be a homogeneous catalyst and the other a heterogeneous catalyst. If both are heterogeneous, the catalysts may be placed in separate regions of the reaction zone, or they may be partially or substantially completely mixed. If both catalysts are homogeneous, they may be introduced separately into the reaction zone, and the introduction points may be in the same or different regions of the reaction zone. Thus, the reaction zone may have a substantially homogeneous concentration of catalyst throughout, or it may have regions that contain the first catalyst and substantially no second catalyst. In the latter case, the relative ratio of the first and second catalysts will vary in the downstream region of the reaction zone as the second catalyst is introduced. If one catalyst is homogeneous and the other is heterogeneous, the density of each catalyst may be the same throughout the reaction zone, or regions may be provided in the reaction zone where the heterogeneous catalyst is less or absent.

[0045]

[0051] In a continuous process, the raw materials are introduced continuously or intermittently into a reaction zone containing a medium. The raw materials may be one or more reactants for producing a chemical product, which may be the main component of the medium. Alternatively, a substantially inert material may be the main component of the medium. The medium may be provided by feeding an inert material separately to the reaction zone or by feeding at least a portion of the inert material in combination with the raw materials when the substantially inert material is the main component of the medium. When an inert material is used to constitute the medium, the inert material may be in the gas phase or in the liquid phase when passing through the reaction zone. In some cases, the inert material is a solvent for at least one of any homogeneous catalyst, raw material, intermediate, and chemical product. The medium can function as a fluid for suspending one or more catalysts using, for example, a fluidized bed or a boiling bed reactor.

[0046]

[0052] The medium flowing through the reaction zone may be a liquid, a gas, or a mixture of gas and liquid. In the case of a mixture of gas and liquid, the gas or the liquid may be the continuous phase. When a homogeneous catalyst is used, the liquid phase is expected to contain the homogeneous catalyst, and the liquid phase may be the continuous phase or the gas phase may be the continuous phase. In some cases, the catalytic conversion can provide a chemical product in a phase different from the feed to the reaction zone under the reaction conditions, or the raw materials in either the gas phase or the liquid phase are converted and the amount of that phase is reduced. In such examples, the properties of the gas phase and the liquid phase of the flow through the reaction zone can change such that the other phase becomes the continuous phase.

[0047]

[0053] As described above, the method for operating a process uses at least one process parameter input of (I) the rate and concentration of the feed of the raw material in step (i) and the conversion efficiency of the raw material into the chemical product, and (II) the concentration of at least one by-product in the withdrawn medium, the concentration of the intermediate in the withdrawn medium, and, if used, the concentration of at least one tracer in the withdrawn medium. One advantage of the method of this invention is that the data required for the process parameter input does not require composition analysis inside the reaction zone.

[0048]

[0054] If the raw material contains more than one reactant, the operational input can result in the supply of each reactant in a predetermined relationship with each other, or the operational input can address each reactant separately, or the operational input can address only one reactant or less than all of the reactants. For example, if the process being controlled is hydrogenation, the operational input may relate only to the reactant being hydrogenated, which may be the rate-limiting raw material for production.

[0049]

[0055] As a general principle, the disclosed method involves determining and responding to changes in the performance of one or both catalysts and the balance between their performances. Thus, it is not so important that the process parameter inputs be accurate such that the changes are accurately detected. Analytical instruments for providing data on process parameter inputs are within the scope of the technician's customary experience and will depend on the process, the arrangement of the apparatus, the conditions used, and the components present in the feed in the reaction zone and chemical products. The instruments can be used, for example, to determine flow rate, composition, temperature, pressure, density, pressure, electrochemical potential, and turbidity. Examples of analytical instruments include in-line and remote instruments used to analyze samples taken from the reaction zone, such as, but not limited to, gas chromatographs, liquid gas chromatographs, IR spectrometers, nuclear magnetic resonance spectrometers, mass spectrometers, Raman spectrometers, colorimetric techniques, and titrations. Examples of flow meters include, but are not limited to, orifice flow meters, flow nozzle meters, venture meters, rotameters, pitot tubes, turbine flow meters, vortex flow meters, electromagnetic flow meters, Doppler flow meters, ultrasonic flow meters, positive displacement flow meters, thermal mass flow meters, and Coriolis flow meters. Process parameter inputs are often obtained through calculations from data from analyzers and flow meters, and such calculations may be performed manually or by machine.

[0050]

[0056] The rate and concentration of the feed of the raw materials in step (i) are based on the raw materials (i.e., the rate-limiting raw materials for production) supplied at a rate that defines the stoichiometric maximum amount of the producible intermediate. By way of illustration and not limitation, if the process involves reacting 1 mole of A with 1 mole of B, the rate-limiting raw material for production is the raw material provided in the lowest molar amount. This raw material is also used to determine the conversion efficiency. When multiple raw materials are used, the process parameter inputs for each raw material can still be used in accordance with the method of the present disclosure, even if only one is used as the operative input. However, in some cases, the process parameter input for one type of raw material is sufficient for a commercial process.

[0051]

[0057] The rate of the feed of the raw materials can be expressed in units such as mass, volume, moles per unit time, etc., from which the conversion efficiency can be calculated directly or indirectly. When the feed is introduced intermittently, the rate of the feed can be determined by either or both of the period during which the feed is supplied or a predetermined time period that defines the average rate. It will also be recognized that the rate of the feed does not necessarily have to be constant and can be periodic. Thus, when the rate of the feed of the raw materials to the reaction zone is adjusted in response to changes in catalyst performance, the rate can be the subject of adjustment in one or more of the period of intermittent introduction, the frequency of intermittent introduction, and the rate at which the raw materials are introduced during intermittent introduction.

[0052]

[0058] The concentration of the feed of the raw materials is the concentration of the raw materials in the medium for contacting with the first catalyst, and thus includes any components contained in the raw materials, such as solvents, impurities, and diluents, in addition to a predetermined portion of the medium introduced separately. In some cases, since the change in the rate of the medium flow to the first catalyst is extremely small, in such examples, it may be sufficient to assume a predetermined rate of the medium flow.

[0053]

[0059] The medium withdrawn from the reaction zone is typically an intermittent or continuous stream passing through the reaction zone. The medium withdrawn from the reaction zone may be a single stream or may be split into two or more equal - divided streams, all of which can be used to determine the concentration of components. In some cases, when the reactor design is such that the medium in the reaction zone and the withdrawn one are substantially the same, for example, in a CSTR, etc., the concentration of at least one of the by - products, intermediates, or tracers, in addition to the concentration of the chemical product, can be determined from a sample of the medium from the reaction zone to determine the conversion efficiency. It should be understood that checking the concentration of a component can be used to determine the amount of that component in a stream of known volume. Thus, even if the process parameter input is the absolute amount of the catalytically active species of the component in the withdrawn stream, it is equivalent to the concentration.

[0054]

[0060] The process parameter inputs used in accordance with the method of this invention constitute a criterion for identifying changes in catalytic performance that require adjustment of the process inputs to meet the objectives of the process. Additional process parameter inputs may be used as needed, and in some cases, it will be recognized that these inputs can improve (quantitatively or qualitatively) the detection of catalyst changes. The method of this invention is generally applicable to chemical processes that use sequential catalytic reactions. Once the principles of this invention and the nature of the particular process to which the method is to be applied are understood, it is well within the capabilities of an ordinary control engineer to select the process parameter inputs used, including the process parameter inputs of (I) and (II), to reflect changes in the catalyst and establish setpoints for operating a window or control algorithm for adjusting at least one of (I) and (II): (I) at least one of the absolute amount of the catalytically active species and the relative amounts of the first and second catalysts, and (II) at least one of the rate and concentration of the feed of raw materials to the reaction zone, to achieve the objectives of the process.

[0055]

[0061] As an example of the present invention, but not limited to, the following discusses various process parameter inputs and their relationship to evaluating the performance of the catalyst.

[0062] The rate and concentration of the raw material feed in step (i), and the conversion efficiency of the raw material to its chemical products, are important for understanding the overall effectiveness of the catalyst in the reaction zone, but do not provide conclusive information on the cause of changes in the conversion efficiency. However, this information is related to the stress imposed on the catalyst. An increase in the raw material feed or an increase in the flow rate can each be predicted to cause a sacrifice in the conversion efficiency, all other conditions being the same. Thereby, it can be confirmed whether a decrease in the conversion efficiency coincides with the observed changes in the raw material feed and / or the flow rate of the medium. If the change is greater than that predicted, additional process parameter inputs are discussed to confirm whether the change is due to a change in the catalyst activity. In some cases, even when there is no change in the conversion efficiency and the conversion efficiency is the predicted value at a given rate of the raw material feed and the medium flow rate, one or both of the catalysts may be undergoing a change in performance. For example, the catalyst may be present in an amount that exceeds the required amount. If the catalyst has a change in activity, since the catalyst is in excess, the conversion efficiency may not change until further deterioration occurs.

[0056]

[0063] The concentration of at least one by-product in the withdrawn medium, the concentration of the intermediate in the withdrawn medium, and, if used, the concentration of at least one tracer in the withdrawn medium, at least one of which can serve as a process parameter that can provide information regarding the performance of the catalyst in combination with the conversion efficiency. In particular, using a model predictive control system, the concentration of one or more by-products in the withdrawn medium, the concentration of the intermediate in the withdrawn medium, and, if used, the concentration of at least one tracer can be used to build a model, but do not necessarily have to be used once the model is built. The use of the tracer precursor may be continuous or intermittent. For example, the tracer precursor can be used intermittently to ensure that the process is carried out as required, or to assist in troubleshooting problems in the operation of the process, and to reconcile the process with the desired operation again.

[0057]

[0064] In some catalytic processes, the amount of by-product produced can be clarified, especially when the by-product or reaction product is produced by either (i) further reaction of the raw material or intermediate either non-catalytically or on a first catalyst, or (ii) catalytic reaction of the raw material on a second catalyst. For example, if the by-product is from the first catalyst, the increase indicates that the second catalyst has a lower activity density in the reaction zone and the raw material or intermediate takes additional time to enter the reaction to form the by-product. Alternatively, if the by-product is produced via the reaction of the raw material on the second catalyst, the increase indicates that, if other conditions are substantially the same, the activity density of the first catalyst has decreased, and thus more raw material contacts the second catalyst. In some cases, the by-product is produced by the first catalyst and further catalytically reacts with another reaction product by the second catalyst. Either an increase in the by-product due to the absence of the second reaction or a decrease in another reaction product indicates a decrease in the catalytic activity of the second catalyst if other conditions are substantially the same.

[0058]

[0065] In some catalytic processes, changes in the concentration of intermediates in the withdrawn medium are useful. An increase indicates a decrease in the catalytic activity of the second catalyst. If the intermediate reacts rapidly, either catalytically or non-catalytically, with the chemical product or by-product and thus is not present at all in the withdrawn medium, the usefulness of this process parameter is limited.

[0059]

[0066] As an alternative or in addition, a tracer precursor may be used. The tracer precursor reacts substantially with only one of the catalysts. The tracer precursor is added to the medium in a known amount and the concentration of at least one of the unreacted tracer precursor or the reaction product of the tracer precursor in the withdrawn medium is determined. A change in the concentration of the tracer indicates a change in catalytic activity. The choice of tracer precursor will depend on the reaction system and the catalyst. In some cases, the tracer precursor may have a lower reactivity under the reaction conditions than the raw material (first catalyst) or the intermediate (second catalyst). The decrease in reactivity may in some cases be due to a steric effect or one or more of the reactive groups having a chemically lower reactivity than that of the raw material or the intermediate. The concentration of the tracer precursor can be widely varied and will depend, for example, on the ability to analytically detect the concentration of the tracer or reaction product in the withdrawn medium. The concentration of the tracer precursor is often in the range of about 1 ppm (one part per million by weight) to 1 weight percent, based on the mass of the medium.

[0060]

[0067] In response to the detected change in catalytic activity, adjustments are made to at least one of (I) the absolute amount of the catalytically active species and the relative amounts of each of the first and second catalysts, and (II) the rate and concentration of the feed of the raw material to the reaction zone. It is usually desirable to determine whether a mechanical failure or other physical event that results in a non-uniform distribution of the catalyst has occurred, or whether other disruptive events have not occurred, before any change occurs in either (I) or (II).

[0061]

[0068] Adjustment in the absolute amount of catalytically active species and the relative amount of catalyst can be carried out, for example, by addition of catalyst to or removal of catalyst from the reaction zone. The manner of addition or removal of catalyst is well within the scope of the art. The optimal technique will depend on the type of reaction system. For example, when a homogeneous catalyst or a suspended catalyst is used, the catalyst can be withdrawn from the reaction zone by using a medium or recycling a sidestream to reduce the amount of that catalyst. Addition of catalyst may be carried out by introducing the catalyst into the reaction zone.

[0062]

[0069] The absolute amount of catalytically active species of a catalyst can also be adjusted by treatment of the catalyst or its environment and / or by improving the problem of non-uniform distribution of the catalyst in the reaction zone. The absolute amount of catalytically active species of a catalyst is based on the effectiveness of the catalyst rather than simply the overall mass of the catalyst. Thus, physical and environmental process conditions, such as non-uniform distribution causing catalyst loss and in situ catalyst conditions, such as coating, poisoning, sintering, loss of catalytic species by solubilization, as well as steric effects or reactions or complexation with raw materials or intermediates, are reflected in the absolute amount of catalytically active species available for the reaction. For example, the formation of deposits on the catalyst reduces the available catalytic sites. Removal of all or part of the deposits increases the number of available catalytic sites and thus is an increase in the absolute amount of catalytically active species of the catalyst. In some cases, the catalytic species in the catalyst are in an oxidized or reduced state. For example, nickel used in a hydrogenation catalyst can be in an oxidized state and may become catalytically inactive. Reduction of nickel oxide is expected to increase the amount of catalytically available nickel and thus is expected to result in an increase in the absolute amount of catalytically active species of the catalyst. Similarly, the catalytic species may be oxidized or reduced or may be converted to more or less active species. This is particularly the case when the catalytic species is or can form a complex.

[0063]

[0070] Additionally, or alternatively, the adjustment to accommodate the change in catalytic activity may be a change in the feed rate of the raw materials. Thus, the raw material feed rate will take into account that at least one of the catalysts in the reaction zone provides fewer catalytically active species. However, the production rate of the chemical product is also expected to decrease. In some cases, changes occur in the feed rate of the raw materials and the flow rate of the medium, and an increase in by-products. If the aim of the process is to minimize the formation of such by-products, the adjustment of the raw material feed rate and the flow rate of the medium can result in a compromise.

[0064]

[0071] The method of the present invention is generally applicable to sequential catalytic processes that can be carried out in a single reaction zone. Thus, the process may be a process for making chemicals, pharmaceuticals, and fuels. The method of the present invention can use the types of raw materials and catalysts used in such processes when operated in a regulated manner.

[0065]

[0072] One application of the method of the present invention is to a process for converting a carbohydrate containing an aldohexose-producing carbohydrate or a ketose-producing carbohydrate in a reaction zone to at least one of ethylene glycol and propylene glycol (lower glycols), which is carried out by subjecting the sugar to catalytic retro-aldol conditions to produce an intermediate that is hydrogenated under catalytic hydrogenation conditions. See, for example, published U.S. Patent Application Nos. 2017 / 0349513 and 2018 / 0086681 and U.S. Patents 9,399,610 and 9,783,472, which are hereby incorporated by reference in their entirety.

[0066]

[0073] The raw materials contain carbohydrates, which are in most cases at least one of pentose and hexose, or compounds that yield pentose or hexose. Examples of pentose and hexose include xylose, lyxose, ribose, arabinose, xylulose, ribulose, glucose, mannose, galactose, allose, altrose, idose, talose, and gulose, fructose, psicose, sorbose, and tagatose. Most biologically derived carbohydrate feedstocks yield glucose upon hydrolysis. Examples of glucose precursors include, but are not limited to, maltose, trehalose, cellobiose, kojibiose, nigerose, isomaltose, β,β-trehalose, α,β-trehalose, sophorose, laminaribiose, gentiobiose, and mannobios. Carbohydrate polymers and oligomers, such as hemicellulose, partially hydrolyzed forms of hemicellulose, disaccharides such as sucrose, lactulose, lactose, turanose, maltulose, palatinose, gentiobiulose, melibiose, and melibiulose, or combinations thereof can be used.

[0067]

[0074] In these processes, an aqueous medium containing carbohydrates is contacted with a retro-aldol catalyst under retro-aldol reaction conditions. The contacting may begin before or upon introduction of the aqueous medium into the portion of the reaction zone containing the hydrogenation catalyst. Preferred temperatures for the retro-aldol reaction are typically about 230 °C to 300 °C, more preferably about 240 °C to 280 °C, although the retro-aldol reaction may be carried out at lower temperatures, such as as low as 90 °C or 150 °C. The pressure (absolute) is typically in the range of about 15 to 200 bar (1500 to 20,000 kPa), for example in the range of about 25 to 150 bar (2500 to 15000 kPa).

[0068]

[0075] 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, but are not limited to, heterogeneous and homogeneous catalysts such as catalysts supported on a carrier, including tungsten and its oxides, sulfates, phosphides, nitrides, carbides, halides, acids, etc. Also included are tungsten carbide supported on zirconia, alumina and alumina-silica, soluble phosphotungsten, and tungsten oxide. Preferred catalysts are provided by soluble tungsten compounds and mixtures of tungsten compounds. Examples of 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 metatungstate and alkali metals, and ammonium tungstate and alkali metals. The presence of ammonium cations often results in the formation of undesirable amine by-products in lower glycol products. Without wishing to be bound by theory, the species exhibiting catalytic activity may or may not be the same as the soluble tungsten compound introduced as the catalyst. Rather, the catalytically active species may be formed as a result of exposure to the retro-aldol reaction conditions. Complexes containing tungsten are typically pH-dependent. For example, a solution containing sodium tungstate at a pH greater than 7 produces sodium metatungstate as the pH decreases. The form of the complexed tungstate anion is generally pH-dependent. The rate at which the complexed anion formed from the condensation of tungstate anions is formed is affected by the concentration of the tungsten-containing anion. Preferred retro-aldol catalysts include an acid, preferably an organic acid having 1 to 6 carbon atoms, such as, but not limited to, ammonium tungstate or an alkali metal partially neutralized with formic acid, acetic acid, glycolic acid, and lactic acid.Partial neutralization is often about 25 to 75%, i.e., on average 25 to 75% of the cations of tungstic acid become acid sites. Partial neutralization may occur before introducing a tungsten-containing compound into the reactor or by using an acid contained in the reactor.

[0069]

[0076] The concentration of the retro-aldol catalyst used can be widely varied 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 from about 0.01 or 0.05 to 100 grams, such as from about 0.02 or 0.1 to 50 grams, of tungsten calculated as elemental metal per liter of the aqueous hydrogenation medium. The retro-aldol catalyst can be added as a mixture with all or part of the carbohydrate feed, or as a separate feed to the aqueous hydrogenation medium, or by recycling the aqueous medium, or by any combination thereof. In some cases, a homogeneous tungsten-containing retro-aldol catalyst can deposit a tungsten-containing compound or complex on the hydrogenation catalyst and have an effect opposite to the activity of the hydrogenation catalyst. Continuous or intermittent circulation of a catalyst containing a predetermined amount of tungsten may cause removal of at least a portion of the deposited tungsten compound or complex. Thus, the methods of the present disclosure anticipate that control of the absolute amount of catalytically active species and the relative amounts of the first and second catalysts, including operation when the purpose of the process is reactivation of the catalyst.

[0070]

[0077] In many cases, the carbohydrate feed is subjected to retro-aldol conditions before being introduced into the aqueous hydrogenation medium in a reaction zone containing a hydrogenation catalyst. Preferably, the introduction into the aqueous hydrogenation medium occurs in less than 1 minute, most often less than 10 seconds, from when the carbohydrate feed is first subjected to retro-aldol conditions. Part 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 is one in which the period between retro-aldol conversion and hydrogenation is short.

[0071]

[0078] Hydrogenation, i.e., the addition of hydrogen atoms to organic compounds without breaking carbon-carbon bonds, can be carried out at temperatures in the range of 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 by the retro-aldol reaction, thereby enhancing the selectivity to ethylene and propylene glycol. Thereafter, the temperature of the aqueous hydrogenation medium may be reduced as needed. However, hydrogenation proceeds rapidly at these higher temperatures. Thus, the temperature for the hydrogenation reaction is often about 230 °C to 300 °C, for example, 240 °C to 280 °C. The pressure is typically in the range of about 15 to 200 bar, for example, about 25 to 150 bar. The hydrogenation reaction requires the presence of hydrogen, in addition to a hydrogenation catalyst. Hydrogen has a 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, for example, about 3 or 3.5 to 8, and in some cases about 3.2 or 4 to 7.5.

[0072]

[0079] Hydrogenation is carried out in the presence of a hydrogenation catalyst. In many cases, the hydrogenation catalyst is a heterogeneous catalyst. This 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, many reduction catalysts are expected to function in this application. The reduction catalyst can be selected from a wide variety of supported transition metal catalysts. Nickel, Pt, Pd, and ruthenium as primary reduction metal components are well-known for their ability to reduce carbonyls. One particularly preferred catalyst for the reduction catalyst in this process is the 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 a preferred reduction metal catalyst and may be supported on alumina, alumina-silica, silica, or other supports. A supported Ni-Re catalyst having B as a promoter is useful. Generally, in the case of a slurry reactor, the supported hydrogenation catalyst is provided in an amount of less than 10, sometimes less than about 5, for example, about 0.1 or 0.5 to 3 grams / liter of nickel (calculated as elemental nickel) per liter of the liquid medium in the reactor. As described above, not all nickel in the catalyst is in the zero-valent state, and not all nickel in the zero-valent state is readily available by glycolaldehyde or hydrogen. Therefore, for a particular hydrogenation catalyst, the optimal mass of nickel per liter of the liquid medium is expected to vary. For example, a Raney nickel catalyst is expected to provide a fairly high nickel concentration per liter of the liquid medium. In many cases, 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 the aqueous hydrogenation medium, and in a packed bed reactor, the hydrogenation catalyst constitutes about 20-80 volume percent of the reactor.In some cases, the weight hourly space velocity is from about 0.01 or 0.05 to 1 / hour, based on the total carbohydrates in the feed. Preferably, the residence time is sufficient if the glycolaldehyde and glucose are less than 0.1 weight percent of the reaction product, and most preferably less than 0.001 weight percent of the reaction product.

[0073]

[0080] The carbohydrate feed is at least 50 grams / liter / hour of carbohydrate and in many cases is in the range of about 100 to 700 or 1000 grams / liter / hour of carbohydrate. In the process of this invention, the combination of reaction conditions (e.g., temperature, hydrogen partial pressure, catalyst concentration, hydraulic distribution, and residence time) is sufficient to convert at least about 95, in many cases at least about 98 weight percent, and sometimes substantially all of the carbohydrate that yields an aldose or a ketose. Determining one or more sets of conditions that are expected to provide the required carbohydrate conversion is well within the skill of those having the benefit of the disclosure herein.

[0074]

[0081] In the method of the present invention applied to the retro-aldol / hydrogenation process for producing lower glycols, the process parameter input is preferably the concentration in at least one withdrawn medium of itol, 1,2-butanediol, and hydroxyacetone. The itol contained in the withdrawn medium results from the reaction with the carbohydrate feed. For example, glucose can be hydrogenated to sorbitol. In the retro-aldol step, glucose can provide glycolaldehyde and erythrose and threose. When these tetroses are hydrogenated, they produce erythritol and threitol. Glucose may also undergo isomerization to fructose, and when fructose is hydrogenated, it becomes mannitol. Also, fructose becomes a compound having three carbons under retro-aldol conditions and can thus produce glycerol. Since itol is produced, insights into the process can be obtained from the type and production rate of itol. When a tracer precursor is used, it is preferably a ketone, for example, a ketone having 3 to 10 carbons.

[0075]

[0082] Generally, an increase in the itol concentration, all other things being substantially constant, indicates that the first catalyst is undergoing loss of catalytically active species, and an example of an operational input is an adjustment to the absolute and relative amounts of each of the retro-aldol catalyst and the hydrogenation catalyst by at least one of (I) increasing the catalytic activity of the retro-aldol catalyst or decreasing the catalytic activity of the hydrogenation catalyst, and (II) reducing the rate of feed of raw materials to the reaction zone.

[0076]

[0083] When the 1,2 - butanediol concentration is used as a process parameter input, the 1,2 - butanediol may be due to the reaction between two glycolaldehyde molecules or the dehydration of tetrose. In the former case, the general rule is that an increase in the 1,2 - butanediol concentration, all other things being substantially the same, reflects the loss of hydrogenation catalyst activity in the reaction zone. In this case, examples of operational input adjustments are (I) increasing the catalytic activity of the hydrogenation catalyst or decreasing the catalytic activity of the retro - aldol catalyst, the absolute and relative amounts of each of the retro - aldol catalyst and the hydrogenation catalyst, and (II) at least one of reducing the rate of feed of raw materials to the reaction zone. In the latter case, the 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 of feed of raw materials to the reaction zone and its concentration is expected to be a responsive operation. Therefore, it may be useful to have another parameter to indicatively show whether there is a change in the concentration of 1,2 - butanediol. For example, if an increase in 1,2 - butanediol is accompanied by an increase in glycerin, since glycerin is produced from fructose and fructose is produced from the isomerization of glucose, this is expected to indicate a reduction in retro - aldol activity. Because the isomerization reaction outpaces the retro - aldol conversion if all other conditions remain the same.

[0077]

[0084] The hydrogenation catalyst may lose its activity for various reasons, including but not limited to deposits that block the catalytic sites, such as the loss of catalytic metal by oxidation or solubilization, and the sintering of the catalytic metal. The method of the present disclosure anticipates, in some cases, as a means of adjusting the catalytic activity of the hydrogenation catalyst, withdrawing the hydrogenation catalyst from the reaction zone and at least partially replacing it with a new or reactivated hydrogenation catalyst. The control method can control the rate of the hydrogenation catalyst withdrawn from and replenished to the reaction zone with respect to both frequency and mass to maintain the hydrogenation activity within a desired range.

[0078]

[0085] Optimizing the retro-aldol process for ethylene glycol production involves optimizing the retro-aldol conversion, which is mainly limited by reaction kinetics, and optimizing the hydrogenation reaction, which is mainly limited by mass transfer. The mass transfer limitation includes the supply of hydrogen to the hydrogenation catalyst sites, and hydrogen deficiency can occur when there are local regions with high hydrogenation catalyst activity. Hydrogen deficiency can be caused, for example, but not limited to, the non-uniform distribution of the hydrogenation catalyst within the reaction zone and local regions with higher feed concentrations in the reaction zone. Thus, hydrogen deficiency can lead to the formation of organic acids, which are by-products in the withdrawn medium and can therefore be used in the process of this invention. For process control purposes, pH measurements can often be used as proxy data for organic acid concentration. In some cases, reducing the feed rate can weaken acid production, but it may also be necessary to manipulate one or both of the absolute and relative amounts of the retro-aldol catalyst and the hydrogenation catalyst.

[0079]

[0086] Hydroxyacetone is usually present in the withdrawn medium at very low concentrations. However, it has been found to be a sensitive indicator of a decrease in the activity of the hydrogenation catalyst. An increase in the hydroxyacetone concentration can be addressed by increasing the catalytic activity of the hydrogenation catalyst and / or reducing the rate of raw material feed to the reaction zone. In some cases, the hydroxyacetone concentration in the withdrawn medium is less than 0.15 weight percent, preferably less than 0.10 weight percent.

[0080]

[0087] Tracers can also be used in the same way as hydroxyacetone. Since internal carbonyls have higher resistance to hydrogenation than aldehyde carbonyls, ketones such as methyl ethyl ketone can be useful tracer precursors. Thus, the degree of hydrogenation of the ketone is an indicator of the hydrogenation activity in the reaction zone.

[0081]

[0088] Although this disclosure has been described with reference to various embodiments, those skilled in the art will recognize that it is possible to make changes in form and detail without departing from the essence and scope of this disclosure.

Claims

1. 1. A model predictive control method for operating a continuous, unregulated, sequential, multiple catalytic reaction process, comprising: Each catalyst undergoes a change in performance during the course of the process, and the catalytic reaction process comprises: (i) continuously or intermittently introducing at least one feedstock and optionally a tracer precursor at a feed rate into a reaction zone containing a medium; (ii) maintaining said reaction zone under catalytic conversion conditions suitable for a first catalytic conversion to produce an intermediate-containing medium, said conditions including temperature, pressure, residence time, concentration of said first catalyst providing catalytically active species, and optionally pH and adjuvants; (iii) contacting the medium containing said intermediate with a second catalyst providing a catalytically active species under conditions suitable for another transformation to produce a chemical product, said conditions including temperature, pressure, residence time, concentration of the second catalyst, and optionally pH and adjuvants; and (iv) continuously or intermittently withdrawing a medium containing chemical products from contact with the second catalyst at a rate providing a continuous process. Including, wherein at least one by-product is produced and the catalytic activity of at least one of said first catalyst and said second catalyst undergoes a change in performance during continuous operation; The control method includes: (a) continuously or intermittently inputting predetermined process parameters from the operation of the process into a model predictive controller having a control model; (b) adjusting operational inputs to said process, as necessary, to meet desired process objectives; and, optionally, (c) adjusting the control model. Including, (A) In component (a), the input predetermined process parameters include: (I) the rate and concentration of the feed of the raw material in step (i) and the efficiency of conversion of the raw material to chemical products, to reflect data on the performance of the catalyst in a control model; and (II): the concentration of by-products in the withdrawn medium, the concentration of the intermediate in the withdrawn medium, and The concentration of at least one tracer in the withdrawn medium. At least one of Including; (B) adjusting, as necessary, at least one of the following (I) and (II) to meet desired process objectives: (I) at least one of the absolute amounts of said catalytically active species and the relative amounts of each of said first and second catalysts, and (II) at least one of the rates and concentrations of said raw materials fed to said reaction zone as operational inputs. The above method.

2. The method of claim 1 , wherein the medium is a liquid.

3. The method of claim 1 , wherein at least one of the first catalyst and the second catalyst is homogeneous.

4. 10. The process of claim 1 , wherein the reaction zone comprises two vessels in flow order.

5. 2. The method of claim 1, wherein adjusting the absolute amount of at least one catalytically active species of the catalyst is by adding an additional amount of the catalyst to the reaction zone.

6. 2. The method of claim 1, wherein adjusting the absolute amount of at least one catalytically active species of the catalyst is by adjusting the effectiveness of the catalyst in the reaction zone.

7. 10. The method of claim 1, wherein the reaction zone is a single-pot reaction zone.

8. 2. The method of claim 1, wherein the process is for converting carbohydrates to lower glycols by sequential retro-aldol catalysis to produce an intermediate from the carbohydrate and hydrogenation catalysis to produce at least one of ethylene glycol and propylene glycol from the intermediate.

9. 9. The method according to claim 8, wherein the concentration of at least one of 1,2-butanediol, propylene glycol, at least one isol, hydroxyacetone, pH and tracer in the withdrawn medium are used to reflect the performance of the catalyst.

10. 10. The method of claim 9, wherein the itol is one or more of erythritol, threitol, glycerin, mannitol, and sorbitol.

11. 1. A method for operating a continuous, unregulated, sequential, multiple catalytic reaction process, comprising: Each catalyst undergoes changes in performance during the course of the process, and the method adjusts operational inputs to provide outputs within predetermined ranges, and the catalytic reaction process comprises: (i) continuously or intermittently introducing at least one feedstock and, optionally, a tracer precursor at a feed rate and concentration into a reaction zone containing a liquid medium; (ii) maintaining said reaction zone under catalytic conversion conditions suitable for a first catalytic conversion to produce a liquid medium containing an intermediate, said conditions including temperature, pressure, residence time, concentration of a first catalyst providing a catalytically active species, and optionally pH and an adjuvant; (iii) contacting the liquid medium containing said intermediate with a second catalyst providing a catalytically active species under conditions suitable for another transformation to produce a chemical product, said conditions including temperature, pressure, residence time, concentration of said second catalyst, and optionally pH and adjuvants; and (iv) continuously or intermittently withdrawing a liquid medium containing the chemical product from contact with the second catalyst at a rate providing a continuous process. Including, wherein at least one by-product is produced and the catalytic activity of at least one of said first catalyst and said second catalyst undergoes a change in performance during continuous operation; The method comprises: (a) continuously or intermittently comparing predetermined process parameters from operation of a process with predetermined windows relating to such operation; and (b) adjusting operational inputs to said process, if necessary, to meet desired process objectives. Including, The above method, wherein in component (a), the inputted predetermined process parameters include (I) the rate and concentration of feed of raw materials in step (i) and the efficiency of conversion of said raw materials to chemical products, and (II) at least one of the concentration of at least one by-product in the withdrawn liquid medium, the concentration of an intermediate in the withdrawn liquid medium, and, if used, the concentration of at least one tracer in the withdrawn liquid medium, and in component (b), adjustments are made to at least one of the following (I) and (II): (I) at least one of the absolute amount of said catalytically active species and the relative amount of each of said first catalyst and second catalyst, and (II) at least one of the rate and concentration of feed of said raw materials to said reaction zone as operational inputs.

12. The method of claim 11 , wherein at least one of the first catalyst and the second catalyst is homogeneous.

13. 12. The method of claim 11 , wherein the reaction zone comprises two vessels in flow order.

14. 12. The method of claim 11, wherein adjusting the absolute amount of at least one catalytically active species of the catalyst is by adding an additional amount of the catalyst to the reaction zone.

15. 12. The method of claim 11, wherein adjusting the absolute amount of at least one catalytically active species of the catalyst is by adjusting the effectiveness of the catalyst in the reaction zone.

16. 12. The method of claim 11, wherein the reaction zone is a single-pot reaction zone.

17. 12. The method of claim 11, wherein the process is for converting carbohydrates to lower glycols by sequential retro-aldol catalysis to produce an intermediate from the carbohydrate and hydrogenation catalysis to produce at least one of ethylene glycol and propylene glycol from the intermediate.

18. The method according to claim 17, wherein 1,2-butanediol, propylene glycol, at least one isol, hydroxyacetone, pH and tracer in the withdrawn medium are used to reflect the performance of the catalyst.

19. 19. The method of claim 18, wherein the itol is one or more of erythritol, threitol, glycerin, mannitol, and sorbitol.