Method for operating a continuous, unregulated, multiple catalytic step process - Patents.com

Abstract

A control method is disclosed for a series of uncontrolled catalytic conversion step processes using at least two catalysts, namely a first catalyst and a second catalyst, that accept variations in the performance of each catalyst and the relative performance of the catalysts. In this method, specific process parameters are used in a manner that indicates variations in catalytic performance, and the control method provides adjustments to at least one of the absolute amount of catalytically active species and the relative amounts of the first catalyst and the second catalyst, as well as at least one of the rate or concentration of feed of raw materials into the reaction zone.

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. Provisional 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

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

[0003]

[0003] Catalytic processes are used in commercial applications for the production of chemicals, pharmaceuticals, fuels, polymers, etc. In some of these processes, a feedstock or raw material 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, which then undergoes one or more conversion steps to provide the desired product.

[0004]

[0004] Traditionally, these multi-step processes proceed in separate steps, i.e., subjecting the feedstock to catalytic conditions to produce an intermediate, which is recovered, and then subjecting it to a second catalytic step to produce a chemical product. For purposes herein, this is referred to as a modulated cascade process. Thus, each step of a modulated cascade process can be controlled to reflect, among other things, the process conditions desired to achieve conversion efficiency and selectivity.

[0005]

[0005] Most catalysts suffer from changes in performance due to deactivation, deterioration or physical losses. Also, in some cases, the production of by-products and other losses of raw materials or intermediates are sometimes directly or indirectly affected by the conditions of the catalyst. In the case of a single catalytic conversion process or a regulated cascade process, the optimization of conditions can take into account the conditions of the catalyst used in a single conversion. Thus, when adjustments are made to reactant temperature, pressure, feed rate, residence time, adjuvants, pH and other controllable process variables, the operator has reasonable confidence as to the effect of the changes. Thus, a multi-stage process offers the benefit of controlling the overall process step by step and also of avoiding conflating the control of one catalytic process with that of another.

[0006]

[0006] Step-by-step control of a regulated cascade process, especially with recovery of intermediates between steps, increases production costs. Operating a multi-step process as an unmodulated cascade process can provide economic benefits, especially when the steps are under an integrated control system. An unmodulated cascade process means that there are separate reaction zones and a liquid stream containing intermediates from a first reaction zone is passed through a subsequent reaction zone, which reacts the liquid stream without removing the intermediates. The subsequent reaction zone may be the next reaction zone or a later reaction zone in the flow sequence.

[0007] In addition to regulated cascade processes, multi-step processes conducted in a single reaction zone ("single pot") have been proposed. In these single pot processes, it is often inevitable that intermediates may react to produce undesirable by-products. Therefore, to achieve viable economics, the intermediates are rapidly subjected to subsequent catalytic reactions to mitigate 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 gives ethylene glycol. On the other hand, glycolaldehyde is highly reactive and may react to produce by-products, for example, 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, where the first vessel contains a first catalyst and is substantially free of any second catalyst.

[0008]

[0008] Typical process control focuses on conversion and selectivity to the desired product, and operational inputs such as one or more of the feed rate, the concentration of raw materials in the feed, temperature, pressure, residence time, pH, and the concentration of adjuvants are inputs to the process control, and one or more of the operational inputs are adjusted to provide operation that meets the process objectives. Changes in the catalytic performance and relative performance of catalysts are confounding factors in process control, and therefore adjustments made in response to operational inputs that are supposed to improve conversion and selectivity may destabilize operation due to the performance of the catalyst. In addition, even if the operational inputs indicate that there are no operational problems, the performance of one or more of the catalysts may deteriorate to the point where destabilization occurs. Summary of the Invention [Problem to be solved by the invention]

[0009]

[0009] There is therefore a need to provide a method for controlling a continuous, unadjusted, multiple catalytic conversion step process to accommodate variations in the performance of each catalyst and in the relative performance of the catalysts. Moreover, it is desirable for such a method to use input parameters that can be reasonably obtained from the process, and particularly input parameters that can be ascertained relatively quickly to provide real-time data for management of the process. [Means for solving the problem]

[0010]

[0010] The present invention provides a control method for carrying out a continuous unregulated multiple catalytic conversion step process using at least two catalysts, i.e., a first catalyst and a second catalyst, that accommodates changes in the performance of each catalyst and the relative performance of the catalysts. The process converts at least one feedstock into a desired chemical product in a medium, and includes contacting a first of the feedstock with a catalyst to provide an intermediate, and then contacting the intermediate with a second catalyst to provide the chemical product. Although the discussion herein refers to two catalysts, this is for ease of understanding purposes. 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 performed before, during, or after the two catalytic reactions. For example, a first catalytic reaction can provide an intermediate that reacts with another chemical contained in the reaction system to form a second intermediate non-catalytically, which can then be catalytically reacted to the desired chemical product. In this method, certain process parameters are used to indicate catalyst performance, and the control method provides for adjustment of at least one of the absolute amount of catalytically active species and the relative amounts of each of the first and second catalysts, and the rate and concentration of the feed of raw materials to the reaction zone.

[0011] The method of the invention includes, from the effluent from the second catalyst (the "withdrawn medium"), (I) determining 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 an intermediate in the withdrawn medium, and the concentration of at least one tracer, if used. Both (I) and (II) may rely on conventional analysis of samples of the raw material feed to the multiple catalytic conversion step process and the product stream from the multiple catalytic conversion step process, and typically analytical equipment for determining the concentrations of the described elements can provide near real-time data, for example within 30 minutes of sampling, often within 10 or 5 minutes.

[0012]

[0012] Without 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-products or tracers are more sensitive to the reaction conditions than the product itself. For example, in the retro-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 a reaction zone is used herein to refer to the effectiveness of the catalyst in the reaction zone, and not necessarily in relation 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 in a relative relationship. Thus, the absolute amount of catalytically active species may be changed without changing the mass of the catalyst, for example, by deactivation, conversion to inactive or relatively less active molecules, addition of promoters, or poisoning. Alternatively, the absolute amount of catalytically active species may be changed by adding or removing the catalyst from the reaction zone. Adjustments may be made to one of the catalysts to balance the performance of the catalyst or the feed rate may be reduced to accommodate the effective capacity of a degraded catalyst. Adjustments to the catalyst include, but are not limited to, the addition of more catalyst to the reaction zone and chemical modification of the catalyst. Chemical modification includes, but is not limited to, the addition of promoters or poisons 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 may be more or less active after changing a parameter, for purposes described herein, such parameter changes are not considered to change the absolute amount of the catalytically active species. If one of the catalysts is a homogeneous catalyst or a finely dispersed heterogeneous catalyst present throughout the reaction zone, the addition or removal of such catalyst can be done using a medium added to 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, if desired, into a more scalable control system for the process, which 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, boundary conditions or windows are predetermined and operation within the window is considered to be under control. In MPC, dynamic process models are often created empirically and take into account the current control status as well as the future effect of the current control status on the process. Control actions can be taken based on the predictive model in anticipation of future events.

[0014] One broad aspect of the invention is a predictive control method for managing a continuous, unregulated, sequential, multiple catalytic reaction process, comprising: Each catalyst undergoes changes in performance during the process, and the process associated with the method of the present invention (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 medium; (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 adjuvants; (iii) contacting the medium containing the intermediate with a second catalyst 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 the medium containing the 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 the first catalyst and the 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 the process, as necessary, to meet the 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 in the control model data on the performance of the catalyst; 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 Includes; (B) adjusting, as necessary, at least one of: (I) the absolute amount of catalytically active species and the relative amounts of each of the first catalyst and the second catalyst; and (II) at least one of the rates and concentrations of feed of raw materials to the reaction zone as operational inputs to meet desired process objectives. The present invention relates to the above method, comprising:

[0015] In a preferred embodiment of this first broad aspect of the invention, the reaction process involves catalytic conversion of a sugar to at least one of ethylene glycol and propylene glycol ("lower glycol") by sequential retro-aldol catalytic conversion to an intermediate (first catalyst), and catalytic hydrogenation of the intermediate to at least one of ethylene glycol and propylene glycol ("lower glycol") (second catalyst). In many instances, the retro-aldol catalyst is homogeneous and the hydrogenation catalyst is heterogeneous. The process is complex and subject to many reactions, both catalytic and non-catalytic. For example, the sugar may isomerize and the intermediate may react to by-products, all of which adversely affect the selectivity to the desired lower glycol. The desired process objective is often selectivity of 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 weight of the feed. By-products of the process include one or more of 1,2-butanediol, hydroxyacetone, one or more isols, pH, and the preferred tracer precursor, if used, is one or more ketones having 3-6, preferably 4-6 carbons, and the tracer is unreacted ketone or a reaction product of the ketone. The predictive control model preferably determines the pH of the effluent, and pH is input to the model. pH can be a useful input, since acid can be a by-product of the process. The reaction process can be a cascade process or a single pot process.

[0016] A second broad aspect of the invention relates to a design space method for managing a continuous, unregulated, sequential, multiple catalytic reaction process, where each catalyst undergoes changes in performance over the course of the process, and the method adjusts operational inputs to provide outputs within predetermined ranges. The process associated with the method of the invention includes: (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 the 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 the first catalyst, and optionally pH and adjuvants; (iii) contacting the liquid medium containing the intermediate with a second catalyst 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 the liquid medium containing the chemical product from 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.

[0017] The method comprises: (a) continuously or intermittently comparing predetermined process parameters from operation of the process with predetermined windows for such operation; and (b) adjusting the operational inputs to the process, as necessary, to meet the desired process objectives. Including, In component (a), the input predetermined process parameters include: (I) the rate and concentration of feed of raw materials in step (i) and the efficiency of conversion of the raw materials to chemical products; 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 Including, wherein in component (b), adjustments are made to (I) at least one of the absolute amounts of catalytically active species and the relative amounts of each of the first and second catalysts, and (II) as operational inputs, at least one of the rates of feed of raw materials to the reaction zone and their concentrations.

[0018] In a preferred embodiment of this first broad aspect of the invention, the reaction process involves catalytic conversion of a sugar to at least one of ethylene glycol and propylene glycol ("lower glycol") by sequential retro-aldol catalytic conversion to an intermediate (first catalyst), and catalytic hydrogenation of the intermediate to at least one of ethylene glycol and propylene glycol ("lower glycol") (second catalyst). In many instances, the retro-aldol catalyst is homogeneous and the hydrogenation catalyst is heterogeneous. The process is complex and subject to many reactions, both catalytic and non-catalytic. For example, the sugar may isomerize and the intermediate may react to by-products, all of which adversely affect the selectivity to the desired lower glycol. The desired process objective is often selectivity of 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 weight of the feed. By-products of the process include one or more of 1,2-butanediol, hydroxyacetone, one or more isols, pH, and the preferred tracer precursor, if used, is one or more ketones having 3-6, preferably 4-6 carbons, and the tracer is unreacted ketone or a reaction product of the ketone. The predictive control model preferably determines the pH of the effluent, and pH is input to the model. pH can be a useful input, since acid can be a by-product of the process. The reaction process can be a cascade process or a single pot process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019]

[0019] 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.

[0020] Detailed Description

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

[0021] definition

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

[0022]

[0022] 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.).

[0023]

[0023] Use of the terms "a" and "an" is intended to include one or more of the described elements.

[0024] 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.

[0024]

[0025] 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.

[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, 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, glycolaldehyde and hydroxyacetone may be capable of further reaction under the conditions of the 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 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 be enzymatic or inorganic, contain one or more catalytic metals, and in the case of heterogeneous catalysts, may include supports, binders and other adjuvants. The 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.

[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 the 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 blocked in the reaction zone, it will be 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 extrinsic catalytic activity.

[0028]

[0029] 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 accumulate or become reactive 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 will be 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 catalyst per unit volume.

[0029]

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

[0030]

[0031] 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.

[0031]

[0032] Conversion efficiency is the mass percent of the feedstock that is converted to chemical products in the process.

[0033] The first catalyst and the second catalyst refer to two different catalysts, and the 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 is in determining certain input values ​​for the control system. For example, the feed may first be contacted with the first catalyst to provide an intermediate, and then contacted with another catalyst that can convert the intermediate into a further intermediate. The further intermediate may be converted into a chemical product on the second catalyst.

[0032]

[0034] Hydraulic distribution refers to the distribution of the aqueous solution in the vessel, including contact with any catalyst contained therein.

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

[0033]

[0036] Intermittent means from time to time, which may be at regular or irregular time intervals.

[0037] 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 provided for 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 may be determined from the raw material concentration in the feed and the feed rate to the reaction zone, and from the concentration of a 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, e.g., a sugar alcohol.

[0039] The medium is a gas, liquid, supercritical or mixed phase fluid that contains the raw materials, intermediates, by-products and chemical products passing through the reaction zone. The medium may be formed using an inert medium, such as a solvent or suspension medium for the 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] pH control agent means one or more of a buffer and an acid or a base.

[0041] The process objective may be one or more of the objectives desired for the operation of the process. For example, the process objective may be to maximize the efficiency of conversion to chemical products or to maximize the rate of production of chemical products. The objective may be primary or secondary, for example, to maximize the production rate subject to maintaining the concentration of by-products below a particular level.

[0036]

[0042] The term feedstock is used to indicate one or more reactants that are added to a reaction zone during a process and is not intended to address the need for purity or purification. A feedstock may also be a product from another chemical or biochemical process. Because reactants include intermediates, the term feedstock is used for ease of understanding.

[0037]

[0043] The reaction zone is the volume that contains 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 regions that contain one of the catalysts or that are rich in one of the catalysts.

[0038]

[0044] 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.

[0039]

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

[0040] Discussion

[0046] The method for operating a continuous, unregulated, sequential, multiple catalytic reaction process of the present invention addresses the changes in catalytic activity of the catalysts and their relative performance during the course of the process. The method includes using certain 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 catalytically active species and the relative amount of each of the first catalyst and the second catalyst, and (II) at least one of the feed rate and concentration of raw materials to the reaction zone as operational inputs. The control system hardware used is not critical to the method of the present disclosure, and individual operational input adjustments to set points, design space control systems, model predictive control systems, and the like can be used.

[0041]

[0047] Design space and model predictive control are well known and multivariate. 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, a design space control system can be designed using predictive models so 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 the process objectives. With respect to 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. Since the present disclosure concerns unregulated sequential catalytic conversion, the control system addresses at least the reaction zone.

[0042]

[0048] With any process control system, a key issue is the selection of inputs to be used and how those inputs are reflected in the process control. It is the selection and resulting control that constitutes this invention. Once the invention is understood, it will be apparent to a control engineer of ordinary skill in the art that it will be possible to implement the invention in a control system.

[0043]

[0049] The methods disclosed herein are generally applicable to chemical processes using continuous, unregulated, sequential, multiple catalytic reactions, where the catalyst undergoes changes in performance during the course of the process. The process can be said to have a single reaction zone in which at least two catalytic transformations occur. The catalytic transformations can occur in different or the same regions of the reaction zone, which may include one or more vessels in parallel or in series, but where the flows are not substantially regulated.

[0044]

[0050] The first and second catalysts may be homogeneous or heterogeneous, or one may be homogeneous and the other heterogeneous. If both are heterogeneous, the catalysts may be located in separate regions of the reaction zone or 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 may have regions that contain the first catalyst and substantially no second catalyst. In the latter case, the relative proportions of the first and second catalysts will change in downstream regions of the reaction zone as the second catalyst is introduced. If one catalyst is homogeneous and the other heterogeneous, the density of each catalyst may be the same throughout the reaction zone, or regions in the reaction zone with less or no heterogeneous catalyst may be provided.

[0045]

[0051] In a continuous process, the raw materials are continuously or intermittently introduced 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 major component of the medium. Alternatively, a substantially inert material may be the major component of the medium. The medium may be provided by feeding the 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 major 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 as it passes through the reaction zone. In some cases, the inert material is a solvent for at least one of any homogeneous catalyst, one or more of the raw materials, intermediates, and chemical products. The medium may function as a fluid to suspend one or more of the catalysts, for example, using a fluidized bed or ebullated bed reactor.

[0046]

[0052] The medium flowing through the reaction zone may be liquid, gas, or mixed gas and liquid. In the case of mixed gas and liquid, the gas or liquid may be the continuous phase. If 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 may provide a chemical product in a different phase than the feed to the reaction zone under the reaction conditions, or a raw material in either the gas or liquid phase is converted to reduce the amount of that phase. In such instances, the nature of the gas and liquid phases of the flow through the reaction zone may be changed so that the other phase becomes the continuous phase.

[0047]

[0053] As discussed above, the method for operating the process uses at least one process parameter input of (I) the rate and concentration of the feed of raw materials in step (i) and the efficiency of conversion of the raw materials to chemical products, and (II) the concentration of at least one by-product in the withdrawn medium, the concentration of an 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 inputs does not require compositional analysis inside the reaction zone.

[0048]

[0054] If the feedstock contains more than one reactant, the operational input can either provide each of the reactants in a predetermined relationship to one another, or the operational input can address each of the reactants separately, or the operational input can address only one or fewer than all of the reactants. For example, if the process being controlled is a hydrogenation, the operational input may be only with respect to the reactant being hydrogenated, which may be the rate-limiting feedstock 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. It is therefore not critical that the process parameter inputs be accurate so that changes are accurately detected. Analytical instruments to provide data on the process parameter inputs are within the routine experience of the engineer and will depend on the process, the arrangement of the instruments, the conditions used, and the components present in the feed to the reaction zone and the chemical products. Instruments can be used to determine, for example, 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 removed 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, venturi 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 feed rates and concentrations of the raw materials in step (i) are based on the raw material that is supplied at a rate that defines the stoichiometric maximum amount of intermediate that can be produced (i.e., the production-limiting raw material). For purposes of illustration and not limitation, if the process involves reacting 1 mole of A with 1 mole of B, the production-limiting raw material is the raw material that is 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 of each raw material can still be used according to the method of the present disclosure, even if only one is used as an operational input. However, in some cases, the process parameter inputs of one raw material are sufficient for a commercial process.

[0051]

[0057] The rate of feed of the raw material may be expressed in units of mass, volume, moles, etc. per unit time, from which conversion efficiency may be calculated directly or indirectly. When the feed is introduced intermittently, the rate of the feed may be determined either over the period during which the feed is provided or over a predetermined time period that defines an average rate, or both. It will also be recognized that the rate of the feed need not necessarily be constant, but may be periodic. Thus, when adjustments are made to the rate of feed of the raw material to the reaction zone in response to changes in catalyst performance, the rate may be subject to adjustment in one or more of the duration of the intermittent introductions, the frequency of the intermittent introductions, and the rate at which the raw material is introduced during the intermittent introductions.

[0052]

[0058] The concentration of the raw material feed is the concentration of the raw material in the medium for contacting the first catalyst, and thus includes any components contained in the raw material, such as solvents, impurities, and diluents, plus any portion of the medium that is introduced separately. In some cases, the change in the rate of medium flow to the first catalyst is minimal, so in such instances it may be sufficient to assume a predetermined rate of medium flow.

[0053]

[0059] The medium withdrawn from the reaction zone is typically an intermittent or continuous stream passing from the reaction zone. The medium withdrawn from the reaction zone may be a single stream or may be split into two or more equal streams, either of which can be used to determine the concentration of the component. In some cases, where the reactor design is such that the medium in the reaction zone and that withdrawn are substantially similar, such as in a CSTR, the concentration of at least one of the by-products, intermediates, or tracers, as well as 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 ascertaining 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 a concentration.

[0054]

[0060] The process parameter inputs used according to the method of the invention constitute a basis for identifying changes in catalyst performance that require adjustment of the process inputs to meet the process objectives. It will be recognized that additional process parameter inputs may be used as necessary, and that in some cases these inputs can improve the detection of catalyst changes (quantitatively or qualitatively). The method of the invention is generally applicable to chemical processes using sequential catalytic reactions. Once the principles of the 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 (I) and (II), to reflect changes in the catalyst and establish set points that operate the windows or control algorithms to adjust at least one of (I) and (II): (I) at least one of the absolute amount of catalytically active species and the relative amount of each of the first catalyst and the second catalyst, and (II) at least one of the rate of feed of raw materials to the reaction zone and its concentration, to achieve the process objectives.

[0055]

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

[0062] The rate and concentration of the feed of the raw material in step (i) and the efficiency of the conversion of the raw material to chemical products are important to understand the overall catalyst effectiveness in the reaction zone, but do not provide conclusive information on the cause of the change in 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 expected to cause a sacrifice in conversion efficiency, all other conditions being equal. It can then be determined whether the decrease in conversion efficiency is consistent with the observed change in the raw material feed and / or the flow rate of the medium. If the change is greater than what is expected, additional process parameter inputs are consulted to determine whether the change is due to a change in catalyst activity. In some cases, even if there is no change in conversion efficiency and the conversion efficiency is what is expected for a given rate of raw material feed and medium flow rate, one or both of the catalysts may have undergone a change in performance. For example, the catalyst may be present in an amount that exceeds the amount required. If the catalyst has a change in activity, the catalyst is overdosed and the conversion efficiency may not change until further deterioration occurs.

[0056]

[0063] At least one of the concentration of at least one by-product in the withdrawn medium, the concentration of an intermediate in the withdrawn medium, and, if used, the concentration of at least one tracer in the withdrawn medium, in combination with the conversion efficiency, serves as a process parameter that can provide information about the performance of the catalyst. In particular with a model predictive control system, the concentration of one or more by-products in the withdrawn medium, the concentration of an intermediate in the withdrawn medium, and, if used, the concentration of at least one tracer can be used to build a model, but not necessarily once the model is built. The use of the tracer precursor can be continuous or intermittent. For example, the tracer precursor can 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.

[0057]

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

[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 quickly with chemical products or by-products, either catalytically or non-catalytically, and is therefore not present at all in the withdrawn medium, the usefulness of this process parameter is limited.

[0059]

[0066] Alternatively or in addition, a tracer precursor may be used. The tracer precursor reacts substantially only with 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 reaction products of the tracer precursor in the withdrawn medium is determined. A change in the concentration of the tracer indicates a change in the catalytic activity. The choice of tracer precursor will depend on the reaction system and catalyst. In some cases, the tracer precursor may have a lower reactivity than the raw material (first catalyst) or intermediate (second catalyst) under the reaction conditions. The decrease in reactivity may be due to steric effects or one or more reactive groups that are chemically less reactive than the reactivity of the raw material or intermediate, as the case may be. The concentration of the tracer precursor can vary widely and will depend, for example, on the ability to analytically detect the concentration of the tracer or reaction products in the withdrawn medium. The concentration of the tracer precursor is often in the range of about 1 ppm (parts per million) to 1 mass percent based on the mass of the medium.

[0060]

[0067] In response to a detected change in catalyst activity, adjustments are made to at least one of (I) the absolute amount of catalytically active species and the relative amounts of each of the first and second catalysts, and (II) the rate of feed of raw materials to the reaction zone and their concentrations. Before a change occurs in either (I) or (II), it is usually desirable to determine whether a mechanical failure or other physical event has occurred that results in catalyst maldistribution, or whether other disruptive events have occurred.

[0061]

[0068] Adjustments in the absolute amount of catalytically active species and the relative amount of catalyst can be made, for example, by adding or removing catalyst to or from the reaction zone. The mode of adding or removing catalyst is well within the skill of the art. The optimal technique will depend on the type of reaction system. For example, if a homogeneous or suspended catalyst is used, the catalyst can be withdrawn from the reaction zone with a medium or by recycling a side stream to reduce the amount of catalyst. Addition of catalyst may be made 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 treating the catalyst or its environment and / or by remedying the problem of catalyst maldistribution in the reaction zone. The absolute amount of catalytically active species of a catalyst is based on the effectiveness of the catalyst and not simply the overall mass of the catalyst. Thus, physical and environmental process conditions, such as maldistribution that causes catalyst loss and in situ catalyst conditions, such as coating, poisoning, sintering, loss of catalytic species due to 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 reaction. For example, the formation of deposits on the catalyst reduces the available catalytic sites. Removing all or part of the deposits increases the number of available catalytic sites and thus an increase in the absolute amount of catalytically active species of the catalyst. In some cases, catalytic species in the catalyst become oxidized or reduced. For example, nickel used in hydrogenation catalysts can become oxidized and not catalytically active. Reducing nickel oxide is expected to increase the amount of catalytically available nickel and thus 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 converted to a more or less active species, particularly if the catalytic species is a complex or is capable of forming a complex.

[0063]

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

[0064]

[0071] The method of the 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 invention can use the types of raw materials and catalysts used in such processes when operated in a controlled manner.

[0065]

[0072] One application of the method of the invention is in a process for converting carbohydrates containing aldohexose- or ketose-bearing carbohydrates in a reaction zone to at least one of ethylene glycol and propylene glycol (lower glycols) 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 2017 / 0349513 and 2018 / 0086681 and U.S. Patents 9,399,610 and 9,783,472, which are incorporated herein by reference in their entireties.

[0066]

[0073] The feedstock comprises 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, disaccharides such as sucrose, lactulose, lactose, turanose, maltulose, palatinose, gentiobiulose, melibiose, and melibiulose, or combinations thereof.

[0067]

[0074] In these processes, the aqueous 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 aqueous 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).

[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 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.

[0069]

[0076] 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, e.g., 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 aqueous 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 circulation of the catalyst containing a given amount of tungsten can cause removal of at least a portion of the deposited tungsten compounds or complexes. Thus, the methods of the present disclosure contemplate control of the absolute amount of catalytically active species and the relative amounts of each of the first and second catalysts, including manipulations where the objective of the process is catalyst reactivation.

[0070]

[0077] 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 begins to be 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 either case, the most preferred process has a short period between retro-aldol conversion and hydrogenation.

[0071]

[0078] 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 and propylene glycol. The temperature of the aqueous hydrogenation medium may then be reduced, if necessary. However, hydrogenation proceeds rapidly at these higher temperatures. Thus, the temperature for the hydrogenation reaction is often about 230°C to 300°C, e.g., 240°C to 280°C. The pressure is 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.

[0072]

[0079] 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, and 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 to provide less than 0.1 weight percent of glycolaldehyde and glucose in 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 often 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, often at least about 98 mass percent, and sometimes substantially all, of the carbohydrate 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 one or more conditions that will provide the desired carbohydrate conversion.

[0074]

[0081] In the method of the invention applied to a retro-aldol / hydrogenation process for making lower glycols, the process parameter input is preferably the concentration in the withdrawn medium of at least one of itol, 1,2-butanediol, and hydroxyacetone. The itol contained in the withdrawn medium results from a reaction with a carbohydrate feed. For example, glucose can be hydrogenated to sorbitol. In the retro-aldol step, 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 become mannitol. Fructose can also become a compound with three carbons under retro-aldol conditions, thus producing glycerol. As it is produced, insight into the process can be gained from the type and rate of production of itol. If a tracer precursor is used, it is preferably a ketone, for example a ketone with 3 to 10 carbons.

[0075]

[0082] Generally, an increase in butyrol concentration would indicate that the first catalyst is undergoing a loss of catalytically active species, all other things remaining substantially constant, and one example of an operational input would be adjustments to the absolute and relative amounts of the retro-aldol catalyst and the hydrogenation catalyst, respectively, 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 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 an increase in 1,2-butanediol concentration reflects a loss of hydrogenation catalyst activity in the reaction zone, all other things remaining substantially the same. In this case, examples of adjustments of operational inputs would be expected to be at least one of (I) increasing the catalytic activity of the hydrogenation catalyst or decreasing the catalytic activity of the retro-aldol catalyst, thereby reducing the absolute and relative amounts of the retro-aldol catalyst and the hydrogenation catalyst, respectively, 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 of feed of raw materials to the reaction zone and their concentration would be expected as responsive operations. Therefore, it may be useful to have another parameter to indicate 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, this would be expected to indicate a decrease in retro-aldol activity since glycerin is produced from fructose, which in turn is produced from the isomerization of glucose, since the isomerization reaction will overtake the retro-aldol conversion if all else remains equal.

[0077]

[0084] Hydrogenation catalysts can lose activity for a variety of reasons, including, but not limited to, deposits that block catalytic sites, loss of catalytic metal, e.g., by oxidation or solubilization, and sintering of the catalytic metal. The methods of the present disclosure contemplate, in some cases, withdrawing the hydrogenation catalyst from the reaction zone and at least partially replacing it with fresh or reactivated hydrogenation catalyst as a means of adjusting the catalytic activity of the hydrogenation catalyst. The control method can control the rate at which hydrogenation catalyst is withdrawn from and replenished into the reaction zone, both in terms of frequency and mass, to maintain hydrogenation activity within a desired range.

[0078]

[0085] 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 therefore result in the formation of organic acids, which are by-products in the drawn medium and can therefore be used in the process of this invention. For process control purposes, pH measurements 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 required.

[0079]

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

[0080]

[0087] Tracers can also be used similarly to hydroxyacetone. Ketones such as methyl ethyl ketone can be useful tracer precursors because the internal carbonyl has a higher resistance to hydrogenation than the carbonyl of an aldehyde. Thus, the degree of hydrogenation of the ketone is an indication of the hydrogenation activity in the reaction zone.

[0081]

[0088] 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 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 the first catalyst is different from the second catalyst, one of the first catalyst and the second catalyst is homogeneous and the other is heterogeneous, at least one by-product is produced, and the catalytic activity of at least one of the first catalyst and the second catalyst undergoes performance changes 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. 10. The process of claim 1 , wherein the reaction zone comprises two vessels in flow order.

4. 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.

5. 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.

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

7. 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.

8. 8. The method according to claim 7, 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.

9. 9. The method of claim 8, wherein the itol is one or more of erythritol, threitol, glycerin, mannitol, and sorbitol.