MXPA00003082A - Method for carrying out heterogeneous catalysis - Google Patents

Abstract

Catalytic distillation reactions are improved by having an inert condensing component present in the reaction which is boiling and condensing within the reaction which washes the catalyst in the system and, in the case of gaseous reactants, occludes a portion of the reactants to facilitate the reaction without unduly high pressures. The inert condensing component is boiling at the conditions within the reactor and is taken overhead for condensation and return as reflux. The inert condensing component may occlude the gaseous reactants allowing for better contact with the catalyst and provides the benefits of concurrent reaction and distillation, for example, the reaction of CO and H2 over a copper catalyst to produce methanol using propane as the inert condensing component.

Description

METHOD FOR CARRYING OUT A HETEROGENIC CATALYSIS DESCRIPTION OF THE INVENTION The present invention is generally related to reactions that are catalyzed by heterogeneous catalysis. More particularly, the invention relates to the reaction of normally gaseous reagents in the presence of a heterogeneous catalyst. More particularly, the invention relates to the use of an inert component in a catalytic distillation column in which the inert component is boiling and condensing. Over the years many methods have been developed to carry out reactions in the presence of a solid heterogeneous catalyst. The most commonly used is probably the fixed downflow bed or the percolating bed reactor. Also used is the upflow reactor which may have a boiling bed if the flow velocity is high enough. When the catalyst is fine and the reactants are gaseous, a common method has been the fluidized bed. Similar to the fluidized bed is the reactor with suspended fuel wherein the solid catalyst is transported in one or more reagent streams. Finally the reaction distillation column has arisen wherein the catalyst is disposed in a distillation column in a suitable form to act as a distillation structure. The final method has additional advantages because the reaction products are separated from the reactants almost immediately upon formation by fractional distillation. This is particularly used in limited equilibrium reactions. The use of catalytic distillation has traditionally been limited by the fact that one of the reactants must be a boiling liquid under the conditions within the reactor. In the above catalytic distillation processes, both reagents were fed to the reactor as liquids. More recently, U.S. Patent No. 5,087,780 has shown that the catalytic distillation method is useful in a process wherein hydrogen is a reaction component. Briefly, the present invention is characterized by having an inert condensation medium or component, which is volatilized and condensed in a catalytic distillation column to provide continuous liquid contact of the inert component with the catalyst and can be described as a method for carrying end reactions catalyzed heterogeneously, comprising the steps of: (a) maintaining an inert condensation component in a distillation column reactor having a distillation reaction zone, the inert condensation component boils under the conditions within the column reactor of distillation; (b) feeding the reactant to the distillation column reactor; and (c) concurrently in the distillation column reactor (i) boiling the condensation component and condensing and returning the inert condensation component to the distillation reaction zone; (ii) contacting the inert condensation component and the reagent with a solid particulate catalyst in the distillation reaction zone, and (iii) separating the product, the reagent and the inert condensation component by fractional distillation. The present invention takes advantage of the characteristic features of catalytic distillation by reacting normally gaseous reactants. The present invention contemplates the use of an inert condensation component means for the reactants. The inert condensation component can be fed separately or mixed with the gas feed. BRIEF DESCRIPTION OF THE DRAWING The Figure is a flow chart in a schematic form of a process using the present invention. In one embodiment, the distillation column reactor operates at the boiling point of the inert condensation component with vapors leaving the top portion being taken and condensed and returned. The reflux of the inert condensation component causes part of the evaporated inert condensation component to condense around the gaseous reactants to occlude the gaseous components and transport them to the active catalytic sites where they are present in a more taut than ordinary form. So far the problem has been that for some reactants the pressures needed to produce a boiling liquid at the reaction temperature have been too high. Sometimes the reaction temperature can in fact be above the critical temperature of the reactants. A solution has been found for the use of an inert condensation component which can be used as a boiling liquid. If the inert condensation component has been sensibly selected it can have a boiling point much higher than the reactants and much lower or much higher than the products allowing easy separation within the distillation column reactor. In some cases, the inert condensation component can be a solvent for the gaseous reactants, however, in some cases, the inert condensation component is not known as a solvent for the reactants. The mechanism proposed for the present processes does not depend on the chemical characteristics or solubility but on the physical characteristics of occlusion. If there is a certain degree of current solubility of the gaseous reactants in the inert condensed component, this may improve the results. Preferably, the inert condensation component is both vaporous and liquid within the column. As described above, the condensation of the inert condensation component occludes a portion of the gaseous reactants and puts them in contact with the catalyst in the catalyst zone. Although it is preferred that the catalyst zone comprises catalytic distillation structures, the catalyst in the catalyst zone can be placed as shown in US Pat. Nos. 4,847,431; 4,847,430; 4,475,005; 5,338,517; and 5,198,196; the total of which are incorporated in the present. When the inert condensing component has a lower boiling point than the products, then the products can be easily separated in the distillation column reactor as waste. Additionally, fractional distillation will remove the products as they are formed which will improve the conversion in normal reactions limited in equilibrium.

Therefore this aspect of the invention could be said to comprise: (a) maintaining an inert condensing component in a distillation column reactor having a distillation reaction zone, the inert condensing component boils under the conditions within the reactor from distillation column; (b) feeding a gaseous stream containing at least one reagent to a distillation column reactor, the reagent is at least partially occluded in the inert condensing component and the reagent is a vapor under the conditions within the reactor; and (c) concurrently in the distillation column reactor (i) boil the inert condensation component and reflux the inert condensation component such that a portion of the inert component is condensed in the distillation reaction zone; (ii) contacting the reagent and the inert condensing component with a solid particulate catalyst in the distillation reaction zone, thereby reacting the reactant portion to form a product, and (iii) separating the product, the reagent and the inert condensation component by fractional distillation. In another aspect of the present invention, wherein the reagents may be either gaseous or liquid within the distillation column reactor, but either reagents or products tend to clog the catalyst forming deposits in the catalyst, the condensate Inert component washes the catalyst and removes the deposits. Finally, if the reactions are exothermic, the boiling of the inert condensation component will remove heat as latent heat of evaporation which can eventually be removed in an elevated condenser. This latter characteristic is especially useful for temperature control because more heat from the reaction only causes more boiling at a given pressure. Therefore, the temperature can simply be controlled by means of pressure. If the reaction requires heat input, a reheater can supply the necessary energy. The present invention takes advantage of the operating characteristics of the catalytic distillation for normally gaseous reactions without operating at the pressures necessary to condense the gases. The advantages of catalytic distillation have been known in recent years. The success of catalytic distillation lies in the understanding of the principles associated with distillation. First, because the reaction occurs concurrently with the distillation, the initial reaction product is removed from the reaction zone as it forms. Second, because the reaction mixture is boiling, the reaction temperature is controlled by the boiling point of the mixture at system pressure. The heat of the reaction simply creates more boiling, but does not increase the temperature. Third, the reaction has an increased activation force because the reaction products have been removed and can not contribute to a reverse reaction (Le Chatelier principle). As a result, much of the control over reaction speed and product distribution can be achieved by regulating system pressure. Also, adjusting the production capacity (residence time = space velocity per hour of weight) provides additional control of product distribution and degree of conversion. The temperature in the reactor is determined by the boiling point of the liquid mixture present at any given pressure. The temperature in the lower portions of the column will reflect the constitution of the material in that part of the column, which will be higher than in the upper part. That is, at a constant pressure a change in the temperature of the system indicates a change in the composition in the column. To change the temperature, the pressure is changed. The temperature control in the reaction zone in this way is controlled by the pressure; By increasing the pressure, the temperature in the system increases, and vice versa. It will also be appreciated that a catalytic distillation as in any distillation exists both a liquid phase (internal reflux) and a vapor phase. In this way, the reagents are partially in the liquid phase which allows a denser concentration of molecules for the reaction, while the concurrent fraction separates the product and unreacted materials, providing the benefits of a liquid phase system ( and a vapor phase system) while avoiding the detriment of having all the components of the reaction system continuously in contact with the catalyst, which would limit the conversion to equilibrium of the components of the reaction system. Another advantage, as mentioned above, is that a liquid condensation reagent occludes a gaseous reagent (such as hydrogen) which improves the catalytic contact and decreases the necessary partial pressure of the entrained gaseous reagent. A further advantage is the further washing action of the inert refluxing component on the catalyst, which are very often obstructed by the reactions.

Catalyst distillation structures and systems have been suitably described in the past as in commonly assigned US Patent Nos. 4,302,356; 4,439,350; 4,443,559; 5,057,468; 5,189.001; 5,262,012; 5,266,546; and 4,348,710; which all are incorporated by reference. In particular, the structure described in the aforementioned patent 5,266,546 has been found to be useful when large quantities of gaseous components such as hydrogen are present. Basically, the patents describe a catalyst in solid particles surrounded by or contained in a porous component to provide the required vapor and liquid fluxes and catalyst contact without undue low pressure. The amount of inert condensation component present in the distillation column reactor is the amount required for efficient distillation of that component. Referring now to FIGURE, a schematic flow diagram of a typical installation for a reaction wherein a gaseous component is entrapped in the inert condensing component. For purposes of illustration, a distillation column reactor for the production of methanol is formed from the reaction of carbon monoxide and hydrogen. A suitable catalyst for this reaction is copper in an atmosphere of hydrogen reduction. Carbon monoxide is fed into the distillation column reactor 10 by means of a flow line 1 and the hydrogen is fed via the flow line 2. Both reactants are fed as gases and are gaseous under the conditions inside the reactor. Since both reagents are gases, they are fed below the distillation reaction zone 12 which contains the appropriate catalyst in the form of a catalytic distillation structure. A suitable condensation component in the case of the methanol synthesis reaction is propane. Since it is not consumed in the reaction but simply recycled, it is fed as reflux by means of the flow line 8. Condensation propane occludes a portion of the carbon monoxide and hydrogen and transports them to the active catalytic sites where they react to form methanol. The methanol, which has a higher boiling point than either the reactant or the solvent, is fractionated out of the distillation zone to an extraction zone 14 which contains standard distillation structures such as screens, bubbler trays or inert packing. In the extraction zone 14 any propane, unreacted carbon monoxide, or hydrogen are withdrawn back to the distillation zone for further reaction. The high purity methanol is withdrawn from the distillation column reactor as waste by means of the flow line 5. A portion of the methanol can be circulated through the reboiler 40 and the flow line 6 to balance the heat requirements. The resulting methanol is transported by means of the flow line 7. The vaporous propane is extracted as vapor leaving the upper part by means of the flow line 3 together with any unreacted carbon monoxide or hydrogen. The vapors that come out at the top are passed through the partial condenser where substantially all of the propane is condensed and all the vapors leaving the top are passed through a separator / connector 20. Any carbon monoxide and hydrogens gaseous media are separated from the liquid propanol in the drum 20 and removed by means of the flow line 4 for recycling in the distillation column reactor if desired. The liquid propane is recycled to the top of the distillation column reactor as reflux by means of the flow line 8. If propane is needed, it can be conveniently added to the drum 20. By using a different catalyst, the same system and reagents can be used to produce methane.

The production of methane from the reaction of hydrogen and carbon monoxide is highly exothermic. To control the reaction, a small volume of reagents are used in relation to the inert component. Also, no waste would be taken. Both the inert component and the product (methane) would be removed as vapors that come out of the upper part. Methane, which is much lighter than propane, would be removed as gas from the separating drum. An example of the use of the inert condensation component to keep the catalyst free is the isomerization reaction of butanes where the presence of the methylacetylene / propadiene impurity (MAPD) causes the isomerization catalyst, i.e. a zeolite, to coke. The use of cyclohexane as an inert condensation component in the reaction reduces coking and substantially extends the use of the catalyst between regenerations.

Claims (18)

1. CLAIMS 1. A method for carrying out heterogeneously catalyzed reactions, characterized in that it comprises the steps of: (a) maintaining an inert condensing component in a distillation column reactor having a distillation reaction zone, the inert condensing component boil under the conditions within the distillation column reactor; (b) feeding the reactant to the distillation column reactor; and (c) concurrently in the distillation column reactor (i) boiling the condensation component and condensing and returning the inert condensation component to the distillation reaction zone; (ii) contacting the inert condensation component and the reagent with a solid particulate catalyst in the distillation reaction zone; and (ii) separating the product, the reagent and the inert condensation component by fractional distillation.
2. 2. A method for carrying out heterogeneously catalyzed reactions, comprising the steps of: (a) maintaining an inert condensing component in a distillation column reactor having a distillation reaction zone, the inert condensation component boiling in the conditions within the distillation column reactor; (b) feeding a gaseous stream containing at least one reagent to a distillation column reactor, a portion of the reagent is occluded in the inert condensing component and the reagent is a vapor under conditions within the reactor; and (c) concurrently in the distillation column reactor (i) boiling the inert condensation component and condensing the inert condensation component and occluding a portion of the gaseous reactant in the inert component in the distillation reaction zone; (ii) contacting the inert condensing component and the occluded reagent with a catalyst in solid particles in the distillation reaction zone, thereby reacting a portion of the reagent to form a product; and (iii) separating the product, the reagent and the inert condensation component by fractional distillation.
3. 3. The method according to claim 2, characterized in that the inert condensing component has a lower boiling point than the product and the product is removed from the distillation column reactor as waste. The method according to claim 2, characterized in that the gas stream contains at least two reagents, the reagents are partially fluid in the inert condensation component and the reactants are vapors under the conditions within the reactor. The method according to claim 2, characterized in that the inert condensation component has a higher boiling point than the product and the product is removed from the distillation column reactor as vapors leaving the top. The method according to claim 5, characterized in that the product is separated by distillation vapors leaving the top part of the inert condensation component and the non-reaction gases are removed from the separating drum. The method according to claim 2, characterized in that the inert condensation component and any reactants without reaction are extracted as vapors leaving the top and the vapors are cooled to condense the inert component and the reagent is separated from the component inert in a separating drum. 8. The process according to claim 2, characterized in that the reagent is at least partially soluble in the inert condensation component. 9. The process according to claim 2, characterized in that the catalyst in solid particles is prepared as a catalytic distillation structure. 10. A method for carrying out heterogeneously catalyzed reactions, characterized in that it comprises the steps of: (a) feeding an inert condensation component as a liquid stream to a distillation column reactor having a distillation reaction zone, the Inert condensation boils under the conditions inside the distillation column reactor; (b) feeding a gaseous stream containing at least one reagent to the distillation column reactor, the reagent is at least partially soluble in the inert condensation component and the reagent is a vapor under the conditions within the vapor; and (c) concurrently in the distillation column reactor (i) boiling the inert condensation component and refluxing the inert condensation component such that a portion of the inert component is condensed in the distillation reaction zone; (ii) contacting the reagent and the inert condensation component with a solid particulate catalyst prepared as a catalytic distillation structure in the distillation reaction zone thereby reacting a portion of the reagent to form a product, and " (iii) separating the product from the reagent and the inert condensing component by means of fractional distillation. 11. The method according to the claim 10, characterized in that the inert condensing component has a lower boiling point than the product and the product is removed from the distillation column reactor as waste. The method according to claim 10, characterized in that the gas stream contains two reagents, both reagents being at least partially occluded in the inert condensation component and the reagents being vapors under the conditions within the reactor. The method according to claim 10, characterized in that the inert condensing component has a higher boiling point than the product and the product is removed from the distillation column reactor as waste together with the inert component. The method according to claim 10, characterized in that the product is separated from the inert condensation component by means of the distillation of vapors leaving the upper part and the non-reaction gases are removed from a separating drum. 15. The method according to claim 10, characterized in that the inert condensation component and any reactants without reaction are extracted as vapors leaving the top and the vapors are cooled to condense the inert component and the reagent is separated from the component. inert in a separating drum. 16. The method according to claim 10, characterized in that the gaseous reactant comprises hydrogen 17. The method according to the claim 16, characterized in that the gaseous reactant comprises carbon monoxids and the product is methanol. 18. The method of compliance with the claim 17, characterized in that the inert condensation component comprises propane. - *, ur ¿_ bA