MXPA01008899A - Production of vinyl acetate in a catalytic reactor equipped with filter and distribution bed - Google Patents

Abstract

A process for the production of vinyl acetate (VA) by reaction in the vapor phase of ethylene, oxygen and acetic acid as reactants, comprising passing at a temperature sufficient to initiate the reaction, a feed gas comprising said reactants and continuously or intermittently containing liquid acetic acid and/or non-volatile components, through a filter and distribution bed of inert material having throughout its volume substantial intercommunicating open spaces among the solid portions, and thence through a plurality of tubes each containing a bed of catalyst for the reaction, and withdrawing a product gas comprising VA. The filter and distribution bed acts to filter out the liquid acetic acid and/or non-volatile components and distribute more evenly the feed gas into the tubes.

Description

PRODUCTION OF VINYL ACETATE IN A CATALYTIC REACTOR EQUIPPED WITH FILTER BED AND DISTRIBUTION BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates to an improved process for producing vinyl acetate (VA) using a catalytic reactor equipped with a filter bed and distribution.

DESCRIPTION OF THE RELATED TECHNIQUE It is known to produce VA by the vapor phase reaction of ethylene, oxygen, and acetic acid using a catalyst, for example, comprising palladium metal and gold supported on an inert porous carrier. Said reaction can be carried out in a reactor having the configuration of a tube and cover heat exchanger, i.e. comprising a plurality of tubes, each containing a bed of catalyst and supported between two "sheets" or rigid plates, with the tubes remaining open at each end. The tube and sheet assembly is enclosed in a cover so that the tube sheets separate two end portions of the interior of the cover that serve as the entry and exit areas for incoming reagents and leaving products, respectively. of the VA reaction. The space between the sheets defines the middle portion of the interior of the cover through which the heat exchange medium, eg, hot water, which surrounds the portions of the tubes containing the catalyst beds, circulates to absorb much. of the heat generated by the exothermic reaction. A problem associated with the production of VA in a reactor of the type described is that the feed gases in addition to non-condensable recycle gases including ethylene, carbon dioxide, methane, oxygen and others, together with vaporized acetic acid, and ends Heavy ones such as higher acetic acid esters can also contain, either continuously or intermittently, non-volatile components such as inhibitor residues and polymers, and / or liquid acetic acid. The non-volatile components and / or the liquid acetic acid are trapped in the vapor flow of the acetic acid vaporizer and are propelled towards the entrance of the reactor tube sheet and towards some or all of the tubes. This results in partial blockage of some of the tubes and uneven distribution of the flow between the reactor tubes, which in turn results in a non-optimal catalyst performance that includes "exhaust pipes", ie reactor pipes that they are operating in a mode that mainly produces carbon dioxide instead of VA. The distribution of the non-volatile and liquid acetic acid through the tubes may be non-uniform so that some of the tubes become more clogged than others. The obstruction of the tubes is essentially non-reversible, so that with any obstruction that occurs, the damage that is done remains for the life of the catalyst, unless the VA unit is shut off to enter the reactor to aspirate some of the catalyst. the entrance of the tubes and replace it. In this way, the obstruction of the tubes seriously reduces the efficiency of the reactor and any ejector that significantly reduces this obstruction would be very valuable.

BRIEF DESCRIPTION OF THE INVENTION According to this invention, the VA is produced by a process of reacting, in the vapor phase, ethylene, oxygen and acetic acid as reagents, which comprises passing a feed gas comprising a sufficient temperature to start the reaction. said reagents and which continuously or intermittently contains liquid acetic acid and / or non-volatile components, through a filter and distribution bed, of inert material, having through its volume substantially open intercommunication spaces between the solid portions, and therefore in a plurality of tubes each containing a catalyst bed for the reaction, and removing a gas product comprising VA. For example, the reactor may have the configuration of a tube and shell heat exchanger containing open end tubes secured between two tube sheets as described above in which each tube contains a catalyst bed for reaction on its part measured between the tube sheets, with a filter bed and inert material distribution as described, for example, made of discrete particles, which cover the entire area of the upstream face of the inlet tube sheet. The bed of inert material acts to filter the liquid acetic acid and / or the non-volatile trapped in the feed gas and to more evenly distribute the feed gas containing said components to the tubes. In this way, the amount of liquid and / or non-volatile acetic acid entering the tubes containing catalyst is substantially reduced resulting in a lower incidence of partial blockage of the tubes and a significant increase in total VA productivity.

BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a front view of a tube and cover VA reactor showing the presence of catalyst and a filter bed and distribution according to this invention.

DETAILED DESCRIPTION OF THE INVENTION One embodiment of this invention involves carrying out the reaction to produce VA in a reactor having a shell and tube heat exchanger as described above. The reactor can have any convenient operative position, for example vertical, in which the flow of reactant and products is either top-down or bottom-up, or horizontal. Preferably, the reactor is vertical in which the flow of reactants and products is from top to bottom. The reactor will have the filter bed in place as described. The material forming the filter and distribution bed of this invention is inert in the presence of the process feed components preheated to the desired inert temperature. Said material is preferably a mass of discrete particles at a size which is effective to more evenly distribute the feed gas in the tubes containing the catalyst bed and to filter a substantial proportion of liquid acetic acid and / or non-volatile acetic acid into the catalyst bed. the feed gas without causing undue large pressure drop across the bed. Among the materials that can be used are those that are known in the art that also serve as a satisfactory support or vehicle for the catalytically active metals, for example, palladium and gold, in catalysts for the VA reaction, such as silica, alumina. , silica-alumina, titanium, zirconium, silicates, aluminosilicates, titanates, spinels, silicon carbide, carbon, and the like. Other materials such as naturally occurring minerals, for example, granite and basalt, can also be used. The particles forming the bed can have any of several regular or irregular shapes, such as spheres, tablets, cylinders, rings, stars, or other shapes, and can have dimons such as diameter, length or width, for example, of about 1 to 10 mm, preferably from about 3 to 9 mm. Spheres having a diameter of about 4 to 8 mm are preferred. Although the filter bed and inert distribution is preferably composed of discrete particles as described, it is also possible to use a unitary mass, that is, not discrete, of an inert material as long as it meets the criterion of containing open intercommunication spaces between the solid portions. Said unitary mass can be made of an inorganic or organic material inert to the reactants and products at the temperature of the VA reaction, for example, by concreting particles of the material, forming a rigid or flexible open cell cell structure by means of well known in the art, or by forming a laminated non-woven or woven structure of fibers of said material. The organic materials resistant to high temperature which can be used in this way are, for example, organopolysiloxanes and certain polyamides and fully aromatic polyesters. The depth of the distribution and filter bed is not critical, as long as it achieves the desired degree of feed gas distribution to the inlet ends of the catalyst-containing tubes while filtering enough non-volatile and / or liquid acetic acid to reduce the occurrence of partial obstruction of the tubes. The depth of the bed can be, for example, from about 5.08 to about 91.4 cm, preferably from about 15.2 to about 30.4 cm. While the depth of the filter bed is larger, the filter capacity and distribution of the bed is higher, and the pressure drop across the bed is higher. In most cases the pressure drop across the filter bed will be no larger than about 0.21 kg / cm2 gravi metric. IF the VA reactor is in a vertical position with top-down flow of the feed and the product, the bed of inert material can be held in place during operation, so that closing structure for the bed material is not necessary to keep said material in position. However, it is often advantageous to provide a system that allows personnel to enter the reactor without crushing the inert bed, for example, a removable open stainless steel structure grid that rests on the tube sheet and remains sufficiently high around the tube sheet to protect the filter medium, and constructed in such a way as to allow the inert support to pass through the openings. Alternatively, the inert bed could be contained in a structure or cartridge that would fit immediately above the upper tube sheet. In the case of a vertical reactor in which the feed and product flow is from bottom to top, or a horizontal reactor in which the flow is parallel to the ground, the position of the inert bed against the upper current side of the Input tube sheet obviously would not be maintained by gravity. Thus, in those types of reactor, it is necessary to use a support structure, for example, a frame or cartridge, fixed to the tube sheet, which is completely filled with the inert bed and contains openings smaller than the particles of said bed so that the feed gases can pass through the bed but the bed particles are prevented from falling. Means for replacing the inert bed when it is spent would also be necessary, for example, by removing the support structure and replacing it with a structure containing fresh material, or by providing the support structure with an adjustable opening through which the spent material is removed. It can be removed and replaced with fresh material. In carrying out the process of the invention, any effective catalyst can be used to catalyze the synthesis of VA by reaction of ethylene, oxygen, and acetic acid. Preferably the catalyst is one of a type well known in the art, in which the catalytically active metals comprising palladium and gold are supported on an inert porous carrier composed of, for example, any of the materials mentioned above as suitable for the support of catalyst and also for the filter and inert distribution bed of this invention, including the linear size limitations described. However, although not necessary for use in said inert bed, such material when used as a catalyst support preferably has a surface area within the scale, for example, from about 10 to 350, preferably about 100 to 200 m2 / g. , an average pore size on the scale, for example from about 50 to 2000 angstroms, and a pore volume on the scale, for example, from about 0.1 to 2, preferably from about 0.4 to 1.2 ml / g. The catalyst may contain, for example, about 1 to about 10 grams of elemental palladium and, for example, about 0.5 to 10 grams of elemental gold per liter of finished catalyst with the amount of gold being from about 10 to 125% by weight. weight based on the weight of palladium. Preferably the catalyst also contains a metalalkyl acetate, more preferably potassium acetate, in an amount, for example, of about 10 to 70 grams per liter of finished catalyst. With reference to Figure 1, the tube and cover reactor 1 of this invention using top-down flow is composed of a cover 2 containing tubes 3 secured between the rigid inlet tube sheet 4 and the tube sheet outlet 5 which are welded or otherwise adhered to the interior of the cover 2. The illustrated tube sheet is rigid in structure. However, non-rigid means can be used with the proviso that the tubes are held securely in place. Each tube contains a catalyst bed 6 and rests on the upstream face of the tube sheet 4 and is a distribution bed 7 of inert material.

In carrying out the process of this invention, a stream of feed gas containing ethylene, oxygen, vaporized acetic acid, heavy ends such as high esters of acetic acid, non-condensable recirculating gases in addition to ethylene and oxygen such as argon, carbon dioxide, methane, and metalalkali nitrogen gas gaseous and continuously or intermittently, non-volatile components such as inhibitor residues and polymers and / or liquid acetic acid, is fed through line 8 by means of a nozzle of input equipped with a distribution or bypass plate (not shown) through the inlet 9 of the cover 2 towards the inlet chamber 10. The composition of the feed gas stream can be varied within wide limits, taking into account the explosive limits, for example, the molar ratio of ethylene to oxygen can be from about 75:25 to 98: 2, the ratio molar of acetic acid to ethylene can be from 10: 1 to 1:10, preferably from 1: 1 to 1: 5, and the content of gaseous alkali metal acetate can be from 1 to 100 ppm based on the weight of acetic acid used . The amount of non-volatiles and / or liquid acetic acid present in the feed gas varies with time and may be present in an amount of up to 5% by weight or higher based on the total weight of the feed gas. The feed gas enters a temperature, for example, of about 150 ° C at which the VA reaction can be initiated, and a pressure that can be reduced, normal or high, preferably up to 20 gravimetric atmospheres flows through the bed of filter and distribution 7 of Inert material which filters at least some if not most of the non-volatile components and / or liquid acetic acid, and enters in a more evenly distributed manner to the open inlet ends 11 of the tubes 3 supported by and passing through the tube sheet 4 and each tube contains a catalyst bed 6. The upper part of each catalyst bed 6 is a short distance below the corresponding opening in the tube sheet 4 with the space in the tube 3 from the top of the catalyst bed 6 to the opening in the tube sheet 4 being filled with an inert material 12, which may be the same as that used in the The filter bed and distribution 7 or any other of the inert materials mentioned above as suitable for said bed, and which functions as a flame suppressor to prevent the return of a flame in the inlet chamber 10 of the reactor. The feed gas passes through the catalyst bed 6 into the tubes 3, causing the reagents in the gas to react exothermically to form VA, and the product gas containing VA, the unreacted reactants of acetic acid, ethylene and oxygen and other non-condensable gases such as CO2 by-product, leaving the tubes 3 through the outlet openings 13 in the outlet pipe sheet 5, entering the outlet chamber 14, leaving the reactor through the outlet 15 at a temperature, for example, that does not exceed about 220 ° C, and are transported through line 16 to downstream purification. It can be seen from the drawing that substantially the entire lengths of the tubes 3 containing catalyst beds 6 as a whole are enclosed in the middle portion of the cover 2 between the tube sheets 4 and 5 so that the outside of the tubes 4 tubes 3 is isolated from the feed stream and product gases passing through the catalyst bed 6. To absorb much of the heat generated by the exothermic reaction and to control the temperature of the reaction so that it remains within a desired range, for example 120-220 ° C, boiling water is circulated as a medium of heat exchange in the middle part of the tubes surrounding the reactor 3 and the catalyst bed 6, with the boiling water entering the outlet 17 through the boiling water. line 18 and steam and water leaving exit 19 through line 20.

Claims (11)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for the production of vinyl acetate (VA) by reaction in the vapor phase of ethylene, oxygen and acetic acid as reagents, comprising passing a sufficient gas to start the reaction, a feed gas comprising said reagents, and continuously or intermittently containing liquid acetic acid and / or non-volatile components, through a filter bed and inert material distribution having through its volume substantially intercommunicating spaces between the solid portions, and to a plurality of tubes each containing a bed of a catalyst for the reaction, and removing a product gas comprising VA, said filter and distribution bed acts to filter at least some of the liquid acetic acid and / or non-volatile components and more evenly distributing said feed gas in said tubes.

2. The method according to claim 1, further characterized in that said reaction is carried out in a reactor having the configuration of a tube and cover heat exchanger containing open end tubes secured between two rigid tube sheets. in which each tube contains a catalyst bed for the reaction in its middle portion between the tube sheets, and said filter and distribution bed covers the entire upstream face of the inlet tube sheet.

3. The method according to claim 2, further characterized in that said reactor is in a vertical position and the feed and product gas flows upwardly downward.

4. The method according to claim 1, further characterized in that said inert material is composed of discrete particles.

5. The process according to claim 1, further characterized in that said catalyst comprises a porous support containing catalytically effective amounts of palladium metal and gold.

6. The method according to claim 5, further characterized in that said filter and distribution bed is composed of the same inert discrete particles as the carrier of said catalyst.

7. A filter and distribution bed for use in the production of vinyl acetate from a feed gas, placed in sequence before the reaction tubes of a reactor, comprising geometrically formed particles composed of inert material in which The largest dimension of the particles formed geometrically measured in any direction is on the scale of 1-10 mm.

8. - The filter bed according to claim 7, further characterized in that the largest dimension of the particles of geometric shape is in the range of 4-8 mm.

9. The filter bed according to claim 7, further characterized in that the geometric shaped particles are spherical with a diameter of 4-8 mm.

10. The filter bed according to claim 7, further characterized in that the inert material is selected from the group consisting of silica, alumina, silica-alumina, titanium, zirconium, silicates, aluminosilicates, titanates, spinels, silicon carbide, and carbon.

11. The filter bed according to claim 7, further characterized in that the size of the filter bed in the flow direction of the feed gas is from 50 mm to 900 mm.