ALKYNE HYDROGENATION PROCESS

Abstract: A method of improving the operation of a process system used for conversion of C2-C6 alkynes (preferably acetylene) contained in a hydrocarbon-containing fluid with hydrogen to the corresponding alkenes. The process system, before improvement, utilizes a volumetric amount of a hydrogenation catalyst required for providing conversion of the C2-C6 alkynes to a conversion product containing less alkynes than the hydrocarbon-containing fluid. The method of improvement involves contacting, in a single-stage adiabatic reaction zone, under reaction conditions, the hydrocarbon-containing fluid containing C2-C6 alkynes (preferably acetylene) with a catalyst containing palladium, silver, and an alkali metal compound (preferably an alkali metal fluoride) in a conversion-improving volumetric amount that is less than the volumetric amount of hydrogenation catalyst.

Description: ALKYNE HYDROGENATION PROCESS BACKGROUND OF THE INVENTION This invention relates to an improved process for catalytically hydrogenating hydrocarbon-containing fluid comprising at least one alkyne in a single- stage reaction zone. The selective hydrogenation of alkynes, which generally are present in small amounts in alkene-containing streams (e.g., acetylene contained in ethylene streams from thermal ethane crackers), is commercially carried out in the presence of alumina-supported palladium hydrogenation catalysts. In the case of the selective hydrogenation of acetylene to ethylene, previous commercial operation includes the use of, for example, an alumina-supported palladium/silver hydrogenation catalyst such as in accordance with the disclosure in U.S. Patent 4,404,124 and its division, U.S. Patent 4,484,015. However, use of these conventional acetylene removal hydrogenation catalysts release substantial heat during operation because of the undesired hydrogenation of ethylene to ethane which can result in loss of ethylene as has been pointed out in the above-identified patents. Since ethylene and hydrogen are present in the reacting stream to substantial excess, there is significant danger that this unselective reaction will occur to such a great extent that a "runaway" reaction, i.e., uncontrollable hydrogenation of ethylene to ethane, will occur. Conventional reactor designs avoid the problem of a possible "runaway" reaction by controlling the extent of the reaction by removing heat part way through the hydrogenation catalyst mass. The removal of heat requires a multi-stage reactor system, such as, for example, at least two catalyst beds, with expensive heat removal apparatus, such as, for example, inter-stage cooling apparatus such as a heat exchanger, between stages, e.g., between catalyst beds. Thus, the development of a process to avoid a "runaway" reaction, and the resulting loss of ethylene, in a single-stage reaction system without expensive heat removal apparatus would be of significant contribution to the art. It is generally known by those skilled in the art that fluctuations in carbon monoxide concentration, especially increases in carbon monoxide concentration, can occur during the catalytic hydrogenation of alkyne-containing feeds such as, for example, when furnaces are brought into operation during the hydrogenation reaction. Sharp increases in carbon monoxide concentration can significantly hinder the hydrogenation of alkynes to corresponding alkenes requiring the temperature of the reaction to be increased to maintain such hydrogenation at the same rate that was occurring before the increase in carbon monoxide concentration. However, when the reaction temperature is increased to counteract the increase in carbon monoxide concentration, there is an increased chance that a "runaway" reaction as described above will occur. The catalytic hydrogenation of alkyne-containing feeds is especially vulnerable to a runaway reaction at this point because of a rapid return of the carbon monoxide concentration to initial levels which is a frequently observed event. The rapid return of the carbon monoxide concentration to initial levels frequently occurs faster than the rate at which heat can be removed. Thus, the reaction system is in an overheated condition. Conventional reactor designs avoid the problem of the reaction system being in an overheated condition by controlling the extent of the reaction by removing heat part way through the hydrogenation catalyst mass as described above. Thus, the development of a method to handle such fluctuations in carbon monoxide concentration, especially increases in carbon monoxide concentration, and the subsequent increase in feed temperature in a single-stage reaction system without expensive heat removal apparatus would also be of significant contribution to the art. SUMMARY OF THE INVENTION It is desirable to carry out the selective hydrogenation, i.e., conversion, of an alkyne(s) containing about 2 carbon atoms to about 6 carbon atoms per molecule to the corresponding alkene(s) utilizing an improved hydrogenation process in the presence of a catalyst (also referred to as "catalyst B") comprising palladium, silver, and an alkali metal compound where such process prevents the uncontrollable hydrogenation of an alkene(s) (e.g., ethylene) to an alkane(s) (e.g., ethane) in a single-stage reaction zone, preferably in a single-stage adiabatic reaction zone, without expensive heat removal apparatus. It is also desirable to carry out the selective hydrogenation, i.e., conversion, of an alkyne(s) containing about 2 carbon atoms to about 6 carbon atoms per molecule to the corresponding alkene(s) utilizing an improved hydrogenation process in the presence of catalyst B and in the presence of fluctuations in carbon monoxide concentration, especially increases in carbon monoxide concentration, and subsequent increases in feed temperature while preventing the uncontrollable hydrogenation of an alkene(s) (e.g., ethylene) to an alkane(s) (e.g., ethane) in a single-stage reaction zone, preferably in a single-stage adiabatic reaction zone, without expensive heat removal apparatus. The present invention is directed to a process of improving the operation of a process system used for selectively hydrogenating, i.e., for the conversion of, a hydrocarbon-containing fluid comprising at least one alkyne, preferably acetylene (ethyne), containing about 2 carbon atoms to about 6 carbon atoms per molecule with hydrogen, preferably hydrogen gas, to at least one corresponding alkene, preferably ethylene (ethene), containing about 2 carbon atoms to about 6 carbon atoms per molecule. The process system utilizes a volumetric amount of a hydrogenation catalyst (also referred to as "hydrogenation catalyst A") which can comprise, for example, an alumina-supported palladium hydrogenation catalyst or alumina-supported palladium/silver hydrogenation catalyst required for providing the conversion of the at least one alkyne so as to provide a conversion product containing less alkyne than the hydrocarbon-containing fluid. The process of improving the operation of such process system utilizing a volumetric amount of a hydrogenation catalyst A comprises substituting such hydrogenation catalyst A with a conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound contained in a single- stage adiabatic reaction zone. The conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound is less than the volumetric amount of such hydrogenation catalyst A present in the process system before utilizing the process of improving. The process also includes contacting under reaction conditions such hydrocarbon-containing fluid with such catalyst B comprising palladium, silver, and an alkali metal compound and charging the hydrocarbon- containing fluid to the single-stage reaction zone at a temperature sufficient to provide for the desired selective hydrogenation. Preferably, the improved process system does not contain any heat removal apparatus such as a heat exchanger, i.e., the improved process system is an adiabatic system. The conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound is generally at least 20 percent of the volumetric amount of hydrogenation catalyst A present in the process system before utilizing the process of improving. The present invention is also directed to a process of charging, at reaction conditions, a hydrocarbon-containing fluid comprising at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule with hydrogen to a single- stage adiabatic reaction zone containing a catalyst B comprising palladium, silver, and an alkali metal compound. The process then includes converting the at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule to at least one corresponding alkene containing about 2 carbon atoms to about 6 carbon atoms per molecule. The process then includes yielding a conversion product containing less alkyne than the hydrocarbon-containing fluid and further, the conversion of the at least one alkyne is at least as high as the conversion of the at least one alkyne would otherwise be for a multi-stage reaction zone having intercooling between stages of such multi-stage reaction zone. The present invention is also directed to a process of modifying a multistage reaction zone, e.g., two or more reactor vessels in series, having intercooling between stages of such multi-stage reaction zone, used for the selective hydrogenation, i.e., conversion, of a hydrocarbon-containing fluid comprising at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule with hydrogen to at least one corresponding alkene containing about 2 carbon atoms to about 6 carbon atoms per molecule. Such multi-stage reaction zone utilizes a volumetric amount of a hydrogenation catalyst A required for providing the conversion of the at least one alkyne so as to provide a conversion product containing less alkyne than the hydrocarbon- containing fluid. The process comprises modifying such multi-stage reaction zone by providing for a single-stage adiabatic reaction zone having a conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound that is less than the volumetric amount of hydrogenation catalyst A present in the multi-stage reaction zone before modifying such multi-stage reaction zone. The modifying of such multi-stage reaction zone can comprise converting e.g., one or more stages (e.g., one or more reactor vessels) of such multi-stage reaction zone into a single- stage adiabatic reaction zone (comprising, for example, an adiabatic reactor vessel or one or more adiabatic reactor vessels) or into a set of single-stage adiabatic reaction zones (comprising, for example, a set of adiabatic reactor vessels). The inventive process offers several benefits such as: (1) a smaller and less expensive reaction zone, (2) the ability to convert an existing multi-stage reaction zone to several single-stage adiabatic reaction zones with at least one single-stage adiabatic reaction zone in service with at least one single-stage adiabatic reaction zone in stand-by allowing an essentially unlimited time to pass between shut-down of the entire reaction system, and (3) expansion of existing reactor capacity with minimal economic investment. Other objects and advantages will become apparent from the detailed description and the appended claims. DETAILED DESCRIPTION OF THE INVENTION Catalyst B which is employed in the selective hydrogenation process, i.e., conversion process, of this invention can be any supported palladium catalyst composition which also comprises silver and an alkali metal compound. Generally, the alkali metal compound is selected from the group consisting of alkali metal halides, alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, alkali metal nitrates, alkali metal carboxylates, and the like and mixtures thereof. Preferably, the alkali metal compound is an alkali metal fluoride. Generally, the alkali metal of such alkali metal compound is selected from the group consisting of potassium, rubidium, cesium, and the like and mixtures thereof. Preferably, the alkali metal of such alkali metal compound is potassium. Most preferably, the alkali metal compound is potassium fluoride. Catalyst B can be fresh or it can be a used and thereafter oxidatively regenerated catalyst composition. Catalyst B can contain any suitable inorganic solid support material. Preferably, the inorganic support material is selected from the group consisting of alumina, titania, zirconia, and the like and mixtures thereof. The presently more preferred support material is alumina, most preferably alpha-alumina. Generally, catalyst B contains in the range of from about 0.001 weight percent palladium (on a total catalyst composition weight basis) to about 1 weight percent palladium. More preferably, catalyst B contains in the range of from about 0.01 weight percent palladium to about 0.5 weight percent palladium and, most preferably, in the range from 0.01 weight percent palladium to 0.2 weight percent palladium. Generally, catalyst B contains in the range of from about 0.05 weight percent alkali metal (on a total catalyst composition weight basis) to about 5 weight percent alkali metal. More preferably, catalyst B contains in the range of from about 0.05 weight percent alkali metal to about 3 weight percent alkali metal and, most preferably, in the range from 0.1 weight percent alkali metal to 1 weight percent alkali metal. Generally, the weight ratio of alkali metal to palladium is in the range of from about 0.05:1 to about 500:1. Preferably, the weight ratio of alkali metal to palladium is in the range of from about 0.2:1 to about 100:1. When catalyst B comprises an alkali metal fluoride, the catalyst contains in the range of from about 0.03 weight percent fluorine (chemically bound as fluoride) (on a total catalyst composition weight basis) to about 10 weight percent fluorine. More preferably, catalyst B contains in the range of from about 0.1 weight percent fluorine to about 5 weight percent fluorine and, most preferably, in the range from 0.2 weight percent fluorine to 1 weight percent fluorine. Generally, the atomic ratio of fluorine to alkali metal is in the range of from about 0.5:1 to about 4:1. Preferably, the atomic ratio of fluorine to alkali metal is in the range of from about 1 :1 to about 3:1. Generally, catalyst B contains in the range of from about 0.01 weight percent silver (on a total catalyst composition weight basis) to about 10 weight percent silver. More preferably, catalyst B contains in the range of from about 0.01 weight percent silver to about 5 weight percent silver and, most preferably, in the range from 0.02 weight percent silver to 2 weight percent silver. Preferably, the silver:palladium (Ag:Pd) weight ratio in the catalyst is in the range of from about 2:1 to about 10:1. Generally, the particles of catalyst B have a size in the range of about 1 mm to about 10 mm, preferably in the range of from about 2 mm to about 6 mm. The particles of catalyst B can have any suitable shape, preferably spherical or cylindrical. Generally, the surface area of the catalyst (determined by the BET method employing N 2 ) is in the range of from about 1 m 2 /g to about 100 m 2 /g. The presently preferred catalysts for use as catalyst B are those described in U.S. Pat. Nos. 5,585,318 and 5,587,348, the disclosures of which are incorporated herein by reference. The selective hydrogenation process, i.e., conversion process, of this invention is generally carried out by contacting a hydrocarbon-containing fluid which comprises at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule and hydrogen with a catalyst B comprising palladium, silver, an alkali metal compound, and an inorganic support material in a single-stage reaction zone, preferably in a single-stage adiabatic reaction zone, wherein such single-stage adiabatic reaction zone does not utilize heat removal apparatus. Thus, the phrase "adiabatic" generally means without a significant loss or significant gain of heat. The selective hydrogenation process of this invention can be used to improve the method of operation of a process system used for selectively hydrogenating, i.e., for the conversion of, a hydrocarbon-containing fluid comprising at least one alkyne, preferably acetylene (ethyne), containing about 2 carbon atoms to about 6 carbon atoms per molecule with hydrogen to at least one corresponding alkene, preferably ethylene (ethene), containing about 2 carbon atoms to about 6 carbon atoms per molecule wherein such process system utilizes a volumetric amount of a hydrogenation catalyst A required for providing the conversion of the at least one alkyne so as to provide a conversion product containing less alkyne than the hydrocarbon-containing fluid. Hydrogenation catalyst A can comprise, for example, an alumina-supported palladium hydrogenation catalyst or alumina-supported palladium/silver hydrogenation catalyst such as in accordance with the disclosure in U.S. Patent 4,404,124 and its division, U.S. Patent 4,484,015. The process of improving the operation of such process system utilizing a volumetric amount of a hydrogenation catalyst A comprises substituting such hydrogenation catalyst A with a conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound (preferably such alkali metal compound is an alkali metal fluoride) contained in a single-stage reaction zone, preferably in a single-stage adiabatic reaction zone. The conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound is less than the volumetric amount of hydrogenation catalyst A present in the process system before utilizing the method of improvement. The process of improving includes contacting under reaction conditions such hydrocarbon-containing fluid with such catalyst B comprising palladium, silver, and an alkali metal compound. The phrase "substituting" generally refers to substituting in whole or substituting in part hydrogenation catalyst A with a conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound. Thus, the phrase "substituting" can refer to the conversion-improving volumetric amount of a catalyst B taking the place of in whole or in part, or being put in the place of in whole or in part, or being exchanged for in whole or in part, the hydrogenation catalyst A present in the process system before utilizing the method of improvement. The conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound (preferably such alkali metal compound is an alkali metal fluoride) is generally in the range of from about 20 volume percent to about 80 volume percent of the volumetric amount of hydrogenation catalyst A (hydrogenation catalyst A can comprise, for example, an alumina-supported palladium hydrogenation catalyst or alumina-supported palladium/silver hydrogenation catalyst), present in the process system before utilizing the method of improvement. Preferably, the conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound is in the range of from about 25 volume percent to about 75 volume percent of the volumetric amount of hydrogenation catalyst A present in the process system before utilizing the method of improvement. More preferably, the conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound is in the range of from about 30 volume percent to about 70 volume percent of the volumetric amount of hydrogenation catalyst A present in the process system before utilizing the method of improvement. Most preferably, the conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound is in the range of from 35 volume percent to 65 volume percent of the volumetric amount of hydrogenation catalyst A present in the process system before utilizing the method of improvement. The phrase "conversion- improving volumetric amount" refers to the volumetric amount of catalyst B comprising palladium, silver, and an alkali metal compound which can be used to improve the conversion of a hydrocarbon-containing fluid in accordance with the inventive processes disclosed herein. The selective hydrogenation process of this invention can also comprise charging, at reaction conditions, a hydrocarbon-containing fluid comprising at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule with hydrogen to a single-stage adiabatic reaction zone containing a catalyst B comprising palladium, silver, and an alkali metal compound (preferably such alkali metal compound is an alkali metal fluoride). The process then includes converting the at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule to at least one corresponding alkene containing about 2 carbon atoms to about 6 carbon atoms per molecule. The process then includes yielding a conversion product containing less alkyne than the hydrocarbon-containing fluid and further, the conversion of the at least one alkyne is at least as high as the conversion of the at least one alkyne would otherwise be for a multi-stage reaction zone having intercooling between stages of such multi-stage reaction zone. The selective hydrogenation process of this invention can also be used to modify a multi-stage reaction zone, e.g., two or more reactor vessels in series, having intercooling between stages (e.g., having heat exchanger(s) between reactor vessels) of such multi-stage reaction zone, used for conversion of a hydrocarbon-containing fluid comprising at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule with hydrogen to at least one corresponding alkene containing about 2 carbon atoms to about 6 carbon atoms per molecule. Such multi-stage reaction zone utilizes a volumetric amount of a hydrogenation catalyst A (such hydrogenation catalyst A can comprise, for example, an alumina-supported palladium hydrogenation catalyst or alumina-supported palladium/silver hydrogenation catalyst) required for providing the conversion of the at least one alkyne so as to provide a conversion product containing less alkyne than the hydrocarbon-containing fluid. The process comprises modifying such multi-stage reaction zone by providing for a single-stage adiabatic reaction zone having a conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound (preferably such alkali metal compound is an alkali metal fluoride) that is less than the volumetric amount of hydrogenation catalyst A present in such multi-stage reaction zone before utilizing such process of modifying. The modifying of such multi-stage reaction zone can comprise converting one or more stages (e.g., one or more reactor vessels) of such multi-stage reaction zone into a single-stage adiabatic reaction zone (comprising, for example, an adiabatic reactor vessel or one or more adiabatic reactor vessels) or into a set of single-stage adiabatic reaction zones (comprising, for example, a set of adiabatic reactor vessels) with each single-stage adiabatic reaction zone having a conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound (preferably such alkali metal compound is an alkali metal fluoride) that is less than the volumetric amount of hydrogenation catalyst A present in such multi-stage reaction zone before utilizing such process of modifying. For example, depending upon the desired levels of selective hydrogenation needed, the modifying of such multi-stage reaction zone may comprise modifying such multi-stage reaction zone to several single-stage adiabatic reaction zones with one single-stage adiabatic reaction zone to be in service while bypassing the other single-stage adiabatic reaction zones (e.g., the other single-stage adiabatic reaction zones can be in stand-by, to be used when the single-stage adiabatic reaction in service needs to be shut down, or to be used for further acetylene removal if necessary) allowing an essentially unlimited time to pass between shut-down of the entire reaction system. Also for example, the modifying of such multi-stage reaction zone may comprise modifying such multi-stage reaction zone to several single-stage adiabatic reaction zones, which can be operated, for example, in parallel or in series, allowing an expansion of existing reactor capacity. The actual physical modifications of such multistage reaction zone into a single-stage adiabatic reaction zone or into a set of single- stage adiabatic reaction zones in accordance with the inventive process, i.e., for example, the piping and equipment changes necessary to modify such multi-stage reaction zone in accordance with the inventive process described herein, are within the capabilities of persons of ordinary skills in the field of selective hydrogenation technology. The conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound (preferably such alkali metal compound is an alkali metal fluoride) used in the modifying of such multi-stage reaction zone is generally in the same ranges of volume percents of the volumetric amount of a hydrogenation catalyst A as disclosed above. The conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound is generally in the range of from about 20 volume percent to about 80 volume percent of the volumetric amount of hydrogenation catalyst A present in the process system before utilizing the process of modifying. Hydrogenation catalyst A can comprise, for example, an alumina-supported palladium hydrogenation catalyst or alumina-supported palladium/silver hydrogenation catalyst as described above. Preferably, the conversion- improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound is in the range of from about 25 volume percent to about 75 volume percent, more preferably, in the range of from about 30 volume percent to about 70 volume percent, and most preferably, in the range of from 35 volume percent to 65 volume percent of the volumetric amount of hydrogenation catalyst A present in the process system before utilizing the process of modifying. Any suitable hydrocarbon-containing fluid which comprises at least one C 2 -C 6 alkyne can be used as the fluid to the single-stage reaction zone, preferably single- stage adiabatic reaction zone, of this invention. The term "fluid" is used herein to denote gas, liquid, vapor, or combinations thereof. Generally, such hydrocarbon- containing fluid contains at least one alkyne as an impurity at a level of about 1 part by weight alkyne per million parts by weight hydrocarbon-containing fluid to about 50,000 parts by weight alkyne per million parts by weight hydrocarbon-containing fluid (i.e., about 1 ppm alkyne to about 50,000 ppm alkyne). Preferably, such hydrocarbon- containing fluid contains at least one alkyne as an impurity at a level of about 1 ppm alkyne to about 30,000 ppm alkyne, more preferably such hydrocarbon-containing fluid contains at least one alkyne as an impurity at a level of about 1 ppm alkyne to about 20,000 ppm alkyne and, most preferably, such hydrocarbon-containing fluid contains at least one alkyne as an impurity at a level of about 1 ppm alkyne to about 10,000 ppm alkyne. Generally, such hydrocarbon-containing fluid is a C 2 -C 6 alkene stream. Non-limiting examples of suitable, available hydrocarbon-containing fluid include ethylene, propylene, and butylene streams, such as those from thermal hydrocarbon-(e.g., ethane, propane, butane, and naphtha) cracking processes, and mixtures thereof. A particularly preferred hydrocarbon-containing fluid is an ethylene stream from a thermal ethane-cracking process. Preferred alkynes include acetylene, propyne, butyne-1, butyne-2 and the like and mixtures thereof. A particularly preferred alkyne is acetylene. These alkynes are primarily hydrogenated to the corresponding alkenes, i.e., acetylene is primarily hydrogenated to ethylene, propyne is primarily hydrogenated to propylene, and the butynes are primarily hydrogenated to the corresponding butenes (butene-1, butene-2). A particularly preferred corresponding alkene is ethylene. It is within the scope of this invention to have additional compounds such as carbon monoxide, sulfur compounds, methane, ethane, propane, butane, water, alcohols, ethers, ketones, carboxylic acids, esters, other oxygenated compounds, and the like and mixtures thereof present in the hydrocarbon-containing fluid, as long as such additional compounds do not significantly interfere with the selective hydrogenation of alkyne(s) to alkene(s). An important benefit of the improved process system is the ability to handle fluctuations in carbon monoxide concentration, especially increases in carbon monoxide concentration, without significantly affecting the hydrogenation reaction. Generally, the sulfur compounds are present in the hydrocarbon-containing fluid in trace amounts, preferably at a level of less than about 1 weight percent sulfur, and preferably at a level of about 0.01 ppm by weight sulfur to about 1,000 ppm by weight sulfur (i.e., about 0.01 to about 1,000 parts by weight sulfur per million parts by weight hydrocarbon-containing fluid). The molar ratio of hydrogen to hydrocarbon of the hydrocarbon- containing fluid in the single-stage adiabatic reaction zone should be in the range of from about 0.01 :1 to about 25:1. Preferably, the molar ratio of hydrogen to hydrocarbon should be in the range of from about 0.01 : 1 to about 10:1. More preferably, the molar ratio of hydrogen to hydrocarbon should be in the range of from about 0.05:1 to about 5:1, and, most preferably, the molar ratio of hydrogen to hydrocarbon should be in the range from 0.10:1 to 1:1. In order to best attain substantially complete removal of C 2 -C 6 alkyne, preferably acetylene, there should be at least one mole of hydrogen for each mole of C 2 -C 6 alkyne present. Generally, the molar ratio of hydrogen to C 2 -C 6 alkyne is in the range of from about 0.5:1 to about 200:1, preferably about 1 :1 to about 100:1. The hydrogen and the hydrocarbon-containing fluid can be charged to the single-stage adiabatic reaction zone by any manner or method(s) which maintains the molar ratio of hydrogen to hydrocarbon. Generally, the hydrocarbon-containing fluid and the hydrogen are premixed before their contact with a catalyst in the single-stage adiabatic reaction zone. The single-stage reaction zone, preferably single-stage adiabatic reaction zone, comprises a structure having an inlet, an outlet, and a length-to-diameter ratio (L:D ratio) in the range of from about 0.25:1 to about 40:1, preferably in the range of from about 0.5:1 to about 30:1, more preferably in the range of from about 0.5:1 to about 20:1, and, most preferably, in the range from 0.5:1 to 5:1. Such structure can comprise, for example, a reactor vessel, preferably an adiabatic reactor vessel. The contacting step (i.e., the contacting of hydrocarbon-containing fluid with a catalyst in the single-stage adiabatic reaction zone) can be operated as a batch process step or, preferably, as a continuous process step. In the latter operation, a solid catalyst bed is generally used although conceptually a moving catalyst bed or a fluidized catalyst bed can be employed. Any of these operational modes have advantages and disadvantages, and those skilled in the art can select the one most suitable for a particular fluid and catalyst. Further discussion is provided in Perry's Chemical Engineers' Handbook, Sixth Edition, published by McGraw-Hill, Inc., copyright 1984, in sections entitled "Reactors for Solid-Catalyzed Reactions" at pages 4-36 through 4-48, and "Uses of Fluidized Beds" at pages 20-70 through 20-75, which pages are incorporated herein by reference. Reaction conditions of the single-stage reaction zone, preferably single- stage adiabatic reaction zone, of the contacting step of the inventive process include a reaction temperature in the range of from about 24 °C to about 260 °C (about 75 °F to about 500 °F). Preferably, the reaction temperature can be in the range of from about 27°C to about 204°C (about 80°F to about 400°F) and, most preferably, the reaction temperature can be in the range from about 32°C to about 149°C ( 90°F to 300°F). The reaction pressure of the single-stage adiabatic reaction zone can be in the range of from below atmospheric pressure upwardly to 6.89MPa (about 1000 pounds per square inch absolute (psia)), preferably, from 689kPa to about 6201kPa (about 100 psia to about 900 psia) and, most preferably, 1378kPa to 4832kPa from (200 psia to 700 psia). The flow rate at which the hydrocarbon-containing fluid is charged (i.e., the charge rate of hydrocarbon-containing fluid) to the single-stage reaction zone, preferably single-stage adiabatic reaction zone, is such as to provide a gas hourly space velocity ("GHSV") in the range of from exceeding 0 hour "1 upwardly to about 100,000 hour "1 . The term "gas hourly space velocity", as used herein, shall mean the numerical ratio of the rate at which a hydrocarbon-containing fluid is charged to the single-stage adiabatic reaction zone in standard cubic feet ("SCF") per hour divided by the SCF of catalyst contained in the single-stage adiabatic reaction zone to which the hydrocarbon- containing fluid is charged. The preferred GHSV of the hydrocarbon-containing fluid to the single-stage adiabatic reaction zone can be in the range of from about 500 hour "1 to about 50,000 hour "1 and, most preferably, in the range from 1000 hour "1 to 20,000 hour "1 . The GHSV of the hydrogen gas stream is chosen so as to provide the molar ratios of hydrogen to hydrocarbon of the hydrocarbon-containing fluid as disclosed above. After catalyst B has been deactivated by, for example, coke deposition or feed poisons, to an extent that the selective hydrogenation has become unsatisfactory, the catalyst can be reactivated by any means or method(s) known to one skilled in the art such as, for example, calcining in air to burn off deposited coke and other carbonaceous materials, such as oligomers or polymers, preferably at a temperature in the range of from about 399°C to about 982°C (about 750°F to about 1800°F). Optionally, the oxidatively regenerated catalyst is reduced with H 2 or a suitable hydrocarbon before its redeployment in the selective alkyne hydrogenation of this invention. The optimal time periods of the calcining depend generally on the types and amounts of deactivating deposits on the catalyst composition and on the calcination temperatures. These optimal time periods can easily be determined by those possessing ordinary skill(s) in the art and are omitted herein in the interest of brevity. The following example is presented to further illustrate this invention and is not to be construed as unduly limiting the scope of this invention. EXAMPLE The data presented in Table I below was developed by testing the novel process in a Phillips Petroleum Company ethylene plant at Sweeny, Texas. The ethylene plant utilized a multi-stage reactor system, i.e., two reactor vessels in series, with intercooling between stages, i.e., with heat removal apparatus comprising a heat exchanger between the two reactor vessels. Each reactor vessel contained a catalyst bed, approximately 3 metres length by 3 metres width (10 feet in length and 10 feet in width), comprising approximately 22.4m 3 (800 cubic feet) (approximately 60,000 pounds) of a commercially available catalyst, available from Phillips Petroleum Company, comprising palladium, silver, and alkali metal fluoride. The hydrocarbon-containing feed was passed through the first reactor vessel and then through the second reactor vessel with the product exiting the second reactor vessel. Heat was removed between the first and second reactor vessel via the heat exchanger. A hydrocarbon-containing feed consisting of an ethylene stream, from a thermal ethane cracker, containing about 25 volume percent hydrogen, about 10 volume percent methane, about 25 volume percent ethane, about 40 volume percent ethylene, about 0.35 volume percent acetylene, and about 0.025 volume percent carbon monoxide was introduced into the first reactor vessel at a pressure of 3803 kPa (about 552 pounds per square inch absolute (psia)) and at a gas hourly space velocity of about 9400 hour "1 . The hydrogen to hydrocarbon molar ratio was about 0.33: 1. The hydrogen to acetylene molar ratio was greater than 50:1. Over a time period of approximately 60 hours, the inlet temperature to the first reactor vessel was slowly raised and the heat removal between the first and second reactor vessels was slowly increased. At maximum available heat removal, the inlet of the second reactor vessel had been reduced from a normal operating condition of 93.3°C (about 200°F) to less than about 65.5°C (about 150°F) while still maintaining the required product specifications of the product exiting the second reactor vessel. The concentration of acetylene in the product exiting from the outlet of the second reactor vessel controlled the inlet temperature of the first reactor vessel. Product specifications required a concentration of acetylene in the product exiting the second reactor vessel of less than 0.3 ppm (i.e., 0.3 parts by weight acetylene per million parts by weight product) throughout the approximately 60-hour run. An increase in concentration of acetylene in the product resulted in an increase in the inlet temperature of the first reactor vessel thus increasing the hydrogenation of acetylene to ethylene, i.e., increasing the severity of the reaction. Increasing the severity of the reaction resulted in more acetylene being hydrogenated to ethylene in the first reactor vessel and thus reducing the concentration of acetylene in the product exiting the second reactor vessel. Thus, the inlet temperature of the first reactor vessel was monitored with any increase in inlet temperature of the first reactor vessel being an indication of hydrogenation of acetylene to ethylene. The inlet temperature of the first reactor vessel was obtained from a thermocouple 3 metres (about 10 feet) from the actual inlet of the first reactor vessel. The outlet temperature of the first reactor vessel was obtained from a thermocouple at the immediate exit, i.e. bottom, of the first reactor vessel. The change in temperature across the first reactor vessel was the difference between the inlet and outlet temperatures. The inlet temperature of the second reactor vessel was obtained by averaging the temperatures from three thermocouples axially located (i.e., one near the wall of the vessel, one about half-way to the center of the vessel, and one near the center of the vessel) about 0.76m (about 2.5 feet) into the second reactor vessel. The outlet temperature of the second reactor vessel was obtained from a thermocouple at the immediate exit, i.e. bottom, of the second reactor vessel. The change in temperature across the second reactor vessel was the difference between the inlet and outlet temperature. Trend data were obtained throughout the approximately 60-hour run testing the above-described novel process. In addition, data were also obtained from specific points in time during the testing of the novel process and are presented in Table I below. The data presented in Table I below were verified against the trend data to ensure that the data presented in Table I are a true reflection of what was indicated in the trend data. TABLE I As the data in Table I, which was verified against the trend data, clearly demonstrate, there was basically no change in temperature across the second reactor vessel indicating that virtually no hydrogenation of acetylene to ethylene was occurring in the second reactor vessel. The data in Table I demonstrate that the inlet temperature of the first reactor vessel, an indication of the severity of the hydrogenation reaction of acetylene to ethylene, had increased only slightly from about 172°F to about 177°F. The data in Table I also demonstrate that due to fluctuations of the carbon monoxide content of the feed, the first reactor vessel temperature varied, but never exceeded about 180°F. Further, the trend data indicated that when the carbon monoxide content of the feed fluctuated as a result of bringing a cold furnace into operation, the inventive process was able to handle the fluctuations in carbon monoxide and subsequent increases in inlet temperature without a "runaway" reaction occurring, i.e., without uncontrollable hydrogenation of ethylene to ethane occurring. The data in Table I also indicate that the change in temperature across the first reactor vessel increased only slightly from about 22 °F to about 26 °F. The data demonstrate that a single-stage adiabatic reaction zone (comprising, for example, one or more adiabatic reactor vessels), utilizing a catalyst comprising palladium, silver, and an alkali metal compound such as alkali metal fluoride, can be used in place of a traditional multi-stage reaction zone, with heat removal apparatus between one or more stages, while still maintaining the product specifications required for products exiting the final stage of such multi-stage reaction zone. Further, since the data demonstrate that the single-stage adiabatic reaction zone of the inventive process can be used in place of an existing multi-stage reaction zone, the data therefore demonstrate that the volumetric amount of a catalyst comprising palladium, silver, and an alkali metal compound such as alkali metal fluoride, used in the inventive process is significantly less than the volumetric amounts of catalyst present in such multi-stage reaction zone before utilizing the inventive process. As demonstrated in the Example, the volumetric amount of catalyst comprising palladium, silver, and an alkali metal compound such as alkali metal fluoride, used in the single-stage adiabatic reaction zone of the inventive process was about half, i.e., about 50 percent of, that used in a two-stage reaction zone with heat removal apparatus between stages. The data further demonstrate that the selective hydrogenation process of the invention can be used to modify at least one stage (e.g., at least one reactor vessel), and conceptually all stages (e.g., all reactor vessels), of a multi-stage reaction zone into a single-stage adiabatic reaction zone (comprising, for example, an adiabatic reactor vessel or one or more adiabatic reactor vessels), or, e.g., into a set of single-stage adiabatic reaction zones (e.g., a set of adiabatic reactor vessels), wherein each single- stage adiabatic reaction zone contains a catalyst comprising palladium, silver, and an alkali metal compound such as alkali metal fluoride. Modifying such multi-stage reaction zone eliminates the need to have intercooling between one or more stages of such multi-stage reaction zone. The above-described modification of a multi-stage reaction zone to several single-stage adiabatic reaction zones allows at least one single- stage adiabatic reaction zone to be in service with at least one single-stage adiabatic reaction zone to be in stand-by or to be used for additional acetylene removal allowing an essentially unlimited time to pass between shut-down of the entire reaction system. The data also demonstrate that increases in feed temperature to offset operational parameter upsets such as fluctuations in carbon monoxide can be handled in the single-stage adiabatic reaction zone of the inventive process. The results shown in the above example clearly demonstrate that the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those inherent therein. Reasonable variations, modifications and adaptations for various operations and conditions can be made within the scope of the disclosure and the appended claims without departing from the scope of this invention.

Claims: C L A I M S 1. A process of improving the operation of a process system used for conversion of a hydrocarbon-containing fluid comprising at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule with hydrogen to at least one corresponding alkene containing about 2 carbon atoms to about 6 carbon atoms per molecule wherein said process system utilizes a volumetric amount of a hydrogenation catalyst A required for providing said conversion of said at least one alkyne so as to provide a conversion product containing less alkyne than said hydrocarbon-containing fluid, the process comprises: substituting said hydrogenation catalyst A with a conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound contained in a single-stage adiabatic reaction zone, wherein said conversion- improving volumetric amount of said catalyst B is less than said volumetric amount of said hydrogenation catalyst A present in said process system before utilizing said process of improving; and contacting under reaction conditions said hydrocarbon-containing fluid with said catalyst B. 2. A process comprising: charging, at reaction conditions, a hydrocarbon-containing fluid comprising at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule with hydrogen to a single-stage adiabatic reaction zone containing a catalyst B comprising palladium, silver, and an alkali metal compound, converting said at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule to at least one corresponding alkene containing about 2 carbon atoms to about 6 carbon atoms per molecule, and yielding a conversion product containing less alkyne than said hydrocarbon-containing fluid and further wherein said conversion of said at least one alkyne is at least as high as the conversion of said at least one alkyne would otherwise be for a multi-stage reaction zone having intercooling between stages of said multi-stage reaction zone. 3. A process of modifying a multi-stage reaction zone, having intercooling between stages of said multi-stage reaction zone, used for conversion of a hydrocarbon- containing fluid comprising at least one alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule with hydrogen to at least one corresponding alkene containing about 2 carbon atoms to about 6 carbon atoms per molecule wherein said multi-stage reaction zone utilizes a volumetric amount of a hydrogenation catalyst A required for providing said conversion of said at least one alkyne so as to provide a conversion product containing less alkyne than said hydrocarbon-containing fluid, the process comprises: modifying said multi-stage reaction zone by providing for a single-stage adiabatic reaction zone having a conversion-improving volumetric amount of a catalyst B comprising palladium, silver, and an alkali metal compound that is less than said volumetric amount of said hydrogenation catalyst A present in said multi-stage reaction zone before utilizing said process of modifying. 4. A process according to any one of preceding claims 1-3, wherein said at least one alkyne is selected from the group consisting of acetylene, propyne, butyne-1, butyne-2, and mixtures thereof and said at least one corresponding alkene is selected from the group consisting of ethylene, propylene, butylene, and mixtures thereof. 5. A process according to claim 4, wherein said at least one alkyne is acetylene and said at least one corresponding alkene is ethylene. 6. A process according to claim 5, wherein said alkali metal compound is selected from the group consisting of alkali metal halides, alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, alkali metal nitrates, alkali metal carboxylates, and the like and mixtures thereof. 7. A process according to claim 6, wherein said catalyst B contains in the range of from about 0.001 weight percent palladium (on a total catalyst composition weight basis) to about 1 weight percent palladium, in the range of from about 0.05 weight percent alkali metal (on a total catalyst composition weight basis) to about 5 weight percent alkali metal, in the range of from about 0.03 weight percent fluorine (on a total catalyst composition weight basis) (chemically bound as fluoride) to about 10 weight percent fluorine, and in the range of from about 0.01 weight percent silver (on a total catalyst composition weight basis) to about 10 weight percent silver. 8. A process according to claim 7, wherein the atomic ratio of said fluorine to said alkali metal in said catalyst B is in the range of from about 0.5:1 to about 4:1. 9. A process according to claim 8, wherein said alkali metal compound is an alkali metal fluoride. 10. A process according to claim 9, wherein said alkali metal fluoride is potassium fluoride. 11. A process according to claim 10, wherein said catalyst B additionally comprises an inorganic support material selected from the group consisting of alumina, titania, zirconia, and mixtures thereof. 12. A process according to claim 11, wherein said inorganic support material is alumina. 13. A process according to claim 12 when depending from claim 1 or from claim 3, wherein said conversion-improving volumetric amount of said catalyst B is in the range of from about 20 volume percent to about 80 volume percent of said volumetric amount of said hydrogenation catalyst A present in said process system before utilizing said process of improving. 14. A process according to claim 12 or 13, wherein said hydrocarbon- containing fluid contains said at least one alkyne at a level of about 1 part by weight said alkyne per million parts by weight said hydrocarbon-containing fluid to about 50,000 parts by weight said alkyne per million parts by weight said hydrocarbon-containing fluid. 15. A process according to claim 14, wherein said hydrocarbon-containing fluid is a C 2 -C 6 alkene stream. 16. A process according to claim 15, wherein said hydrocarbon-containing fluid is selected from the group consisting of ethylene, propylene, and butylene streams, such as those from thermal hydrocarbon-(e.g., ethane, propane, butane, and naphtha) cracking processes, and mixtures thereof. 17. A process according to claim 16, wherein said hydrocarbon-containing fluid is an ethylene stream from a thermal ethane-cracking process. 18. A process according to claim 17, wherein said single-stage adiabatic reaction zone comprises a structure wherein said structure comprises an inlet, an outlet, and a length-to-diameter ratio (L:D ratio) in the range of from about 0.25:1 to about 40:1. 19. A process according to claim 18, wherein said structure comprises an adiabatic reactor vessel. 20. A process according to claim 19, wherein said reaction conditions comprise: a reaction temperature in the range of from about 24°C to about 260°C (about 75 °F to about 500 °F), a reaction pressure in the range of from below atmospheric pressure upwardly to about 6.89 MPa (about 1000 pounds per square inch absolute (psia)), a molar ratio of said hydrogen to hydrocarbon of said hydrocarbon- containing fluid in the range of from about 0.01 :1 to about 25:1, and a charge rate of said hydrocarbon-containing fluid to said single-stage adiabatic reaction zone such that the gas hourly space velocity is in the range of from exceeding 0 hour "1 upwardly to about 100,000 hour "1 .

Inventors: CALLEJAS RICARDO J, KIMBLE JAMES B, MORALES L ALBERTO, CALLEJAS, RICARDO, J., KIMBLE, JAMES, B., MORALES, L., ALBERTO
Applicants: CALLEJAS RICARDO J, KIMBLE JAMES B, MORALES L ALBERTO, PHILLIPS PETROLEUM CO, CALLEJAS, RICARDO, J., KIMBLE, JAMES, B., MORALES, L., ALBERTO, PHILLIPS PETROLEUM COMPANY
Application year: 2000
Main classification: C07C5
IPC codes: C07C5, C07C7