KR910009001B1 - Process for isomerization of c4 to c6 hydrocarbons with once - through hydrocarbons - Google Patents

Abstract

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Description

Isomerization of C4 to C6 Hydrocarbons

1 shows a method for isomerizing C ₅ to C ₆ hydrogen,

2 is a series of graphs illustrating the inlet and outlet characteristics of feed and effluent streams associated with the reaction zones of the present invention and the prior art.

The present invention relates to a method for catalytically isomerizing C ₄ to C ₆ hydrocarbons using hydrogen without recycling hydrogen. In particular, the present invention relates to a method for catalytically isomerizing light flies using one-through hydrogen and a solid catalyst selected in an amount such that the product stream has a very small amount of hydrogen.

High octane gasoline is required for modern gasoline engines. Conventionally, it is common to increase the octane number by using various lead-containing additives. As lead is gradually phased out in gasoline for environmental reasons, the need to rearrange the structure of hydrocarbons used in gasoline mixing increases to increase the octane number. Catalytic reforming and catalytic isomerization are two widely used methods for raising the octane number.

Gasoline mixed pools include C ₄ and higher hydrocarbons having a boiling point of less than 205 ° C. (395 ° F.) at atmospheric pressure. Hydrocarbons in this range include C ₄ to C ₆ paraffins, especially C ₅ and C ₆ normal paraffins with relatively low octane numbers. Since C ₄ to C ₆ hydrocarbons are very sensitive to the increase in octane number due to the addition of lead, the octane number was previously increased in this way. The octane number can also be increased by using an isomerization method that rearranges the structure of paraffinic hydrocarbons into side chain paraffins or by modifying C ₆ and higher hydrocarbons with aromatic compounds. Since normal C ₅ hydrocarbons are not readily converted to aromatic compounds, a common practice is to isomerize light hydrocarbons to the corresponding side chain isoparaffins. Although it is possible to modify C ₆ and higher hydrocarbons to aromatic compounds via hydrogenation, converting C ₆ hydrocarbons to aromatic compounds increases the density and the yield of gas, which in turn reduces the yield of the amount of liquid. Therefore, it is common to isomerize C ₆ paraffins to obtain C ₆ isoparaffinic hydrocarbons. Thus, the octane number is typically increased using catalytic isomerization converting C ₆ and higher boiling hydrocarbons and catalytic reforming converting C _{7 to} higher boiling hydrocarbons.

Isomerization of paraffins is a reversible first order reaction. This reaction is limited by thermodynamic equilibrium. The basic types of catalyst systems used to effectively proceed the reaction are aluminum chloride-based and supported aluminum chloride catalysts promoted by hydrochloric acid. Any catalyst is highly reactive and can cause undesirable side reactions such as disproportionation and cracking. The side reactions not only reduce the yield of the product but also combine with the catalyst to form olefin fragments and shorten the life of the catalyst. A common way of suppressing this undesirable reaction is to carry out the reaction in the presence of hydrogen.

The isomerization process which carries out the reaction in the presence of a halogenated platinum aluminum catalyst uses a relatively high ratio of hydrogen: hydrocarbons. US Pat. No. 2,798,105 teaches the use of platinum aluminum catalysts in the process of isomerizing C ₄ to C ₅ hydrocarbons by adding small amounts of molecular hydrogen having a molar ratio of hydrogen to hydrocarbon of 0.5: 4 to the reaction mixture. Isomerization of C ₄ to C ₇ hydrocarbons using a low platinum content alumina catalyst (containing a halogen component) and hydrogen having a molar ratio to hydrocarbon of at least 0.17 is taught in US Pat. No. 2,906,798. The addition of halogens to the isomerization process is taught in US Pat. No. 2,993,938, in which a catalyst having an aluminum support, a platinum metal and a halogen added thereon isomerized in a reaction where the molar ratio of hydrogen to hydrocarbon is 0.2: 10. Used as a catalyst. References to other isomerization methods that teach the use of halogenated platinum alumina catalysts to isomerize C ₄ to C ₆ hydrocarbons include US Pat. Nos. 3,391,220 and 3,791,960. The molar ratio of hydrocarbon is described as 0.1: 15. Therefore, it has long been recognized in the field of isomerization to use catalysts having a platinum group metal and a halogen on an alumina support for isomerizing C ₄ to C ₆ hydrocarbons. However, it has generally been recognized that these isomerization methods require a relatively high ratio of hydrogen: hydrocarbons to obtain a satisfactory catalyst lifetime and product yield.

One reason to use high ratios of hydrogen: hydrocarbons is that common platinum-alumina catalysts are very sensitive to deactivation by sulfur. Even at low sulfur concentrations, such as 1 ppm, platinum erodes and at least temporarily deactivates the catalyst. After deactivation by sulfur, in most cases rapid coking of the catalyst is seen. If not obstructed, coking will be so severe that it is necessary to completely regenerate the catalyst. Excess hydrogen modulates or prevents deactivation of the catalyst during transient deactivation by sulfur. Commercial methods have facilities for sulfur treatment and removal. Despite such facilities, sulfur contamination sometimes results in temporary catalytic deactivation. Thus, a relatively high ratio of hydrogen / hydrocarbons is maintained in the isomerization zone to improve coking and suppress the need for catalyst regeneration when temporarily deactivated by sulfur.

Despite the need to maintain high ratios of hydrogen: hydrocarbons and deactivation by sulfur, these halogenated platinum-alumina catalysts have been commonly used due to their high conversion and high product yield. However, maintaining a relatively high ratio of hydrogen to hydrocarbon increases the cost and complexity of the isomerization process. Most of these costs relate to recovery and recycling of hydrogen to the isomerization zone. Very small amounts of hydrogen entering the isomerization zone are consumed in the process. Thus, a separation plant is needed to remove hydrogen from the product effluent flowing out of the isomerization reaction zone. The recovered hydrogen is recycled to the isomerization zone to minimize the amount of hydrogen added to the process. However, the compression plant must raise the pressure of the hydrogen gas before hydrogen returns to the isomerization zone.

It is an object of the present invention to provide a catalytic isomerization process of C ₄ to C ₆ hydrocarbons using a catalyst having halogen and platinum group components on an alumina support and hydrogen and having excellent stability without recycling the recovered hydrogen. will be.

Another object of the present invention is to avoid the use of a recirculation device to maintain a high ratio of hydrogen to hydrocarbon ratios in the catalytic isomerization process.

The present invention is a method of catalytically isomerizing C ₄ to C ₆ normal paraffins using very low concentrations of hydrogen while maintaining high conversion and good stability. The present invention utilizes a high activity platinum / aluminum catalyst with chlorine added to the isomerization reaction which maintains stability in the presence of a chemical theoretical amount required for the isomerization reaction or slightly higher amounts of hydrogen. Due to the sensitivity of the catalyst to deactivation and water toxicity by sulfur, it is still necessary to treat the feedstream to remove water and sulfur. This treatment increases the cost of using the catalyst and thus reduces the economic benefits. The catalyst is more popular because of its amazing ability to isomerize C ₄ to C ₇ hydrocarbons for extended periods of time without the use of excess hydrogen and offsets the disadvantages associated with the removal of water and sulfur. Even more surprisingly, the catalyst composition causes little coking when temporarily deactivated by sulfur. As a result, the process of the invention can be carried out with very low hydrogen / hydrocarbon ratios without the need for frequent regeneration.

Thus, the present invention is a _{process for} isomerizing a feedstream containing C ₄ to C ₆ normal hydrocarbons.

The feedstream typically has a typical sulfur concentration of less than 0.5 ppm and a water concentration of less than 0.1 ppm based on the weight or mass of the feedstream. The feed stream has an H ₂ / HC molar ratio that mixes with hydrogen to produce an effluent stream having a hydrogen: hydrocarbon (H ₂ : HC) molar ratio of less than 0.05: 1. The feed streams and hydrocarbon mixtures are present in the reaction zone with 0.01 to 25% by weight of platinum at 40 to 235 ° C (104 to 455 ° F) temperature, 7 barsg to 70 barsg (bats gauge) pressure, and isomerization conditions with a space velocity of 0.1 to 10hr ^-1 Contact with an isomerization catalyst comprising alumina having from 2 to 10 weight percent chloride component. A chloride concentration of 30 to 300 ppm, based on the weight or mass of the feedstream, is maintained in the reaction zone. The effluent stream is sent directly to the ballast and then separated into a product stream of C ₄ to C ₆ hydrocarbons and a fuel gas stream which is removed in the process without recycling even a portion thereof.

The invention also relates to the details of the feed stream composition, the effluent stream composition, the reactor arrangement, the hydrogen concentration and the catalyst.

Referring to FIG. 1, the feed stream enters through line 10 and then passes through dryer 12 to receive a small amount of single pass hydrogen coming from line 14 while removing moisture. The feedstock and single pass hydrogen pass through the multistage reaction zone 16 and enter the ballast 18. Line 20 accepts a product stream containing C ₅ and C ₆ hydrocarbons having an increased concentration relative to the feedstock stream of isoparaffin. Line 22 is connected from top to bottom from the ballast to a scuba mover 24 that removes chloride from the product stream and moves fuel gas through line 26.

2 is a series of graphs illustrating inlet and outlet characteristics of feedstock and effluent streams associated with the reaction zone of the present invention and the prior art.

Feedstocks that can be used in the present invention include hydrocarbon aliquots rich in C ₄ to C ₆ normal paraffins. The term “rich” means a stream having at least 50% of the above components. Preferred feedstocks are C ₄ to C ₆ nearly pure normal paraffin streams or mixtures of nearly pure normal paraffins. Examples of other useful feedstocks include natural light gasoline, straight run naphtha, gas oil condensate, light raffinate, light modifier, light hydrocarbons, field butane, distillation endpoints of about 77 ° C. (170 ° F.) and C ₄ to C There is a straight run distillate containing the actual mass of ₆ paraffins. The feed stream may also comprise low concentrations of unsaturated hydrocarbons and C ₆ or higher hydrocarbons. The concentration of unsaturated hydrocarbons is limited to 10% by weight and the concentration of C ₆ or more hydrocarbons should be limited to 20% by weight to inhibit hydrogen consumption and cracking reaction.

The single pass hydrogen is mixed with the feedstock in an amount such that the ratio of hydrogen: hydrocarbons flowing out of the isomerization zone is 0.5: 1 or less. A molar ratio of hydrogen to hydrocarbon in the effluent of 0.05: 1 or less provides hydrogen that is sufficiently excess to carry out the process stably. Although not all of the hydrogen is consumed in the isomerization reaction zone, the isomerization reaction zone has a total consumption of hydrogen expressed in terms of stoichiometric hydrogen requirements associated with a number of side reactions. Such side reactions include cracking and disproportionation reactions. Other reactants that consume hydrogen are olefins and aromatic saturates. For raw materials with low concentrations of unsaturateds, the molar ratio of hydrogen to hydrocarbon in the inlet stream must be between 0.03: 1 and 0.1: 1 to satisfy the stoichiometric hydrogen requirements. Maintaining more than the theoretical theoretical amount of hydrogen for the side reaction in the reaction zone changes the stoichiometric hydrogen demand to compensate for changes in the composition of the feed stream, providing high stability and conversion, and thus inhibiting side reactions to prolong the life of the catalyst do. If not restrained, side reactions reduce the conversion and produce hydrocarbon-based compounds referred to as coke, which contaminate the catalyst. The amount of hydrogen required to inhibit the coke product appeared to not need to exceed the dissolved hydrogen concentration. The molar ratio of hydrogen present in the solution under the general conditions of the effluent of the isomerization zone is about 0.02: 1 to 0.01: 1 for hydrocarbons. Excess hydrogen, relative to the stoichiometric requirement for good stability and conversion, is present in a molar ratio of hydrogen: hydrocarbon of 0.01: 1 to less than 0.05: 1 as measured in the effluent of the isomerization reaction zone. Adding a dissolved excess of hydrogen fraction with a molar ratio of hydrogen to hydrocarbon of 0.05: 1 in the effluent satisfies the requirements for most feedstocks.

If the molar ratio of hydrogen: hydrocarbon exceeds 0.05: 1, it is economically undesirable to carry out the isomerization process without recycling hydrogen to the isomerization reaction zone. As the amount of hydrogen flowing out of the product recovery device increases, an additional amount of C ₄ and other product hydrocarbons is taken by the fuel gas stream from the product recovery device. The additional costs associated with the loss of product or with the recovery device to prevent the loss of the product make it not advantageous to carry out the method without hydrogen recycling when the molar ratio of hydrogen to hydrocarbon is greater than 0.05.

Hydrogen may be added to the feedstock mixture in such a way that the hydrogenation of the quantity can be properly controlled. Metering and monitoring devices for this purpose are well known to those skilled in the field. When implemented, control valves are used to meter the amount of hydrogen added to the feedstock mixture. The hydrogen concentration in one aliquot of the effluent stream or of the effluent stream effluent from the fractionation zone is measured by a hydrogen monitor and the fixed position of the control valve is adjusted to maintain the desired hydrogen concentration. The effluent flowing directly out of the reaction zone contains a relatively high concentration of chloride that can attack the monitor's metals. Thus, the monitor preferably measures the concentration of hydrogen in the stream subjected to corrosion treatment (for chloride removal), such as the gas stream exiting the ballast. The hydrogen concentration of the effluent is calculated based on the total flow rate of the effluent.

The feed mixture of hydrogen and hydrocarbon is in contact with the isomerization catalyst in the reaction zone. Isomerization catalysts consist of a high concentration of chloride catalyst on platinum containing alumina supports. Preferred alumina supports are anhydrous gamma-alumina of high purity. The catalyst may also contain other platinum group metals. Platinum group metals are precious metals selected from the group consisting of platinum palladium, ruthenium, rhodium, osmium and iridium, with the exception of silver and gold. The metals differ in activity and selectivity, and platinum has been found to be most suitable for the present invention. The catalyst contains about 0.01 to 25 weight percent platinum. Other platinum group metals may also be present at concentrations of from 0.01 to 25% by weight.

The platinum component is present in the final catalyst complex as an oxide or halide or metal element. It is shown that the presence of the reduced platinum component is most suitable for the present invention.

The catalyst also contains chlorides. For the combined chlorides, the chlorides are present in an amount of about 2 to 40 weight percent based on the anhydrous support. The amount of chloride most suitable for the process is at least 5% by weight. There are various methods of preparing a catalyst complex and then combining platinum and chloride therein. The best result in the present invention is to prepare a catalyst by contacting with an aqueous solution of a water soluble degradation compound in platinum group metals to impregnate the carrier material. Impregnation of the carrier material in the chloroplatinic acid solution yields the best results. Other solutions that can be used are ammonium chloroplatinic acid, chloroplatinic acid or platinum dichloride. The chlorinated platinum compound has the dual action of combining the platinum component and at least a small amount of chloride in the catalyst. The addition amount of chloride should be formulated into the catalyst by adding or forming aluminum chloride to or on the platinum-aluminum catalyst support. Another way to increase the halogen concentration in the catalyst composite is to use an alumina hydrosol to form an alumina carrier material that contains at least a portion of the halogen. Halogen may also be added to the carrier material by contacting the calcined carrier material with an aqueous halogen acid solution, such as hydrogen chloride, hydrogen fluoride or hydrogen bromide.

This type of high chloride platinum-alumina catalyst is known to be very sensitive to compounds containing sulfur and oxygen. Therefore, the feedstock should be relatively free of sulfur and oxygen. The sulfur concentration in the feedstock should be less than 0.5 ppm by weight. Sulfur present in the feedstock acts to temporarily deactivate the catalyst by the platinum poison. The activity of the catalyst can be recovered by removing sulfur with hot hydrogen in the catalyst complex or by desorbing sulfur adsorbed to the catalyst by lowering the sulfur concentration of the incoming feed stream to 0.5 ppm or less. Water can serve to permanently deactivate the catalyst by removing high activity chloride from the catalyst and then replacing it with inert aluminum hydroxide. Thus, the oxygen must be present in very low concentrations, as well as oxygenates, in particular C ₁ to C ₅ oxygenates, which can decompose to produce water. Generally, the oxygates in the feedstock are limited to less than about 0.1 ppm, measured as ppm by weight of water equivalent in the feed. The feedstock can be treated in any way to remove water and sulfur compounds. Sulfur may be removed from the feed stream by water treatment. Various dryers on the market are useful for removing water from feeds. Adsorption methods for removing sulfur and water from hydrocarbon streams are well known to those skilled in the art.

The operating conditions in the isomerization zone are chosen to maximize the production of isoalkanes product from the feed. In general, the temperature in the reaction zone is about 40-235 ° C. (100-455 ° F.). At low temperatures, low reaction temperatures are preferred since an equilibrium mixture of normalalkanes to isoalkanes is produced. Low temperatures are useful for treating feeds consisting of C ₅ to C ₆ alkanes. This is because at low temperatures an equilibrium mixture with the highest concentration of side chain isoalkanes is produced. When the feed mixture is mainly C ₅ to C ₆ alkanes, the reaction temperature is preferably 60 to 160 ° C. Higher reaction temperatures are required to maintain catalytic activity to isomerize large amounts of C ₄ hydrocarbons. Therefore, when the feed mixture contains a large amount of C ₄ to C ₆ alkanes, the most suitable reaction temperature is 145 to 225 ° C. The pressure in the reaction zone is wide. The pressure when isomerizing C ₄ to C ₆ paraffins is 7 barsg to 70 barsg, and 20 barsg to 30 barsg is preferred in the present method. The feed rate to the reaction zone is also wide.

For example, a liquid hourly space velocity from 0.1 to 10hr ^-1, of from 1 to 6hr ^-1 are preferred.

In addition, a small amount of organic chloride promoter is required to manipulate the reaction zone. The organic chloride promoter acts to maintain a high concentration of active chloride on the catalyst since the catalyst is continuously removed slightly by supply of hydrocarbons. The promoter concentration in the reaction zone is maintained at 30 to 300 ppm relative to chloride equivalents based on the mass of the feed. Preferred promoters are carbon tetrachloride. Examples of other suitable promoters are oxygen free degradable organic chlorides such as propyldichloride, butyl chloride and chloroform. To keep the reactants dry, the reactants must be enriched in the presence of organic chlorides that can be partially converted to hydrogen chloride. The stream of the process remains dry and the presence of small amounts of hydrogen chloride does not adversely affect the reaction.

1 shows two reaction systems having a first reactor 28 and a second reactor 30 in the reaction zone. The catalyst used in the present invention should be evenly distributed between the two reactors. The reaction does not necessarily have to be carried out in two reactors, but with the use of two reactors and special valving (not shown), the catalyst system can be partially removed without removing the isomerization unit from the stream. The reactant can be introduced into only one reactor so that the catalyst is replaced in the other reactor. In addition, the two reactors help to keep the catalyst temperature low. This can be accomplished by carrying out exothermic reactions, such as hydrogenation of unsaturated substances, in the first reactor 28 and other reactions in the final stage of the reactor under better temperature conditions. FIG. 1 shows the mode of operation of passing a relatively cold hydrogen and hydrocarbon feed mixture flowing through line 32 through a cold feed exchanger 34 which heats the effluent coming from second reactor 30. Line 36 conveys the feed from the cold feed exchanger to the hot feed exchanger 38, where the feed is in contrast to the effluent conveyed from the first reactor 28 by line 40. Heated.

Line 42 conveys the partially heated feed from hot feed exchanger 42 through inlet exchanger 44 (which provides additional heat to the feed) and then to first reactor 28. The effluent from the first reactor 28 passes through the exchanger 38, as described above, and then is conveyed to the second reactor 34 by line 40. Line 46 conveys the isomerization zone effluent in the second reactor 30 through the cold feed exchanger and then directly to the separator as described above. Transport it to the separator. The separator separates the reaction zone effluent into a product stream comprising C ₄ and C ₄ or higher hydrocarbons and a gas stream of lighter hydrocarbons and hydrogen. Suitable designs for rectifying tubes and separators are well known to those skilled in the art. Also, the spray device may include a general recovery device of isoalkanes. Typical isoalkanes recovered from the separator are recycled to the isomerization zone to convert more normal alkanes to isoalkanes. 1 shows a separation device including a stabilizer 18. Line 46 conveys the effluent from the second reactor 30 to the stabilized column 48. The stabilization tower 48 delivers the fraction containing C ₄ and C ₄ or more hydrocarbons down, and the C ₃ hydrocarbons and lighter compounds up there. The stabilizer tower includes a reboiler tube 52 that introduces a C ⁺ ₄ product stream into line 52. The product entering line 52 passes through a product exchanger 54 which heats the reaction effluent before entering the tower 48. The cooled product is recovered from exchanger 54 via product line 20. C ₃ and C ₃ or less hydrocarbons and excess hydrocarbons flowing out of the reaction zone are recovered at the top of the stabilizer 48 via line 56 and then cooled in condenser 58 and separated by separator 60. It is separated into gas stream and reflux. Line 26 recovers reflux from separator 60 to the top of tower 48 and line 22 conveys all gas from separator 60 to scrubber device 24.

The scrubber device 24 contacts the gas entering the separator 60 with a suitable treatment solution to neutralize and / or remove the acidic components generated by the addition of chloride in the isomerization zone and present in the gas stream. Typically, the treating solution is a caustic pumped around the contact vessel 64 in the loop 66. The spent (fully used) caustic is recovered and then fresh caustic is added to the scrubber apparatus by line 68. After processing in the scrubber device 24, all gas is removed from the present invention via line 26. The gas recovered by line 26 is commonly used as fuel.

EXAMPLE

The process of the present invention can be characterized by high conversion, high selectivity and good stability, as can be seen in the following examples. In this example, a hydrocarbon feed having the composition shown in the table was charged to the two reaction zone systems generally shown in FIG. Prior to entering the reaction zone, hydrogen is mixed with the hydrocarbon feed to provide a mole ratio of hydrogen: hydrocarbon of 0.7: 1 to 0.1: 1, as measured in Figure 2, which molar ratio is measured at the outlet of the reaction zone. did. Each reaction zone contained an alumina catalyst with 0.25 weight percent platinum and 5.5 weight percent chlorine.

[table]

A catalyst was prepared by impregnating an alumina support in a chloroplatinic acid, 2% hydrochloric acid and a 3.5% nitric acid solution at a volume ratio of 9 parts to 10 parts with respect to the solution to obtain a colloidal support material having a platinum solution: support ratio of about 0.9. did. The resulting mixture was cooled for about 1 hour and then evaporated to dryness. The chloride content was then adjusted by oxidizing the catalyst and contacting the chloride with the 1M hydrochloric acid solution at 525 ° C. at a rate of 45 kW / hr for 2 hours. The catalyst was then reduced in electrolytic hydrogen at 565 ° C. for 1 hour to include about 0.25 weight percent platinum and about 1 weight percent chloride. After sublimation of aluminum chloride with hydrogen, the amount of active chloride was brought to about 5.5% by contacting the sublimed aluminum chloride with the catalyst at 550 ° C. for about 45 minutes.

The hydrocarbon feed mixture was introduced into the first reaction zone at about 160 ° C. The feed mixture was introduced into the first reaction zone at about 175 ° C., then heat exchanged with the inlet feed and then into the second reaction zone at about 140 ° C. The outlet temperature of the second reaction zone was maintained at about 140 ° C., and the feed was passed through the reaction zone at a liquid space velocity of about 2.4 hr −1 per hour. The average pressure in the two reaction zones was maintained at 31 barsg. Effluent from the second reaction zone was recovered at about 140 ° C. At the beginning of the operation, the H ₂ / HC molar ratio at the exit was maintained at about 0.7: 1. It was identical to the range of representative low H ₂ / HC ratios implemented in the prior art. Over several months, the H ₂ / HC ratio was adjusted as low as the ratio of the present invention. The average value of isopentane: C ₅ hydrocarbon ratio, 2,2-dimethylbutane: C ₆ hydrocarbon ratio and the research octane in the effluent is plotted across the entire method at the molar ratio of the selected H ₂ / HC effluent. As shown in the data, the method of the present invention was able to maintain a nearly constant value for this parameter as the ratio of H ₁ / HC was reduced. The reaction system was operated continuously over 1200 hours at a H ₂ / HC molar ratio of about 0.05: 1 without significant loss of conversion of normal paraffins or reduction of octane number in the recovered effluent. As a result, it was found that the method of the present invention using the catalyst as described above can stably convert normal paraffins to isoparaffins by adding hydrogen to the effluent in a molar ratio of 0.05: 1 or less with respect to hydrocarbons.

Claims (3)

A feed stream 10 comprising C ₄ to C ₆ hydrocarbons and having a water content of less than 0.1 ppm is mixed with hydrogen 14: a temperature of 40 to 235 ° C. (104 to 455 ° F.), a pressure of 7 to 70 barsg and 0.1 The feed stream and hydrogen mixture in reaction zone 16 with an alumina-containing isomerization catalyst containing 0.01-25 wt% platinum and 2-10 wt% chloride under isomerization conditions having a space velocity of from 10 hr ⁻¹ . (42) contacting: maintaining the chloride concentration in the reaction zone at 30 to 300 ppm and recovering the effluent stream 46 from the reaction zone: the amount of hydrogen mixed with the feed stream is determined by the hydrogen in the effluent stream: The gaseous stream 22 is selected to have a hydrocarbon molar ratio of less than 0.05: 1 and the effluent stream is passed directly through a stabilization column 48 to be removed without recycle to the product stream 20 of C ₄ to C ₆ hydrocarbons. Isomerization method of C ₄ to C ₆ hydrocarbons. The process of claim 1, wherein the feed stream is introduced with a hydrogen concentration above the dissolved hydrogen concentration in the reaction zone by an amount equal to the stoichiometric requirement. The method of claim 1, wherein the concentration of hydrogen in the eluate is measured to adjust the amount of hydrogen to be added to the reaction zone according to the concentration.

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