WO2007053061A2

WO2007053061A2 - Plant for the production of concentrated aromatic hydrocarbons from c3 and c4 hydrocarbons

Info

Publication number: WO2007053061A2
Application number: PCT/RU2006/000560
Authority: WO
Inventors: Genrikh Falkevich; Nikolay Rostanin; Galina Iniyaeva; Leonid Vilenskiy
Original assignee: Genrikh Falkevich; Nikolay Rostanin; Galina Iniyaeva; Leonid Vilenskiy
Priority date: 2005-11-02
Filing date: 2006-10-25
Publication date: 2007-05-10
Also published as: WO2007053061A3

Abstract

This plant relates to the production of aromatic hydrocarbons from light hydrocarbons and can be used in the oil and gas industries.

Description

PLANT FOR THE PRODUCTION OF CONCENTRATED

AROMATIC HYDROCARBONS FROM C₃ AND C₄

HYDROCARBONS

Long distillates of light hydrocarbons consisting mainly from propane and butane are by-products obtained at gas producing and gas processing factories. Lower paraffins and olefins are also obtained as by-products at oil refineries. Their excessive quantities can be converted to aromatic hydrocarbons using catalysts based on medium- porous metal silicates that show high activity, selectivity and stability in aliphatic to aromatic hydrocarbon conversion reactions.

For most of the currently known methods of producing aromatic hydrocarbons from light hydrocarbons, the flow of raw materials mainly consists of C₂-C₄ hydrocarbons and is converted without separation into components in a single reaction zone characterized by specific conditions of raw material exposure to the catalyst, whereas propane is converted to aromatic hydrocarbons with a higher heat release compared to butane, propylene and butylene, and ethane conversion requires an even higher temperature. Therefore the commingled raw material flow is exposed to the catalyst either at a high temperature which is suitable for less active raw material components and hence increasing the coke formation rate and reducing the catalyst lifetime, or at a lower temperature with relatively low propane and ethane conversion rates and a high unconverted raw material recycling rate. For other methods, raw material components are converted in multiple reaction zones. For example, US Patent No. 5171912, 1992, C 07 C 1/00 characterizing a process of C₅₊ gasoline production from propane and butane describes a C₅₊ hydrocarbon production plant comprising two reactors for the separate conversion of propane and butane, wherein the raw material is separated into the propane containing fraction and the butane containing fraction and the stabilization gases are stabilized and separated into raw material fractions in a single rectifier column.

RU Patent No. 2175959, 2001, C 07 C 001/00 characterizing a method of converting C₂-Ci₂ aliphatic hydrocarbons to aromatic hydrocarbons or high-octane gasoline describes a plant comprising raw material heaters, a reactor comprising two reaction zones (the high- and the low-temperature ones) and two raw material input lines, heat exchangers, a cooler for the cooling and partial condensation of the reaction product flow at the reactor output, a vapor-liquid separator for the separation of the unstable aromatic hydrocarbon containing liquid product from the reaction product flow and a rectifier column for its stabilization. The stabilization gases and part of the vapor phase flow from the separator output are recycled to the first reactor zone.

The product forming in the first reactor zone or in the first reactor is fed to the second reactor zone, and the final product is separated from the second reactor zone (second reactor) product. The aromatic hydrocarbons forming in the first reactor zone are exposed to the catalyst in the second zone and participate in the alkylation and coke formation reactions thus increasing the fraction of heavy alkylbenzenes in the product and reducing the second reactor zone catalyst lifetime. Another disadvantage of this plant is the high content of C₅₊ hydrocarbons, including aromatic ones, in the flue gas and the recycled flows, this being another problem for the first reactor zone.

In RU Patent No. 2001124533, 2003, C 10 G 35/095 characterizing a method of producing high-octane gasoline fractions or aromatic hydrocarbons, the final product is obtained using at least two reactors with intermediate heat supply for maintaining the intermediate reaction flow temperature at the second reactor input at a level 5-50⁰C below that at the first reactor input or for maintaining the second reactor temperature at a level 5-50⁰C below that in the first reactor. The resultant product flow is separated by means of cooling, condensation, separation and rectification. This method and any device for its implementation have the same disadvantages related to the catalytic process as described above.

When the raw material is exposed to the catalyst under the conditions suitable for the production of aromatic hydrocarbons, the product flow contains hydrogen, Ci-C₄ paraffins and aromatic hydrocarbons, mainly C₆-C₈. The raw hydrocarbons are recycled to the process with the Ci-C₄ fraction, or the C₃-C₄ fraction is separated. The degree of recycled product refinement from aromatic hydrocarbons in the former case and the degree of aromatic hydrocarbon extraction from the flue gases affect the economic parameters of the process.

The products are separated using cooling, condensation, compression, separation, rectification and some other processes implemented on appropriate process equipment. Good separation of the gaseous products requires high pressure and deep cooling of the separation zone, otherwise the final product and raw material losses can be very large, especially if diluted raw materials are used.

US Patent No. 4634799, 1987, C 07 C 015/42 characterizing a method of separating dehydrocyclodimerization process products describes a plant for the production of aromatic hydrocarbons from C₃ and/or C₄ containing raw materials comprising devices for cooling, partial condensation, separation and rectification of the components, wherein the raw material flow is sued for cold reflux of the liquid product rectifier column.

In US Patent No. 4528412, 1985, C 07 C 003/03 characterizing a method of dehydrocyclodimerization, the reactor output product containing C₆₊ aromatic hydrocarbons is cooled, condensed, separated into a liquid phase flow containing the aromatic hydrocarbons and a vapor phase flow containing hydrogen, Ci and C₂ hydrocarbons, raw material hydrocarbons and C₆. The liquid product is further separated in the rectifier column into the C₆ H C₇₊ fractions part of which is used as an absorbent for the separation of the C₃₊ components from the vapor phase flow obtained after the initial reactor product separation, following which a liquid flow of raw hydrocarbons and then a liquid flow of C₂₊ hydrocarbons are separated from the absorber flue gas containing hydrogen, Ci and C₂ hydrocarbons and raw hydrocarbons using partial condensation and vapor phase flow separation. The recycled flows of this device contain minor amounts of hydrogen and methane. Thus, absorption is used for the separation of the C₆₊ components from the vapor phase flow obtained after the initial reactor product separation, and raw hydrocarbons are separated using deep cooling.

The object of the invention disclosed herein is to provide a plant for the production of concentrated aromatic hydrocarbons from C₃ and C₄ hydrocarbons.

The plant according to this invention allows raw material conversion under the conditions that are optimum for the required conversion of specific raw material component groups without preliminary separation of the raw material flow, thus providing for a higher stability of the catalyst due to the use of two reactors and separation of aromatic hydrocarbons from the intermediate product. Other characteristics of this invention are related to the use of an adsorption process for the separation of aromatic hydrocarbons from the gas flows and absorption or adsorption processes for the separation of raw hydrocarbons from the flue gases.

The plant is described as a sequence of basic components (basic process equipment) having specific functions and operation conditions. Each device operates under the conditions providing for the implementation of its specific function. Different embodiments of this plant differ by the presence of additional devices or functionally interrelated groups of devices (units) used for the implementation of a specific action upon the input flow of said device or unit for changing the properties of such flow, wherein the output flow of said device or unit with changed properties is directed to another device or unit instead of the input flow or flued from the plant. The plant comprises pumps, pipelines and other lines between the devices for providing the flow of raw materials and products within the plant and process control functions. The plant further comprises fire heaters or recovery heat exchangers for heating the raw materials fed to the devices to the temperature as is required for efficient processing. The plant comprises known rectifying, heat exchanging, pumping and compressor equipment, as well as known reactors, adsorbers and absorbers.

The plant for the production of concentrated aromatic hydrocarbons from C₃ and C₄ hydrocarbon containing raw materials comprises sequence pipeline connected raw material heater, reactor for exposing the heated raw material to the dehydrocyclodimerization reaction catalyst under the conditions of conversion of max. 70% propane and min. 80% butane from which the first flow of products containing hydrogen, methane, ethane, raw hydrocarbons and aromatic hydrocarbons are output, heat exchangers and coolers for product flow cooling and condensation of the C₅₊ hydrocarbons, a vapor-liquid separator for the separation of the vapor-liquid mixture from which a vapor phase flow containing hydrogen, methane, ethane and mainly raw hydrocarbons and a liquid phase flow containing the aromatic hydrocarbons are output and a rectifier column for the stabilization of the liquid phase flow containing the aromatic hydrocarbons from which the concentrated aromatic hydrocarbons and the stabilization gases of the concentrated aromatic hydrocarbons are output. The plant further comprises the following sequence pipeline connected devices for the production of aromatic hydrocarbons from raw hydrocarbons contained in said vapor phase flow output from the separator: a vapor phase flow heater, a (second) reactor for the exposure of the heated vapor phase flow to the dehydrocyclodimerization reaction catalyst under the conditions of aromatic hydrocarbon production from propane, from which the second product flow containing hydrogen, methane, ethane, raw hydrocarbons and aromatic hydrocarbons are output, as well as heat exchangers and coolers for the cooling of said second product flow and condensation of the Cs₊ hydrocarbons and a vapor-liquid separator for the separation of the vapor-liquid mixture from which a vapor phase flow containing hydrogen, methane, ethane and mainly raw hydrocarbons and a liquid phase flow containing aromatic hydrocarbons further fed to the rectifier column for stabilization are output.

The raw material for the plant are hydrocarbon fractions containing C₃ and C₄ hydrocarbons, i.e. propane-butane fractions, C₃- C₄ olefin containing fractions, Ci-C₄ paraffin and olefin mixtures and long distillate of light hydrocarbons. If the raw material contains C₅₊ components, these are separated in a rectifier column. In this latter case said plant further comprises a rectifier column and equipment required for its operation, i.e. a raw material heater, a reboiler or an evaporator for rectifier column boiler heating, a cooler, a reflux tank and a pump for cold reflux of the rectifier column. The C₃ and C₄ hydrocarbon containing vapor phase flow output from the top of the rectifier column after reflux separation is further processed.

If the raw material represents separate fractions of saturated hydrocarbons and olefin containing fractions, the latter can be fed separately to each reactor for reducing the endothermic effect of propane and butane conversion until the achievement of chemical process conditions close to isothermal ones. In a preferred embodiment of this invention, olefin containing raw materials are mixed with paraffin containing raw materials of each reactor to obtain a mixture of C₃ and C₄ hydrocarbons containing 25 wt.% olefins. The flows are mixed before feeding the raw material to the heaters.

The raw material may contain impurities that are detrimental for said dehydrocyclodimerization reaction catalyst, such as sulfur compounds. Sulfur may also be undesired in the plant output product, i.e. in concentrated aromatic hydrocarbons, and the most reliable method of achieving the required quality of the final product is sulfur removal from the raw material. Preferably, dry refining methods are used, for example, those with active zinc oxide (Nitrogen Engineer's Handbook, ed. E. Ya. Melinkov, Moscow, Khimiya, 1967, vol. 1, p. 491; Production of Process Gas for Ammonium and Methanol Synthesis from Hydrocarbon Gases, ed. A.G. Leibush, Moscow, Khimiya, 1971, p. 286). For sulfur removal from the raw material, said plant further comprises a reactor (contact device) and a raw material heater. The raw material flow with a high sulfur content or a mixture of raw material fractions are refined. Raw materials containing C₃ and C₄ hydrocarbons or their mixture with the recycled flows are fed to the heater and further to the sulfur refining reactor, and the refined raw materials are output from the reactor. In the preferred embodiment of this invention, the sulfur content in the raw materials is within 5-10 wt.% of the C₃ and C₄ hydrocarbon content. The refined raw materials are fed to the heater and then to the dehydrocyclodimerization reactor. In the preferred embodiment of this invention, raw material exposure to the catalyst is provided on a fixed bed of granulated catalyst in an isothermal or an adiabatic reactor. The use of an isothermal reactor allows reducing or avoiding inert heat carrying components in the raw material and provides favorable thermal conditions for its conversion. The preferred operation conditions of an adiabatic reactor are reactor temperature difference of within 3O⁰C with an appropriate volume of heat carrier in the reactor input raw material flow.

The process is implemented with known dehydrocyclodimerization reaction catalysts that are active in the production of aromatic hydrocarbons from lower olefins and paraffins at 400-650⁰C. The preferred products are benzene, toluene and xylenes. High selectivity in the formation of these hydrocarbons is a feature of catalysts based on medium-porous zeolites and other metal silicates, e.g. those with a pentasil structure. These catalysts are well known in the industry (A.Z. Dorogochinsky et al., Aromatization of Low-Molecular Weight Paraffin Hydrocarbons on Zeolite Catalysts. Review Information. Moscow, TsNIITENeftekhim, 1989, No. 4). The known catalysts contain at least one metal having a dehydrating, activity, such as platinum, palladium, zinc, chromium, cadmium, molybdenum and gallium. The catalyst may further contain phosphorus, fluorine, rare-earth metal oxides and other components increasing its activity, selectivity or stability. Catalysts can be those according to Patents RU No. 2165293, 20.04.2001, B Ol J 29/40; RU No. 2098455, 10.12.1997, C 10 G 35/095; RU No. 2133640 27.07.1999, B 01 J 29/46; RU No. 2087191, 20.08.1997, B

01 J 29/40. Similar or different catalysts can be used in the plant reactors.

During raw material conversion on the catalyst bed, coke is produced and decreases the catalyst activity which is usually compensated by an increase in the process temperature. At some threshold level of catalyst deactivation, raw material feeding to the reactor is stopped, and the catalyst is regenerated using known methods, usually, by oxidation with a nitrogen/air mixture. For uninterrupted plant operation, the plant comprises additional reactors installed parallel to the main ones, with at least one additional reactor for each main reactor, and a catalyst regeneration unit having a known design and integrated with the plant using a known method without affecting the interconnections and functionality of the main plant components.

The raw material is exposed to the catalyst in the first reactor under conditions suitable for the formation of aromatic hydrocarbons, preferably, at 460-610⁰C and 1.8 MPa. The first reactor provides for an almost complete conversion of olefins, min. 80% butane and max. 70% propane. The preferred conditions are those under which propane conversion is within 50%, e.g. a relatively low temperature. The reactor output product flow contains hydrogen, methane, ethane, unconverted raw hydrocarbons and Cs₊ components, mainly aromatic , ones. Preferably, the content of aliphatic hydrocarbons in the C₅₊ fraction is within 1 wt.%. Further conversion of propane and other more active raw components occurs in the second reactor after separation of the aromatic hydrocarbons produced in the first reactor. The first reactor output product flow is cooled, and the

C₅₊ components are condensed. The plant comprises recovery heat exchangers and coolers connected in sequence by pipelines to the first reactor output, i.e. air, water or propane coolers, wherein the product flow is gradually cooled to form a vapor-liquid mixture fed to the vapor-liquid separator at within 4O⁰C, preferably not higher than -5⁰C. The separator output contains a vapor phase flow containing hydrogen, methane, ethane, unconverted raw hydrocarbons and aromatic hydrocarbons and a liquid phase flow containing aromatic hydrocarbons and solute gases. The deeper the product flow cooling, the lower the heavy vapor fraction in the vapor phase flow and the more efficient is the second reactor input raw material refinement from aromatic hydrocarbons.

More complete condensation of the Cs₊ components can be achieved at a higher pressure of the vapor phase flow. In this embodiment the plant comprises a compression unit comprising the following devices connected in sequence by pipelines to the vapor phase flow output from the first product flow separator: a compressor for increasing the pressure of the vapor phase flow output from the separator, a cooler for cooling the compressed flow and condensation of the C₅₊ components and a vapor-liquid separator for the separation of the vapor-liquid mixture from which the aromatic hydrocarbon containing liquid phase further fed to the rectifier column for stabilization and a vapor phase flow are output. The high-pressure vapor phase flow is fed to the second reactor heater. In the preferable embodiment, this method of separating aromatic hydrocarbons is implemented at a higher pressure of raw material exposure to the catalyst compared to the first reactor.

For more efficient separation of aromatic hydrocarbons from the second reactor input raw material without the use of high pressure and deep cooling, the plant may comprise one or more adsorbers for uninterrupted refining of the vapor phase flow separated from the first product flow. Aromatic hydrocarbons can be adsorbed from a mixture of C₁-C₄ hydrocarbons using known adsorbents such as activated charcoal, silica gel and zeolites. Preferred is the use of activated charcoal as an easily regenerated sorbent with a high adsorption capacity. Adsorption is achieved in conventional adsorbers. Aromatic hydrocarbons adsorption conditions depend on the properties of the sorbent used and are preferably identical to the parameters of the vapor phase flow being refined.

The vapor phase flow output from the separator is fed to the adsorber, preferably, without preparation, and the vapor phase flow output from the adsorber is depleted of aromatic hydrocarbons and contains hydrogen, methane, ethane and raw hydrocarbons. The degree of aromatic hydrocarbon separation from the vapor phase flow is preferably min. 95% for a complete adsorption cycle.

The adsorbent saturated with aromatic hydrocarbons is regenerated by raising the adsorber temperature and simultaneously blowing the adsorber with part of the vapor phase flow depleted of aromatic hydrocarbons output from another adsorber (blowout gas). The desorbed aromatic hydrocarbons are separated from the saturated blowout gas containing less noncondensable components than the adsorption input flow, and their condensation can therefore be achieved with smaller losses.

In regeneration mode, the adsorber is blown with heated blowout gas, i.e. part of the vapor phase flow depleted of aromatic hydrocarbons output from another adsorber, and the blowout gas saturated with aromatic hydrocarbons is output from the adsorber. For adsorbent regeneration the plant comprises a blowout gas heater and heat exchangers and coolers connected in sequence by pipelines to the adsorber output and used for the cooling and condensation of aromatic hydrocarbons contained in the saturated blowout gas, as well as a separator for the separation of the vapor-liquid mixture from which a liquid phase flow containing aromatic hydrocarbons further fed to the rectifier column for stabilization and a vapor phase flow further mixed with the vapor phase flow depleted of aromatic hydrocarbons output from another adsorber are output.

The adsorption unit comprises adsorbers and adsorber regeneration equipment. The input flow is the aromatic hydrocarbon containing vapor phase flow output from the product flow separator or from the compression unit, and the output flow is a vapor phase flow depleted of aromatic hydrocarbons.

Also possible is embodiment of the plant with sequence connected units for the compression of the vapor phase flow output from the first product flow separator and for the adsorption of aromatic hydrocarbons from the high-pressure vapor phase flow output from the compression unit. The structure of said units is described above. The vapor phase flow that is output from the first product flow separator and depleted of aromatic hydrocarbons in the plant embodiments comprising a compression unit or an adsorption unit is fed to the heater and further to the second reactor. In the second reactor, the raw material is exposed to the catalyst under conditions suitable for the formation of aromatic hydrocarbons, preferably, at 460-610⁰C and 1.8 MPa. Preferably, the propane conversion rate in the second reactor is within 70%. The product flow output from the reactor contains hydrogen, methane, ethane, unconverted propane, possible small amount of butane and aromatic hydrocarbons.

The second reactor output product flow is cooled to condensate the C₅₊ components. The plant comprises recovery heat exchangers and coolers connected in sequence by pipelines to the first reactor output, i.e. air, water or propane coolers, wherein the product flow is gradually cooled to form a vapor-liquid mixture further fed to the vapor-liquid separator at within 4O⁰C, preferably not higher than -5°C. The separator output contains a vapor phase flow containing hydrogen, methane, ethane, unconverted raw hydrocarbons and aromatic hydrocarbons and a liquid phase flow containing aromatic hydrocarbons and solute gases.

The liquid flows output from all the separators comprised in the plant are unstable concentrated aromatic hydrocarbons that are fed to the rectifier column for stabilization. The output of the column boiler is the final product of the plant, i.e. concentrated aromatic hydrocarbons, and stabilization gases are output from the top of the rectifier column part of which, after reflux separation, is fed for mixing with the input raw material of at least one reactor in any embodiments of this plant.

The method of processing the vapor phase product output from the primary product separator of the second reactor depends on the required raw material conversion rate, catalyst activity and some other factors and determines specific plant design embodiments. For example, recycling of unconverted raw material requires refining aromatic hydrocarbons from the recycled flows and, possibly, raw hydrocarbons from the plant flue gases. If an adiabatic reactor is used, the recycled flow may contain methane and ethane, but alternatively a C₃-C₄ hydrocarbon fraction can be separated for recycling.

For more complete separation of aromatic hydrocarbons and raw material components, compression and cooling of the vapor phase flow output from the second product flow separator can be used. In this embodiment the plant comprises a compression unit comprising the following devices connected in sequence by pipelines to the vapor phase flow output from the second product flow separator: a compressor for increasing the pressure of the vapor phase flow, a cooler for cooling the compressed flow and condensation of the C₅₊ components, preferably C₃₊, and a vapor-liquid separator for the separation of the vapor-liquid mixture from which the aromatic hydrocarbon containing liquid phase further fed to the rectifier column and a vapor phase flow from which a recycled flow is separated and fed to at least one reactor or flued from the plant are output.

For more complete refining of the recycled flow from aromatic hydrocarbons, the vapor phase flow from the compression unit or the second product flow separator can be fed to the adsorption unit described above. The output of the adsorption unit contains a vapor phase flow depleted of aromatic hydrocarbons from which a recycled flow is separated and fed to at least one reactor or flued from the plant.

In a plant comprising two aromatic hydrocarbon adsorption units, refined gas of the final unit can be used as a blowout gas for adsorbent regeneration.

If unconverted raw hydrocarbons, usually propane, should be separated from the flue gas, the plant comprises a propane adsorption unit or a propane absorption unit.

In the former of these two embodiments, at least part of the vapor phase flow refined from aromatic hydrocarbons output from the aromatic hydrocarbon adsorption unit is fed to the absorption column the absorbent of which is the consumable gasoline fraction cooled in the cooler of the adsorption unit, or stable gasoline Cs₊ or its fraction, that are separated in the head rectifier column of the plant from the raw material. The absorber output contains a hydrogen containing gas refined from propane and butane that is fed for hydrogen separation or used as a fuel, and the absorbent saturated with C₃ and C₄ hydrocarbons. The saturated absorbent is fed to the sequence pipeline connected absorbent heater and saturated absorbent rectification column the output of which contains the stable absorbent that is fed to the heat exchanger and the cooler for cooling and absorbent stabilization gases at least part of which is mixed with the raw material for at least one reactor. Thus, the absorbent is circulated in the absorption unit within a circuit comprising the sequence pipeline connected heat exchanger and absorbent cooler, the absorption column, the saturated absorbent heater and the rectifier column. The absorption unit input is the flow output from the adsorption unit depleted of aromatic hydrocarbons containing C₃-C₄ hydrocarbons and an absorbent infeed, and the output of this unit is a dry hydrogen containing gas as a plant product and a flow of raw hydrocarbons further mixed with the raw material of at least one reactor. If the absorbent is the gasoline fraction separated by the plant, the saturated absorbent is fed for stabilization to the head rectifier column, and the raw hydrocarbons so separated are fed to the first reactor.

The propane adsorption unit comprises an adsorber or adsorbers and adsorbent regeneration equipment. The propane adsorption unit input is at least part of the gas output from the aromatic hydrocarbon adsorption unit refined from aromatic hydrocarbons. The output of this unit is a dry hydrogen containing gas as a plant product and a flow of raw hydrocarbons further mixed with the raw material of at least one reactor. The structure and operation of the propane adsorption unit and the aromatic hydrocarbon adsorption unit are similar.

C₃4- components can be adsorbed from a hydrogen containing mixture of C₁-C₄ hydrocarbons using known adsorbents such as activated charcoal, silica gel and zeolites. Adsorption is achieved in conventional adsorbers. The adsorption conditions depend on the properties of the sorbent used and are preferably identical to the parameters of the flow being refined.

The flow output from the aromatic hydrocarbon adsorption unit or part thereof after the separation of the recycled flow is fed to the adsorber, preferably, without preparation, and the vapor phase flow output from the adsorber is depleted of C₃₊ hydrocarbons and contains mainly hydrogen, methane and ethane, i.e. is a dry hydrogen containing gas.

The sorbent saturated with the adsorbed hydrocarbons is regenerated by raising the adsorber temperature and simultaneously blowing the adsorber with part of the vapor phase flow depleted of aromatic hydrocarbons output from another adsorber (blowout gas). The desorbed aromatic hydrocarbons are separated from the saturated blowout gas containing less noncondensable components than in the flow input for adsorption, and their condensation can therefore be achieved with smaller losses.

In regeneration mode, the adsorber is blown with heated blowout gas, i.e. part of the vapor phase flow depleted of C₃₊ hydrocarbons output from another adsorber, and the blowout gas saturated with the desorbed hydrocarbons is output from the adsorber. For adsorbent regeneration the plant comprises a blowout gas heater and heat exchangers and coolers connected in sequence by pipelines to the adsorber output and used for the cooling and condensation of C₃₊ hydrocarbons contained in the saturated blowout gas, as well as a separator for the separation of the vapor-liquid mixture from which a liquid phase flow containing C₃₊ hydrocarbons further fed to the rectifier column and a vapor phase flow further mixed with the vapor phase flow depleted of aromatic hydrocarbons output from another adsorber are output.

Combinations of the product separation units described hereinabove provide for the multiple design embodiments of the plant for the production of aromatic hydrocarbons from raw materials of various composition. In all the embodiments the plant provides for an increase in the stable operation lifetime of the catalyst used in two reactors compared to a single-reactor design for the same quantity of catalyst and similar raw material conversion rate. The raw material and product losses will depend on the method and conditions of product separation.

Figure 1 shows a simplified schematic of the plant for the production of aromatic hydrocarbons from the Ci-C₄ hydrocarbon fraction containing propane, butane and butylene that illustrates the advantages of the plant for the simplest product separation method. Only liquid product stabilization gases are used as a recycled flow in this plant.

The raw materials are mixed with the recycled flow, heated in the recovery heat exchanger H-I and furnace F-I and fed to the dehydrocyclodimerization reactor R-I where they are exposed to the catalyst at a reactor output temperature of 46O⁰C and 1.8 MPa with a butane conversion rate of 80% and a propane conversion rate of 23%. The first product flow containing hydrogen, methane, ethane, propane, butane and aromatic hydrocarbons is output from the reactor. This flow is cooled in the heat exchanger H-I and coolers C-I and C-2, and fed to the vapor-liquid separator for separation into a liquid phase flow containing Cβ₊ hydrocarbons and solute gases and a vapor phase flow that is further heated in the recovery heat exchanger H-2 and furnace F-2 and fed to the dehydrocyclodimerization reactor R-2 where it is exposed to the catalyst at a reactor output temperature of 610⁰C and 1.6 MPa with a propane conversion rate of 70%. The second product flow containing hydrogen, methane, ethane, propane and C₆₊ hydrocarbons is output from the reactor R-2, cooled in the heat exchanger H-2 and coolers C-3 and C-4, and fed to the vapor-liquid separator S-2 for separation into a liquid phase flow containing C₆₊ hydrocarbons and solute gases and a vapor phase flow that is removed from the plant. The liquid phase flows output from the separators S-I and S-2 (the pump at the output of the separator S-2 is not shown) is fed to the rectifier column RC-I. The column boiler is heated with the evaporator H-3, and cold reflux is fed to the column with the pump P-I from the reflux tank T-3. The vapors output from the column top are cooled in the cooler C-5 and fed for mixing with the raw material by the circulating compressor CC-I. The final products of the plant output from the column are concentrated aromatic hydrocarbons used as a high-octane gasoline component. The stable operation lifetime of the catalyst in this plant is 1.3 times longer than for a single-reactor plant converting the same raw material with the same quantity of catalyst.

Figure 2 shows schematic of the plant for the production of aromatic hydrocarbons from the long distillate of light hydrocarbons containing 20% C₅₊ components and a butylene hydrocarbon fraction containing 50% C₃H₆ and 50% C₄H₈. The plant comprises a rectifier column for the separation of the C₅₊ components from the long distillate of light hydrocarbons, a reactor for raw material refining from sulfur, two dehydrocyclodimerization reactors, a concentrated aromatic hydrocarbon stabilization rectifier column, a compression unit of vapor phase flow of the first product separation of second rector products, two aromatic hydrocarbon adsorption units comprising two adsorbers each that accomplish the adsorption and desorption (regeneration) cycles in an alternating manner, an a unit for the absorption of C3₊ components from the plant flue gas. The plant provides for recycling of the concentrated aromatic hydrocarbon stabilization gases to the second reactor and recycling of the gases separated from the second product flow and refined from aromatic hydrocarbons in the second adsorption unit. The plant uses flue gas heated isothermal tubular reactors, two in each unit, operating in reaction and regeneration modes in an alternating manner thus providing for an uninterrupted process (only one reactor in reaction mode is shown in the Figure). The catalyst contains 65% Al₂O₃, 33% ZSM-5 type zeolite in decationized form and 2% ZnO applied into the catalyst by impregnation.

The long distillate of light hydrocarbons is fed from the raw material tank T-I with the pump P-I to the heat exchanger H-I, and the flow heated to 120⁰C at 1.6 MPa is fed to the rectification column RC-I the boiler of which is heated using the thermosyphon type evaporator E-I. The middle distillate containing mainly the C₅ and Ce hydrocarbons is output from the column, cooled in the cooler C-2 and fed to the storage. At 235⁰C₅ the gasoline fraction is output from the column boiler containing mainly the C^₊ hydrocarbons part of which is used as absorbent in the absorption unit. From the top of the column, vapors at 63⁰C are output, cooled in the cooler C-I and then the condensate from the reflux tank T-3 is fed with the pump P-2 for column cold reflux, and the vapors containing the C₃ and C₄ hydrocarbons are mixed with part of the olefin containing raw material and the recycled flow, heated in the H-2 heat exchanger and fed to the ZnO filled refining reactor RR where it is refined from sulfur at 300⁰C and 1.2 MPa. The refined raw material fraction is heated in recovery heat exchangers H-3 and H-4 and fed to the reactor R-I where it is exposed to the catalyst at 55O⁰C and 1.1. MPa with a 50% propane conversion rate and a 93% butane conversion rate. The first flow is output from the reactor R-I, cooled to -5⁰C in the heat exchangers H-3 and H-2, the air cooler AC-I, the water and propylene coolers C-3 and C4 and the heat exchanger H-5, and then a liquid phase flow is output from the vapor-liquid separator S-4 at 0.83 MPa containing mainly aromatic hydrocarbons and a vapor phase flow containing hydrogen, C₁-C₄ hydrocarbons, including unconverted raw hydrocarbons, and aromatic hydrocarbons, said flow containing about 33% of aromatic hydrocarbons produced in the first reactor. The liquid phase flow output from the separator with the pump P-3 is fed to the rectifier column RC-2 for the stabilization of concentrated aromatic hydrocarbons. The vapor phase flow is mixed with the concentrated aromatic hydrocarbon stabilization gases and fed to the activated charcoal filled adsorber 1 of the first adsorption unit operating in aromatic hydrocarbon adsorption mode. The adsorption occurs at -4° C and 0.82 MPa. The adsorber output is a flow depleted of aromatic hydrocarbons that is further heated in the heat exchanger H-5, mixed with part of the olefin containing raw material and the recycled flow, i.e. the vapor phase output from the liquid product degassing tank T-10, heated in the recovery heat exchangers H-6 and H-7 and fed to the dehydrocyclodimerization reactor R-2. The raw material is exposed to the catalyst at 600⁰C and 0.66 MPa₅ the propane conversion rate being 70%. The second product flow is output from the reactor, heated in the heat exchanger H-6 and then in the air cooler AC-2 and the water cooler C-5 to 40⁰C, and the resultant vapor-liquid mixture is fed to the vapor- liquid separator S-5. The separator output is a liquid phase flow mainly containing aromatic hydrocarbons that is fed to the rectifier column RC-2 with the pump P-4. The vapor phase flow output from the second product flow separator at 40⁰C and 0.5 MPa contains 9.3% aromatic hydrocarbons or about 65% of their content in the second product flow and is fed to the compression unit comprising compressor buffer tanks T-6 and T-7, compressor CC-I₅ coolers C-6 and C-7, heat exchanger H-8 for compressed flow cooling to -5⁰C and separator S-8. The liquid phase flows output from the compression unit are fed to the degassing tank T-10 and then with the pump P-5 to the rectifier column RC-2. The vapor phase flow output from the separator S-8 at -5⁰C and 1.44 MPa contains 0.85% aromatic hydrocarbons or 5.5% of their content in the second product flow and its further refining in the second aromatic hydrocarbon adsorption unit. The vapor phase flow output from the separator S-8 is fed to the adsorber 3 from which a flow depleted of aromatic hydrocarbon is output and further separated into the recycled flow that is heated in the heat exchanger H-8 and mixed with the first reactor raw material before the sulfur refining reactor heater. Part of the flow output from the second adsorption unit is heated in heat exchangers H-9 and H- 10 and fed as a blowout gas to the adsorbers 2 and 4 operated in desorption mode. The aromatic hydrocarbon saturated blowout gases from both adsorbers are cooled to -5°C in the heat exchangers H-9 and H-IO and the coolers C-8 and C-9 and fed to the vapor-liquid separator S-9 the output vapor phase flow of which is mixed with the gas separated from the second aromatic hydrocarbon adsorption unit, and the liquid phase flow output from the separator is fed to the liquid flow degassing tank T-IO. The balance quantity of the aromatic hydrocarbon depleted flow from the second aromatic hydrocarbon adsorption unit is refined from the C₃₊ components in the adsorber A-3. The absorbent is the part of the gasoline fraction output from the column boiler RC-I at 1.35 MPa and cooled to -5°C in the heat exchanger H- 12 and the propylene cooler C-10, and the output from the column and the plant is a hydrogen containing gas containing 3.7% C₃4- components, mainly propane. The raw material component losses in this plant are 1.78% ort 2.78% for paraffins. The C₃₊ component saturated absorbent is fed with the pump P-6 to the heat exchanger H- 12 and then for mixing with the long distillate of light hydrocarbons for stabilization in the rectifier column RC-I. The liquid phase flows output from all the separators are heated to 120°C in the heat exchanger H- 13 and then fed at 1.6 MPa to the rectifier column for the separation of the plant final product, i.e. concentrated aromatic hydrocarbons. From the top of the column, vapors are output at 6I⁰C and cooled in the cooler C-I l, reflux is output from the reflux tank T- 11 to the column with the pump P-7, and the stabilization gases and fed for mixing with the second reactor raw materials and the vapor phase flow output from the first product flow separator fed to the adsorption unit, the column boiler is heated with the column thermosyphon evaporator E- 14, and the stable concentrated aromatic hydrocarbons are output from the bottom of the column and fed for storage through the heat exchanger H- 13 and the cooler C- 12.

Claims

What is claimed is a

1. Plant for the production of concentrated aromatic hydrocarbons from C₃ and C₄ hydrocarbon containing raw materials comprising sequence pipeline connected raw material heater, reactor for exposing the heated raw material to the dehydrocyclodimerization reaction catalyst under the conditions of conversion of max. 70% propane and min. 80% butane from which the first flow of products containing hydrogen, methane, ethane, raw hydrocarbons and aromatic hydrocarbons are output, heat exchangers and coolers for product flow cooling and condensation of the C₅₊ hydrocarbons, a vapor-liquid separator for the separation of the vapor-liquid mixture from which a vapor phase flow containing hydrogen, methane, ethane and mainly raw hydrocarbons and a liquid phase flow containing the aromatic hydrocarbons are output and a rectifier column for the stabilization of the liquid phase flow containing the aromatic hydrocarbons from which the concentrated aromatic hydrocarbons and the stabilization gases of the concentrated aromatic hydrocarbons are output, wherein said plant further comprises the following sequence pipeline connected devices for the production of aromatic hydrocarbons from raw hydrocarbons contained in said vapor phase flow output from the separator: a vapor phase flow heater, a second reactor for the exposure of the heated vapor phase flow to the dehydrocyclodimerization reaction catalyst under the conditions of aromatic hydrocarbon production from propane, from which the second product flow containing hydrogen, methane, ethane, raw hydrocarbons and aromatic hydrocarbons are output, as well as heat exchangers and coolers for the cooling of said second product flow and condensation of the C₅₊ hydrocarbons and a vapor-liquid separator for the separation of the vapor-liquid mixture from which a vapor phase flow containing hydrogen, methane, ethane and mainly raw hydrocarbons and a liquid phase flow containing the aromatic hydrocarbons further fed to the rectifier column for stabilization are output.

2. Plant according to Claim I₅ wherein said first reactor allows vapor phase flow exposure to the dehydrocyclodimerization catalyst under the conditions suitable for the conversion of max. 50% propane.

3. Plant according to either of Claims 1 or 2, wherein said second reactor allows vapor phase flow exposure to the dehydrocyclodimerization catalyst under the conditions suitable for the conversion of max. 50% propane fed for the reaction.

4. Plant according to Claim 1, wherein said plant further comprises a rectifier column for C₅₊ component separation from the raw material the top part of which is connected to the first reactor raw material heater for feeding the C₃ and C₄ hydrocarbon containing vapor phase flow after reflux separation.

5. Plant according to Claim 1, wherein said plant further comprises a reactor for sulfur refining from at least part of the raw material allowing the input of heated raw material or its mixture with the recycled flows and the output of the sulfur refined raw material for feeding to the first reactor raw material heater.

6. Plant according to Claim 1, wherein said plant allows processing a raw material flow containing within 5 10^"4 wt.% sulfur of the C₃ and C₄ hydrocarbon content.

7. Plant according to Claim 1, wherein said plant allows mixing olefin containing raw materials with paraffin containing raw materials to obtain a mixture of C₃ and C₄ hydrocarbons containing 25 wt.% olefins.

8. Plant according to Claim 1, wherein said plant allows mixing part of the vapor phase flow output from the second product flow separator and concentrated aromatic hydrocarbon stabilization gases with the raw material of at least one of the reactors.

9. Plant according to Claim 1, wherein said plant further comprises at least one adsorber filled with an adsorbent and selectively adsorbing aromatic hydrocarbons, allowing the input of the vapor phase flow output from the first or second product flow separator and the output of a vapor phase flow depleted of aromatic hydrocarbons containing hydrogen, methane, ethane and raw hydrocarbons.

10. Plant according to Claim 9, wherein said plant further comprises at least two adsorbers further wherein at least one adsorber allows the input of the heated blowout gas, i.e. part of the output flow of the other adsorber depleted of aromatic hydrocarbons, and the output of the blowout gas saturated with aromatic hydrocarbons, further wherein said plant comprises a blowout gas heater and heat exchangers and coolers connected in sequence to the adsorber output and used for the cooling and condensation of aromatic hydrocarbons from the saturated blowout gas, as well as a vapor-liquid mixture separator the output of which contains a liquid phase flow containing aromatic hydrocarbons fed to the rectifier column for stabilization and a vapor phase flow mixed with the output flow of another adsorber depleted of aromatic hydrocarbons.

11. Plant according to Claim 9, wherein said plant further comprises an adsorber for the selective adsorption of aromatic hydrocarbons from the vapor phase flow output from the second product flow separator.

12. Plant according to Claim H₅ wherein said plant allows mixing part of the vapor phase flow output from the second product flow separator and depleted of aromatic hydrocarbons and concentrated aromatic hydrocarbon stabilization gases with the raw material of at least one of the reactors.

13. Plant according to either of Claims 9-11, wherein said plant further comprises an absorber for the refining from C₃ and C₄ hydrocarbon of at least part of the vapor phase flow output from the adsorber and depleted of aromatic hydrocarbons, and absorbent regeneration and circulation devices, wherein said adsorber allows the input of the cooled gasoline fraction as an absorber and the output of a dry hydrogen containing gas and saturated absorbent that is fed to the sequence pipeline connected absorbent heater and saturated adsorbent stabilization rectifier column from which the stable absorbent is output for feeding to the heat exchanger and the cooler for cooling, and absorbent stabilization gases at least part of which is mixed with the raw material of at least one of the reactors.

14. Plant according to Claim 13, wherein said absorber allows the input of part of the C₅₊ component separated from the raw material, as an absorbent, wherein the saturated adsorbent stabilization rectifier column is the rectifier column for C₅₊ component separation from the raw material.

15. Plant according to either of Claims 9-11, wherein said plant further comprises at least one adsorber filled with an adsorbent for C₃₊ hydrocarbon refining allowing the output of a dry hydrogen containing gas.

16. Plant according to Claim 15, wherein said plant further comprises at least two adsorbers, further wherein at least one adsorber allows the input of the heated blowout gas, i.e. part of the output flow of the other adsorber depleted of C₃₊ hydrocarbons, and the output of the blowout gas saturated with C₃₊ hydrocarbons, further wherein said plant comprises a blowout gas heater and heat exchangers and coolers connected in sequence to the adsorber output and used for the cooling and condensation of the C₃₊ hydrocarbons from the saturated blowout gas, as well as a vapor-liquid mixture separator the output of which is a liquid phase flow containing C₃₊ hydrocarbons fed to the rectifier column for stabilization and a vapor phase flow mixed with the output flow of another adsorber depleted of C₃₊ hydrocarbons.

17. Plant according to Claim 1, wherein said plant further comprises the following devices connected in sequence by pipelines to the vapor phase flow output from the first product flow separator: a compressor for increasing the pressure of the vapor phase flow output from the separator, a cooler for cooling the compressed flow and condensation of the C₅₊ components and a vapor-liquid separator for the separation of the vapor-liquid mixture from which the aromatic hydrocarbon containing liquid phase further fed to the rectifier column for stabilization and a vapor phase flow fed to the second reactor heater are output.

18. Plant according to Claim 1, wherein said plant further comprises the following devices connected in sequence by pipelines to the vapor phase flow output from the second product flow separator: a compressor for increasing the pressure of the vapor phase flow output from the separator, a cooler for cooling the compressed flow and condensation of the C₅₊ components and a vapor-liquid separator for the separation of the vapor-liquid mixture from which the aromatic hydrocarbon containing liquid phase further fed to the rectifier column for stabilization and a vapor phase flow fed to the second reactor heater, or flued from the plant or separated for the recycled hydrocarbons flow are output.