CN113149802B

CN113149802B - Method and device for improving dehydrogenation conversion efficiency of fixed bed

Info

Publication number: CN113149802B
Application number: CN202110358359.6A
Authority: CN
Inventors: 卓润生; 谢进宁; 汪石发
Original assignee: Chengdu Runhe Shengjian Petrochemical Engineering Technology Co ltd
Current assignee: Chengdu Runhe Shengjian Petrochemical Engineering Technology Co ltd
Priority date: 2021-04-01
Filing date: 2021-04-01
Publication date: 2024-05-14
Anticipated expiration: 2041-04-01
Also published as: CN113149802A

Abstract

The invention relates to a method and a device for improving dehydrogenation conversion efficiency of a fixed bed, in particular to an improved method and a device for producing olefin by low-carbon alkane through fixed bed dehydrogenation, and belongs to the technical field of petrochemical production. In the invention, the fixed bed reactor is provided with a high-temperature-resistant and thermal shock-resistant nano ceramic coating protective lining; under the conditions of high temperature and micro positive pressure, a reaction bed layer formed by a gamma-alumina catalyst loaded with VIB and IIIB elements and an alumina auxiliary agent loaded with IB and IIA elements is adopted to store heat and supply heat in an intermittent mode of alternate reaction and regeneration; and the heat of dehydrogenation-hydrogenation reaction process is used for coupling, and the heat supply pipes in the bed layers of gas, molten salt and caustic high-temperature heat medium are used for realizing heat balance in the conversion process and temperature balance of the reaction bed layer; the causticizing, temperature difference, thermal cracking and coking side reactions in the reaction process are reduced, and the investment and operation cost are reduced; conversion activity, selectivity, single pass reaction time, running stability and maintainability are improved.

Description

Method and device for improving dehydrogenation conversion efficiency of fixed bed

Technical Field

The invention relates to a method and a device for dehydrogenation conversion of a low-carbon alkane fixed bed, in particular to an improved process method and a reaction device for dehydrogenation production of olefin by the low-carbon alkane fixed bed, and belongs to the technical field of petrochemical production.

Background

The low-carbon olefin is a basic organic raw material with larger demand and wide application range in petrochemical industry, such as propylene is widely used for producing chemical products such as polypropylene, propylene oxide, acrylic acid, acrylonitrile, isopropylbenzene and the like. With the development requirement of clean fuel, the derived product can be used for producing high-octane gasoline components, so that the butene is also developed and utilized, and meanwhile, the butene can also be used for producing chemical products such as polybutene, sec-butyl alcohol and the like.

At present, the oil refining capacity of China is relatively excessive, but the demand for low-carbon olefin resources is still increased. Therefore, measures such as transformation of oil refining to chemical industry and integration of oil refining are improved, and low-carbon olefin is used as basic organic raw material in petrochemical industry and an intermediate product link in transformation of oil refining to chemical industry, so that the production of the low-carbon olefin gradually attracts attention.

Propylene, an important member of the lower olefins, supplies by-products mainly from the naphtha cracking process to ethylene and heavy oil catalytic cracking. Due to the increase of propylene demand, the original propylene source cannot fully meet the actual demand, and the technology for producing propylene by propane dehydrogenation, which is an important production technology for expanding the propylene source, is paid attention to and rapidly developed.

The demand of another important member butene in the low-carbon olefin is also rapidly growing, and a process route for preparing isobutene by using isobutane dehydrogenation is also an important preparation method, and is also paid attention to and rapidly developed in recent years.

The method has the advantages that the method has abundant light hydrocarbon resources such as liquefied petroleum gas, condensate and the like in China, contains a large amount of low-carbon alkane such as propane, butane and the like, and has good basic conditions for developing the technology for producing olefin by dehydrogenating the low-carbon alkane.

Various low-carbon alkane dehydrogenation processes have been developed by research and development institutions at home and abroad, and very representative processes are the Catofin process of ABB Lummus company, the Oleflex process of UOP company, and the like. The technical information of the prior art can be referred to the "process for producing C ₃～C₄ olefins by catalytic dehydrogenation of alkanes" summarized in Xiaojin Tang [ J ]. Natural gas industry, 1994, 14 (2) - (4) and (6).

The Catofin process by Lummus corporation is one of the widely used low-carbon alkane dehydrogenation processes, as described in Graig R G,Delaney T J,Duffalo J M."Catalytic Dehydrogenation Performance of Catofin Process".Petrochemical Review.Houston.Dewitt.1990, and Feldman R J, lee e. "Commercial Performance of the Hourdry Catofin Process"1992, npra.

The core apparatus of the Catofin process is a number of fixed bed reactors, which is similar to the conventional HOUDRY recycle fixed bed process route disclosed in the earlier document USP 2419997. The temperature of the reaction process is about 600 ℃, under the conditions of high temperature, negative pressure or low pressure, propane absorbs a large amount of heat through a bed catalyst to complete dehydrogenation reaction to prepare propylene, meanwhile, along with side reactions such as thermal cracking and the like, the catalyst needs to be regenerated once every more than ten minutes, and the temperature of the catalyst bed is increased at intervals.

A relatively inexpensive and efficient Cr ₂O₃/A1₂O₃ chromium-based catalyst is employed in the Catofin process, as described in USP6486370, USP 6756515. The chromium catalyst of non-noble metal has high selectivity, high alkane conversion rate and small circulation quantity. In recent years, along with the enhancement of environmental protection, nontoxic Mo ₂O₃/A1₂O₃ molybdenum catalysts are also paid attention to and applied, but the conversion activity and selectivity are still to be further improved.

The Catofin process has the advantages of high alkane conversion rate, good product selectivity, strong raw material adaptability, high device online rate and the like; because the circulating multi-reactor system is adopted, more products can be obtained by less raw materials, more reactors can be easily added into the device, the productivity is easily enlarged, and the scale economy is improved.

However, the Catofin process has the obvious defects that the reaction device is operated intermittently, and the product recovery part needs to be pressurized, so the energy consumption of the whole process is high. Since hydrocarbon dehydrogenation reactions are strongly endothermic reactions, adequate heat utilization, heat balance and heat supplementation are very important factors for improving conversion efficiency and reducing energy consumption.

A more common heat balance and reuse method is to make full use of the heat generated during catalyst regeneration, such as CN105120997a, by performing an exothermic catalyst regeneration reaction, transferring the heat to an integrated fluidized bed reactor, and performing an endothermic reaction through at least a portion of the transferred heat to dehydrogenate alkanes.

CN103003221a uses a reaction in the presence of a mixture of inert heat exchange particles and catalyst particles, heats the heat exchange particles in a heating zone and returns to the reaction zone to provide the desired heat of reaction, and the catalyst is regenerated in a non-oxidizing atmosphere, which is difficult to use in a fixed bed reaction apparatus.

In order to improve the thermal efficiency of the intermittent heat storage-reaction mode in the conventional fixed bed reactor, in some recent technical reports, reports of using a heat generating material as an auxiliary agent in a catalyst reaction bed have been disclosed. As disclosed in USP0259265A1, CN106029612A, USP7973207B2, USP7622623B, USP5108973, etc., a method for utilizing a heat generating material in an endothermic dehydrogenation process of alkanes, in which a heat generating material having a metal element such as copper, manganese, etc., supported on alumina is used in addition to a catalyst and inert α -alumina, including reacting hydrocarbons with a multicomponent catalyst bed and regenerating the catalyst bed with air, wherein the air and hydrocarbons used in the regeneration step are of a low air/hydrocarbon ratio and a pressure close to atmospheric pressure, improving the efficiency.

The use of heat in the exothermic reaction is clearly a good means of heat reuse, as CN101061084a in the catalytic dehydrogenation of light paraffins to produce olefins, by fully hydrogenating all of the unsaturated hydrocarbons contained in the whole hydrocarbon stream prior to introduction into the dehydrogenation reactor, thereby leaving the energy released in the exothermic hydrogenation substantially fully in the hydrocarbon stream, and therefore reducing the energy consumption for preheating the reactant stream to the reaction temperature, and the formation of coke in the dehydrogenation reactor is also significantly reduced.

CN103772093A is used for carrying out alcohol dehydrogenation and low-carbon olefin hydrogenation in a tubular reactor in parallel, heat released by the olefin hydrogenation is supplied to the alcohol dehydrogenation for heat absorption, the heat absorption and the heat release of the two reactions are well matched to achieve balance, the heating and cooling processes are omitted, the process flow is simplified, the device investment and the operation cost are saved, the coke generation is reduced, the service life of the catalyst is prolonged, the heat exchange technology of two simultaneous reaction processes is well utilized, the efficiency is improved, and the process and the device equipment are simplified.

Furthermore, CN106365936a discloses a tubular hydrogen selective permeable membrane module reactor, which performs alcohol liquid phase dehydrogenation reaction and hydrogen gas phase oxidation reaction on two sides of the membrane respectively, that is, hydrogen as a dehydrogenation reaction product permeates out of the reaction system in time, so that the reaction rate is improved, the equilibrium conversion rate of the reaction is also improved, and the permeation side can provide heat for dehydrogenation by controlling the rate of oxidation reaction, so that the heat exchange efficiency is further improved, and the purpose of in-situ heat supply is achieved.

CN101165031a discloses a zoned alkane dehydrogenation process wherein a portion of the alkane is exothermically converted to alkene by oxidative dehydrogenation in the presence of oxygen and a catalyst in an exothermic reaction zone, and then the product of the exothermic reaction zone is passed into the endothermic reaction zone of the reactor, and at least a portion of the remaining unconverted alkane is endothermically dehydrogenated in the presence of carbon dioxide and other catalysts. Similarly, CN106986736a also used a similar zoned thermal coupling method during the oxidative coupling of methane.

However, the method of carrying out heat coupling by partition reaction fundamentally reduces the efficiency of heat utilization, so the prior art center also discloses a technique of carrying out heat recycling in situ and time-division, for example, CN107074683A discloses a process for catalytic dehydrogenation of alkane into alkene, cr ₂O₃ is used as a catalyst, CO is introduced as a reducing gas to reduce the catalyst during the reduction process, CO reduces CuO components in the catalyst to form Cu and CO ₂ and releases heat, and CO ₂ generated by reduction can also react with H ₂ generated by dehydrogenation to form CO and H ₂ O. But in-situ time-phased heat reuse is certainly similar in nature to intermittent heat storage.

The difference in the thermal effects of the two reactions is clearly the most desirable way to carry out the thermal coupling in situ in real time, as CN107223119a discloses a process for converting paraffins, especially light paraffins such as C ₃～C₈ paraffins, to higher boiling range liquid paraffins comprising the endothermic dehydrogenation of the light paraffins and thermal coupling in combination with an exothermic reaction such as olefin oligomerization to provide heat for the endothermic conversion reaction.

In addition, besides the report of reducing the load of the heating furnace by the front-end electric heating pipe disclosed in the prior art, the electric heating pipe built in the catalyst bed is also mentioned in the prior art, and CN104072325A discloses a method for improving the dehydrogenation reaction performance of the low-carbon alkane, which adopts the front-end electric heating pipe in the dehydrogenation process and simultaneously installs the fixed bed reactor of the electric heating pipe in the reaction bed, so as to provide heat for the catalyst in the dehydrogenation reaction process of the low-carbon alkane, reduce the temperature drop of the catalyst bed caused by strong endothermic dehydrogenation reaction, reduce the thermal load of the electric heater in front of the reactor, thereby reducing the thermal cracking of the low-carbon alkane in the electric heater, finally improving the dehydrogenation reaction performance of the low-carbon alkane, increasing the yield of the target product alkene, but the high temperature of the surface of the electric heating pipe also aggravates the generation of coking.

In other industries and fields, application reports of high-temperature molten salt heat medium are presented, such as CN107177348A discloses a metal-carbonic acid molten salt material with high heat conduction, and the metal-carbonic acid molten salt material is considered to have good application prospect in the fields of renewable energy sources, high-temperature industrial waste heat recovery and the like; CN107034386a discloses a high-temperature composite material for resisting molten salt corrosion and a reactor core structural member of the molten salt reactor, and has good application prospect; CN103911126A, CN101289612a and CN101508888a both disclose a carbonic acid molten salt heat transfer and storage medium, which can meet the working temperature range required by the solar thermochemical reactor, and has good thermal stability and large phase change latent heat. However, similar prior art reports are not yet available in the technical field of alkane dehydrogenation processes and devices.

Although various improved processes and catalysts are reported in the prior art, due to pressure drop difference caused by catalyst filling, unavoidable factors such as material bias flow caused by process piping exist, when low-carbon alkane is dehydrogenated on a catalyst surface active site, the temperature distribution and temperature drop of a catalyst bed cannot be uniform along with a strong endothermic process, the service life of the catalyst and the product yield of the low-carbon alkene are seriously affected, the process cannot be satisfactory in the aspects of severity, stability, operability, operation period and the like, and further continuous improvement and improvement are required.

Disclosure of Invention

In the catalytic dehydrogenation reaction, the process of converting lower alkanes such as propane, butane and the like into olefins is an endothermic reaction with increased molecular numbers, and the high temperature and low pressure are favorable for the reaction from the chemical thermodynamics point of view. In the dehydrogenation of light alkanes, frequent regeneration of the catalyst is required while providing the required heat.

Therefore, the fixed bed low-carbon alkane dehydrogenation process adopts a circulation mode, hydrocarbon materials are dehydrogenated in a full circulation period, the inside of the reactor is cleaned by steam, purged by air, the catalyst is preheated, a small amount of coke deposited on the catalyst is burned off, and then the reactor is vacuumized and restored to start another circulation.

However, the too high and uneven reaction and regeneration temperature of the reactor bed layer and the too strong cracking reaction of the reaction system can cause the reduction of the selectivity of the dehydrogenation reaction products, and the carbon deposition speed of the catalyst bed layer can be increased, thereby reducing and even inactivating the conversion performance of the whole reaction system.

Therefore, in the process of dehydrogenation conversion of the fixed bed low-carbon alkane, the catalyst bed layer is balanced in heat quantity during reaction and regeneration as much as possible, the temperature of the catalyst bed layer is kept uniform, the reaction severity is reduced as much as possible, and the catalyst bed layer is a key factor for keeping high efficiency and stability during the reaction process of preparing the low-carbon alkane by dehydrogenation of the alkane.

The invention aims to overcome the defects in the prior art, improve the temperature distribution of a catalyst bed layer of a fixed bed reactor, reduce the reaction and regeneration severity, inhibit side reaction, improve the product yield, and provide an improved fixed bed low-carbon alkane dehydrogenation process method which comprises a conversion method comprising reaction and heat coupling, and an improved conversion catalyst and an auxiliary agent.

Another technical problem to be solved by the present invention is to provide a low-carbon alkane dehydrogenation device capable of meeting the above reaction and regeneration requirements during dehydrogenation reaction, comprising an improved dehydrogenation conversion reactor.

The invention provides a low-carbon alkane dehydrogenation conversion reaction system comprising a reactor, a process device, reaction materials, a catalyst, an auxiliary agent and a bed heating pipe while solving the problems.

Accordingly, in view of the above, the present invention provides a fixed bed dehydrogenation process for light paraffins which is improved to enhance conversion efficiency, and specifically comprises:

The invention relates to a dehydrogenation conversion method of a low-carbon alkane fixed bed, which is characterized in that a reaction bed layer formed by a gamma-alumina catalyst loaded with VIB and IIIB elements and an alumina auxiliary agent loaded with IB and IIA elements is adopted in a high-temperature micro-positive pressure fixed bed reactor, and heat is stored and supplied in an intermittent mode of alternate reaction and regeneration; the heat of dehydrogenation-hydrogenation reaction process is coupled with a heating pipe in a high-temperature heat medium bed layer of an external heat source, so that heat balance in the conversion process and temperature balance of a reaction bed layer are realized; dehydrogenation of C ₃～C₅ light alkane to light alkene.

The invention relates to a fixed bed dehydrogenation conversion method of low-carbon alkane, which comprises the following specific steps:

(1) Preheating C ₃～C₅ low-carbon alkane feed gas, CO and/or CO ₂ gas at 200-500 ℃;

(2) The catalyst is put into a reactor to be contacted with gamma-alumina dehydrogenation catalysts of VIB and IIIB elements, alumina auxiliaries of IB and IIA elements and inert alumina balls of a heat storage/support body, and dehydrogenation conversion is carried out under the reaction conditions that the reaction temperature is 550-700 ℃, the reaction pressure is 0.1-0.15 MPa, the reaction time is 10-30 minutes and the mass space velocity (WHSV) is 0.1-5 hours ^-1;

(3) The low-carbon olefin and byproducts generated by the reaction and conversion enter a subsequent washing and separating device to obtain the low-carbon olefin, hydrogen-rich gas and fuel gas, and unconverted low-carbon alkane returns to the reactor;

(4) The conversion process comprises a periodic regeneration process of a catalyst bed, after steam purging, hot air with the temperature of 560-730 ℃ and the pressure of 0.01-1 MPa is introduced to regenerate and heat the bed, and the bed is evacuated and reduced, wherein the cycle time of each cycle is 15-70 minutes; the reduction process comprises treating the catalyst bed with a hydrogen-rich gas, and the reduction treatment is carried out by separating the hydrogen-rich gas, which can also be conveniently provided by commercially available hydrogen.

The invention relates to a low-carbon alkane fixed bed dehydrogenation conversion method which is characterized in that the preferable reaction process is carried out in the micro positive pressure range of 560-620 ℃ and 0.103-0.105 MPa, the preheating temperature of raw materials and CO and/or CO ₂ gas is 300-450 ℃, the reaction time is 18-25 minutes, and the dehydrogenation reaction conversion is carried out under the conditions of 0.3-2 hours ^-1 of mass airspeed (WHSV). The preferable regeneration condition is that hot air with the temperature of 600-700 ℃ and the pressure of 0.05-0.5 MPa is introduced during regeneration, and the cycle time of each cycle is 30-40 minutes.

The invention relates to a dehydrogenation conversion method of a low-carbon alkane fixed bed, which is characterized in that the heat coupling process of the reaction process is realized by carrying out exothermic reaction on CO and/or CO ₂ gas accounting for 1-20 m% of the total amount of raw materials and hydrogen generated in the reaction process, and the preferential proportion is CO and/or CO ₂ gas of 1.5-5 m%; facilitating the progress of the process by its hydrogenation reaction with the dehydrogenation product H ₂ during the conversion process; the raw material gas for heat coupling can be provided by separating the flue gas of the process and returning the separated flue gas to the reactor, and can also be conveniently obtained by commercially purchased CO and CO ₂.

The invention relates to a fixed bed dehydrogenation conversion method of low-carbon alkane, which is characterized in that the catalyst contains 15-30 m% of Cr ₂O₃, 0.1-5 m% of rare earth element and 65-80 m% of gamma-Al ₂O₃; the chromium-based catalyst has good conversion activity and product selectivity.

The invention provides a low-carbon alkane fixed bed dehydrogenation conversion method which is characterized by also providing a chromium-free catalyst, wherein the catalyst contains 15-30 m% of Mo ₂O₃, 0.1-5 m% of rare earth elements and 65-80 m% of gamma-Al ₂O₃; molybdenum-based catalysts are inferior to chromium-based catalysts in dehydrogenation conversion performance, but are superior to chromium-based catalysts in terms of environmental protection and safety because of their non-toxicity.

The invention relates to a dehydrogenation conversion method of a low-carbon alkane fixed bed, which is characterized in that the auxiliary agent contains 5-30 m% of CuO, 10-35 m% of CaO and 50-80 m% of Al ₂O₃, is arranged in a bed layer in an amount of 1-25 v% of the total volume of the catalyst bed layer, and is selectively arranged in a bed layer area with insufficient heat.

The invention provides a process method for dehydrogenating low-carbon alkane, which is characterized in that the time ratio of dehydrogenation reaction, steam blowing, heating of catalyst bed and vacuumizing/reduction reaction in a single reaction-regeneration cycle is (20-22.5): 3:9:3.

In the dehydrogenation process method of the low-carbon alkane, the low-carbon alkane refers to small-molecular alkane of C ₂～C₅ and is also called alkane; preferably refers to a C ₃～C₄ lower alkane; more preferred are one or more of propane, isobutane and n-butane, which are commercially available.

In the dehydrogenation process method of the low-carbon alkane, the filling volume ratio of the dehydrogenation catalyst, the auxiliary agent, the inert alumina balls serving as a heat accumulator and the inert alumina porcelain balls serving as a support is 1 (0.1-0.2) (0.4-0.7) (0.4-0.6); the preferable filling volume ratio is 1 (0.15-0.18): (0.5-0.6): (0.45-0.55). The inert alumina balls as heat accumulator and the inert alumina porcelain balls as support have the composition of Al ₂O₃ -99.5 m%, heat capacity of 0.2-0.35cal/g deg.c, and preferably 0.25-0.32 cal/g deg.c, and the highest use temperature of 1400 deg.c, and may be obtained through commercial purchase.

In the dehydrogenation process method of the low-carbon alkane, the catalyst and auxiliary agent filling and arranging, steam blowing, evacuating and reducing processes are conventional in the field and are well known and routinely applied by those of ordinary skill in the art.

The invention relates to a dehydrogenation conversion method and a dehydrogenation conversion device for a low-carbon alkane fixed bed, which are characterized in that a high-temperature heat medium of a heating pipe in an external heat source high-temperature heat medium bed is selected from gas, molten salt and caustic alkali; molten salt is preferred; the difficulty of molten salt selection is that it must be able to meet and match the heat balance requirements of the reaction process, as well as to accommodate the requirements of the reaction apparatus.

The invention also provides a low-carbon alkane fixed bed dehydrogenation conversion device which is characterized by comprising a raw material preheating furnace and an air preheating/heating furnace and being connected to a reactor through pipelines; 3-6 parallel fixed bed reactors are alternately in the reaction, regeneration and purging states; a series separation device connected to the outlet of the reactor for washing and separation of the reaction products; the compression and gasification equipment connected in the pipeline is used for compressing, circulating and gasifying hydrocarbon and air respectively; the heat exchange, condensation equipment and the waste heat boiler in the process pipeline are respectively used for heat exchange, condensation and heat recovery of raw materials, reaction coupling gas, products and exhaust gas entering and exiting the reactor.

The invention provides a method and a device for dehydrogenation and conversion of a low-carbon alkane fixed bed, which are characterized in that the fixed bed reactor comprises a shell and a catalyst reaction bed layer arranged in the shell; the shell is of a hollow metal structure and is connected with the end cover and the steel cylinder body through flanges; the protective lining is provided with an outer heat-insulating layer, a high-temperature-resistant thermal shock-resistant nano ceramic coating; a catalyst bed layer formed by a catalyst and an auxiliary agent is filled above the supporting space in the cylinder body; a multi-point thermocouple and a high-temperature heat medium heating pipe are arranged in the bed layer, and the heating pipe is connected to a heating furnace outside the reactor through an inlet pipeline and an outlet pipeline after being integrated in an end cover area; the material inlet is connected with the reactor from the upper part, and the material outlet is connected with the reactor from the lower part.

The invention also provides a low-carbon alkane dehydrogenation reaction system which is characterized by comprising heating equipment, a reactor, separation equipment, reaction raw materials, reaction coupling gas, a catalyst, an auxiliary agent, a heat accumulator inert alumina ball and a support inert alumina porcelain ball; in the dehydrogenation reaction stage, low-carbon alkane and reaction coupling gas enter a reactor from the top of the reactor after being preheated, are contacted with a dehydrogenation catalyst and a heat supply auxiliary agent, and a heat accumulator inert alumina ball is contacted with a support inert alumina porcelain ball, and are subjected to dehydrogenation conversion reaction and heat coupling reaction under the reaction conditions of high temperature and micro positive pressure, and heat balance in the conversion process and temperature balance of a reaction bed layer are realized by a high-temperature heat medium heating pipe; discharging the converted product after the reaction to connected back-stage washing and separating equipment from the bottom of the reactor to separate low-carbon olefin, hydrogen-rich gas and fuel gas; returning unconverted low-carbon alkane to the reactor; in the regeneration stage, the feeding is stopped, steam is used for blowing, heated hot air enters the reactor from the top of the reactor to regenerate the catalyst bed, and the temperature of the bed is increased to store heat.

It is well known to those skilled in the art that the process, apparatus and reaction system comprising catalyst and promoter constitute the aspects, systems and features of the present invention and are distinguished from the prior art as the most important factors affecting the catalytic conversion of hydrocarbons, since the mutual influence is subject to great uncertainty, it is difficult to obtain direct teaching from the prior art, and it is difficult to obtain the expected results by simple permutation and combination tests on the basis of the prior art, and systematic research and exploration is required to obtain valuable results.

The alkane dehydrogenation reaction process, device and reaction system provided by the invention have higher heat and reaction coupling conversion performance, and can ensure that the temperature distribution of the reaction process and the catalyst bed is more balanced and uniform, thereby slowing down the severe temperature difference of the bed caused by factors such as poor pressure drop of the bed, bias flow of materials, strong heat absorption and the like, reducing and eliminating local hot spots, and inhibiting the generation of side reactions and coking.

The invention reduces the temperature of the regenerated air inlet or the regenerated air flow, thereby reducing the energy consumption of the device; the temperature of the inlet of the reactor is reduced, the thermal cracking side reaction possibly occurring in the pipeline from the outlet of the heating furnace to the bed layer of the reactor is reduced, the heat dissipation loss is reduced, the material consumption is reduced, and the investment requirement on equipment is reduced.

The invention reduces the highest temperature of the bed and the deactivation probability of the catalyst at the top of the bed on the premise of keeping the total heat unchanged, reduces the temperature drop in one reaction period, and can improve the selectivity under the condition of keeping the conversion rate unchanged, so the invention synergistically improves the stability of the alkane dehydrogenation reaction process and the product yield of the low-carbon olefin, prolongs the service life of the catalyst, and is beneficial to the long-period operation and running of the dehydrogenation process. Furthermore, the present invention improves investment, operating costs and maintainability by the improved method and apparatus described above.

Drawings

FIG. 1 is a schematic flow chart of a process for dehydrogenating light alkane.

In fig. 1: 1-a reactor; 2-a raw material heating furnace; 3-a washing tower; 4-a flash column; 5-a reaction gas compressor; 6-waste heat recovery; 7-lower alkane feedstock; 8-circulating low-carbon alkane; 9-CO/CO ₂ gas; 10-product gas; 11-fuel gas; 12-water vapor; 13. reducing gas; 14-regeneration gas; 15-softening water; 16-oily sewage.

FIG. 2 is a schematic structural diagram of a fixed bed reactor for dehydrogenating light paraffins.

In fig. 2: 17-catalyst bed; 18-a heat supply pipe; 19-a high temperature hot air inlet; 20-multipoint thermocouple; a 21-steam-CO/CO ₂ gas-reducing gas inlet; 22-lower alkane feed inlet; 23-hydrocarbon product outlet; 24-waste heat air outlet; 25-evacuation-emergency exit; 26-reactor steel shell; 27-reactor end caps; 28-high temperature heat medium inlet/outlet; 29-a connection flange; 30-a high temperature resistant reactor liner; 31-a thermal insulation coating outside the reactor; 32-a support space within the reactor.

Detailed Description

The following describes a low-carbon alkane fixed bed dehydrogenation conversion method, a low-carbon alkane fixed bed dehydrogenation conversion device and a specific embodiment of a low-carbon alkane dehydrogenation reaction system comprising a reaction device, reaction materials, a catalyst and an auxiliary agent with reference to the accompanying drawings.

FIG. 1 is a schematic flow chart of a fixed bed dehydrogenation conversion method of low-carbon alkane, and also a schematic diagram containing the contents of a fixed bed dehydrogenation conversion device and a reaction system of low-carbon alkane.

FIG. 2 is a schematic diagram of a fixed bed dehydrogenation conversion reactor for light alkane.

In a fixed bed dehydrogenation conversion unit for light alkanes, as shown in fig. 1, the unit comprises: a raw material preheating furnace, an air preheating furnace and a heating furnace are connected to the reactor through process pipelines; 3-6 parallel fixed bed reactors are alternately in the reaction, regeneration and purging states; a series separation device connected to the outlet of the reactor for washing and separation of the product; the compression and gasification equipment connected in the pipeline is used for compressing, circulating and gasifying air, products, process gas and fuel gas respectively; in addition, the heat exchange and condensation device and the waste heat boiler are connected in the pipeline and are respectively used for heat exchange, condensation and heat recovery of raw materials, products and circulating materials.

In the alkane dehydrogenation process method, the reaction conversion process comprises the following steps: the low-carbon alkane raw material gas 7 and CO/CO ₂ gas 9 accounting for 1-20m percent of the low-carbon alkane raw material are heated to 200-500 ℃ through a process pipeline system and a heat exchange and preheating 4 and a heating furnace 2, and then enter a reactor 1 in a reaction state from the top parts 21 and 22 of the reactor; unconverted lower alkane 8 is also fed into the reactor 1 together with fresh feedstock 7; is contacted with a chromium alumina dehydrogenation catalyst, an auxiliary agent and inert alumina balls as a heat accumulator and inert alumina porcelain balls as a support in the fixed bed reactor 1.

The reaction and the conversion are carried out under the reaction conditions of 500-700 ℃ of reaction temperature, 0.1-0.15 MPa of reaction pressure and 0.1-5 hours ^-1 of mass airspeed (WHSV) of reaction time of 15-30 minutes; the temperature distribution condition of the reaction bed layer is detected by a multi-point thermocouple 20, and the heat supply pipe 18 participates in the heat supply and heat balance in the reaction process and the balance control of the local temperature of the bed layer by controlling the flow of an external heat source; the time ratio of dehydrogenation reaction, steam purging, heating catalyst bed and vacuumizing/reducing reaction in the single cycle is (20-22.5): 3:9:3.

The low-carbon olefin and by-product 10 generated by the reaction conversion are discharged from the lower part 23 of the fixed bed reactor, steam is generated by the heat exchanger 6, the steam enters the subsequent washing 3 and compression 5, the low-carbon olefin, hydrogen-rich gas and by-product fuel gas 11 which is a part of fuel gas are obtained by the subsequent separation device, and unconverted low-carbon alkane 8 and fresh raw material 7 are circulated back to the reactor 1 for reconversion after full heat exchange and heating.

The conversion process comprises a periodic regeneration process of a catalyst bed (17 in fig. 2), wherein 3-6 fixed bed reactors are alternately in different states (reaction, purging and regeneration); after the reaction conversion is finished, the catalyst bed 17 stops feeding, steam entering from 12 is purged, hot air 14 with the temperature of 560-730 ℃ and the pressure of 0.01-1 MPa is introduced from 19 for regeneration, and waste gas is discharged from the reactor 1 through 24 or enters a subsequent separation device.

After the regeneration process of the catalyst bed 17 is completed, the dehydrogenation and coupling reaction process is repeated again after the evacuation and reduction processes are performed; the cycle time of each cycle is 30-40 minutes; the reduction process comprises the step of reducing the catalyst bed 17 in a regenerated state by using the hydrogen-rich gas 13 obtained by the separation equipment, wherein the catalyst bed is filled with the dehydrogenation catalyst and the auxiliary agent in a volume ratio of 100:1-25 and is supported by the inert alumina balls of the heat accumulator and/or the internal components.

In the above-mentioned dehydrogenation conversion method and reaction system of a low-carbon alkane fixed bed provided by the invention, the gamma-alumina catalyst loaded with VIB and IIIB elements in the catalyst bed layer can be prepared by partially referring to the steps and contents in the patent ZL200910210905.0 of the inventor; in the invention, the preferable chromium/gamma-alumina dehydrogenation catalyst comprises 15-30 m% of Cr ₂O₃, 0.1-5 m% of rare earth element and 65-80 m% of gamma-Al ₂O₃.

Under the condition of increasing environmental protection requirements, a non-chromium dehydrogenation catalyst can be selected, and the preferable molybdenum/gamma-alumina dehydrogenation catalyst comprises 15-30 m% of Mo ₂O₃, 0.1-5 m% of rare earth elements and 65-80 m% of gamma-Al ₂O₃.

In the above-mentioned method and reaction system for dehydrogenation and conversion of low-carbon alkane by fixed bed, the preparation steps of the alumina assistant loaded with IB and IIA elements of the catalyst bed layer can be carried out according to the contents of documents 201711457256.5 and 201810119334.9 of the previous application of the inventor. In the invention, the auxiliary agent contains 5-30 m% of CuO, 10-35 m% of CaO and 50-80 m% of Al ₂O₃, and is arranged in the catalyst bed layer in an amount accounting for 1-25 v% of the total volume of the catalyst bed layer; and according to the obtained operation data, the catalyst is preferably arranged in a local area with insufficient heat and low conversion temperature in the conversion process in the reaction bed layer.

In the dehydrogenation conversion method and device for the low-carbon alkane fixed bed and the reaction system provided by the invention, the inert alumina balls serving as the heat accumulator and the inert alumina porcelain balls serving as the support in the catalyst bed layer have the composition of Al ₂O₃ -99.5 m%, the heat capacity is 0.2-0.35 cal/g ℃, and the highest use temperature is higher than 1400 ℃ so as to be used as an effective accumulator of heat and ensure stable use in a severe use environment.

The invention provides a dehydrogenation conversion method of a low-carbon alkane fixed bed, which is characterized in that the high-temperature heat medium of a heating pipe in an external heat source high-temperature heat medium bed is selected from gas, molten salt and caustic alkali.

The following examples are provided to further illustrate the process, apparatus and reaction system for the dehydrogenation of light alkanes and the use thereof, and are illustrative of the embodiments of the present invention and are not to be construed as limiting the broad interpretation of the invention as set forth in the appended claims.

In an embodiment, the catalyst bed temperature change is detected by a multi-point thermocouple in the bed; the composition analysis of the raw materials and the reaction products was completed by an Agilent 6890N gas chromatograph.

Other analytical tests can be found in (national standard for Petroleum and Petroleum products testing methods, chinese Standard Press publication 1989) and (petrochemical analysis method (RIPP testing method), scientific Press publication 1990).

Example 1

Example 1a chromium/gamma-alumina dehydrogenation conversion catalyst and copper-calcium alumina promoter as required in the present invention was prepared. Referring to the procedure in the patent issued to the present inventors ZL200910210905.0, a chromium/alumina dehydrogenation catalyst was prepared containing 23m% Cr ₂O₃, 1m% La ₂O₃, and >75m% γ -Al ₂O₃.

Referring to the steps in the present inventors 201711457256.5 and 201810119334.9 application, an auxiliary agent containing 15m% CuO, 17m% CaO, and >67m% Al ₂O₃ was prepared.

Example 2

Example 2 preparation of the desired molybdenum/gamma-alumina dehydrogenation catalyst of the present invention a gamma-Al ₂O₃ catalyst containing 23m% Mo ₂O₃, 1m% La ₂O₃ and >75m% was prepared in a similar manner to example 1.

Example 3

Example 3 illustrates the effect of the fixed bed dehydrogenation conversion method, apparatus and reaction system of the present invention for the dehydrogenation of propane over a chromium-based catalyst.

The test flow of the dehydrogenation reaction of the low-carbon alkane is shown in the accompanying figures 1 and 2, and the dehydrogenation catalyst and the auxiliary agent prepared in the embodiment 1 are arranged in the bed layers in 4 industrial fixed bed reactors; lithium carbonate fused salt is selected as a high-temperature heat medium in the heat supply pipe in the bed layer.

According to the process method described by the invention, 4 fixed bed reactors are put into operation in sequence at intervals of 3 minutes, 1 reactor is in dehydrogenation reaction process at any moment, and the other 3 reactors are in regeneration and reheating, steam purging or vacuumizing/reducing processes respectively. A single cycle period of about 35 to 40 minutes, with a dehydrogenation reaction of 20 to 22.5 minutes, a steam purge of about 3 minutes, a regeneration of about 9 minutes and a reheat of the catalyst bed, with a time of about 3 minutes for the evacuation and reduction reactions.

Table 1, raw material composition for propane dehydrogenation:

Project	Composition/m%
		Propane	≥95
Other components	≤5

TABLE 2 propane dehydrogenation and regeneration Processes

Project	Data
		Reaction feed temperature/°c	591
Reactor pressure/MPa (absolute pressure)	0.105
		Space velocity/(WHSV) h of feed ^-1	0.5
CO accounts for v/v% of the volume of the raw material gas	5
		Single pass reaction time/min	20～22.5
Regeneration air feed temperature/°c	670

Table 1 shows the properties of industrial-grade propane raw materials for the dehydrogenation of propane, and Table 2 shows the operating conditions of the dehydrogenation and regeneration processes in the dehydrogenation of propane according to the present invention, and CO gas was used for the heat coupling reaction.

Comparative example 1

Comparative example 1 illustrates the application of the prior art low carbon alkane fixed bed dehydrogenation conversion process, apparatus and reaction system in the dehydrogenation of propane over chromium based catalysts.

Referring to the content of USP2419997, the same technical grade propane raw material as in example 1, commercially available Cr/Al ₂O₃ industrial dehydrogenation catalyst obtained by commercial purchase, commercially available commercial heating material auxiliary agent, was used, and the reaction was operated under typical HOUDRY type circulating fixed bed dehydrogenation process conditions, the reaction and regeneration temperature, and the feed space velocity were the same as in example 3, the reaction pressure was 0.045MPa, and the single-stage reaction time was 9 minutes.

Example 4

Example 4 illustrates the effect of the fixed bed dehydrogenation conversion method, apparatus and reaction system of the present invention for the dehydrogenation of propane over a molybdenum-based catalyst.

The molybdenum/gamma-alumina dehydrogenation catalyst of example 2 and the promoter of example 1 were used and the propane dehydrogenation conversion run was performed as described in the feedstock, process conditions and operating procedure of example 3.

Comparative example 2

Comparative example 2 illustrates the application of the prior art low carbon alkane fixed bed dehydrogenation conversion process, apparatus and reaction system in the propane dehydrogenation process with molybdenum-based catalyst.

Referring to the content of USP2419997, the reaction run was carried out under the circulating fixed bed dehydrogenation process conditions of comparative example 1 using the same technical grade propane feed as in example 1, a commercially available commercial Mo/Al ₂O₃ industrial dehydrogenation catalyst, a commercially available commercial exothermic material aid.

Example 5

Example 5 illustrates the effect of the process, apparatus and reaction system of the present invention for dehydrogenating light alkane, when applied to a mixed raw material of propane and isobutane for a chromium-based catalyst, in the course of dehydrogenation reaction.

The dehydrogenation catalysts and assistants of examples 1 and 2 were charged in a fixed bed reactor in the same manner as in example 3, and the dehydrogenation reaction of the mixed feed of propane and isobutane was carried out according to the process flow of the present invention and the feed and operating conditions of tables 3 and 4 below; potassium hydroxide is selected as a high-temperature heat medium in the heat supply pipe in the bed layer.

Table 3, propane and isobutane blend stock composition:

Project	Composition/m%
		Propane	≥56
Isobutane	≥37
		Other components	≤7

The data listed in Table 3 are for the properties of industrial mixed feed of propane and isobutane, and the CO gas was separated from the regeneration effluent gas of the apparatus of the present invention using a separation device.

TABLE 4 dehydrogenation reaction and regeneration operating conditions for propane and isobutane mixed feed

Table 4 shows the dehydrogenation reaction and regeneration conditions of the process for dehydrogenating light alkane of the present invention applied to the dehydrogenation reaction of propane and isobutane mixed material.

Example 6

Example 6 illustrates the effect of the fixed bed dehydrogenation conversion method, apparatus and reaction system of the present invention for the dehydrogenation of a mixed feed of propane and butane over a molybdenum-based catalyst.

The molybdenum/gamma-alumina dehydrogenation catalyst of example 2 and the promoter of example 1 were used and the dehydrogenation conversion run of the propane and isobutane mixed feed was performed as per the feed, process conditions and operating procedure of example 5.

The high-temperature heat medium in the heat supply pipe arranged in the reaction bed layer is composed of the catalyst and the auxiliary agent, and the high-temperature-resistant compressed carbon dioxide gas is used as the high-temperature gas heat medium.

Comparative example 3

Comparative example 3 illustrates the application of the prior art low carbon alkane fixed bed dehydrogenation conversion process, apparatus and reaction system in the dehydrogenation process of a chromium-based catalyst propane and isobutane mixed feed.

Referring to the content of USP2419997, the dehydrogenation reaction was run in the mode of operation of comparative example 1 using the same technical grade propane and isobutane mixed feed as in example 5 with commercially available Cr/Al ₂O₃ industrial dehydrogenation catalyst and exothermic material aid, but at the same reaction and regeneration temperature, feed space velocity as in example 5, at a reaction pressure of 0.045MPa and a single stage reaction time of 9 minutes.

Comparative example 4

Comparative example 4 illustrates the application of the prior art low carbon alkane fixed bed dehydrogenation conversion process, apparatus and reaction system in the dehydrogenation process of a molybdenum-based catalyst propane and isobutane mixed feed.

Referring to the content of USP2419997, a commercial Mo/Al ₂O₃ commercial dehydrogenation catalyst, commercially available commercial heating material aid, was used with the same commercial grade propane and isobutane blend stock as in example 5, operating in the cyclic fixed bed dehydrogenation mode and operating conditions of comparative example 3.

Example 7

Example 7 illustrates the operation and performance of inventive examples 3-4 in comparison to comparative examples 1-2 in the dehydrogenation conversion of propane feed, as shown in tables 5 and 6.

Table 5, comparison of propane dehydrogenation operating conditions

Project	Example 3	Comparative example 1	Example 4	Comparative example 2
					Catalyst case	Example 1	Commercially available	Example 2	Commercially available
Catalyst composition	Cr/γ-Al₂O₃	Cr/Al₂O₃	Mo/γ-Al₂O₃	Mo/Al₂O₃
					Case of auxiliary agent	Example 1	Commercially available	Example 1	Commercially available
Auxiliary agent composition	Cu-Ca/Al₂O₃	-	Cu-Ca/Al₂O₃	-
					Reaction heat coupling	CO hydrogenation	Without any means for	CO hydrogenation	Without any means for
High temperature thermal medium	Lithium carbonate	Without any means for	Sodium chloride	Without any means for

In table 6 below, the total conversion of propane is calculated as the product yield in the unconverted lower alkane return mode of operation.

TABLE 6 comparison of propane dehydrogenation run results

Project	Example 3	Comparative example 1	Example 4	Comparative example 2
					Propane single pass conversion/%	46	45	40	40
Total conversion of propane/%	≥86	≥85	≥82	≥80
					Propylene selectivity/%	88	85	83	82
Raw coke	Benchmark-20%	Datum	Benchmark-20%	Datum
					The reaction time is in percent	63	41	62	40
Operating costs	Benchmark-11%	Datum	Benchmark-10%	Datum
					Investment amount	Benchmark-40%	Datum	Benchmark-40%	Datum

Compared with the typical operation condition of the fixed bed dehydrogenation process in the prior art, the method comprises the application of the existing heating material, and has better implementation effect, conversion efficiency and selectivity in the dehydrogenation reaction of the propane industrial raw material.

On the dehydrogenation operation result, the invention improves the reaction process in the catalyst bed more effectively, improves the dehydrogenation conversion effect and reduces various losses of the process.

These operating results are advantageous in comparison with the implementation results obtained, in terms of reducing the requirements of the process units and equipment, as well as of the materials, design and operation of the reaction system.

Example 8

Example 8 illustrates the effect of the present invention in comparison with the effect of comparative examples 3 to 4 in dehydrogenation conversion of propane and butane mixed feed, to examine the effect of the present invention in dehydrogenation conversion of butane and mixed feed, and Table 7 shows the comparison of the dehydrogenation reaction operation conditions of propane and butane mixed feed.

Table 7, comparison of dehydrogenation reaction operating conditions for propane and butane mixed feedstock

Project	Example 5	Comparative example 3	Example 6	Comparative example 4
					Catalyst case	Example 1	Commercially available	Example 2	Commercially available
Catalyst composition	Cr/γ-Al₂O₃	Cr/Al₂O₃	Mo/γ-Al₂O₃	Mo/Al₂O₃
					Case of auxiliary agent	Example 1	Commercially available	Example 1	Commercially available
Auxiliary agent composition	Cu-Ca/Al₂O₃	-	Cu-Ca/Al₂O₃	-
					Reaction heat coupling	CO hydrogenation	Without any means for	CO hydrogenation	Without any means for
High temperature thermal medium	Potassium hydroxide	Without any means for	Carbon dioxide	Without any means for

Table 8 shows the comparison of the dehydrogenation reaction run results of the propane and butane mixed feed, and the conversion of both lower alkanes was good in the mixed feed with the unconverted lower alkanes returned to the mode of operation.

Table 8, comparison of the results of dehydrogenation runs on propane and butane mixed feeds

Project	Example 5	Comparative example 3	Example 6	Comparative example 4
					Propane single pass conversion/%	49％	45％	40	39
Propylene selectivity/%	88％	85％	82	80
					Butane single pass conversion/%	48％	45％	42	40
Butene Selectivity/%	87％	85％	83	80
					Raw coke	Benchmark-20%	Datum	Benchmark-20%	Datum
The reaction time is in percent	63	41	62	41
					Operating costs	Benchmark-10%	Datum	Benchmark-10%	Datum
Investment amount	Benchmark-40%	Datum	Benchmark-40%	Datum

Compared with the typical operation condition of the fixed bed dehydrogenation process in the prior art, the method comprises the application of the existing heating material, and has better conversion rate and selectivity of propane and isobutane and better implementation effect in the dehydrogenation reaction of mixed industrial raw materials of propane and isobutane. The method, the device and the reaction system provided by the invention have good raw materials and process adaptability to mixed low-carbon hydrocarbon with more complex composition.

Finally, it should be noted that the above-mentioned embodiments are merely for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A dehydrogenation conversion method of a low-carbon alkane fixed bed is characterized in that a reaction bed layer formed by a gamma-alumina catalyst loaded with VIB and IIIB elements and an alumina auxiliary agent loaded with IB and IIA elements is adopted in a high-temperature micro-positive pressure fixed bed reactor, and heat is stored and supplied in an intermittent mode of alternate reaction and regeneration; the heat of dehydrogenation-hydrogenation reaction process is coupled with a high-temperature heat medium heat supply pipe of an internal and external heat source in the bed layer, so that heat balance in the conversion process and temperature balance of the reaction bed layer are realized; dehydrogenating the C3-C5 light alkane to convert the light alkane into the light alkene;

The heat coupling in the reaction process is realized by carrying out exothermic reaction on CO and/or CO ₂ gas accounting for 1-20 m% of the total amount of the raw materials and hydrogen generated in the reaction process;

The catalyst contains 15-30 m% of Cr ₂O₃, 0.1-5 m% of rare earth element and 65-80 m% of gamma-Al ₂O₃; or the catalyst contains 15-30 m% of Mo ₂O₃, 0.1-5 m% of rare earth element and 65-80 m% of gamma-Al ₂O₃;

The high-temperature heat medium is selected from gas, molten salt and caustic alkali;

The fixed bed reactor comprises a shell and a catalyst reaction bed layer arranged in the shell; the shell is of a hollow metal structure and is connected with the end cover and the steel cylinder body through flanges; the protective lining is provided with an outer heat-insulating layer, a high-temperature-resistant thermal shock-resistant nano ceramic coating; a catalyst bed layer formed by a catalyst and an auxiliary agent is filled above the supporting space in the cylinder body; a multi-point thermocouple and a high-temperature heat medium heating pipe are arranged in the bed layer, and the heating pipe is connected to a heating furnace outside the reactor through an inlet pipeline and an outlet pipeline after being integrated in an end cover area; the material inlet is connected with the reactor from the upper part, and the material outlet is connected with the reactor from the lower part.

2. The method for the fixed bed dehydrogenation conversion of light alkane according to claim 1, wherein the reaction is carried out at a temperature of 560 to 620 ℃ and a slight positive pressure of 0.103 to 0.105 Mpa.

3. The method for the dehydrogenation conversion of the light alkane fixed bed according to claim 1, wherein the auxiliary agent comprises 5-30 m% of CuO, 10-35 m% of CaO and 50-80 m% of Al ₂O₃, and is arranged in the catalyst bed in an amount of 1-25 v% of the total volume of the catalyst bed.