With the rapid development of China's economy, the demand for paraxylene, the most important basic organic chemical raw material, has increased strongly in the past five years. With the rapid development of downstream products (mainly PTA industry), the PX market demand will show a rapid upward trend in the next few years. It is estimated that the annual consumption growth rate is 22.4%, with an average annual growth rate of 24.9%. It is predicted that by 20 10, the PX consumption of PTA plant will reach 54-6 1Mt, and the capacity construction of the plant can't keep up with the growth of demand, and the gap between demand and output of PX in China will further widen.
The production method of p-xylene is to separate xylene and its isomer mixture from naphtha by multistage low-temperature crystallization separation or molecular sieve simulated moving bed adsorption separation technology (adsorption separation for short). If o-xylene, m-xylene and ethylbenzene are treated, mixed xylene isomerization technology (isomerization for short) is often used, so p-xylene is isomerized. Toluene disproportionation and transalkylation technology make full use of cheap industrial toluene and c9 aromatic hydrocarbon /C 10 (C9A/C 10A) to convert them into mixed xylene and benzene. Aromatic hydrocarbon plant, this technology produces more than 50% mixed xylene, and this technology is the main means of industrial production of p-xylene. Selective disproportionation of toluene to xylene is a new way. In recent years, great progress has been made in the continuous improvement of catalyst performance in this process. With the continuous improvement of ethylene production capacity, the total amount of toluene will show an upward trend, so it has a good market prospect.
In this paper, the progress of these two kinds of xylene production technology routes in recent years is reviewed, and the technical development trend in this field is put forward.
1 toluene disproportionation and transalkylation technology
1. 1 typical production process
The traditional production process of toluene disproportionation is Tatoray process in which hydrogen exists in a fixed bed, which was jointly developed by UOP Toray Company of Japan in the late 1960s. After more than 30 years of technical development, 1997 has completed the research and development of S-TDT process and realized industrialization. Compared with Tatoray process, S-TDT process allows heavy aromatics to contain C 10, and HAT toluene disproportionation catalyst has the international advanced level, and the energy consumption of equipment and materials is low, which makes this process have good technical and economic indicators.
The brief treatment process of S-TDT toluene disproportionation is as follows: C9A, a raw material containing toluene and C 10 heavy aromatic hydrocarbon, is mixed with circulating hydrogen, heated by a heating furnace to the inlet and outlet of the reactor heat exchanger to form a fixed bed adiabatic reactor, and the reacted benzene and xylene are mixed under the action of a catalyst. The reaction effluent passes through the heat exchanger at the inlet and outlet of the reactor, flows into the high-pressure separation tank after cooling, and the separated aromatic liquid enters the downstream fractionation device. Which part of the gas effluent is separated, most of the gas and supplementary hydrogen are mixed by the circulating hydrogen compressor, which pressurizes the circulating hydrogen.
Progress in toluene disproportionation and transalkylation of 1.2 R&D
1.2. 1 TA toluene disproportionation catalyst and Tatoray
Starting from 1969, the industrialization technology of Tatoray toluene disproportionation and transfer technology of Toray Company in Japan, jointly developed with UOP Company in the United States, is the most advanced technology in China. The technology adopts fixed bed hydrogen phase reaction, which has stable operation and long operation period. This technical and economic index has been adopted by more than 50 sets of equipment all over the world and is the main technical field of industrialization. Industrial application of TA-4 process catalyst and TA-5 catalyst since 1997 in 1990s. At present, TA-4 and TA-5 catalysts are mainly used in lithium tantalate process abroad.
A new generation of TA-20 metal hydrogenation catalyst newly developed by UOP Company. The heavy aromatics of the catalyst with metal hydrocracking function and improved treatment capacity can be processed into toluene, and the raw materials containing 65438 0% alkanes are allowed to be mixed with 30% mass fraction. Compared with the original TA-4 and TA-5 catalysts, the long-term stability of TA-20 catalyst has also been improved.
1.2.2 HAT series toluene disproportionation catalyst and S-TDT technology.
The capacity expansion and transformation to meet the demand of aromatic hydrocarbon combined plant has not changed. HAT series catalysts for toluene disproportionation and transalkylation, HAT-095 and HAT-096, developed by 1996 HAT-097 catalyst, have been successfully applied to the core technology of domestic1.3-123,000 tons/year toluene disproportionation plant.
TDT toluene disproportionation technology and catalyst have been exported to Iran. Table 1 lists the main performance indexes of HAT catalyst industrialization. It can be seen from the table 1 that the catalyst of HAT-097 is the catalyst of HAT-095. The treatment capacity of this catalyst is greatly improved, and the ratio of hydrogen to hydrocarbon is getting lower and lower. The condition of the compressor in the existing device remains unchanged, and the expansion can be achieved only by replacing the catalyst. At the same time, the C 10A is higher and higher, and the heavy aromatics and disproportionation unit can be treated, which can effectively improve the yield of benzene and mixed xylene and improve economic benefits.
Compared with similar foreign industrial catalysts, the aromatic hydrocarbon treatment capacity of HAT catalyst is greatly improved. The industrial operation results show that its comprehensive performance has reached the international advanced level. HAT-099 catalyst completed the development of C 10A reaction. As the first three raw materials, the mass fraction of C9A raw material C 10A is allowed to be as high as 25%-30%. The successful development of HAT-099 catalyst will effectively improve heavy aromatics, which is the purpose of greatly increasing mixed xylene and xylene to improve the utilization rate of production.
In recent years, toluene disproportionation unit can meet the demand of increasing xylene production capacity by producing more C8A from high concentration C9A raw materials. MXT-0 1 catalyst SRIPT macroporous β zeolite was used to catalyze the disproportionation and transalkylation of toluene and C9A. The experimental results show that under the condition of 70%, the reaction raw material C9A has a high space velocity, the total molar conversion of low-hydrogen hydrocarbon is above 46%, and the molar ratio of C8A aromatic hydrocarbon to benzene is above 3.7. The catalyst HAT MXT-0 1 has a high yield of mixed xylene. The mordenite catalyst in the industrial side-line production plant which has been completely disproportionated at present was tested and compared.
1.2.3 MTDP-3 toluene disproportionation and transalkylation technology
MTDP-3 toluene disproportionation and transalkylation technology C9A capacity technology developed by Mobil Company. ZSM-5 zeolite is used in this process, and the mass fraction of C9A in the reaction feed is less than 25%. Competitive advantages of technologies that allow low molar ratio of hydrogen to hydrocarbon (less than or equal to 3).
On the basis of Mobil Corporation of MTDP-3 technology and China Petroleum and Natural Gas Group Corporation (CPC) of Taiwan Province Province, China, in the process of developing TransPlus, in order to improve the processing capacity of C9A part C 10A raw materials, the first petrochemical plant was industrialized in 1997 in the forest garden of Taiwan Province Province, China. This technology utilizes the light function of catalyst A to optimize heavy aromatics, which makes it possible to treat raw materials containing a certain amount of C 10A and C9A. It is said that the mass fraction of C 10A in C9 raw material can reach more than 25%, and the mass fraction of C9A reaction mixture can reach more than 40%, but there is no industrial data reported yet. Typical operating conditions: reaction temperature is 385-500℃, reaction pressure is 2. 1-2.8MPa, aromatic hydrocarbon WHSV is 2.5-3.6h-1+0, and the molar ratio of hydrogen to hydrocarbon is not more than 3.45%-50%.
1.2.4 Other technologies
Ako -IFP and xylene (the yield of xylene+) were industrialized in 1968. The rare earth Y molecular sieve used has low activity and selectivity of 28%. -30% and 92.5% respectively; Because of the moving bed reactor, the catalyst needs continuous regeneration and consumes a lot of energy. Toluene and C9A can be used as raw materials. c？ Only 4 sets of original materials for 9A content are allowed, so far, the industrialized equipment in the world. one
Costen T2BX was industrialized in France on 1985. The working pressure was relatively high (4. 1MPa) and the conversion rate was 44% respectively. Mordenite is used as a catalyst for toluene and C9A aromatics. In recent years, there is no new report.
Production of high concentration xylene by selective disproportionation of toluene
2. 1 overview
Shape-selective catalysis can effectively inhibit side reactions, greatly improve the selectivity of required products, simplify the separation process, greatly reduce energy consumption and investment, and make the device effectively improve economic benefits. Shape selective disproportionation of toluene can only be used for pure toluene feed. about
Selection of high critical position, suitable pore size and external surface passivation of zeolite for shape selective disproportionation of toluene. The outer surface of the passivated zeolite crystal is designed to make the zeolite channel, p-xylene and molecular sieve diffuse rapidly in the isomerization reaction that does not occur outside the surface, and also produce the thermodynamic equilibrium mixture xylene.
Up to now, the patent report of selective disproportionation of toluene on ZSM-5 molecular sieve comes from Mobil Company, which is a small part of the pore structure of ZSM-5 zeolite ZSM-1/molecular sieve.
2.2 The developed technology is abroad.
2.2. 1 MSTDP and PXMAX toluene shape selective disproportionation
The first industrial toluene shape-selective disproportionation technology reformed the MSTDP process of Mobil 1988 technology in situ. In the Italian city of Gera, the refinery of MSTDP Enichem has been successfully operated. Its industrialization technical indicators are: toluene conversion is 25%-30%, the molar ratio of benzene to xylene is 85%-90%, and the reaction product is 1.44.
1996 company introduced ex-situ modification technology of PX-MAX, with xylene selectivity over 90% and toluene conversion rate of 30%. Compared with MSTDP technology, the molar ratio of benzene to xylene in the reaction product is lower than that of PXMAX technology, so more p-xylene can be obtained.
2.2.2 PX-PLUS toluene optional disproportionation technology
UOP Company is suspected of introducing PX-PLUS technology in 1997 compared with MSTDP technology. The main indexes are: toluene conversion rate is 30%, para-selectivity is 90%, the molar ratio of benzene to xylene in the reaction product is 1.37, and the yield of p-xylene is about 4 1% (converted into toluene). 1998, industrialization of the first set of equipment.
The combination of UOP technology and molecular sieve adsorption separation of healthy and strict xylene aromatics has a good complementary effect. PX-PLUS technology is used to produce high concentration xylene. After simple crystallization and separation, p-xylene with high mass fraction can be obtained. The residual liquid of p-xylene in the product is still above 40%, which is much higher than the usual xylene mixture. The content of xylene can directly enter the adsorption and separation department.
2.3 domestic development, domestic research in this field began in the early 1990s, and the industrial side-line test of 1L catalyst in RIPP was completed in 1999. The main results are as follows: the conversion of toluene is more than 30% and the selectivity is more than 90%, but the molar number of benzene and xylene is higher, about 1.6.
SRIPT catalyst for selective disproportionation of toluene was studied in 1997, and good results have been achieved so far. The experimental results show that the conversion of toluene is 65438 0.4, and the molar ratio of benzene and xylene is 30% and 90% respectively. The expansion catalyst test has been completed, and the line test on the industrial side is ready.
Heavy aromatics, improving refining capacity, increasing the scale and quantity of continuous reforming aromatics production units, dealkylation technology in the process of dealkylation of heavy aromatics
Accelerate development. The aromatics produced by C9A can be hydrogenated to produce mixed xylene, which can effectively reduce the plant scale and make full use of heavy aromatics resources. Abroad, in this field, UOP technology has been used in the process of Dongli TAC9, and Zeolyst has prepared GT-TransAlk technology of ATA technology company GTC company.
3. Production technology of selective conversion of heavy aromatic mixed xylene by1Toray TAC9 C9-C 10 aromatic hydrocarbon.
Mixed xylene technology produced in Toray TAC9 process. C 10A is also used to produce mixed xylene, which may be a serious additional mixed xylene aromatic product. Like Tatoray technology, it is also used in the presence of TorayTAC9 process. In the presence of hydrogen, in order to prevent coking, dealkylated aromatic compounds and non-aromatic compounds are mainly consumed from hydrogen. In order to ensure a high yield of mixed xylene, the reaction of benzene and toluene and the tower separation of reactor feed for separating heptane are returned.
There are three aspects in the production of mixed xylene: the distribution of methyl phenyl, C9A and C 10A isomers, and the ratio of C9/C 10A value to the total feed. For pure C9A feed, the yield of mixed xylene is about 75%, and the yield of light fraction is about 2 1%. With the increase of feed C 10A, the yield of mixed xylene decreased.
The technology showed good stability in the first industrial application of 1996. The initial operation period is more than two years. By 1998, the factory has two sets of processes in use, and the equipment scale reaches 850 carats/year.
3.2 preparation of molecular sieve/dealkylation and transalkylation technology of sk heavy aromatics
South Korea's SK cooperative R&D was prepared and industrialized by using Zeolyst technology, which was first applied to South Korea's SK aromatics complex in 1999.
ATA- 1 1 adopts noble metal catalyst, which has good stability, initial running time of more than 3 years and low ethylbenzene mass fraction (about 2% of C8A can be produced by hydrogenation), and is a good isomerization raw material. However, due to the strong cracking effect, the temperature of the strongly exothermic reaction bed rose excessively, and the contact time loss between the required materials and the catalyst was not long, so the operation was carried out at high space velocity. Excessive consumption and exothermic reaction of hydrogen make it difficult to feed the heating furnace and the downstream stripper. Before using this technology, the current equipment will. This technology is suitable for C9+ hydrodealkylation.
3.3 Dealkylation and transalkylation of heavy aromatics in GT-Transalk
GTC's GT-TransAlk technology is used to treat light C9A/C 10A heavy aromatics. The characteristic of this technology is that the raw material does not contain toluene, and a group of aromatic hydrocarbon technologies are formed by methylation and crystallization separation technology of toluene.
4. Development trend of xylene production technology in the future
The market prospect of p-xylene, in the next few years, as well as in enterprises whose main goal is to transform existing equipment and expand, some enterprises also have the demand for new mobile equipment. The improvement of new technology and existing technology has become the focus of research and development in petrochemical industry.
4. 1 traditional toluene disproportionation and transalkylation technology
The development direction of toluene disproportionation and transalkylation unit in the future is to improve the selectivity of required products, effectively reduce equipment consumption materials, further improve the ratio of space velocity to hydrogen, reduce hydrocarbon research, and develop new catalysts to meet the expanding equipment energy demand.
In order to improve the selection of suitable macropores and the surface acidity modulation of catalytic materials, properly strengthen transalkylation reaction and inhibit toluene disproportionation reaction, thus improving the yield of mixed xylene, reducing the yield of mixed xylene of benzene and achieving the purpose of p-xylene yield. At present, SRIPT has been successfully developed and tested on the industrial side of mordenite catalyst MXT-0 1. The results show that when the space velocity is 2.5 hours-1 and the reaction temperature is below 400℃, the total conversion of the catalyst is not less than 46% and not less than 89%, the molar selectivity ratio of benzene to xylene is 3.5 or higher, and the selectivity of mixed xylene is 73%.
The aromatics plant has a large scale and a considerable amount of heavy aromatics. How to make full use of the economic benefits of heavy aromatics has a great influence on the merger of the whole plant. During the operation of the plant, in order to prevent the reactor feed from containing heavier hydrocarbon components than C 1 1, some hydrocarbons at the boundary of C 10A C 1 1A were discharged, resulting in heavy aromatic hydrocarbon loss. Therefore, developing a C 10A catalyst can treat busy aromatics, and its technology will focus on heavy aromatics in the future.
Direct processing of toluene with high aromatic content without aromatic hydrocarbon is also one of the future development trends. This technology can effectively reduce the load of extraction unit, expand its realization goal and reduce energy consumption. However, the content of non-aromatic benzene in the whole plant increased. Therefore, it is very important to ensure the quality of benzene and research and develop catalysts suitable for treating high content of non-aromatic toluene raw materials.
4.2 Toluene xylene
4.2. Shape-selective disproportionation of1toluene and methylation system.
Further improving the selection of closing position and xylene technology will be the focus of future research. Higher and higher grade selectivity will greatly reduce the separation energy and effectively reduce the production cost of p-xylene.
4.2.2 Combined process of toluene shape-selective disproportionation and benzene/benzene C9 transalkylation.
Selective disproportionation of toluene can produce high mixed xylene, but this technology can only use xylene with pure toluene content. In aromatic hydrocarbon plant, the cheap C9 and above aromatic hydrocarbon resources are largely underutilized. Therefore, the selective disproportionation technology of toluene in SRIPT aromatics plant is combined with the combined process of benzene /C9A and alkyl.
The technology transfer of SRIPT benzene and C9 alkyl R&D was completed in March 2003. The results show that when the mass ratio of benzene to C9A is 60/40 and the weight hourly space velocity of the reaction is 1.5h-1, the total conversion is over 50%, and the selectivity of benzene to C9A and toluene to mixed xylene is over 90%.
In the process of merger, benzene /C9A generated by random disproportionation of toluene is used as the raw material of benzene transalkylation unit. Before C9A of benzene /C9A and toluene generated by transalkylation unit are used as raw materials, toluene selective disproportionation technology and C9A used are fully applied to produce mixed xylene with high xylene content to the maximum extent.
In recent years, great progress has been made in separation technology, and the study of crystallization mechanism of frozen crystallization has improved its economic index. The content of mixed xylene with high xylene content and the crystallization separation technology combined with production technology will significantly reduce the separation cost and be competitive with molecular sieve adsorption separation technology. The application of p-xylene production technology and crystallization separation technology has a good market prospect.
4.2.3 High concentration xylene in toluene methylation system
Alkylation of toluene, methanol and xylene is a new process route and a new way to produce xylene by using toluene conversion rate and cheap methanol. The selective alkylation synthesis of Y zeolite ZSM-5 zeolite catalyst with toluene as raw material has been studied at home and abroad since 1970s, especially the relationship between Al ratio, particle size, modified P, Si, modified B elements of Pt, Mg, Sb/alkali metals (alkaline earth metals) and the structure, acidity and catalytic performance of steam treatment catalyst. Mobil Company uses silicoaluminophosphate molecular sieve with molar ratio of 450,970℃ to steam treat P/HZSM-5 catalyst for 45 minutes, for example, at the reaction temperature of 600℃ and the reaction pressure of 0.28MPa, WHSV4h- 1, N (toluene) /n (methanol) /N (water) /N (hydrogen). Benzene, the reaction does not produce few by-products, mainly hydrocarbons less than C5 and mass fraction less than 1%.
There are two main advantages: research and development of industrial catalysts with good stability and long life and technical economy. New progress has been made in the development of GT-lAlkSM toluene methanol alkylation technology and the technical and economic evaluation of 200kt/aPX production plant jointly reported by Indian Petrochemical Company (IPCC) and GTC. Using toluene alkylated in a fixed bed reactor and proprietary high-silica zeolite catalyst, under the conditions of reaction temperature of 400-450℃, reaction pressure of 0. 1-0.5MPa, and the mass ratio of toluene to methanol of 1.35/ 1, the PX selectivity can reach over 85%, and the running time of the catalyst is 6-. This technology: the main feature of toluene reforming is that it is directly transported to toluene alkylation unit to produce high concentration PX aromatics from low-cost methanol. The cost of xylene is low, simple crystallization unit can effectively revive PX, and the construction investment of crystallization separation unit to obtain high purity PX is much lower than that of traditional adsorption separation unit. In addition, the by-product benzene can be ignored. Each agricultural product 1tPX only needs to consume: 1 ton of toluene (in the process of selective disproportionation of toluene, it needs to consume about 2.5 tons of benzene, toluene and by-products: b and PX: 1 .36-1.60). Technical and economic evaluation of raw material toluene 2.34 mt/ APX: the annual PX concentration of methanol 1.73 mt/ a in the 200kt/aPX plant is 2.33Mt/A, the prices of toluene and methanol are 260 USD/ton10 USD/ton respectively, and the annual net profit is about190,000.
This technology, such as toluene, methanol and methyl technology, GT- transalkylation heavy side hydrocarbon technology, GT-IsomPX isomerization technology and CrystPX crystallization technology, combined with other aromatics and distillation units, will show greater superiority and flexibility in the production of modern PX combined units. The recovery method and equipment of 400,000 tons/year PX plant can save cash cost 10% per ton compared with the traditional adsorption separation of mixed xylene feed, and the investment cost of PX recovery in modern portfolio is reduced by 2.6%, which is about 53.8% lower than the requirement of naphtha raw materials.
Due to the high price of methanol, the technology of producing wastewater and maintaining the long-term industrial prospect needs further study. However, the development of natural gas chemical industry and advanced catalyst technology have good application prospects.
4.3 Engineering research
In the development of aromatic catalytic technology, with the increase of equipment scale, the cost of producing products is getting lower and lower, so it is necessary to further study the engineering process and the separation of these two technologies. During the reaction, the main core reactors, large-scale heat transfer equipment and devices were jointly studied. With the size of the equipment, choosing the appropriate reactor type and how to ensure the uniform distribution of gas flow in the reactor are the main contents. The uniform distribution of SRIPT gas flow in an axial fixed bed is deeply studied and can be used in industrial design. The efficiency of horizontal heat exchanger largely determines the energy consumption level of the whole device. The plate heat exchanger of PAKINNOX company in France represents the most advanced level. At present, SRIPT's 870 carats and 654.38+100,000 tons toluene disproportionation devices have been used in heat exchangers, which is expected to greatly shorten the load of the reactor furnace.
The products mainly focus on advanced crystallization separation technology, Deniro separation technology /TNO frozen crystallization separation and purification technology. This technology is a separation and purification technology developed by Bremen University in 1993, which are respectively "De Niro Technology and TNO Institute of Environmental Science, Energy Technology and Technological Innovation". Compared with the traditional frozen crystallization layered frozen crystallization process and the separation and purification technology of suspension frozen crystallization process based on Niro/TNO frozen crystallization separation and purification technology, the comprehensive energy consumption is reduced to about 10% of the traditional frozen crystallization process.
At present, this research has not been reported.
5. Develop a forward-looking new technology-synthesis of p-xylene.
The new process route recently reported by ExxonMobil Company is a new process of C4+ olefins (such as cyclopentadiene, butadiene, pentadiene, hexadiene, methylcyclopentadiene, etc.). ) and C 1-C3 oxygenates (such as methanol, dimethyl ether, ethanol, ether or the mixture of methanol and dimethyl ether) are selectively converted into p-xylene, ethylene and propylene. ZSM-5 catalyst contains 4.5 mass% P zeolite (the molar ratio of silica to alumina is 450). In a fixed bed reactor, the reaction temperature is 430℃ and the reaction pressure is 0.65438±0 MPa. WHSV 0.5H- 1 and raw materials m (isoprene) /m (toluene) /m (methanol) /m (water)1.25/1.25/22.5/75 have high selectivity, and the conversion to xylene and methanol is equally high. The product quality includes: 30% p-xylene, 25% ethylene, 22% propylene and the remaining C4+ olefins, as well as C8+/ aromatics except xylene.
Synthesis of trimethylbenzene synthesis gas catalyzed by ExxonMobil methyltoluene. Cr-Zn-Mg -O supported MgO/HZSM-5 catalyst, the ratio of n(H 2)/ n (low carbon CO)/ n (toluene) in raw materials was 2/ 1/0.25, the reaction temperature was 460℃, the reaction pressure was 0. 17 MPa WHSV was 60. The added metal oxide is used to inhibit the formation of acid centers on the outer surface of zeolite, thereby reducing the generated zeolite, reducing the ortho position of pores and m-xylene, that is, reducing the right position of unalkylated toluene and inhibiting the isobutyl structure of p-xylene, thereby improving the selectivity of p-xylene.
UOP recently improved the liquid phase hydrogen-free toluene disproportionation transalkylation technology and prepared C9A zirconium and sulfuric acid spray impregnation catalyst. When the raw material contains 30% by mass of 1, 2,4-trimethylbenzene and toluene, the xylene yield is the highest under the reaction conditions of 160℃, 900kPa and 2.0h- 1 liquid hourly space velocity. At this time, the linear analysis results of the reaction products show that the mass fraction of 17% xylene and mesitylene is 20%. The deactivated catalyst can be regenerated.
The research and development of new technologies for selective conversion of heavy olefins and syngas, by-products toluene and xylene, and methanol is a research trend worthy of attention.
conclusion
Due to the influence of the downstream product market, the p-xylene market will present the market position of suppliers. The expansion of new equipment or existing equipment will become an inevitable trend. On the basis of the existing scale, mixing xylene and increasing the use of new technology are the main technical means to increase the total naphtha quota to produce p-xylene. Isomerization catalyst, high ethylbenzene conversion rate, adsorption and separation of p-xylene with increased feed concentration, and main ways of aromatic hydrocarbon expansion. Selective disproportionation of toluene to p-xylene is a new technical route. The combination of toluene shape selective disproportionation and benzene /C9A transalkylation will effectively reduce the cost and produce p-xylene, which can significantly increase the output of p-xylene and look forward to industrialization. The utilization of heavy aromatics technology will also focus on the future and strive for new breakthroughs in the near future.