The world's first aromatic moving bed light hydrocarbon aromatization unit was successfully put into operation

In recent years, the raw materials processed by traditional light hydrocarbon aromatization equipment are mainly carbon tetra-unsaturated hydrocarbons, and the products are mainly gasoline blending components, with low economic benefits. The Petroleum Science and Technology Institute timely grasped the development trend of the transformation from oil refining to chemical industry, conducted in-depth research on reaction pathways and catalyst action mechanisms, and developed a new generation of light hydrocarbon aromatization catalysts and process technologies. It has realized the expansion of light hydrocarbon aromatization raw materials into low-value light naphtha and liquefied petroleum gas and other saturated hydrocarbon components. The products have been transformed into high value-added products such as aromatics, propane, and hydrogen, and the technical and economic efficiency has been greatly improved.

In order to overcome the shortcomings of fixed-bed light hydrocarbon aromatization, such as low aromatic yield, fast coking rate, and short operating cycle, and to meet the requirements of moving bed technology for catalyst circulation and regeneration, the Petroleum Science and Technology Research Institute pioneered the development of a small spherical light hydrocarbon aromatization catalyst with non-precious metals and high molecular sieve content. It has the advantages of high activity, high aromatic selectivity, high strength, high hydrothermal stability, low coking rate, and good regeneration performance. In terms of process technology development, based on its advantages in the moving bed technology platform and combined with the unique reaction and regeneration characteristics of light hydrocarbon aromatization catalysts, Petrochemical Research Institute has developed moving bed reaction and continuous regeneration technology, so that the aromatization reaction of light hydrocarbons is always carried out continuously under high-severity conditions. The raw material and product structure can be flexibly adjusted according to market demand, which significantly improves the adaptability and market competitiveness of the technology, and opens up a new technical approach for the efficient utilization of light hydrocarbon resources.

Dalian Academy of Petrochemical Sciences and Catalyst again

Light aromatics, including benzene, toluene and xylene (B, T, X), are important basic organic chemical raw materials and important blending components for the production of high-octane gasoline. Traditional production of light aromatics mainly uses naphtha as raw material and is obtained through catalytic reforming units. With the increasing market demand for light aromatics, the supply of conventional naphtha resources is limited and the market cannot be satisfied. In this context, the new technological route of producing light aromatics through aromatization devices using light hydrocarbon resources that were originally mainly used as fuel as raw materials has received attention. Dozens of light hydrocarbon aromatization devices have been built in China.

Technical Development Catalytic reforming technology appeared earlier. Russian chemist Zelinsky discovered the basic reaction of catalytic reforming in 1911. In 1940, the world's first catalytic reforming device was built and put into operation in the United States. The device was a fixed-bed reactor and the catalyst was MoO3/Al2O3. However, this device had problems such as short reaction cycle, small processing capacity, and high operating costs. In 1949, UOP developed platinum reforming technology using Pt/Al2O3 as a catalyst. It also used a fixed-bed reactor. The reaction cycle was extended to more than half a year, and the liquid yield and aromatic selectivity were also improved. The emergence of platinum reforming technology enabled the rapid development of catalytic reforming technology. In 1967, Chevron invented the Pt-Re/Al2O3 bimetallic reforming catalyst and industrialized it. Compared with platinum reforming, the stability of platinum-rhenium reforming technology was doubled, further improving catalytic reforming technology. In addition, in terms of process and equipment, the emergence of continuous reforming technology has made catalytic reforming technology more perfect. The reforming equipment can adopt the design of ultra-low pressure, high conversion rate and large processing capacity. my country's first catalytic reforming unit was completed and put into operation in Daqing in 1965. Now the total processing capacity of my country's catalytic reforming units has exceeded 10 million tons/year. In terms of technology research and development, our country has been committed to the research and development of catalytic reforming technology since the early days of the founding of the People's Republic of China. It has mastered core technologies such as catalysts, processes, equipment, and engineering models, and successfully applied them industrially.

Light hydrocarbon aromatization technology can be considered to have originated from catalytic reforming technology. Research began in the 1940s, which was the period when catalytic reforming technology was just industrialized. In the early stage of the research on light hydrocarbon aromatization technology, we mainly drew on platinum reforming technology and used Pt/Al2O3 catalyst to realize the aromatization of light hydrocarbons. However, the catalyst was severely coked and the aromatic hydrocarbon content in the product was low. Research progress at this stage was slow. Until the 1970s, the ZSM-5 molecular sieve developed by Mobil Company was used in the research of light hydrocarbon aromatization technology. Its good reactivity and strong resistance to carbon deposition made a breakthrough in light hydrocarbon aromatization technology and made industrialization possible. The world's first light hydrocarbon aromatization industrial unit was built in the UK in 1990, using the Cycla process jointly developed by BP and UOP. At present, foreign light hydrocarbon aromatization technologies include the Ccla process, the M-2 process developed by Mobil, the Aroforming process developed by IFP and SALUTEC, and the Z-Forming process developed by Mitsubishi Petroleum and Chiyoda.

Domestic research institutions are also at the forefront of the world in the research of light hydrocarbon aromatization technology. The more representative ones include Dalian University of Technology, Sinopec Petrochemical Research Institute and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. The technology has been industrialized, and multiple sets of equipment have been built and are operating stably. The first domestic light hydrocarbon aromatization device uses patented technology from Dalian University of Technology. It was completed and put into operation in Zibo City, Shandong Province in 2006. The device scale is 100,000 tons/year. At present, more than 60 light hydrocarbon aromatization units have been built in China, with a total processing capacity of more than 12 million tons per year.

Reaction Principle and Catalyst Catalytic Reforming is a process in which C6 to C11 fraction hydrocarbon molecules are rearranged into a new molecular structure under certain reaction conditions and the action of a catalyst, which is the so-called "reforming". The main reactions of catalytic reforming include five reactions: dehydrogenation of six-membered cycloalkanes, isomerization dehydrogenation of five-membered cycloalkanes, cyclodehydrogenation of alkanes, isomerization reaction and hydrocracking reaction. The first three reactions are reactions to generate aromatics, which directly affect the yield of the product aromatics. Therefore, the content of naphthenes in the raw material determines the octane number of the reformed product and the yield of aromatics. In production, the "potential aromatic content" is usually used to indicate the excellent reaction performance of reforming raw materials. It can be seen that not all naphtha is suitable as reforming raw materials. In addition, naphtha will contain a certain amount of C5 components, which not only is not conducive to the generation of aromatics in the reforming unit, but also increases the energy consumption of the unit and reduces the purity of hydrogen. Therefore, the reforming raw material needs to first fractionate the C5 components, that is, "head pulling."

The reaction mechanism of aromatization of light hydrocarbons is relatively complex, and the academic community has not yet formed a more consistent view. It is generally believed that the alkane component is first converted into olefins, and the olefins generate long-chain olefins through oligomerization under the action of the acid center of the catalyst, and then the cyclization reaction generates cycloalkanes. There are two reaction pathways thereafter.: Under low temperature conditions, aromatic hydrocarbons and alkanes are mainly generated through hydrogen transfer. ； Under high temperature conditions, aromatic hydrocarbons and hydrogen are mainly generated through dehydrogenation. Since the reaction mechanism is different from that of catalytic reforming, the requirements for raw materials for aromatization of light hydrocarbons are relatively broad. C3 to C9 alkanes and olefins can be used as raw materials for aromatization, and there is no requirement for "aromatic hydrocarbon potential content". Catalytic reforming reaction catalysts need to have dual functions: The metal center catalyzes the hydrogenation and dehydrogenation reactions of hydrocarbons, mainly provided by precious metals such as Pt. ； The acidic center mainly catalyzes the rearrangement reaction of hydrocarbons and is provided by halogen-containing Al2O3. Therefore, the catalytic reforming catalyst is composed of basic active components (such as Pt), acidic carrier (such as halogen-containing Al2O3) and cocatalyst (such as Re).

Currently, there are two main types of reforming catalysts used in industry, namely platinum-rhenium catalysts for fixed-bed reactors and platinum-tin catalysts for moving-bed reactors, both of which have been domestically produced. For Pt-containing catalytic reforming catalysts, arsenic, lead, copper, iron, nickel, mercury, sodium, etc. are permanent poisons, and sulfur, nitrogen, oxygen, etc. are non-permanent poisons. The reforming raw materials need to be refined to avoid catalyst poisoning. The reforming catalyst will be deactivated due to coke deposition during operation. It is technically regenerated through charring. However, the halogen in the catalyst will be lost during the charring process. Therefore, chlorination treatment is required after charring to restore the activity of the reforming catalyst. The catalyst for the aromatization of light hydrocarbons is a modified ZSM-5 molecular sieve catalyst. It is a shape-selective molecular sieve with a high silicon-to-aluminum ratio and three-dimensional straight channels. It has excellent catalytic alkylation, isomerization and aromatization reaction properties. ZSM-5 molecular sieve has L acid center and B acid center. The former mainly acts on the dehydrogenation of alkanes and cyclic olefin intermediates, and the latter mainly acts on olefin polymerization, cracking, cyclization and hydrogen transfer. In order to improve the aromatization reaction activity and catalyst life of the catalyst, it is necessary to introduce metal ions such as Ga and Zn to modify the ZSM-5 molecular sieve so that it has a suitable acid amount and intensity distribution.