In 1970s, people have been concerned about the light heavy aromatic work was mainly by the pyrolysis and catalytic dealkylation method for light hydrocarbon, disadvantage is high reaction temperature, high pressure, low airspeed, hydrogen consumption. In the late 80s, many researches on heavy aromatics light reduction at low temperature and low pressure were reported. In general, mainly through the hydrodealkylation of heavy aromatics to light, generating higher added value of benzene, xylene and xylene and other basic petrochemical products, which can not be separated into all four toluene etc.. The process of heavy aromatics hydrogenation and alkylation involves thermal hydrogenation, alkylation, and catalytic hydrogenation. Dealkylation has high reaction efficiency, low hydrogen consumption, high conversion rate, good selectivity, low operation temperature and high yield of liquid catalytic hydrogenation, catalytic hydrogenation dealkylation process now the focus of the research is to develop improved catalyst and catalyst for industrialization.

Light technology of heavy aromatics abroad

(1) Toray and TAC9 heavy aromatics to produce mixed xylene Technology

The Toray TAC9 process was introduced in 1995 for selective conversion of C9 - C10 aromatics to produce mixed xylene. The technology uses mordenite as the catalyst active component, reforming or pyrolysis gasoline in the C9 - C10 aromatics, distilled as the raw material of this process, the content of C9+ in raw materials more than 50%, the total conversion rate of about 50%.

TAC9 uses hydrogen fixed bed reactor technology to operate hydrogen, in order to prevent coking; two is hydrogen to participate in aromatics hydrogenation, alkyl reaction and non aromatic cracking reaction. In order to ensure a high yield of mixed xylene, the reacted benzene and toluene are separated from the heptane tower and returned to the reactor feed.

The yield of mixed xylene is affected by three factors, that is, the ratio of methyl to phenyl, the ratio of methyl to ethyl, the distribution of C9 and C10 aromatic isomers, and the ratio of C9/C10 aromatics in feed. The higher the methyl to ethyl ratio in the feed, the higher the yield of xylene. For pure C9 aromatics, the yield of mixed xylene is about 75% (W), and the yield of light fraction is about 21% (W).

(2) alkyl and alkyl transfer technologies for ATA-11 heavy aromatics

ATA-11 technology was first industrial application in Korea in 1999. The composite molecular sieves loaded with noble metals were used as active components, which were suitable for C9+ aromatics hydrogenation and alkylation reaction. The suitable reaction conditions of the technology are: 360 DEG C, space velocity 2.3 H-1, hydrogen hydrocarbon ratio 3.6, pressure 2.6 MPa, the yield of mixed xylene is less than 35%, the processing capacity of heavy aromatics is low, and the catalyst is easy to deactivation.

(3) TransPlus process

The process was first applied in CNPC in 1997. The typical gas phase fixed bed reaction was used to produce xylene from toluene and C9 heavy aromatics, and zeolite beta was the active component of the catalyst. When the liquid raw material and the circulating hydrogen are preheated, they are mixed into the heating furnace and heated to the reaction temperature to enter the reactor. The main reactions in the reactor are alkyl aromatics, alkyl removal, alkyl transfer and disproportionation. The main products are benzene, C8 aromatics, hydrogen enriched mixed cycle reactor, unconverted toluene and C9 aromatics into reactor circulation. The reaction temperature is 385~500 DEG C, the reaction pressure is 2.1~2.8MPa, the hydrocarbon to hydrocarbon ratio is 1~3, the space velocity is 2.5~3.5h-1, and the conversion rate is 45%~50%.

Research progress of heavy aromatics in China

At present, domestic production of heavy aromatics is mainly based on light production and high value of BTX. The representative technology is the heavy aromatics light technology of Beijing Petrochemical Research Institute (RIPP) and the technology of toluene and heavy aromatics disproportionation and alkyl transfer in Shanghai Petrochemical Research Institute (SRIPT).

(1) the technology of heavy aromatics hydrogenation of RIPP

The technology uses adiabatic reactor, the reaction temperature 360~460, reaction pressure 1~3MPa, space velocity 1~3h-1, volume ratio of hydrogen to oil under the condition of 500~1500:1, the heavy aromatics into BTX light, was about 30%, while the C9 and C10 changes in the distribution of aromatic hydrocarbons. The technology of heavy aromatics hydrogenation was only about 85%, and the loss of alkyl was great. Ethane and propane were produced by the hydrogenation of ethyl and propyl. The defects of this technology are: in order to ensure that the liquid is closed and not saturated, the pressure of the aromatic ring is lower, so the material is mainly C9 and C10, and the conversion rate of C11 and above material is low.

(2) SRIPT toluene and heavy aromatics disproportionation and alkyl transfer technology

The technology is based on toluene and C9, C10 aromatics as raw materials to produce benzene and xylene, by-product C5 and its following light hydrocarbons and C10 and above heavy aromatics. Many brands of catalysts have been successfully used in industry and occupied most of the market in china. The catalysts used in the process are treated with modified mordenite or beta zeolite to treat heavy aromatic hydrocarbons, which are limited by pore space and low processing capacity of heavy aromatics. If the conversion rate of C10 aromatics is increased by increasing the reaction temperature, the conversion of C9 will be limited.