Issue 4/2013 - New advances in styrene production technology

New advances in styrene production technology

■ Yan Feng

The traditional production methods of styrene in the world mainly include ethylbenzene dehydrogenation method, propylene oxide-styrene co-production method, pyrolysis gasoline extraction method and butadiene synthesis method
.
Among them, ethylbenzene dehydrogenation is currently the main method of producing styrene at home and abroad, and about 90% of the world's styrene is produced
by this method.
In recent years, people have made great progress in the development of new styrene technologies, and many new production technologies
have been developed.

1.
Pyrolysis gasoline to extract styrene

In recent years, with the large-scale of ethylene, the amount of styrene in pyrolysis gasoline has increased significantly, such as separating styrene before hydrogenation, not only can obtain cheap styrene, but also greatly reduce the hydrogenation load of the device, and the value of C8 aromatics without ethylbenzene as isomerized raw materials has also increased
accordingly.
The pyrolysis gasoline extraction styrene route generally extracts the styrene rich in ethylene pyrolysis gasoline at low temperature through traditional distillation, extraction rectification, selective hydrogenation and refining process, and the highest purity can reach 99.
9%, and the production cost is only half
of the ethylbenzene dehydrogenation method.

In July 2011, China's first 30,000-ton pyrolysis gasoline styrene extraction plant was successfully
trial-produced in Xinhuayue, Maoming, Guangdong.
In December 2011, Sinopec Beijing Yanshan Petrochemical Company's 27,000-ton pyrolysis gasoline C8 extraction styrene plant was also successfully
started.

2.
Ethane preparation of styrene technology

Dow Chemical Company and Italy's Snamprogetti have jointly developed a new process for preparing styrene from ethane and benzene, the SNOW process
.
The route is characterized by low ethane feedstock costs and no upstream investment (ethylene from steam cracking).

The process is to mix ethylbenzene and ethane from an alkylation unit, preheat and send it to a dehydrogenation plant equipped with a catalyst to produce both ethylene and styrene
.
The new process uses a microsphere catalyst
that supports gallium, potassium and platinum on silica-modified alumina.
At the heart of the process is an advanced fluidized bed reactor with catalyst circulation
.

3.
CO2 oxidative dehydrogenation to prepare styrene

In recent years, the green reaction system of using CO2 as a mild oxidant to replace superheated steam to selectively oxidize ethylbenzene to prepare styrene has attracted people's attention
.
It is estimated that the energy consumption of producing 1 ton of styrene is reduced from 62.
70×108J for direct dehydrogenation of ethylbenzene to 7.
94×108J for the new process, the dehydrogenation temperature is reduced by 50 °C, and the use of CO2 instead of superheated steam can also improve the conversion of ethylbenzene and the selectivity of styrene, and inhibit the inactivation
of the catalyst to a certain extent.
The catalysts used are mainly supported metal oxide catalysts, among which the catalysts with better oxidative dehydrogenation performance are mainly Fe series and V series catalysts
.

4.
Biosynthetic styrene

Researchers at Arizona State University in the United States have designed engineered E.
coli (E.
Coli), which can be used to produce styrene
.
This biosynthesis of styrene is achieved using genes from plants, yeast and bacteria
.
The research team verified that by redesigning and developing new metabolic pathways, styrene can be synthesized
with the help of renewable resource substrates such as glucose.
Through the joint action of phenylalanine ammonia lyase and trans-cinnamic acid decarboxylase, endogenous synthesis of L-phenylalanine can be converted into styrene.

5.
Non-metallic materials catalyze the direct dehydrogenation of ethylbenzene to styrene

Coke deposits have always been a key problem
plaguing the alkane conversion industry.
The traditional solution is to add additives such as alkali metals and rare earth metal oxides to properly delay the deactivation process, or introduce a large amount of water vapor for in-situ decarbonization to protect the active center, but the effect is not satisfactory
.
Shenyang National (Joint) Laboratory of Materials Science, Institute of Metal Research, Chinese Academy of Sciences, with the help of highly curved oxygen-doped graphene active structure on the surface of nanodiamond, achieved direct dehydrogenation of ethylbenzene to produce styrene under low temperature conditions protected by oxygen-free and anhydrous steam, and its catalytic activity is about 3 times
that of industrial iron oxide catalysts.

6.
Catalytic cracking dry gas to prepare styrene

The Dalian Institute of Physics and Chemistry of the Chinese Academy of Sciences has successfully developed a technology
to produce ethylbenzene from dilute ethylene (with a volume fraction of more than 10%) and petroleum benzene in the dry gas of the refinery catalytic cracking (FCC), and then dehydrogenate to produce styrene.
Compared with the production of ethylbenzene from pure ethylene, the production cost of this process can be greatly reduced, and it has obvious characteristics of
low cost and energy saving and emission reduction.
The dry gas produced by the catalytic cracking production unit in China's existing refinery equipment is at least 2 million tons, which contains 300,000~500,000 tons of ethylene
.
At present, this technology has been used in
more than 10 sets of styrene production plants such as North China Petrochemical, Daqing Petrochemical, Dalian Petrochemical and Jinzhou Petrochemical.

7.
Ethanol direct alkylation to styrene technology

In October 2009, Shandong Heze Yuhuang Chemical Co.
, Ltd.
used ethanol direct gas phase alkylation to prepare ethylbenzene and negative pressure adiabatic dehydrogenation to produce styrene new process technology of 200,000 tons of styrene plant was completed and put into operation
.
Among them, the ethylbenzene unit adopts the direct hydrocarbonization process of ethanol and benzene to produce ethylbenzene developed by Jiangsu Danyang Chemical and Pharmaceutical Design and Research Institute, which can complete the two reactions
of ethanol dehydration to ethylene and ethylene alkylation in one adiabatic bed reactor at the same time.
The catalyst for ethanol dehydration/ethylene and benzylation jointly developed by Dalian University of Technology and Nanjing Xuanda Chemical Co.
, Ltd.
has less side reactions and high
ethylene utilization rate.

8.
New technology for energy saving and consumption reduction

Affected by operating conditions and the composition of unsaturated diolefin materials, serious polymerization and scaling often
occur in towers, reboilers and storage tanks of styrene production plants.
The use of new domestic coordinated polymerization inhibitor can increase the yield of styrene plant by 1.
92%, reduce the content of styrene in tar by 40.
2%, reduce the tar polymer of crude styrene tartar by 17.
4%, and reduce the polymer of thin film evaporator by 26.
4%.


The preparation of styrene by ethylbenzene dehydrogenation is a typical endothermic reaction
.
Setting an air preheater is one of the commonly used energy-saving technologies for heating furnaces, preheating air can not only increase the combustion temperature, improve the combustion process, and improve the thermal efficiency
of the heating furnace.

PetroChina Lanzhou Petrochemical Company uses a new oil-soluble alkaline compressor scale inhibitor
specially produced in China for the weak acid medium process of styrene plants.
Compared with imported products, the new product can reduce the compressor machine-controlled outlet polymer by 42.
5%, the exhaust condenser inlet polymer by 32.
2%, the ethylbenzene vapor evaporator does not have corrosion leakage, and the corrosion of the dehydrogenation unit equipment is effectively controlled
.

In 2010, Sinopec Shanghai Petrochemical Research Institute and others successfully developed the second generation of energy-saving styrene technology - sequential separation constant boiling heat recovery technology
.
The technology includes a series of new technologies such as sequential separation constant boiling heat recovery energy-saving process, high-efficiency dehydrogenation catalyst, new
azeotropic heat exchanger, and low-pressure drop dehydrogenation reactor.
In June 2012, Sinopec Baling Petrochemical Branch used this technology to build a 120,000-ton styrene plant, and the operation results showed that the azeotropic heat exchanger at the top of the ethylbenzene-styrene tower recovered about 70% of the heat on the top of the tower, saving about 7 tons of water vapor per hour, and the comprehensive energy consumption of the device could be reduced by more than
15%.