Dry Gas: China Summary Ethylbenzene, used in the production of many plastics, is derived from benzene and ethylene. Producing ethylene usually has required the construction and operation of an expensive high-temperature plant. An alternative, cheap source of ethylene is the so-called “dry gas,” a by-product of gasoline production, which contains some 20 percent ethylene. Separation has presented difficul- ties, however. For this reason, ethylene cre- ated during the production of gas normally has been burned off for heat recovery. Now, a new process using a carefully designed cat- alyst has provided a high conversion rate of ethylbenzene from the dry gas. Two plants in China are operating with the new technology.

Ethylene is an important raw chemical substance used all over the world. For example, polystyrene is produced by the alkylation of benzene with ethylene - that is, the reaction of ethylene with benzene to form ethylbenzene. (Styrene is then pro- duced from the dehydrogenation of ethyl- benzene and polystyrene from polymeriza- tion.) Worldwide, the annual consumption of polystyrene for manufacture of plastic com- modities is some 100 million tonnes.

Ethylene has normally been produced through high-temperature cracking of petroleum feedstocks; the plant needed for this requires enormous financial invest- ments. However, a cheap source of ethylene does exist. This is the dry gas produced by the fluid catalytic cracking (FCC) plants in petroleum refineries. Such plants, which

convert low-cost heavy petroleum oil into valuable gasolines, are key installations in all refineries.

In addition to the main product gasoline, FCC plants yield large amounts of by-prod- uct gases. Among these by-products is “dry gas” which contains large amounts of nitrc- gen, carbon dioxide and carbon monoxide - none of which are useful. The dry gas also contains about 20 percent volume of ethylene, which is a valuable chemical sub stance. The ethylene, however, is not easy to separate from the other components and is normally burned off in the refineries for heat recovery.

The basis of the innovative experience described here is the development of new technologies to exploit the ethylene for use in the production of ethylbenzene, with sub stantial economic benefits. Eight years of research led scientists at the Dalian Institute of Chemical Physics (DICP) in China to develop a new chemical process for produc- tion of ethylbenzene that enabled the ethy- lene sourced from FCC dry gases to react with benzene. New plants based on this tech- nology have been built in China for com- mercialization.

The first of these new plants that use the technology of direct alkylation of benzene with FCC dry gas, without any pre-treat- ment, to produce ethylbenzene was estab- lished in 1993. The technology is based on a sophisticated catalyst developed by DICP. The chemical industry often turns to cata- lysts as the only route to a certain product. A

VOLUME ONE- SCIENCE AND TECHNOLOGY 43

DRY GAS: CHINA

catalyst’s “activity” can accelerate the pro- duction rate of a chemical reaction. At the same time, its “selectivity” dictates a cata- lyst’s ability to enhance the production rate of the desired product and minimize the for- mation of by-products.

In the first commercial plant based on the DICP technology, the catalyst’s activity and selectivity have remained high after five years of operation. Conversion of the ethy- lene in the dry gas has exceeded 95 percent, the selectivity to ethylbenzene has been more than 99 percent, and the purity of the ethylbenzene produced has averaged 99.6 percent of its weight. A second plant is oper- ating with similar results.

Background and Justification FCC is an important heavy-oil conversion technology in refineries. In China, the total capacity of FCC plants has reached 56 mil- lion tonnes per year. Dry gas, meanwhile, is produced at an annual rate of 1.68 million tonnes. The latter usually contains some 20 percent volume of ethylene that is burned off as refinery fuel.

To exploit the ethylene in dry gas, DICP developed a process of direct alkylation of benzene with the dry gas without any special pretreatment. Application of this technology not only allows better exploitation of the ethylene resources in the FCC dry gas, but also addresses the problem of shortage of ethylbenzene in China.

Outside China, processes using dilute ethylene to produce ethylbenzene have been developed. All these efforts, however, rely on pretreatment of the dry gas to remove

small amounts of such impurities as hydro- gen sulfide, carbon dioxide and water vapor. These impurities could damage the catalyst and so must be removed if the catalyst is to maintain a long and stable operational lie. The unique feature of the DICP technology is the development of a catalyst that is resis- tant to sulfur and water and has a long oper- ational life.

Description Use of a catalyst with ethylene in the FCC dry gas to alkylate with benzene to produce ethylbenzene began in 1985. DICP research, first on a laboratory scale and then in a pilot plant, under conditions simulating commer- cial plants led to development of a novel cat- alyst for this new technology by 1988. The next two years saw the manufacture of the catalyst on a semi-commercial scale (500 tonnes annually). Design of a commercial- scale plant, with production capacity of 30,000 tonnes per year, then followed, and the plant was built and put into continuous operation in 1993.

In the conventional production process of ethylbenzene, impurities such as hydrogen sultide, carbon dioxide and water vapor in the FCC dry gas can lower the ethylbenzene selectivity and operational life of the catalyst, and also the quality of the ethylbenzene pro- duced. To counter these unfavorable effects, the catalyst was moditied with rare-earth oxide components during its preparation and treatment with steam at high temperature.

The new catalyst can be used under a wide range of reaction temperatures and low pressures, and allows good benzene alkyla- tion with the original dry gas. The catalyst

44 SHARING INNOVATIVE EXPE RIENCES

DRY GAS: E ~ I N A

has a long operational of 90 to 100 days before requiring regeneration.

The ethylene content in FCC dry gas is 10 to 30 percent of volume. The heat evolved during the chemical reaction results in a temperature rise of 60o to 180o C. Multi- stage reactors are used during the process. After pre-heating, benzene enters the first reactor which contains a catalyst and exchanges heat directly with the high-tem- perature effluent to absorb the reaction heat. The problem of heat removal in an adiabatic reactor is thus solved as the temperature rise of the inlet and outlet flow is lowered to between 50" and 70" C. Temperatures in the various reactors are quite uniform.

Recovery of benzene vapor from the tail gas reactor effluent is vital to the reduction of benzene consumption. Because only the ethylene in the dry gas undergoes reaction, more than 70 percent of the gas will exit the reactors as inert gas. The new DICP tech- nology allows the tail gas benzene to be absorbed by the reaction raw material, and gives a recovery rate of at least 99 percent of weight at room temperature. The gas leav- ing the absorber is led to the refinery fuel- gas system.

The catalyst displays good performance characteristics: high activity, high tolerance to harmful impurities, long operational life and easy regeneration. In addition, this pro- prietary technology possesses several advantageous features: (1) because the FCC dry gas needs no pretreatment, the produc- tion process is simpliied; (2) benzene in the tail gas can be recovered by passing this gas through an adsorption tower; (3) the cata- lyst, a so-called molecular sieve, does not

generate harmful or poisonous pollutants during the alkylation reaction; and (4) the exhaust tail gas can be used as a fuel to the refineries, making the technology environ- mentally friendly.

Patenting and Commercialization The results of the test operations at the Fushun Refinery showed a slow decrease of catalyst activity over time, but constant selectivity to ethylbenzene and ethylben- zene purity. In addition, raw material con- sumption remained constant.

The data from this plant indicate the average conversion of ethylene to exceed 95 percent, selectivity to ethylben- zene to exceed 99 percent, and purity of ethylbenzene produced to exceed 99.6 per- cent. Consumption of benzene and ethyl- benzene was 0.76-0.78 tonnes and 0.270- 0.275 tonnes, respectively, for the production of 1 tonne of ethylbenzene, with overall ener- gy consumption of about 400 kg-FOE per tonne ethylbenzene produced.

A detailed specification of the ethylben- zene produced at the commercial plant indi- cates that it meets the China National Stan- dard premium grade and can be used in the manufacture of styrene, pharmaceuticals and perfumes.

The plant was put into operation in 1993 at the No. 2 Refinery of the SINOPEC Fushun Petrochemical Company, and has been running satisfactorily to date. In December 1996, a second plant was put into operation. This plant is located in the SINOPEC Linyuan Refinery in northern China. The plant capacity is 30,000 a year.

V O L U M E ONE- SCIENCE A N D T E C H N O L O G Y 45

Operational results of this second plant are similar to those of Refinery No. 2 of the SINOPEC Fushun Petrochemical Company.

The developers of this new technology are ready to collaborate with foreign enter- prises on technology transfer, and to provide services including:

Lessons learned A novel catalyst-based technology for pro- duction of ethylbenzene by alkylation of ben- zene with dilute ethylene in FCC dry gas has been developed and commercialization in China has begun. The technology is simple to apply, has significant cost benefits, and is

Project proposals. Feasibility reports. Technical consultation. Basic, preliminary and detailed designs. Contracting and procurement services. Construction supervising. Commissioning of new plants. Personnel training.

Following the initial experience in China, the developers are confident that the new technology is especially cost-effective and suitable for commercialization in other developing countries.

Partnerships This new technology has been developed solely in China. DICP was responsible for creating the new catalyst, while the design and process development were the respon- sibility of the public partnership SINOPEC Fushun Petrochemical Company.

Replicability The manufacturing technology of the cata- lyst has proved satisfactory for commercial- scale production.

environmentally friendly. This technology can allow the ethylene

resources in FCC dry gas to be exploited, and may also be a solution to the shortage of ethylbenzene in China.

Outside China, processes using dilute ethylene to produce ethylbenzene have been developed, but all rely on pre-treatment of the dry gas to remove impurities.

Impact Application of the new technology

through commercialization can bring the advantages of cleaner and more efficient industrial processes, with ensuing cost ben- efit. The technology is now proven on a com- mercial basis. 0

Implementing Institution: Dalian Institute of Chemical Physics Head: Yang Bailing, Director Address: Chinese Academy of Sciences, PO. Box 10, 116023, Dalian Zhongshan Road 457, China Tel.: 086-41 1-467 1991 Fax: 086-411-4691570E-mail: <<hyperlink mailto:lyx>> Cost: government support US$2 million

46 S H A R I N G INNOVATIVE EXPERIENCES