C4 Resources
— Processing and Utilization in China

The utilization of four-carbon (C4) hydrocarbons as conventional consumer liquefied gas will be gradually reduced due to the development of the natural gas industry in recent years. In addition, along with the domestic demand growth for ethylene, propylene and other polymer materials, China will build several sets of million-ton ethylene steam crackers, which will greatly expand the production of C4 hydrocarbons as a by-product. Therefore, t rational use of C4 resources has become a high priority in China's chemical industry.
There are four sources of C4 in China, but most of it is a by-product of either fluid catalytic crackers (FCC) in refineries or ethylene crackers. It is estimated that China produced about 10 million tons of C4 hydrocarbon resources in 2010.
China has generally used C4 fractions as fuel, and in oil refining and chemical synthesis. In oil refining, C4 distillate blended with gasoline without any reaction processing is used to adjust vapor pressure and the distillate is used to produce liquid fuel and other products through chemical reaction. It is usually used to produce high octane gasoline components, such as gasoline alkylate, oligomerization of light olefins for diesel manufacture, methyl tert-butyl ether(MTBE), etc; and some is used for the production of polybutylene and polyisobutylene as lubricant additives. In chemical processing applications of C4 fractions, 1,3-butadiene, butene, isobutene and isobutane are the most valuable. They are generally used in the production of rubber elastomer, 1-butene, methyl ethyl ketone, acrylonitrile-butadiene-styrene (ABS), styrene-butadiene blocks elastomer (SBS), MTBE, methyl methacrylate (MMA) and 1,4 butanediol, etc.  
A scarcity of 1,3-butadiene restricts China's development of its synthetic rubber industry. Current producers of 1,3-butadiene are basically extracting the C4 by-products of ethylene cracking process. Zibo Qixiang Tengda Chemical Co., Ltd is building a production plant for catalytic oxidative dehydrogenation (ODH) of raffinate C4 to produce 1,3–butadiene for its own synthetic rubber production.
1-butene could be used in polyethylene production as co-monomer. Poly (1-butylene) is widely used as a thermoplastic resin. Butene's oligomers, C8 and C12 olefins are widely used in automotive liquids, lubricant additives, synthetic detergent agents, surfactants, etc. Shanghai Research Institute of Petrochemical Technology Company (SRIPTC) developed a technology to expand 1-butene production by applying an isomerization process. There is already a 30 000 t/a 1-butene production facility that uses this technology, operated by Sinopec's Zhongyuan Petrochemical Company. SRIPTC has also developed butene hydroisomerization technology.
The main products made from 2-butene are
* gasoline alkylate from indirect alkylation (accounting for 70% of 2-butene consumption)
* propylene synthesized from 2-butene and ethylene
* methyl ethyl ketone produced via butene hydration and dehydrogenation
* octene from dimerization of 2-butene
Steam cracking n-butane to produce ethylene is most promising, constrained by the comparative costs of other cracking feedstocks. N-butane can also be used to produce maleic anhydride via gas-phase oxidation with existing V2O5-P2O5 catalysts, but this technology is rarely applied in China.
Isobutane is mainly used to produce propylene oxide via co-oxidation, or isobutene via dehydrogenation, or aromatics via aromatization. Panjin Zhenao Chemical Co., Ltd of Panjin Heyun Industrial Group, located in Liaoning province, is building an isobutylene plant, adopting isobutane dehydrogenation technology licensed from Russia.
As world's demand for propylene grows, the average annual growth rate of propylene market has exceeded that of ethylene. Thus any new propylene production technology using C4 hydrocarbons as raw material arouses wide interest.
SRIPTC has developed S-OCC technology to produce propylene via olefin cracking. Zhongyuan Petrochemical's 60 000 t/a propylene industrial demonstration unit has successfully started up with a single pass yield of 28.5 wt%. It adopts an adiabatic fixed bed reactor with a low investment.
SRIPTC also developed the S-OMT technology for olefin metathesis (OMT), with a butadiene conversion rate of 100%, butene conversion no less than 87.7%, and total yield no less than 98.6%. Sinopec Beijing Yanshan Petrochemical's 200 000 t/a S-OMT unit is expected to be put into operation in 2012.
China has also made some progress in researching C4 hydrocarbon aromatization process technology. The aromatization of liquefied gas to produce high octane gasoline technology, a process developed by Dalian Institute of Chemical Physics CAS, was successfully used in a 200 000 t/a liquefied petroleum gas comprehensive utilization device of Guangxi Yuchai Petrochemical Company at the end of 2011.

China's Typical Fractional Composition of By-product C4 from FCC & Ethylene Cracking
Composition wt%
     Isobutane    n-Butane    Isobutene    1-butene    Butene-2    Butadiene
Steam cracking        1    2    22    14    11    50
FCC        34    10    15    13    28    -