Present Status of C4/C5 Resources Used in the Production of Synthetic Rubbers - ORGANICS

By Ma Jie, China National Petroleum & Chemical Planning Institute

C4 cuts

1. Butadiene

   More than 90% of butadiene in China comes from ethylene steam cracking and small amounts are from the butylene oxidative dehydrogenation process. The total capacity of ethylene steam cracking is around 18 000 kt/a today and around 3 600 kt of butadiene can be coproduced a year (Outputs of coproduced butadiene have some difference with different ethylene raw materials). The total capacity of butadiene using the butylene oxidative dehydrogenation process is 430 kt/a.
   Major downstream products of butadiene in China include BR, SBR, ABS, styrene/butadiene thermoplastic elastomers (mainly SBS) and NBR. The total consumption of butadiene was around 3 000 kt in 2017. The consumption in the rubber sector (including latex) was around 2 300 kt, accounting for around 77% of the total.
   Traditional rubbers such as BR and SBR are developing towards high-end varieties in recent years and the contribution to the growth of the butadiene consumption is quite small. The growth of butadiene/styrene thermoplastic elastomers is rather flat. The future butadiene downstream market will therefore mainly be driven by the increase of the ABS output. The development of the ABS sector has a promising prospect, but the consumption of butadiene per ton of ABS is relatively low and the influence on the butadiene consumption is quite limited. It is therefore expected that the consumption of butadiene in China will maintain a stable increase in future.
   Judging from the overall supply/demand status of butadiene in China in 2017, the self-sufficiency rate of butadiene is only 88% and there will still be a development space in future. It is estimated that the capacity of ethylene will make a further increase in next few years. The raw material pattern will take oil-based materials as the lead and coal-based materials and light hydrocarbons as the supplement. The operating rate of ethylene units will also be kept at a relatively high level. The overall supply of butadiene will be sufficient. The operating rate of butadiene units using the butylene oxidative dehydrogenation process will still be quite low.

2. Isobutylene

   Sources of isobutylene include direct separation and indirect conversion. C4 cuts as raw materials for direct separation mainly come from ethylene cracking and refinery byproducts. Raw materials for indirect conversion mainly include butane/n-butylene-enriched etherified C4 cuts. The etherification process is usually used today to purify isobutylene contained in C4 cuts. In other words, isobutylene contained in C4 cuts is converted into MTBE for separation. The cracking of MTBE is then conducted to get high-purity isobutylene. As a matter of fact, most of isobutylene is directly taken to the gasoline addition sector after being etherified into MTBE rather than converted into high-purity isobutylene.
   Pushed by the demand in the gasoline addition sector, there were over 200 MTBE producers in China in 2017, the capacity was around 20 000 kt/a, the output was around 11 660 kt and the operating rate was around 58%. According to the incomplete statistics made to 206 MTBE producers, the capacity of MTBE using the air separation etherification process was 10 430 kt/a, accounting for 57% of the total. The capacity of MTBE using the isomerization etherification process (the major raw material being n-butylene) was 3 410 kt/a, accounting for 19%. The capacity of MTBE using the dehydrogenation etherification process was 2 920 kt/a, accounting for 16%. The capacity of MTBE using the co-oxidation process was 1 500 kt/a, accounting for 8%.
   The apparent consumption of MTBE in China was 11 790 kt in 2017, an increase of 2.8% over the previous year (the apparent consumption of gasoline having an increase of 1.8% in the same period). The consumption in gasoline blending was around 11 200 kt, accounting for 95% of the total. The consumption in conversion into high-purity isobutylene was around 590 kt, accounting for 5%. High-purity isobutylene was mainly used to produce MMA, IIR and polyisobutylene. The consumption in the MMA sector was around 240 kt, accounting for around 40.7%. The consumption in the IIR sector was around 220 kt, accounting for around 37.3%. The consumption in the polyisobutylene sector was around 110 kt, accounting for around 18.6%. Other sectors are mainly concentrated in fine chemicals and the consumption was around 20 kt, accounting for around 3.4%.
   It is defined in the “Implementation Scheme for Enlarging the Production of Biofuel Ethanol and Promoting the Application of Vehicle Ethanol Gasoline” jointly issued by 15 government departments including the National Development and Reform Commission, the National Energy Administration and the Ministry of Finance that “the nationwide application promotion of vehicle ethanol gasoline will be conducted and the full coverage will be basically achieved by 2020”. According to the “Ethanol Gasoline for Motor Vehicles” (GB18351-2017) issued in September 2017, the content (mass fraction) of other organic oxygen-containing compounds in National VI ethanol gasoline should not be over 0.5%. It means that components such as MTBE and etherified light gasoline will not be allowed to be used as gasoline blends. Starting from 2020 great quantities of MTBE will have no outlets. It is expected that the capacity of MTBE will make a drastic reduction.
   The major downstream synthetic rubber of isobutylene is IIR. The capacity of IIR in China was 395 kt/a in 2017, the output was around 140 kt and the consumption was around 400 kt. It is expected that the annual increase of the IIR consumption will be maintained at around 20 kt in next few years. The capacity in China fails to fully meet the existing and potential demand. The capacity of IIR in China will still have a growth space of around 100 kt in next few years.

C5 cuts

   C5 cuts can be used as cracking raw materials or directly as fuels. They can also be used to produce C5 resins or as gasoline additives. The use of C5 cuts as single components after separation has aroused widespread attention in recent years. C5 cuts contain various chemical products with high added value. Examples include isoprene (ISP), dicyclopentadiene (DCPD), piperlene (PIP), isopentene, 1-pentene, 2-butyne, 3-methyl-1-butylene, cyclopentane, cyclopentene, isopentane and n-pentane. The content of the first 3 olefins put together accounts for 40-55% of total cracking C5 cuts. ISP accounts for 15-20% of total C5 cuts and is mainly used to produce IR, SIS and IIR.
   The synthesis process was the main source of ISP in the mid-1970s. With the development of separation technology, the synthesis process is gradually replaced by the cracking C5 cuts separation process with higher cost-effectiveness and wider raw material source. Commodity ISP in the world today mainly comes from the separation of C5 cuts. More than 70% of ISP in the world is used to produce IR. The second major application sector of ISP is the production of SIS. SIS is mainly used to produce adhesives. The consumption of ISP in the SIS sector accounts for around 20% of the total. The third major application sector of ISP is the production of IIR and the consumption in the sector accounts for around 4% of the total.
   Based on an ethylene steam cracking capacity of 18 000 kt/a in China, around 3 000 kt of C5 cuts can be coproduced a year and the output of ISP is around 600 kt. There are more than a dozen C5 separation units in China today and the capacity of C5 processing is over 2 000 kt/a.
   The commercialization of C5 separation has provided abundant low-price raw materials for the development of downstream sectors in the production of IR, SIS, IIR, petroleum resins, anhydride curing agents, pyrethroid insecticides, unsaturated polyester resins (UPR) and other fine chemicals. The import amount of ISP in China was around 32 kt in 2017 and the export amount was around 31 kt.
   The demand of products from C5 separation is on the whole quite small in China. Great quantities of C5 cuts still finally flow to the fuel sector and the consumption in chemical uses is quite limited. The consumption of ISP in China was only around 100 kt in 2017 and the future growth will be very limited either. IR is the most important large-volume downstream product of ISP. Qingdao Yikesi New Material Co., Ltd., Zibo Luhua Hongjin New Material Co., Ltd., Fushun Yikesi New Material Co., Ltd., Beijing Yanshan Petrochemical Co., Ltd. and Ningbo Jinhai Co., Ltd. have all constructed IR units. The total capacity of IR has reached 290 kt/a, but the operating rate is quite low, being less than 30% for long years. The major application of IR is to replace natural rubber. The abundant supply and the low price of natural rubber will however not be changed in near future. It is therefore expected that the market development space of IR will be very limited in next few years. The status of lacking the backing from large-volume products to the ISP market will also last for long. The profit-earning ability of C5 separation units will therefore be greatly affected. In such case, the use of hydrogenated C5 cuts as ethylene cracking raw materials will hopefully become an important aspect of C5 chemical uses in future.