By Ren Yunfeng, CIESC

Brisk world production and demand

Low-carbon olefins (with the number of carbon atoms no higher than four), represented by ethylene, propylene, butadiene (BD) are basic raw materials for the organic chemical industry. They can be used to produce organic compounds and polymer materials, such as polyethylene (PE), polypropylene (PP), acrylonitrile (ACN), ethylene oxide (EO), monoethylene glycol (MEG) and synthetic rubber.  

   World ethylene capacity reached 171 million t/a in 2017, up by 18.4% from 2010, with output at 152 million tons, up by 24% and consumption at 154 million tons, up by 25.8%. By 2020, global ethylene capacity is expected to rise to 195 million t/a, up by 14.0% from 2017 and output at 173 million tons, up by 13.8%. 

   World propylene capacity totalled 132 million t/a in 2017, up by 28.7% from 2010, with output at 105 million tons, up by 31.9% and consumption at 105 million tons, up by 33.3%. By 2020, global propylene capacity is expected to reach 150 million t/a, up by 13.6% from 2017 and output at 121 million tons, up by 15.2%. 

   World BD capacity amounted to 14.98 million t/a in 2017, up by 21.2% from 2010, with output at 11.46 million tons, up by 19.4% and consumption at 11.39 million tons, up by 18.3%. By 2020, global BD capacity is expected at 15.83 million t/a, up by 5.6% from 2017, with output at 12.28 million tons, up by 7.1%. 

   China’s self-sufficiency rate of low-carbon olefins has been on the rise. Table 1 shows that most downstream products of ethylene were in tight supply and rely on imports to meet demand. Table 2 reflects most downstream products of propylene are in balanced supply-demand, but overall market competition is intense. The distribution of BD downstream demand is scattered. Around 70% of BD supply goes into butadiene rubber (BR), styrene butadiene rubber (SBR) and ABS production, and the remaining 30% feeds SBR latex, NBR and NBR latex.  

   Table 1  Domestic ethylene downstream products in 2018  (kt/a, kt)

Table 2  Propylene downstream products in 2018 (kt/a, kt)

Diversified and lightweight feedstock for low-carbon olefins

   China’s huge supply gap of low-carbon olefins has attracted a large number of investors to build up ethylene, propane dehydrogenation (PDH) and methanol-to-olefin (MTO) plants. Private enterprises, such as Zhejiang Petrochemical, Shenghong Refining and Chemical and Hengli Petrochemical are striving to gain a foothold in the upstream industrial chain. The investment boom, with the aim to foster “oil refining-PX-PTA-PET-polyester”whole industrial chain under the help of refining-chemical integration projects has resulted in diversified feedstock routes for  low-carbon olefins, tightened market competitions and boosted domestic capacities. 

   In the structure of feedstock ethylene, the proportion of ethane, methanol and LPG is on the rise, while that of naphtha is declining. As for feedstock propylene, the volume of cracked propylene is shrinking, to be replaced by refinery grade propylene from FCC propylene separation, PHD, MTO/MTP (methanol-to-propylene) and CTO (coal-to-olefin). In BD feedstock structure, BD extraction currently accounts for 94%. The growing number of CTO/MTO plants is expected to raise the ratio of oxidative dehydrogenation of butene route. But the extraction process will remain the dominant source of BD and sustain a share of 94% by 2025.  

Low-carbon olefin technology

   1. Petroleum-based low-carbon technology

   Petroleum is the major feedstock source of world low-carbon olefin production. Steam cracking in tube furnace is the major technology and development trends will focus on low energy-consuming, low-investment, improving feedstock adaptability and extending operating cycle. Other production processes include catalytic cracking of naphtha to ethylene, catalytic cracking of heavy oil to ethylene, PDH to propylene, FCC-based propylene, oxidative dehydrogenation of butene to BD, catalytic cracking of olefins to low-carbon olefins and direct cracking of crude oil to ethylene, etc.    

   2. CTO technology

   The key step of CTO lies in MTO, which includes MTO and MTP. 

   3. Natural gas-based low-carbon olefin technology

   The technology mainly includes direct and indirect conversion of natural gas to ethylene routes. 

   Other new technologies are emerging both at home and aboard. A typical one is direct cracking of crude oil to low-carbon olefins. In January 2014, ExxonMobil officially started up in Singapore a 1 000 kt/a world-scale commercial steam cracker that produces olefins directly from crude oil. Diversified and lightweight raw materials of low-carbon olefins and emerging new production technologies will have a profound impact on chemical industry development.