Ethylene, CH2=CH2, the most-produced organic chemical in the world, is used to make hundreds of products. The major product is polyethylene, but other important ones include poly(vinyl chloride), polystyrene, antifreeze (ethylene glycol), adhesives, solvents, and detergents. See also: Adhesive; Detergent; Ethylene; Ethylene glycol; Polyolefin resins; Polystyrene resin; Polyvinyl resins; Renewable resources; Solvent
When you think of polymers from natural sources (biopolymers), polyethylene doesn’t usually come to mind because most ethylene is produced by steam cracking hydrocarbons such as ethane and naphtha. However, the Brazilian petrochemical company Braskem has been producing commercial quantities of polyethylene using bio-based ethylene (bioethylene) since 2010. See also: Biopolymer; Cracking; Naphtha
Bioethylene is made by dehydration of plant-derived ethanol (bioethanol) at high pressure and temperature in the presence of an aluminum oxide (Al2O3) catalyst; that is CH3–CH2–OH → CH2=CH2 + H2O. Most bioethanol is produced by fermentation of sugars from corn, sugar beet, sugarcane, and sweet sorghum. See also: Catalysis; Corn; Ethyl alcohol; Fermentation; Sorghum; Sugar crops; Sugarbeet; Sugarcane; Chemicals from renewable feedstocks
According to the U.S. National Renewable Energy Laboratory (NREL), production of ethylene from hydrocarbons is the largest carbon dioxide–emitting process in the chemical industry. Compared to hydrocarbon processes, bioethylene from ethanol reduces carbon dioxide (CO2) emissions by 70–80%.
Because ethylene is a commodity chemical, the downstream products made from it are very sensitive to its price. Over the past 10 years, the global average price of ethylene has fluctuated from $400 to $1300 per metric ton. The current global price for ethylene is around is $1200 per metric ton, while the U.S. price is about $1000 per metric ton, largely because U.S. ethylene producers are benefiting from the low price of ethane from shale gas. Currently, Brazilian ethanol from sugarcane is the lowest priced bioethanol in the world. Even so, the production cost of bioethylene is about $1200 per metric ton, which makes it noncompetitive in the world market. Braskem, however, uses its bioethylene to make premium-priced biopolymers (high-density polyethylene and linear low-density polyethylene) for consumer-goods manufacturers (cosmetics, food, and so forth) who use them to make green-packaging materials.
Although bioethylene is a niche product, the outlook could change if a cost-efficient process for converting lignocellulosic biomass to ethanol can be developed. This is still an emerging technology, as the current production cost of ethylene from cellulosic ethanol is around $2000 per metric ton. See also: Biomass; Cellulose