About Ethylene. Ethylene (a.k.a. Ethene) is an unsaturated organic compound, the simplest member of the alkene class of hydrocarbons. Even though it has no direct use, being used almost exclusively as a building block, Ethylene is the largest-volume petrochemical produced worldwide. It has one double bond and, in room temperature, ethene is a sweet odor and taste gas, colorless and extremely flammable. It has been produced since the 1930s; however, its production grew rapidly in the middle of the twentieth century, when oil and chemical companies began separating it from refinery waste gas and producing it from natural gas and ethane (obtained from byproduct refinery streams). Ethylene may also be produced from renewable sources. In such cases, it may be referred to as Bio-Ethylene or Green Ethylene.

Most of Ethylene production is based on feedstocks derived from petroleum, being steam cracking – high temperature pyrolysis in the presence of steam – the main technology used. The petroleum-based feedtocks used in steam cracking are grouped as gaseous (ethane, propane, n-butane, natural gas liquids and any mixture of them) and liquid (field condensates, natural gasoline, BTX raffinate, light naphtha, naphtha). Such different feedstocks, according to cracking conditions, generate slates of characteristic product yields with varying compositions. In general, high yields of Ethylene with small amounts of by-products are obtained from gaseous feedstocks, while lower Ethylene yields with larger amounts of by-products are obtained from liquid feedstocks.

Most recently, growing environmental concerns have increased interest over alternative routes to conventional petroleum-based ethylene production, specially the dehydration of bio-derived ethanol. With such a diverse range of derivative products, Ethylene demand is very sensitive to economic cycles. In fact, it is often used as a reference in the performance evaluation of the petrochemical industry. The economics of Ethylene production is largely dependent on the prices for feedstocks and co-products, mainly propylene. It is worth noting that, in general, heavier feeds leads to higher costs of production and capital investment required.

It is stored as liquid under high pressure or at low temperatures. However, most of the times, Ethylene is directly supplied to consumers, via pipeline grids. In such pipelines, Ethylene is usually under a pressure of 4–100 MPa. The upper end of the pressure range is significantly above the critical pressure. Below critical conditions, the temperature must be grater than 4 °C to prevent liquid Ethylene from forming. Ethylene is also transported by ship, barge, railcar, and tank truck. Ships can transport between 2,000 and 6,500 t. These vessels are of the semi-refrigerated type, and transport liquid ethylene at atmospheric pressure and -104 °C. The tankers include reliquefaction plants on board since it is too expensive to vent Ethylene.

Ethylene is primarily produced by the pyrolysis of hydrocarbons and by recovery from some refinery products. It can also be produced from other pathways, such as ethanol dehydration or methanol-to-olefins plants. Raw materials and the respective production processes employed in the manufacturing of Ethylene are listed below.

The uses and applications of Ethylene may vary according to its specification. The main forms of Ethylene are technical grade (95% min purity) and polymer grade (PG, 99.9% min purity).

Polyethylene (PE) is responsible for about 60% of the global Ethylene demand. The main class of polyethylene produced in the world is high density polyethylene (HDPE), which is responsible for the consumption of a third of the available Ethylene, followed by low density (LDPE) and linear low density (LLDPE) varieties. Ethylene oxide, another relevant derivative of Ethylene, is an intermediate to ethylene glycol synthesis.