Ethylene Basics

Ethylene: Ethylene (H2C=CH2) is

• The largest volume building block for many petrochemicals
• End products such as plastics, resins, fibers, etc.
• Colorless, flammable gas with a slight odor
• A very reactive intermediate and, therefore, is involved in many chemical reactions
  • Polymerization – one of the main reactions for the production of polyethylene (including Low-density Polyethylene – LDPE, High-density Polyethylene – HDPE, and Linear Low-density Polyethylene – LLDPE)
  • Oxidation – for production of ethylene oxide and ethylene glycols (used in PET and fibers)
  • Addition – many addition reactions are important.
    • Halogenation-hydrohalogenation reaction chemistry is used for forming Ethylene Dichloride (EDC) which is cracked to produce Vinyl Chloride Monomer (VCM) used in the production of Polyvinyl Chloride (PVC).
    • Similarly, Ethylbenzene (EB) is produced from benzene and ethylene. Ethylbenzene is dehydrogenated for styrene manufacture and used for producing Polystyrene (PS).
    • Oligomerization for the production of alpha-olefins and linear primary alcohols
    • Ethanol is manufactured from ethylene by hydration
• Slightly more potent anesthetic than nitrous oxide; smell can cause choking, so it is no longer used as an anesthetic.
• Used in controlled ripening of fruits and vegetables

Ethylene manufacturing

• Thermal cracking of hydrocarbons (ethane and heavier) is the major route for industrial ethylene production
  • Also produces valuable by-products – like propylene, butadiene, butenes (Butene-1, Butene-2, Isobutene), Benzene, Toluene, and hydrogen. Less valuable by-products include methane and fuel oil.
  • Thermal cracking is accomplished in tubular reactors commonly known as cracking furnaces. These are direct-fired reactors for providing high-temperature heat of reaction and sensible heat. Most plants have 6 to 8 cracking furnaces for achieving the desired plant capacity.
    • Cracking furnaces experience coke laydown inside the tubes and need decoking at frequent intervals to stay within the temperature limits of tube metallurgy
    • Coke mitigation technologies are used to minimize the coke laydown
    • Cracking furnaces operate with the lowest optimum pressure to maximize the reaction selectivity for light olefins. Dilution steam is used for minimizing the secondary reactions that eventually lead to coke formation
    • Conversion of feed or severity of operation is selected based on the desired product slate and overall plant optimization
  • Feedstocks include – ethane, propane, butanes, naphtha (light to heavy), gas oils (light to vacuum, including hydrotreated and/or hydrocracked), condensates, light crudes, refinery off-gases, etc.
  • Cracking furnace effluents are cooled and compressed for recovering ethylene and by-products. The separation of lighter products requires very low temperatures that are achieved by application of the refrigeration systems.
  • Ethylene is a highly energy-intensive process; therefore, energy recovery and conservation are important to minimize the cost of production and improve environmental performance. Sustainability, environmental performance, and emission reduction have been a constant theme over the years and are now at the forefront during the process of energy transition and net-zero targets.
• Methanol to Olefins (methanol is mostly produced either starting from coal or methane) utilizes catalytic processes for converting methanol to ethylene and/or propylene.
• A small amount of ethylene is recovered from refinery conversion processes (like Fluid Catalytic Cracking) and the Fischer-Tropsch process.
• A small amount of ethylene is produced by dehydrating ethanol (mostly produced from biomass).

Alternate Routes for Ethylene Production: These technologies are potential options for ethylene production.

1. Oxidative coupling of methane – was developed in the late 1970s and 1980s. This process concept has been demonstrated and so far has no commercial application.
2. Catalytic oxy-dehydrogenation of ethane – this process is available for commercial applications (currently no plant in operation) and produces a large amount of acetic acid as a by-product.
3. Catalytic pyrolysis process (based on the free radical mechanism – like thermal cracking) for production of ethylene (and light olefins) using heavy hydrocarbon feeds. This process has been used in commercial applications in China.
4. Ethane dehydrogenation process based on the chemical looping concept is currently under development, as a potential option for decarbonizing ethylene manufacturing.
5. Shockwave reactor concept using supersonic speeds (Roto Dynamic Reactor), currently under development, is a potential option for using carbon-free electric power for ethylene production.