Dehydration of Ethanol With Aluminium Oxide

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Ethanol is an important chemical feedstock that is polymerised to make plastics and other products. It is traditionally made from fossil fuels but a significant effort is being put into developing processes that can produce it from renewable sources such as corn or cellulosic ethanol. Ethanol can be dehydrated to form alkenes such as ethylene which is a critical precursor to many industrial products. The dehydration reaction is an exothermic reaction that releases a lot of heat. This article describes a simple but interesting way of producing a gaseous alkene such as ethylene from ethanol by passing it over heated aluminum oxide powder.

Ethanol vapor is blown over the aluminium oxide which is half-way along a long Pyrex tube. This allows the ethanol to be 'cracked' or dehydrated to form ethene, an unsaturated hydrocarbon. The ethene can be collected over water and tested for typical properties of an unsaturated hydrocarbon such as boiling and melting points. The experiment can be used as a demonstration or class experiment. It is important to read the standard health and safety guidance before using this experiment. It involves handling hot glassware and manipulating the apparatus for safe gas collection over water without suck-back into the tube (which could shatter it).

The experimental set up was based on a 1983 patent on a process that uses a fluidized bed reactor to dehydrate alcohols to produce ethylene. This is a much more efficient process than the traditional fixed bed reactions used to convert ethanol to ethylene as it minimizes byproduct formation, resulting in lower separation and catalyst regeneration costs. It is also much more environmentally friendly than traditional processes that are based on petroleum sources.

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