Industrial production of Ethyl acetate
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Industrially, ethyl acetate can be produced by the catalytic dehydrogenation of ethanol. For cost reasons, this method is primarily applied to conversion of surplus ethanol feedstock as opposed to predetermined generation on an industrial scale. In addition, it is commonly accepted as far less practical and less cost effective.
Catalysts for dehydrogenation include copper, operating at an elevated temperature but below 250 °C. The copper may have its surface area increased by depositing it on zinc, promoting the growth of snowflake, fractal like, structures. This surface area can be again increased by deposition onto a zeolite, typically ZSM-5. Traces of rare earth metals or alkalies, such as that of sodium and potassium, have also been found to be beneficial to the process. Byproducts of hydrogenation include diethyl ether (thought to primarily arise due to aluminum sites in the catalyst), acetaldehyde, acetaldehyde aldol products, higher esters and ketones. Acetaldehyde and MEK complicate conversion and purification as ethanol forms an azeotrope with water, as does ethyl acetate with ethanol and water and MEK with both ethanol and the acetate. To obtain a high purity product, these azeotropes must be "broken", and this can be achieved by making use of pressure swing distillation.
The composition of the distillate removed from the conversion products is biased towards acetate at atmospheric pressure and ethanol at increased pressure. First, the raw product is fed into a high pressure column where the bulk of the contaminating ethanol is removed. By then feeding the ethanol depleted distillate into a low pressure column, the acetate can be removed from the remaining ethanol azeotrope.
MEK forms during the conversion process from 2-butanol. The latter fails to form an azeotrope with the acetate and so MEK can be removed by hydrogenation of the contaminated product over nickel and further distillation to strip away 2-butanol. This provides the simultaneous benefit of removing the acetylaldehyde contaminant by returning it to an ethanol form and is easily accomplished as hydrogen is a byproduct of the initial dehydrogenation process.
It may also be possible to break the azeotropes with the use of membrane distillation, molecular sieves, an entrainer or absorption medium.
The distilled ethanol and rehydrogenated contaminants can then be recycled into the raw feedstock.
Catalysts for dehydrogenation include copper, operating at an elevated temperature but below 250 °C. The copper may have its surface area increased by depositing it on zinc, promoting the growth of snowflake, fractal like, structures. This surface area can be again increased by deposition onto a zeolite, typically ZSM-5. Traces of rare earth metals or alkalies, such as that of sodium and potassium, have also been found to be beneficial to the process. Byproducts of hydrogenation include diethyl ether (thought to primarily arise due to aluminum sites in the catalyst), acetaldehyde, acetaldehyde aldol products, higher esters and ketones. Acetaldehyde and MEK complicate conversion and purification as ethanol forms an azeotrope with water, as does ethyl acetate with ethanol and water and MEK with both ethanol and the acetate. To obtain a high purity product, these azeotropes must be "broken", and this can be achieved by making use of pressure swing distillation.
The composition of the distillate removed from the conversion products is biased towards acetate at atmospheric pressure and ethanol at increased pressure. First, the raw product is fed into a high pressure column where the bulk of the contaminating ethanol is removed. By then feeding the ethanol depleted distillate into a low pressure column, the acetate can be removed from the remaining ethanol azeotrope.
MEK forms during the conversion process from 2-butanol. The latter fails to form an azeotrope with the acetate and so MEK can be removed by hydrogenation of the contaminated product over nickel and further distillation to strip away 2-butanol. This provides the simultaneous benefit of removing the acetylaldehyde contaminant by returning it to an ethanol form and is easily accomplished as hydrogen is a byproduct of the initial dehydrogenation process.
It may also be possible to break the azeotropes with the use of membrane distillation, molecular sieves, an entrainer or absorption medium.
The distilled ethanol and rehydrogenated contaminants can then be recycled into the raw feedstock.
