Simulative Study On Aldehydes Removing Technology For Alcohol Production Based On Reactive Distillation

China is a big country of edible alcohol production and consumption.The maintechnology for alcohol purification is distillation at present,of which the energy consumption is relatively high.Multiple effect distillation is widely used in fuel ethanol separation,the energy-saving effect is prominent.Aldehydes are one kind of the impurities hard to be removed in edible alcohol separation process.There is significance for the development of new type edible alcohol energy-saving separation process to study on the distribution of aldehydes in multi-effect distillation.In the distillation,the ethanol will react with acetaldehyde to produce acetal,which will affect the separation of aldehyde.This paper studied the influences of temperatures and acetic acid as catalyst on the reaction between ethanol and acetaldehyde with a 500 ml reaction kettle.It was found that the condensation reaction of ethanol and acetaldehyde could take place in a neutral environment,and the acetic acid showed also obvious catalytic effect on the reaction.Using thermodynamics analysis,the reaction enthalpy change?35?_rHof-24.13 k J/mol and the reaction entropy change?35?_rSof-64.49 J/?mol·K?could be obtained,respectively.The appropriate reaction kinetics equations for two different kinds of conditions were obtained by the regression of experimental data.In a neutral environment,the rate equation was as following:r=e^{3.6839-4423.7/T}x_A² x_B-e^{11.4409-7326.3/T}x_C x_DIn the presence of acetic acid,the rate equation was as following:r=e^{0.0017-0.0002/T}x_HAc^0.5x_A² x_B-e^{7.7597-2902.6/T}x_HAc^0.5x_C x_DThen a multi-effect distillation process based on fuel ethanol production process was developed using ordinary distillation module in ASPEN PLUS for edible alcohol separation.The simulation results showed that,with the methanol removing column added,the products could reach the standard of premium grade edible alcohol.But such results did not tally with the actual situation.Thus the aldehyde distribution were studied with reaction rectification module.The simulation results showed that,in a column with high alcohol concentration,the ability of removing aldehydes was greatly weakened as part of acetaldehyde turned into acetal.It made the total aldehydes content in the product get 105.9 mg/L,which was close to the aldehydes content in actual products.And in the rational range of energy and material consumptions,the aldehydes content could not reach the premium grade standard only by adjusting the operating parameters.It indicated that,to get qualified products,the aldehydes should be separated in low alcohol concentration.By the analysis of aldehydes distribution in the process,it was found that the liquid flows at the top of the first crude distillation column was the main channel for aldehyde impurities went into the high alcohol area.Thus a water extraction tower was adopted to deal this liquid flow in this paper.The simulation results showed that,the water extraction tower could effectively remove aldehydes.Through technological optimization,the total aldehyde content in the product could be decreaced to 1.58 mg/L,which reached the standard of premium grade edible alcohol,and the steam consumption to product one ton alcohol was reduced to 1.99 t,superior to the traditional processes.This article provided a new idea on optimizing the energy-saving of edible alcohol production process and the multi-product transformation in fuel ethanol production.