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Simulation of An Industrial Vinyl Acetate Production Plant

Daniel Martínez1, Juan Camilo Naranjo1, Samuel Ramírez1, Juan Pablo Contreras Ayala1, and Ivan Dario Gil Chaves2. (1) Department of Chemical Engineering, Universidad de los Andes, Carrera 1 #18A-10 ML 787, Bogotá, Colombia, (2) Department of Chemical Engineering, Universidad Nacional de Colombia, Carrera 30 45-03, Bogotá, Colombia

The production of Vinyl Acetate is very important due to its various applications.

This monomer is implemented like a subunit for the synthesis of many other polymers that at the same time have a wide variety of uses. Polyvinyl Acetate (PVA) is used in the fabrication of adhesives and water based paints. Polyvinylic alcohol (PVOH) is also used in adhesives and coatings. Polyvinyl acetal is used as an insulator. Vinyl and ethylene acetate copolymer are used in the production of fibers and coatings. Ethylene and alcohol vinilyc copolymers are used in packages.

This work describes the conceptual design step through the process simulation for the Vinyl Acetate (VAM) process which takes into account the main process variables, like, a detailed design of the reactor and the separation train. The process centers on the reaction of ethylene, oxygen and acetic acid on a Pd/Au catalyst which produces vinyl acetate and water. There is an unwanted secondary reaction in which carbon dioxide and water is produced as a byproduct of the ethylene oxidation. The exiting gaseous streams of the reactor are cooled in separator, with the objective of making a partial condensation to separate the gas from the liquid. The gas is then washed with acetic acid from a recycled stream to recover vinyl acetate in the absorber. Finally, gas enters a process to eliminate CO2 which is then recycled to an entering reactor stream, so it can react with the existing ethylene.

The liquid streams that exit the separator and the acetic acid used to wash the gas are fed to an azeotropic distillation column where the acetic acid is to be separated (bottom) from a mixture of water and vinyl acetate (distillate). The distillate stream enters a settling tank, where the organic product (mainly vinyl acetate) is divided into two streams, the first stream is a recycling stream that enters the distillation column and the other stream heads to a separation train process, where the objective is to purify vinyl acetate until the required purity is reached. The liquid stream from the decanter is discarded, some of the acetic acid that exits the column as a bottom stream is used as a washing agent in the absorber, and some is also mixed with the pure acetic acid that comes from the feed, this mixture enters an evaporation process. The gaseous acetic acid is obtained mixing the recycle gas and the oxygen and ethylene from the feed before it enters the reactor.

The simulation was done in Aspen Plus 2006 taking into account some technical characteristics that are implemented at an industrial level, while at the same time establishing a set of conditions, for example, the location of the plant in Cartagena (Colombia), the annual production of 50.000 tons per year. Thanks to the simulation of the kinetics and the hydrodynamic characteristics of a PBR reactor the reaction system was carefully designed. Using residue curves and sensitivity analyses of each of the units used in the separation train process, the best operating conditions were obtained that ensured the optimum product standard for commercial use. Finally, a heat integration analysis was used, and also a control system for the reactor unit.

As a result of the simulation, another separation unit was needed to get commercial specifications of VAM. Glycerol was used as mass separating agent of water from azeotropic VAM-water mixture, getting interesting results. Finally, it was found that the process for VAM production is efficient from economic and technical point of view.