Fedevych O. The principles of technology of crotonic acid obtaining and regeneration of acetic acid

The dissertation is devoted to the elaboration of principles of technology of crotonic acid receiving by means of crotonic aldehyde oxydation and use of this reaction for the purification of acetic acid from a by-product-crotonic aldehyde on the production of vinylacetate. That permitts to increase the economy of the process. On the basis of the realized experiments it was stated that the optimal medium for the process of crotonic aldehyde oxydation was ethylacetate. Regularities of the process were studied in the wide range of temperatures (285-333 K) and partial preassures of oxygen (0,021-1,62 МPa). In was discovered that with the raise of initial concentration of crotonic aldehyde up to 5 mol/dm3 the rates of its oxydation and accumulation of the main products increase. The formal reaction order to aldehyde is the first. The further increasing of initial concentration of aldehyde is not profitable because under these conditions the rate of its oxydation already does not increase, and selectivity t o main products remains to decrease. The increase of partial pressure of oxygen from 0,021 to 0,1 МPa essentially intensifies the process of oxydation (reaction order to oxygen is 0,6) with practically stable summary selectivity to crotonic and percrotonic acsids. This fact permits to use the increased pressure of oxygen to decrease the temperature of oxydation that provides higher selectivity and yield of the main products. These results induced the author for the first time to systematically investigation of the oxydation of crotonic aldehyde at higher preassures of O2 up to 1,6 МPa, but the general kinetic regularities did not change essentially. It was stated that the existence of limit partial preassures of oxygen (Po2lim.) under which the rate of oxydation was already constant and did not depend from Po2. It was discovered the linear increase of Po2lim. with the rise of temperature of crotonic aldehyde oxydation. The last fact permitted to intensify the oxydation of crotonic aldehyde at low temperatures for the account of increasing of Po2. On the base of the obtained experimental data the optimum conditions of crotonic aldehyde oxydation have been chosen. Thery were proposed to oxydate crotonic aldehyde at 300-309 K and Po2 = 0,3-0,7 МPa. Under these conditions the convertion of aldehyde reaches 50-60 % after of 60 minutes with summary selectivity to crotonic and percrotonic acids - 80-82 %. The conversion of crotonic aldehyde after the treating of oxydate in an inert gas medium at 303 K during 8 hours increases to 75-85 %, and the selectivity to crotonic acid to 85-90 %. We elaborated a original scheme of oxydation products separation and purification of crotonic acid, which reduces to minimum the losses of initial aldehyde as well as the crotonic acid. For these purpose the feed of heat in the rectification tower one realize by means of condensation of steam of an additional solvent - n-octane. This solvent formed an azeotrop with crotonic aldehyde in consequence of its temperature in the rectification to wer decreases more than over 200. With a view to minimalize the losses of crotonic acid at the separation of still liquid as well as provite its appropriate purity one realize the extraction of crotonic acid by water from its solution in n-octane. The attained results permitted the author to improve the production of vinylacetate by reaction of acetylene with acetic acid. In this production acetic acid is containated a by-product-crotonic aldehyde and therefore in the existing production it is nesessary to remove that part of recyclic acid. The author elaborated the way of purifying of recyclic acetic acid from crotonic aldehyde by its oxidation with molecular oxygene at 353 K in the presence of catalyst with an additional introduction of acetic aldehyde to oxydate.