Study On The Synthesis Of Carboxylic Acid Through Aldehyde Hydra-oxidization

Aliphatic carboxylic acid is a very important kind of chemical compounds and low carbon fatty acids are obtained mainly through synthetic ways.Oxidation process is one important way,but there are problems such as excessive oxidation and air pollution.The process of production of acid from aldehyde through hydra-oxidization is new and eco-friendly.In this process,with aldehyde and water as raw materials,acid was obtained through disproportionation,hydrolysis and dehydrogenation with alcohol and ester as intermediate products,hydrogen as side product.In this paper,acetaldehyde hydra-oxidization was studied as a model. Thermodynamic calculation was carried out in detail.The effects of temperature, pressure and the ratio of water to acetaldehyde on the equilibrium compositions were discussed;optimal theoretical reaction temperature was determined,about 600K;with the increase of pressure and the ratio of water to acetaldehyde,the content of acetic acid in the product increased.Conversion of acetaldehyde was 97.14%,with yield of acetic acid 83.37%and selectivity to acetic acid 85.82%at 0.1MPa,600K and ratio of water to acetaldehyde 4.The effects of preparation conditions,components,content of component and process conditions for the acetaldehyde hydra-oxidization process were studied in a continuous flow tube-reactor.The results show that catalyst had a high activity with NaOH as a precipitant,with short time aging and with calcination temperature at 500?; Cu was mainly for dehydrogenation and Zn helpd disproportionation;Catalyst activity with Zr was higher than that with Al;Catalyst activity with Pd?NO3?2 as precursor was higher than that with PdCl₂ and Cl^-1 caused catalyst deactivation;internal diffusion decreased acetic acid selectivity;with the increase of the ratio of water to acetaldehyde, conversion of acetaldehyde increased,but selectivity to acetic acid decreased.Catalyst had a good catalytic activity at temprature between 260-320?,conversion of acetaldehyde increased,but selectivity to acetic acid decreased as temperature increased; acetic acid was supposed to be produced through disproportionation of acetaldehyde and acetic acetate through esterification of ethanol and acetic acid;high temperature helped produce acetic acetate.All these results laid a certain foundation for further studies of aldehyde hydra-oxidization producing carboxylic acid and catalyst design.