The pathways of the phthalic anhydride selectivity and yield increase at C4-C5-hydrocarbons oxidation

The investigation of n-butane and n-pentane oxidation in system with two consecutive reactors confirmed the mechanism of phthalic anhydride formation by Diels-Alder reaction between maleic anhydride and C4 unsaturated hydrocarbons. The process is limited by low stationary concentration of C4 unsaturated hydrocarbons in reaction mixture which is connected with high rate of their oxidation to maleic anhydride. It was shown that n-butane oxidation leads to formation of maleic anhydride only but the introduction of unsaturated C4-hydrocarbons on inlet of the second catalytic reactor accompanied by phthalic anhydride appearance on outlet of these two consecutive reactors system. It was established that in case of 1,3-butene introduction in the second reactor the quantity of phthalic anhydride formed is more than in case of 2-butene addition. It was predicted that a decrease of the temperature in the second reactor can leads to an increase the phthalic anhydride selectivity and its yield as result of Diels-Alder reaction effectiveness. This assumption was confirmed by experimental results. In results the method of phthalic anhydride production by the use of two consecutive reactors was proposed. The summary yield of this product on this new process can reach up to 35 mol. %. In the case of n-pentane oxidation the formation of maleic and phthalic anhydrides was observed with excess of first product but the introduction of unsaturated C4-hydrocarbons in the inlet of second reactor leads to an increase of the phthalic anhydride concentration and its selectivity and yield. In result the yield of phthalic anhydride equal to 35 mol. % can be obtained. So, the proposed by us mechanism of phthalic anhydride was confirmed by new experimental results and other pathways for the selectivity and yield of this product can be predicted.