Abstract: The subject invention relates to a process for the crystallization of di-carboxylic acids comprising dissolving the crude dicarboxylic acid at a temperature sufficient to dissolve the crude diacid in the solvent, whereby portion of the said solvent evaporates, increasing the concentration of the dicarboxylic acid in the said solution, transferring the said solution from the evaporator to a crystallizer, comprising a solid cylindrical impeller conforming to the shape of the crystallizer related by means of a cylindrical shaft attached to the spped motor, adding the additives selected from surfactants, buffer salts and/or acid salts or mixture thereof in the said evaporated solution in the said crystallizer, cooling the said mixture resulting in the formation of crystals of dicarboxylic acids, wherein the said crystallization takes place in the annular space between the impeller and the crystallizer wall.

Abstract: The present invention relates to a process for the preparation of benzene dicarboxylic acids by liquid phase oxidation of Xylene isomers using oxygen or air by oxidising in the presence of acetic acid as solvent, cobalt salt as catalyst and an initiator. The oxidation step is followed by flashing the said reaction mixture to remove volatile substances and cooling and filtering to get crude benzene di-carboxylic acid as a solid product and filtrate. The dicarboxylic acid solid product is recrystallised to get at least 99% pure benzene. The filtrate may be recycled.

Abstract: The present invention relates to one-step oxidation process for preparation of cyclohexane to adipic acid, using molecular oxygen, in liquid phase, in the presence of catalyst, containing either cobalt or cobalt and iron. The catalyst is activated outside the reactor and molecular oxygen is used as an oxidant. The use of molecular oxygen as oxidant along with preactivated catalyst in the reactor and also by restricting the conversion of cyclohexane between 20-30% with catalyst in the reactor results in enhanced selectivity to adipic acid. The reaction mixture of cyclohexane and preactivated catalyst is subjected to oxidation by bubbling pure molecular oxygen while stirring the homogenous mixture while bubbling the oxygen at a predetermined temperature, pressure and space velocity conditions. The product selectivity to form adipic acid is found to be at least 5% better than the maximum attainable using the conventional processes.