| Adiponitrile is an important raw material for the production of hexamethylenediamine, caprolactam, nylon 66,1,6-hexamethylene diisocyanate (HDI), and it can also be used for manufacturing rubber fertilizer, insecticides, fungicides, rocket fuel, and high polymer materials. Ammoniation of adipic acid is an important method for the production of adiponitrile in industry, and this method becoming economically favorable because the market supply of adipic acid is relatively abundant which reduce the raw material cost in the production of adiponitrile. In the research the kinetic of adipic acid ammoniation was systematically investigated, and the effects of temperature, ammonia partial pressure, stirring speed and a new solid catalyst on the reaction were discussed. What’s more, based on the experimental results one proposal to improve the operation of industrial proces was put forward. And a pilot test was designed to verify this proposal.The detailed results were summarized as follows:(1) Firstly, relevant experiments were made to identify the stirring speed and total volume flow rate of gas. Then, the kinetic experiments were conducted in a 1 L semi-continuous stirred reactor at temperature of 210 ℃ to 260℃with 0.2 wt% phosphoric acid,600 L.h-1 ammonia and 1800 rpm stirring speed. It showed that when the concentration of adipic acid in the reactor was higher than or equal to 0.1 mol.L-1 at 250℃, the neutralization of adipic acid would be controlled by mass transfer and the neutralization of adipic acid was first-order with respect to adipic acid and the apparent activation energy was 42.9 kJ.mol-1. When the concentration of adipic acid in the reactor was lower than 0.1 mol.L-1 at 250℃, the reaction was controlled by kinetics, and it became second-order and the activation energy was 52.7 kJ.mol"1. Through the theoretical model analysis, it was concluded that intrinsic reaction kinetic order with respect to adipic acid was two. Besides, at a temperature of 260℃, phosphoric acid concentration of 0.2 wt%, stirring speed of 1800 rpm and the same total pressure, the variation of adipic acid concentration with reaction time was investigated at a volume flow rate of ammonia between 200 L.h-1 to 600 L.h-1. Experimental results uncovered that intrinsic reaction kinetic order with respect to ammonia was one.(2) Secondly, a kind of solid catalyst was prepared with celatom as the support and the feasibility was discussed in the adipic acid ammoniation to produce adiponitrile. An orthogonal experiment was designed to investigate the effect of calcination temperature, impregnating concentration on the reaction. Then, the optimal condition for solid catalyst preparation was determined, as following:the impregnating concentration of phosphoric acid was 75 wt%, the calcination temperature was 400℃, and the catalyst concentration was 1.37 wt% used in the reaction. Also, a comparison between the solid catalyst and traditional catalyst phosphoric acid was made. The results indicated that the solid catalyst can be used in the adipic acid ammoniation. The active groups in solid catalyst were silicon ortho-phosphate(Si3(PO4)4) and silicon pyro-phosphate(SiP2O7). Different impregnating concentration of phosphoric acid in the preparation of solid catalyst resulted in different active components in solid catalyst, and therefore resulted in different catalytic activity. What’s more, the catalytic activity of solid catalyst was relevant to its amount of acid centers. In solid catalyst phosphorus atom presented the Lewis acid centers and hydroxyl-oxygen presented the Bronsted acid centers, and the more acid centers the solid catalyst contained, the greater catalystic activity was.(3) Finally, one proposal was put forward to solve the problems that the high concentration of adipic acid and high temperature in the dehydration column section of industrial production units which would increase coking. Combining experimental results and existed literatures, the proposal was to increase the volume of bubble column, so that a lower adipic acid concentration in the column section would there be after a longer residence time in neutralization process, thus reduced the coke. Based on the industrial process, the remedy was to install a bubble column pre-reactor with sieve plate before the main reactor to prolong the residence time in the neutralization section, and increase the conversion of adipic acid, and finally lead to a lower adipic acid concentration in the column section. The pre-reactor would also enhance the gas liquid mass transfer by dispersing bubbles and increasing gas liquid interfacial area, and as a result to reduce the adipic acid concentration in the column section. In this research, the proposal was designed in detail with the main size of pre-reactor and reactor in order to actually verify the feasibility and validity of the improved scheme. |
PDF Full Text Request