Study On Engineering Foundation Of Comprehensive Utilization Of Mixed Dibisic Acids

The basic engineering study of comprehensive utilization of mixed dibasic acids is a sponsored item of basic and frontal technique research plan of Henan Province (Project number 072300420020) .The mixed dibasic acids ,which are also called nylon acids,are byproducts of the production process of adipic acid.The output of the mixed basic acids are 400-600 thousand tons in China every year.Because they contain some impurity and a lot of water and their color presents green or yellowish brown, they are hard to employ. Generally, they are sent to sewage-treatment devices for burning or landfill at abroad;they are recovered by recrystallization method in China, but the recovery rate is lower than 60%.So much wasted water not only pollute the environment, but also result in the waste of resources.In order to make full use of resources and protect our environment,it is necessary to carry on a research on the separation, recovery and reuse methods of mixed dibasic acids. This research not only has practical engineering meaning, but also has important theoretical meaning in the study of solid-liquid phase equilibrium, esterification of acids and reaction kinetics rugulations etc. In this article, the solubility datas of solid-liquid phase equilibrium were measured, then the theory of solid-liquid phase equilibrium of succinic acid, glutaric acid and adipic acid in various solvents were studied, finally the separation,recovery and reuse methods of mixed dibasic acids were carried on a systemetical research.A set of mesurement equipments with laser monitoring system for deciding the solubility, which made use of synthesis method and could control the temperature through a programme, were set up. The equipments were mainly used for determining the solubilities of the matters which have a high solid-liquid phase equilibrium rate. At the same time, for the alternatives, another set of devices was also set up according to balanced method. From above two experiments, we got solubility datas of succinic acid, glutaric acid and adipic acid in six solvents of water, ethanol, n-butanol,choloroform, acetone and toluene, of which most were measured for the first time. These datas lay a foundation for the separation and recovery of mixed dibasic acids by solvent method and related solid-liquid phase equilibrium research.By using Apelblat three parameters solubility equation and empirical equation to relate the experimental datas, whose princepal is molecular thermodynamics model, and comparing of the model calculation value and emperimental value of 161 sets and 181 data points, the total average relative deviations were 1.53% and 1.82% respectively.The solid-liquid phase equilibrium datas which adopted the Wilson equation,λh equation and modified UNIFAC model to the measured system were calculated and we also gave related model parameters,their average relative deviations were 9.32%, 2.32%, and 5.08% respectively. By comparison, the calculation accuracy ofλh equation was the best, while that of the Wilson equation was worse. However, by defining three new base group(SA, GA, ADA) and optimizing the capacity parameters,superficial area parameters and the correlation parameters of the new base group, the modified UNIFAC model had an eminent regression results for solubility datas of most systems.We also carry on a research on the separation and recovery methods of mixed dibasic acids, which are the byprodocts of nylon acids,according to the experimental solubility datas. By using Refractive Index Detector,we set up a high performance liquid chromotagragh analytical method for analyzing mixed dibasic acids qualitatively. We made use of the solubility differences of three acids in chloroform, n-butanol and water under different temparatures by solvent separation method,then we separated the succinic acid, glutaric acid and adipic acid with high purity from mixed dibasic acids successfully.The preparation methods of phosphotungstic acid catalyst with Keggin structure were under discussion and research. In order to gain the maximum yield, the best experimental conditions were determined by orthogonal test. And they were characterized by IR, XRD,TG-DSC and Hammett. The experiment research for the preparation methods of supported catalysts were enlarged according to the above orthogonal tests and single-factor experiments, we got the best preparation condions of H₃PW₁₂O₄₀ /SiO₂, which were enlarged by 10 times, and the supported catalysts of H₃PW₁₂O₄₀/SiO₂ were characterized by IR, XRD, TG-DSC and Hammett. The result showed that H₃PW₁₂O₄₀ still kept its original Keggin structure well and had a good dispersion and very high sour intensity, and its thermal stability got a further improvement. From the experimental esterification rate of DBE,which resulted from DBA, we could see that the esterification reaction of heterpoly acids catalysts with Keggin structure presented a homogeneous reaction system and, compared to concentrated sulfuric acid, their catalytical activity and product color were good.The synthesis methods of dibutyl succinate, dibutyl glutarate and dibutyl adipate were researched systematically. By using phosphotungstic acid as catalyst and toluene as water carrying reagent and average experiments and single-factor experiments to test the influences of molar ratio of alcohol to acid, the amount of water carrying reagent and catalyst and reaction time on the recovery rate, the best technology conditions of the three matters were determined. Compared to other reaction systems ,this technology had many advantages, such as protecting the environment, cleaness, high recovery rate, wasting less and so on.Therefore, it was a better choice for green production.The esterification reaction kinetics were carried on a thorough study according to the consecutive reaction laws. Under the conditions of using toluene as water carrying reagent, the experiment determined the recovery rate of dibutyl succinate, dibutyl glutarate and dibutyl adipate in different circumstances. We determined the parameters in kinetics equations through the regression of experimental datas. Finally, we got a kinetics equation which can accurately describe the reaction convertion rate with the change of reaction temperature, reaction time and ratio of alcohol to acid in the experiment. The result showed that the three esterification reactions all obeyed second-order irrevisible kinetics model under the experimental conditions. It had been proved that the fixed reaction kinetics mathematical model in the text was reliable and could be used for guiding industrial practices.