Study On Separation Of Nickel Catalysts By Ceramic Membranes In P-Aminophenol Production

Application of ceramic microfiltration membrane to the filed of solid-liquid separation began in China at the end of last century. Today it has been used in a variety of industrial applications. The existing applications were all conducted under the normal pressure and temperature. The fine particles of the catalyst in p-aminophenol production were removed by ceramic microfiltration membrane, it is a rather difficult teclinical process because the pressure and temperature of the feed system, which is p-aminophenol dissolving in the mixture solvent of the alcohol-water, must be kept constant at about 0.6 MPa and 105℃ in a sealing states to prevent p-aminophenol crystallization. If the temperature of the system could not be controlled effectively by keeping the error of the temperature control within ±5 ℃, the feed material would vaporize in a higher temperature or crystallize in a lower temperature, which will result in the failure of the filtering process. Therefore, it is a new attempt using ceramic microfiltration membrane in chemical industry production under such rigorous conditions.The crossflow filtration is influenced by a great number of parameters. A lot of models have been developed so far to describe the processes of the CMF, but only a few are sufficient to describe the processes in reality and explain various experimental and practical results. Assuming that the feed fluid was Newtonian fluid, we proposed a model for simulating the critical crossflow velocity in microfiltration of rigid particle suspension on the basis of the traditional cake-layer and concentration-polarization models. In the proposed model the concept of critical cake thickness was introduced. A power function relationship between the critical crossflow velocity and the length of the membrane tubes was obtained by simplifying the model, which had been verified by experiments. The model predicted the relationships between the critical cross-flow velocity and the process parameters and the filtrating conditions. It also established a theoretical base for eliminating the cake fouling on membrane surface in application.Targeting the difficulty of the filtering process, this thesis first studied the solid-liquid equilibriums of p-aminophenol dissolving in the mixture solvent of the alcohol-water using thermodynamic methods. There is no report so far on the solubility of p-aminophenol in alcohol and alcohol-water in the world. The solubility of p-aminophenol in water, alcohol, and the mixture solvent of the both weredetermined. The activity coefficients and solubility of/7-aminophenol were calculated by using the molecular thermodynamics model. Using the theory of the S-H ideal solution to the solid-liquid equilibrium, the study successfully calculated out the duality interact parameters /,y of the duality and ternary systems, and built a thermodynamic model of /?-aminophenol solubility.Effects of the pore size of membrane, transmembrane pressure, crossflow velocity, feed concentration and temperature on permeate flux were investigated in lab. The optimal process parameters were determined, which are 0.2 urn in membrane pore size and a transmembrane pressure of 0.25 MPa. The experimental results indicated that membrane flux could be maintained steady for a long period of time at the feed concentration of lower than 1.5%. The nickel content in the permeate could not be detected by an atomic absorption spectrophotometer (AA-6401F) in all runs, which suggested that the ceramic membrane microfiltration had no problem in meeting the quality requirement for p-aminophenol products. These experimental results from the study provided useful technical parameters for the application of the ceramic membrane in p-aminophenol production.In the study, the fouling mechanism of ceramic membrane in microfiltration of Raney nickel catalysts suspension was investigated using the resistance model through the experiments. It clearly showed that in most cases the dominating resistance came from the cake. Resistance from internal blockage by catalyst particles was not influenced by TMP. The relationships of the permeate flux with the process parameters cyclic variations were also studied. The results of the experiments indicated that the particle attachment to the layer was an irreversible process and that adhesive and friction forces were dominating on a deposited particle to make the cake irreversibility. The removal of the layer could take place only by removing large agglomerates or large layer fragments. A removal of the layer in the form of reverse transportation from single particles could not be observed. The cake thickness remained constant until a velocity corresponding to the erosion shear stress for the cake was reached so that the particle on the cake surface was carried out to the membrane tube outlet or diffused into the bulk suspension. Such a velocity was defined as critical crossflow velocity.The commercial large-scale membrane device was designed according to the experimental results. The operating guideline of the industrial device of ceramic microfiltration membrane was established. The membrane fouling in the plantexhibited the same fouling mechanism as the experiments did. That was the progressive accumulation of filter cakes on the membrane surfaces decreased the permeate flux. The component of the powder pollutant and the fouled membrane were analyzed with a JSM-6300 scanning electron microscope (SEM; JEOL, Japan) equipped with an energy dispersive X-ray spectrometer (EDX; KEVEN, USA). A cleaning method for effectively reducing the cake was proposed based on the results of the analyses. The method is: washing the membranes in 50% vol. solution of alcohol-water at 100°C for 10 min, then rinsing it with lower than 1% vol. solution of NaOH for 20 min, further washing it in 3% vol. nitric acid solution for 60 min, and finally rinsing it in tap water for 60 min at 90°C. The average permeate flux obtained in the plant of 150-hour running time was 400L-m"2-h"', and the nickel content in the permeate could not be detected by an atomic absorption spectrometry in all runs.There were a few problems in the application of the membranes in the plant production on the beginning, which was that p-aminophenol in the feed had been crystallized in the supports of the membrane tubes, leading to the blockage of the pores in new membranes. The membrane filtration in the plant resumed after taking the corrective actions. Other problems found in running industrial device in the time period of over a year were also overcome by taking actions proposed by us. Currently the membrane filtration device in the plant is running steadily. Annual production capacity ofp-aminophenol is 10000 tons (compared to 3000 tons in the past) with a membrane area of only 16.72m2, which means 2-3 hundred million RMB in value.In conclusion, the microfiltration of Raney nickel catalysts in p-aminophenol production with a ceramic membrane filter in industrial conditions is a reliable and efficient clarification technology, which opens the door to the application of ceramic membrane in chemical industrial production. Through analyzing the fouling mechanism of ceramic membrane and establishing the theoretical model, the study contributes to fouling mechanism theory of crossflow microfiltration of membrane.