Research On Development Of Catalyst For Simultaneous Catalytic Hydrolysis Of COS And CS₂and The Reaction Mechanism

Phosphorus chemical industry is one of the industries of important economy pillar. Recently, the output of yellow phosphorus can achieve to80million tons every year in our country. The off-gas of yellow phosphorus is containing plenty of CO, in the process of one ton yellow phosphorus, the off-gas is2500-3000m3, and the CO content is high to85%-95%. In recent years, with the development of one carbon (C1) chemical industry, it is possible to synthesize many organic compounds with economic value from one carbon chemical industry. However, organic sulfurs (COS, CS2, etc.) in the yellow phosphorus off-gas are the harmful gas which can pollute the environment and result in the deactivation of catalysts. For example, in the off-gas of yellow phosphorus, COS content is700-1000mg/m3, CS2content is20～80mg/m3. Thus, yellow phosphorus off-gas is as the virgin gas of one carbon chemical industry, the COS and CS2must be removed. COS and CS2are coexistent in the yellow phosphorus off-gas, little research focuses on simultaneous catalytic hydrolysis of COS and CS2.On account of above problems and according to the characters of yellow phosphorus tail gas, the COS and CS2can be removed simultaneously by catalytic hydrolysis method in this research. The main research contents include:development of modified microwave coal-based activated carbon (MCAC), development of modified microwave coconut shell activated carbons (MCSAC), regeneration performance research of modified microwave coconut shell activated carbons, kinetic studies on simultaneous catalytic hydrolysis of COS and CS2, the reaction mechanism of simultaneous catalytic hydrolysis of COS and CS2. The main research contents and conclusions as follows:Development study of modified MCAC:A series of MCAC catalysts loaded by metal oxides were prepared by sol-gel method and tested for the simultaneous catalytic hydrolysis of COS and CS2at relatively low temperatures. The influences of preparation conditions on catalytic activity were studied, which were the kinds and amount of the first additive, calcination temperatures, types and content of alkali, the kinds and amount of the second additive, the kinds and amount of the third additive. The influences of reaction temperatures, O2concentration, relative humidity (RH) and inlet concentration ratio of COS/CS2on catalytic hydrolysis activity were investigated. The results show that catalysts with5.0%Fe2O3, n(Fe):n(Cu):n(Ni)=10:2:0.5after calcining at300℃for3h and13%KOH have superior activity for the simultaneous catalytic hydrolysis of COS and CS2. When the reaction temperature was above50℃, catalytic hydrolysis activity of COS could be enhanced, but catalytic hydrolysis activites of CS2was inhibited. Too high RH and O2content also could inhibit the simultaneous catalytic hydrolysis activities of COS and CS2. In addition, when the inlet concentration ratio of COS/CS2decreased from40:1to3:1, the simultaneous catalytic hydrolysis activities of COS and CS2decreased evidently.Development study of modified MCSAC:The catalytic hydrolysis activity of blank MCAC was lower than that of blank MCSAC. The MCAC and MCSAC loading with metal oxides were prepared by sol-gel method for simultaneous catalytic hydrolysis of COS and CS2and their catalytic hydrolysis performances at the relatively low temperature of50℃were investigated. The sulfur capacity of Fe-Cu-Ni/MCAC and Fe-Cu-Ni/MCSAC are38.54mgS/g and56.77mgS/g, respectively. The influences of operational conditions on simultaneous catalytic hydrolysis activity of Fe-Cu-Ni/MCSAC were investigated. The results showed that:The sulfur capacity of Fe-Cu-Ni/MCSAC was increased with the increased of reaction temperatures, but when the reaction temperature was above50℃, increasing the amplitude of sulfur capacity was not obvious. The sulfur capacity of Fe-Cu-Ni/MCSAC catalyst was highest when the RH was32%, and sulfur capacity was decreased with the increased of RH from32%to96%. The sulfur capacity of Fe-Cu-Ni/MCSAC catalyst could maintain about60mgS/g in the RH range of17%-49%, so it was the ideal RH range. When the O2content was0%, the sulfur capacity of Fe-Cu-Ni/MCSAC catalyst achieved maximum, and sulfur capacity was decreased with the increased of O2contents. The catalytic hydrolysis activities of Fe-Cu-Ni/MCSAC were relatively stable in the space velocity range of8000h-1～20000h-1. In addition, when the inlet concentration ratio of COS/CS2decreased from40:1to3:1, the sulfur capacity of Fe-Cu-Ni/MCSAC catalyst decreased evidently, and the sulfur capacity was highest when the inlet concentration ratio of COS/CS2was40:1.When the CO was as carrier gas instead of N2, the effect of CO on simultaneous catalytic hydrolysis of COS and CS2over Fe-Cu-Ni/MCSAC catalyst was studied. The experimental results showed that the catalytic hydrolysis activities of COS and CS2under the CO environment were lower than those of under the N2environment, but the downtrend was not obvious. Thus, CO could reduce the catalytic hydrolysis activity, but the effect was limited. Meanwhile, the influence of H2S on simultaneous catalytic hydrolysis of COS and CS2over Fe-Cu-Ni/MCSAC catalyst was investigated. When H2S was introduced the reaction system, the catalytic hydrolysis activity of Fe-Cu-Ni/MCSAC catalyst was decreased. The downtrend of catalytic hydrolysis efficiencies of COS and CS2were more and more obvious with the increased of H2S concentration, but when the H2S concentration was not so high (70mg/m3), the downtrend of catalytic hydrolysis activity of catalyst was not obvious. This demonstrated that Fe-Cu-Ni/MCSAC had the certain adsorption capacity for H2S, the effect of low concentration H2S on the simultaneous catalytic hydrolysis of COS and CS2Over Fe-Cu-Ni/MCSAC catalyst was not evident.It is a systematic research on the regeneration of exhausted Fe-Cu-Ni/MCSAC catalysts. The results showed that "water scrubbing+N2calcinations purging+alkaline regeneration" method was the best one, and the N2calcinations purging temperature was500℃, the KOH content was13%. The reasons of activities difference among the regeneration processes were studied by BET, XPS, XRD, TG-DTA methods,"water scrubbing+N2calcinations purging+alkaline regeneration" was consist of "water scrubbing","N2calcinations purging" and "alkaline regeneration". First, a small quantity of S/sulfate on the exhausted catalyst’s surface could be removed with the "water scrubbing" process; parts of sulfate could be decomposed to SO2in the process of "N2calcinations purging", active component Fe2O3on the catalyst’s surface could be recovered,"alkaline regeneration" could provide the alkaline groups for catalytic hydrolysis reaction. After regenerating by this way, the catalyst was close to the fresh catalyst, so the recovery of catalytic hydrolysis activity was the most obvious. Besides, the catalytic hydrolysis activity was decreased with the increased of regeneration frequency, but the effect of regeneration frequency was limited. Thus, this regeneration method was feasible and good stability.The reaction kinetics of simultaneous catalytic hydrolysis of COS and CS2over Fe-Cu-Ni/MCSAC catalyst was calculated and analysed. First, the reaction kinetics of COS catalytic hydrolysis and CS2catalytic hydrolysis were analyzed and fitted respectively by power function dynamic equivalent model. The reaction kinetics equations of COS catalytic hydrolysis and CS2catalytic hydrolysis were obtained:(?)On this basis, through the relationship between the two reaction kinetics equations and the deduction of simultaneous catalytic hydrolysis of COS and CS2, we deduced and calculated the reaction kinetics equation of simultaneous catalytic hydrolysis of COS and CS2:(?)Meanwhile, the comparison and verification between the actual and the calculation formula of the simultaneous catalytic hydrolysis reaction rates showed that:the relative error was increased with the decreased of inlet concentration ratio of COS/CS2. But the relative error could keep about5%, so the error was not obvious. Thus, the above reaction kinetics equation of simultaneous catalytic hydrolysis of COS and CS2was applicative.The research on the reaction mechanism of simultaneous catalytic hydrolysis of COS and CS2over Fe-Cu-Ni/MCSAC catalyst:Basis on the activity evaluation of catalysts, effect of reaction conditions, characterization tests of different catalysts (BET, SEM/EDS, XPS), regeneration analysis, the reaction mechanism of simultaneous catalytic hydrolysis of COS and CS2over Fe-Cu-Ni/MCSAC catalyst was obtained. The reaction process of simultaneous catalytic hydrolysis of COS and CS2over Fe-Cu-Ni/MCSAC catalyst included two steps:hydrolysis reaction process of COS/CS2and the oxidation process of H2S. COS and CS2could be catalytic hydrolyzed to H2S (intermediate product of CS2catalytic hydrolysis included COS, but COS could be further catalytic hydrolyzed to H2S), and H2S could be oxidized to sulfate with O2conditions. First of all, on the conditions of no H2O or lower RH (RH=49%), CS2and H2O could be adsorbed on the surface of catalyst, catalytic hydrolysis of CS2could be achieved on the actions of alkaline groups and active components, but most of gaseous COS and a small quantity of the adsorption state COS could react with adsorbed water. The catalytic hydrolysis of CS2was the control step. However, at the conditions of high RH (RH=96%), COS and H2O could be adsorbed on the surface of catalyst, catalytic hydrolysis of COS could be achieved, and no CS2or a small quantity of CS2could be adsorbed on the surface of catalyst, most of gaseous CS2and a small quantity of the adsorption state CS2could react with adsorbed water. When the O2was introduced in the system, the oxidation process of H2S was:H2Sâ†'S/RSORâ†'SO2Râ†'RSO2ORâ†'SO42-/sulfate. Meanwhile, the contents of SO42-/sulfate were increased during the reaction, and they could occupy the activity sites of catalyst’s surface, the alkaline groups were destroyed, the active components were deleted which could result in the deactivation of catalysts.