Thread Content
The activity of COS hydrolysis catalysts at room temperature generally decreases significantly after 1 to 2 years of operation in industrial plants. Research has found that catalyst deactivation is caused by sulfur deposition, which destroys the active components on the catalyst surface and blocks its micropores, as well as by the loss of a small amount of active components. Since the content of active components in the deactivated catalyst remains high and its mechanical strength changes little, it is necessary to regenerate it in order to extend the catalyst’s service life. In view of the characteristics of hydrolysis catalyst deactivation, this paper conducts research on its regeneration using an effective regenerating agent. The effect of regeneration process conditions on catalyst activity was investigated using an atmospheric-pressure microreactor, and the activity and stability of the regenerated catalyst were compared with those of a fresh catalyst. 1 Experiment 1.1 Catalyst regeneration process Process 1: The deactivated catalyst is impregnated with a regenerator, then dried and calcined. Process 2: The deactivated catalyst is washed and dried, impregnated with a regenerator, then dried and calcined. Process 3: The deactivated catalyst is calcined at high temperature, then impregnated with a regenerator, and subsequently dried and calcined. 1.2 Catalyst activity evaluation (determination of COS conversion rate) (1) Microreactor test: The hydrolysis activity of the catalyst is determined using a microreactor system at atmospheric pressure; the activity evaluation setup is shown in Figure 1. http://www.nmtech.com.cn/jishuwang/upload/0605091631201504.jpg Test conditions: Catalyst load of 0.5 mL (20–40 mesh), packing height-to-diameter ratio of 4.0, reaction temperature of 50°C, space velocity of 3,000 h⁻¹, at atmospheric pressure, with water vapor content at the saturated concentration at room temperature (20–25°C). The gas used in the experiment was composed of pure COS gas mixed with nitrogen in a certain ratio, with a COS concentration of 50–100 mg/m3 in the gas. After the test conditions stabilized, the WISP-852 micro-sulfur analyzer was used to periodically measure the COS content in the gases entering and leaving the reactor, thereby determining the hydrolysis conversion rate of COS. Catalyst activity is expressed as the COS conversion rate. (2) Primary particle size test: To accurately evaluate the performance of the catalyst, the activity of the primary particle size hydrolyzer is measured at atmospheric pressure. Test conditions: Catalyst load of 30 mL (diameter 3–5), reaction temperature of 50°C, water vapor content at the saturated concentration at room temperature (20–25°C), space velocity of 1,500 h⁻¹, and atmospheric pressure. The reaction tube is a glass tube with dimensions of Φ30×1.5. The gas used in the experiment is a mixture of pure COS and nitrogen in a certain ratio, with a COS concentration of 50–100 mg/m3. The process flow is similar to that of normal-pressure microreactors. 2 Results and Discussion 2.1 Physicochemical properties of deactivated and regenerated catalysts As can be seen from Table 1, compared with the fresh catalyst, the specific surface area and pore volume of the deactivated catalyst decreased, while its bulk density increased slightly. A large amount of S and Cl accumulated in the deactivated samples, blocking the catalyst pores, which was the main cause of catalyst deactivation; a small amount of S and Cl remained in the catalyst after regeneration. After regeneration, the pore volume of the catalyst is essentially restored, and the specific surface area can be recovered by over 90%. http://www.nmtech.com.cn/jishuwang/upload/0605091632225180.jpg 2.2 Retained activity of deactivated catalysts The activity of the hydrolysis catalyst used by a certain factory after 8 months of use was measured in a microreactor system; the results are shown in Table 2. http://www.nmtech.com.cn/jishuwang/upload/0605091633088449.jpg As can be seen from Table 2, the deactivated catalyst basically has no activity left. 2.3 Selection of catalyst deactivation regeneration processes Table 3 shows that different regeneration processes have varying effects on the regeneration efficiency; among them, the catalyst regenerated by Process 3 has activity roughly comparable to that of a fresh catalyst. http://www.nmtech.com.cn/jishuwang/upload/0605091633554563.jpg (1) Effect of calcination temperature on catalyst activity and the content of active components. Process 3 was used to investigate the effect of calcination temperature on the activity of the regenerated catalyst, and the results are shown in Table 4. http://www.nmtech.com.cn/jishuwang/upload/0605091634455681.jpg As can be seen from Table 4, there are significant differences in the activity of the regenerated catalysts at different calcination temperatures: as the calcination temperature increases, the catalyst activity rises gradually before decreasing again ； The regenerated catalyst exhibits the highest activity at a calcination temperature of 550°C. There are significant differences in the content of active components and sulfur content in the regenerated catalysts at different calcination temperatures: as the calcination temperature increases, sulfur is gradually removed, resulting in a marked decrease in sulfur content ； At 550°C, the sulfur content is lowest, while the content of the active component in the catalyst increases significantly. These results are consistent with the catalyst activity results. (2) XRD of the regenerated catalyst. The crystal structures of fresh, deactivated, and regenerated catalysts were studied using XRD. It was found that although the deactivated catalyst contained large amounts of sulfur, no XBD diffraction pattern corresponding to sulfates appeared, indicating that the sulfur was likely dispersed in the catalyst in an amorphous form ； The strong diffraction peaks of NaKAl2O2(CO3)2 and KCl indicate that the active components have aggregated significantly into crystalline phases, thereby reducing the content of these active components as well as the catalyst’s activity; hence, direct regeneration of the deactivated catalyst is not effective ； The deactivated catalyst regenerated by calcination and impregnation with a regenerating agent exhibited a spectrum similar to that of the new catalyst, with the exception of the K2SO4 peak; this indicates that the crystal phase on the surface of the regenerated catalyst is similar to that of the fresh catalyst. It shows that sulfur deposition and regeneration did not cause damage to the catalyst’s crystal phase, and it also implies that the deactivation of the catalyst was not due to structural damage. 2.4 Evaluation of the activity of regenerated catalysts: The original-grain size regenerated catalysts and fresh catalysts were placed in a microreactor under normal pressure, and comparative tests were conducted at different temperatures and space velocities. (1) Comparison of catalyst activity at different temperatures: 30 mL of each catalyst was taken, in its original particle size, and a space velocity of 1,500 h⁻¹ was selected for the tests; the test results are shown in Figure 2. As can be seen from Figure 2, the hydrolytic activity of the catalyst increases as the temperature rises ； At a reaction temperature of 80°C, the activity of the regenerated catalyst is comparable to that of the fresh catalyst ； Within the range of 40–60°C, the activity of the regenerated catalyst can reach 90% of that of a fresh catalyst. This is mainly because trace amounts of S and Cl on the surface of the regenerated catalyst block the catalyst’s pores, reducing its surface utilization rate and affecting internal diffusion. (2) Comparison of catalyst activity at different space velocities: 30 mL of each catalyst was used, in its original particle size, and testing was conducted at a temperature of 50°C; the test results are shown in Figure 3. http://www.nmtech.com.cn/jishuwang/upload/0605091636003330.jpg As can be seen from Figure 3, the trend of the effect of space velocity on the activity of the regenerated catalyst is the same as that of the fresh catalyst. Within the range of air velocities of 1,500–6,000 h⁻¹, the activity of the regenerated catalyst exceeds 90% of that of the fresh catalyst. 2.5 Reproducibility of the regeneration process To evaluate the reproducibility of the regeneration process, samples from different batches were prepared. 30 mL of each catalyst was taken, at its original particle size, and tests were conducted at a temperature of 50°C and a space velocity of 1,500 h⁻¹; the test results are shown in Table 5. The results show that the performance of the samples from each batch is essentially consistent, indicating that process scaling is feasible. http://www.nmtech.com.cn/jishuwang/upload/0605091636576874.jpg 2.6 Stability of Regenerated Catalysts The activity stability of regenerated catalysts and fresh catalysts was compared under the same experimental conditions. The evaluation conditions are: reaction temperature of 50°C, space velocity of 1,500 h⁻¹, original particle size, and volume of 30 mL. The test results are shown in Figure 4. http://www.nmtech.com.cn/jishuwang/upload/0605091637498119.jpg As can be seen from Figure 4, after 150 hours of testing, the COS conversion rate remained at around 91%, indicating that the activity and stability of the regenerated catalyst are good. 3 Conclusions (1) The regeneration conditions for the deactivated catalyst are: calcination at 550°C for 3 hours, followed by impregnation with a regenerator, and then drying and calcination. The regenerated catalyst exhibits high activity, with a COS conversion rate of over 90% that of the fresh catalyst. (2) The regenerated catalyst still maintains good activity stability