Evaluating catalyst performance in the emission control system of the FORMOX™ process

Sammanfattning

Air emissions are becoming a larger problem in today’s society and therefore the limits are getting stricter. This means that chemical-producing industries which create multiple byproducts, acting like air pollutants, requires to improve their emission limiting systems. Johnson Matthey Formox AB is a company who sells licenses and catalysts for formaldehyde production by the FORMOXTM process. Production leads to emissions like carbon monoxide (CO), dimethyl ether (DME), methanol (MeOH) and formaldehyde (FA). An emission control system (ECS) oxidizes emissions using Pt and Pd based catalysts. Johnson Matthey aims to get a better understanding of the ECS to be able to ensure operation below emission limits. Therefore, this master’s thesis will investigate the impact of different operating conditions, like temperature and flowrate, and how ageing of the present catalysts can be predicted. Catalyst testing was performed in an ECS pilot reactor. By using fresh catalysts in different loading plans under varying conditions the performance of the ECS was evaluated based on the slips of CO, DME and MeOH. One loading plan was shown to be the best alternative with a slip of total volatile organic compound lower than 20 mg C/Nm3, which is the current emission limit set by the EU. A design-of-experiment approach was used to develop a model that could predict the impact of different parameters. This showed that gas hourly space velocity, reactor temperature and emission concentrations had the largest impact on ECS performance and its outlet temperature. This information assisted the development of an online ageing method, ageing the catalysts within the pilot reactor in six hours. Offline ageing is the previously used method for evaluating ageing for the ECS catalysts, therefore this method was used as comparison. Similar results are seen but conclusions cannot be drawn since the temperature inside the reactor during online ageing is unknown in the current pilot setup. In order for Johnson Matthey Formox AB to reach their goals, this work is a good starting point, proving that online ageing is a possible method to predict performance over time. The method can be optimized both in setting and in relation to actual customer data.