PTQ Q4 2024 Issue

Understanding the decomposition of TBPS for efficient catalyst sulphiding

Identifying optimal operating conditions for sulphiding without negatively impacting the performance of hydroprocessing catalysts

Jennifer A Jackson The Lubrizol Corporation Tiago Vilela Avantium R&D Solutions

H ydroprocessing plays a crucial role in the refining industry. To ensure the catalytic activity of hydro- treating catalysts, sulphiding is employed. Sulphiding involves the conversion of initially inactive metal oxides present in the catalysts into active metal sulphides, signif- icantly enhancing their performance in hydroprocessing. However, achieving efficient catalyst activation through sul - phiding is not without challenges. The sulphiding process requires careful selection of sul- phiding agents that can effectively convert metal oxides into sulphides under specific operating conditions. One notable sulphiding agent is tert-butyl polysulphide (TBPS), a com - mercially available compound provided by The Lubrizol Corporation and under the proprietary tradename SulfrZol 54. In contrast to traditional sulphiding agents like dimethyl disulphide (DMDS), TBPS offers several advantages. It has more ideal health and safety characteristics, a higher flash point (DMDS: 16°C vs TBPS: 100°C), reduced odour (DMDS: foul, TBPS: diesel-like), and improved emissions profile. When TBPS is used as a sulphiding agent, it pro - duces butane and hydrogen sulphide (H₂S) as by-prod - ucts, while DMDS yields methane (and methylmercaptan) and H₂S. This distinction is significant as it contributes to a safer, cleaner, and more effective catalyst activation pro- cess in refineries. Decomposition profile The primary objective of this study is to investigate and illustrate the decomposition profile of TBPS as a sulphiding agent. To achieve this objective, an experimental programme was conducted involving the sulphiding of three commercial catalysts commonly used in diesel and naphtha hydrotreat- ing processes: CoMo, NiMo, and NiW. The experimental tests covered a wide range of operat- ing conditions, including varying temperatures, pressures, space velocities, and gas-to-oil ratios. These conditions were carefully selected to simulate real-world hydrotreating processes and to evaluate the impact of different parame- ters on the sulphiding process. By exposing the catalysts to TBPS under selected operating conditions, we aimed to facilitate the decomposition of the sulphiding agent into H₂S and isobutane, with intermediary components consist - ing of butyl mercaptans and iso-butene.

Relatively low temperatures used in this study (ranging from 150°C to 240°C) were chosen to reflect typical oper - ating conditions in sulphiding hydrotreating processes. At these temperatures, only a fraction of the surface metals on the catalysts are likely to convert into sulphides. The trans- formation from metal oxides to sulphides typically occurs sequentially as operating temperature increases. Therefore, understanding the TBPS decomposition profile is crucial for optimising the sulphiding process. This investigation focused on determining the decompo- sition profile of TBPS under different operating conditions. The aim was to identify the temperature at which TBPS starts decomposing and the influence of catalysts on its decomposition. Additionally, we analysed the formation and consumption rates of the intermediate components (isobutene and C₄ mercaptans) and the final products (H₂S and isobutane), considering factors such as temperature, catalyst type, H₂ partial pressure, gas-to-oil ratio, and liquid hourly space velocity (LHSV). By comprehensively studying the decomposition profile of TBPS and its effects on catalysts, the sulphiding pro - cess can be optimised to ensure efficient activation without compromising catalyst performance. Results of this study will provide valuable insights for refiners, helping advance hydroprocessing techniques and contributing to the devel - opment of cleaner and more sustainable refining practices. Experimental This study was conducted in a 16-parallel fixed-bed reac - tor system with stainless-steel reactors with a diameter of 2mm and a total length of 561mm, including an isothermal section of 300mm. The gaseous product was analysed using an online gas chromatograph (GC), while the liquid reaction product from each reactor was collected in individual sample vials for subsequent offline analyses. Two liquid samples per 24 hours were collected, and two were selected for offline analysis. To maintain stable con - ditions during gas-liquid separation, the sample vials were temperature-controlled. Gas exiting the vials was analysed using the online GC, which provided measurements of hydrocarbons, H₂, He, and H₂S. Avantium’s Flowrence technology relies on the use of sin- gle-string reactors, wherein catalyst particles are arranged in

PTQ Q4 2024