Development of Novel Catalysts for the Hydrodeoxygenation of Vegetable Oils

Abstract

Traditional hydrotreating catalysts and NiMo supported on various support materials, were evaluated for their catalytic activity towards HDO of oleic acid. It was concluded that NiMo supported on γ-Al2O3 offered better catalytic activity in terms of oleic acid conversion and selectivity towards n-octadecane. Extensive characterization of the NiMo supported on γ- Al2O3 was conducted to understand the structure-activity relationship for the NiMo/γ-Al2O3 using Raman mapping and X-ray absorption spectroscopy. Raman analysis indicates that the Mo and Ni species are not uniformly distributed on the support material. Raman spectroscopy indicated that Mo is present in the form of clusters and these Mo clusters interact with the support material. Mo L3-edge clearly indicated that γ-Al2O3 and SBA-15 supports offered distorted tetrahedral-octahedral and tetrahedral geometry, respectively. Better catalytic performance of γ-Al2O3 supported catalyst was attributed to the occurrence of distorted tetrahedral-octahedral geometry. NiMo/γ-Al2O3 was impregnated with Cu, Cr and Fe to understand the performance of supported trimetallic catalyst systems for HDO of oleic acid. Reactions were carried out at 300°C, hydrogen pressure of 6.89 MPa and agitation speed maintained at 600 rpm. Maximum hydrodeoxygenation conversion of 92% was obtained using CuNiMo/γ-Al2O3 followed by FeNiMo/γ-Al2O3. It was concluded that Cu and Fe have the potential to actively participate in redox reactions and aid in the removal of oxygen from the feedstock by reverse Mars-van Krevelen mechanism. Optimization of the process parameters (reaction temperature, catalyst loading, hydrogen pressure, reaction time) was performed using orthogonal design matrix (OA16 matrix) for the best performing catalyst (CuNiMo/γ-Al2O3). The order of significant factors affecting the conversion of oleic acid was found to be: reaction temperature > catalyst loading > hydrogen pressure > reaction time. FeCu supported on γ-Al2O3 was prepared by impregnation method to evaluate its HDO performance. For comparison, the unsupported mixed metal oxide catalyst, commercial NiMo and FeCu supported catalysts were evaluated for HDO of oleic acid. During hydrodeoxygenation of oleic acid at different reaction temperatures, the conversion obtained using a mixed metal catalyst (MMC) was higher (>90%) in comparison to commercial NiMo/γ-Al2O3 (80-85%) and FeCu/γ-Al2O3 catalyst (>85%). However, the product selectivity study indicated that FeCu/γ-Al2O3 catalyst works better for HDO of oleic acid at similar process conditions. Additionally, the FeCu catalyst systems offered higher HDO conversion (>85%) at less severe operating conditions (T< 320° C; PH2 < 8.96 MPa, reaction time < 8 h) and regeneration studies were performed on the same catalyst. Life cycle and techno-economic assessment of the HDO process were carried out to understand the environmental and economic impact of the HDO process using canola oil as feedstock. It was found that the green diesel production pathway (HDO process) is 95% energy efficient while the biodiesel pathway (transesterification process) is only 85% energy efficient.