Catalytic Hydrothermal Liquefaction of Camelina Sativa Residues for the Production of Biogasoline Range Liquid Biofuel

Abstract

Camelina Sativa residue was used as a feedstock to investigate the production of biogasoline from the biomass material by catalyst-assisted hydrothermal liquefaction process. In the new process development, a non-catalytic experimental performance evaluation was conducted as a baseline process to compare and evaluate catalytic performance. Four commercially available catalysts otherwise called precursors were initially tested to set the stage for the performance evaluation of the in-house developed catalysts. The commercial catalysts used were HZSM-5, SiO2-Al2O3, SBA-15 and γ-Al2O3. The performance activities of the commercial catalysts show no sign of improved biomass conversion compared to non-catalytic process, which has a maximum biomass conversion of 72 wt. %. However, of all commercial catalysts used, γ-Al2O3 under subcritical water condition produced the best biogasoline yield performance of 15 wt. %, an improvement over the non-catalytic process which produced 12 wt. % under same condition. The marginal increase was even further improved when 5% cobalt was impregnated on the γ-Al2O3 to form a new bifunctional catalyst, 5Co/γ-Al2O3. In this case, the biogasoline yield increased from 15 wt. % to 23 wt. %. When molecular hydrogen was introduced into the process at pressure 5 MPa hydrogen pressure and 14 MPa process autogenic pressure, 5Co/γ-Al2O3 produced even an improved performance, with biogasoline yield was increase to 28 wt. %. Furthermore, different bifunctional and dual support catalysts were developed with two commercial catalysts as precursors. This development produced new hybrid and synergy catalysts. These catalysts were tested for performance evaluation and the best performing catalyst was 5Co/γ-Al2O3/HZSM-5. The new catalyst under the same experimental conditions gave the best performance, and the biomass conversion increased to 79 wt. %, an improvement over 70-72 wt. % obtained from most catalyst-assisted and non-catalytic cases. Also, the biogasoline yield was 43%, which was the highest obtained in all cases. Addition of nickel as promoter did not add values to the process as the biogasoline yield declined. The best process parameters optimization show that biomass size of 1.0 mm, catalyst metal loading 5%, catalyst weight/biomass weight ratio of 0.2, hydrogen pressure 2 MPa, and retention time 30 minutes are optimum for the best performance. The intrinsic kinetic analysis of this process shows there are two different temperature regimes with different kinetic parameters; this effect was attributed to different factors, one was the ionic product of water that varies exponentially with temperature and second was the heating rate of 5oC/min that was used as a fixed parameter. The low and high temperatures regimes have order of reaction 2 and 1 respectively. The activation energies were 16,420 and 12,627 J/mol respectively and the collision factors were also 0.7603 and 0.1715 s-1 respectively. An overall kinetic parameter shows that the slower high temperature reaction was the rate controlling with collision factor of 0.1970 s-1, activation energy 12,783 J/mol and reaction order 1.0. The parity chart for the experimental and model predicted rate using the overall model gave an average deviation of 6.64%. Two other regression models were developed to estimate the performance of the best selected catalyst for solid biomass conversion and biogasoline range liquid production. The models are given in equation 7.1 and 7.2 respectively. The parity chart developed using results from these models showed an average deviation of 0.99% and 6.53% between the experimental and model derived values. The statistical analysis provided showed relationships between various parameters which could optimize the process. The conclusion of this section would be based on future economic analysis.