Preparation and testing of catalysts for fuel upgrading

Mudi, Ismaila ORCID: 0000-0002-9537-2020 (2024). Preparation and testing of catalysts for fuel upgrading. University of Birmingham. Ph.D.

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Abstract

In this study, biochar which is a by-product of pyrolysis was used as a support to develop robust, novel, and renewable Ni/biochar catalyst for hydrodeoxygenation (HDO) of bio-oil and its model oxygenate organic compounds, such as vanillin and furfural. Through chemical treatment with H2SO4 (sulfuric acid) and KOH (potassium hydroxide), the textural and physicochemical features of the biochar support were modified to increase mass transfer and active metal dispersion. The catalysts were characterised by a range of physical and chemical techniques. The catalysts were used in the HDO of vanillin, hydrogenation of furfural, and the HDO of bio-oil itself using a 100 mL Parr reactor, catalyst loading 0.4–0.8 g, temperature 100°C to 150°C, hydrogen (H2) pressures of 30 to 50 bar, and a stirring rate of 1000 rpm. The three catalysts were tested for the HDO of vanillin, a typical oxygenate phenolic compound found in bio-oil, into creosol. Over the unmodified 15wt% Ni/biochar catalyst, vanillin conversion of up to 97% with 91.17% selectivity to p-creosol was achieved; in addition to being extremely selective and active for p-creosol, which can be used as a future biofuel, the catalyst was stable for four successive experimental cycles. Chemical treatments of the biochar support increased its physicochemical characteristics, which led to a better catalytic performance in terms of vanillin conversion and p-creosol production in the sequence Ni/biochar(H2SO4) > Ni/biochar (KOH) > Ni/biochar, which is the same order of specific surface area and mesoporosity increase. The kinetics of liquid-phase furfural hydrogenation into 2-methylfuran also was studied using 15wt% Ni/biochar(H2SO4) catalyst. The results demonstrate that at 1000 rpm stirring rate and 106 µm catalyst particle size, both external and intraparticle mass transport constraints were insignificant, ensuring kinetically controlled experiments. Three plausible Langmuir–Hinshelwood-Hougen-Watson (LHHW) kinetic type models, competitive (Model I), with a competitive adsorption site (Model II) and a non-competitive adsorption site (Model III), were screened based on the fact that an R2 value greater than 99% demonstrated that the experimental data were satisfactorily fit to the model. Based on the correlation coefficient of more than 99% between experimental and predicted rates, the best fit is model III, which is a dual-site adsorption mechanism involving furfural adsorption as well as hydrogen dissociative adsorption and surface reactions. It was found that when the sulfuric acid treatment duration of the biochar used to prepare Ni/biochar(H2SO4) catalyst increased from 3 to 9 hours, the conversion of furfural and the yield of 2-methyl furan increased. In addition to the hydrogen present in the solution, the competitive adsorption of furfural and vanillin for the catalyst active sites limits the conversion due to hydrogenation and HDO in a binary model compounds process. The conversion of furfural via hydrogenation was substantially greater than HDO of vanillin in the binary system of model compounds. Based on the results of four successive experimental studies, the developed Ni/biochar(H2SO4) catalyst proved remarkable stability in terms of furfural conversion (96%) and 2-methylfuran yield (54%) at the 4th experiment compared to 99% and 57% for the 1st experiment. In terms of the bio-oil itself, HDO catalytic upgrading of bio-oil decreased oxygenates from 13.02% (crude bio-oil) to 8.3% (commercial TK-341 catalyst) and 5.93% (sulfided Ni/biochar(H2SO4) catalyst. Whilst the hydrocarbon components of the upgraded bio-oil can be summarised as thus: 90.39% (commercial TK-341 catalyst) and 93.56% (sulfided Ni/biochar(H2SO4) catalyst) catalytic upgrading was accomplished, compared to 71.26% for the crude bio-oil. Thus, the developed 15wt% Ni/biochar(H2SO4) catalyst demonstrated superior performance than the commercial TK-341 catalyst in this investigation. This can be attributed to the enhanced mesopores, and surface of the biochar support treated with sulfuric acid.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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