Abstract:Pyrolysis is considered the most promising way to convert biomass to fuels. Upgrading biomass pyrolysis oil is essential to produce high quality hydrocarbon fuels. Upgrading technologies have been developed for decades, and this review focuses on the hydrodeoxygenation (HDO). In order to declare the need for upgrading, properties of pyrolysis oil are firstly analyzed, and potential analysis methods including some novel methods are proposed. The high oxygen content of bio-oil leads to its undesirable properties, such as chemical instability and a strong tendency to re-polymerize. Acidity, low heating value, high viscosity and water content are not conductive to making bio-oils useful as fuels. Therefore, fast pyrolysis oils should be refined before producing deoxygenated products. After the analysis of pyrolysis oil, the HDO process is reviewed in detail. The HDO of model compounds including phenolics monomers, dimers, furans, carboxylic acids and carbohydrates is summarized to obtain sufficient information in understanding HDO reaction networks and mechanisms. Meanwhile, investigations of model compounds also make sense for screening and designing HDO catalysts. Then, we review the HDO of actual pyrolysis oil with different methods including two-stage treatment, co-feeding solvents and in-situ hydrogenation. The relative merits of each method are also expounded. Finally, HDO catalysts are reviewed in order of time. After the summarization of petroleum derived sulfured catalysts and noble metal catalysts, transitional metal carbide, nitride and phosphide materials are summarized as the new trend for their low cost and high stability. After major progress is reviewed, main problems are summarized and possible solutions are raised.

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An EtOAc/H2O biphasic solvent–Ru/C coupling biorefinery process was developed to selectively produce aromatics from cornstalk hydrolysis residue (CHR). In this process, CHR was depolymerized in an ethyl acetate (EtOAc)/H2O biphasic solvent system over Ru/C catalyst, which produced aromatics and carbohydrates instantly separated by EtOAc and H2O. Most lignin in CHR was converted to aromatics and nonvolatile fractions, accompanied with partial degradation of cellulose. Optimized results showed that more than 42.7% of aromatics can be obtained under 260 °C for 5 h without external hydrogen pressure. Monophasic and biphasic parallel experimental results show that the strong lignin dissolving ability of the biphasic dissolution/separation system is helpful for aromatics production and separation, which promoted CHR depolymerization over Ru/C. Furthermore, CHR, products, depolymeirzation residue solid (DRS), and catalysts were carefully characterized by gas chromatography (GC-MS), Fourier transform infrared (FT-IR), gel permeation chromatrography (GPC), high-performance liquid chromatrography mass spectrometry (HPLC-MS), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis. Results demonstrated that the biphasic solvent–Ru/C coupling process can significantly alleviate repolymerization reactions. Based on these analysis results, the catalytic process in biphasic EtOAc/H2O was discussed. This work demonstrates that such a green biphasic catalytic/separation coupling system highlights a promising route for efficient biomass degradation and product separation at mild conditions without external hydrogen pressure.

Fast pyrolysis is one of the most promising methods to convert lignin into fuels and chemicals. In the present study, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was used to evaluate vapor phase product distribution of lignin fast pyrolysis. During the non-catalytic pyrolysis process, lignin was pyrolyzed at 400°C, 500°C and 600°C respectively, finding that the highest yield of aromatic hydrocarbons was obtained at 600°C. Catalytic pyrolysis experiments were also conducted to investigate the effects of catalyst pore structure and acidity on the product distributions. Five different catalysts (HZSM-5, MCM-41, TiO 2 , ZrO 2 and Mg(Al)O) were applied to lignin catalytic pyrolysis, and the catalytic performance was estimated by analyzing the pyrolytic products. The catalysts were characterized by using X-ray diffraction (XRD), BET, and NH 3 (CO 2) temperature programmed desorption. Based on these characterizations, discussion was carried out to explain the formation of the produc distributions. Among the five catalysts, HZSM-5 exhibited the best performance on the formation of aromatic hydrocarbons.

A solid acid catalyst SO42−/TiO2/La3+ was prepared via sol-gel method using tetrabutyl titanate as TiO2 precursor. The catalyst simultaneously catalyzed esterification and transesterification resulting in the synthesis of biodiesel from waste cooking oil with high content of free fatty acids as feedstock. The optimization of reaction conditions was also performed. The maximum yield of more than 90% could be obtained under the optimized conditions that catalyst amount 5 wt. % of oil, 10:1 molar ratio (methanol to oil), temperature 110 °C, and esterification of 1 h. The catalyst can be reused for five times by activation without observing the decrease of its catalytic performance. The final products were purified by molecular distillation and detected by GC-MS. The content of fatty acid methyl esters was 96.16%.

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A series of core-shell catalysts with different shell thickness were synthesized and the effect of microporous silica shell on product distribution of Fischer-Tropsch synthesis was analyzed. Fe 3 O 4 core was prepared by hydrothermal method and the amorphous SiO 2 shell was coated on the Fe 3 O 4 core by sol-gel method. N 2 adsorption-desorption analysis indicated an irregular and microporous silica shell and the pore size distribution moved to smaller diameter with the shell thickness increased. In Fischer-Tropsch synthesis, inactive silica shell increased catalytic activity (FTY) and stability by restricting catalyst cracking and sintering. Product distribution shifted to C 1 -C 4 gaseous hydrocarbons with the increasing shell thickness probably due to the diffusion limitations on reactants/products and structure confinement and separation effect of microporous silica shell on restricting the growth of catalytic active particles. Selectivities of C 5 + were restricted within 10% for core-shell catalysts. WGS reaction activity is reduced as well, which constrains side reaction and amplifies FTS catalytic productivity to hydrocarbons.