• Energy Research

In this work, the mesoporous SBA-15 and a series of modified catalysts based on it, such as Al-SBA-15 and Ni/Al-SBA-15, were synthesized and used for eliminating the char formation during the depolymerization of hydrolyzed lignin. The temperature, time and solvent effects on the lignin depolymerization were also investigated. Results showed that the repolymerization was effectively suppressed over SBA-15 due to its well-ordered pore structure and large pore size. The addition of Al and Ni elements in SBA-15 could improve the lignin depolymerization performance and saturate the instable intermediates. Ethanol was found to be more effective in suppressing repolymerization than other solvents. 81.4% liquefaction degree and 21.90wt% monomer yield was achieved, and no obvious char was observed after the depolymerization of hydrolyzed lignin in ethanol solvent at 300°C for 4h over Ni/Al-SBA-15(20) catalyst.

Abstract Current global resources of fossil fuels are gradually depleting and the energy crisis induces increasing concerns on the research of new effective substitution of these fossil fuels by renewable energy, especially bio-fuels from biomass such as bio-oils. However, bio-oils, generally originated from the pyrolysis of biomass, contain a great deal of carboxylic acids such as acetic acid and these acids can easily decrease the stability and the quality of oil. Meanwhile, these acids are highly corrosive to reaction equipments. Bio-oil could be upgraded before its utilization in the feedstocks of fuels and chemicals. In this work, the removing of these carboxylic acids was investigated by esterification in supercritical ethanol. The effects of reaction temperature, the ratio of ethanol to bio-oil, and reaction time on the conversion of acids were studied as well as the addition of external acid such as H2SO4, H3PO4 or zeolite. The results showed that carboxylic acids in crude bio-oil easily esterified with ethanol in the supercritical system. More ethyl acetate was formed at higher volume ratio of ethanol to bio-oil and 100% of the selectivity was achieved at the volume ratio of 5:1 after 2 h reaction, whereas more side reactions were present in lower or higher ratio of ethanol to bio-oil. The addition of external acid decreased distinctly the formation of esters, indicating that these carboxylic acids could be effectively removed under the acidic system arising from the internal ionization of ethanol. These would be very useful in the upgrading of bio-oil into high quality fuels in the future biorefinery.

Abstract To improve the quality of fast pyrolysis bio-oil, an efficient catalytic upgrading process is proposed with pristine Ni/MgO catalyst and ethanol. Esterification, hydrogenation, alkylation of aromatic ring and depolymerization of lignin-derived pyrolytic oligomers simultaneously occurred in the upgrading process. Esters, ketones and alkyl-substituted aromatic compounds were found to be the main components in the volatile fraction of the upgraded bio-oil. Under the optimal conditions, pH value and HHV (high heating value) of the upgraded bio-oil were 5.01 and 24.9 MJ kg −1 , respectively. This result suggested that the properties of bio-oil could be effectively improved by the catalytic upgrading process. Moreover, carbon efficiency of this upgrading process was relatively high because that formation of coke is suppressed in the upgrading process.

Many efficient methods have been proposed to realize lignin depolymerization, while effective usage of lignin depolymerization products at mild conditions is still a big challenge. Conversion of them to stable products in thermal and chemical properties is a necessary step. Herein, a mild hydrogenation process of lignin depolymerization products over Ni/SiO2 catalyst was proposed. Model compound of 2,3-dihydrobenzofuran exhibited a good reaction result. Nearly 100% conversion was obtained at 130 °C, and the selectivity of 2-ethylcyclohexanol product reached 94.6%. The lignin depolymerization products also had a good hydrogenation result, in which not only the hydrogenation of unsaturated groups but also the cleavage of β-O-4 bonds occurred. Stable products in thermal and chemical properties were formed, which possessed high heated value and low molecular weight. This treatment is conducive to suppressing the occurrence of condensation and favorable for the further catalytic conversion.

Serious char formation caused by the repolymerization of unsaturated decomposition products is a considerable challenge for current lignin utilization. Here, a novel and efficient base-catalyzed depolymerization and in situ hydrogenolysis process for lignin decomposition and char elimination was proposed using the synergic catalyst of NaOH coordinated with Ru/C. In which, lignin was first depolymerized to phenolic monomer and its oligomer, and then the oligomer was further converted to more stable aliphatic alcohols simultaneously. The results showed that more than 92.5% of lignin was converted, giving 12.69% phenolic monomer, 6.12% aliphatic alcohol and less than 14.03% residual solid. This residual solid selectivity was far lower than it from the single catalyst condition. Furthermore, the products were analyzed using GC–MS, GPC, HPLC–MS and 1H NMR. The synergistic effect between depolymerization and hydrogenolysis was also investigated through comparative analysis of the feedstock, products, and the recovered lignin.

The aim of this study is to explore the reaction mediums and conditions for producing high yield of valuable monomers from concentrated sulfuric acid hydrolyzed lignin. The solvent, temperature and time effects on the hydrogenolysis of hydrolyzed lignin were investigated under the catalysis of Pd/C and CrCl3. Supercritical methanol exhibits the best depolymerization performance, because of its unique diffusion, dissolution and acid-base properties. Afterwards, the influence of reaction temperature and time on depolymerization, repolymerization and coking during hydrogenolysis was examined in methanol. The high temperature is found to favor the depolymerization, with the β-O-4 linkages cleaved significantly. However, the repolymerization is promoted simultaneously, and a high amount of β-β groups form. These reactions are in constant competition with each other and the repolymerization is preferred at excessive high temperature, producing bulk char residues, that is coking. This study will provide a beneficial reference for the maximization of lignin waste valorization.

Abstract Ni/CMK-3 catalyst, the mesoporous carbon material loading Ni activity, was prepared and used in the in-situ hydrogenation of mixed model compounds (including acetone, acetic acid, furfural, o-cresol, ethanediol and water) of bio-oil (MCB) and actual bio-oil in this paper. The effects of hydrogen donors, solvents and the dosages of catalyst were all investigated in the in-situ hydrogenation process. The results showed that the hydrogen donor of methanol, ethanol and formic acid could all provide hydrogen for the in-situ hydrogenation but the product distributions of bio-oils were different after in-situ hydrogenation. Using alcohols as hydrogen donors, esterification reaction happened between the hydrogen donors and acetic acid. The formic acid could promote the phenols conversion but the conversion of acetic acid was restrained. When the radio of water and methanol was 10:3 and 10:5, most of ketones and aldehydes in the raw bio-oil converted to alcohols and the conversion of acids and phenols was beyond 50%. The contents of alcohols and esters in raw bio-oil increased from 18.52% to 51.14% and 48.21%.

Abstract Pyrolytic lignin obtained by separation of the fast pyrolysis bio-oil of biomass is problematic for use as a fuel and chemical. A catalytic cracking process for pyrolytic lignin was therefore explored using pristine catalysts (MoO3, HZSM-5, and α-Al2O3). The results demonstrated that pyrolytic lignin can be converted into aromatic hydrocarbons and phenols in a one-pot process. Among the three catalysts, MoO3 was more efficient for aromatic hydrocarbons and phenols, with yields of up to 9.2 and 7.9 wt%, respectively, under the conditions of 340 °C and an H2 atmosphere. Catalyst dosage, reaction temperature, and H2 pressure were investigated in detail, and it was found that the aromatic hydrocarbon yield was highly catalyst dosage dependent. The regeneration of used catalyst was also explored, and the catalytic activity of regenerated MoO3 catalyst was recovered by calcination in the presence of O2. This work provides a potential alternative for the production of aromatic hydrocarbons and phenols from pyrolytic lignin.

Abstract Selective production of cyclohexanol from renewable lignin derived phenolic has been presented using the cost-efficient catalyst Ni/MgO which shows excellent catalytic activity in the hydrogenation reaction and dehydroxylation inhibition. Guaiacol, one of the most abundant lignin depolymerization products, was selected as the model compound. The hydrogenation performance of guaiacol was investigated over various catalysts. The effect of the reaction parameters was also studied. The results showed that guaiacol could be efficiently converted to cyclohexanol, which is a highly value-added precursor and additive for bio-fuel that is generally obtained from unsustainable fossil resources. Under the mild condition (160 °C, 3 h and 3 MPa H2), more than 97.74% of guaiacol conversion with 100% cyclohexanol selectivity can be achieved in the presence of 20% Ni/MgO. Intensive catalyst characterization demonstrated that the efficient promotion effect of the base carrier for the Ni active center was responsible for efficient guaiacol conversion and selective cyclohexanol production. Furthermore, the Ni/MgO catalyst showed excellent recyclability, where no significant activity loss was observed even after four runs. Moreover, the reaction pathway and the catalytic mechanism are proposed.