Bio-Crude Production Improvement during Hydrothermal Liquefaction of Biopulp by Simultaneous Application of Alkali Catalysts and Aqueous Phase Recirculation

This study focuses on the valorization of the organic fraction of municipal solid waste (biopulp) by hydrothermal liquefaction. Thereby, homogeneous alkali catalysts (KOH, NaOH, K2CO3, and Na2CO3) and a residual aqueous phase recirculation methodology were mutually employed to enhance the bio-crude yield and energy efficiency of a sub-critical hydrothermal conversion (350 °C, 15–20 Mpa, 15 min). Interestingly, single recirculation of the concentrated aqueous phase positively increased the bio-crude yield in all cases, while the higher heating value (HHV) of the bio-crudes slightly dropped. Compared to the non-catalytic experiment, K2CO3 and Na2CO3 effectively increased the bio-crude yield by 14 and 7.3%, respectively. However, KOH and NaOH showed a negative variation in the bio-crude yield. The highest bio-crude yield (37.5 wt.%) and energy recovery (ER) (59.4%) were achieved when K2CO3 and concentrated aqueous phase recirculation were simultaneously applied to the process. The inorganics distribution results obtained by ICP reveal the tendency of the alkali elements to settle into the aqueous phase, which, if recovered, can potentially boost the circularity of the HTL process. Therefore, wise selection of the alkali catalyst along with aqueous phase recirculation assists hydrothermal liquefaction in green biofuel production and environmentally friendly valorization of biopulp.

Bio-Derived Catalysts: A Current Trend of Catalysts Used in Biodiesel Production

Biodiesel is a promising alternative to fossil fuels and mainly produced from oils/fat through the (trans)esterification process. To enhance the reaction efficiency and simplify the production process, various catalysts have been introduced for biodiesel synthesis. Recently, the use of bio-derived catalysts has attracted more interest due to their high catalytic activity and ecofriendly properties. These catalysts include alkali catalysts, acid catalysts, and enzymes (biocatalysts), which are (bio)synthesized from various natural sources. This review summarizes the latest findings on these bio-derived catalysts, as well as their source and catalytic activity. The advantages and disadvantages of these catalysts are also discussed. These bio-based catalysts show a promising future and can be further used as a renewable catalyst for sustainable biodiesel production.

Metal-Alkali Catalytic Valorization of Lignocellulose Towards Aromatics and Small Molecular Alcohols and Acids in a Holistic Approach

In this work, we developed an approach of one-pot completely catalytic conversion of woody biomass into two value product streams: lignin-derived aromatics (68.54% monomer and 29.65% oligomer yields of lignin) and (semi-)cellulose-derived small molecular alcohols (about 59.60% of biomass mass). These could be afforded by conducting lignocellulose depolymerization over metal-alkaline catalysts in a mixture n-butanol/H2O solvent system at 250 °C and 30 bar H2. In the valorization process, the homogenous mixture of n-butanol-H2O solvents extract and depolymerize both lignin and hemicellulose, while the catalysts and H2 are essential to cleave the inter-/intramolecular linkages of lignocellulose into target products. After the reaction, phase separation of n-butanol and H2O takes place when systematic temperature at room temperature, providing a mild and effective strategy to isolate lignin-derived aromatics (n-butanol phase) from small molecular alcohols/acids (aqueous phase). Ru/C and alkali catalysts are collected by filtration from n-butanol phase and H2O phase, respectively. Meanwhile, the effect of metal-alkali coupled catalysts enables facilitating the cleavage of β-O-4 linkage of lignin and increasing the attainability of (semi-)cellulose-derived oligomers and the small molecular alcohols. This catalytic system provides a versatile valorization approach for biomass catalytic to bio-based chemicals.

Mathematical modeling of transesterification process kinetics of triglycerides catalyzed by TMAH

Biodiesel is a renewable fuel mainly produced by methylation of triglycerides of vegetable oils or animal fats. The production processes nowadays are particularly based on the utilization of inorganic alkali catalysts. However, it has been proved that an organic alkali – tetramethylammonium hydroxide (TMAH) – can also be used as a very efficient transesterification catalyst. The work presented herein is focused on mathematical modeling of the kinetics of TMAH-catalyzed transesterification of triglycerides at different reaction conditions, specifically at varying reaction temperature with the aim to understand the reaction mechanism and identify the key variables for optimization of the production process. The main kinetic parameters were calculated based on the mathematical- statistical processing of experimental kinetic data. The reaction rate constants for individual consecutive and reversible reactions and the corresponding activation energies were calculated.

Preparation and Application of Biochar-Based Catalysts for Biofuel Production

Firstly, this paper reviews two main methods for biochar synthesis, namely conventional pyrolysis and hydrothermal carbonization (HTC). The related processes are described, and the influences of biomass nature and reaction conditions, especially temperature, are discussed. Compared to pyrolysis, HTC has advantages for processing high-moisture biomass and producing spherical biochar particles. Secondly, typical features of biochar in comparison with other carbonaceous materials are summarized. They refer to the presence of inorganics, surface functional groups, and local crystalline structures made up of highly conjugated aromatic sheets. Thirdly, various strategies for biochar modification are illustrated. They include activation, surface functionalization, in situ heteroatom doping, and the formation of composites with other materials. An appropriate modification is necessary for biochar used as a catalyst. Fourthly, the applications of biochar-based catalysts in three important processes of biofuel production are reviewed. Sulfonated biochar shows good catalytic performance for biomass hydrolysis and biodiesel production. Biodiesel production can also be catalyzed by biochar-derived or -supported solid-alkali catalysts. Biochar alone and biochar-supported metals are potential catalysts for tar reduction during or after biomass gasification. Lastly, the merits of biochar-based catalysts are summarized. Biochar-based catalysts have great developmental prospects. Future work needs to focus on the study of mechanism and process design.

A CaMnAl-hydrotalcite solid basic catalyst toward the aldol condensation reaction with a comparable level to liquid alkali catalysts

A CaMnAl-hydrotalcite solid basic catalyst was prepared based on the memory effect of LDHs, which exhibited extremely high heterogeneous catalytic performance toward the aldol condensation reaction.

PREPARATION OF SPENT BLEACHING EARTH-SUPPORTED CALCIUM FROM LIMESTONE AS CATALYST IN TRANSESTERIFICATION OF WASTE FRYING OIL

An investigation was conducted on palm oil refinery waste-spent bleaching earth (POR-SBE), POR-SBE supported by calcium as catalysts for methyl esters production through transesterification process using waste frying oil. The catalysts showed longer lasting activity than the traditional alkali catalysts. The optimum conditions for the process were: Ca-POR-SBE catalyst amount 7 %; methanol to oil molar ratio 12:1; and a reaction duration is 4 h. The process was able to transesterify oil to methyl esters at 96.8 % conversion at 65 C. The catalysts were easily separated from the reaction mixture and the final product met selected biodiesel fuel properties in accordance with European Standard EN 14214.