Catalytic and non-catalytic low-pressure hydrothermal liquefaction of pinewood sawdust, polyolefin plastics and their mixtures

Hydrothermal co-liquefaction of biomass and polyolefin plastic feedstocks offers the advantage of potential synergistic reaction environments for producing liquid products of high fuel quality. In this present study, hydrothermal liquefaction and co-liquefaction of sawdust, low-density polyethylene and high-density polyethylene were investigated in a batch reactor from 350 °C to 450 °C and autogenic pressures below 30 bar. The novel low-pressure hydrothermal processing method was carried out with and without low-cost Ni–Cu/Al2O3 bimetallic catalyst. Thermal degradation of the sawdust started at 350 °C, whereas the plastics could only completely degrade at 450 °C, which was then chosen as the optimum reaction temperature. The catalysed process led to an increase in oil yield from the sawdust, with carbon enrichment by 16.3% and 22% deoxygenation. Furthermore, the catalyst promoted the formation of ketones and aromatic hydrocarbons, while consuming phenols and furfural in the sawdust-derived bio-oils. For the plastics, the catalyst, gave slight decreases in oils yield in favour of gas and/or char formation, with the promotion of in situ hydrogenation to enhance the yields of alkanes over alkenes. Results from hydrothermal co-liquefaction tests showed that synergistic interactions occurred between the degradation products of sawdust and the plastics. The observed synergy was further promoted by the presence of the catalyst, leading to dramatic deoxygenation of the oil products to produce hydrocarbon-rich fuels with less than 4 wt% oxygen contents (≈90% deoxygenation). This low-pressure hydrothermal co-liquefaction process is an efficient and cost-effective pathway for single-loop conversion of widely available biomass and plastics feedstocks into highly deoxygenated oils for use as sustainable fuels

Hydrogen production from the catalytic supercritical water gasification of process water generated from hydrothermal liquefaction of microalgae

The integration of hydrothermal liquefaction (HTL) and hydrothermal gasification (HTG) is an option for enhanced energy recovery and potential biocrude upgrading. The yields and product distribution obtained from the HTL of Chlorella vulgaris have been investigated. High conversion of algae to biocrude as well as near complete gasification of the remaining organic components in the aqueous phase was achieved. The aqueous phase from HTL was upgraded through catalytic HTG under supercritical water conditions to maximise hydrogen production for biocrude hydrotreating. High yields of hydrogen were produced (∼30 mol H2/kg algae) with near complete gasification of the organics (∼98%). The amount of hydrogen produced was compared to the amounts needed for complete hydrotreating of the biocrude. A maximum of 0.29 g H2 was produced through HTG per gram of biocrude produced by HTL. The nutrient content of the aqueous phase was analysed to determine suitability of nutrient recovery for algal growth. The results indicate the successful integration of HTL and HTG to produce excess hydrogen and maintain nutrient recovery for algal growth

Catalytic supercritical water gasification of eucalyptus wood chips in a batch reactor

Eucalyptus wood chips were reacted under supercritical water conditions to evaluate the effect of a NiFe2O4 catalyst, residence time and temperature parameters. Experiments were performed in a batch reactor at 400 °C , 450 °C and 500 °C using three different amounts of catalyst (0, 1.0, 2.0 g) and three different residence times (30, 45, 60 min). Results showed that eucalyptus wood chips reacted and produced CO2 as the dominant gas in all cases, followed by H2 and CH4. However, the presence of NiFe2O4 catalyst led to a 60% increase in H2 produced, while significantly reducing the solid residue and enhancing the percentage of methyl derivatives in the organic liquid products. The highest H2 mol% was at 450 °C, 2 g of catalyst and 60 min of residence time. Analysis of the derived oils showed that they were mostly composed of ketones, aldehydes, methylbenzenes and alkylated phenols. Increasing the reaction temperature to 500 °C increased the molar composition of methane by 62% compared to its yield at 450 °C. In generally, this work showed that NiFe2O4 acted as an effective heterogeneous catalyst for improved production of H2 and CH4 via supercritical water gasification process