Optimization of process parameters for hydrothermal conversion of castor residue

A Review of Hydrothermal Liquefaction of Biomass for Biofuels Production with a Special Focus on the Effect of Process Parameters, Co-Solvents, and Extraction Solvents

Hydrothermal liquefaction is one of the common thermochemical conversion methods adapted to convert high-water content biomass feedstocks to biofuels and many other valuable industrial chemicals. The hydrothermal process is broadly classified into carbonization, liquefaction, and gasification with hydrothermal liquefaction conducted in the intermediate temperature range of 250–374 °C and pressure of 4–25 MPa. Due to the ease of adaptability, there has been considerable research into the process on using various types of biomass feedstocks. Over the years, various solvents and co-solvents have been used as mediums of conversion, to promote easy decomposition of the lignocellulosic components in biomass. The product separation process, to obtain the final products, typically involves multiple extraction and evaporation steps, which greatly depend on the type of extractive solvents and process parameters. In general, the main aim of the hydrothermal process is to produce a primary product, such as bio-oil, biochar, gases, or industrial chemicals, such as adhesives, benzene, toluene, and xylene. All of the secondary products become part of the side streams. The optimum process parameters are obtained to improve the yield and quality of the primary products. A great deal of the process depends on understanding the underlined reaction chemistry during the process. Therefore, this article reviews the major works conducted in the field of hydrothermal liquefaction in order to understand the mechanism of lignocellulosic conversion, describing the concept of a batch and a continuous process with the most recent state-of-art technologies in the field. Further, the article provides detailed insight into the effects of various process parameters, co-solvents, and extraction solvents, and their effects on the products’ yield and quality. It also provides information about possible applications of products obtained through liquefaction. Lastly, it addresses gaps in research and provides suggestions for future studies.

Research progress and hot spots of hydrothermal liquefaction for bio-oil production based on bibliometric analysis

Hydrothermal liquefaction (HTL) of biomass used HTL reaction under high temperature and pressure to produce bio-oil. This technology is considered as one of the most promising converting technology of biomass to biofuels. This paper summarized current research developments of HTL for bio-oil and analyzed its reaction mechanism and influencing factors based on bibliometric analysis. The results showed that reaction conditions and catalyst have been still global researching focuses about HTL. Compared with homogeneous catalysts, the study of HTL by using heterogeneous catalyst developed more quickly. With promotion of resource recovering, food waste, sludge, and other organic waste can also be used as raw materials for HTL for bio-oil now. The structure of this paper was shown in graphic abstract. Firstly, bibliometric analysis was conducted on hydrothermal liquefaction for bio-oil production. According to the emergency frequency of key words, catalyst, microalgae, reaction conditions, and biomass waste as raw material for hydrothermal liquefaction were determined as four parts of the paper. Finally, we speculated the development trend of hydrothermal liquefaction for bio-oil production.

Unsupported Ni metal catalyst in hydrothermal liquefaction of oak wood: Effect of catalyst surface modification

Hydrothermal liquefaction of oak wood was carried out in tubular micro reactors at different temperatures (280-330 °C), reaction times (10-30 min), and catalyst loads (10-50 wt%) using metallic Ni catalysts. For the first time, to enhance the catalytic activity of Ni particles, a coating technique producing a nanostructured surface was used, maintaining anyway the micrometric dimension of the catalyst, necessary for an easier recovery. The optimum conditions for non-catalytic liquefaction tests were determined to be 330 °C and 10 min with the bio-crude yield of 32.88%. The addition of metallic Ni catalysts (Commercial Ni powder and nanostructured surface-modified Ni particle) increased the oil yield and inhibited the char formation through hydrogenation action. Nano modified Ni catalyst resulted in a better catalytic activity in terms of bio-crude yield (36.63%), thanks to the higher surface area due to the presence of flower-like superficial nanostructures. Also, bio-crude quality resulted improved with the use of the two catalysts, with a decrease of C/H ratio and a corresponding increase of the high heating value (HHV). The magnetic recovery of the catalysts and their reusability was also investigated with good results.