Hydrothermal liquefaction of lignocellulosic biomass feedstock to produce biofuels: Parametric study and products characterization

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

“…In early studies, Ogi et al [88] observed that on increasing initial pressure from 0.5 to 4 MPa, the bio-oil yield increased from 6 to 20 wt% and had a negligible effect on a further increase in pressure up to 10 MPa at 350 • C. Mathanker et al [24] observed that pressure had no effect on oil yield in the supercritical region (374 • C), whereas at a 300 • C increase in initial pressure from 2 to 4 MPa, there was an increase in the bio-oil yield from 21 wt% to 27 wt%. Similarly, Brand et al [98], Yang et al [79], and Tekin et al [37] observed that an initial pressure of inert N 2 had little effect on the yield of bio-oil.…”

“…Mathanker et al [24] published a parametric study to understand how the process parameters, such as temperature (250-375 • C), pressure (P i : 2-4 MPa), and retention time (0-60 min) affect the liquefaction of corn stover. It was observed that for the fixed initial pressure of 4 MPa and retention time of 15 min, a yield of heavy oil reached a maximum limit with an increase in temperature from 250 • C (22.2 wt%) to 300 • C (27.2 wt%), where the yield of solid char was minimum.…”

“…The increase in local solvent density allows more contact and better penetration and interaction of hydrolysis ions with the crystallized zone of cellulose and the surface of cellulose, hemicellulose, and lignin. Once the supercritical condition is achieved, the pressure has a negligible impact on the yield of bio-oil [24,98]. The increase of pressure in the supercritical region increases the local solvent density, causing a cage effect, which prevents C-C bond cleavage and thus reducing the fragmentation of lignocellulosic material [86].…”

“…As shown in Figure 7, the heating cycle for an electrically heated batch autoclave reactor can be divided in two zones. Zone A and B have a heating rate of 10 • C min −1 and 2.5 • C min −1 , respectively [24]. In general, biomass spends a larger part of the heating period in a high subcritical temperature range (Zone B) before reaching the desired reaction temperature.…”

“…The plotted analysis of results from previous studies on different forest-based feedstocks as shown in Figure 3b it was observed that the w cellulose /w hemicellulose ratio was dominant over the cellulose content in determining the bio-oil yield for forest feedstock. Effect of cellulose and cellulose/hemicellulose ratio on bio-oil yield for (a) agricultural feedstocks [23][24][25][26][27][28], (b) forest feedstock [26,27,29,32,33,35,38,40,41].…”