Thermochemical conversion is an effective process in production of biocrude. It mainly includes techniques such as torrefaction, liquefaction, gasification and pyrolysis in which Hydrothermal Liquefaction (HTL) has the potential to produce significant energy resource. Algae, one of the third-generation feedstocks is placed in the top order for production of bio-oil compared to the first and second-generation feedstock, as the algae can get multiplied in shorter time with the uptake of greenhouse gases. In HTL, the subcritical water helps the biomass to undergo thermal depolymerisation and produce various chemicals such as nitrogenates, alkanes, phenolics, esters, etc. The produced “biocrude” or “bio-oil” may be further upgraded into value-added chemicals and fuels. In addition, the bio-gas and bio-char are also synthesized as by-products. This review provides an overview of different routes available for thermochemical conversion of biomass. It also provides an insight on the operating parameters such as temperature, pressure, dosage of catalyst and solvent for lignocellulosic and algal biomass under HTL environment. In extent, the article covers the conversion mechanism for these two feedstocks and also the effects of the operating parameters on the yield of biocrude are studied in detail.
Waste lignocellulosic biomass obtained from the dry plant matter is the most abundantly available resource for the production of biofuels, and biochar. The invasive weed tree of Prosopis juliflora was employed as feedstock for the extraction process, which converts biomass into biogas, bio-oil, and biochar in the presence of subcritical water at high temperatures (250 °C to 374 °C) and pressures (4-22 MPa). The extraction process was performed inside a 50 ml stainless steel hydrothermal reactor with 3.5 g of feedstock and varying process parameters such as temperatures (250–325 °C) and reaction time (30–120 min) and biomass to water loading (10–30 % w/v). The response surface methodology was employed to optimize the parameters for maximizing the bio-oil yield under subcritical condition using Design Expert 8.0.7.1 software. The % yield of bio-oil and biochar during this process were taken as responses. The biomass and bio-oil were characterized using proximate and ultimate elemental analysis, thermogravimetric analysis, and gas-chromatography mass spectroscopy. The results showed that the maximal yield of bio-oil 3.65 % was obtained at a temperature of 277.62 °C, reaction time 59.98 min and biomass to water loading 20.13 % w/v. The resulted bio-oil was found to contain long-chain alkanes, ketones, carboxylic acids, amines, and phenols.
The rising demand for cleaner energy among the nations has turned the focus from fossil fuel-based energy sources to renewables like biomass, solar, wind, etc. Biomass conversion to fuel has increased research in recent times due to its ease and availability throughout the year. Hydrothermal liquefaction is the process where biomass converts to a liquid product via complex reaction mechanisms. This review aims to summarize the hydrothermal liquefaction of algal biomass and the improvements in the bio-crude yield using heterogeneous and homogenous catalysts. Many references have been reviewed to provide the sources for the process and have been critically well structured. This review also provided information regarding the reaction pathway for algal biomass and the effects of process parameters like temperature, residence time, pH, etc. The focus of the review is on the effects of various catalysts based on their dosage whose results collected from various sources have been tabulated. The review briefly discusses the applications of products formed during hydrothermal liquefaction after post-processing.
In the present study, nanocomposite polymeric membranes are fabricated using polyvinyl alcohol (PVA), cellulose acetate (CA) as polymers, and dimethyl sulfoxide (DMSO) as the solvent. To enhance the performance of the membrane, nanoparticles like TiO2, CaO, CdO, and ZrO are added to the polymeric solution and the doped polymeric solution is cast on a glass plate. Nine combinations of membranes are fabricated with two different concentrations (0.1% and 0.2%) of nanoparticles. The basic properties of the membranes such as density, porosity, viscosity, permeability, pure water flux, and water content are studied for the samples. Membrane pore structure and surface properties are identified and it is found that doping nanoparticles on the surface of membranes improve mechanical strength, stability, pore size, etc., allowing the membranes to perform better in extreme industrial‐level effluent treatment applications. High‐resolution scanning electron microscopy (SEM) shows the homogeneous dispersion of ZrO, TiO2, CaO, and CdO nanoparticles on the surface of the PVA‐CA membrane. The doping of nanoparticles on the PVA‐CA membrane results in improved mechanical strength and good chemical oxidation stability. In comparison, the PCD‐TiO2 sample shows high thermal stability and oxidation stability at high temperatures until 200°C, which has a high potential for treating industrial effluents.
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