Bhavya B. Krishna

Opportunities for utilization of non-conventional energy sources for biomass pretreatment

The increasing concerns over the depletion of fossil resources and its associated geo-political issues have driven the entire world to move toward sustainable forms of energy. Pretreatment is the first step in any biochemical conversion process for the production of valuable fuels/chemicals from lignocellulosic biomass to eliminate the lignin and produce fermentable sugars by hydrolysis. Conventional techniques have several limitations which can be addressed by using them in tandem with non-conventional methods for biomass pretreatment. Electron beam and γ (gamma)-irradiation, microwave and ultrasound energies have certain advantages over conventional source of energy and there is an opportunity that these energies can be exploited for biomass pretreatment.

Pyrolysis of azolla, sargassum tenerrimum and water hyacinth for production of bio-oil

Pyrolysis of azolla, sargassum tenerrimum and water hyacinth were carried out in a fixed-bed reactor at different temperatures in the range of 300-450°C in the presence of nitrogen (inert atmosphere). The objective of this study is to understand the effect of compositional changes of various aquatic biomass samples on product distribution and nature of products during slow pyrolysis. The maximum liquid product yield of azolla, sargassum tenerrimum and water hyacinth (38.5, 43.4 and 24.6wt.% respectively) obtained at 400, 450 and 400°C. Detailed analysis of the bio-oil and bio-char was investigated using 1H NMR, FT-IR, and XRD. The characterization of bio-oil showed a high percentage of aliphatic functional groups and presence of phenolic, ketones and nitrogen-containing group. The characterization results showed that the bio-oil obtained from azolla, sargassum tenerrimum and water hyacinth can be potentially valuable as a fuel and chemicals.

Slow pyrolysis of prot, alkali and dealkaline lignins for production of chemicals

Effect of different lignins were studied during slow pyrolysis. Maximum bio-oil yield of 31.2, 34.1, and 29.5wt.% was obtained at 350, 450 and 350°C for prot lignin, alkali lignin and dealkaline lignin respectively. Maximum yield of phenolic compounds 78%, 80% and 92% from prot lignin, alkali and dealkaline lignin at 350, 450 and 350°C. The differences in the pyrolysis products indicated the source of lignins such as soft and hard wood lignins. The biochar characterisation revealed that the various ether linkages were broken during pyrolysis and lignin was converted into monomeric substituted phenols. Bio-oil showed that the relative contents of each phenolic compound changes significantly with pyrolysis temperature and also the relative contents of each compound changes with different samples.

Non-isothermal kinetic study of de-oiled seeds cake of African star apple (Chrosophyllum albidum) using thermogravimetry.

Thermal decomposition and kinetics behaviour of the de-oiled seed cake of African star apple (Chrosophyllum albidum) has been investigated using thermogravimetry under the nitrogen atmosphere from ambient temperature to 900 °C. The thermogravimetric data for the cake decomposition at six different heating rates (5, 10, 15, 20, 30 and 40 °C/min) were used to evaluate the kinetic decomposition of the cake using Friedman (FD), Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) models. Thermal decomposition of the cake showed thermograms indicating dehydration and devolitilization stages (200–400 °C). The maximum temperature for the decomposition of the cake (Tmax) increases from 289.42–335.96 °C with increase in heating rates. The average apparent activation energy (Ea) values of 153.15, 145.14 and 147.15 kJ/mol were calculated using Friedman, Kissinger-Akahira-Sunose, and Flynn-Wall-Ozawa models respectively. The extent of mass conversion (α) shows dependence on apparent activation Ea values which is an evidence of multi-step decomposition kinetic. The thermal profile and kinetic data obtained could be helpful in evaluating the thermal stability of the cake as well as modeling, designing and developing a thermo-chemical system for the conversion of the cake to fuel.

Hydrothermal Liquefaction of Lignocellulosic Biomass Components: Effect of Alkaline Catalyst

The fundamental studies to understand the role of individual biomass components (cellulose and lignin) on the production of valuable hydrocarbons during hydrothermal liquefaction (HTL) is presented. Thermal and catalytic HTL of cellulose and lignin was performed at 280 °C under biomass:H2O ratio of 1:6 at 15 min residence time. The use of alkaline catalysts significantly increased both bio-oil yield and conversion for cellulose as well as lignin. Maximum bio-oil yield (28%) and conversion (90%) in case of cellulose was observed with KOH. Similarly in case of lignin maximum bio-oil yield (17 wt%) as well as conversion (72%) was observed with KOH. From the analysis of bio-oil and bio-residue, it was observed both cellulose and lignin have undergone hydrolytic cleavage during HTL to form low molecular weight liquid products. The FTIR and NMR (1H and 13C) of the bio-oil obtained from lignin indicated the presence of phenols and aromatic ethers.