• Energy Research

Biomass pyrolysis has recently gained increasing attention as a thermochemical conversion process for obtaining value-added products, thanks to the development of cutting-edge, innovative and cost-effective pyrolysis processes. Over time, new and novel pyrolysis techniques have emerged, and these processes can be tuned to maximize the production of high-quality hydrogen. This review examines recent advancements in biomass pyrolysis by classifying them into conventional, advanced and emerging approaches. A comprehensive overview on the recent advancements in biomass pyrolysis, highlighting the current status for industrial applications is presented. Further, the impact of each technique under different approaches on conversion of biomass for hydrogen production is evaluated. Techniques, such as inline catalytic pyrolysis, microwave pyrolysis, etc., can be employed for the sustainable production of hydrogen. Finally, the techno-economic analysis is presented to understand the viability of pyrolysis at large scale. The outlook highlights discernments into future directions, aimed to overcome the current shortcomings.

Excessive utilization of fossil fuels has resulted in serious concerns about climate change. Integrating biorefinery technology to convert waste-derived-lignocellulosic biomass into biofuels and biopolymers has become an emerging topic toward our sustainable future. Pretreatment to fractionate the building block chemicals from the biomass is a crucial unit operation to ease the downstream processes in biorefinery. However, application of solvents and chemicals in the process can create many operational and environmental challenges in sensitive areas like highly populated cities. To shed light on how to determine a green biorefinery, this study presents the sustainability metrics of various pretreatment techniques and their operational risks during urbanization. The proposed green indexes include fractionation outputs, chemical recyclability, operational profile, and safety factors. In line with the design principles of lignin valorization, the issue of urban biomass and water-and-energy nexus are addressed to support future development and application of urban biorefinery for municipal waste management.

Abstract Progressive replacement of petroleum chemicals with biomass derived products is an essential research goal toward sustainability. However, the progress of the development of new generation biorefinery has been affected by many factors, i.e., prices of crude oil, food, and carbon. To quantify the environmental and social impacts of the technologies, this study constructed a sustainability index for calculating two new bio-butanediol production processes with oil palm empty fruit bunches as example feedstock. The performance of organosolv pretreatment using butanediol was compared with the whole slurry conversion process using sulfite pretreated biomass, over the petroleum refinery and first generation biorefinery with food crop feedstock. The organosolv biorefinery process successfully converted the biomass into 77.3 ± 1.63 g/L of bio-butanediol (0.45 g/g yield), which is slightly higher (5.5%) than that of the sulfite-based process. The integration of biorefinery techniques, with oil palm farming shall result in 6.8 kg-CO2 and 0.5 kg-food benefits per kg butanediol produced, yielding a sustainability index of 7.30. The food index for first generation biorefinery is −1.04 kg food per kg butanediol produced. Using empty fruit bunches for butanediol production could save 1.54 kg food crop consumption, which turns the “food vs. fuel competition” into a “food plus fuel nexus”.

Bioenergy and biochemicals can be sustainably produced through fermentation and anaerobic digestion (AD). However, this bioconversion processes could be more economical if the hydrolysis rates of substrates in bioreactors can be accelerated. In this review, the feasibilities of including enzymatic hydrolysis (EH) in various bioconversion systems were studied to facilitate the biological synergy. The reaction kinetics of EH in bioconversion systems comparing pretreated lignocellulosic biomass (LCB) and food waste (FW) substrates were reviewed. Possible strategies to improve the hydrolysis efficiency were explored, including co-cultivation during enzyme production and replacement of pure enzyme with on-site produced fungal mash during EH. Key insights into improvement of current AD and fermentation technologies were summarized and further formed into suggestions of future directions in techno-economic feasibility of biorefinery using mixture of the first-generation food crop feedstock with FW; and/or co-digestion of FW with LCB.

Effective utilization of cellulose and hemicelluloses is essential to sustainable bioconversion of lignocellulose. A newly isolated xylose-utilizing strain, Klebsiella pneumoniae PM2, was introduced to convert the biomass "whole sugars" into high value 2,3-butanediol (2,3-BDO) in a biorefinery process. The fermentation conditions were optimized (30°C, pH 7, and 150 rpm agitation) using glucose for maximum 2,3-BDO production in batch systems. A sulfite pretreated oil palm empty fruit bunches (EFB) whole slurry (substrate hydrolysate 119.5 g/L total glucose mixed with pretreatment spent liquor 80 g/L xylose) was fed to strain PM2 for fermentation. The optimized biorefinery process resulted in 75.03 ± 3.17 g/L of 2,3-BDO with 0.78 ± 0.33 g/L/h productivity and 0.43 g/g yield (87% of theoretical value) via a modified staged separate hydrolysis and fermentation process. This result is equivalent to approximately 135 kg 2,3-BDO and 14.5 kg acetoin precursors from 1 ton of EFB biomass without any wastage of both C6 and C5 sugars.

Abstract Lignocellulosic biomass is an emerging resource of carbohydrates and bio-based aromatics derived from biorefinery. However, pretreatment of biomass to fractionate building-block chemicals is an energy-intensive process affecting the sustainability of the whole process. This study aims to investigate the energy and carbon benefits of a novel biphasic pentanol-water pretreatment. To compare, three different pretreatment scenarios i.e., dilute acid, conventional ethanosolv, and biphasic pentanol-water pretreatments were investigated for the conversion of Acacia Confusa wood chips to produce benchmark fuel and reactive lignin. The results showed that the proposed biphasic pretreatment yielded 70.3% lignin dissolution in the organic phase while leaving cellulose as an insoluble solid residue. Simultaneous saccharification and fermentation resulted in 92.2% cellulose digestibility of pretreated substrates and ethanol yield of 0.41 g/g-glucan in the fermentation broths. Biphasic pretreatment also preserved 42.5% of reactive β-aryl ether linkages in fractionated lignin which is higher than ethanosolv pretreatment (31.1%). Carbon balance showed that the biphasic process recovered 50.3% wood carbon in the product streams as ethanol and reactive lignin, which is higher than the dilute acid (17.1%) and ethanosolv (49.6%) approaches. The overall energy balance showed that the biphasic process yielded net positive energy of 1.1 MJ/kg-wood which was much higher than the dilute acid (−0.16 MJ/kg) and ethanosolv (−1.6 MJ/kg) processes. This was due to the physical separation of dissolved sugars and lignin which reduced about 32.4% of the total energy consumption compared to ethanosolv biorefinery indicating the feasibility of the proposed biphasic process.

We investigated the potential application of anaerobically digested residues for generating bioenergy in the presence of alkali bifunctional material, sodium zirconate (Na2ZrO3, NZ) using a thermogravimetric analyzer connected to a mass spectrometer. Isoconversional kinetic models, compensation effect and master-plots method were used on data obtained under multiple heating rates (10, 15 and 20 °C min-1) to calculate the activation energy (Eα) and pre-exponential value (A) and reaction mechanism. The average Eα for blend samples C-DSW (NZ mixed with digested municipal solid waste (DSW)), and C-DSM (NZ mixed with digested swine manure (DSM)) were 172.24 and 171.63 kJ mol-1, which were much lower when compared to plain samples, DSW (202.51 kJ mol-1) and DSM (215.22 kJ mol-1). The total gas yields increased by 19.5 and 17.1% for NZ blended samples C-DSW and C-DSM, respectively. In addition, the hydrogen yields also increased by 79 and 44% for C-DSW and C-DSM, respectively.