Sustainability is a key principle in natural resource management, and it involves operational efficiency, minimisation of environmental impact and socio-economic considerations; all of which are interdependent. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the green house gas emissions associated with their use. Therefore, there are vigorous research initiatives aimed at developing alternative renewable and potentially carbon neutral solid, liquid and gaseous biofuels as alternative energy resources. However, alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world's forests. Second generation biofuels derived from lignocellulosic agriculture and forest residues and from non-food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. Microalgae are photosynthetic microorganisms with simple growing requirements (light, sugars, CO 2 , N, P, and K) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both biofuels and valuable co-products. This study reviewed the technologies underpinning microalgae-to-biofuels systems, focusing on the biomass production, harvesting, conversion technologies, and the extraction of useful co-products. It also reviewed the synergistic coupling of microalgae propagation with carbon sequestration and wastewater treatment potential for mitigation of environmental impacts associated with energy conversion and utilisation. It was found that, whereas there are outstanding issues related to photosynthetic efficiencies and biomass output, microalgae-derived biofuels could progressively substitute a significant proportion of the fossil fuels required to meet the growing energy demand.

/pdf/biofuels-from-microalgae-a-review-of-technologies-for-1t1wwr5e69.pdf

Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products

The state of the art of hydrolysis-fermentation technologies to produce ethanol from lignocellulosic biomass, as well as developing technologies, is evaluated. Promising conversion concepts for the short-, middle- and long-term are defined. Their technical performance was analysed, and results were used for economic evaluations. The current available technology, which is based on dilute acid hydrolysis, has about 35% efficiency (HHV) from biomass to ethanol. The overall efficiency, with electricity co-produced from the not fermentable lignin, is about 60%. Improvements in pre-treatment and advances in biotechnology, especially through process combinations can bring the ethanol efficiency to 48% and the overall process efficiency to 68%. We estimate current investment costs at 2.1 k€/kW HHV (at 400 MW HHV input, i.e. a nominal 2000 tonne dry/day input). A future technology in a 5 times larger plant (2 GW HHV ) could have investments of 900 k€/kW HHV . A combined effect of higher hydrolysis-fermentation efficiency, lower specific capital investments, increase of scale and cheaper biomass feedstock costs (from 3 to 2 €/GJ HHV ), could bring the ethanol production costs from 22 €/GJ HHV in the next 5 years, to 13 €/GJ over the 10–15 year time scale, and down to 8.7 €/GJ in 20 or more years.

Ethanol from lignocellulosic biomass: techno-economic performance in short-, middle- and long-term

In pursuit of more sustainable and competitive biorefineries, the effective valorisation of lignin is key. An alluring opportunity is the exploitation of lignin as a resource for chemicals. Three technological biorefinery aspects will determine the realisation of a successful lignin-to-chemicals valorisation chain, namely (i) lignocellulose fractionation, (ii) lignin depolymerisation, and (iii) upgrading towards targeted chemicals. This review provides a summary and perspective of the extensive research that has been devoted to each of these three interconnected biorefinery aspects, ranging from industrially well-established techniques to the latest cutting edge innovations. To navigate the reader through the overwhelming collection of literature on each topic, distinct strategies/topics were delineated and summarised in comprehensive overview figures. Upon closer inspection, conceptual principles arise that rationalise the success of certain methodologies, and more importantly, can guide future research to further expand the portfolio of promising technologies. When targeting chemicals, a key objective during the fractionation and depolymerisation stage is to minimise lignin condensation (i.e. formation of resistive carbon–carbon linkages). During fractionation, this can be achieved by either (i) preserving the (native) lignin structure or (ii) by tolerating depolymerisation of the lignin polymer but preventing condensation through chemical quenching or physical removal of reactive intermediates. The latter strategy is also commonly applied in the lignin depolymerisation stage, while an alternative approach is to augment the relative rate of depolymerisation vs. condensation by enhancing the reactivity of the lignin structure towards depolymerisation. Finally, because depolymerised lignins often consist of a complex mixture of various compounds, upgrading of the raw product mixture through convergent transformations embodies a promising approach to decrease the complexity. This particular upgrading approach is termed funneling, and includes both chemocatalytic and biological strategies.

/pdf/chemicals-from-lignin-an-interplay-of-lignocellulose-1th1dk0l26.pdf

Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

Lignin is an abundant biopolymer with a high carbon content and high aromaticity. Despite its potential as a raw material for the fuel and chemical industries, lignin remains the most poorly utilised of the lignocellulosic biopolymers. Effective valorisation of lignin requires careful fine-tuning of multiple "upstream" (i.e., lignin bioengineering, lignin isolation and "early-stage catalytic conversion of lignin") and "downstream" (i.e., lignin depolymerisation and upgrading) process stages, demanding input and understanding from a broad array of scientific disciplines. This review provides a "beginning-to-end" analysis of the recent advances reported in lignin valorisation. Particular emphasis is placed on the improved understanding of lignin's biosynthesis and structure, differences in structure and chemical bonding between native and technical lignins, emerging catalytic valorisation strategies, and the relationships between lignin structure and catalyst performance.

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis.

Based on the principles and metrics of green chemistry and sustainable development, biocatalysis is both a green and sustainable technology. This is largely a result of the spectacular advances in molecular biology and biotechnology achieved in the past two decades. Protein engineering has enabled the optimization of existing enzymes and the invention of entirely new biocatalytic reactions that were previously unknown in Nature. It is now eminently feasible to develop enzymatic transformations to fit predefined parameters, resulting in processes that are truly sustainable by design. This approach has successfully been applied, for example, in the industrial synthesis of active pharmaceutical ingredients. In addition to the use of protein engineering, other aspects of biocatalysis engineering, such as substrate, medium, and reactor engineering, can be utilized to improve the efficiency and cost-effectiveness and, hence, the sustainability of biocatalytic reactions. Furthermore, immobilization of an enzyme ...

/pdf/role-of-biocatalysis-in-sustainable-chemistry-5b3e0qe0ep.pdf

Role of Biocatalysis in Sustainable Chemistry

Ethanol-based organosolv fractionation of wheat straw for the production of lignin and enzymatically digestible cellulose.

Acetone-based organosolv fractionation of wheat straw was studied to produce sugars and lignin in a lignocellulose biorefinery. The influence of acetone−water ratio, reaction time, and temperature on fractionation degree, lignin yield, and enzymatic digestibility of the cellulose fraction was examined. The solvent−water ratio was found to influence delignification and hemicellulose hydrolysis by its effect on lignin solubility and pH. Organosolv treatment in 50:50% w/w acetone−water during 1 h at 205 °C resulted in 82% hemicellulose hydrolysis, 79% delignification, and 93% cellulose recovery. A substantial part of the sugars formed upon hemicellulose hydrolysis seems to have reacted further including possible formation of lignin−furfural condensation products. Finally, aqueous acetone pretreatment was found to substantially improve the enzymatic digestibility of the cellulose fraction (glucose yield: up to 87% vs 16% for untreated wheat straw).

/pdf/pretreatment-and-fractionation-of-wheat-straw-by-an-acetone-jsks1u44hv.pdf

Pretreatment and Fractionation of Wheat Straw by an Acetone-Based Organosolv Process

BACKGROUND: Ethanol-based organosolv fractionation of lignocellulosic biomass is an effective pretreatment technology for enzymatic cellulose hydrolysis to produce sugars and lignin within a biorefinery. This study focuses on the catalytic effect of H2SO4, HCl, and MgCl2 on organosolv pretreatment of willow wood and wheat straw.



RESULTS: The use of catalysts improved fractionation of both feedstocks. The maximum enzymatic cellulose digestibility obtained was 87% for willow wood (using 0.01 mol L−1 H2SO4 as catalyst) and 99% for wheat straw (0.02 mol L−1 HCl). Non-catalytic organosolv fractionation at identical conditions resulted in 74% (willow wood) and 44% (wheat straw) glucose yield by enzymatic hydrolysis. Application of catalysts in organosolv pretreatment was particularly effective for wheat straw. The influence of the acid catalysts was found to be primarily due to their effect on the pH of the organosolv liquor. Acid catalysts particularly promoted xylan hydrolysis. MgCl2 was less effective than the acid catalysts, but it seemed to more selectively improve delignification of willow wood.



CONCLUSION: Application of catalysts in organosolv pretreatment of willow wood and wheat straw was found to substantially improve fractionation and enzymatic digestibility. The use of catalysts can contribute to achieving maximum utilization of lignocellulosic biomass in organosolv-based biorefineries. Copyright © 2011 Society of Chemical Industry

/pdf/catalytic-organosolv-fractionation-of-willow-wood-and-wheat-1a5095s9ur.pdf

Catalytic organosolv fractionation of willow wood and wheat straw as pretreatment for enzymatic cellulose hydrolysis

https://pure.rug.nl/ws/files/6733243/2009JAnalApplPyrolysisDeWild.pdf

Biomass valorisation by staged degasification: A new pyrolysis-based thermochemical conversion option to produce value-added chemicals from lignocellulosic biomass

Volumetric productivity of Monodus subterraneus cultivated in an outdoor pilot-plant bubble column was predicted with a mathematical model. Two border cases to model the photobioreactor were chosen. Firstly, a model with no light integration in which it is assumed that microalgae can adapt immediately to local light conditions. Secondly, full light integration implicating that microalga can convert all absorbed light with a photosynthetic yield based on average light intensity. Because temperature and light conditions in our photobioreactor changed during the day, photosynthetic yields at any combination of temperature and light intensity were needed. These were determined in repeated-batch lab-scale experiments with an experimental design. The model was evaluated in an outdoor bubble column at different natural light conditions and different temperatures. Volumetric productivities in the bubble column were predicted and compared with experimental volumetric productivities. The light integration model over-estimated productivity, while the model in which we assumed no light integration under-estimated productivity. Light integration occurred partly (47%) during the period investigated. The average observed biomass yield on light was 0.60 g·mol-1. The model of partly light integration predicted an average biomass yield on light of 0.57 g·mol-1 and predicted that productivity could have been increased by 19% if culture temperature would have been maintained at 24°C.

J.H. Reith

Papers

Ethanol-based organosolv fractionation of wheat straw for the production of lignin and enzymatically digestible cellulose.

Pretreatment and Fractionation of Wheat Straw by an Acetone-Based Organosolv Process

Catalytic organosolv fractionation of willow wood and wheat straw as pretreatment for enzymatic cellulose hydrolysis

Biomass valorisation by staged degasification: A new pyrolysis-based thermochemical conversion option to produce value-added chemicals from lignocellulosic biomass

Prediction of volumetric productivity of an outdoor photobioreactor