Industrial sugar beets to biofuel: Field to fuel production system and cost estimates

Specialized varieties of sugar beets (Beta vulgaris L.) may be an eligible feedstock for advanced biofuel designation under the USA Energy Independence and Security Act of 2007. These non-food industrial beets could double ethanol production per hectare compared to alternative feedstocks. A mixed-integer mathematical programming model was constructed to determine the breakeven price of ethanol produced from industrial beets, and to determine the optimal size and biorefinery location. The model, based on limited field data, evaluates Southern Plains beet production in a 3-year crop rotation, and beet harvest, transportation, and processing. The optimal strategy depends critically on several assumptions including a just-in-time harvest and delivery system that remains to be tested in field trials. Based on a wet beet to ethanol conversion rate of 110 dm³ Mg⁻¹ and capital cost of 128 M$ for a 152 dam³ y⁻¹ biorefinery, the estimated breakeven ethanol price was 507 $ m⁻³. The average breakeven production cost of corn (Zea mays L.) grain ethanol ranged from 430 to 552 $ m⁻³ based on average net corn feedstock cost of 254 and 396 $ m⁻³ in 2014 and 2013, respectively. The estimated net beet ethanol delivered cost of 207 $ m⁻³ was lower than the average net corn feedstock cost of 254–396$ m⁻³ in 2013 and 2014. If for a mature industry, the cost to process beets was equal to the cost to process corn, the beet breakeven ethanol price would be $387 m^-3 (587 $ m⁻³ gasoline equivalent).     

Valorization of Eucalyptus wood by glycerol-organosolv pretreatment within the biorefinery concept: An integrated and intensified approach

The efficient utilization of lignocellulosic biomass and the reduction of production cost are mandatory to attain a cost-effective lignocellulose-to-ethanol process. The selection of suitable pretreatment that allows an effective fractionation of biomass and the use of pretreated material at high-solid loadings on saccharification and fermentation (SSF) processes are considered promising strategies for that purpose. Eucalyptus globulus wood was fractionated by organosolv process at 200 °C for 69 min using 56% of glycerol-water. A 99% of cellulose remained in pretreated biomass and 65% of lignin was solubilized. Precipitated lignin was characterized for chemical composition and thermal behavior, showing similar features to commercial lignin. In order to produce lignocellulosic ethanol at high-gravity, a full factory design was carried to assess the liquid to solid ratio (3–9 g/g) and enzyme to solid ratio (8–16 FPU/g) on SSF of delignified Eucalyptus. High ethanol concentration (94 g/L) corresponding to 77% of conversion at 16FPU/g and LSR = 3 g/g using an industrial and thermotolerant Saccharomyces cerevisiae strain was successfully produced from pretreated biomass. Process integration of a suitable pretreatment, which allows for whole biomass valorization, with intensified saccharification-fermentation stages was shown to be feasible strategy for the co-production of high ethanol titers, oligosaccharides and lignin paving the way for cost-effective Eucalyptus biorefinery.     

Feedstock loss from drought is a major economic risk for biofuel producers

High cost of technology is seen as the primary barrier to full commercialization of cellulosic biofuels. There is broad expectation that once conversion technology breakthroughs occur, policy support is only needed to accelerate cost reductions through “learning by doing” effects. In this study, we show that droughts pose a significant economic risk to biofuel producers and consumers regardless of the rate at which technology costs fall. We model a future switchgrass derived cellulosic biorefinery industry in Kansas based on spatially resolute historic (1996–2005) weather data, representing a rainfall regime that could reflect drought events predicted to occur throughout the U.S. Midwest by climatologists (Karl et al. (2009) U.S. Global Change Research Program USA). We find that droughts reduced modeled biorefinery capacity factors, on average, by 47%, raising biofuel production costs by 35% between a modeled dry and wet year. Interestingly, we find that two logical strategies to plan for drought; (1) building large biorefineries to source feedstock from a larger area and, (2) Storing switchgrass in good production years for use in drought years; are not very effective in reducing drought risks. Our findings should be of particular concern to low carbon fuel policies like California's Low Carbon Fuel Standard and the U.S. Second Renewable Fuel Standards (RFS2) whose costs of compliance may be much higher than expected.     

Dissolving grade eco-clean cellulose pulps by integrated fractionation of cardoon (Cynara cardunculus L.) stalk biomass

A biorefinery scheme with separate processing of the two main carbohydrate streams (cellulose and hemicellulose-derived) was employed to the energy crop cardoon (Cynara cardunculus L.) to fractionate the whole stalk material. A high quality xylose-enriched substrate was obtained after selective one-step dilute sulfuric acid hydrolysis of hemicelluloses, yielding 18.1 g of xylose per 100 g of dry biomass. The xylan-free solid residue was delignified by sulfur-free organosolv pulping to produce dissolving grade pulps having 93.8% of α-cellulose (33.1 g per 100 g dry initial biomass) and 79.5% degree of crystallinity. About 76% of crop lignin (13.8 g per 100 g dry initial biomass) was recovered from the spent pulping liquor as a high purity reactive precipitated organosolv lignin. Response surface methodology was used for statistical modeling and optimization of the applied separation processes. The central composite rotatable design was applied to assess the effects of the principal technological parameters on the main reaction outputs.     

Methanol as an alternative electron donor in chain elongation for butyrate and caproate formation

Chain elongation is an emerging mixed culture biotechnology converting acetate into valuable biochemicals by using ethanol as an external electron donor. In this study we proposed to test another potential electron donor, methanol, in chain elongation. Methanol can be produced through the thermochemical conversion of lignocellulosic biowaste. Use of methanol in chain elongation integrates the lignocellulosic feedstocks and the thermochemical platform technologies into chain elongation. After such integration, the feedstocks for chain elongation are solely from 2^nd generation biomass resources. A proof-of-principle study of chain elongation using methanol and acetate was performed in both a batch and a continuous experiment. In the batch experiment, butyrate (191 mMC) and caproate (3 mMC) production from methanol and acetate was observed. A mixed culture microbiome taken from a previous chain elongation reactor fed with ethanol was responsible for the observed organic acid production. The continuous experiment was performed in an upflow anaerobic bioreactor (UAB). The hydraulic retention time (HRT) was 36 h and the operational period lasted for 45 days. In the continuous experiment, butyrate production (Rate > 30 mMC/day) was observed; the caproate concentration was below the detection limit during the entire continuous operational period. In both experiments, methanol and acetate were both substrates contributing to the butyrate production. To the authors' current knowledge, this study is the first attempt at a mixed culture fermentation utilising methanol and acetate for biochemical production. Further research should focus on elevating the butyrate production rate and concentration in the continuous operation of methanol chain elongation, which may stimulate caproate formation.     

Harvesting microalgae by CTAB-aided foam flotation increases lipid recovery and improves fatty acid methyl ester characteristics

Foam flotation is an effective and energy efficient method of harvesting microalgae. This study has investigated the influence of growth phase and lipid content on harvesting efficiency. The highest biomass concentration factors were gained during active culture growth. Surprisingly, the quantities of lipid recovered from microalgae harvested by foam flotation using the surfactant cetyl trimethylammonium bromide (CTAB), were significantly higher than from cells harvested by centrifugation. Further, cells harvested by CTAB-aided foam flotation exhibited a lipid profile more suited to biodiesel conversion containing increased levels of saturated and monounsaturated fatty acids. The enhanced lipid recovery was partially explained by the interaction of the cells with the surfactant, CTAB, which adsorbed onto the algae and was carried over into the total lipid extraction process. However, further evidence also suggested that CTAB promoted in situ cell lysis by solubilising the phospholipid bilayer, thus increasing the amount of extractable lipid. This work demonstrates substantial added value of foam flotation as a microalgae harvesting method beyond energy efficient biomass recovery.     

Critical parameters in cost-effective alkaline extraction for high protein yield from leaves

Leaves are potential resources for feed or food, but their applications are limited due to a high proportion of insoluble protein and inefficient processing. To overcome these problems, parameters of alkaline extraction were evaluated using green tea residue (GTR). Protein extraction could be maximized to 95% of total protein, and, after precipitation by pH adjustment to 3.5, 85% of extracted protein was recovered with a purity of 52%. Temperature, NaOH amount, and extraction time are the protein yield determining parameters, while pH and volume of extraction liquid are critical parameters for production cost. The cost of energy and chemicals for producing 1 t GTR proteins is minimized to 102€, and its nutritional value is comparable to soybean protein. Furthermore, this technology was successfully applied to other sources of biomass and has potential to be used as a part of an integrated bio-refinery process.     

Economic value and environmental impact (EVEI) analysis of biorefinery systems

The selection of product portfolios, processing routes and the combination of technologies to obtain a sustainable biorefinery design according to economic and environmental criteria represents a challenge to process engineering. The aim of this research is to generate a robust methodology that assists process engineers to conceptually optimise the environmental and economic performances of biorefinery systems. A novel economic value and environmental impact (EVEI) analysis methodology is presented in this paper. The EVEI analysis is a tool that emerges from the combination of the value analysis method for the evaluation of economic potential with environmental footprinting for impact analysis. The methodology has been effectively demonstrated by providing insights into the performance of a bioethanol plant as a case study. The systematisation of the methodology allowed its implementation and integration into a computer-aided process engineering (CAPE) tool in the spreadsheet environment.     

Integrated processing of plant-derived waste to produce value-added products based on the biorefinery concept

BackgroundPlant-derived wastes from agriculture, processing, distribution, and retail are generated in large quantities. The majority of the wastes are underutilized and may cause severe environmental problems if not properly handled. The plant-derived wastes are usually rich in lignocellulose and other valuable compounds including protein, fat, sugar, and phytochemicals. Valorization of these compounds in food waste not only reduces environmental concerns but also improves sustainability and economic competitiveness of agro-food industries.Scope and approachThis review paper first discussed different phases of the biorefinery concepts and their associated applications, and then introduced recent advances in the integrated processing of plant-derived waste for producing various value-added products. Finally, techno-economic, environmental, and social assessments along with relevant policies were introduced and discussed.Key findings and conclusionsDuring the past ten years, research attentions focused on integrated utilization of plant-derived waste to produce various products have flourished. Compared to production of a single component for food waste valorization, integrated processing of food waste via a combination of different novel technologies to produce multiple products based on a biorefinery concept has significant advantages, including full utilization of feedstocks, minimization of waste generation during processing, synergy effects of different technologies, and diversification of the revenues by covering multiple markets. With the rationale design of biorefinery processes, underutilized plant-based wastes can be valuable resources for the sustainable production of food, chemicals, and biofuels. However, detailed economic, environmental, and social analyses for the biorefinery process are still needed in the future.     

A shortcut method for the preliminary synthesis of process-technology pathways: An optimization approach and application for the conceptual design of integrated biorefineries

Synthesis and screening of technology alternatives is a key process-development activity in the process industries. Recently, this has become particularly important for the conceptual design of biorefineries. This work introduces a shortcut method for the synthesis and screening of integrated biorefineries. A structural representation (referred to as the chemical species/conversion operator) is introduced. It is used to track individual chemicals while allowing for the processing of multiple chemicals in processing technologies. The representation is used to embed potential configurations of interest. An optimization approach is developed to screen and determine optimum network configurations for various technology pathways using simple data. The solution to the optimization formulation provides a quick and effective method for screening and interconnecting the technological pathways and to distributing the flows over the network. Case studies are solved to illustrate the applicability of the proposed approach.