Biofuel Production Process Research Articles

Preface to Special Column on Progress in Catalysis in China during 1982–2012

A current aim of society is to produce fuels from non-food biomass and catalysis is central to achieving this aim. Catalytic steam-reforming of biomass gives synthesis gas and this can be further transformed to give transport fuels using catalysis. Biofuels and fuel additives can also be obtained by catalytic upgrading of bio-oil produced by non-catalytic pyrolysis of biomass. This upgrading can be performed by low temperature esterification with alcohols (followed by water separation) or by high temperature gasification, cracking or hydrotreating processes. Upgraded bio-oil can also be obtained by pyrolysis of biomass in the presence of catalysts. This review considers recent trends in the chemistry of these processes for biofuel production and the catalysts used.

Genetic Improvement of Biofuel Plants: Recent Progress and Patents

Due to depleting reserves of fossil fuels, political uncertainties, increase in demand of energy needs and growing concerns of environmental effects, bioenergy as an alternative source of energy needs had taken centre stage globally. In this report, we review the progress made in lignocellulose, cellulose and fermentation based biofuels in addition to tree borne oil seeds. Algae as a source of feedstock for the biofuel has also been reviewed. Recent efforts in genome sequencing of biofuel crops and molecular breeding approaches have increased our understanding towards crop improvement of major feedstocks. Besides, patenting trends in bioenergy sector were assessed by patent landscape analysis. The results showed an increasing trend in published patents during the last decade which is maximum during 2011. A conceptual framework of "transgenesis in biofuels to industrial application" was developed based on the patent analytics viz., International Patent Classification (IPC) analysis and Theme Maps. A detailed claim analysis based on the conceptual framework assessed the patenting trends that provided an exhaustive dimension of the technology. The study emphasizes the current thrust in bioenergy sector by various public and private institutions to expedite the process of biofuel production.

Use of Multi-parameter Flow Cytometry as Tool to Monitor the Impact of Formic Acid on Saccharomyces carlsbergensis Batch Ethanol Fermentations

The use of lignocellulosic materials as substrate for bioethanol production is considered a cost-effective approach to make the biofuel production process economically sustainable. However, lignocellulosic hydrolysis releases toxic compounds such as weak acids which inhibit microorganism growth and ethanol production. In order to understand the physiological response of Saccharomyces carlsbergensis when fermenting glucose in the presence of formic acid (HF), the yeast growth was monitored by multi-parameter flow cytometry. Cytoplasmic membrane potential decreased as the HF concentration increased and as the yeast culture reached the stationary phase. However, the proportion of cells with permeabilized membrane did not increase with the HF concentration increase. The accumulation of reactive oxygen species was also monitored. Control and fermentations at low HF concentrations (<1 g/L) resulted in a high proportion of highly oxidized cells at the stationary phase. The multi-parameter flow cytometry approach proved to be a useful tool to monitor the physiological stress response of S. carlsbergensis growth and ethanol production in the presence of HF, an inhibitor present in lignocellulosic hydrolysates. The information here obtained at near real time can be used to enhance second-generation bioethanol production process efficiency.

Thermodynamic modelling of fate and removal of alkali species and sour gases from biomass gasification for production of biofuels

The development of advanced synthesis gas cleaning technologies based on chemical conversion and physical separation can improve the efficiency of gasification processes for production of biofuels. This paper outlines thermodynamic equilibrium calculations on the release and removal of alkali species and sour gases during gasification of 24 different types of herbaceous and woody biomass under the conditions of the gasifier in Gussing, Austria. In general, the calculation results are in good agreement with former experimental results. The composition of the gasifier derived as well as the cleaned gas strongly depends on the used feedstock. The alkali concentration can be limited to values below 100 ppbv using aluminosilicates at 850 °C. The H2S concentration cannot be limited to values below 200 ppmv using conventional Ca- or Cu-based sorbents but can be limited to values below 1 ppmv by stabilised BaO at 850 °C. The HCl concentration can be limited to values below 1 ppmv by alkali carbonates at temperatures below 550 °C.

Biological conversion of carbon dioxide to photosynthetic fuels and electrofuels

To achieve sustainable growth of human society, fossil fuels must eventually be replaced with renewable resources. Ultimately, the energy and carbon in fuels and chemicals synthesized must come from the sun and CO2 directly. Biological systems hold the promise to catalyze the synthesis of such fuels or chemicals. This article discusses recent advances in developing biofuel production processes from CO2, which include photosynthetic processes using algae and cyanobacteria and the non-photosynthetic “electrofuel” processes using Ralstonia eutropha and other lithoautotrophic microorganisms. Each of these processes involves strengths and weaknesses. While none of these processes have achieved industrial success, the challenges involved may point the direction for further improvement within the limit of theoretical possibility. Finally, all biological processes produce cell mass rich in protein. Regenerating ammonium by deamination of hydrolyzed proteins may close the loop of the global nitrogen cycle, which is also one of the major challenges in large scale biological processes.

Quantitative Uncertainty Analysis of Life Cycle Assessment for Algal Biofuel Production

As a result of algae's promise as a renewable energy feedstock, numerous studies have used Life Cycle Assessment (LCA) to quantify the environmental performance of algal biofuels, yet there is no consensus of results among them. Our work, motivated by the lack of comprehensive uncertainty analysis in previous studies, uses a Monte Carlo approach to estimate ranges of expected values of LCA metrics by incorporating parameter variability with empirically specified distribution functions. Results show that large uncertainties exist at virtually all steps of the biofuel production process. Although our findings agree with a number of earlier studies on matters such as the need for wet lipid extraction, nutrients recovered from waste streams, and high energy coproducts, the ranges of reported LCA metrics show that uncertainty analysis is crucial for developing technologies, such as algal biofuels. In addition, the ranges of energy return on (energy) invested (EROI) values resulting from our analysis help explain the high variability in EROI values from earlier studies. Reporting results from LCA models as ranges, and not single values, will more reliably inform industry and policy makers on expected energetic and environmental performance of biofuels produced from microalgae.

A Comparison of Energy Conversion Between Pyrolysis and Gasification Process for Bio-Fuel Production from Sugarcane Trash

A Comparison of Energy Conversion Between Pyrolysis and Gasification Process for Bio-Fuel Production from Sugarcane Trash

Characterization of cellulases of fungal endophytes isolated from Espeletia spp.

Endophytes are microorganisms that asymptomatically invade plant tissues. They can stimulate plant growth and/or provide defense against pathogen attacks through the production of secondary metabolites. Most endophyte species are still unknown, and because they may have several applications, the study of their metabolic capabilities is essential. We characterized 100 endophytes isolated from Espeletia spp., a genus unique to the paramo ecosystem, an extreme environment in the Andean mountain range. We evaluated the cellulolytic potential of these endophytes on the saccharification of the oil palm empty fruit bunch (OPEFB). The total cellulolytic activity was measured for each endophyte on filter paper (FPA). In addition, the specific carboxymethyl cellulase (CMCase), exoglucanase, and β-glucosidase activities were determined. We found four fungi positive for cellulases. Of these fungi, Penicillium glabrum had the highest cellulolytic activity after partial purification, with maximal CMCase, exoglucanase and β-glucosidase enzyme activities of 44.5, 48.3, and 0.45 U/ml, respectively. Our data showed that the bioprospection of fungi and the characterization of their enzymes may facilitate the process of biofuel production.

Iron Oxide Filled Magnetic Carbon Nanotube–Enzyme Conjugates for Recycling of Amyloglucosidase: Toward Useful Applications in Biofuel Production Process

Biofuels are fast advancing as a new research area to provide alternative sources of sustainable and clean energy. Recent advances in nanotechnology have sought to improve the efficiency of biofuel production, enhancing energy security. In this study, we have incorporated iron oxide nanoparticles into single-walled carbon nanotubes (SWCNTs) to produce magnetic single-walled carbon nanotubes (mSWCNTs). Our objective is to bridge both nanotechnology and biofuel production by immobilizing the enzyme, Amyloglucosidase (AMG), onto mSWCNTs using physical adsorption and covalent immobilization, with the aim of recycling the immobilized enzyme, toward useful applications in biofuel production processes. We have demonstrated that the enzyme retains a certain percentage of its catalytic efficiency (up to 40%) in starch prototype biomass hydrolysis when used repeatedly (up to ten cycles) after immobilization on mSWCNTs, since the nanotubes can be easily separated from the reaction mixture using a simple magnet. The enzyme loading, activity, and structural changes after immobilization onto mSWCNTs were also studied. In addition, we have demonstrated that the immobilized enzyme retains its activity when stored at 4 °C for at least one month. These results, combined with the unique intrinsic properties of the nanotubes, pave the way for greater efficiency in carbon nanotube-enzyme bioreactors and reduced capital costs in industrial enzyme systems.

Pulp mill wastewater sediment reveals novel methanogenic and cellulolytic populations

Pulp mill wastewater generated from wheat straw is characterized as high alkalinity and very high COD pollution load. A naturally developed microbial community in a pulp mill wastewater storage pool that had been disused were investigated in this study. Owing to natural evaporation and a huge amount of lignocellulose's deposition, the wastewater sediment contains high concentrations of organic matters and sodium ions, but low concentrations of chloride and carbonate. The microbiota inhabiting especially anaerobic community, including methanogenic arhcaea and cellulolytic species, was studied. All archaeal sequences fall into 2 clusters of family Halobacteriaceae and methanogenic archaeon in the phylum Euryarchaeota. In the methanogenic community, phylogenetic analysis of methyl coenzyme M reductase A (mcrA) genes targeted to novel species in genus Methanoculleus or novel genus of order Methanomicrobiales. The predominance of Methanomicrobiales suggests that methanogenesis in this system might be driven by the hydrogenotrophic pathway. As the important primary fermenter for methane production, the cellulolytic community of enzyme GHF48 was found to be dominated by narrower breadth of novel clostridial cellulase genes. Novel anoxic functional members in such extreme sediment provide the possibility of enhancing the efficiency of anoxic treatment of saline and alkaline wastewaters, as well as benefiting to the biomass transformation and biofuel production processes.

A review of the harvesting of micro-algae for biofuel production

Many researchers consider efficient harvesting is the major challenge of commercialising micro-algal biofuel. Although micro-algal biomass can be ‘energy rich’, the growth of algae in dilute suspension at around 0.02–0.05 % dry solids poses considerable challenges in achieving a viable energy balance in micro-algal biofuel process operations. Additional challenges of micro-algae harvesting come from the small size of micro-algal cells, the similarity of density of the algal cells to the growth medium, the negative surface charge on the algae and the algal growth rates which require frequent harvesting compared to terrestrial plants. Algae can be harvested by a number of methods; sedimentation, flocculation, flotation, centrifugation and filtration or a combination of any of these. This paper reviews the various methods of harvesting and dewatering micro-algae for the production of biofuel. There appears to be no one method or combination of harvesting methods suited to all micro-algae and harvesting method will have a considerable influence on the design and operation of both upstream and downstream processes in an overall micro-algal biofuel production process.

Experimental methods for laboratory-scale ensilage of lignocellulosic biomass

Anaerobic fermentation is a potential storage method for lignocellulosic biomass in biofuel production processes. Since biomass is seasonally harvested, stocks are often dried or frozen at laboratory scale prior to fermentation experiments. Such treatments prior to fermentation studies cause irreversible changes in the plant cells, influencing the initial state of biomass and thereby the progression of the fermentation processes itself. This study investigated the effects of drying, refrigeration, and freezing relative to freshly harvested corn stover in lab-scale ensilage studies. Particle sizes, as well as post-ensilage drying temperatures for compositional analysis, were tested to identify the appropriate sample processing methods. After 21 days of ensilage the lowest pH value (3.73 ± 0.03), lowest dry matter loss (4.28 ± 0.26 g. 100 g-1DM), and highest water soluble carbohydrate (WSC) concentrations (7.73 ± 0.26 g. 100 g-1DM) were observed in control biomass (stover ensiled within 12 h of harvest without any treatments). WSC concentration was significantly reduced in samples refrigerated for 7 days prior to ensilage (3.86 ± 0.49 g. 100 g−1 DM). However, biomass frozen prior to ensilage produced statistically similar results to the fresh biomass control, especially in treatments with cell wall degrading enzymes. Grinding to decrease particle size reduced the variance amongst replicates for pH values of individual reactors to a minor extent. Drying biomass prior to extraction of WSCs resulted in degradation of the carbohydrates and a reduced estimate of their concentrations. The methods developed in this study can be used to improve ensilage experiments and thereby help in developing ensilage as a storage method for biofuel production.

Can Numerical Models Estimate Indirect Land-Use Change?

Motivated by the conclusions from various modelling studies, modifications to the bioenergy sector regulations are under way in Europe and in the USA to account for emissions from indirect land-use change (ILUC). Despite their influence on the policy-making, evaluations of the capacity of numerical models to estimate ILUC are sparse. To address this void, this paper reviews recent developments in land-use modelling, with a particular focus on the solutions adopted to estimate ILUC due to biofuel production. As indirect effects of bioenergy result from the interplay of various mechanisms, their modelling is a major challenge for land-use science. In recent years, numerical models have been significantly upgraded to provide a more comprehensive vision of the agricultural system. This has been performed by improving the representation of land supply and the biofuel production process in general equilibrium models (e.g., GTAP, MIRAGE, DART). At the same time, modelling systems coupling partial equilibrium models with CGE (e.g., KLUM@GTAP) or economic modules with spatially explicit models (e.g., MAgPIE, GLOBIOM, LEITAP), and modelling architecture combining land-use and life-cycle assessment models (e.g., FASOM/FAPRI/GREET) have been developed. In spite of these advances, some limitations remain and uncertainties are still numerous.

Long-term operation of biomass-to-liquid systems coupled to gasification and Fischer–Tropsch processes for biofuel production

Long-term operation of the biomass-to-liquid (BTL) process was conducted with a focus on the production of bio-syngas that satisfies the purity standards for the Fischer–Tropsch (FT) process. The integrated BTL system consisted of a bubbling fluidized bed (BFB) gasifier (20kWth), gas cleaning unit, syngas compression unit, acid gas removing unit, and an FT reactor. Since the raw syngas from the gasifier contains different types of contaminants, such as particulates, condensable tars, and acid gases, which can cause various mechanical problems or deactivate the FT catalyst, the syngas was purified by passing through cyclones, a gravitational dust collector, a two-stage wet scrubber (packing-type), and a methanol absorption tower. The integrated system was operated for 500h over several runs, and stable operating conditions for each component were achieved. The cleaned syngas contained no sulfur compounds (under 1ppmV) and satisfied the requirements for the FT process.

Lipid production optimization and optimal control of heterotrophic microalgae fed-batch bioreactor

Interior point optimization and model predictive control along with moving horizon estimator are used to maximize and regulate lipid production in a fed-batch heterotrophic microalgae cultivation of Auxenochlorella protothecoides. Motivation for microalgae bioreactor optimal control arises from the need to increase lipid production rate, which results in economic feasibility of microalgae bio-fuel production process. A complex time-varying microalgae fed-batch growth and lipid production model (De la Hoz Siegler et al., 2011) is used and a large-scale nonlinear programming optimization along with moving horizon estimator and model predictive control are applied to maximize the lipid concentration in the bioreactor. An optimal feeding strategy for lipid production is determined using the state-of-the-art interior point optimizer (IPOPT) solver. Moving horizon estimator (MHE) and model predictive controller (MPC) are used to estimate unmeasurable state (nitrogen concentration) and provide regulation of a highly nonlinear and time-varying microalgae growth process as a realizable real-time control strategy. In addition to the constrained large-scale optimization, naturally present input constraints (lower and upper bound on feed rates) and state constraints (lower bound on all concentration related states and upper bound on glucose concentration) are accounted for in an explicit manner with moving horizon estimator and model predictive controller. The estimator and controller design is based on a set of linearized models in microalgae growth fed-batch process. The paper provides a reliable and computationally efficient optimization, estimation and regulation procedure suitable for the real-time microalgae bioreactor operation. The procedure takes into account present constraints on inputs and states, and measurement noises present in the realistic operation conditions and is computationally efficient, along with the improvement in results with respect to previous methods.

Energy saving processes of biofuel production from fermentation broth

The energy used for distillation in bioethanol production reaches the 40 % of the total energy demand. The pervaporation is an important alternative process to distillation that can be applied as a hybrid process or even as a single process to produce high quality biofuel. It will be shown how the energy demand, MJ/kgEthanol energy, can be saved applying pervaporation process with different separation factors and operating modes. It is stated that relatively high separation factor is needed to lower the energy demand below a simple distillation column.

RNAi suppression of lignin biosynthesis in sugarcane reduces recalcitrance for biofuel production from lignocellulosic biomass

Sugarcane is a prime bioethanol feedstock. Currently, sugarcane ethanol is produced through fermentation of the sucrose, which can easily be extracted from stem internodes. Processes for production of biofuels from the abundant lignocellulosic sugarcane residues will boost the ethanol output from sugarcane per land area. However, unlocking the vast amount of chemical energy stored in plant cell walls remains expensive primarily because of the intrinsic recalcitrance of lignocellulosic biomass. We report here the successful reduction in lignification in sugarcane by RNA interference, despite the complex and highly polyploid genome of this interspecific hybrid. Down-regulation of the sugarcane caffeic acid O-methyltransferase (COMT) gene by 67% to 97% reduced the lignin content by 3.9% to 13.7%, respectively. The syringyl/guaiacyl ratio in the lignin was reduced from 1.47 in the wild type to values ranging between 1.27 and 0.79. The yields of directly fermentable glucose from lignocellulosic biomass increased up to 29% without pretreatment. After dilute acid pretreatment, the fermentable glucose yield increased up to 34%. These observations demonstrate that a moderate reduction in lignin (3.9% to 8.4%) can reduce the recalcitrance of sugarcane biomass without compromising plant performance under controlled environmental conditions.

Thermodynamic analysis of a high-yield biochemical process for biofuel production

This paper presents a thermodynamic analysis of a high-yield biochemical process for biofuel production from lignocelluosic biomass based on a previously proposed process. Unlike the standard biochemical process, which ferments sugar intermediates to ethanol, the process under consideration converts sugars to acetic acid which is esterified and hydrogenated to produce ethanol. This process has a significantly higher yield and produces no carbon dioxide. However, we find that the thermodynamic efficiency of the process is not increased in proportion to the yield gain. An additional survey of various biofuel production processes showed no direct correlation between yield and thermodynamic efficiency. This survey and the detailed thermodynamic analyses lead us to conclude that yield alone is an unreliable performance metric for biofuel technologies.

Epigallocatechin gallate incorporation into lignin enhances the alkaline delignification and enzymatic saccharification of cell walls

BackgroundLignin is an integral component of the plant cell wall matrix but impedes the conversion of biomass into biofuels. The plasticity of lignin biosynthesis should permit the inclusion of new compatible phenolic monomers such as flavonoids into cell wall lignins that are consequently less recalcitrant to biomass processing. In the present study, epigallocatechin gallate (EGCG) was evaluated as a potential lignin bioengineering target for rendering biomass more amenable to processing for biofuel production.ResultsIn vitro peroxidase-catalyzed polymerization experiments revealed that both gallate and pyrogallyl (B-ring) moieties in EGCG underwent radical cross-coupling with monolignols mainly by β–O–4-type cross-coupling, producing benzodioxane units following rearomatization reactions. Biomimetic lignification of maize cell walls with a 3:1 molar ratio of monolignols and EGCG permitted extensive alkaline delignification of cell walls (72 to 92%) that far exceeded that for lignified controls (44 to 62%). Alkali-insoluble residues from EGCG-lignified walls yielded up to 34% more glucose and total sugars following enzymatic saccharification than lignified controls.ConclusionsIt was found that EGCG readily copolymerized with monolignols to become integrally cross-coupled into cell wall lignins, where it greatly enhanced alkaline delignification and subsequent enzymatic saccharification. Improved delignification may be attributed to internal trapping of quinone-methide intermediates to prevent benzyl ether cross-linking of lignin to structural polysaccharides during lignification, and to the cleavage of ester intra-unit linkages within EGCG during pretreatment. Overall, our results suggest that apoplastic deposition of EGCG for incorporation into lignin would be a promising plant genetic engineering target for improving the delignification and saccharification of biomass crops.

Progression of lipid profile and cell structure in a research-scale production pathway for algal biocrude

Abstract Although there has been a large research effort associated with individual parts of various algal biofuel production pathways, few studies have tracked changes in product composition throughout an integrated biofuel production process. This study uses microscopy and chromatography to analyze the progression of lipid profile and cell structure of algal cells throughout a research-scale production pathway for biocrude. For the specific processing methods used in this pathway, it is shown that TAG content decreased, while DAG and FFA content increased during processing. The changes in the lipid content corresponded to cell degradation that was observed by SEM and TEM throughout processing. These results demonstrate the dynamic nature of lipid composition in an algal culture used for biofuel production and emphasize the need to monitor changes in lipid profile, as those changes can directly impact biofuel productivity.