Search

Following the COP21 conference in Paris, most of the world’s industrialized countries, as well as emerging markets, pledged to reduce or stabilize their greenhouse gas (GHG) emissions in light of increasing concerns regarding climate change [1]. The necessity to decrease GHG emissions will have implications on the consumption patterns of different types of energies around the world. Apart from the obvious need to replace part of the increasing fossil fuel consumption in transportation (including road, rail, air and sea), there is a growing demand in other sectors as well, such as for electricity production, heating and cooling. Many opportunities are being investigated to address some of the issues related to this green energy transition, including the increased harnessing of alternative energy sources such as wind, solar, hydro, geothermal and biomass. Despite varying potential for each of the mentioned energy sources to help replace or supplement fossil fuels, only biomass currently has the potential to address most of these needs without requiring significant changes to existing energy distribution networks. For example, biomass can be burnt to generate combined heat and power, but it can also be used as a source of carbon to produce biofuels. In the latter case, biofuels such as ethanol could be blended into the existing fuel pool as well as distributed and utilized in engines without requiring significant modifications to the existing chain of distribution. This adaptiveness is not necessarily the case when considering electric vehicles (EV), although they are also of crucial importance towards collectively reducing GHG emissions. This manuscript will review the Biorefinery Done Right-concept, developed by the company RéSolve Énergie in close collaboration with the Biomass Technology Laboratory. This simple feedstock-agnostic technology allows conversion of any type of residual biomass (including but not limited to softwood bark) to three-types of biofuels. The first objective is to take advantage of the carbohydrate content in the biomass through hydrolysis of the constitutive hemicellulose and cellulose. The fermentable sugars are then converted to ethanol, achieved without any constraints, since the RéSolve process generates a hydrolysate with very low inhibitor levels. The lignin recovered from the process is essentially unmodified lignin and after washing, it is pelletized. Pellets, containing the most energetic components of the lignocellulosic biomass, can provide up to 26 GJ/tonne. Finally, the non-fermentable sugars (C5), as well as the lignin that does not comply with Grade A lignin characteristics, are predigested for utilization in a classical biomethanation system. Hence, through this approach, 100% of the carbon from the biomass is converted into commercial products, which at this point are all related to the energy market. The authors would like to acknowledge the participation of RéSolve Énergie to this project as well as the CRIBIQ, MITACS and NSERC who contributed in funding this work.

Full feedstock potential needs to be tapped to make lignocellulosic ethanol an economically viable reality. This work focuses on the Saccharomyces cerevisiae ethanol fermentation of fresh sorghum carbohydrates extracted through a mild steam-treatment process, and the subsequent Chlorella vulgaris cultivation using the generated liquid and gaseous fermentation effluents. The first section of the manuscript focuses on the effect of nutrient addition (fermentation effluent, yeast extract and urea) on the conversion efficiency of the sorghum carbohydrates to ethanol. Overall, the fermentation time was reduced to half when yeast extract and urea were supplemented to the free and hemicellulosic carbohydrate stream, accelerating the total sugar consumption time from 24 h to under 12 h. However, regarding the cellulosic carbohydrate hydrolysate, the sole addition of urea resulted in a slight improvement of the fermentation kinetics. The second half of the manuscript presents the impact of these different fermentation effluents and various process parameters (addition of yeast extract, antibiotic and CO2) on the microalgal cultivation and composition. The cellulosic hydrolysate yielded the highest concentrations of microalgal carbohydrates (507 mg/L) under a CO2-rich environment. Further cultivation scale-up assays confirmed these observations in the presence of 10% CO2 using the mixed fermentation effluents of the free and constitutive sorghum carbohydrates. Thus, an integrated sorghum-based first- (free carbohydrates), second- (constitutive carbohydrates) and third-generation (microalgal carbohydrates) ethanol production process was thoroughly investigated. This work could represent a step towards bridging the gap leading to full-scale commercialization of these advanced-biofuel technologies.

Both free carbohydrates and hemicelluloses from green sweet sorghum [Sorghum bicolor (L.) Moench] were extracted using a steam process to produce combined first and second generation ethanol. Once the carbohydrates removed, Soxhlet extraction was used to extract the lipophilic secondary metabolites from the plant fibers and the results were compared to those obtained with the biomass extracted without prior steam treatments. This allowed assessing if the carbohydrate removal process had an impact on the secondary metabolites that could be recovered from the biomass. Soxhlet extracts where characterized using several techniques such as gas chromatography-mass spectrometry, liquid chromatography-triple quadrupole mass spectrometry and liquid chromatography-UV detection followed by high-resolution mass spectrometry. A total of 13 compounds were detected and quantified in the non-polar soxhlet fraction and were mainly fatty acids (6), phenyl glycosides (5) and sterols (2) at concentrations ranging between 0.015 g kg−1 and 1.5 g kg−1 (dry biomass). Comparison of the extractive content before and after steam process showed that most of the compounds were found in a lesser extent (up to 71%) although still recoverable after the steam process while other compounds (namely phytosterols) were as concentrated as they were prior to steam treatments. These results show that in the case of sweet sorghum, the preliminary extraction of the carbohydrate content with a steam process may not completely hinder the possibility to extract high value secondary metabolites, which would in this case come second in a biorefinery approach.

Recent years marked an increased focus towards the valorization of biorefinery side-streams for the production of various high added-value molecules and platform chemicals. The present study tackles the opportunity of using liquid ethanol fermentation effluents of bark hydrolysates for microalgal conversion to various marketable molecules. Initially, 12 green microalgae strains were screened for their ability to thrive on these substrates and uptake some of the available organic compounds. Once the most suitable strains were identified, three mixed microalgal consortia were formulated and investigated in order to maximize, either individually or both simultaneously, their biomass production and phytoremediation performances. For instance, the consortium α containing Scenedesmus obliquus, Acutodesmus obliquus, Chlorella sorokiniana and Chlorella vulgaris strains was able to consume up to 70% of C5 sugars (xylose and arabinose) and 60% of C6 sugars (fucose and hexose). The uptake of these organic compounds initially present in the fermentation effluent accounted for the removal of 27% of the total organic carbon. In addition, the microalgal community produced 55 mg/L/d, 41 mg/L/d and 26 mg/L/d of carbohydrates, lipids and proteins respectively. The photosynthetic pigments accumulated in the harvested biomass comprised of 25.8 mg/L of total chlorophyll and 5.9 mg/L of carotenoids. Finally, the pyrolysis characteristics of the algal biomass were evaluated trough thermogravimetric analysis and the elemental composition was compared with conventional lignocellulosic feedstocks. Thus, this work proves the dual opportunity of both reducing the toxicity of lignocellulosic ethanol fermentation effluents as well as generating high-value biomass by employing specifically-designed microalgal populations.

Cellulosic ethanol could play a major role in the upcoming circular-economy once the process complexity, low carbohydrate extraction yields and high costs are resolved. To this purpose, different steam-treatment severity factors were employed on whole sweet sorghum biomass, followed by the delignification and hydrolysis of resulted lignocellulose fibers. A modified ASTM International (American Society for Testing and Material) standard cellulose hydrolysis approach as well as a newly developed SACH (Sulfuric Acid Cellulose Hydrolysis) process were used, recovering up to 24.3 wt% of cellulosic carbohydrates. This amounted to a total extractable and constitutive carbohydrate recovery of 51.7 wt% (dry basis) when a mild steam-treatment of whole sorghum biomass and the SACH cellulose hydrolysis were employed. An ethanol potential of 6378 L/ha/year was determined, comparable to values obtained from biomass such as sugarcane in warmer climates, supporting thus the opportunity of implementing this novel approach on a wider scale.

This work aims at demonstrating the possibility of producing 2-butanol from lignocellulosic biomass through a new thermochemical approach. The production of biobutanol was carried out using different lignocellulosic feedstock through a 3-step process: first the whole lignocellulosic biomass is hydrolyzed under acid catalyst to produce levulinates, then the levulinates go through decarboxylation to produce 2-butanone which is, in a final step, reduced to produce of 2-butanol. The experimental conditions for the first two steps of the process were optimized using the response surface methodology (RSM). The latter could represent an opportunity for the production of economical second-generation butanol without having to go through the classical pathway requiring the production of sugar prior to microbial conversion. The authors are grateful for the financial support to MITACS (Grant number ITO3931) and for the grant to the Natural Sciences and Engineering Research Council of Canada (NSERC, Grant number EGP 487206-15).

Maximizing the extracted carbohydrates from lignocellulosic biomass represents one critical step towards a wide implementation of industrial-scale second-generation ethanol production. To this purpose, a novel steam-based treatment strategy targeting the whole sweet sorghum biomass was developed. This extraction was followed by a non-enzymatic hydrolysis of the hemicellulose fraction and ethanol fermentation. By doing so, both the free carbohydrates present in the plant stems as well as the hemicelluloses trapped inside the various structural components were recovered and converted. A statistical design of experiments (DoE) approach was developed to investigate the most suitable steam-treatment severity to maximize the recovery of these carbohydrates while simultaneously minimizing the production of fermentation inhibitors. The severity of the treatment was estimated from the combined effects of temperature (150 °C – 210 °C) and cooking time (1–7 min). The optimal treatment conditions identified in this work (3 min retention time at 180 °C) successfully allowed recovering 30% of monomeric carbohydrates (based on sorghum dry weight). Three of the most efficient steam-explosion severities were investigated further in order to evaluate their impact on the subsequent ethanol fermentation using Saccharomyces cerevisiae yeast. A maximum ethanol yield of above 95% was achieved using the mixed carbohydrate streams recovered using the optimal steam-based extraction conditions. Thus, the present work thoroughly describes for the first time and to the best of our knowledge, a single-stage recovery of sorghum extractives and hemicelluloses, followed by their efficient fermentation to ethanol.

International audience; In this work, the direct production of levulinates from cheap residual lignocellulosic biomass was performed using an affordable homogeneous catalyst. A central composite design (CCD) using the response surface methodology (RSM) was applied to analyze the effects of the four selected factors (acid concentration, temperature, α-cellulose content, and reaction time) on the production of levulinates (levulinic acid derivatives). This optimization led to a total production of levulinates of 78 wt%, 72.5 wt%, 83 wt%, and 73 wt% using α-cellulose, poplar, sorghum, and softwood bark, respectively.

Sweet sorghum was subjected to an impregnation step, which recovered most of the 1st generation sugars, prior to a steam-treatment extraction of the 2nd generation sugars, at three different severity factors (SF). A medium severity (3.56 SF) treatment proved to be an optimal compromise between the amount of sugars extracted and the fermentation inhibitors generated following the subsequent depolymerization approaches applied on the broth. Next, a series of detoxification approaches (ozonation, overliming and a combination of both) were investigated following a concentration and depolymerization step. Results show that higher steam-treatment severity required more intense detoxification steps. However, when combining the 1st and 2nd generation streams at a 2:1 ratio, the inhibitors did not affect the fermentation process and ethanol yields above 90% of the theoretical maximum were achieved.

The purpose of this work is to determine the best conditions allowing the optimal recovery of the first and second generation sugars found in sweet sorghum. This optimization was performed using the severity factor, combined with response surface methodology (RSM) and based on a two-variable central composite design. Dry sorghum was first impregnated with water and then submitted to steam processes. Sugars were recovered in solution, both after the impregnation step and after the steam treatments. A central composite design and response surface methodology was applied to analyze the effects of the reaction time (2–8 min) and the temperature (200–220 °C) on the mass loss and sugar yields. Mass loss and different sugar yields were also correlated to the severity factor and compared to the RSM analysis. Similarly, the response surfaces and the isoresponse curves from the experimental design allowed understanding the mass loss as well as understanding several sugar yields according to the temperature and reaction time. The best operating conditions (i.e. for a severity factor of 3.6 or 2 min at 215 °C) allowed recovery of 37.3 wt% total sugars based on dry sorghum.

International audience; The purpose of this work was to determine the main factors influencing the phenolic content of bark during acid hydrolysis. The optimization of polysaccharides hydrolysis was done by response surface methodology. The hydrolysis was performed under atmospheric pressure in an aqueous solution of sulfuric acid. An experimental design was applied to analyze the effects of the reaction time (5 to 24 hours), acid concentration (3 to 20%), and solid/liquid ratio (1/10 to 1/5) on the weight loss, lignin content, holocellulose content, and sugar yield for the hydrolysis. The pretreated bark had a high lignin content of 60% resulting from hemicelluloses hydrolysis and phenolic compound condensation.