Sugar Platform Research Articles

Red algae industrial residues as a sustainable carbon platform for the co-production of poly-3-hydroxybutyrate and gluconic acid by Halomonas boliviensis.

Polyhydroxyalkanoate (PHA) production using halophilic bacteria has been revisited because less severe operational conditions with respect to sterility can be applied, also alleviating production costs. Halomonas boliviensis was selected because it is a moderate halophile able to grow and attain high poly-3-hydroxybutyrate (P3HB) contents under 5–45 g/L NaCl concentrations, conditions that discourage microbial contamination. Industrial residues of the red alga Gelidium corneum after agar extraction were used as sugar platform to reduce costs associated with the carbon source. These residues still comprise a high carbohydrate content (30–40% w/w) of mainly cellulose, and their hydrolysates can be used as substrates for the bioproduction of value-added products. Preliminary assays using glucose were carried out to determine the best conditions for growth and P3HB production by H. boliviensis in bioreactor fed-batch cultivations. Two strategies were addressed, namely nitrogen or phosphorus limitation, to promote polymer accumulation. Similar P3HB cell contents of 50% (gpolymer/gCDW) and yields Y P3HB/glucose of 0.11–0.15 g polymer/g glucose were attained under both conditions. However, higher specific productivities were reached under P-limitation, and thus, this strategy was adopted in the subsequent study. Two organic acids, resulting from glucose metabolism, were identified to be gluconic and 2-oxoglutaric acid. Reducing the oxygen concentration in the cultivation medium to 5% sat was found to minimize organic acid production and enhance the yield of polymer on sugar to 0.20 gP3HB/gglucose. Finally, fed-batch cultivations using G. corneum hydrolysates as the only C-source achieved an overall volumetric productivity of 0.47 g/(L.h), 40% polymer accumulation, and negligible gluconic acid production.

Chemical Recycling of a Textile Blend from Polyester and Viscose, Part I: Process Description, Characterization, and Utilization of the Recycled Cellulose

Material recycling requires solutions that are technically, as well as economically and ecologically, viable. In this work, the technical feasibility to separate textile blends of viscose and polyester using alkaline hydrolysis is demonstrated. Polyester is depolymerized into the monomer terephthalic acid at high yields, while viscose is recovered in a polymeric form. After the alkaline treatment, the intrinsic viscosity of cellulose is decreased by up to 35%, which means it may not be suitable for conventional fiber-to-fiber recycling; however, it might be attractive in other technologies, such as emerging fiber processes, or as raw material for sugar platforms. Further, we present an upscaled industrial process layout, which is used to pinpoint the areas of the proposed process that require further optimization. The NaOH economy is identified as the key to an economically viable process, and several recommendations are given to decrease the consumption of NaOH. To further enhance the ecological end economic feasibility of the process, an increased hydrolysis rate and integration with a pulp mill are suggested.

Coproduction of xylooligosaccharides and monosaccharides from hardwood by a combination of acetic acid pretreatment, mechanical refining and enzymatic hydrolysis

Sequential biorefinery treatments of acetic acid (HAC) pretreatment, Papir Forsknings Institutet (PFI) milling and enzymatic hydrolysis were demonstrated for coproduction of xylooligosaccharides (XOS) and fermentable monosaccharides. Results indicated that 36.2% XOS (50.8% X2-X3) and 17.0% low DP xylans were achieved using a HAC pretreatment with a combined severity factor of 0.78. The HAC pretreatment resulted in a XOS-rich prehydrolyzate with a low molecular weight of 1.28 kDa. The endo-xylanase hydrolysis was conducted on the pretreatment liquor to elevate XOS yield and the content of higher-value X2-X3. Moreover, fermentable glucose production from the pretreated residue increased by 2.3 folds when introducing an additional step of PFI refining prior to enzymatic digestion. Properties of substrate including cellulose accessibility, crystallite size, crystalline index and water retention value were in close relationships with enzymatic digestibility. The implementation of proposed biorefinery process will give more insights into the efficient construction of a wood-derived sugar platform.

Towards sustainable production of bio-based lactic acid via a bio-based technical route: Recent developments and the use of palm kernel cakes in the bioconversion

The continued reliance on non-renewable fossil resources has led to serious environmental issues. In light of these concerns, the transition from non-renewable sources to more sustainable ones have been explored, as exemplified by the production of bio-based lactic acid via lignocellulosic biomass bio-refinery process. Malaysia, the second-largest producer of palm oil in the world, generates abundant, cheap, and underutilized oil palm biomass in the form of palm kernel cakes. Comprised of 50% fermentable hexose sugars, palm kernel cakes have emerged as an interesting feedstock substitute in the production of bio-based fine chemicals, e.g., lactic acid. This paper focuses on current work based on selected literature published in the 21st century on the exploitation of palm kernel cakes as a novel feedstock in bio-refinery processes after addressing the current global demand and potential commodity applications of bio-based lactic acid. It then discusses current research on potential lactic acid-producing microorganisms, with particular attention to bacteria, and different pretreatment methods for carbohydrate recovery from palm kernel cakes. It also highlights the potential of oil palm biomass, especially palm kernel cakes, as a promising commodity that contributes to sugar platforms in value-added products, e.g., biofuel, bioenergy, ethanol, acids, and fine chemicals.

Seaweeds as a sustainable source of bioenergy: Techno-economic and life cycle analyses of its biochemical conversion pathways

This study evaluates the environmental impacts, economic potential, and merits of producing bioenergy from seaweed via biological conversion pathways, including the: 1) sugar pathway; (2) volatile fatty acids pathway; and (3) methane pathway to produce ethanol, ethanol and heavier alcohols, and heat and power, respectively. The maximum seaweed price and minimum product selling price are both calculated as economic indicators. Overall, results demonstrate that the sugar platform is economically superior, as it provides a higher average maximum seaweed price of USD 121.6/t compared with USD 57.7/t and USD 24.2/t for volatile fatty acids platform and methane platform, respectively. The minimum product selling price calculated for a range of biomass purchase prices (USD 50–150/dry t) and plant scales (100,000–700,000 dry t of seaweed) indicated that the sugar platform is capable of selling ethanol at prices lower than its 2019 wholesale price (USD 1.38/gal) at smaller plant scales and higher seaweed price compared with volatile fatty acids platform. Cradle-to-grave life cycle assessments were conducted to identify the key drivers of its environmental profile. Three scenarios for the preparation and transportation of seaweed were considered, namely: (1) grinding + pumping; (2) chopping + wet transportation; and (3) chopping + dry transportation. Seaweed grinding and pumping in the biorefinery was identified to be the most sustainable mode of transportation. In addition, our results demonstrated that biofuels can lead to better environmental profiles compared with generation of bioelectricity, as a larger burden is displaced by substituting fossil fuels in the transportation sector.

Progress in the production of lignocellulolytic enzyme systems using Penicillium species

The efficient production of lignocellulolytic enzyme systems is an important support for large-scale biorefinery of plant biomass. On-site production of lignocellulolytic enzymes could increase the economic benefits of the process by lowering the cost of enzyme usage. Penicillium species are commonly found lignocellulose-degrading fungi in nature, and have been used for industrial production of cellulase preparations due to their abilities to secrete complete and well-balanced lignocellulolytic enzyme systems. Here, we introduce the reported Penicillium species for cellulase production, summarize the characteristics of their enzymes, and describe the strategies of strain engineering for improving the production and performance of lignocellulolytic enzymes. We also review the progress in fermentation process optimization regarding the on-site production of lignocellulolytic enzymes using Penicillium species, and suggest prospect of future work from the perspective of building a "sugar platform" for the biorefinery of lignocellulosic biomass.

Renewable Biomass Utilization: A Way Forward to Establish Sustainable Chemical and Processing Industries

Lignocellulosic biomass feedstocks are promising alternatives to fossil fuels for meeting raw material needs of processing industries and helping transit from a linear to a circular economy and thereby meet the global sustainability criteria. The sugar platform route in the biochemical conversion process is one of the promising and extensively studied methods, which consists of four major conversion steps: pretreatment, hydrolysis, fermentation, and product purification. Each of these conversion steps has multiple challenges. Among them, the challenges associated with the pretreatment are the most significant for the overall process because this is the most expensive step in the sugar platform route and it significantly affects the efficiency of all subsequent steps on the sustainable valorization of each biomass component. However, the development of a universal pretreatment method to cater to all types of feedstock is nearly impossible due to the substantial variations in compositions and structures of biopolymers among these feedstocks. In this review, we have discussed some promising pretreatment methods, their processing and chemicals requirements, and the effect of biomass composition on deconstruction efficiencies. In addition, the global biomass resources availability and process intensification ideas for the lignocellulosic-based chemical industry have been discussed from a circularity and sustainability standpoint.

Reusable alkaline catalyzed organosolv pretreatment and delignification of bagasse for sugar platform biorefinery

An alternative sodium methoxide (CH3ONa) in methanol medium was investigated for the pretreatment of bagasse. The use of CH3ONa as an alkaline promoter resulted in relatively high delignification efficiency and solid glucan recovery. The modified pretreatment process helps improve the enzymatic hydrolysis for sugar production. The effect of the reaction condition was evaluated by response surface methodology (RSM) to determine the maximized glucose yield. The optimal condition was performed at 150 °C for 63.9 min in the presence of CH3ONa promoter of 5.1% w/v, leading to the delignification of 86.5% and the maximized glucose yield of 83.9%. The reusability suggests that the recovery of the solvent mixture without the purification process showed efficiency in consecutive batch processing with five cycles. Structural characteristic analysis (i.e., SEM and XRD) of pretreated bagasse demonstrated significant removal of lignin fraction, resulting in increased cellulose digestibility in enzymatic hydrolysis for sugar platform biorefinery.

Acidogenic mixed consortium isolated from soil of agricultural field: acid production behaviour and growth kinetics under the influence of pretreatment hydrolysate of rice straw (RS)

ABSTRACT The present study was conducted to assess the possibilities of biofuel production through volatile fatty acid (VFA) platform using mixed consortia isolated from a natural source (soil of rice cultivation field). The acid production potential of the isolated acidogenic mixed consortium UACJUChE1, using pretreatment hydrolysate of rice straw as the carbohydrate source, was assessed. Growth kinetic parameters i.e. maximum specific growth rate (μ max) and substrate saturation constant (KS ) of UACJUChE1 have been determined separately for both glucose and hydrolysate in the Reinforced Clostridial Medium (RCM). A summative type growth model has been observed to be valid when the combination of glucose and RS-hydrolysate (RSH) is used as the carbon sources. The summative model has been validated by successful comparison of model predictions with the experimental data. The presence of VFAs in the culture broth of the consortium grown on glucose, RS-hydrolysate and their combination (Glc:RSH: 2:3; 1:4 (w/w)) has been established. The survival and growth of solventogenic Clostridium acetobutylicum in a growth medium amended with the effluent of these batch cultures of UACJUChE1 have been ascertained. This indicates a strong potential of UACJUChE1 in the hybridisation of the VFA platform and conventional sugar platform for the generation of butanol from RS.

Understanding the role of the substrate and the metal triflate acidic catalyst in sugar platform biorefineries: A comprehensive systematic approach to catalytic transformations of (poly)carbohydrates in ethanol

We systematically explore a range of model conversions of mono- and disaccharides, and of linear and branched polysaccharides under the catalytic action of metal trifluoromethanesulfonates (metal triflates) in ethanol. This highlights the preferred reactivity of specific (poly)carbohydrates, and the interplay between selectivities of the reactions and the dominating catalyst activity (Brønsted or Lewis). It unambiguously delineates that selectivities of acid-catalysed transformations of (poly)carbohydrates into value added platform chemicals rely on the origin of the substrate, any (pre)treatment, the acidic catalyst, and the reaction conditions. The optimised catalytic systems enable very efficient conversion of cellulosic carbohydrates into significantly value added ethyl glucosides (yields up to 63%), ethyl xylosides (yields up to 69%), ethyl levulinate (yields up to 75%), ethyl lactate (yields up to 98%), ethoxyacetaldehyde diethylacetal (yields up to 33%), and furfural diethylacetal (yields up to 44%), depending on the substrate and reaction conditions.

Valorization of Bamboo Biomass by Selective Liquefaction Reaction for the Production of Sugar and Phenolic Platform Chemicals

Liquefaction is a thermochemical conversion used to derive value-added chemicals from lignocellulosic biomass. The objective of this study was to understand the changes in the chemical and anatomic...

Production of cellulose nanocrystals integrated into a biochemical sugar platform process via enzymatic hydrolysis at high solid loading

This work evaluated the viability of integrating the isolation of cellulose nanocrystals (CNCs) via enzymatic hydrolysis at a high solid loading into the biochemical platform process for the production of sugars from sugarcane bagasse (SCB). SCB was first processed at a biochemical conversion pilot plant and bleached to yield a cellulose-rich pulp, which was enzymatically hydrolyzed at high solid and low enzyme loadings. The resulting hydrolysate had high sugar concentration (>120 g/L glucose) and the CNCs (20 nm in diameter) isolated directly from the hydrolysis residue showed superior properties (higher thermal stability, higher crystallinity index, and higher particle diameter uniformity) than the CNCs prepared from commercial bleached eucalyptus Kraft pulp. These findings demonstrate the technical viability of the proposed integrated process that combined with the high CNCs yield (approximately50%) and the no need for the costly ultrasonic dispersion treatment step to obtain nanoparticles can further contribute for improving the economic and environmental viability of the proposed enzyme-mediated isolation process.

Sustainable approach of high-pressure agave bagasse pretreatment for ethanol production

Agave bagasse is one of the most abundant lignocellulosic residues readily available for valorization. The agave bagasse was pretreated by applying high-pressure CO2–H2O mixture at temperatures ranging from 150 to 190 °C for a residence time varying from 10 to 50 min. Subsequently, solid phase obtained from pretreatment was subject to enzymatic hydrolysis at high solid loadings. Under optimal conditions, the process integrating pretreatment followed by enzymatic hydrolysis yielded 75.8 mol% of the polysaccharides present in the biomass converted into oligo- or monosaccharides, providing 110.5 g/L of reducing sugars. The monosaccharides present in the obtained hydrolysate were successfully fermented into ethanol, demonstrating the feasibility of performing its biological conversion to commercial biofuels or biochemicals. Thereby, the present study has demonstrated the proof of concept of use of more sustainable high-pressure CO2–H2O pretreatment in the context of lignocellulosic residual biomass valorization based on the biochemical sugar platform.

Concentrated sulfuric acid hydrolysis of softwood with t-butyl alcohol

To date, concentrated sulfuric acid hydrolysis is the most effective process to recover the maximum yield of monomeric sugars from woody biomass because concentrated sulfuric acid can completely swell and hydrolyze cellulose. During this process, sulfuric acid lignin is quantitatively produced as a by-product, which is difficult to use because of self-condensation between the lignin molecules under acidic conditions. In this study, to achieve a high yield of both sugars and lignin, we aimed to valorize the lignin with a unique additive, t-butyl alcohol, in the concentrated sulfuric acid hydrolysis of softwood. When t-butyl alcohol was added, sugar yields were unchanged and were nearly equal to the amount of compositional sugars. Thermoplastic lignin with good solubility in acetone was successfully recovered in a yield higher than 40%. The economic efficiency of the concentrated acid hydrolysis was significantly improved by upgrading the lignin. Thus, this unique process could be a new candidate in the realization of sugar platform biorefineries.

Anaerobic bioprocessing of wastewater-derived duckweed: Maximizing product yields in a biorefinery value cascade

This study integrated the sugar and carboxylate platforms to enhance duckweed processing in biorefineries. Two or three bioprocesses (ethanol fermentation, acidogenic digestion, and methanogenic digestion) were sequentially integrated to maximize the carbon-to-carbon conversion of wastewater-derived duckweed into bioproducts, through a series of laboratory-scale experiments. Reactors were fed either raw (dried), liquid-hot-water-pretreated, or enzymatically-saccharified duckweed. Subsequently, the target bioproduct was separated from the reactor liquor and the residues further processed. The total bioproduct carbon yield of 0.69 ± 0.07 g per gram of duckweed-C was obtained by sequential acidogenic and methanogenic digestion. Three sequential bioprocesses revealed nearly as high yields (0.66 ± 0.08 g of bioproduct-C per duckweed-C), but caused more gaseous carbon (dioxide) loss. For this three-stage value cascade, yields of each process in conventional units were: 0.186 ± 0.001 g ethanol/g duckweed; 611 ± 64 mg volatile fatty acids as acetic acid/g VS; and 434 ± 0.2 ml methane/g VS.

Assessing the potential of facile biofuel production from corn stover using attrition mill treatment

Lignocellulosic biomass can be used for producing biochemicals and biofuels through a sugar platform. However, the required pretreatment processes and hydrolysate conditioning typically involve high operational and installation costs. This study investigated the possibility of facile biofuel production using an attrition mill. After milling for one hour, 73.5% (w/w) of corn stover particles had diameters of less than 100 µm, with a mean diameter of 61.3 ± 3.3 µm. Attrition milling of corn stover produced only 0.39 ± 0.01 g L−1 soluble phenolic compounds. The enzymatic conversion of corn stover particles less than 100 µm was 79.8% after 72 h enzymatic hydrolysis. The hydrolysate (i.e., natural sugar) was not inhibitory towards the growth of Saccharomyces cerevisiae. The attrition mill did not require high temperature or pressure conditions and did not inhibit cell growth. Therefore, when the attrition mill is used for pretreatment, a simple biofuel process that does not require washing, detoxification, and solvent recovery could be feasible.

Analysis of the Coffee Cut Stems as Raw Material for the Production of Sugars for Acetone–Butanol–Ethanol (ABE) Fermentation: Techno-Economic Analysis

Lignocellulosic biomass is generally considered as a promising feedstock for the production of value added compounds, due to its availability, low cost and potential sustainable use. Coffee cut-stems (CCS) are a cut of 15–20 cm of length above the land where the coffee plant is cultivated and it is obtained at high quantities after crop renewal. Its high cellulose content makes it a potential sugar platform for different products. The objective of this work is to determine the potential of CCS as a raw material for acetone–butanol–ethanol (ABE) fermentation in technical, economic and environmental terms. The overall ABE fermentation was simulated using the commercial software Aspen Plus to obtain the mass and energy balances. Simulation included the composition of lignocellulosic residue, which was determined experimentally. The whole slurry obtained in the acid pretreatment was sent to enzymatic saccharification. Then the liquid fraction (rich in pentoses and hexoses) was used for fermentation step as carbon source. The process was proposed in this way to determine the influence of inhibitors in ABE fermentation yield through the comparison with other works that include detoxification step. The yield for the process was 140 kg ABE per ton of CCS. The operating costs were calculated using the software Aspen Economic Analyzer. The influence of the cost of the raw materials on the Net Present Value (NPV), the production cost of ABE solvents and the distribution cost by process stages were determined. Additionally, a scale analysis was performed to determine its influence on the NPV. The simulation demonstrated a Minimum Processing Scale for Economic Feasibility (MPSEF) of 64.6 ton/h of CCS. Finally, an environmental assessment using the Waste Reduction Algorithm (WAR) software was proposed to determine environmental impact.

Converting a residue from an edible source (Ceratonia siliqua L.) into a bio-oil

The direct liquefaction of the wastes from carob pod processing industry leaded to a biooil with 88% of conversion, further water extraction afforded two extracts that can be used, e.g., as alternatives to the synthetic antioxidants. The hydroxyl number, as well as acid value, were screened for the reaction crude and both extracts. The organic extract, despite its high concentration of phenolic compounds (19.3 g GA eq/mg extrc), proved to be less antioxidant (1.05 μL/mL) than the aqueous congener (total phenolic content, 0.92 GA eq/mg extrc; antioxidant activity, 1.19 μL/mL). Nevertheless, both extracts have proved to be more active than BHT. The composition of the aqueous extract regarding its sugar's content was also studied, revealing the presence of glucose, fructose, and sucrose. The higher heating value, estimated by Dulong’s formula, along with the analysis of van Krevelen diagram indicate that the organic extract can be potentially used as a fuel, an additive or as components in fuel blends. Briefly, this work proves that carob waste can be valued as an antioxidant additive, as fuels or even as a sugar platform.

Carbohydrate‐Scaffolded Thymine Multimers: Scope and Limitations of the Allylation–Hydroboration Sequence

Carbohydrates serve as versatile molecular scaffolds and platforms in organic chemistry, for example in combinatorial chemistry or for the multivalent presentation of ligands. Carbohydrate scaffolds are frequently employed in the synthesis of multivalent glycoconjugates and utilized for the study of fundamental parameters of carbohydrate recognition. However, facile procedures are required to achieve a useful variety of sugar platforms. Here, we report on the synthesis of a series of divalent und tetravalent hydroxypropylated mannosides, using an allylation‐hydroboration sequence. The hydroxypropyl‐linkers were further functionalized with thymine in a Mitsunobu reaction to achieve multivalent glycothymine scaffolds for intramolecular [2+2] photocyclization. This will be of importance to further investigate the influence of the 3D orientation in carbohydrate recognition. We discuss the scope of the allylation‐hydroboration sequence comparing 2,3‐, 2,6‐, and 4,6‐difunctionalization and 2,3,4,6‐tetrafunctionalization of protected 2‐aminoethyl α‐d‐mannopyranosides.

Pyridinium based ionic liquid: A pretreatment solvent and reaction medium for catalytic conversion of cellulose to total reducing sugars (TRS)

In the last decade, the transformation of lignocellulosic biomass into biofuel through a sugar platform has been an active research subject due to depletion of fossil fuel sources. Total reducing sugars (TRS) obtained from lignocellulosic materials are considered intermediates for the preparation of various valuable chemical compounds. In this work, pyridinium based ionic liquids were synthesized and utilized for the dissolution of cellulose and further conversion to TRS in the presence of metal salts as catalysts. The prepared ILs were characterized using 1H NMR and evaluated for the dissolution of cellulose and found that [C4C1Py][Cl] is the best solvent to dissolve it up to 28% at 110 °C. Optical microscopy in conjunction with FTIR, SEM, XRD and TGA analyses were employed to monitor dissolution phenomenon and ascertain structural changes in regenerated cellulose. SEM results showed disrupted flaky construction for regenerated cellulose. The thermal stability decreased for regenerated cellulose as observed by TGA analysis. This desirable change in cellulose after IL pretreatment was utilized to facilitate metal salts based on the catalytic conversion of cellulose to TRS. Among metal salts, CoCl2 was identified as the best one to generate the highest yield of TRS i.e. 78% at 110 °C for 4 h. Various reaction conditions like time, temperature, and catalyst loading were optimized for catalytic conversion. The optimum conditions were observed at 4 h treatment time, 120 °C and 12% catalyst loading.