The comparison of obtaining fermentable sugars from cellulose by enzymatic hydrolysis and fast pyrolysis

Simultaneous Fe3O4 Nanoparticle Formation and Catalyst-Driven Hydrothermal Cellulose Degradation

Breakdown and utilization of cellulose are critical for the bioenergy sector; however, current cellulose-to-energy conversion schemes often consume large quantities of unrecoverable chemicals, or are expensive, due to the need for enzymes or high temperatures. In this paper, we demonstrate a new method for converting cellulose into soluble compounds using a mixture of Fe²⁺ and Fe³⁺ as catalytic centers for the breakdown, yielding Fe₃O₄ nanoparticles during the hydrothermal process. Iron precursors transformed more than 61% of microcrystalline cellulose into solutes, with the composition of the solute changing with the initial Fe³⁺ concentration. The primary products of the breakdown of cellulose were a range of aldaric acids with different molecular weights. The nanoparticles have concentration-dependent tuneable sizes between 6.7 and 15.8 nm in diameter. The production of value-added nanomaterials at low temperatures improves upon the economics of traditional cellulose-to-energy conversion schemes with the precursor value increasing rather than deteriorating over time.

Impact of ball-milling and ionic liquid pretreatments on pyrolysis kinetics and behaviors of crystalline cellulose

In this work, the kinetic mechanisms of pyrolysis of cellulose with different physical structures were illustrated. The crystalline cellulose showed better thermal stability and required higher energy for decomposition with more concentrated reactions due to the highly ordered structure. The crystallinity of the ball milling and ionic liquid pretreated cellulose decreased and the structure was relatively loose and disordered, thereby reducing the thermal stability, so the global activation energy of both samples decreased and the intensive reaction caused by the collapse of structure was alleviated. In fast pyrolysis, crystalline cellulose favored fast pyrolytic saccharification, and the highest levoglucosan yield reached 64.3 wt% at 400 °C. This research was helpful to deduce the influence of physical structure on the pyrolytic product distribution of cellulose, thereby providing useful information to promote the development of pyrolytic saccharification.

Effects of reduced severity of ammonium sulfite pretreatment on bamboo for high cellulose recovery

In this study, the conditions for the pretreatment of bamboo by ammonium sulfite to achieve high cellulose recovery were investigated and optimized. To obtain higher cellulose recovery under low-severity pretreatment conditions such as ammonia sulfite concentration, pretreatment time and pretreatment temperature, three-factor and three-level experiments were designed by the Box–Behnken design based on response surface methodology. The results showed that the cellulose recovery yield after 48 h enzymatic hydrolysis could reach 58.36–59.87%; moreover, the recovered cellulose was pretreated with 20% ammonium sulfite at 150 °C for 6 h, and the obtained yield was in agreement with the predicted yield (58.87%). It was about 13-fold higher than that of the untreated bamboo (4.41%). Pretreatment temperature and ammonia sulfite concentration are significantly important factors than pretreatment time in the design space for achieving high cellulose recovery. Moreover, SEM analysis of the pretreated bamboo substrate under optimized conditions illustrated that the biomass surface had become more rough and porous after pretreatment.

In this study, the conditions for the pretreatment of bamboo by ammonium sulfite to achieve high cellulose recovery were investigated and optimized.

A comparative investigation of fast pyrolysis with enzymatic hydrolysis for fermentable sugars production from cellulose

In this study, ball milling and ionic liquid pretreatments were utilized to alter cellulose structure prior to fast pyrolysis and enzymatic hydrolysis. The variations in the products distribution of cellulose fast pyrolysis, and their dependence on the structure of cellulose, and the temperature of fast pyrolysis were illustrated. Fast pyrolysis of pretreated cellulose yielded more levoglucosan than crystalline cellulose (14.7%) at 300 °C. Nevertheless, the levoglucosan achieved higher yield (64.3%) from crystalline cellulose at 400 °C. At last, a comparison between fast pyrolysis and enzymatic hydrolysis for cellulose saccharifaction was made. Fast pyrolysis was a promising alternative to liberate levoglucosan from cellulose. Further investigation and development were required to maximize the levoglucosan production.

Elevated production of the aromatic fragrance molecule, 2-phenylethanol, using Metschnikowia pulcherrima through both de novo and ex novo conversion in batch and continuous modes

BACKGROUND

2-phenylethanol (2PE) is a fragrance molecule predominantly used in perfumes and the food industry. It can be made from petrochemicals inexpensively, however, this is unsuitable for most food applications. Currently, the main method of production for the bio-derived compound is to extract the trace amounts found in rose petals, which is extremely costly. Potentially fermentation could provide an inexpensive, naturally sourced, alternative.

RESULTS

In this investigation, 2PE was produced from the yeast Metschnikowia pulcherrima, optimised in flasks before scaling to 2 L batch and continuous operation. 2PE can be produced in high titres under de novo process conditions with up to 1500 mg L-1 achieved in a 2 L stirred bioreactor. This is the highest reported de novo titre to date, and achieved through high sugar loadings coupled with low nitrogen conditions. The process successfully ran in continuous mode also, with a concentration of 650 mg L-1 of 2PE being maintained. The 2PE production was further increased by the ex novo conversion of phenylalanine and semi-continuous solid phase extraction from the supernatant. Under optimal conditions 14 000 mg L-1 of 2PE was produced.

CONCLUSIONS

The work presented here offers a novel route to naturally sourced 2PE through a scalable fermentation with a robust yeast highly suited to industrial biotechnology. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effect of Glycerol Pretreatment on Levoglucosan Production from Corncobs by Fast Pyrolysis

In this manuscript, glycerol was used in corncobs' pretreatment to promote levoglucosan production by fast pyrolysis first and then was further utilized as raw material for chemicals production by microbial fermentation. The effects of glycerol pretreatment temperatures (220⁻240 °C), time (0.5⁻3 h) and solid-to-liquid ratios (5⁻20%) were investigated. Due to the accumulation of crystalline cellulose and the removal of minerals, the levoglucosan yield was as high as 35.8% from corncobs pretreated by glycerol at 240 for 3 h with a 5% solid-to-liquid ratio, which was obviously higher than that of the control (2.2%). After glycerol pretreatment, the fermentability of the recovered glycerol remaining in the liquid stream from glycerol pretreatment was evaluated by Klebsiella pneumoniae. The results showed that the recovered glycerol had no inhibitory effect on the growth and metabolism of the microbe, which was a promising substrate for fermentation. The value-added applications of glycerol could reduce the cost of biomass pretreatment. Correspondingly, this manuscript offers a green, sustainable, efficient and economic strategy for an integrated biorefinery process.

Quantitative approaches for illustrating correlations among the mechanical fragmentation scales, crystallinity and enzymatic hydrolysis glucose yield of rice straw

Mechanical fragmentation is an important pretreatment in the biomass biotransformation process. Mechanical fragmentation at the tissue scale significantly reduced the particle size of rice straw but did not significantly change its crystalline properties; the increase in the glucose yield was limited from 28.75% (95.55mg/g substrate) to 35.29% (115.28mg/g substrate). Mechanical fragmentation at the cellular scale destroyed the cell wall structure and reduced its crystalline properties. Thus, the glucose yield also showed a significant increase from 35.29% (115.28mg/g substrate) to 81.71% (287.07mg/g of substrate). The quantitative equations among the particle size, crystalline properties and glucose yield (mg/g substrate) are as follows: CrI=44.14×[1-exp(-0.03658×D₅₀)] and CP=(8.403×logD₅₀-24.1836)/(1-4.225/D₅₀^0.5); GY=-5.636CrI+343.7 and GY=-14.62CP+512.1; and GY=97.218+247.5×exp(-0.03824×D₅₀). The quantitative correlations among the mechanical fragmentation scales and crystalline properties can determine the effect and mechanism of mechanical fragmentation on biomass and can further promote the construction of a cost-competitive biotransformation process for biomass.

Cellulose: To depolymerize… or not to?

Oxidation of the primary OH groups in cellulose is a pivotal reaction both at lab and industrial scale, leading to the value-added products, i.e. oxidized cellulose which have tremendous applications in medicine, pharmacy and hi-tech industry. Moreover, the introduction of carboxyl moieties creates prerequisites for further cellulose functionalization through covalent attachment or electrostatic interactions, being an essential achievement designed to boost the area of cellulose-based nanomaterials fabrication. Various methods for the cellulose oxidation have been developed in the course of time, aiming the selective conversion of the OH groups. These methods use: nitrogen dioxide in chloroform, alkali metal nitrites and nitrates, strong acids alone or in combination with permanganates or sodium nitrite, ozone, and sodium periodate or lead (IV) tetraacetate. In the case of the last two reagents, cellulose dialdehydes derivatives are formed, which are further oxidized by sodium chlorite or hydrogen peroxide to form dicarboxyl groups. A major improvement in the cellulose oxidation was represented by the introduction of the stable nitroxyl radicals, such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). However, a major impediment for the researchers working in this area is related with the severe depolymerisation occurred during the TEMPO-mediated conversion of CH₂OH into COOH groups. On the other hand, the cellulose depolymerisation represent the key step, in the general effort of searching for alternative strategies to develop new renewable, carbon-neutral energy sources. In this connection, exploiting the biomass feed stocks to produce biofuel and other low molecular organic compounds, involves a high amount of research to improve the overall reaction conditions, limit the energy consumption, and to use benign reagents. This work is therefore focused on the parallelism between these two apparently antagonist processes involving cellulose, building a necessary bridge between them, thinking how the reported drawbacks of the TEMPO-mediated oxidation of cellulose are heading towards to the biomass valorisation, presenting why the apparently undesired side reactions could be turned into beneficial processes if they are correlated with the existing achievements of particular significance in the field of cellulose conversion into small organic compounds, aiming the general goal of pursuing for alternatives to replace the petroleum-based products in human life.

Lignin-rich biomass of cotton by-products for biorefineries via pyrolysis

Pyrolysis was demonstrated to investigate the thermal decomposition characteristics and potential of lignin-rich cotton by-products cotton exocarp (CE) and spent mushroom substrate consisted of cotton by-products (MSC) for biorefineries. The chemical component and structure alteration of CE and MSC was found to affect their thermochemical behaviors. The bio-oil yield from CE was 58.13wt% while the maximum yield from MSC was 45.01% at 600°C. The phenolic compounds obtained from CE and MSC were 33.9% and 39.2%, respectively. The yield of acetic acid from MSC between 400 and 600°C was about 30-38% lower than that from CE, which suggests the high quality of bio-oil was obtained. Biochar from MSC via slow pyrolysis had a high mass yield (44.38wt%) with well-developed pore structure.

The integration of dilute acid hydrolysis of xylan and fast pyrolysis of glucan to obtain fermentable sugars

BACKGROUND

Fermentable sugars are important intermediates in the biological conversion of biomass. Hemicellulose and amorphous cellulose are easily hydrolyzed to fermentable sugars in dilute acid, whereas crystalline cellulose is more difficult to be hydrolyzed. Cellulose fast pyrolysis is an alternative method to liberate valuable fermentable sugars from biomass. The amount of levoglucosan generated from lignocellulose by fast pyrolysis is usually lower than the theoretical yield based on the cellulose fraction. Pretreatment is a promising route to improve the yield of levoglucosan from lignocellulose.

RESULTS

The integration of dilute sulfuric acid hydrolysis and fast pyrolysis to obtain fermentable sugars was evaluated in this study. Dilute sulfuric acid hydrolysis could remove more than 95.1 and 93.4 % of xylan (the main component of hemicellulose) from sugarcane bagasse and corncob with high yield of xylose. On the other hand, dilute sulfuric acid hydrolysis was also an effective pretreatment to enhance levoglucosan yield from lignocellulose. Dilute acid hydrolysis could accumulate glucan (the component of cellulose) and remove most of the alkali and alkaline earth metals which were powerful catalysts during fast pyrolysis. Further increase in dilute acid concentration (from 0 to 2 %) in pretreatment could promote the yield of levoglucosan in fast pyrolysis. The acid pretreated sugarcane bagasse and corncob gave levoglucosan yields of 43.8 and 35.2 % which were obvious higher than those of raw sugarcane bagasse (12.0 %) and corncob (7.0 %).

CONCLUSIONS

Obtaining fermentable sugars by combination dilute acid hydrolysis of xylan and fast pyrolysis of glucan could make full utilization of biomass, and get fermentable sugars economically from biomass for bio-refinery.

Bioconversion of anhydrosugars: Emerging concepts and strategies

As methods for the use of anhydrosugars in chemical and biofuel production continue to develop, our collective knowledge of anhydrosugar processing enzymes continues to improve, including their mechanistic details, structural dynamics and modes of substrate binding. Of particular interest, anhydrosugar kinases, such as levoglucosan kinase (LGK) and 1,6-anhydro-N-acetylmuramic acid kinase (AnmK), utilize an unusual mechanism whereby the sugar substrate is both cleaved and phosphorylated. The phosphorylated sugar can then be routed to other metabolic pathways, thereby allowing its further bioconversion. Advanced engineering efforts to improve the catalytic efficiency and stability of LGK have been steadily progressing. Other enzymes that cleave the glycosidic bond of disaccharide sugars containing an anhydrosugar component are also being identified and characterized. Accordingly, the potential future use of these enzymes in large-scale production strategies is becoming increasingly viable. Here, a mini-review of the observed characteristics of anhydrosugar processing enzymes is presented along with recent developments in the bioconversion of these sugars. © 2016 IUBMB Life 68(9):700-708, 2016.

Efficient and repeated production of succinic acid by turning sugarcane bagasse into sugar and support

Here we reported an endeavor in making full use of sugarcane bagasse for biological production of succinic acid. Through NaOH pre-treatment and multi-enzyme hydrolysis, a reducing sugar solution mainly composed of glucose and xylose was obtained from the sugarcane bagasse. By optimizing portions of cellulase, xylanase, β-glucanase and pectinase in the multi-enzyme "cocktail", the hydrolysis percentage of the total cellulose in pre-treated sugarcane bagasse can be as high as 88.5%. A. succinogenes CCTCC M2012036 was used for converting reducing sugars into succinic acid in a 3-L bioreactor with a sugar-fed strategy to prevent cell growth limitation. Importantly, cells were found to be adaptive on the sugarcane bagasse residue, offering possibilities of repeated batch fermentation and replacement for MgCO3 with soluble NaHCO3 in pH modulation. Three cycles of fermentation without activity loss were realized with the average succinic acid yield and productivity to be 80.5% and 1.65g·L(-1)·h(-1).

Cellulosic micelles as nanocapsules of liposoluble CdSe/ZnS quantum dots for bioimaging

Sustainable light-emitting nanoaggregates obtained by encapsulating liposoluble CdSe/ZnS QDs in novel cellulosic micelles show promise in bioimaging.