The present study attempts to cultivate Porphyridium purpureum under different scale-up conditions for further development and commercialization of microalgae-derived PUFAs such as ARA and EPA. Different temperatures (25, 30, and 35 °C) and light intensities (70, 165, and 280 μmol/m2s) were applied to the 50 L pilot-scale cultivation of P. purpureum in ASW. The cultivation under the light intensity of 280 μmol/m2s at 35 °C obtained biomass concentration up to 9.52 g/L, total fatty acid content to 56.82 mg/g, and ARA content to 22.29 mg/g. While the maximum EPA content of 7.00 mg/g was achieved under the light intensity of 280 μmol/m2s at 25 °C and the highest ratio of UFAs to TFAs of 74.66% was also obtained in this trial. Both biomass concentration and TFAs content were improved by increasing light intensity and temperature. Moreover, the ratio of ARA to EPA was enhanced by increasing cultivation temperature under the light intensity of 280 μmol/m2s. In contrast with flask culture, the conversion of linoleic acid (C18:2) to ARA was enhanced in scale-up culture, leading to more ARA content. Phosphate limitation enhanced the synthesis of lipid and LPUFAs. Moreover, the biomass concentration and biosynthesis of palmitic acid were preferred by sufficient C (NaHCO3).

•High yield of 5-HMF was obtained from deep eutectic solvent reaction system.•Extremely low Brönsteda acid shown superior catalysis in the dehydration of fructose.•We reported a biphasic DES/MeCN system with excellent recyclability.•With a high fructose dosage up to 20 wt%, 90.3% yield of 5-HMF was obtained at 100 °C for 4 h.5-Hydroxymethylfurfural (5-HMF) is one of the most important platform chemicals in biorefinery. In this work, an effective and green route for 5-HMF production in deep eutectic solvents (DESs) was demonstrated using extremely low concentration of hydrochloric acid as the catalyst. Moreover, the DES/acetonitrile (MeCN) biphasic reaction system adopted in this research showed excellent recyclability, which could be directly reused for multiple times without downgrading of the 5-HMF yield.Download high-res image (96KB)Download full-size image

The microalga Porphyridium purpureum within Rhodophyta abundantly produces several valuable proteins, polysaccharides, pigments and long-chain polyunsaturated fatty acid; it is especially effective in accumulating arachidonic acid (ARA). However, this high ARA yield is always achieved in conditions unfavourable for cell growth. In this study, we present a method for obtaining desirable ARA levels from P. purpureum while simultaneously promoting cell growth using appropriate concentrations of the growth hormone 5-Aminolevulinic acid (5-ALA).Both the biomass and the ARA content of P. purpureum were enhanced by stimulation with 20 mg/L 5-ALA, leading to an optimal ARA yield of 170.32 mg/L—a 70.82% increase compared with control conditions. This ARA yield is the highest ever reported for microalgae. Based on variations in the fatty acid composition, total lipids, total proteins, total carbohydrates and pigment content during the cultivation period, we propose that the accumulation of ARA stimulated by 5-ALA occurs at the expense of other UFAs and total proteins, which may be related to decreased zeaxanthin. Lipidomic analysis revealed that triacylglycerols (TAGs) accounted for 47.5 ± 3.6% of all detected lipids, followed by phosphatidylglycerol (PG) and digalactosyldiacylglycerol (DGDG). As the levels of the most abundant TAGs increased under 5-ALA promotion and because 78.1 ± 3.4% (by weight) of detected TAG-branched chains contained ARA, the increase of ARA was mainly caused by TAG accumulation.This work demonstrated a simple and effective strategy to promote both biomass and ARA yield in P. purpureum by introducing a small amount of 5-ALA. These results are helpful for understanding the microalgae metabolic pathways affected by phytohormones and for guiding the development of bioproducts from microalgae.

Biomass-derived 5-hydroxymethylfurfural (HMF) is hailed as an all-purposed platform molecule that holds great promise to address a number of high volume markets for chemicals, polymeric materials, and transportation fuels. HMF-derived diols, including 2,5-bishydroxymethylfuran (BHMF), 2,5-bishydroxymethyltetrahydrofuran (BHMTF), and 1,6-hexanediol (1,6-HD), are key intermediates for the catalytic upgrading of HMF in a biorefinery. These diols can be employed as renewable polymeric monomers, and among them BHMF and BHMTF are also attractive precursors for biofuels, such as 2,5-dimethylfuran (DMF), 2,5-bis(alkoxymethyl)furans (BAMFs), and 2,5-dimethyltetrahydrofuran (DMTHF). Hence, gaining more insights into the chemoseletive hydrogenation of HMF to these diols is of particular importance. In this review, we comprehensively summarize the advances in the selective hydrogenation of HMF into these diols in terms of the diversity of hydrogen sources, mainly including molecular H2, alcohols, formic acid and water, over homogeneous or heterogeneous catalysts. Assessment of the relative merits of different hydrogen sources for the hydrogenation of HMF is performed as well. We also discuss challenges and opportunities in employing these HMF-derived diols for the production of polymeric materials and biofuels.

Herein we report a tandem thionation of biomass derived levulinic acid (LA) to generate thiophenic compounds. LA is initially converted to several thiophenones and then an aromatic di-thionated product, 5-methylthiophene-2-thiol, is obtained with the highest yield of 78%. An overall synthesis of thiophenic products from cellulose is also developed.

An efficient process for the catalytic transfer hydrogenation of biomass-derived 5-hydroxymethyl furfural (HMF) to 2,5-bishydroxymethyl furan (BHMF) is presented using ethanol as a hydrogen donor and solvent over low-cost ZrO(OH)2. A HMF conversion of 94.1% and a DHMF selectivity of 88.9% were achieved at 423 K in 2.5 h. The fresh, spent, and regenerated catalysts were characterized comprehensively, and the OH group of ZrO(OH)2 as sites for ligand exchange with ethanol was considered to be important for the activity.

Correction for ‘Green catalytic conversion of bio-based sugars to 5-chloromethyl furfural in deep eutectic solvent, catalyzed by metal chlorides’ by Miao Zuo et al., RSC Adv., 2016, 6, 27004–27007.

5-Chloromethylfurfural (5-CMF), a biomass-derived platform chemical with great potential applications, was synthesized by a novel method from sugars, using metal chlorides as catalysts in a deep eutectic solvent (DES). AlCl3·6H2O was verified as the most effective catalyst among various metal chlorides, and provided a 5-CMF yield of 50.3% along with 8.1% 5-HMF yield at 120 °C in 5 h. By this green, mild and cost-effective approach, the dependence of 5-CMF production on the large amount and high concentration of hydrochloric acid in previous studies was eliminated.

•CuCr prepared with different Cr sources and calcination temperatures were evaluated.•The catalysts were tested under solvent-free conditions for converting EL to GVL.•CuCr prepared under mild conditions showed the highest efficiency and stability.•In-situ reduced CuCr acted more effectively than ex-situ reduced catalyst.Noble metal free CuCr based catalysts have been adopted for the production of γ-valerolactone (GVL) which is a biomass derived crucial platform molecule and potential liquid fuel candidate. However, the preparation of CuCr catalysts varies and in this research, a CuCr catalyst synthesized under mild conditions showed rather high catalytic capacity for the solvent-free hydrogenation of ethyl levulinate (EL) to GVL in a yield up to 95%. The catalyst was in-situ reduced and displayed excellent recycle capacity with no obvious activity decline within 5 successive runs, which was much more stable than ex-situ reduced CuCr catalyst. The high efficient, low cost and recyclability of this CuCr catalyst provides a promising pathway for biomass derived GVL production.

γ-Valerolactone (GVL), a versatile biomass derived platform molecule, was synthesized with a highest yield of 89.8% from methyl levulinate (ML) using self-supplied H2 coming from the decomposition of MeOH derived partially from ML. Cu–Cr acted as a bi-functional catalyst for both H2 production from MeOH and carbonyl hydrogenation. An extremely low amount of MeOH (29 mol% relative to ML) was initially necessary to start up the hydrocyclization of ML to GVL and MeOH, which is in turn employed as an in situ H2 source for ML hydrogenation, providing an atom-economical pathway for GVL production.

In the present study, cellulolytic enzyme lignin, which was isolated from enzymatic hydrolysis residues of bamboo, could be efficiently depolymerized into oily products with a yield of over 60 wt % using a range of acidic zeolites and/or Raney Ni catalysts. The degraded products are mainly composed of phenolic monomers, which can be used as versatile chemicals or the precursor for biofuel production. The yields of monophenols were 12.9 wt % and no more than 5.0 wt % when catalyzed by Raney Ni or acidic zeolites, respectively. However, a yield of monophenols as high as 21.0–27.9% was obtained using a Raney Ni combination with acidic zeolite catalysts. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis revealed that the depolymerization level of the oily fraction catalyzed by a combination of catalysts was more complete in comparison to those catalyzed by an independent catalyst. The results indicated that the catalytic activity of a fully heterogeneous catalyst combination for the depolymerization of cellulolytic enzyme lignin was proven to be superior to that of either component alone.

Lignocellulosic derived gamma-valerolactone was effectively converted into methyl 4-methoxypentanoate, a potential liquid biofuel, solvent and fragrance, by the catalysis of a hydrogen exchanged ultra-stable Y zeolite (HUSY) and insoluble carbonates such as CaCO3. The catalytic competing generation process between methyl 4-methoxypentanoate and pentenoate esters was also analysed.

•Active oxygen cooking process is an efficient pretreatment process for biomass conversion.•Most of lignin and hemicelluloses were removed during the heating up period.•The glucosidic bonds were seriously damaged during the cooking stage.This work described the morphologic changes of corn stalk and the structural characterization of its hemicelluloses dissolved in yellow liquor at different cooking stages. The results showed that active oxygen cooking process was an efficient method to depolymerize the corn stalk into cellulose, hemicelluloses, and lignin as a pretreatment of biomass conversion. This cooking process can also be divided into three phases: bulk delignification, extended delignification, and residual delignification. During the heating-up period 57.67% of hemicelluloses and 62.31% of lignin were removed from the raw material. However, only 15% of hemicelluloses and 23.21% of lignin were removed during at temperature’ period. The hemicelluloses from the corn stalk and yellow liquor were composed of (1→4)-β-D-xylopyranose backbones substituted with α-l-arabinofuranosyl, 4-O-methyl-α-D-glucuronic acid, and some methoxyl residues. The backbones of hemicelluloses were gradually cleaved during the cooking process. The acetyl groups substituted with xylopyranosyl residues were completely cleaved during the cooking process.

A simple and efficient process was presented for the selective hydrogenation of 5-hydroxymethylfurfural (HMF) into the high-quality liquid fuel 2,5-dimethylfuran (DMF) in the presence of tetrahydrofuran (THF). Among the employed metal catalysts, the relatively inexpensive carbon-supported ruthenium (Ru/C) displayed the highest catalytic performance, which led to 94.7% DMF yield with 100% HMF conversion at a relatively mild reaction temperature of 200 °C for only 2 h. Although Ru/C had a little loss in the catalytic activity when it was used for five successive reaction runs, the partially deactivated Ru/C could be easily regenerated by heating at a mixed flow of H2 and N2. Moreover, the plausible mechanism involving an aldehyde group, a hydroxyl group, and a furan ring for the selective hydrogenation of HMF into DMF was also proposed. Subsequently, DMF was separated from the crude hydrogenation mixture according to their various boiling points by the combination of atmospheric distillation and vacuum distillation, and then, the chemical structures and physical properties of the separated DMF were confirmed to be consistent with the authentic DMF. More gratifyingly, Ru/C and THF were also found to be a good combination for the direct hydrogenation of carbohydrate-derived HMF into DMF, which is very important for the practical production of DMF from a variety of biomass-derived carbohydrates such as fructose, glucose, sucrose, maltose, cellobiose, starch, and cellulose.

Hydrothermal or alcoholysis liquefaction are common pathways to produce biofuel in mild reaction conditions. However, the application was limited by the reliance of corrosive acid and base catalysts and high-cost hydrogen donors. In this research, in-situ-prepared nano-Cu was employed for the first time as a methanol decomposition catalyst in a glycerol–methanol–water solvent to generate hydrogen in situ for the hydrogenation–liquefaction of Miscanthus. Methanol was effectively decomposed to H2, CO, and CO2 by the catalysis of Cu. The percentage of conversion of biomass into liquid product was over 90% at 350 °C for 4 h. Bio-oil with main components, including alcohols, esters, ethers, alkyl phenolics, and other glycerol-derived molecules, were obtained. This strategy also showed an excellent liquefaction capacity when other woody and herbaceous biomasses were selected as feedstock.

A series of organic solvents were screened for the extraction of ethyl levulinate (EL) from the concentrated ethanolysis products of sucrose. Among these organic solvents, toluene was confirmed as an outstanding extracting agent for separating EL with less humins from the concentrated reaction products. The EL extraction rate was strongly related to the temperature and duration applied in the vacuum concentration; a maximum EL recovery of 96.7% can be achieved through the extraction by toluene from the ethanolysis products. Herein, the catalytic transfer hydrogenation (CTH) of biomass-derived EL to γ-valerolactone (GVL) was also performed over inexpensive metal oxides using ethanol as a hydrogen donor. On the basis of these scenarios, a novel process for the production and separation of EL and GVL from carbohydrates was proposed to integrate the ethanolysis of carbohydrates and the CTH of EL.

A green and efficient process was developed for the conversion of biomass-derived ethyl levulinate (EL) into γ-valerolactone (GVL) using supercritical ethanol as the hydrogen donor and the reaction medium over low-cost and eco-friendly ZrO2 catalysts, which were prepared by the precipitation method and characterized by BET, SEM, XRD, FT-IR, TGA-DTA, TPD-NH3 and TPD-CO2. The results indicated that amorphous ZrO2 with a high specific surface area and a large number of acid–base sites exhibited the highest catalytic activity, an excellent GVL yield of 81.5% with 95.5% EL conversion was achieved at 523 K over 3 h. In addition, combined with the results of poisoning experiments, a plausible mechanism of catalytic transfer hydrogenation (CTH) via a six-membered ring transition state was also presented.

In recent years, substantial interest has been devoted to the conversion of biomass-derived carbohydrates into furanic aldehydes such as furfural, 5-hydroxymethylfurfural (HMF) and 5-halomethylfurfural, because these products are considered as important versatile intermediates that can be further transformed into a wide variety of high performance fuels and high value-added chemicals. However, low yields and high production costs that are due to the special chemical structures and properties of biomass-derived carbohydrates to a large extent have limited the practical production of furanic aldehydes. Recently, various catalytic conversion strategies have been developed to overcome these limitations. In this review, we systematically summarize and discuss catalytic conversion strategies from the perspective of catalysts and reaction solvents as well as formation mechanisms and influencing factors for the production of furanic aldehydes from biomass-derived carbohydrates. Meanwhile, we also outline the synthesis of furanic aldehyde-based fuels such as 2-methylfuran (MF), 2,5-dimethylfuran (DMF), 5-ethoxymethylfurfural (EMF) and alkanes and chemicals such as levulinic acid (LA), 2,5-diformylfuran (DFF) and 2,5-furandicarboxylic acid (FDCA). Moreover, some potential research orientations are proposed based on the major problems encountered in recent research.

A high yield of lignin was generated when solid alkali (MgO) and active oxygen (O2 and H2O2) were used in bagasse cooking as a pretreatment for lignin conversion. In the present work, the lignin present in raw material, pulp, and yellow liquor was characterized by Fourier transform infrared spectroscopy (FTIR) and heteronuclear single-quantum coherence (HSQC) NMR. The results showed that 95.4% of the lignin was obtained from the raw material and present in the yellow liquor. The syringyl (S/S′/S″) units could be changed completely and removed from the raw material, and a novel G′ unit with a carbonyl group was generated through an oxidizing reaction. The phenolic structures had a high reactivity during the cooking process, and the β-O-4′ (A/A′/A″) structures had different levels of reactivity. Moreover, the H unit, P structure, and nonphenolic β-5′ and β–β′ structures were stable throughout the cooking process.

A novel, efficient, and environmentally friendly technology is used in cornstalk cooking, active oxygen (O2 and H2O2) cooking with solid alkali (MgO). After the cooking, the milled wood lignin in the raw material and pulp and the water-soluble and insoluble lignin in the yellow liquor were all characterized by attenuated total reflectance Fourier transform infrared spectroscopy and two-dimensional heteronuclear single-quantum coherence NMR. The results showed that the cooking procedure with solid alkali and active oxygen had a high selectivity for delignification, which could remove 85.5% of the lignin from the raw material. The syringyl (S/S′/S′) units could be dissolved preferentially because of their high reactivity, and a novel guaiacyl unit with a carbonyl group (G′) was generated in the cooking process. Moreover, during the cooking, the β-O-4′ (A/A′/A″) structures as the main side-chain linkages in all the lignins could be partly broken and the β-O-4′ (A′) with a ring-conjugated structure was readily attacked by oxygen, whereas the H unit and β-5′ and β-β′ structures were found to stay stable without characteristic reaction.

An efficient process was developed for the conversion of glucose into 5-hydroxymethylfurfural (HMF) in the relatively low-toxicity and inexpensive catalytic system of chromium(III) chloride (CrCl3·6H2O) catalyst and tetraethylammonium chloride (TEAC) ionic liquid. An HMF yield of 71.3% was achieved at 130 °C for only 10 min under conventional oil-bath heating. The TEAC/CrCl3·6H2O system was found to be tolerant to high water content and high glucose concentration and could be recycled, exhibiting stable activity after five successive runs. Moreover, satisfactory results were achieved when fructose, sucrose, and cellobiose were used as feedstocks. This work might also provide useful information for the production of HMF from biomass.

This work describes the structural changes of bagasse hemicelluloses during the cooking process involving active oxygen (O2 and H2O2) and solid alkali (MgO). The hemicelluloses obtained from the bagasse raw material, pulp, and yellow liquor were analyzed by high-performance anion-exchange chromatography (HPAEC), gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), and 1H–13C 2D hetero-nuclear single quantum coherence spectroscopy (HSQC). The results revealed that the structure of the bagasse hemicelluloses was l-arabino-(4-O-methylglucurono)-d-xylan. Some sugar units in hemicelluloses were oxidized under the cooking conditions. Additionally, the backbones and the ester linkages of hemicelluloses were heavily cleaved during the cooking process.Graphical abstractHighlights► The backbone of the hemicelluloses was significantly destroyed. ► The side chain was cleaved from the backbone. ► The carbohydrates were oxidized by the active oxygen under the cooking conditions. ► The ester bonds in hemicelluloses were also damaged during the cooking process.

A direct synthesis of methyl levulinate from cellulose alcoholysis in methanol medium under mild condition (180–210 °C) catalyzed by extremely low concentration sulfuric acid (≤0.01 mol/L) and the product isolation were developed in this study. Effects of different process variables towards the catalytic performance were performed as a function of reaction time. The results indicated that sulfuric acid concentration, temperature and initial cellulose concentration had significant effects on the synthesis of methyl levulinate. An optimized yield of around 50% was achieved at 210 °C for 120 min with sulfuric acid concentration of 0.01 mol/L and initial cellulose concentration below 100 g/L. The resulting product mixture was isolated by a distillation technique that combines an atmospheric distillation with a vacuum distillation where n-dodecane was added to help distill the heavy fraction. The light fraction including mainly methanol could be reused as the reaction medium without any substantial change in the yield of methyl levulinate. The chemical composition and structural of lower heavy fraction were characterized by GC/MS, FTIR, 1H-NMR and 13C-NMR techniques. Methyl levulinate was found to be a major ingredient of lower heavy fraction with the content over 96%. This pathway is efficient, environmentally benign and economical for the production of pure levulinate esters from cellulose.An efficient and economical strategy for the direct conversion of cellulose into methyl levulinate catalyzed by extremely low concentration sulfuric acid has been developed, over which the maximum yield reached 50%.Download full-size image

•5-[(Formyloxy)methyl]furfural (FMF) was produced directly from cellulose in formic acid reaction system with a yield of 29.4% mol/mol.•Alkali metal bromides were discovered to effectively catalyze cellulose conversion to FMF.•Up to 2% water or acid in reaction system does not affect the FMF yield.•FMF with purity up to 97% mol/mol could be conveniently recovered in a two-step process.5-(Hydroxymethyl)furfural (HMF) is an important platform chemical, but the large scale production is limited by its instability. In this research, 5-[(formyloxy)methyl]furfural (FMF), derived from HMF, was produced directly from cellulose in formic acid reaction system with a yield of 33.4 mol% at 150 °C for 2 h. Among numerous metal salt catalysts screened in this study, alkali metal bromides were found to be effective in catalyzing cellulose conversion to FMF. Bromide anions facilitation of the esterification of HMF to form FMF was confirmed. In addition, the effects of water, acid and other reaction parameters also were investigated when NaBr was used as the catalyst. Up to 2% of water or acid in this reaction system did not impact on the FMF yield. Increasing the temperature for every 20 °C from 130 °C to 170 °C halved the reaction time but did not change the maximum yield. FMF was more hydrophobic and thermostable than HMF, which made it easier to be recovered. In a two-step process, FMF with a recovery of 29.4 mol% and purity of 97 mol% was obtained.Download full-size image

We present here the results of an investigation aimed at identifying catalysts for the dehydration of glucose and xylose to 5-hydroxymethylfurfural (HMF) and furfural in a diphasic reaction system, and the subsequent conversion of HMF and furfural to 2,5-dimethylfuran (DMF) and 2-methyl furan (MF) was also investigated. For the dehydration of glucose and xylose mixture, a series of SO42–/ZrO2–TiO2 solid acid catalysts were prepared by precipitation and impregnation method. Effects of various reaction parameters and catalyst reuse cycle toward the reaction performance were studied. Experimental results indicated that the product yield could reach 30.9 mol % (for HMF) and 54.3 mol % (for furfural) under the optimal experimental conditions. The SO42–/ZrO2–TiO2 catalyst is recoverable from the resulting product mixture and reused multiple times after calcination without any substantial change on the HMF and furfural yield. Furthermore, effects of various hydrogenation parameters of HMF and furfural in n-butanol promoted by carbon-supported ruthenium (Ru/C) were discussed, and the highest yield could reach 60.3 mol % (for DMF) and 61.9 mol % (for MF) under the optimal experimental conditions by starting with HMF and furfural in pure n-butanol, but the target products of DMF and MF could not be detected when directly used by the separated organic phase as solvent and substrate. However, the DMF and MF yield could reach 32.7 and 17.5 mol %, respectively, when the separated organic phase undergoes a further purification, which indicated that the purification of the organic phase is a key step for the further hydrogenation of HMF and furfural to DMF and MF.

γ-Valerolactone (GVL), a versatile biomass derived platform molecule, was synthesized with a highest yield of 89.8% from methyl levulinate (ML) using self-supplied H2 coming from the decomposition of MeOH derived partially from ML. Cu–Cr acted as a bi-functional catalyst for both H2 production from MeOH and carbonyl hydrogenation. An extremely low amount of MeOH (29 mol% relative to ML) was initially necessary to start up the hydrocyclization of ML to GVL and MeOH, which is in turn employed as an in situ H2 source for ML hydrogenation, providing an atom-economical pathway for GVL production.