Separation of galactose, 5-hydroxymethylfurfural and levulinic acid in acid hydrolysate of agarose by nanofiltration and electrodialysis

Electrodialysis as a potential technology for 4-nitrophenol abatement from wastewater

4-Nitrophenol is a widely used emerging pollutant in various industries, including the production of agrochemicals, drugs, and synthetic dyes. Due to its potential environmental harmful effects, there is a need to study its reuse and removal from wastewater. This study used electrodialysis technology to separate 4-nitrophenol ions using a four-compartment stack. The effects of supporting electrolyte concentration, pH, voltages, and current density on the performance of electrodialysis for separating 4-nitrophenol were investigated. A high extraction percentage of 77% was achieved with low energy consumption (107 kWh kg-1) when high 4-nitrophenol flows and transport numbers were reached.

Effect of peracetic acid generation in hydrogen peroxide-acetic acid pretreatment on production of xylooligosaccharides from poplar by organic acid hydrolysis

Hydrogen peroxide-acetic acid (HPAA) compositions affect the peracetic acid generation and subsequent delignification of lignocellulosic materials. However, the effects of HPAA compositions on lignin removal and poplar hydrolyzability after HPAA pretreatment are not fully elucidated yet. In this work, different volume ratios of HP to AA were used to pretreat poplar, AA and lactic acid (LA) hydrolysis of delignified poplar to produce XOS was compared. Peracetic acid was mainly produced in 1 h of HPAA pretreatment. HPAA with HP to AA ratio of 8:2 (HP₈AA₂) generated 4.4% peracetic acid and removed 57.7% of lignin at 2 h. Furthermore, XOS production from HP₈AA₂-pretreated poplar by AA and LA hydrolysis was increased by 97.1% and 14.9% compared to those from raw poplar, respectively. After alkaline incubation, the glucose yield of HP₈AA₂-AA-pretreated poplar increased from 40.1% to 97.1%. The study results indicated that HP₈AA₂ was conducive to XOS and monosaccharides production from poplar..

Perspective of reactive separation of levulinic acid in conceptual mixer settler reactor

Levulinic acid is a carboxylic acid present in industrial downstream. It is an important chemical and can be transformed into various important chemicals such as 1,4-pentanediol, aminolevulinic acid, succinic acid, gamma valarolactone, hydoxyvaleric acid, and diphenolic acid. It is considered one of the top ten most important building block chemicals and bio-derived acids. Levulinic acid can be directly produced using biomass, chemical synthesis, and fermentation processes at industrial and laboratory scales. The biomass process produces the char, whereas the fermentation process generates waste during the production of levulinic acid, leading to an increase in the production cost and waste streams. The separation of levulinic acid from the waste is expensive and challenging. In the present study, reactive extraction was employed using trioctylamine in i-octanol for the separation of levulinic acid. The experimental results were expressed in terms of performance parameters like distribution coefficient (0.099-6.14), extraction efficiency (9-86%), loading ratio (0.09-0.7), and equilibrium complexation constant (11.34-1.05). The mass action law model was also applied and found the predicted values were in close agreement with the experimental results. The mixer settler extraction in series was used to achieve more than 98% separations of acid. Furthermore, the conceptual approach for separation of levulinic acid using a mixer settler reactor scheme was discussed and presented various design parameters including extraction efficiency, diffusion coefficient, equilibrium complexation constant, and loading ratio. The study is helpful in recovering the valuable chemicals present in industrial downstream and reducing their environmental impacts if any.

The potency of HPLC-DAD and LC-MS/MS combined with ion chromatography for detection/purification of levulinic acid and bio-compounds from acid hydrolysis of OPEFB

This work reports a new strategy for the detection and purification of levulinic acid (LA) and bio-compounds from the acid hydrolysis and enzymatic treatment of oil palm empty fruit bunch (OPEFB) through high-performance liquid chromatography (HPLC) techniques combined with ion/ligand chromatography. The detections of LA, biomass-saccharides, hydroxymethylfurfural (HMF), and furfural were successfully elucidated by optimizing the multiple reaction monitoring mode (MRM) and liquid chromatography conditions using a Pb²⁺ ligand exchange column in the liquid chromatography with tandem mass spectrometry (LC-MS/MS) approach. High-performance liquid chromatography with diode-array detection (HPLC-DAD) combined with an H⁺ ion exchange column also showed potency for detecting chromophoric compounds such as LA, HMF, furfural, and acid (by-products) but not biomass-saccharides. Both techniques showed acceptable validation in terms of linearity, limit of detection (LOD), limit of quantitation (LOQ), accuracy, precision, and stability in both quantitative and qualitative analysis. However, the LC-MS/MS approach showed higher sensitivity for detecting LA and HMF compared with HPLC-DAD. Samples comprised of cellobiose, glucose, HMF, and LA from the acid hydrolysis of cellulose to LA with a mineral acid, and the biocatalysis of cellulase and β-glucosidase catalyzed cellulose (from OPEFB) to glucose were successfully monitored through the LC-MS/MS approach. In addition, using the optimal HPLC conditions obtained from LC-MS/MS, the purification of LA from other substances obtained from the hydrolysis reaction of cellulose (5 g) was successfully demonstrated by HPLC-DAD equipped with a fraction collector combined with an H⁺ ion exchange column at gram-scale of 1 g LA with a purification rate of 0.63 g ml⁻¹ min⁻¹.

The analytical approach for detection and purification levulinic acid from and bio-compound in hydrolysis biomass.

Preparation of 5-hydroxymethylfurfural from Schisandra chinensis (Turcz.) Baill by high-speed counter-current chromatography: Comparison of conventional and consecutive separation

Schisandra chinensis is a kind of plant with high medicinal value, which contains many medicinal ingredients, including 5-hydroxymethylfurfural. In the present study, an efficient method based on high-speed counter-current chromatography was established for the preparation of 5-hydroxymethylfurfural from Schisandra chinensis. Petroleum ether-ethyl acetate-methanol-water (2:5:2:5, v/v) was selected as the solvent system for high-speed counter-current chromatography. In order to improve the yield of single separation, the sample size was continuously optimized and improved. The result showed that 1250 mg was the most suitable sample size, and 41 mg of the target compound with 97% purity was obtained by a single run. To further improve the yield, consecutive high-speed counter-current chromatography was introduced and compared with the results of high-speed counter-current chromatography single run. The results showed that although the purity was reduced to 92%, 430 mg of the target compound was obtained from 12.5 g of ethanol extract within 670 min after 10 consecutive injections. It indicated that consecutive separation not only increased the yield of the target compound, but also saved the separation time and greatly improved the separation efficiency of high-speed counter-current chromatography.

Optimized production of xylooligosaccharides from poplar: A biorefinery strategy with sequential acetic acid/sodium acetate hydrolysis followed by xylanase hydrolysis

The preparation of xylooligosaccharides (XOS) from lignocelluloses by organic acid hydrolysis has the advantages of high efficiency and simplicity, but reducing the production of by-products, especially xylose, is a prerequisite for commercial preparation of XOS using organic acid. In this work, to reduce the production of by-products, the acetic acid/sodium acetate conjugate system (AC/SA) was used to prepare XOS from poplar. Under the optimal conditions (0.15 M AC/SA, molar ratio of 3.0, 175 °C, 60 min), the maximum XOS yield was 33.6% with a low xylose/XOS ratio of 0.19. Xylanase hydrolysis effectively converted XOS with DP above 6 in the AC/SA hydrolysate to X2-X6 with little xylose produced. The XOS yield increased to 42.1%, with a xylose/XOS ratio was only 0.17. This work shows that AC/SA in combination with xylanase hydrolysis of poplar successfully achieved high XOS yield with low by-products yields without the extraction of xylan from the substrate.

Acid-Catalyzed Conversion of Cellulose Into Levulinic Acid With Biphasic Solvent System

In this work, acid-catalyzed conversion of cellulose into levulinic acid in a biphasic solvent system was developed. Compared to a series of catalysts investigated in this study, the Amberlyst-15 as a more efficient acid catalyst was used in the hydrolysis of cellulose and further dehydration of derived intermediates into levulinic acid. Besides, the mechanism of biphasic solvent system in the conversion of cellulose was studied in detail, and the results showed biphasic solvent system can promote the conversion of cellulose and suppress the polymerization of the by-products (such as lactic acid).The reaction conditions, such as temperature, time, and catalyst loading were changed to investigate the effect on the yield of levulinic acid. The results indicated that an appealing LA yield of 59.24% was achieved at 200°C and 180 min with a 2:1 ratio of Amberlyst-15 catalyst and cellulose in GVL/H2O under N2 pressure. The influence of different amounts of NaCl addition to this reaction was also investigated. This study provides an economical and environmental-friendly method for the acid-catalyzed conversion of cellulose and high yield of the value-added chemical.

Nanofiltration for separation and purification of saccharides from biomass

Saccharide production is critical to the development of biotechnology in the field of food and biofuel. The extraction of saccharide from biomass-based hydrolysate mixtures has become a trend due to low cost and abundant biomass reserves. Compared to conventional methods of fractionation and recovery of saccharides, nanofiltration (NF) has received considerable attention in recent decades because of its high selectivity and low energy consumption and environmental impact. In this review the advantages and challenges of NF based technology in the separation of saccharides are critically evaluated. Hybrid membrane processes, i.e., combining NF with ultrafiltration, can complement each other to provide an efficient approach for removal of unwanted solutes to obtain higher purity saccharides. However, use of NF membrane separation technology is limited due to irreversible membrane fouling that results in high capital and operating costs. Future development of NF membrane technology should therefore focus on improving material stability, antifouling ability and saccharide targeting selectivity, as well as on engineering aspects such as process optimisation and membrane module design.

Study of a New Process for the Preparation of Butyl Levulinate from Cellulose

Butyl levulinate (BL) is a versatile chemical utilized widely in food and chemical industries, the production of which by using cellulose in biomass resources is of great significance to its sustainable development. Traditional synthesis processes for n-butyl levulinate are confronted with various problems such as high cost of raw materials, difficulty in separating products, etc. In this paper, a novel process for the preparation of BL from cellulose is proposed. The process is composed of five main unit operations including fed-batch hydrolysis, decolorization, extraction, esterification and purification. A 171.63 g/L concentration of the intermediate levulinic acid was obtained at the fifth feeding through the fed-batch hydrolysis process. The resin-activated carbon secondary decolorization method was adopted to remove the soluble humin byproducts with an accumulative decolorization rate of 89%. In the extraction process, the product BL was chosen as the extractant to avoid the introduction of new impurities. After purification, the purity of the final product BL reaches up to 98 wt %. The proposed technique allows for cost-effective and eco-friendly production of BL from biomass resources.

A perspective on galactose-based fermentative hydrogen production from macroalgal biomass: Trends and opportunities

This review analyses the relevant studies which focused on hydrogen synthesis by dark fermentation of galactose from macroalgal biomass by discussing the inoculum-related pretreatments, batch fermentation and inhibition, continuous fermentation systems, bioreactor designs for continuous operation and ionic liquid-assisted catalysis. The potential for process development is also revisited and the challenges towards suppressing glucose dominance over a galactose-based hydrogen production system are presented. The key challenges in the pretreatment process aiming to achieve a maximum recovery of upgradable (fermentable) sugars from the hydrolysates and promoting the concomitant detoxification of the hydrolysates have also been highlighted. The research avenues for bioprocess intensification connected to enhance selective sugar recovery and effective detoxification constitute the critical steps to develop future red macroalgae-derived galactose-based robust biohydrogen production system.

Physico-Chemical Alternatives in Lignocellulosic Materials in Relation to the Kind of Component for Fermenting Purposes

The complete bioconversion of the carbohydrate fraction is of great importance for a lignocellulosic-based biorefinery. However, due to the structure of the lignocellulosic materials, and depending basically on the main parameters within the pretreatment steps, numerous byproducts are generated and they act as inhibitors in the fermentation operations. In this sense, the impact of inhibitory compounds derived from lignocellulosic materials is one of the major challenges for a sustainable biomass-to-biofuel and -bioproduct industry. In order to minimise the negative effects of these compounds, numerous methodologies have been tested including physical, chemical, and biological processes. The main physical and chemical treatments have been studied in this work in relation to the lignocellulosic material and the inhibitor in order to point out the best mechanisms for fermenting purposes. In addition, special attention has been made in the case of lignocellulosic hydrolysates obtained by chemical processes with SO₂, due to the complex matrix of these materials and the increase in these methodologies in future biorefinery markets. Recommendations of different detoxification methods have been given.

Simulated moving bed separation of agarose-hydrolyzate components for biofuel production from marine biomass

The economically-efficient separation of galactose, levulinic acid (LA), and 5-hydroxymethylfurfural (5-HMF) in acid hydrolyzate of agarose has been a key issue in the area of biofuel production from marine biomass. To address this issue, an optimal simulated moving bed (SMB) process for continuous separation of the three agarose-hydrolyzate components with high purities, high yields, and high throughput was developed in this study. As a first step for this task, the adsorption isotherm and mass-transfer parameters of each component on the qualified adsorbent were determined through a series of multiple frontal experiments. The determined parameters were then used in optimizing the SMB process for the considered separation. Finally, the optimized SMB process was tested experimentally using a self-assembled SMB unit with four zones. The SMB experimental results and the relevant computer simulations verified that the developed process in this study was quite successful in the economically-efficient separation of galactose, LA, and 5-HMF in a continuous mode with high purities and high yields. It is thus expected that the developed SMB process in this study will be able to serve as one of the trustworthy ways of improving the economic feasibility of biofuel production from marine biomass.

Production of 5-hydroxymethylfurfural from agarose by using a solid acid catalyst in dimethyl sulfoxide

In this study, an effective method for 5-HMF production from agarose, a biomass material derived from red-algae, is proposed.

Microwave-assisted conversion of microcrystalline cellulose to 5-hydroxymethylfurfural catalyzed by ionic liquids

Ionic liquid (IL) has been widely investigated in 5-HMF production from biomass. However, most of studies employed IL as reaction solvent which requires a large amount of IL. In the present study, IL was utilized as catalyst in the conversion of microcrystalline cellulose (MCC) to 5-HMF under microwave irradiation (MI) in N,N-dimethylacetamide (DMAc) containing LiCl. 1,1,3,3-tetramethylguanidine (TMG)-based ILs, including 1,1,3,3-tetramethylguanidine tetrafluoroborate ([TMG][BF4]) and 1,1,3,3-tetramethylguanidine lactate ([TMG]L) which were commonly used in the absorption of SO2 and CO2 from flue gas, were synthesized and applied in the conversion of MCC to 5-HMF for the first time. Of the catalysts employed, [TMG]BF4 showed high catalytic activity in 5-HMF production from MCC. The condition including the ratio of IL to MCC, temperature and time for MCC conversion was optimized using Central Composite Design (CCD) and Response Surface Methodology (RSM). The highest 5-HMF yield of 28.63% was achieved with the optimal condition.

Ethanol production from galactose by a newly isolated Saccharomyces cerevisiae KL17

A wild-type yeast strain with a good galactose-utilization efficiency was newly isolated from the soil, and identified and named Saccharomyces cerevisiae KL17 by 18s RNA sequencing. Its performance of producing ethanol from galactose was investigated in flask cultures with media containing various combination and concentrations of galactose and glucose. When the initial galactose concentration was 20 g/L, it showed 2.2 g/L/h of substrate consumption rate and 0.63 g/L/h of ethanol productivity. Although they were about 70 % of those with glucose, such performance of S. cerevisiae KL17 with galactose was considered to be quite high compared with other strains reported to date. Its additional merit was that its galactose metabolism was not repressed by the existence of glucose. Its capability of ethanol production under a high ethanol concentration was demonstrated by fed-batch fermentation in a bioreactor. A high ethanol productivity of 3.03 g/L/h was obtained with an ethanol concentration and yield of 95 and 0.39 g/L, respectively, when the cells were pre-cultured on glucose. When the cells were pre-cultured on galactose instead of glucose, fermentation time could be reduced significantly, resulting in an improved ethanol productivity of 3.46 g/L/h. The inhibitory effects of two major impurities in a crude galactose solution obtained from acid hydrolysis of galactan were assessed. Only 5-Hydroxymethylfurfural (5-HMF) significantly inhibited ethanol fermentation, while levulinic acid (LA) was benign in the range up to 10 g/L.