Hydrothermal microwave valorization of eucalyptus using acidic ionic liquid as catalyst toward a green biorefinery scenario

Current challenges of hydrothermal treated wastewater (HTWW) for environmental applications and their perspectives: A review

Hydrothermal treatment (HT) is an emerged thermochemical approach for the utilization of biomass. In the last decade, intense research has been conducted on bio-oil and hydrochar, during which extensive amount of hydrothermal treated wastewater (HTWW) is produced, containing large amount of organic compounds along with several toxic chemicals. The composition of HTWW is highly dependent on the process conditions and organic composition of biomass, which determines its further utilization. The current study provides a comprehensive overview of recent advancements in HTWW utilization and its properties which can be changed by varying different parameters like temperature, residence time, solid concentration, mass ratio and catalyst including types of biomasses. HTWW characterization, parameters, reaction mechanism and its application were also summarized. By considering the challenges of HTWW, some suggestions and proposed methodology to overcome the bottleneck are provided.

The Effect of the Chemical Character of Ionic Liquids on Biomass Pre-Treatment and Posterior Enzymatic Hydrolysis

Ionic liquids have been recognised as interesting solvents applicable in efficient lignocellulosic biomass valorisation, especially in biomass fractionation into individual polymeric components or direct hydrolysis of some biomass fractions. Considering the chemical character of ionic liquids, two different approaches paved the way for the fractionation of biomass. The first strategy integrated a pre-treatment, hydrolysis and conversion of biomass through the employment of hydrogen-bond acidic 1-ethyl-3-methyimidazolim hydrogen sulphate ionic liquid. The second strategy relied on the use of a three-step fractionation process with hydrogen-bond basic 1-ethyl-3-methylimidazolium acetate to produce high purity cellulose, hemicellulose and lignin fractions. The proposed approaches were scrutinised for wheat straw and eucalyptus residues. These different biomasses enabled an understanding that enzymatic hydrolysis yields are dependent on the crystallinity of the pre-treated biomass. The use of acetate based ionic liquid allowed crystalline cellulose I to change to cellulose II and consequently enhanced the glucan to glucose yield to 93.1 ± 4.1 mol% and 82.9 ± 1.2 mol% for wheat straw and eucalyptus, respectively. However, for hydrogen sulphate ionic liquid, the same enzymatic hydrolysis yields were 61.6 ± 0.2 mol% for wheat straw and only 7.9 ± 0.3 mol% for eucalyptus residues. These results demonstrate the importance of both ionic liquid character and biomass type for efficient biomass processing.

Hydrothermal liquefaction of agricultural and forestry wastes: state-of-the-art review and future prospects

Hydrothermal liquefaction has been widely applied to obtain bioenergy and high-value chemicals from biomass in the presence of a solvent at moderate to high temperature (200-550°C) and pressure (5-25MPa). This article summarizes and discusses the conversion of agricultural and forestry wastes by hydrothermal liquefaction. The history and development of hydrothermal liquefaction technology for lignocellulosic biomass are briefly introduced. The research status in hydrothermal liquefaction of agricultural and forestry wastes is critically reviewed, particularly for the effects of liquefaction conditions on bio-oil yield and the decomposition mechanisms of main components in biomass. The limitations of hydrothermal liquefaction of agricultural and forestry wastes are discussed, and future research priorities are proposed.

The Beneficial Sinergy of MW Irradiation and Ionic Liquids in Catalysis of Organic Reactions

The quest for sustainable processes is becoming more and more important, with catalysis playing a major role in improving atom economy and reducing waste. Organic syntheses with less need of protecting/de-protecting steps are highly desirable. The combination of microwave irradiation, as energy source, with ionic liquids, as both solvents and catalysts, offered interesting solutions in recent years. The literature data of the last 15 years concerning selected reactions are presented, highlighting the importance of microwave (MW) technology coupled with ionic liquids.

Pretreatment of eucalyptus with recycled ionic liquids for low-cost biorefinery

It is urgent to develop recycled ionic liquids (ILs) as green solvents for sustainable biomass pretreatment. The goal of this study is to explore the availability and performance of reusing 1-allyl-3-methylimidazolium chloride ([amim]Cl) and 1-butyl-3-methylimidazolium acetate ([bmim]OAc) for pretreatment, structural evolution, and enzymatic hydrolysis of eucalyptus. Cellulose enzymatic digestibility slightly decreased with the increased number of pretreatment recycles. The hydrolysis efficiencies of eucalyptus pretreated via 4th recycled ILs were 54.3% for [amim]Cl and 72.8% for [bmim]OAc, which were 5.0 and 6.7-folds higher than that of untreated eucalyptus. Deteriorations of ILs were observed by the relatively lower sugar conversion and lignin removal from eucalyptus after 4th reuse. No appreciable changes in fundamental framework and thermal stability of [amim]Cl were observed even after successive pretreatments, whereas the anionic structure of [bmim]OAc was destroyed or replaced. This study suggested that the biomass pretreatment with recycled ILs was a potential alternative for low-cost biorefinery.

Microwave assisted alkaline pretreatment to enhance enzymatic saccharification of catalpa sawdust

Catalpa sawdust, a promising biofuel production biomass, was pretreated by microwave-water, -NaOH, and -Ca(OH)₂ to enhance enzymatic digestibility. After 48h enzymatic hydrolysis, microwave-Ca(OH)₂ pretreated sample showed the highest reducing sugar yield. The content of hemicellulose and lignin in catalpa sawdust decreased after microwave-alkali pretreatment. SEM observation showed that the catalpa sawdust surface with microwave-Ca(OH)₂ pretreatment suffered the most serious erosion. Crystallinity index of catalpa sawdust increased after all three kinds of pretreatment. The optimum conditions of microwave-Ca(OH)₂ pretreatment were particle size of 40mesh, Ca(OH)₂ dosage of 2.25% (w/v), microwave power of 400W, pretreatment time of 6min, enzyme loading of 175FPU/g, and hydrolysis time of 96h, and the reducing sugar yield of microwave-Ca(OH)₂ pretreated catalpa sawdust reached 402.73mg/g, which increased by 682.15% compared with that of raw catalpa sawdust. The catalpa sawdust with microwave-Ca(OH)₂ pretreatment is promising for biofuel production with great potential.

Suitability assessment of a continuous process combining thermo-mechano-chemical and bio-catalytic action in a single pilot-scale twin-screw extruder for six different biomass sources

A process has been validated for the deconstruction of lignocellulose on a pilot scale installation using six types of biomass selected for their sustainability, accessibility, worldwide availability, and differences of chemical composition and physical structure. The process combines thermo-mechano-chemical and bio-catalytic action in a single twin-screw extruder. Three treatment phases were sequentially performed: an alkaline pretreatment, a neutralization step coupled with an extraction-separation phase and a bioextrusion treatment. Alkaline pretreatment destructured the wall polymers after just a few minutes and allowed the initial extraction of 18-54% of the hemicelluloses and 9-41% of the lignin. The bioextrusion step induced the start of enzymatic hydrolysis and increased the proportion of soluble organic matter. Extension of saccharification for 24h at high consistency (20%) and without the addition of new enzyme resulted in the production of 39-84% of the potential glucose.