Jiajun Fan

Direct Microwave-Assisted Hydrothermal Depolymerization of Cellulose

A systematic investigation of the interaction of microwave irradiation with microcrystalline cellulose has been carried out, covering a broad temperature range (150 → 270 °C). A variety of analytical techniques (e.g., HPLC, (13)C NMR, FTIR, CHN analysis, hydrogen-deuterium exchange) allowed for the analysis of the obtained liquid and solid products. Based on these results a mechanism of cellulose interaction with microwaves is proposed. Thereby the degree of freedom of the cellulose enclosed CH2OH groups was found to be crucial. This mechanism allows for the explanation of the different experimental observations such as high efficiency of microwave treatment; the dependence of the selectivity/yield of glucose on the applied microwave density; the observed high glucose to HMF ratio; and the influence of the degree of cellulose crystallinity on the results of the hydrolysis process. The highest selectivity toward glucose was found to be ~75% while the highest glucose yield obtained was 21%.

Use of green chemical technologies in an integrated biorefinery

A new concept is demonstrated for an integrated close to zero waste wheat straw biorefinery combining two novel green technologies, CO2 extraction and low temperature microwave pyrolysis, to produce a variety of products, including energy and CO2 which can be internally recycled to sustain the processes. CO2 adds value to the process by extracting secondary metabolites including fatty acids, wax esters and fatty alcohols. Low temperature microwave pyrolysis (<200 °C) is shown to use less energy and produce higher quality oils and chars than conventional pyrolysis. The oils can be fractionated to produce either transport fuels or platform chemicals such as levoglucosan and levoglucosenone. The chars are appropriate for co-firing. The quality of the chars was improved by washing to remove the majority of the potassium and chlorine present, lowering their fouling potential. The economic feasibility of a wheat straw biorefinery is enhanced by intergrating these technologies.

Low-temperature microwave-assisted pyrolysis of waste office paper and the application of bio-oil as an Al adhesive

The conversion of waste office paper (printed or photocopied) to bio-oil via low temperature (<200 °C) microwave-assisted pyrolysis, and its utilisation as an adhesive for aluminium–aluminium bonding are reported. The yields for the organic and aqueous phase bio-oil are 19% and 23%, respectively. The pyrolysis products were characterized by ICP-MS, ATR-IR, GC-MS and NMR to reveal broad categories of compounds indicative of sugars (carbohydrates), aromatics and carbonyl-containing moieties. Application of the organic phase bio-oil (70 mg) to Al plates (50 mm × 50 mm) followed by curing at different temperatures and time periods revealed that a maximum tensile strength of approximately 2300 N could be attained at 160 °C for 8 h cure. Also, at a fixed temperature, the tensile strength increased with increasing curing time. To gain an in-depth understanding of the adhesive properties of bio-oil, a liquid–liquid fractionation of the organic phase bio-oil was conducted. The ‘acidic’ fraction showed far better adhesion properties than the ‘neutral’ fraction with no bonding achieved for the aqueous fraction. A combination of the ‘acidic’ and ‘neutral’ fraction gave better adhesion, thus suggesting a possible synergistic or co-operative effect.

Conventional and microwave assisted hydrolysis of urban biowastes to added value lignin-like products

The hydrolysis of five fermented water insoluble urban wastes is shown to convert the insoluble recalcitrant organic lignin-like fraction to added value soluble lignin-like products in high yields. The hydrolysate products are a mixture of complex polymeric molecules which maintain the memory of the proximates of the pristine materials. For a composted biowaste, taken as the case study, a process feasibility study comparing the microwave (MW) assisted versus the conventional (CON) reaction is reported. Product yields and quality are investigated as a function of four process parameters: i.e. pH (8–13), temperature (60–200 °C), and liquid–solid w/w ratio (4 and 10) and contact time (1 min–4 h). Microwave heating allows obtaining the same products, and in the same yields, as conventional heating in 1–2 orders of magnitude lower time. It is possible to achieve 50–60% yields of soluble lignin-like products at relatively low temperatures ≤100 °C. The obtained yield vs. temperature trend indicates that even higher yields may be obtained at higher temperatures. The potential scalability of MW assisted versus CON hydrolysis to the industrial level is discussed in relation to the reaction rate and reactor cost. The results offer worthwhile research scope to compare MW and CON heating for the hydrolysis of other fermented and non-fermented material as collected biowastes.

A new perspective in bio-refining: levoglucosenone and cleaner lignin from waste biorefinery hydrolysis lignin by selective conversion of residual saccharides

An unexpected opportunity is reported to improve the sustainability of biorefineries whereby 8 wt% levoglucosenone (LGE) can be derived from unconverted saccharides in a lignin-rich biorefinery waste stream in a highly selective fashion (>90%). Additionally, in the process a purer lignin is obtained which can be used for further processing or materials applications. LGE is a valuable and versatile product with a plethora of applications.

Microwave-assisted hydrothermal selective dissolution and utilisation of hemicellulose in Phyllostachys heterocycla cv. pubescens

A green process for the microwave-assisted hydrothermal selective dissolution and utilisation of hemicellulose in Phyllostachys heterocycla cv. Pubescens (shortened to pubescens) was developed. The process facilitated the efficient dissolution of hemicellulose at 200 °C, while obtaining hemicellulose-free residue that could be further used as starting materials within many industrial processes. A variety of analytical techniques (e.g., HPLC, FT-IR, SEM, TG/TGA, Py-GC/MS, TG-IR, 13C liquid NMR, 2D HSQC NMR, and 13C CPMAS NMR analysis) were used for the analysis of the obtained liquid and solid products, which revealed that hemicellulose was completely extracted from pubescens. A solid residue left after this process consists of cellulose and lignin in a pure form and can be used for production of glucose and aromatic compounds. Interestingly, a new route to produce hemicellulose-based films that could potentially be used for food packaging was achieved. The developed approach opens avenue for a low-cost and sustainable bamboo-based biorefinery.

Environmental impact assessment of wheat straw based alkyl polyglucosides produced using novel chemical approaches

This paper evaluates and quantifies the environmental performance of alkyl polyglucosides sourced from wheat straw (WS-APG), a low-cost and low-ecological impact agricultural residue, compared to that of their commercial counterpart, which is sourced from palm kernel oil and wheat grain (PW-APG). Escalating pressure to consider the environmental sustainability of fossil derived surfactant consumption has driven biosurfactants to become the product of choice within the surfactant market, and a class of ‘plant’ based non-ionic surfactants called alkyl polyglucosides (APG) are particularly prevalent. However, the existing food based feedstock of APG such as coconut oil, palm oil, wheat and corn (in addition to being expensive) will potentially undermine the claimed ‘sustainability’ of the APG products (i.e. the ‘food vs. chemical’ issue). Here, we present the “cradle-to-gate” life cycle impact assessment of a suggested alternative, hybridised APG synthesis technique where the Fisher glycosidation method is supplemented by novel, green chemistry based techniques. This evaluation provides a quantitative insight into direct GHG intensity and other ecological impact indicators, including land use, waste generation and energy consumption. Upon evaluation, the wheat straw-derived pathway delivered GHG-emission savings in the range of 84–98%, compared to that of the palm kernel–wheat grain pathway. Waste generated from the production of unit mass of the product amounted to 0.43 kg and 10.73 kg per kg of WS-APG and PW-APG, respectively. In addition to the above mentioned facts, the ‘cradle–gate’ stages of WS-APG production were also found to consume relatively lower amounts of water and fossil-derived energy. In conclusion, of the two APG production pathways, the suggested ‘hybrid’ pathway using an agricultural residue, wheat straw, was found to be sustainable and to demonstrate better environmental performance.

Mechanistic understanding of salt-assisted autocatalytic hydrolysis of cellulose

Depolymerisation of cellulose is a critical step for biomass-based bio-refining processes to produce valuable chemicals. Herein, we propose the mechanism of the promoting effect of NaCl on the cellulose hydrolysis process based on a systematic kinetic study involving variable temperature studies and the use of deuterated agents. It has been found that the presence of NaCl simultaneously enhances the generation of acidic products from cellulose decomposition and pushes the generated protons to the surface of cellulose, dramatically increasing surface acidity and facilitating the autocatalytic hydrolysis of cellulose. Cl− disrupted the intermolecular hydrogen bonding of cellulose, especially in the first surface layer. Thus, the solid cellulose chains were peeled off layer-by-layer, leading to an accelerated hydrolysis of cellulose by the adsorbed protons. Without the need for traditional acidic catalysts, this autocatalytic depolymerisation of cellulose in water, assisted by salt provides a practically viable route to the enhanced conversion of biomass to chemicals.

Microwave assisted extraction of phenolic compounds from four economic brown macroalgae species and evaluation of their antioxidant activities and inhibitory effects on α-amylase, α-glucosidase, pancreatic lipase and tyrosinase

Four economically important brown algae species (Ascophyllum nodosum, Laminaria japonica, Lessonia trabeculate and Lessonia nigrecens) were investigated for phenolic compound extraction and evaluated for their antioxidant, anti-hyperglycemic, and pancreatic lipase and tyrosinase inhibition activities. Microwave assisted extraction (MAE) at 110 °C for 15 min resulted in both higher crude yield and higher total phenolic content (TPC) for all algae species compared with those obtained by conventional extraction at room temperature for 4 h, and Ascophyllum nodosum yielded the highest TPC. Antioxidant tests indicated that extracts acquired by MAE from four species all exhibited higher DPPH, ABTS free radical scavenging ability and reducing power than the conventional method. The extract of Lessonia trabeculate exhibited good α-amylase, α-glucosidase, pancreatic lipase, and tyrosinase inhibition activities, and the MAE extract showed even better α-glucosidase inhibitory activity than acarbose.

CHAPTER 3:Low-Temperature Microwave Pyrolysis and Large Scale Microwave Applications

The following chapter discusses the potential uses of microwave technology in the low temperature decomposition of biologically derived materials and its application on both laboratory and commercial scales. In so doing, we examine the historic development of microwave technology from its origins (with Kassner in 1937) to the present day. The mechanism of microwave heating is examined, with specific attention given to dielectric losses and the dipolar polarisation mechanism, with further emphasis on the changing interaction of microwaves with increased material temperature. Further to this, the specific application of microwaves on the laboratory scale is reviewed with focus given to the microwave decomposition of the constituent components of biomass (cellulose, hemicellulose and lignin) and real life examples, such as the decomposition of barley, wheat, wood, etc. The resulting decomposition materials and chemicals are reviewed, for example the production of levoglucosan and levoglucosenone from cellulose. Finally, consideration is given to current large scale commercial applications of microwave technology, looking at both 915 MHz and 2450 MHz applications, which include microwave drying, exfoliated vermiculite, chemical extraction and pasteurisation. Specific attention is given to large scale microwave activation of biomass for the production of bio-chars and bio-oils.