Selective primary alcohol oxidation of lignin streams from butanol-pretreated agricultural waste biomass

We would like to thank the CRITICAT Centre for Doctoral Training for financial support [Ph.D. studentship to IP; Grant code: EP/L016419/1] and BBSRC Global Challenges Research Fund Impact Acceleration Account at St Andrews BB/GCRFIAA/20. CSL thanks the Leverhulme Trust for funding an Early Career Fellowship.Chemically modified lignins are important for the generation of biomass-derived materials and as precursors to renewable aromatic monomers. A butanol-based organosolv pretreatment has been used to convert an abundant agricultural waste product, rice husks, into a cellulose pulp and three additional product streams. One of these streams, a butanol-modified lignin, was oxidized at the γ position to give a carboxylic acid functionalized material. Subsequent coupling of the acid with aniline aided lignin characterization and served as an example of the flexibility of this approach for grafting side chains onto a lignin core structure. The pretreatment was scaled up for use on a multi-kilogram scale, a development that enabled the isolation of an anomeric mixture of butoxylated xylose in high purity. The robust and scalable butanosolv pretreatment has been developed further and demonstrates considerable potential for the processing of rice husks.PostprintPeer reviewe

Conventional and microwave-assisted pyrolysis of biomass under different heating rates

Biomass was subjected to conventional and microwave pyrolysis, to determine the influence of each process on the yield and composition of the derived gas, oil and char products. The influence of pyrolysis temperature and heating rate for the conventional pyrolysis and the microwave power was investigated. Two major stages of gas release were observed during biomass pyrolysis, the first being CO/CO and the second one CH/H. This two-stage gas release was much more obvious for the conventional pyrolysis. While similar yield of liquid was obtained for both cases of conventional and microwave pyrolysis (∼46 wt.%), higher gas yield was produced for the conventional pyrolysis; it is suggested that microwave pyrolysis is much faster. When the heating rate was increased, the peak release of CO and CO was moved to higher reaction temperature for both conventional (500 °C) and microwave pyrolysis (200 °C). The production of CH and H were very low at a conventional pyrolysis temperature of 310 °C and microwave pyrolysis temperature of 200 °C (600 and 900 W). However, at higher heating rate of microwave pyrolysis, clear release of CH was observed. This work tentatively demonstrates possible connections and difference for biomass pyrolysis using two different heating resources (conventional and microwave heating)

CO₂ gasification of bio-char derived from conventional and microwave pyrolysis

Thermal-chemical processing of biomass is expected to provide renewable and clean energy and fuels in the future. Due to the nature of endothermic reactions, microwave and conventional heating have been applied to this technology. However, more studies need to be carried out to clarify the difference between these two heating technologies. In this work, we investigated two bio-char samples produced from conventional pyrolysis of wood biomass (yield of bio-char: 38.48 and 59.70 wt.%, respectively) and one bio-char produced from microwave pyrolysis with a yield of 45.16 wt.% from the same biomass sample at different process conditions. Various methodologies have been used to characterise the bio-chars. CO₂ gasification of bio-char has also been studied using a thermogravimetric analyser (TGA) and a fixed-bed reaction system. The results show that volatile and carbon contents of the bio-char derived from microwave pyrolysis were between the two conventional bio-chars. However, the microwave bio-char is more reactive for CO₂ gasification, as more CO was released during TGA experiments, and the CO release peak was narrower compared with the CO₂ gasification of the conventional bio-chars. It is suggested that the conventional bio-char is less reactive due to the presence of more secondary chars which are produced from secondary reactions of volatiles during the conventional biomass pyrolysis. While the microwave pyrolysis generates more uniform bio-chars with less secondary char, and therefore, has advantages of producing bio-char for downstream char gasification

The use of supported palladium catalysts and other clean chemical technologies in the synthesis of drug molecules

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Influence of Density on Microwave Pyrolysis of Cellulose

Herein we present the influence of sample density on the microwave induced pyrolysis of crystalline cellulose, with heating rate, biochar and bio-oil yields investigated. This Letter demonstrates that sample density is a fundamental parameter influencing microwave-assisted biomass pyrolysis, with a direct impact on heating rate, the speed of volatiles diffusion through the sample matrix and distribution of products. Of significant interest was that the maximum heating rate and bio-oil yield corresponded to an optimum sample density as a result of heat and mass transfer effects. Increase in density above this value stimulated a rise in biochar yield. The increased understanding of the mechanisms influenced by sample density in a microwave field gives increased ability for users to produce bio-oil or biochar, giving rise to improved microwave-based biorefineries for future energy and chemical needs.This work is financially supported by EPSRC for research grant no. EP/K014773/1, the Industrial Biotechnology Catalyst (Innovate UK, BBSRC, EPSRC) to support the translation, development and commercialization of innovative industrial Biotechnology processes (EP/N013522/1). P.S.S. also gratefully acknowledges the Spanish Ministry Economy and Competitivity (MINECO) for a Ramón y Cajal senior research fellowship (RYC-2014-16759) and a proyecto de I+D+I para jóvenes investigadores (MAT2014-59674-JIN)Peer Reviewe

The potential of microwave technology for the recovery, synthesis and manufacturing of chemicals from bio-wastes

Through a series of case studies it is demonstrated that microwave dielectric heating can be a powerfultool to recover and synthesize valuable molecules from a wide range of biomass types. In addition, undermicrowave irradiation the production of chemicals from biomass proceeds at markedly lower temper-atures (up to 150?C) compared to conventional heating. This has a secondary benefit in that moleculeswith a high degree of functionality are produced while conventional heating tends to produce a greatproportion of lower value gases. Furthermore, the technical set-up of a microwave reactor can easilyaccommodate for an in-situ separation of acids and valuable products therewith improving the shelf lifeof the latter. The benefits of combining hydrothermal conditions with microwave irradiation are alsoillustrated. In addition, a specialized case of selective heating in a biphasic reaction system is discussed,allowing for improved yields and selectivity.Peer Reviewe

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.Peer Reviewe

Unravelling the mechanisms of microwave pyrolysis of biomass

This study uses empirical observations and mass transfer simulations to establish a new mechanism for microwave pyrolysis of biomass. Experiments were conducted on cellulose and hemicellulose, using microwave equipment that could vary the observed heating rate. No microwave-absorbing additives were used. At high heating rates it is shown categorically that microwave pyrolysis can significantly reduce the pyrolysis temperatures for hemicellulose and cellulose, but when microwave heating is used to deliver a low heating rate the pyrolysis behaviour is identical to that obtained with conventional heating. Dielectric properties are shown to vary by over an order of magnitude depending on the heating rate. The implications of heating rate on mass transfer and phase behaviour are developed and discussed within the paper, with liquid-phase water identified as a key driver for the observed differences in the microwave pyrolysis process. This is the first study in microwave pyrolysis that is able to reconcile microwave heating phenomena against simple and well-understood mass transfer and phase equilibria effects. As a result, a number of processing strategies have emerged with the potential to use microwave heating to enable more selective pyrolysis and bio-oils with more targeted quality than has been possible with conventional approaches