Jennifer R. Dodson

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.

A Sustainable Freeze-Drying Route to Porous Polysaccharides with Tailored Hierarchical Meso- and Macroporosity

Bio-derived polysaccharide aerogels are of interest for a broad range of applications. To date, these aerogels have been obtained through the time- and solvent-intensive procedure of hydrogel fomation, solvent exchange, and scCO2 drying, which offers little control over meso/macropore distribution. A simpler and more versatile route is developed, using freeze drying to produce highly mesoporous polysaccharide aerogels with various degrees of macroporosity. The hierarchical pore distribution is controlled by addition of different quantities of t-butanol (TBA) to hydrogels before drying. Through a systematic study an interesting relationship between the mesoporosity and t-butanol/water phase diagram is found, linking mesoporosity maxima with eutectic points for all polysaccharides studied (pectin, starch, and alginic acid). Moreover, direct gelation of polysaccharides in aqueous TBA offers additional time savings and the potential for solvent reuse. This finding is a doorway to more accessible polysaccharide aerogels for research and industrial scale production, due to the widespread accessibility of the freeze drying technology and the simplicity of the method.

Supported palladium nanoparticles synthesized by living plants as a catalyst for Suzuki-Miyaura reactions.

The metal accumulating ability of plants has previously been used to capture metal contaminants from the environment; however, the full potential of this process is yet to be realized. Herein, the first use of living plants to recover palladium and produce catalytically active palladium nanoparticles is reported. This process eliminates the necessity for nanoparticle extraction from the plant and reduces the number of production steps compared to traditional catalyst palladium on carbon. These heterogeneous plant catalysts have demonstrated high catalytic activity in Suzuki coupling reactions between phenylboronic acid and a range of aryl halides containing iodo-, bromo- and chloro- moieties.

Alkali silicates and structured mesoporous silicas from biomass power station wastes: the emergence of bio-MCMs

The waste ashes from a commercial biomass combustion facility are successfully converted into mesoporous structured silica utilising a biorefinery approach, with potential high value applications in catalysis, adsorption and separation processes. Potassium silicate solutions are formed via a simple hydrothermal extraction of miscanthus bottom ashes, rich in amorphous silica, with a reproducible extraction of 60–70%. The extension and validation of a rapid and facile infrared method for the quantification of the silicate solutions is demonstrated with important industrial applications for continuous online screening and tuning of the silicate solution ratio and concentration. The alkali solutions from the waste ashes are used for the formation of a structured high surface area mesoporous silica, MCM-41 (1043 m2 g−1, 1.12 cm3 g−1). The resulting mesoporous silica was analysed by XRD, N2 adsorption porosimetry and TEM.

The chemical value of wheat straw combustion residues

Considerable mineralogical changes occur during the combustion of biomass such as wheat straw, which lead to variation in the physical, chemical and textural properties of the ashes formed. Mineralogical and chemical changes occur above combustion temperatures of 500 °C causing reductions in the solubility of potassium, chloride, silica and sulfate. This can be directly correlated to the evaporation of KCl, dissociation of K2SO4, softening of silica and formation of alkali silicates. Calcium extraction increased above combustion temperatures of 700 °C due to the decomposition of CaCO3. We have discovered, for the first time, that the inherent alkali in unleached wheat straw is sufficient to solubilise up to 30% of the silica in the ash at room temperature. This could be used to produce potassium silicate solution as a new valuable by-product of wheat straw combustion. It was also found that incomplete combustion at high temperatures, following leaching of ashes can lead to the formation of porous activated carbons and inorganic materials, demonstrating yet another valuable use for this waste material.

Green Acetylation of Solketal and Glycerol Formal by Heterogeneous Acid Catalysts to Form a Biodiesel Fuel Additive

A glut of glycerol has formed from the increased production of biodiesel, with the potential to integrate the supply chain by using glycerol additives to improve biodiesel properties. Acetylated acetals show interesting cold flow and viscosity effects. Herein, a solventless heterogeneously catalyzed process for the acetylation of both solketal and glycerol formal to new products is demonstrated. The process is optimized by studying the effect of acetylating reagent (acetic acid and acetic anhydride), reagent molar ratios, and a variety of commercial solid acid catalysts (Amberlyst-15, zeolite Beta, K-10 Montmorillonite, and niobium phosphate) on the conversion and selectivities. High conversions (72-95%) and selectivities (86-99%) to the desired products results from using acetic anhydride as the acetylation reagent and a 1:1 molar ratio with all catalysts. Overall, there is a complex interplay between the solid catalyst, reagent ratio, and acetylating agent on the conversion, selectivities, and byproducts formed. The variations are discussed and explained in terms of reactivity, thermodynamics, and reaction mechanisms. An alternative and efficient approach to the formation of 100% triacetin involves the ring-opening, acid-catalyzed acetylation from solketal or glycerol formal with excesses of acetic anhydride.

Direct synthesis of Pd nanoparticles on alginic acid and seaweed supports

The direct synthesis of Pd catalysts using biosorption onto alginic acid and seaweed supports has been successfully achieved. The materials were carbonised to 300 °C and tested in C–C coupling reactions. The heating rate used during the stabilisation of the material had a direct effect on the activity of the catalyst with slower heating rates resulting in increased rates of reaction. Over 120 minutes the alginic acid catalysts achieved an 81% yield for the Heck reaction of iodobenzene with methyl acrylate. Both the seaweed and alginic acid catalysts were successfully reused 2 and 3 times respectively and demonstrated a significant improvement over Pd on carbon 1 wt% (Pd/C) which was not reusable. Overall, this work has shown that active nanoparticles of Pd could be produced using sustainable raw materials and green chemical processes. Such methods may open new doors for future metal capture and use.

Shaped mesoporous materials from fresh macroalgae

Reproducible highly mesoporous monolithic materials (0.5–0.7 cm3 g−1, 9–15 nm) are prepared from a variety of fresh shaped abundant macroalgae using a simple green approach without the necessity for supercritical carbon dioxide (scCO2) drying. This opens up the possibility for low cost and sustainable structured materials for chromatography, catalyst supports and drug delivery systems.

Ring opening metathesis polymerisation of a new bio-derived monomer from itaconic anhydride and furfuryl alcohol

A new oxa-norbornene bio-based lactone obtained from the 100% atom economic reaction of furfuryl alcohol and itaconic anhydride via a tandem Diels–Alder addition and lactonisation is presented. Esterification of the resulting acid gives a monomer for the production of a bio-based polymer with low polydispersity and well controlled molecular weight via ring-opening metathesis polymerisation (ROMP).

Glycerol acetals with antioxidant properties

Abstract Glycerol acetals were prepared from glycerol and aromatic aldehydes (benzaldehyde, anisaldehyde, or furfural) using a solid acid (Amberlyst-15) catalyst. The acetals show promising antioxidant activity using the DPPH test with the glycerol/anisaldehyde acetal showing the best antioxidant properties, attributed to the additional radical stabilization by the electron-releasing methoxy group. The acetals formed have a wide range of potential industrial applications particularly enabling integration of the biodiesel manufacturing chain.