Understanding Microwave Heating in Biomass-Solvent Systems

A new mechanism is proposed to provide a viable physical explanation for the action of microwaves in solvent extraction processes. The key innovation is Temperature-Induced Diffusion, a recently-demonstrated phenomenon that results from selective heating using microwaves. A mechanism is presented which incorporates microwave heating, cellular expansion, heat transfer and mass transfer, all of which affect the pressure of cell structures within biomass. The cell-pressure is modelled with time across a range of physical and process variables, and compared with the expected outputs from the existing steam-rupture theory. It is shown that steam-rupture is only possible at the extreme fringes of realistic physical parameters, but Temperature-Induced Diffusion is able to explain cell-rupture across a broad and realistic range of physical parameters and heating conditions. Temperature-Induced Diffusion is the main principle that governs microwave-assisted extraction, and this paves the way to being able to select processing conditions and feedstocks based solely on their physical properties. Graphical abstract Keywords Microwave processing, heat transfer, mass transfer, plant cell rupture, cellular expansion mechanics, solvent extractio

Current status of microwave-assisted extraction of pectin

There is an urgent need to develop new pectin extraction processes, as the established commercial extraction process damages the pectin (limiting the potential product applications) and is harmful to the environment. Microwave-Assisted Extraction could offer a sustainable route to pectin extraction from a wide range of food wastes and agricultural residues. We present the current state of the art in Microwave-Assisted Extraction of pectin, including the current understanding of the unique heat and mass transfer mechanisms at play during extraction. We review all of the recent literature, testing the commonly held view that microwave heating offers a general improvement in yield and dramatic reductions in processing time compared with conventional solvent extraction. In most of the literature reviewed, there was no evidence that this is the case. However, there is emerging evidence that Microwave-Assisted Extraction can provide processing advantages under some conditions, and that the feedstock dielectric properties and heating rate are important parameters. Preliminary attempts to scale this technology up have shown promise in terms of pectin yield, quality and Life Cycle Analysis compared with conventional extraction. The next steps should be to test more continuous processing concepts for a wider range of feedstocks, and develop more robust Life Cycle Analysis and technoeconomic models. This is the first review paper to focus on the Microwave-Assisted Extraction of pectin

Fast regeneration of activated carbons saturated with textile dyes: Textural, thermal and dielectric characterization

This study presents an investigation for comparing the regeneration process of two activated carbons saturated with Basic Blue 9 (BB9) and Acid Blue 93 (AB93) using conventional (250–500 °C) and microwave heating (100–300 W). The effect of the textile dye used on the regeneration performance was analyzed by determining their dielectric properties using the perturbation cavity method from 20 to 600 °C and by TG/DTG analysis. The efficacy of the regenerated carbons was investigated by their physical properties characterized by pore structural analysis using N2 adsorption isotherms. Results showed only 3 min are required by microwaves to achieve similar textural parameters obtained by conventional heating at 190 min. The results indicate that the adsorbate plays a determining role on the regeneration efficiency as results of their interaction with the adsorbent, being easily regenerated when AB93 is the adsorbate. The adsorption capacity of microwave regenerated samples for AB93 and BB9 was 192–240 and 154–175 mg/g, respectively. Additionally, the equilibrium isotherms were simulated using the Langmuir and Freundlich isotherms models and the results suggest the textile dye removal is achieved on multilayer adsorption

Understanding the influence of processing conditions on the extraction of rhamnogalacturonan-I “hairy” pectin from sugar beet pulp

Sugar beet pectin is rich in rhamnogalacturonan-I (RG-I) region, which is a potential source of prebiotics. RG-I pectin cannot be extracted the same way as commercial homogalacturan-rich pectin using hot acid. Therefore, this study has explored several alternative methods, including microwave-assisted extraction (MAE) and conventional- solvent extraction (CSE) at atmospheric pressure using different solvents, and microwave-assisted hydrothermal extraction (MAHE) under pressure using water. No conclusive differences in microwave and conventional heating were found with heating rate controlled. The optimum treatment times of both MAE and CSE at 90 °C atmospheric pressure and regardless of the solvents used were 120 min; however, MAHE at 130 °C under pressure can dramatically reduce the time to 10 min. Alcohol-insoluble solids (AIS) extracted using pH13 solvent by MAE had both the highest RG-I yield at 25.3% and purity at 260.2 mg/g AIS, followed by AIS extracts using water by MAHE with 7.5% and 166.7 mg/g AIS respectively

Investigating the role of solvent type and microwave selective heating on the extraction of phenolic compounds from cacao (Theobroma cacao L.) pod husk

Cacao pod husk (CPH) is a primary waste in the cacao industry that contains favourable natural antioxidants based on phenolic compounds. This study reported an investigation of the effect of extraction parameters to maximise the bioactive yields of CPH extract. The preliminary extraction was focused on high total phenolic content and continued to maximise the total monomeric anthocyanin and antioxidant activity that have the potential to be applied as food additives. The solvent selection and particle size were the key parameters for extraction to reach the maximum phenolic yield (100.4 ± 0.5 mg GAE/g dw). It was confirmed that 50% (v/v) aqueous ethanol was the most appropriate solvent, either based on experimental results or Hansen Solubility parameter prediction. At the same time, the comparison of microwave and conventional heating suggested that Microwave-assisted Extraction was the best method to get high phenolic content due to its selective heating effects. The results showed that the maximum bioactive yields were 0.37 ± 0.0 mg Cy3GE/g dw of anthocyanin and 3.36 ± 0.02 mg TE/g dw of antioxidants obtained under 50 °C and 5 min extraction time. Gallic acid, catechin, epicatechin, coumaric acid and quercetin were identified in CPH extract using High-Performance Liquid Chromatography

Rapid, simple and sustainable synthesis of ultra-microporous carbons with high performance for CO2 uptake, via microwave heating

A one step microwave pyrolysis-activation method has been developed for the preparation of activated carbons from biomass with high CO2 capture efficiency (5.3 mmol g−1) by employing a low impregnation ratio (1) of KOH and K2CO3. The high microwave susceptibility identified by the dielectric properties enabled the preparation of a series of activated carbons in short processing times (<6 min), and the pyrolysis-activation simultaneously enhanced the formation of ultra-micropores leading to high CO2 uptake at 15 and 100% CO2 in the temperature range of 0–100 °C. The high CO2/N2 selectivity of up to 36 the adsorptive capacities were directly correlated to a pore size of ~0.7 nm, which favoured CO2 uptake up to 5.3 and 4.5 mmol g−1 at 1.1 bar and 0 °C and an uptake of 3.7 and 3.3 at 25 °C for activated samples with KOH and K2CO3, respectively. The activated carbons presented in this study are the first examples of samples that have been prepared by this simple and rapid method, which represents a 96.66% reduction in the processing times in comparison to conventional heating routes, and the CO2 uptake is comparable to the largest reported in literature for activated carbons. The outstanding uptake and selectivity, the simple synthesis using microwave technology in addition to the utilisation of a waste biomass as a carbon precursor, satisfy the requirements for the development of new and more sustainable energy environmental processes

A review on development and application of plant-based bioflocculants and grafted bioflocculants

Flocculation is extensively employed for clarification through sedimentation. Application of eco-friendly plant-based bioflocculants in wastewater treatment has attracted significant attention lately with high removal capability in terms of solids, turbidity, color, and dye. However, moderate flocculating property and short shelf life restrict their development. To enhance the flocculating ability, natural polysaccharides derived from plants are chemically modified by inclusion of synthetic, nonbiodegradable monomers (e.g., acrylamide) onto their backbone to produce grafted bioflocculants. This review is aimed to provide an overview of the development and flocculating efficiencies of plant-based bioflocculants and grafted bioflocculants for the first time. Furthermore, the processing methods, flocculation mechanism, and the current challenges are discussed. All the reported studies about plant-derived bioflocculants are conducted under lab-scale conditions in wastewater treatment. Hence, the possibility to apply natural bioflocculants in food and beverage, mineral, paper and pulp, and oleo-chemical and biodiesel industries is discussed and evaluated

Microwave plasma : pollution reducer or producer?

No abstract available

Design study for the destruction of trichloroethene

The research documented in this paper is being undertaken by IRIS in collaboration with the CRC for Intelligent Manufacturing Systems and Technologies (IMS&T) and HPM. The project commenced in March 2001 and is expected to be completed in 2004. The aim of this research is to develop a novel microwave-induced ioniser capable of neutralising industrial pollution. Chemical modelling has been used to aid in the experimental design. It has shown that the treatment of dilute pollutant mixtures is likely to be possible using this method, whereas the treatment of pure pollutant streams is not desirable