Tânia Forster-Carneiro

Subcritical and supercritical technology for the production of second generation bioethanol

Abstract There is increased interest in reducing our reliance on fossil fuels and increasing the share of renewable raw materials in our energy supply chain due to environmental and economic concerns. Ethanol is emerging as a potential alternative to liquid fuels due to its eco-friendly characteristics and relatively low production costs. As ethanol is currently produced from commodities also used for human and animal consumption, there is an urgent need of identifying renewable raw materials that do not pose a competitive problem. Lignocellulosic agricultural residues are an ideal choice since they can be effectively hydrolyzed to fermentable sugars and integrated in the context of a biorefinery without competing with the food supply chain. However, the conventional hydrolysis methods still have major issues that need to be addressed. These issues are related to the processing rate and generation of fermentation inhibitors, which can compromise the quality of the product and the cost of the process. As the knowledge of the processes taking place during hydrolysis of agricultural residues is increasing, new techniques are being exploited to overcome these drawbacks. This review gives an overview of the state-of-the-art of hydrolysis with subcritical and supercritical water in the context of reusing agricultural residues for the production of suitable substrates to be processed during the fermentative production of bioethanol. Presently, subcritical and/or supercritical water hydrolysis has been found to yield low sugar contents mainly due to concurrent competing degradation of sugars during the hydrothermal processes. In this line of thinking, the present review also revisits the recent applications and advances to provide an insight of future research trends to optimize on the subcritical and supercritical process kinetics.

CHAPTER 1:Uses and Applications of Extracts from Natural Sources

Scientific knowledge about the use of natural products with functional properties, consumer demand for high‐quality products, as well as legislative actions to reduce the use of synthetic food additives have led to an increase in the use of products from natural sources. This chapter aims to provide context information about the potential commercial uses of extracts from natural sources obtained by various extraction techniques, illustrating their importance in industry and identifying the scope of the techniques and aspects discussed in the following chapters. The main commercial applications of extracts from natural sources discussed here comprise their use as colorants, functional food, nutraceuticals, flavors and fragrances, preserving agents, and edible/non‐edible oils and fats applied to cosmetic, pharmaceutical and food industries. However, due to their nature, natural products are complex and therefore several aspects must be considered for each application, including importance, chemical characteristics of main compounds present and possible mechanisms of action.

Obtaining bixin from semi-defatted annatto seeds by a mechanical method and solvent extraction: Process integration and economic evaluation

This work involves the application of physical separation methods to concentrate the pigment of semi-defatted annatto seeds, a noble vegetal biomass rich in bixin pigments. Semi-defatted annatto seeds are the residue produced after the extraction of the lipid fraction from annatto seeds using supercritical fluid extraction (SFE). Semi-defatted annatto seeds are use in this work due to three important reasons: i) previous lipid extraction is necessary to recovery the tocotrienol-rich oil present in the annatto seeds, ii) an initial removal of the oil via SFE process favors bixin separation and iii) the cost of raw material is null. Physical methods including i) the mechanical fractionation method and ii) an integrated process of mechanical fractionation method and low-pressure solvent extraction (LPSE) were studied. The integrated process was proposed for processing two different semi-defatted annatto materials denoted Batches 1 and 2. The cost of manufacture (COM) was calculated for two different production scales (5 and 50L) considering the integrated process vs. only the mechanical fractionation method. The integrated process showed a significantly higher COM than mechanical fractionation method. This work suggests that mechanical fractionation method is an adequate and low-cost process to obtain a rich-pigment product from semi-defatted annatto seeds.

The study of model systems subjected to sub- and supercritical water hydrolysis for the production of fermentable sugars

Bioenergy obtained from lignocellulosic biomass is considered the most efficient way to achieve sustainable development in the future. However, there still are challenges in the cellulose conversion to hexoses, which could be used as raw material for the bioenergy production. Sub- and supercritical water hydrolysis have been researched as emergent technologies to obtain simple sugars from lignocellulosic biomass; however, the reaction pathways and kinetics of the hydrolysis of cellulose into oligomers and monomers, and their degradation under sub- and supercritical conditions, are not completely understood yet. Thus, this review provides an overview of the state-of-the-art on hydrolysis with sub- and supercritical water of model systems, cellulose and starch, in the context of elucidating the reaction pathways and kinetic behavior of the biomass hydrolysis to produce suitable fermentation substrates for the production of second generation bioethanol and other biofuels.

Anaerobic Digestion and Biogas Production: Combine Effluent Treatment with Energy Generation in UASB Reactor as Biorefinery Annex

The issue of residues and industrial effluents represents an unprecedented environmental challenge in terms of recovery, storage, and treatment. This work discusses the perspectives of treating effluents through anaerobic digestion as well as reporting the experience of using an upflow anaerobic sludge blanket (UASB) reactor as biorefinery annex in a pulp and paper industrial plant to be burned in the boilers. The performance of the reactors has shown to be stable under considerable variations in load and showed a significant potential in terms of biogas production. The reactors UASB treated 3600.00 m3 of effluent daily from a production of 150.00 tons. The biogas generation was 234.000 kg/year/mill, equivalent in combustible oil. The results of methane gas generated by the anaerobic system UASB (8846.00 kcal/m3) dislocate the equivalent of 650.0 kg of combustible oil (10000.00 kcal/kg) per day (or 234.000 kg/year). The production of 8846.00 Kcal/m3 of energy from biogas can make a run at industrial plant for 2 hours. This substitution can save US

A review of research trends in the enhancement of biomass-to-hydrogen conversion

128.700 annually (or US

Start-up phase of a two-stage anaerobic co-digestion process: hydrogen and methane production from food waste and vinasse from ethanol industry

550.0 of fuel oil/tons). The companies are invested in the use of the biogas in diesel stationary motors cycle that feed the boilers with water in case of storage electricity.

Formation of an external char layer during subcritical water hydrolysis of biomass

Different types of biomass are being examined for their optimum hydrogen production potentials and actual hydrogen yields in different experimental set-ups and through different chemical synthetic routes. In this review, the observations emanating from research findings on the assessment of hydrogen synthesis kinetics during fermentation and gasification of different types of biomass substrates have been concisely surveyed from selected publications. This review revisits the recent progress reported in biomass-based hydrogen synthesis in the associated disciplines of microbial cell immobilization, bioreactor design and analysis, ultrasound-assisted, microwave-assisted and ionic liquid-assisted biomass pretreatments, development of new microbial strains, integrated production schemes, applications of nanocatalysis, subcritical and supercritical water processing, use of algae-based substrates and lastly inhibitor detoxification. The main observations from this review are that cell immobilization assists in optimizing the biomass fermentation performance by enhancing bead size, providing for adequate cell loading and improving mass transfer; there are novel and more potent bacterial and fungal strains which improve the fermentation process and impact on hydrogen yields positively; application of microwave irradiation and sonication and the use of ionic liquids in biomass pretreatment bring about enhanced delignification, and that supercritical water biomass processing and dosing with metal-based nanoparticles also assist in enhancing the kinetics of hydrogen synthesis. The research areas discussed in this work and their respective impacts on hydrogen synthesis from biomass are arguably standalone. Thence, further work is still required to explore the possibilities and techno-economic implications of combining these areas for developing robust and integrated biomass-to-hydrogen synthetic schemes.

Correction to: Characterization and analysis of specific energy consumption in the Brazilian agricultural sector

The start-up conditions of mesophilic anaerobic co-digestion of restaurant food waste and vinasse, a waste from sugarcane industry, was investigated for efficient biogas production. A pilot plant, containing two reactors, was designed and used sequentially and semi-continuously for biogas production. All effective operational parameters were controlled in both reactors over the course of the study. The results indicated that the organic matters were quickly decreased during the start-up phase in the first reactor, resulting in 52% and 64% reduction in total solids and total volatile solids, respectively, while the corresponding reductions in the methanogenic reactor were 39.7% and 51.4%. The production of hydrogen was observed during the first 20 d of digestion, where the maximum concentration of 76.5% was detected after 8 d when the pH stood at 5.96. After 21 d of digestion, hydrogen concentration was decreased to less than 4.5%, while methane content was increased leading to an accumulated biogas yield of over 300 mL per g of total volatile solids. The high concentration of hydrogen in biogas was possibly due to the improvement in the growth of acidogenic bacteria in response to maintaining pH at their optimum value, leading to a more efficient organic residues hydrolysis.

Characterization and analysis of specific energy consumption in the Brazilian agricultural sector

Flow-through subcritical water hydrolysis (FT-SWH) consists of flowing hot liquid water over a fixed bed packed with biomass particles to produce fermentable carbohydrates and other valuable small molecules. In this work, we studied FT-SWH of green coffee powder as a model lignocellulosic feed, investigating temperatures in the range from 150 to 250 °C and 22.5 MPa. Batch SWH was performed as a basis of comparison for the FT-SWH tests. The focus of the study was characterization of the treated solids; specifically, bulk (primarily thermogravimetric analysis, TGA) and surface (both attenuated total reflectance infrared Fourier transform spectroscopy, ATR-FTIR, and Raman microscopy) methods were used to investigate the hemicellulose, cellulose, and lignin content of the solids. Bulk analysis indicated that the solids treated under FT-SWH conditions retained substantial holocellulose content, even when treated under the most aggresisve FT-SWH conditions studied here (250 °C). On the other hand, surface analysis indicated that the treated materials were primarily composed of char, with the surface content of bound carboxylic acids also increasing with increasing hydrolysis temperature. To understand the apparent discrepancy between bulk and surface analysis, the cross sections of the treated samples were analyzed using both FTIR and Raman microscopy. These techniques confirmed that the surface consisted of a char material, whereas the particle interior was primarily holocellulose. Formation of the external char layer seems to prevent hydrolysis of the internal holocellulose, limiting sugar yields. In comparison with FT-SWH, batch SWH at a similar severity factor resulted in reduced sugar yields, decreased the onset temperature for formation of detectable char quantities, and increased char formation. Comparison with batch conditions suggests that flow conditions reduce external char formation but do not prevent it. This study explains the benefits of FT-SWH and inform development and refinement of pretreatment technologies that can reduce char formation rates.