Juliana M. Prado

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.

Extraction Kinetics and Anethole Content of Fennel (Foeniculum vulgare) and Anise Seed (Pimpinella anisum) Extracts Obtained by Soxhlet, Ultrasound, Percolation, Centrifugation, and Steam Distillation

Foeniculum vulgare (fennel) and Pimpinella anisum (anise) extracts were obtained by Soxhlet, cold percolation, ultrasound assisted extraction, and centrifugal extraction using ethanol as solvent; anise extracts were also obtained by steam distillation. Soxhlet presented the highest yields for both fennel and anise seed (16.8% and 23.3%, respectively). The highest anethole content among ethanolic extracts was obtained for centrifugal extraction (6.8 mg/g and 143 mg/g for fennel and anise extracts, respectively). Steam distillation presented low yield (0.26%), but high anethole content (68–98%, area). Anise ethanolic extracts also tested positive for flavonoids.

CHAPTER 12:Economic Evaluation of Natural Product Extraction Processes

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.

Supercritical Fluid Extraction Of Lemon Verbena (Aloysia triphylla): Process Kinetics and Scale-Up, Extract Chemical Composition and Antioxidant Activity, and Economic Evaluation

The extract of lemon verbena ( Aloysia triphylla ) was obtained by supercritical fluid extraction (SFE) using laboratory and pilot scale equipments. The scale-up criterion selected (maintaining solvent to feed ratio constant) was successfully used for a 14-fold scale-up. The extract obtained in pilot scale was separated in three fractions, which were characterized as for their phytochemical profile, total flavonoids content, and antioxidant activity. The extracts obtained by SFE were compared to classical Soxhlet extraction method. Maximum yield obtained for SFE was 1.8%, and for Soxhlet, 7.1%. The chemical composition revealed different phytochemical profiles for SFE and Soxhlet extracts; the last ones presented more flavonoids, while SFE extracts were more concentrated in volatile compounds. The major compounds identified in the volatile fraction of the extracts were spathulenol, phytol and octadecatrienal. Some extracts presented pro-oxidant activity and others presented antioxidant activity. The SFE process was shown to be economically feasible for obtaining lemon verbena extracts; the minimum manufacturing cost (COM) obtained was US

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

1070.00/kg, with a payback time of 2 years.

CHAPTER 2:Extraction of Natural Products: Principles and Fundamental Aspects

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.

Chapter 17 – Biomass Pretreatment With Carbon Dioxide

In this chapter, the principles and fundamental aspects of the extraction of bioactive compounds from natural products are discussed in detail. Conventional extraction techniques like soaking, Soxhlet and distillation with water and/or steam are presented, and their applications in the extraction of bioactive compounds from natural sources are discussed. The main variables that influence the conventional extraction techniques (solvent choice, temperature, time, solvent to feed ratio) are also discussed. Moreover, examples of different application are presented, mainly related to the effects of process parameters in the final yield.

Chapter 6 – Conventional extraction

This chapter presents a literature review of biomass pretreatments that make use of carbon dioxide. Two supercritical technologies are considered: supercritical carbon dioxide explosion and sub/supercritical water hydrolysis with carbon dioxide. The main advantages presented by both techniques are the short time and improved sugar yield. Nonetheless, they are still under development and need further optimization, along with studies on economics, before they can become feasible at the industrial level.

Scale-Up Issues and Cost of Manufacturing Bioactive Compounds by Supercritical Fluid Extraction and Ultrasound Assisted Extraction

Traditional extraction technologies, such as solvent extraction and steam distillation, have been used for the recovery of natural extracts from plant and animal sources for a long time. These extracts have mainly been used as food additives and medicines. Later, other more efficient and environmentally friendly methods like enzyme-, ultrasound-, and microwave-assisted extraction, and supercritical fluid extraction were developed. Following the tendency of modern society to decrease pollution, recovery of bioactive compounds from food wastes is an alternative option that adds value to such residues and at the same time decreases their environmental footprint. In this chapter, the use of well-established extraction technologies to recover bioactive compounds from food industry wastes is presented.