Integrating Green Chemistry and Sustainable Engineering

Shahid Ul Islam, Shahid Ul-Islam

• Publisher: Wiley-Scrivener
• Year: 2019
• ISBN:
  9781119509820
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

This groundbreaking book covers the recent advances in sustainable technologies and developments, and describes how green chemistry and engineering practices are being applied and integrated in various industrial sectors.

Over the past decade, the population explosion, rise in global warming, depletion of fossil fuel resources and environmental pollution have been the major driving force for promoting and implementing the principles of green chemistry and sustainable engineering in all sectors ranging from chemical to environmental sciences. It plays a growing role in the chemical processing industries. Green chemistry and engineering are relatively new areas focused on minimizing generations of pollution by utilizing alternative feedstocks, developing, selecting, and using less environmentally harmful solvents, finding new synthesis pathways, improving selectivity in reactions, generating less waste, avoiding the use of highly toxic compounds, and much more.

In an effort to advance the discussion of green chemistry and engineering, this book contains 19 chapters describing greener approaches to the design and development of processes and products.

The contributors describe the production of third generation biofuels, sustainable and economic production of hydrogen by water splitting using solar energy, efficient energy harvesting, mechanisms involved in the conversion of biomass, green nanocomposites, bio-based polymers, ionic liquids as green solvents, sustainable nitrogen fixation, bioremediation, and much more.

The book aims at motivating chemists and engineers, as well as postgraduate and PhD students and postdocs to pay attention to an acute need for the implementation of green chemistry principles in the field of chemical engineering, biomedical engineering, agriculture, environmental engineering, chemical processing and material sciences.

Chapter 1
Third Generation Biofuels: A Promising Alternate Energy Source

Mushtaq Ahmad Rather^1,* and Parveena Bano²

¹Associate Professor, Chemical Engineering Department, National Institute of Technology (NIT) Srinagar Kashmir

²Assistant Professor, SKUAST-K, Srinagar Kashmir, Shalimar, India

*Corresponding author: [email protected]

Abstract

Global energy demand is projected to increase by at least 50 % by 2030. Fossil fuels available at present cannot catch-up the current demand. Continuous use of fossil fuels for energy purposes has caused devastating effects to our environment due to greenhouse gas emissions. Thus search for ‘clean energy’ or green and sustainable renewable energy as an alternative to fossil fuels is the need of hour. Green and sustainable renewable energy sources are important to foster a transition towards more sustainable energy availability. Among the several alternatives available at present, biofuels have attracted huge attention. Use of biofuels provides environmental benefits by decreasing the harmful emissions of gases like CO₂, SO_x etc. Biofuels have attracted intense debate from a variety of perspectives, including societal, economic, and environmental. First-generation biofuels are made from sugars, starch and vegetable oils, so have an impact on the food security. Second generation biofuels generated from plant material may lead to felling of trees and shrubs. Biofuels generated from non-food crops like microalgae and macroalgae are referred to as third generation biofuels, have great potential to meet part of future global energy demand without making any compromise with human food security. In the present chapter, we present a review of recent research interests in the different aspects of production of third generation biofuels by hydrothermal conversion, one of the thermal conversion routes.

Keywords: Hydrothermal conversion, biofuels, energy, biomass

1.1 Introduction

Fossil fuels have been primary source of energy for centuries now. However their fast depletion and associated harmful effects on the climate (by increasing the atmospheric green house gas emissions), has led to search for ‘clean energy’. To tackle the problem, environmentally friendly alternate sources of energy are being harnessed. Some of the options of clean energy sources available are solar, wind, tidal and biomass. Utilization of biomass in various transformed forms has proved to be an adequate way-out for meeting the part of global energy demand [1]. Various forms of biomass in nature are wood, vegetation, crops, aquatic plants and algae etc. Biomass can be transformed into a versatile fuel referred to as biofuel, being studied and implemented universally nowadays. Study of biofuels has transformed into an area of complex interest and debate from various reasons including societal, economic, and environmental. Biofuels are renewable fuels, having potential to decrease several harmful emissions such as soot, carbon monoxide, and carbon dioxide [2]. Among the main biofuel producing countries in world for transportation, USA and UE have taken lead and already set specific targets for future.USA has planned to substitute 20% of road transport fuel with biofuel by 2022, while UE has adopted 10% as a goal of biofuel for transport energy by 2020 [3].

Green and sustainable renewable energy sources are important to foster a transition towards more sustainable energy availability. Biomass can be used to produce and substitute fossil fuels in many choices, to replace the petrochemical compounds. As oil is processed in a refinery to fuels, and chemicals; the “biorefinery” concept is equivalent to an oil refinery because biomass is transformed into various products, ranging from chemicals to biofuels [4].

Biofuels are made through the conversion of biomass in three different ways; thermal conversion, chemical conversion and biochemical conversion. The resulting biofuel can be produced in solid, liquid or a gaseous form.

Microalgae can be converted to biofuels mainly by two routes viz. biochemical fermentation (anaerobic digestion) and thermo chemical processes. Thermochemical processes include gasification, pyrolysis and hydrothermal processing. Gasification involves the partial controlled oxidation of organic material to syngas. Syngas contains CO, H₂ and CO₂. Apart from direct combustion, the other promising application of syngas is its conversion to synthetic gas which later can be converted to liquid fuel (GTL), by the Fisher-Tropsch process. Above converts H₂ and CO to straight chain liquid hydrocarbons which are suitable renewable substitute to petroleum derived diesel fuel. Pyrolysis refers to the thermal decomposition of feedstocks in the absence of air. The process drives off the moisture and volatiles, improves the handling properties and increases the carbon content of a fuel. At temperatures up to 300 °C the process is known as torrefaction which is being increasingly used to process biomass to a more suitable solid fuel for co-combustion with coal. At higher temperatures the product distribution favours the production of liquid bio oil, a highly oxygenated, acidic liquid resembling crude oil.

Pyrolysis in the presence of subcritical liquid water is called hydrothermal conversion (HT) [5]. The process generates both solid and liquid biofuels. The process may be referred to as hydrothermal carbonization (HTC) or hydrothermal liquefaction (HTL) based up on whether solid or liquid product respectively, has been emphasized in the generation process. The solid fuel generated in HT conversion is referred to as hydrochar (biochar) and liquid product as bio-crude or bio oil.

Hydrothermal conversion involves the reaction of biomass in water at high temperature and pressure with or without the catalyst. The hydrothermal processing of biomass was investigated by Shell research in the 1980s [6]. Hydrothermal processing of lignocellulosic biomass has received extensive attention over the last two decades for production of solid fuels, liquid fuels (subcritical conditions) and for gaseous fuels (supercritical conditions) [7, 8].

A non hydrothermal energy conversion pyrolysis process of biomass requires its prior drying. Prior drying of biomass necessitates expensive and energy intensive dewatering and drying steps for processing of aquatic weeds and microalgae, which have enormous amounts of water accompanied with them. An alternative route is to convert the aquatic biomass into biofuels in the aqueous phase itself, thereby obviating biomass drying. A simple comparison of the enthalpies of liquid water at 350 °C and water vapor at 50 °C (i.e., drying the biomass) indicates that processing in liquid water saves 921 kJ/kg. Hot compressed liquid water near its thermodynamic critical point (T_c = 373.95 °C, P_c = 22.064 MPa) behaves very differently from liquid water at room temperature. As water is heated along its vapor–liquid saturation curve, its dielectric constant decreases due to the hydrogen bonds between water molecules being fewer and less persistent. The reduced dielectric constant enables hot compressed water to solvate small organic molecules, allowing organic reactions to occur in a single fluid phase. Additionally, the ion product of water increases with temperature up to about 280 °C, but then decreases as the critical point is approached. This higher ion product leads to higher natural levels of hydronium ions in hot compressed water, which can accelerate the rates of acid-catalyzed hydrolytic decomposition reactions [9]. Hydrothermally processing wet biomass can produce a hydrochar that retains a large proportion of the chemical energy and lipids in the original biomass. These char-bound lipids can be reacted with alcohol to produce biodiesel. At same time processing of wet aquatic biomass also produces crude bio-oil. Figure 1.1 given above presents a general schematic diagram of a hydrothermal conversion reactor used to produce the third generation biofuels.

Figure 1.1 Schematic diagram of a hydrothermal conversion reactor.

Biomass consists primarily of proteins, carbohydrates, and lipids; the principal role of hydrothermal conversion is to decompose the biomacromolecules into smaller molecules that can then be further treated, if desired, to produce specific fuels.

The hydrothermal environment promotes the hydrolytic cleavage of ester linkages in lipids, peptide linkages in proteins, and glycosidic ether linkages in carbohydrates. These cleavage reactions can be accelerated by catalysts [9].

Cellulose is not soluble in water at standard conditions, but starts dissolving at 180 °C and completely dissolves around 330 °C. Due to amorphous structure, hemicellulose is easily hydrolyzed in waters at temperatures above 160 °C to monomers, which could be, at acid water conditions further transformed into chemicals. Lignin is chemically most resistant component of lignocelluloses. Dissolution and hydrolysis to monomers starts in near and supercritical water [10]. Homogenous catalysts like Na₂CO₃, K₂CO₃, NaOH, KOH, HCOOH, CH₃COOH, zeolite have received attention for hydrothermal conversion. Recently some common heterogeneous catalysts have also been studied [9].

Present chapter gives an exhaustive overview of different biofuel types, advantages of third generation biofuels and the technology involved in their production. Fur...

Table of contents

• Cover
• Title page
• Copyright page
• Preface
• Chapter 1: Third Generation Biofuels: A Promising Alternate Energy Source
• Chapter 2: Recent Progress in Photocatalytic Water Splitting by Nanostructured TiO2-Carbon Photocatalysts – Influence of Interfaces, Morphological Structures and Experimental Parameters
• Chapter 3: Heterogeneous Catalytic Conversion of Greenhouse Gas CO2 to Fuels
• Chapter 4: Energy Harvesting: Role of Plasmonic Nanocomposites for Energy Efficient Devices
• Chapter 5: Catalytic Conversion of Biomass Derived Cellulose to 5-Hydromethyl Furfural
• Chapter 6: Raman “Green” Spectroscopy for Ultrasensitive Analyte Detection
• Chapter 7: Microwave Synthesized Conducting Polymer-Based Green Nanocomposites as Smart Promising Materials
• Chapter 8: Biobased Biodegradable Polymers for Ecological Applications: A Move Towards Manufacturing Sustainable Biodegradable Plastic Products
• Chapter 9: Cashew Nut Shell Liquid (Phenolic Lipid) Based Coatings: Polymers to Nanocomposites
• Chapter 10: Ionic Liquids as Potential Green Solvents Their Interactions with Surfactants and Antidepressant Drugs
• Chapter 11: Role of Green and Integrated Chemistry in Sustainable Metallurgy
• Chapter 12: Biological Nitrogen Fixation and Biofertilizers as Ideal Potential Solutions for Sustainable Agriculture
• Chapter 13: Natural Products in Adsorption Technology
• Chapter 14: Role of Microbes in the Bioremediation of Toxic Dyes
• Chapter 15: Valorization of Wastes for the Remediation of Toxicants from Industrial Wastewater
• Chapter 16: Wound Healing Potential of Natural Polymer: Chitosan “A Wonder Molecule”
• Chapter 17: Nanobiotechnology: Applications of Nanomaterials in Biological Research
• Chapter 18: Biotechnology: Past-to-Future
• Chapter 19: Biogenic Nanoparticles as Theranostic Agents: Prospects and Challenges
• Index
• End User License Agreement