Higher Alcohols Production Platforms: From Strain Development to Process Design

Higher Alcohols Production Platforms: From Strain Development to Process Design comprehensively covers the production of higher alcohols, from the fundamentals to the latest research. Bringing together experts from industry and academia, the book sheds light on the practical aspects of higher alcohol production and offers a roadmap for researchers to follow. In addition to the fundamentals of higher alcohol production, readers are presented with detailed information on up and downstream processes, including microbial processes and the various production pathways available. A discussion of metabolic pathways has a dedicated chapter, as do C2, C3-C8, and C4 sugar fermentation platforms.

A lifecycle assessment is also presented, addressing the energy, environmental, social and economic factors in the sustainability of higher alcohol production. Readers will find this to be a unique and comprehensive reference on the production of higher alcohols that will be of interest to students, researchers and industry professionals involved in bioenergy and renewable energy, and more.

• Provides comprehensive coverage of the energy, environmental and economic aspects of higher alcohols biofuels
• Presents a rational basis for assessing alcoholic products that can be used as a roadmap for their further developments
• Analyzes and synthesizes the latest research and developments on the production of higher alcohols as biofuels for audiences in academia and industry

• Language: English
• Publisher: Academic Press
• Release date: Sep 27, 2023
• ISBN: 9780323986311

Book preview

Preface

Hamid Amiri, Meisam Tabatabaei and Abdul-Sattar Nizami

This book is about higher alcohols ranging from C2 to C8 alcohols and aims to offer a comprehensive overview of the fundamentals and cutting-edge research findings that can provide a big picture of higher alcohols from energy, environmental, and economic points of view. Metabolic pathways for microbial production of higher alcohols are promising bridges between renewable carbohydrate resources and liquid fuels. Higher alcohols’ potential as liquid fuels justifies the vast efforts in developing synthetic pathways for their efficient microbial synthesis. However, despite the high-profile publications on strain development, there is a long way to reach a real-world production scale.

The present book, which is the second book in the series on Biomass and Biofuels, is the result of the collaboration among experienced academics from different disciplines working on cutting-edge research studies. The 10 chapters critically review the strategies for enhanced production of higher alcohols, including potential feedstocks for large-scale production, using metabolic engineering, the industrially utilized sugar and syngas fermentation platforms, and downstream processes for bioalcohol separation. In addition, higher alcohol production plants are scrutinized from the perspective of process design and scale-up as well as their sustainability, including life cycle assessment, life cycle impact assessment, and life cycle costing. In addition, a market analysis of higher alcohols is also presented. Higher alcohol production platforms: from strain development to process design also covers the different features of higher alcohols as liquid fuels, synthetic chemistry reagents, and industrial solvents. The book is intended for researchers, practitioners, and professionals in the fields of industrial biotechnology, green chemistry, synthetic biology, and chemical engineering, especially those with a particular interest in biorefinery platforms and advanced biofuel production. The book’s content will also benefit policy- and decision-makers, as well as industry experts, to scrutinize the different aspects of higher alcohol production and utilization.

The present volume on higher alcohols is expected to contribute to minimizing the gap between theoretical knowledge and practical expertise in different aspects of higher alcohol production from upstream to downstream. We are thankful to the authors of all the chapters for their efficient cooperation and readiness to revise the manuscripts. We also would like to extend our appreciation to the reviewers who assisted us by evaluating the manuscripts and providing their critical comments to improve them. Our sincere thanks to Mrs. Moloud Nohrozian for the captivating book cover illustration. We would like to sincerely thank Dr. Peter Adamson and his team at Elsevier, Ms. Zsereena Rose Mampusti, Mr. Prasanna Kalyanaraman, Ms. Aleksandra Packowska, and Ms. Sharmila Kirouchenadassou, for their cooperation and efforts in producing this book. We are also grateful to Ms. Jai Marie Jose and Ms. Czarina Mae S. Osuyos, who were involved in the earlier stages of the development of this volume.

1

Higher alcohols: applications as fuels and chemicals

Hamid Amiri¹, ², Meisam Tabatabaei³, ⁴ and Abdul-Sattar Nizami⁵,    ¹Department of Biotechnology, Faculty of Biological Science and Technology, University of Isfahan, Isfahan, Iran,    ²Environmental Research Institute, University of Isfahan, Isfahan, Iran,    ³Higher Institution Centre of Excellence (HICoE), Institute of Tropical Aquaculture and Fisheries (AKUATROP), Universiti Malaysia Terengganu, Kuala Nerus, Terengganu, Malaysia,    ⁴Biofuel Research Team (BRTeam), Terengganu, Malaysia,    ⁵Sustainable Development Study Centre, Government College University, Lahore, Pakistan

Abstract

Alcohols have high potential as fuels, solvents, and building blocks for the production of a wide range of chemicals. To become a proper fuel, candidates should pass several assessments based on the physical properties such as density and viscosity and chemical properties such as combustion energy. The primary aliphatic alcohols between C3 and C7, the so-called higher alcohols, have recently attracted interest owing to their possible production from renewable carbohydrate resources through microbial pathways. In this chapter, different features of the higher alcohols are discussed to assess their potential as liquid fuels, reagents in synthetic chemistry, or solvents in industry. The considerable potentials of higher alcohols justify the enormous research efforts on developing synthetic pathways for their efficient microbial synthesis.

Keywords

Higher alcohols; liquid fuel; synthetic chemistry; solvent; energy density

1.1 Introduction

Higher alcohols are those alcohols with more than two carbon atoms such as isoamyl alcohol, propanol, isobutanol, and n-butanol. Traditionally, higher alcohols have been known for their interference in the downstream processing of ethanol and methanol. A mixture of higher alcohols is typically separated in the rectifying columns of ethanol plants as a by-product, which is known as fusel oil, a German term that means inferior or bad spirits. Isoamyl, isobutyl, and n-amyl alcohols are typically the main constituents of fusel oil separated in ethanol plants. The amino acids released from hydrolysis of proteins present in the mash and also the proteins of the cell itself are the main origin of the main constituents of fusel oil [1]. Distillers typically sell fusel oil to other industries for further processing as its discharge into the environment would cause serious environmental problems. Being natural products, these alcohols may have a high commercial value, but their presence generally deteriorates the quality of ethanol. Furthermore, the yield of higher alcohol production in ethanol plants is too low to seriously affect the economy of the process, where only 2.5 L of fusel oil is obtained in the production of each 1000 L of ethanol [2]. However, this is not the whole story of higher alcohols, particularly when their characteristics as liquid fuels are taken into consideration.

The idea of moving beyond ethanol for better liquid biofuels has been first presented in the early 2000s, when the key features of n-butanol as a liquid fuel attracted huge attention. Despite losing its economic attractiveness in its competition with the petrochemical industry in the mid-20th century, the old ABE fermentation, ABE stands for acetone-butanol-ethanol, has been reconsidered for fuel-grade n-butanol production. In 2010, enhanced biological production of isobutanol was patented by Butamax Advanced Biofuels LCC, a 50/50 joint venture between BP and DuPont, opening new windows on the efficient production of higher alcohols with advantageous characteristics. In 2011, Gevo Inc. developed the yeasts for high-yield isobutanol production and established commercial-scale production of isobutanol from kernels in Luverne, Minnesota [3]. Meanwhile, key advances in metabolic engineering like those on Escherichia coli [4] paved the way for higher alcohols.

1.2 Higher alcohols as biofuels

There are several properties of fluid that determine its qualification as a liquid fuel. The boiling point is a key factor of biofuel candidates, particularly for those whose distillation is the main separation approach. The higher boiling point, the higher energy required for separation and purification. Hydrocarbons that have only hydrogen and carbon in their structure compose a major part of the current liquid fuels. Among hydrocarbons, alkanes are saturated structures with the proper characteristics as liquid fuels. Based on the electronegativity scale, developed by Linus Pauling in 1932, carbon (2.55) and hydrogen (2.20) have a slight difference. Therefore, the carbon–hydrogen bonds have only a small dipole, so alkanes are nonpolar molecules with no permanent dipole moment. Alcohols, on the other hand, have oxygen with an electronegativity of 3.44 in their molecules making them polar structures with a permanent dipole moment. Having different intermolecular interactions, alkanes and alcohols with comparable molar mass have different properties, like normal boiling points (Fig. 1.1).

Figure 1.1 Normal boiling point of linear (filled points) or branched (hollow points) alcohols (circle) and alkanes (square) [5]. Source: National Institute of Standards and Technology, 2022.

Alkanes with one to four carbon atoms are in the gas state at room temperature, but even the smallest alcohol, that is, methanol, is in a liquid state (Fig. 1.1). The boiling point is the temperature at which thermally induced motions of molecules become large enough to overcome the attractive forces of molecules. It is an approximate indication of the strength of intermolecular interactions. Alkanes with the weakest intermolecular interaction of London or dispersion forces have significantly lower normal boiling point compared to alcohols with hydrogen bonds which are much stronger. In the case of alkanes, London forces depend on the sixth power of the intermolecular distance, and only very short London forces affect the molecular characteristics [6]. Therefore, the larger a molecule’s surface area of alkanes, the larger polarization of electron cloud and higher boiling point. Furthermore, the heavier molecules require higher thermal energy to acquire velocities large enough to move them from the liquid into the vapor phase. In the case of alcohols, the hydrogen bonds lead to between 100 and130 K higher normal boiling points. Like the shift in the boiling points of alkanes, an alcohol with one more carbon atom in its structure has an approximate 20 K higher normal boiling point. Furthermore, like branched alkanes, the branched alcohols have lower boiling points compared to the linear molecules with comparable molecular mass (Fig. 1.1).

Adoption of the extra CH2– group in the three-dimensional configuration of a higher alcohol leads to a nonproportional increase in specific gravity (Fig. 1.2). For example, 1-propanol with over 30% higher molecular mass compared to ethanol has a 1.7% higher specific gravity. Density is an important factor of liquid fuels because the amount of fuel that can be carried on vehicles is delimited by volume and not by mass. The molecular disordered configurations in liquids such as coiling, tangling, or bending of the chains of carbon atoms due to the freedom of motion in liquids lead to the further closeness of the molecules. Considering density as the number of molecules that can be packed into a given volume, the molecular shape is also a key factor besides the molecular volume. Comparing the specific gravity of 1-pentanol, 2-methyl-1-butanol, and 3-methyl-1-butanol as C5 alcohols with the same atoms but different arrangements, it can be concluded that the position of the methyl group determines the efficiency of packing. The same can be concluded for 1-hexanol, 3-methyl-1-pentanol, and 4-methyl-1-pentanol.

Figure 1.2 Specific gravity of linear (filled points) and branch-chained (hollow points) higher alcohols. Source: National Institute of Standards and Technology, 2022.

The viscosity is another important property of liquids affecting their flow pattern and particularly pumping conditions [7]. In the case of liquid fuels, the concerns about their viscosity are more crucial than just pumping problems. Both high and low viscosities may negatively affect engine performance. With high viscosities, we are faced fuel with poor atomization, large droplets, and high spray jet penetration, where we have a solid stream instead of a spray of small droplets. In this condition, improper mixing with air leads to poor combustion and loss of energy. Furthermore, in the case of small engines, the lubricating oil film might be washed away due to the contact of improperly sprayed fuel with the cylinder wall intensifying the wear problems. On the other hand, fuels with too low viscosities form a soft spray and do not penetrate far enough to properly mix with air [7]. Furthermore, low viscosity can lead to problems such as excessive leakage of fuel, inaccurate metering of it, reduced engine efficiency, and excessive wear of the engine by reducing the lubricity of the fuel.

Higher alcohols have viscosities higher than the viscosities of gasoline and diesel, which are 0.6 and 1.352 mPa.S at 25°C, respectively. The friction loss due to the pumping of the fluids is directly proportional to their viscosity. The dynamic viscosity of n-butanol, 1-pentanol, and 1-hexanol is 2.6, 3.6, and 5.6 mPa.S, respectively. The branched-chain alcohols have even higher viscosities up to 13.7 mPa.S for 5-methyl-1-heptanol. Fuels with kinematic viscosities between 1.8 and 5.8 centistokes (cSt) at 38°C are typically used in high-speed engines, and those with viscosities higher than 5.8 cSt are only used in slower-speed engines. Very viscous fuels are limited in application to large stationary and marine engines that normally require preheating for proper pumping, injection, and atomization. As shown in Fig. 1.3B, the kinematic viscosity of the higher alcohols at 38°C ranges between 1.77 and 13.69 cSt. The viscosity of most of the higher alcohols whose biological production has been studied dropped within the range of 1.8–5.8 cSt, but some of them such as branched chain C7 and C8 alcohols have higher viscosities.

Figure 1.3 Dynamic viscosity at 25°C (A) and kinematic viscosity at 38°C (B) of linear (filled points) and branch-chained (hollow points) higher alcohols. The blue bond shows the acceptable range of viscosity for the fuels used in high-speed engines. Source: National Institute of Standards and Technology, 2022.

The hydrogen bond has an important role in the freezing point of alcohols, making them higher than those of n-alkanes with the same molecular weight. Gasoline is a blend of hydrocarbons frozen in a relatively wide range of temperatures depending on the freezing points of its hydrocarbons [8], but the gasoline freeze point ranged mostly between 223 and 233 K. The low-temperature performance of fuels depends on their freezing point of them. In the case of jet fuel (Turbine fuel), the kerosene-type jet fuels, that is, Jet A and Jet A-1, have freezing points of 233 and 226 K, respectively. The aviation gasoline, that is, Jet B, has a freezing point of 223 K, and the naphtha-type jet fuels of JP-4, JP-5, and JP-have freezing points of 215, 227, and 226 K, respectively. With the freezing points well below 230 K (Fig. 1.4), most of the higher alcohols can be utilized at low temperatures.

Figure 1.4 Freezing point of linear (filled points) and branch-chained (hollow points) higher alcohols. Source: National Institute of Standards and Technology, 2022.

The energy density of a fuel is critically important for energy storage particularly when the fuel should be used in the transportation sector. The heat of combustion defined as the enthalpy of the reaction with oxygen indicates the amount of heat released when a unit (mass, mole, or volume) of fuel is burned. The heat of combustion per unit volume is sometimes called energy density. Other terms such as calorific value and heating value are also used for representing this quantity. Like any reaction, the heat of the reaction can be derived from the heat of the formation of reactants and products (Eq. 1.1). In the case of combustion, a fuel reacts with oxygen into water and carbon dioxide (R 1.1). Depending on whether the produced water is in the form of gas or liquid, two types of the heat of combustion are typically considered, higher heating value (HHV) and lower heating value (LHV). HHV includes the heat of condensation of water considering liquid water as a product (Eq. 1.2), whereas LHV is the net heat of combustion considering vapor water as a product (Eq. 1.3).

Equation (R 1.1)

Equation

(1.1)

Equation (1.2)

Equation (1.3)

where ΔHfoAlcohol, ΔHfoCO2, and ΔHfoH2O are the heat of formation of alcohol, CO2, and H2O at standard conditions.

As shown in Fig. 1.5A, the heat of formation of higher alcohols varied between 255 and 316 MJ/kmole. Alcohols with higher carbon numbers have higher absolute energy of formation, and branch-chained alcohols have higher absolute energy of the formation compared to linear alcohol with the same carbon number. The heat of combustions in terms of HHV of the alcohols is shown in Fig. 1.5B. Ethanol with 30.6 MJ/kg HHV has 36% of gasoline energy content, and shifting from ethanol to higher alcohols means moving 22%–54% closer to the gasoline’s energy density of 47.5 MJ/kg. The first step from ethanol to n-butanol and isobutanol has led to biofuels with 36.7 MJ/kg, which is 37% closer to gasoline, and the second step toward the higher alcohols up to C7 provided the opportunity for energy storage with a density of 39.6 MJ/kg. In the case of alkanes, the heat of combustion per mass decreases as molecular size or atomic C/H increases [9]. On a mass basis, methane has the highest heat of combustion of 55 MJ/kg among alkanes. Interestingly, when their heat of combustion per unit of volume is considered, it increases with the increasing molecular size of alkanes [9]. On the other hand, compared with the typical rechargeable lithium batteries, the energy density of higher alcohols is more than 41-fold higher than that of batteries, that is, less than 0.9 MJ/kg [10].

Figure 1.5 Heat of formation (A) and higher heating value (B) of linear (filled points) and branch-chained (hollow points) higher alcohols. Source: National Institute of Standards and Technology, 2022.

The vapor pressure of gasoline is typically expressed by Reid vapor pressure (RVP), which is the pressure inside a closed vessel containing four volume portions of vapor above one portion of liquid at 38°C. The RVP of a typical gasoline can be about 10 psi, whereas that of the alcohols is between 0.60 and 2.69 psi. In hot weather, evaporation of fuel with high vapor pressure in the line of reaching the engine can cause a serious problem known as vapor lock, in which deficiency in fuel pumping and injection lead to engine stalling [11]. In cold weather, on the other hand, a fuel with low vapor pressure may not be volatile enough to vaporize when injected into the cylinder. Therefore the higher alcohols with relatively low vapor pressures may lead to fewer vapor lock problems but worse the cold-start performance. Blending with gasoline is one possible option to improve cold-start behavior of higher alcohols.

Engine knock is known for its serious problems of reducing the engine efficiency and putting mechanical stress on engine parts. The knocking behavior of fuel is represented by two parameters of research octane number (RON) and motor octane number (MON). The octane numbers have been defined as a scale to quantify the knocking behavior of fuels assuming zero for heptane as a linear alkane and 100 for the highly branched alkane of 2,2,4-trimethylpentane. The performance of a fuel in a single-cylinder engine at 600 or 900 rpm is compared with that of blends of heptane and 2,2,4-trimethylpentane for RON or MON measurements, respectively. The octane numbers of higher alcohols have been measured by Lawyer [12]. Most of the commercial grades of gasoline have a RON between 87 and 94. Ethanol has a relatively high RON of about 107, while the RON of higher alcohols significantly depends on the alcohol structure. Isopropanol with RON of 112.5 and MON of 96.7 has the highest knocking performance among the C2–C6 alcohols. 2-Propanol and isobutanol have relatively the same octane numbers as ethanol. n-Butanol and 3-methyl-1-butanol with less than 10% reduction in octane numbers compared to ethanol still placed beyond the gasoline’s range. Having higher octane numbers compared to gasoline, C2-C4 alcohols can be blended with gasoline as an octane booster. 1-Pentanol and 1-hexanol, however, showed octane numbers beyond the range of gasoline’s octane number (Fig. 1.6).

Figure 1.6 Reid vapor pressure (RVP) (A), research octane number (RON) (B), and motor octane number (MON) (C) of linear (filled points) and branch-chained (hollow points) higher alcohols. Source: K.M. Lawyer, Incorporation of Higher Carbon Number Alcohols in Gasoline Blends for Application in Spark-Ignition Engines, Michigan Technological University, 2017.

The toxicity of higher alcohols in terms of the median lethal dose (LD50) tested on mice can also be considered a qualification factor. Gasoline with LD50 of 14,063 mg/kg is a relatively nontoxic substance, when compared to edible chemicals such as lactose with LD50 of 10,000 mg/kg or vitamin C with LD50 of 11,900 mg/kg. The toxicity of ethanol with LD50 of 7060 mg/kg is still lower than some sugars such as fructose (LD50 of 4000 mg/kg). As shown in Fig. 1.7, the higher alcohols have a relatively wide range of LD50 down to 210 mg/kg for 1-pentanol, which is even lower than hydrochloric acid (238–277 mg/kg). Interestingly, alcohols with the same carbon number may have significantly different toxicities. For instance, isobutanol with LC50 of 2460 mg/kg is less toxic than n-butanol with LC50 of 790 mg/kg.

Figure 1.7 Median lethal dose (LD50) of linear (filled points) and branch-chained (hollow points) higher alcohols [13]. Source: E.C. Agency 2022.

1.3 Potentials of higher alcohols in synthetic chemistry

Alcohols are ideal reagents in synthetic chemistry owing to the generation of water as the only by-product in their reactions, which is important from both atom economy and environmental points of view. A wide range of products can be synthesized by utilizing bio-based higher alcohols opening new windows onto green chemistry. Alcohols can be involved in synthetic reactions as the reagents by either (1) the activation of the hydrogen atom of hydroxyl group of alcohol as O-nucleophile, (2) the activation of α-H of alcohol, as C-nucleophile, leading to alcohol oxidation or C-H functionalization reaction, or (3) nucleophilic substitution reaction where OH of alcohol is the leaving group.

Esterification is one of the key reactions from the first category converting alcohols into esters. Esters traditionally produced from the condensation of activated carboxylic acid derivatives and alcohols have a wide range of applications. In the recent years, several catalysts have been developed for producing different esters. Biologically produced higher alcohols that are among the aliphatic primary alcohols were also applied to synthesize various esters. In 2011, for instance, direct aerobic oxidative esterification of benzylic alcohols with higher alcohols catalyzed by palladium using bulky phosphine ligands [14] or P-olefin ligands [15] was developed. Oxa-Michael addition is the other reaction in the first category with particular importance for C–C bond formation in organic synthesis. This type of reaction leads to the intermediate enolates as starting points for domino reactions or protonation reactions to give β-hydroxy carbonyl or carboxyl compounds. Etherification of higher alcohols also provides the routes for the production of aryl ethers.

From the second type of reactions, alcohol oxidation as C-nucleophiles to corresponding aldehydes and ketones through either metal- or metal-free-catalyzed reactions is another important role of higher alcohols in organic chemistry. Furthermore, α-C-H functionalization can transform alcohols into value-added chemicals, which are important for biopharmaceuticals. In the recent years, impressive studies dedicated to utilizing alcohols as alkylating reagents through the selective functionalization of α-C-H [16]. From the third type, the reaction of alcohols as electrophiles with amine as a nucleophilic reagent is a powerful pathway for the production of amine derivatives used in the pharmaceuticals and fine chemicals.

1.4 Potentials of higher alcohols as solvents

Alcohols with their hydroxyl functional group are powerful solvents particularly for dissolving polymeric and resin-like materials owing to their high hydrogen-bonding character. The aliphatic primary alcohols containing C1–C10 are clear colorless liquids at room temperature, while alcohols containing more than C12 are solids. Methanol, ethanol, and propanol are miscible with water at any proportion, while higher alcohols are partially soluble in water.

The alcohols are versatile solvents used in many products from cough syrup and antiseptics to adhesives and coatings. Methanol is a strongly toxic solvent of dyes, inks, and lacquer. Ethanol is extensively used as a solvent in the manufacturing of varnishes and perfumes and the extraction of essences and flavorings. Methylated spirits, a common industrial solvent composed of ethanol along with 10%–15% methanol, are used in many processes such as those with paints, resins, soaps, and dyes [17]. In the formulation of the products such as after-shaves, perfumes, and cosmetics, ethanol dissolves the ingredients and splashes them all over while using, but evaporates after use leaving behind the ingredients.

1-Propanol is typically used in the printing ink industry as a solvent for flexographic inks with controlled evaporation to provide a proper ink drying time. Isopropanol known as Rubbing Alcohol is used in cosmetics such as perfumes, liquid soaps, antiseptic solutions, and cleaners as well as some types of coatings, liniments, and medications. As a four-carbon straight-chain alcohol, n-butanol has key roles in surface-coating formulations such as urea-formaldehyde and melamine-formaldehyde resins used in wood laminating adhesives, but it is the growing water-based coatings that significantly boost butanol consumption. In the formulation of lacquers such as nitrocellulose lacquer, n-butanol improves their blush resistance, flow, and leveling properties. In addition, n-butanol is a proper solvent for metal degreasing, rubber manufacturing, and machinery manufacturing. Isobutanol is also used as a solvent in coating formulations with or without n-butanol as a cosolvent. Both n-butanol and isobutanol are used as latent solvent, which do not dissolve the resin, but have a synergistic effect when used in conjunction with an active solvent. Alcohols have been known for their performance both as active and latent