**2. Alcohols**

#### **2.1 Methanol, ethanol, propanol and butanol**

Bio-based ethanol is currently the most produced of all bio-solvents and is produced through biological transformation of sugars. These processes use either edible (sugarcane and corn) or nonedible (cellulose) feedstocks [19]. However, due

**5**

*Bio-Solvents: Synthesis, Industrial Production and Applications*

to concerns over edible feedstock causing the rise of food prices, there has been a move towards optimizing processes that produce cellulosic ethanol [20, 21], and indeed the world's first cellulosic ethanol commercial-scale production plant was commissioned in 2013 by Beta Renewable. This plant is situated in Milan, Italy, and uses Proesa™ technology for the pretreatment of agricultural waste (such as rice straw, giant cane (*Arundo donax*) and wheat straw) for production of ethanol at

Ethanol's most common uses are as a biofuel and solvent in consumer products

The presence of the hydroxyl group in ethanol makes it capable of hydrogen bonding, and it is therefore miscible with water and other solvents such as toluene,

Large-scale production of methanol is currently achieved using fossil-derived sources, by hydrogenation of carbon monoxide in the presence of a catalyst such as ZnO/Cr2O3 and Cu/ZnO/Al2O3 [23]. It can be obtained in small amounts in fermentation broths and from the gasification of biomass to produce bio-based syngas for subsequent conversion to methanol. The commercial viability of the latter is still

Due to the structural similarity of methanol to ethanol, the former is often used in place of ethanol in synthetic procedures. However, its toxicity has limited its widespread application as a solvent in consumer products. Still, other useful applications where methanol features not only as a solvent but as a reagent and fuel do exist. For instance, methanol is used in methanol fuel cells and is a key reagent in the manufacture of fatty acid methyl esters (FAMEs) (biodiesel) through transesterification of triglycerides and in dimethyl ether (DME) (diesel substitute) production [24]. It is also used in acid-catalyzed formation of methyl levulinate from bio-derived furfural

Thermochemical synthesis of alcohols such as methanol, ethanol and propanol (1-propanol and 2-propanol) from glycerol raw materials (**Figure 2**) is also known. This process is often promoted by a catalyst through a hydrogenolysis reaction [26–28]. *n*-Butanol production was first commercialized in the early 1900s, in the Weizmann process (ABE fermentation). Here, *n*-butanol, acetone and minute amounts of ethanol are produced from starch feedstock using *Clostridium acetobutylicum* [10, 29]. Later, fossil-based production of *n*-butanol became more costeffective which led to abandonment of the Weizmann process. Today there are some ABE fermentation production units; however, most *n*-butanol is produced mainly from petroleum by either (1) the oxo synthesis which involves hydroformylation of propene and then hydrogenation of the afforded butraldehyde, in the presence of a rhodium or cobalt homogeneous catalysts, (2) the Reppe synthesis (which involves the treatment of propene with CO and H2O) in the presence of a catalyst such as iron or (3) a multistep, catalytic hydrogen borrowing, cascade process involving self-aldol condensation of acetaldehyde, dehydration and then hydrogenation of the

*n*-Butanol has a low order of toxicity and has an energy density of 29.2 MJ/L, which is comparable to that of gasoline (32.5 MJ/L). It is also miscible with gasoline, and so it is not surprising that this alcohol is sometimes blended with gasoline to improve its properties. *n*-Butanol is also used as a solvent for coatings (varnishes, resins and waxes), paints and cosmetics and is an intermediate for making solvents (e.g. butyl propanoate, dibutyl ether and butyl acetate), polymer monomers

(e.g. butyl acrylate and butyl vinyl ether) and plasticizers (e.g. butyl phthalates) [31].

such as perfumes, food coloring and flavoring, alcoholic drinks and in certain mediation. The latter can be in both synthetic medicines and natural products. For example, highly efficient ethanol-assisted extraction of artemisinin, an active

antimalarial drug, from *Artemisia annua*, has been demonstrated [22].

alcohol (FA) and 2,5-hydroxymethylfurfural (HMF) [25].

*DOI: http://dx.doi.org/10.5772/intechopen.86502*

60,000 tons/year [9].

pentane and acetone.

under investigation [24].

resultant croton aldehyde [30].

### *Bio-Solvents: Synthesis, Industrial Production and Applications DOI: http://dx.doi.org/10.5772/intechopen.86502*

*Solvents, Ionic Liquids and Solvent Effects*

*The various sustainable solvents derived from biomass.*

drug discovery, process development and drug manufacturing processes [3]. They are also used to extract and separate compounds from mixtures or natural products. Solvents are also important for performing compound purifications and form part of many manufacturing protocols as well as consumer products including fragrances, cleaning agents, cosmetics, paints, flavors, adhesives and inks, to name a few [1]. Many organic solvents are volatile, flammable and toxic; therefore, their use poses safety and health risks and impacts negatively on the environment. In order to address these issues, 'solvent-free' chemistry has been proposed, to mitigate against solvent exposure risks, and for chemical manipulations and formulations that absolutely require solvents, a system of ranking them by their environmental, safety and health (ESH) attributes has been introduced. This system aims to aid in selecting and using those solvents with minimum ESH risks and good green profiles [4–6]. Making use of renewable resources in producing solvents is a promising and important strategy to move towards sustainable chemical processing and to replace organic solvents derived from fossil raw materials. To this end, bio-based feedstocks such as carbohydrates, carbohydrate polymers, proteins, alkaloids, plant oils and animal fats have been used to produce bio-based solvents (**Figure 1**). This often requires prior processing of the raw materials (typical by thermochemical and biochemical conversion methods) to give familiar solvents or to provide completely new and innovative solvent entries [7, 8]. There are some, such as essential oils extracted from citrus peels (which are rich in terpenes), that are used directly.

The main processing methods include biochemical and thermochemical conversion [7]. Using one or a combination of these processing techniques, several classes of bio-based solvents (including alcohols [9–11], esters [12, 13], ethers [14], alkanes

[15], aromatics [16] and neoterics [17, 18]) can be manufactured (**Figure 1**).

Bio-based ethanol is currently the most produced of all bio-solvents and is produced through biological transformation of sugars. These processes use either edible (sugarcane and corn) or nonedible (cellulose) feedstocks [19]. However, due

**2.1 Methanol, ethanol, propanol and butanol**

**4**

**2. Alcohols**

**Figure 1.**

to concerns over edible feedstock causing the rise of food prices, there has been a move towards optimizing processes that produce cellulosic ethanol [20, 21], and indeed the world's first cellulosic ethanol commercial-scale production plant was commissioned in 2013 by Beta Renewable. This plant is situated in Milan, Italy, and uses Proesa™ technology for the pretreatment of agricultural waste (such as rice straw, giant cane (*Arundo donax*) and wheat straw) for production of ethanol at 60,000 tons/year [9].

Ethanol's most common uses are as a biofuel and solvent in consumer products such as perfumes, food coloring and flavoring, alcoholic drinks and in certain mediation. The latter can be in both synthetic medicines and natural products. For example, highly efficient ethanol-assisted extraction of artemisinin, an active antimalarial drug, from *Artemisia annua*, has been demonstrated [22].

The presence of the hydroxyl group in ethanol makes it capable of hydrogen bonding, and it is therefore miscible with water and other solvents such as toluene, pentane and acetone.

Large-scale production of methanol is currently achieved using fossil-derived sources, by hydrogenation of carbon monoxide in the presence of a catalyst such as ZnO/Cr2O3 and Cu/ZnO/Al2O3 [23]. It can be obtained in small amounts in fermentation broths and from the gasification of biomass to produce bio-based syngas for subsequent conversion to methanol. The commercial viability of the latter is still under investigation [24].

Due to the structural similarity of methanol to ethanol, the former is often used in place of ethanol in synthetic procedures. However, its toxicity has limited its widespread application as a solvent in consumer products. Still, other useful applications where methanol features not only as a solvent but as a reagent and fuel do exist. For instance, methanol is used in methanol fuel cells and is a key reagent in the manufacture of fatty acid methyl esters (FAMEs) (biodiesel) through transesterification of triglycerides and in dimethyl ether (DME) (diesel substitute) production [24]. It is also used in acid-catalyzed formation of methyl levulinate from bio-derived furfural alcohol (FA) and 2,5-hydroxymethylfurfural (HMF) [25].

Thermochemical synthesis of alcohols such as methanol, ethanol and propanol (1-propanol and 2-propanol) from glycerol raw materials (**Figure 2**) is also known. This process is often promoted by a catalyst through a hydrogenolysis reaction [26–28].

*n*-Butanol production was first commercialized in the early 1900s, in the Weizmann process (ABE fermentation). Here, *n*-butanol, acetone and minute amounts of ethanol are produced from starch feedstock using *Clostridium acetobutylicum* [10, 29]. Later, fossil-based production of *n*-butanol became more costeffective which led to abandonment of the Weizmann process. Today there are some ABE fermentation production units; however, most *n*-butanol is produced mainly from petroleum by either (1) the oxo synthesis which involves hydroformylation of propene and then hydrogenation of the afforded butraldehyde, in the presence of a rhodium or cobalt homogeneous catalysts, (2) the Reppe synthesis (which involves the treatment of propene with CO and H2O) in the presence of a catalyst such as iron or (3) a multistep, catalytic hydrogen borrowing, cascade process involving self-aldol condensation of acetaldehyde, dehydration and then hydrogenation of the resultant croton aldehyde [30].

*n*-Butanol has a low order of toxicity and has an energy density of 29.2 MJ/L, which is comparable to that of gasoline (32.5 MJ/L). It is also miscible with gasoline, and so it is not surprising that this alcohol is sometimes blended with gasoline to improve its properties. *n*-Butanol is also used as a solvent for coatings (varnishes, resins and waxes), paints and cosmetics and is an intermediate for making solvents (e.g. butyl propanoate, dibutyl ether and butyl acetate), polymer monomers (e.g. butyl acrylate and butyl vinyl ether) and plasticizers (e.g. butyl phthalates) [31].

**Figure 2.** *Bio-based solvents derived from glycerol.*
