**2. Production of acetic acid**

*Biotechnological Applications of Biomass*

production routes, which are chemical and fermentative. Among the chemical manufacturing processes, the key processes are Cavita process (carbonylation of methanol), oxidation of aldehyde and oxidation of ethylene. The major players are BP chemicals and BASF, which follow carbonylation route. The major consumption of acetic acid mainly comes from the preparation of vinyl acetate monomer (VAM), acetic anhydride and C1-C4 acetates and it is used as a solvent in synthesis of terephthalic acid (PET). VAM is one of the main ingredients used in polymer industry with application as emulsifier, resins, as intermediate in surface coating agent, acrylic fiber and polymer wires. It is also used in textile industry to generate synthetic fibers as a result of condensation reaction. The other condensation reaction of acetic acid produces acetic anhydride used as typical acetylation agent, which is subsequently utilized to produce cellulose acetate, used in synthetic textiles and for silver-based photographic films. Most derived esters of acetic acid are ethyl acetate, n-butyl acetate, isobutyl acetate and propyl acetate, which are frequently used as solvents for inks, paints and coatings. Glacial acetic acid is an excellent polar protic solvent that is frequently used as a solvent for recrystallization to purify organic compounds. Several researchers are working on developing a sustainable process with the simple design to produce acetic acid that meets current demand.

**282**

**Figure 1.**

*Commercial routes for synthesis of acetic acid and applications.*

Acetic acid is mainly produced via chemical route that involves homogeneous as well as heterogeneous catalytic methods. The carbonylation of methanol via Monsanto process is the most adopted route, which further evolved as Cavita process with a choice of catalysts and process intensification. In the recent decade, the fermentative approach has also gained attention; however the commercial approach is not established yet. The current trends in sustainable manufacturing demand an urgent paradigm shift to develop and pursue more sustainable routes to reduce environmental burden. An approach is also made with the development of membrane-based technology, which offers a very simple design with eco-friendly production [7].

#### **2.1 Conventional process**

#### *2.1.1 Methanol carbonylation process*

Carbonylation process is a most employed commercial route for synthesis of acetic acid, also known as Monsanto process (**Figure 2**). Methanol and carbon monoxide are reacted in liquid phase in the presence of rhodium (Rh)-based catalyst at 150–200°C temperature and 30–50 bar pressure to produce acetic acid with 95% selectivity and 5% side products such as formic acid and formaldehyde [8]. Hydrogen iodide is used as an alkali promoter in this process. The reaction proceeds in liquid phase with methyl acetate as solvent using homogeneous catalyst. Controlled amount of water is required for the reaction, which is generated *in situ* by reaction of methanol with hydrogen iodide. The rate of reaction in the Monsanto process depends on the concentration of water. CO2, H2 and methanol are obtained

**Figure 2.** *Production of acetic acid by carbonylation method.*

as by-products in the reaction. The generated methanol in the reaction is recycled. The process has evolved with time and different strategies have been adopted to separate pure acetic acid from a mixture of water and by-products. This process was modified by BP chemicals replacing rhodium-based catalyst with iridium (Ir) catalyst known as Cavita process [4]. The choice of Ir as a coordination metal is relatively more economic process than rhodium. The use of an iridium catalyst improves the overall rate of reaction.

The safety and the environmental hazards arising from the current methods are a serious concern. Acetic acid is highly corrosive, and the production processes need to be more sustainable and environmentally benign by reducing the amount of energy required in production and subsequent separation technologies as well as using heterogeneous catalysts. The Japanese firm Chiyodo developed a heterogeneous Rh catalysed process, wherein Rh metal was immobilized on the vinylpyridine resin. The use of heterogeneous catalyst prevails the loss of catalyst in the liquid phase and facilitates easy separation from the reaction mixture. The amount of water used in the reaction is very low and thus the separation of water from acetic acid is more energy-efficient compared to the other processes mentioned.

#### *2.1.2 Acetaldehyde oxidation process*

Acetaldehyde oxidation was the predominant process followed for the synthesis of acetic acid, wherein acetaldehyde is first prepared by oxidation of ethylene using palladium and copper chloride and it was further oxidized to form acetic acid (**Figure 3**). The same process is reported using cobalt and chromium-based catalyst at 55 bar pressure and 150°C temperature. The one-step process for conversion of ethylene to acetic acid is also practised using lead and lead-platinum based catalyst at high pressure compared to the acetaldehyde oxidation process with a low yield of acetic acid [9].

#### *2.1.3 Hydrocarbon oxidation process*

Hydrocarbons derived from petroleum stock such as butane and naphtha are utilized to generate acetic acid using cobalt acetate and chromium acetate catalyst (**Figure 4**). The reaction proceeds at a comparatively higher temperature range (150–230°C) and pressure (50–60 bar). The process involves petroleum feedstock, which contains hydrocarbon mixture, which leads to the formation of other byproducts such as acetone, formic acid, propionic acid along with acetic acid. Thus,

**285**

*Production Pathways of Acetic Acid and Its Versatile Applications in the Food Industry*

this process fails to give pure acetic acid. This process is more suitable for manufac-

Fermentative route is mostly adapted for the generation of food-grade acetic acid that is vinegar. This process mainly involves the use of renewable carbon resources such as apple, grape, pears, honey, cane, coconut, date, syrup cereals, hydrolysed starch, beer and wine [10]. The fermentation process is mainly divided into two steps: the treatment with yeast followed by acetic acid bacteria (AAB). Commercial production of vinegar is done via oxidative fermentation using AAB. *Acetobacter* and *Gluconacetobacter* are most used species among ten classified genera. *Acetobacter pasteurianus* is traditionally used for commercial production of vinegar with concentration not exceeding 6% (v/v), whereas, *Gluconacetobacter europaeus* is utilized to produce high-concentration vinegar (10% v/v). The price of the vinegar varies with the kind of source used and the region where it is generated.

This method is well established, traditional and preferred for low-volume production of acetic acid. Derived from the French word Orléans, wooden barrels are used to ferment the feed in this process. This method is followed to prepare exotic brands of vinegar in different regions of the world with specific raw material available in the specific season. The traditional balsamic vinegar is produced in different parts of the world such as sherry from Spain, oxos from Greece, and Modena in Italy.

This process was developed to overcome the slow rate of acetification in Orleans

process [11]. The process intensification was done to improve the acetic acid bacteria and substrate interaction. The alcoholic substrate was sprayed over the fermentation in continuous loop to achieve the desired concentration of acetic acid. The heat of the reaction was controlled by passing the air through the system. The process has the drawback of accumulating gelatinous material on the surface the

This modern fermentation method is followed to produce vinegar in masses. This is the most widely method and has a high yield along with a fast rate of oxidation as compared to the previous method. This method is 30 times faster than the Orleans method with higher efficiency for production of acetic acid. This process requires comparatively small space with higher yields. The Fringe fermenter is used

membrane, which reduces the rate of reaction over the period.

*2.2.3 The continuous submerged process*

*DOI: http://dx.doi.org/10.5772/intechopen.92289*

turing a mixture of volatile fatty acids.

*Production of acetic acid by hydrocarbon oxidation.*

**2.2 Fermentation route**

**Figure 4.**

*2.2.1 Orleans method*

*2.2.2 Trickling process*

**Figure 3.** *Production of acetic acid by acetaldehyde oxidation.*

*Production Pathways of Acetic Acid and Its Versatile Applications in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.92289*

#### **Figure 4.**

*Biotechnological Applications of Biomass*

improves the overall rate of reaction.

*2.1.2 Acetaldehyde oxidation process*

*2.1.3 Hydrocarbon oxidation process*

*Production of acetic acid by acetaldehyde oxidation.*

acetic acid [9].

as by-products in the reaction. The generated methanol in the reaction is recycled. The process has evolved with time and different strategies have been adopted to separate pure acetic acid from a mixture of water and by-products. This process was modified by BP chemicals replacing rhodium-based catalyst with iridium (Ir) catalyst known as Cavita process [4]. The choice of Ir as a coordination metal is relatively more economic process than rhodium. The use of an iridium catalyst

The safety and the environmental hazards arising from the current methods are a serious concern. Acetic acid is highly corrosive, and the production processes need to be more sustainable and environmentally benign by reducing the amount of energy required in production and subsequent separation technologies as well as using heterogeneous catalysts. The Japanese firm Chiyodo developed a heterogeneous Rh catalysed process, wherein Rh metal was immobilized on the vinylpyridine resin. The use of heterogeneous catalyst prevails the loss of catalyst in the liquid phase and facilitates easy separation from the reaction mixture. The amount of water used in the reaction is very low and thus the separation of water from acetic acid is more energy-efficient compared to the other processes mentioned.

Acetaldehyde oxidation was the predominant process followed for the synthesis of acetic acid, wherein acetaldehyde is first prepared by oxidation of ethylene using palladium and copper chloride and it was further oxidized to form acetic acid (**Figure 3**). The same process is reported using cobalt and chromium-based catalyst at 55 bar pressure and 150°C temperature. The one-step process for conversion of ethylene to acetic acid is also practised using lead and lead-platinum based catalyst at high pressure compared to the acetaldehyde oxidation process with a low yield of

Hydrocarbons derived from petroleum stock such as butane and naphtha are utilized to generate acetic acid using cobalt acetate and chromium acetate catalyst (**Figure 4**). The reaction proceeds at a comparatively higher temperature range (150–230°C) and pressure (50–60 bar). The process involves petroleum feedstock, which contains hydrocarbon mixture, which leads to the formation of other byproducts such as acetone, formic acid, propionic acid along with acetic acid. Thus,

**284**

**Figure 3.**

*Production of acetic acid by hydrocarbon oxidation.*

this process fails to give pure acetic acid. This process is more suitable for manufacturing a mixture of volatile fatty acids.

#### **2.2 Fermentation route**

Fermentative route is mostly adapted for the generation of food-grade acetic acid that is vinegar. This process mainly involves the use of renewable carbon resources such as apple, grape, pears, honey, cane, coconut, date, syrup cereals, hydrolysed starch, beer and wine [10]. The fermentation process is mainly divided into two steps: the treatment with yeast followed by acetic acid bacteria (AAB). Commercial production of vinegar is done via oxidative fermentation using AAB. *Acetobacter* and *Gluconacetobacter* are most used species among ten classified genera. *Acetobacter pasteurianus* is traditionally used for commercial production of vinegar with concentration not exceeding 6% (v/v), whereas, *Gluconacetobacter europaeus* is utilized to produce high-concentration vinegar (10% v/v). The price of the vinegar varies with the kind of source used and the region where it is generated.

#### *2.2.1 Orleans method*

This method is well established, traditional and preferred for low-volume production of acetic acid. Derived from the French word Orléans, wooden barrels are used to ferment the feed in this process. This method is followed to prepare exotic brands of vinegar in different regions of the world with specific raw material available in the specific season. The traditional balsamic vinegar is produced in different parts of the world such as sherry from Spain, oxos from Greece, and Modena in Italy.

#### *2.2.2 Trickling process*

This process was developed to overcome the slow rate of acetification in Orleans process [11]. The process intensification was done to improve the acetic acid bacteria and substrate interaction. The alcoholic substrate was sprayed over the fermentation in continuous loop to achieve the desired concentration of acetic acid. The heat of the reaction was controlled by passing the air through the system. The process has the drawback of accumulating gelatinous material on the surface the membrane, which reduces the rate of reaction over the period.

#### *2.2.3 The continuous submerged process*

This modern fermentation method is followed to produce vinegar in masses. This is the most widely method and has a high yield along with a fast rate of oxidation as compared to the previous method. This method is 30 times faster than the Orleans method with higher efficiency for production of acetic acid. This process requires comparatively small space with higher yields. The Fringe fermenter is used for this process to increase the rate of the acetification. The yield of acetic acid is 98%. The pure substrates are required to achieve the high quality of acetic acid. This fermentation process is much economical, of simple design with easy process control.

The Fermentation process for acetic acid is economically feasible with comparatively simple operations. The application of this process is very limited to the present global demand. Whereas, the conventional process involves several steps such as fractional distillation, condensation and crystallization, which add to the high machinery cost. The operating conditions are harsh considering the process temperature and pressure along with the corrosive nature of acetic acid [12]. The purification of acetic acid from water is a multi-step process consuming a high amount of energy, which makes overall process complex and critical. In addition to this, the process requires huge manpower with stringent safety protocols and norms.
