n-Butanol or n-butyl alcohol or normal butanol is a primary alcohol with a 4-carbon structure and the chemical formula C4H9OH. It belongs to a group of chemicals referred to as “Öxo-Alcohols”
The term “oxo-alcohols” is used to describe alcohols obtained from the “oxo process,” which involves reaction of olefins and synthesis gas (a mixture of hydrogen & carbon monoxide), to produce aldehydes, which are converted to alcohols. Since a major application of oxo-alcohols is for making plasticisers, they are also referred to as plasticiser alcohols. The list includes:
- n-Butanol (NBA)
- 2-Ethylhexanol (2-EHA)
- 2-Propylheptanol (2-PH)
- Isononyl alcohol (INA)
- Isodecyl alcohol (IDA).
In addition, several higher alcohols are also produced from different olefins using the oxo process.
NBA is a colourless, flammable liquid of medium volatility with a banana-like odour. It has restricted miscibility (about 7-8%) in water, but is freely miscible with all common organic solvents such as glycols, ketones, alcohols, aldehydes, ethers and aromatic & aliphatic hydrocarbons.
Table 1: Typical specifications of NBA
Source: Company websites
NBA and its isomer, isobutanol (IBA), are versatile solvents used in a range of applications, notably in coating formulations. They are also widely used as raw materials in the manufacture of glycol ethers, acetate esters and acrylate esters.
Apart from these, NBA is used in rubber chemicals, printing inks, resins, pharmaceuticals, urethane catalysts, dyes, varnishes, adhesives, nitrocellulose lacquers, pesticides etc.
The uses of NBA vary by geographic area, but in general it is used to make other chemicals (mainly plasticisers), or used as a solvent or an ingredient in formulated products such as cosmetics.
NBA is considered to be flammable liquid under the European Union Directive 67/548/EEC and is labelled by hazard symbol Xn. Its shipment, in tankers as well as steel drums, is carried out under the hazard class 3, as flammable liquid, with UN no. UN 1120 and UN packing group III.
Oxo-alcohols, in general, are produced by the oxo-process, more formally known as hydroformylation. This is the reaction of an olefin with mixture of carbon monoxide (CO) and hydrogen(H2) (synthesis gas or syngas) to give an aldehyde. Subsequent hydrogenation of the aldehydes leads to oxo-alcohols.
The oxo-process is used to produce different alcohols via the respective aldehydes using different olefin feedstock. Although there are several versions of processes to produce aldehydes from olefins, using different catalysts, the hydrogenation steps to produce oxo-alcohols from aldehydes, are similar for most manufacturers. Propylene is used as raw material to produce NBA, 2-EHA and IBA by reaction with synthesis gas. The first step – hydroformylation to convert propylene to a mixture of aldehydes – is common to all three oxo-alcohols. Further processing to obtain the individual alcohols, differs slightly.
During hydroformylation step, a mixture of two aldehydes – n-butyraldehyde&isobutyraldehyde – is obtained. This mixture is either separated initially, and the individual aldehydes isomers hydrogenated to the respective alcohols; or the mixture of isomeric aldehydes is hydrogenated directly and the NBA and IBA product mix separated by distillation.
The technology can also be used to produce higher alcohols such as C11 to C14 from olefins produced from Fischer-Tropsch synthesis.
There are several other commercial processes for manufacture of NBA, which have been used historically or are still in use in some geographies, due to local availability of the required raw materials.
NBA has been produced from ethanol by successive dehydrogenation to acetaldehyde; condensation to crotonaldehyde and hydrogenation. Alternatively, the intermediate acetaldehyde for this process was obtained from ethylene by the Wacker process.
Zeigler-Natta chain growth reaction has also been employed using ethylene as a raw material to produce NBA. Sasol uses a Ziegler process, which dimerises ethylene, followed by oxidation and hydrolysis to give NBA. In the late 1990s, BASF patented the butadiene route to NBA and butyraldehyde. Butadiene is catalytically converted into a mixture of linear and branched butenyl ethers. These are isomerised to linear butenyl ether, and subsequently converted into linear butyraland finally hydrogenated to NBA. Alternatively, the intermediate acetal can be hydrolysed to n-butyraldehyde. High overall efficiencies to NBA and n-butyraldehyde have been claimed.
The feedstocks used for the production of bio-NBA are the same as those used for the production of bio-ethanol – sugar beets, sugarcane, corn, wheat, cassava etc. Non-food items like agricultural waste and grasses can also be used. Also, it is reported that existing bio-ethanol plants can be cost-effectively retrofitted for bio-NBA production.
The earliest commercial process to produce bio-NBA employs fermentation of molasses or corn products with Clostridium acetobutylicum. Acetone and methanol are obtained as co-products (the process is termed as acetone, butanol, ethanol or ABE fermentation). This process has been used on industrial scale (multi-tonnes per day per facility) in the USA in early 20th century, in South Africa until the early 1980s, in Russia until the late 1980s, and is currently performed industrially in China.
It is used to make Butyl acrylate monomer [BAM] BAM is an ester of acrylic acid and NBA, and is used as a monomer for producing polymers – homopolymers, as well as copolymers(with other monomers such as acrylic acid & its salts, methacrylates, amides & esters, acrylonitrile, vinyl acetate, styrene, butadiene, etc.)
These polymers are used are used in a variety of products as dispersions or solutions. BAM is used as a raw material for fibre processing agents, caulks, adhesives& sealants, emulsion polymers for latex paints &coatings, inks, plastics, leather, acrylic rubber & emulsions etc.
NBA is also used to make Butyl methacrylate used as a monomer for producing a variety of polymers. It is used in plastic sheet, moulded and extruded plastic products, as well as harder components of copolymers. Butyl methacrylate is also used as a binding agent for screen-printing.
Butyl acetate made from NBA is one of the most important derivatives of NBA. NBA is also used in making plasticizers like Dibutyl phthalate (DBP) NBA is a feedstock for the production of butyl glycol ethers by reaction with ethylene and propylene oxides. The major glycol ethers include ethylene glycol monobutyl ether, di- and triethylene glycol monobutyl ethers, and the corresponding butyl ether acetates.
Other chemical derivatives
Butyl esters of various dicarboxylic acids like sebacic acid and adipic acid, and stearic acid, are used as synthetic and semi-synthetic lubricants and hydraulic fluids.
Several other esters of NBA like benzylbutyl phthalate (BBP),dibutylsebacate (DBS) and dibutylazelate (DBZ) are plasticisers of lesser importance.
NBA is widely used as an etherification alcohol in the manufacture of amino resins that are used as curing agents in baking and physical-drying finishes.
NBA is also used as a feedstock for the manufacture of flotation aids (agents), e.g. butyl xanthate.
NBA is a general-purpose solvent in the chemical industry. It is used as solvent for paints, coatings, varnishes, resins, gums, dyes (e.g., in printing inks), camphor, vegetable oils, fats, waxes, shellac, rubber and alkaloids. It is used as a solvent for a wide variety of ambient, dry and baking coatings – automotive, decorative, industrial, maintenance and marine. Also, it is a solvent for curable lacquers and cross-linked baking finishes. It is a very effective solvent for cellulose nitrate lacquers and ambient-cured enamels, reducing the formulation viscosity and providing excellent flow and levelling during film formation. It improves the flow and gloss in cellulose lacquers and amino-baking finishes.
About half the production of NBA and its derivatives (primarily esters) are used as solvent in the coating industry. NBA(5-10%) prevents blushing of certain coatings when they dry under humid conditions.
The most important emerging application of NBA is as biofuel – as a substitute for diesel fuel and gasoline. Renewable biofuel use of NBA has been mandated by United States Energy Policy Act of 2005, and updated by the US Energy Independence and Security Act of 2007. According to the modified Renewable Fuels Standards (RFS2), the U.S. alone is targeting production of 36 billion gallons per year by 2022.
NBA contains 99,800 British Thermal Units (Btu) of energy per gallon, as compared to 76,300 Btu/gallon contained in ethanol and 116,000 Btu/gallon in gasoline. As compared to ethanol, NBA is less susceptible to phase separation in gasoline, and can be blended into gasoline at higher percentages than ethanol. Additionally, NBA has been demonstrated to work in vehicles designed to use gasoline without any modification. NBA also has the potential to be upgraded to aviation jet fuel. An assortment of technologies exists and continues to be developed that dehydrate NBA to 1-butene, and further polymerize 1-butene into a suitable jet fuel. .If this end-use grows significantly, demand for NBA can increase exponentially.
Andhra Petrochemicals Ltd. (APL) is the only producer of oxo-alcohols in India and accounts for just 32% of the market. It produces NBA, IBA and 2-EHA. As on today, the company has 73,000-tpa of capacity at its facility in Visakhapatnam, in the state of Andhra Pradesh. The facility began its operations in 1994 with an initial capacity of 30,000-tpa. The plant uses oxo process technology provided by Davy Process Technology. Over the years, the company enhanced its production capacity to 73,000-tpa. APL invested about $65-mn (Rs. 320-crore) in the expansion.
Production of NBA in India by APL is given in Table 2 while the trend in production, imports, exports and consumption is provided in Table 3
Table 2: NBA Production in India by APL
Production of NBA by APL constitutes only around 32% of the total consumption of NBA. Imports of NBA have more than doubled from around 25,381 tons in 2010-11 to 53,679 tons in 2017-18. Imports are mainly sourced from Malaysia, Saudi Arab, South Africa and Singapore. Exports of NBA are insignificant.
Table 3: Trend in Production, Imports, Exports and Consumption of NBA in India
Source: DGCIS – Kolkata
Consumption of NBA has increased from 38 thousand tons in 2010-11 to around 72 thousand tons in 2017-18 registering CARG of 10.8%.
Consumption Pattern of NBA
Plasticiers account for the 20% of the total consumption of NBA, while Solvents in coatings, inks and adhesives account for the maximum of 45%. Applications in Pharma and NBA derivatives account for 14% and 15% respectively. The balance 6% are consumed by the miscellaneous uses.
Demand for NBA
Demand for NBA is expected to grow at CAREG of 10.8% for the next two years . However, thereafter it is expected to grow at over 20% Demand will be driven by above average growth for making plasticisers and new demand for manufacture of butyl acrylate.
Bharat Petroleum Corporation Ltd. (BPCL), as a part of its Integrated Refinery Expansion Project (IREP), is putting up a petrochemical complex at Kochi. The proposed complex consists of three major process units: acrylic acid, oxo-alcohols and acrylates. About 329-ktpa of products will be manufactured from 250-ktpa of propylene. The projects is under implementation and the commercial production is expected in mid-2019. The capacity of butyl acrylate will be 180,000-tons and that of OXO Alcohols 212,000-tons. Of this the capacity of Butanol will be 150,000-tons.
In March 2018 Indian Oil Corporation has also announced to invest in Acrylics / OXO Plant means the Plant to produce Butanol and Butyl Acrylate by using the process technology licensed by Mitsubishi Chemical Corporation. The capacity of the plant for butanol is expected to be 92,000-tons and that of butyl acrylate 153,000-tons.
The global scenario for butanol will be covered separately under global scenario for Oxo Alcohols.