Ethoxylation
Encyclopedia
Ethoxylation is an industrial process in which ethylene oxide
is added to alcohol
s and phenol
s to give surfactant
s. The invention of the process is attributed to Schöller and Wittwer at I.G. Farben industrie.
(KOH), which serves as a catalyst. The reactor is pressurised with nitrogen
and heated to about 150 °C. Typically 5-10 units of ethylene oxide are added to each alcohol:
A distribution of products are obtained. The amount of ethylene oxide and the reaction time determine the degree of ethoxylation (the value of n in the equation above), which in turn determines the surfactant properties of the ethoxylated product. Traditionally the alcohols were obtained by hydrogenation
of fatty acids, but currently most are "oxo alcohols," obtained via hydroformylation
. In addition to alcohol
s, amine
s and phenol
s are commonly ethoxylated.
Most frequently alcohol ethoxylates (AEs) are derived from primary alcohols and ethylene oxide
by use of a base catalyzed reaction of potassium or sodium hydroxide followed by treatment with a neutralizing agent such as acetic or phosphoric acid. Less often, they are produced from secondary alcohols. More than 435,000 metric tons of linear alcohol ethoxylates were produced in North America and Western Europe in 2000. AE is considered to be a high production volume (HPV) chemical by the US EPA.
," because poly(ethylene oxide) is also known as poly(ethylene glycol), abbreviated as PEG.
Ethoxylated fatty alcohol
s are often converted to the organosulfate
. A well known example is sodium laureth sulfate
, a foaming agent
in shampoo
s and toothpaste
s, as well as an industrial detergent
. The conversion typically uses sulfur trioxide
or chlorosulfuric acid
:
.
Alcohols containing ethylene oxides of C6-C18 length are considered to be rapidly biodegradable. AEs are usually released down the drain, where they may be adsorbed into solids and biodegrade through anaerobic processes. About 28-58% of AEs degrade in the sewer. The remaining AEs are treated at waste water treatment plants and biodegrade by aerobic processes. Less than 0.8% of AE remains and is released in effluent. If released into surface waters, sediment or soil, AEs will degrade through aerobic and anaerobic processes or be taken up by plants and animals.
With an increase in ethylene oxide and decrease in carbon length, the aquatic toxicity decreases. The toxicity of synthetic alcohol ethoxylates are toxic to certain invertebrates, with a range of EC50
values for linear AE from 0.1 mg/l to larger than 100 mg/l. For branched alcohol exthoxylates, toxicity ranges from 0.5 mg/l to 50 mg/l.
Additional studies have been conducted regarding toxicity on algae and fish. The EC50 toxicity for algae from linear and branched AEs was 0.05 mg/l to 50 mg/l. Acute toxicity to fish is varied, ranging from LC50 values for linear AE of 0.4 mg/l to 100 mg/l, and branched is 0.25 mg/l to 40 mg/l. For invertebrates, algae and fish the essentially linear and branched AEs are considered to not have greater toxicity than Linear AE.
Ethylene oxide
Ethylene oxide, also called oxirane, is the organic compound with the formula . It is a cyclic ether. This means that it is composed of two alkyl groups attached to an oxygen atom in a cyclic shape . This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered...
is added to alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s and phenol
Phenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
s to give surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
s. The invention of the process is attributed to Schöller and Wittwer at I.G. Farben industrie.
Production
In industrial ethoxylation, an alcohol is treated with ethylene oxide and potassium hydroxidePotassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
(KOH), which serves as a catalyst. The reactor is pressurised with nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and heated to about 150 °C. Typically 5-10 units of ethylene oxide are added to each alcohol:
- ROH + n C2H4O → R(OC2H4)nOH
A distribution of products are obtained. The amount of ethylene oxide and the reaction time determine the degree of ethoxylation (the value of n in the equation above), which in turn determines the surfactant properties of the ethoxylated product. Traditionally the alcohols were obtained by hydrogenation
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
of fatty acids, but currently most are "oxo alcohols," obtained via hydroformylation
Hydroformylation
Hydroformylation, also known as oxo synthesis or oxo process, is an important industrial process for the production of aldehydes from alkenes. This chemical reaction entails the addition of a formyl group and a hydrogen atom to a carbon-carbon double bond...
. In addition to alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s, amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
s and phenol
Phenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
s are commonly ethoxylated.
Most frequently alcohol ethoxylates (AEs) are derived from primary alcohols and ethylene oxide
Ethylene oxide
Ethylene oxide, also called oxirane, is the organic compound with the formula . It is a cyclic ether. This means that it is composed of two alkyl groups attached to an oxygen atom in a cyclic shape . This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered...
by use of a base catalyzed reaction of potassium or sodium hydroxide followed by treatment with a neutralizing agent such as acetic or phosphoric acid. Less often, they are produced from secondary alcohols. More than 435,000 metric tons of linear alcohol ethoxylates were produced in North America and Western Europe in 2000. AE is considered to be a high production volume (HPV) chemical by the US EPA.
PEGylation
Ethoxylation is commonly practiced, albeit on a much smaller scale, in the biotechnology and pharmaceutical industries to increase water solubility and, in the case of pharmaceuticals, circulatory half-life of non-polar organic compounds. In this application, ethoxylation is known as "PEGylationPEGylation
PEGylation is the process of covalent attachment of polyethylene glycol polymer chains to another molecule, normally a drug or therapeutic protein. PEGylation is routinely achieved by incubation of a reactive derivative of PEG with the target macromolecule...
," because poly(ethylene oxide) is also known as poly(ethylene glycol), abbreviated as PEG.
Applications of ethoxylated products
Alcohol ethoxylates (AE) are non-ionic surfactants found in products such as laundry detergents, surface cleaners, cosmetics and for use in agriculture, textiles and paint. Carbon chain length is 8-18 while the ethoxylated chain is usually 3 to 12 ethylene oxides long in home products. hey feature both a lipophilic tails (R in the equation above) and a relatively polar head group ((OC2H4)nOH in the above example).Ethoxylated fatty alcohol
Fatty alcohol
Fatty alcohols are aliphatic alcohols consisting of a chain of 8 to 22 carbon atoms. Fatty alcohols usually have even number of carbon atoms and a single alcohol group attached to the terminal carbon. Some are unsaturated and some are branched...
s are often converted to the organosulfate
Organosulfate
Organosulfates are a class of organic compounds sharing a common functional group commonly with the structure R-O-SO3-. The SO4 core is a sulfate group and the R group is any organic residue. All organosulfates are formally esters derived from alcohols and sulfuric acid, although many are not...
. A well known example is sodium laureth sulfate
Sodium laureth sulfate
Sodium laureth sulfate, or sodium lauryl ether sulfate , is a detergent and surfactant found in many personal care products . SLES is an inexpensive and very effective foaming agent. SLES, SLS and ALS are surfactants that are used in many cosmetic products for their cleansing and emulsifying...
, a foaming agent
Foaming agent
A foaming agent is a surfactant, which when present in small amounts, facilitates the formation of a foam, or enhances its colloidal stability by inhibiting the coalescence of bubbles....
in shampoo
Shampoo
Shampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair...
s and toothpaste
Toothpaste
Toothpaste is a paste or gel dentifrice used with a toothbrush as an accessory to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it serves as an abrasive that aids in removing the dental plaque and food from the teeth, assists in suppressing...
s, as well as an industrial detergent
Detergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...
. The conversion typically uses sulfur trioxide
Sulfur trioxide
Sulfur trioxide is the chemical compound with the formula SO3. In the gaseous form, this species is a significant pollutant, being the primary agent in acid rain. It is prepared on massive scales as a precursor to sulfuric acid.-Structure and bonding:Gaseous SO3 is a trigonal planar molecule of...
or chlorosulfuric acid
Chlorosulfuric acid
Chlorosulfuric acid is the inorganic compound with the formula HSO3Cl. It is also known as chlorosulfonic acid. It is a distillable, colorless liquid that should be handled with care. It is a hygroscopic and a powerful lachrymator.-Structure and properties:Chlorosulfuric acid is a tetrahedral...
:
- R(OC2H4)nOH + SO3 → R(OC2H4)nOSO3H
Human health
Research on associated health risks have found alcohol ethoxylates are not mutagenic, carcinogenic, skin sensitizers, nor cause reproductive or developmental effects. Undiluted AEs can cause dermal or eye irritation. In liquid solution the level of irritation is dependent on the concentration. AEs are considered to have low to moderate toxicity for acute oral exposure, low acute dermal toxicity, and have mild irritation potential for skin and eyes when at concentrations found in consumer products.Aquatic and environmental aspects
Some ethoxylated materials have been controversial because of their widespread use and the toxicity to aquatic life of their degradation products, such as nonylphenolNonylphenol
Nonylphenol is a family of closely related organic compounds, a subset of the alkylphenols. This collection of compounds is a precursor to commercially important detergents...
.
Alcohols containing ethylene oxides of C6-C18 length are considered to be rapidly biodegradable. AEs are usually released down the drain, where they may be adsorbed into solids and biodegrade through anaerobic processes. About 28-58% of AEs degrade in the sewer. The remaining AEs are treated at waste water treatment plants and biodegrade by aerobic processes. Less than 0.8% of AE remains and is released in effluent. If released into surface waters, sediment or soil, AEs will degrade through aerobic and anaerobic processes or be taken up by plants and animals.
With an increase in ethylene oxide and decrease in carbon length, the aquatic toxicity decreases. The toxicity of synthetic alcohol ethoxylates are toxic to certain invertebrates, with a range of EC50
EC50
The term half maximal effective concentration refers to the concentration of a drug, antibody or toxicant which induces a response halfway between the baseline and maximum after some specified exposure time...
values for linear AE from 0.1 mg/l to larger than 100 mg/l. For branched alcohol exthoxylates, toxicity ranges from 0.5 mg/l to 50 mg/l.
Additional studies have been conducted regarding toxicity on algae and fish. The EC50 toxicity for algae from linear and branched AEs was 0.05 mg/l to 50 mg/l. Acute toxicity to fish is varied, ranging from LC50 values for linear AE of 0.4 mg/l to 100 mg/l, and branched is 0.25 mg/l to 40 mg/l. For invertebrates, algae and fish the essentially linear and branched AEs are considered to not have greater toxicity than Linear AE.