Synthetic Detergent and Linear Alkyl Benzene
A detergent is a surfactant or a mixture of surfactants having cleaning properties in dilute solutions. Commonly, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water.
Table M-IV 2.1: Types of Specialty Surfactants
Betaines and siltaines
Although Linear alkyl benzene is the major detergent being used due its low cost as derived from petroleum feed, other surfactants used widely are fatty alcohol sulphates(FAS), Fatty alcohol ether sulphates[FES), fatty alcohol ethoxylates (AE).
There has been rapid growth in the use of fatty alcohols due its low toxilogical profile and safe use, continued substitution of soap by alcohol based surfactants in the personal care industry, strong sales of laundary liquids that use higher levels of alcohol based surfactants, displacement of LAS surfactants by alcohol based surfactants, the substitution of alkyl phenol eythoxylates by alcohol based surfactants[ Brent, 2004].the global market for fatty alcohol has shown significant growth. Oleochemical route to alcohols starting from vegetable/animal oils and fats has dominant share(70%) of global capacity of about 3.3 million tones synthetic alcohol produced from petrochemically derived ethylene still continues to have a about 30% share
Classification of Detergent
The detergency of the anionic detergent is vested in the anion. The anion is neutralized with an alkaline or basic material, to produce full detergency . Typical anionic detergents are alkylbenzenesulfonates. There are three kinds of anionic detergents: a branched sodium dodecylbenzenesulfonate, linear sodium dodecylbenzenesulfonate, and soap. The alkylbenzene portion of these anions is lipophilic and the sulfonate is hydrophilic. Two varieties have been popularized, those with branched alkyl groups and those with linear alkyl groups.
The detergency is in the cation, which can be a substantially sized molecule. Strong acids are used, such as hydrochloric acid to produce the CI anion as the neutralizing agent although in essence, no neutralization takes place in the manufacturing process. Cationic detergents are similar to the anionic ones, with a hydrophobic component, but instead of the anionic sulfonate group, the cationic surfactants have quaternary ammonium as the polar end. The ammonium center is positively charged.
Ethoxylates:Ethoxylates are compounds that have long hydrocarbon chains, but terminate with (OCH2CH2)nOH group. These groups are not charged, but they are highly hydrophilic owing to the presence of many oxygen centres.
Non-Ionic or Zwitterionic Detergents: This detergent consists of no inonic constituents which are ionically inert. The vast majority of all non-ionic detergents are condensation products or ethylene oxide with a hydrophobe. This grop of detergents is enormous, and the permutation endless. These are characterized by their (net) uncharged, hydrophilic head groups. They are based on polyoxyethylene (i.e. Tween, Triton and Brij series), Chaps, glycosides (i.e. octyl-thioglucoside, maltosides), bile acids such as DOC, lipids (HEGAs), or phosphine oxides. Zwitterionic detergents possess a net zero charge arising from the presence of equal numbers of +1 and -1 charged chemical groups.
Basic Components of Detergent
Some of the enzymes used in detergent are protease,amlases,liapse and celolases. The enzymes catalyses the breakdown of chemicalds through addition of water and helps in the removal of soils. Polymers and enzymes play important role in improving the detergency. Polymers help in soil removal, prevent insoluble salt incrustation work as anti-soil re-deposition, inhibit dye transfer. Use of optical brightner enhance the brightness and whiteness. processing aids when added to slurries of detergent powder improve stability and homogeneity of slurries during mixing and reduce viscosity.
Linear Alkyl Benzene
LAB basic raw material for detergent which was introduced in 60's as substitute for nonbiodegradable branched. Other surfactants are alcoholsulphate (AS), alcoholethoxylates (AE), Secondary alkane sulphonate, and alpha olefin sulphonates. LAB is a clear colourless liquid with characteristic odour. It is most widely used as the basic raw material for the manufacture of synthetic detergent. The linear alkyl Benzene produced from the C10 – C13 or C11 – C14 linear mono olefins are useful detergent intermediate and can be readily sulphonated to yield linear alkyl benzene sulphonates. These compounds constitute the “active” ingredients of many house hold detergents. They are surface active compounds (surfactants) which are combined with various builders (often inorganic salts) to make up a detergent formula.
Linear alkyl benzene (LAB) is the basic raw material for production of most widely used detergent. Linear alkyl benzene was introduced as substitute for non biodegradable branched alkyl benzene. Process involved for LAB manufacturing is mention in Table M-IV 2.3.
Although LAB demand grew by 14% per annum during 1984-90, future demand in the country is projected to increase at a healthy growth rate of 7-8% as against 2-4% worldwide. India and China with huge population are the largest market for LAB LAB manufactured in India started in 1985 by IPCL in 1985 followed by Reliance Industries, Tamilnadu Petro products, Nirma, IOC. Application of LAB in India is mention in Table M-IV 2.2.
Table M-IV 2.2: LAB Application in India
Consumer Cleaning Products
a. Synthetic detergents for fabric wash
b. Scouring products
c. Liquid detergents
Industrial & Institutional Cleaners
Other Industrial Application
Non-surfactant Applications( varnish, cable fluid oil, lubricant)
To obtain C10-C14 range hydrocarbons from kerosene. (n-C10 to n- C13 for light and n-C11to n-C14 for heavy LAB).
The LAB unit requires a very specific feed in terms of carbon number. The prefractionation unit is designed to process a high purity C9 to C15 linear (normal) paraffin feed and to separate out a heart cut with the desired carbon number which will range from n C10 to n13 for light LAB and nc11 - nc14 for heavy LAB.
To remove sulphur compounds from feed stock
The purpose of this unit is to remove sulfur and nitrogen from the feed without greatly changing its B.P. If not removed, sulfur and nitrogen would poison the sieve in the Molex Unit.
Separation (Parex process)
To remove n-paraffins from kerosene by selective adsorption using molecular sieve. The UOP MOLEX process is an effective method of continuously separating normal paraffins from a stream of co- boiling hydrocarbons by means of physically selective adsorption.
The feed stock is separated into a high purity normal paraffin fraction at high recoveries and a non-normal paraffin.
of Paraffins (Pacol Process)
Dehydrogenation of n-paraffins to olefins.
This process dehydrogenates the high purity linear paraffin feed stock from the pre-fractionation unit into the corresponding non-olefins, suitable as feed stock for the down stream detergent alkylate unit.
Alkylation of benzene with olefins to obtain LAB in presence of HF or
solid zeolite catalyst
This process alkylates benzene with linear olefins produced by the Pacol unit in the presence of HF acid catalyst to yield linear alkyl benzenes, LAB. The LAB thus produced can be readily sulfonated to form a suitable ingredient for many household detergents. This unit consists of three processing section :
Figure M-IV 2.2: Manufacture of linear alkyl Benzene Sulponate
Lab by Solid Acid Catalyst
The conventional catalyst AlCl3, H2SO4 and HF commercially used has the disadvantage of causing corrosion of equipment as well as waste production. There has been continuous search for development of non corrosive solid catalyst with similar catalytic properties. Some of the catalyst which have been developed are SiO2-Al2O3, H-,ontmorillonite, amberlyst, H-Y, HBeta, HM . World LAB capacity was around 3 million tones with nearly 85percent based on HF alkylation, 5percent on the aluminium chloride process, and 10 percent on the newly developed fixed bed alkylation. The fixed bed alkylation was first introduced on commercial scale in 1995 in Canada by Petresa. Figure M-IV 2.3 gives details for LAB Manufacture from Fixed Bed Technology.
Manufacturing of Detergents
Detergents use a synthetic surfactant in place of the metal fatty acid salts used in soaps. They are made both in powder and liquid form. Most detergents have soap in their mixture of ingredients, but it usually functions more as a foam depressant than as a surfactant. Various processes in manufacturing of detergents is mention in Table M-IV 2.4.
A synthetic detergent, a sodium alkyl sulfate called sodium dodecylsulfate, will be prepared by reacting dodecyl alcohol (dodecanol) with sulfuric acid.
The resulting dodecylsulfate is converted to the sodium salt by a reaction with sodium hydroxide.
Table M-IV 2.4: Various Processes for Making Detergent
The solid and liquid raw ingredientsare dropped into a large tank known as a slurry mixer. As the ingredients are added the mixture heats up as a result of two exothermic reactions: the hydration of sodium tripolyphosphate and the reaction between caustic soda and linear alkylbenzenesulphonic acid. The mixture is then further heated to 85oC and stirred until it forms a homogeneous slurry.
The slurry is deaerated in a vacuum chamber and then separated by an atomiser into finely divided droplets. These are sprayed into a column of air at 425oC, where they dry instantaneously. The resultant powder is known as ’base powder’, and its exact treatment from this point on depends on the product being made.
Other ingredients are now added, and the air blown through the mixture in a fluidiser to mix them into a homogeneous powder. Typical ingredients are
Soda ash (anhydrous Na2CO3), Bleach (usually sodium perborate. NaBO3), Bleach activator (e.g. tetraacetylethylenediamine), Enzymes (e.g. alkaline protease), Colour and perfume
Soap premix manufacture
Liquid detergent contains soap as well as synthetic surfactants. This is usually made first as a premix, then other ingredients are blended into it. This step simply consists of neutralizing fatty acids (rather than fats themselves) with either caustic soda (NaOH) or potassium hydroxide.
All ingredients except enzymes are added and mixed at high temperature. The ingredients used in the liquid detergent manufacture are typically sodium tripolyphosphate, caustic soda, sulphonic acid, perfume and water. The functions of these ingredients have been covered above.
The mixture is cooled and milled, and the enzymes added in powder form.