INTRODUCTION:
During the Second World War there was shortage of edible fats in Germany. The problem was further compounded by the fact that available edible fats were diverted for the manufacture of soaps. There was therefore the compelling need for scientist to develop other methods of manufacturing soaps other than from fats. Extensive scientific investigations revealed that certain homologs of bezene possess good surfactant qualities.
Basically, every surfactant is an organic compound consisting of two parts, (1) a hydrophobic portion (non-water soluble) and (2) a hydrophilic portion (water soluble), as illustrated below.
Surfactants are subdivided into four major categories:1 non-ionics which do not dissociate in solution and find application in automatic-dishwashing detergents and laundry detergents,2 amphoterics which contain both anionic and cationic groups finds application in toothpaste compositions, shampoos, cosmetics, corrosion inhibitors and water-emulsion paints. Surfactants are effective in either aqueous and non-aqueous systems, depending on their solubility characteristics, the molecule may be tailored for either systems.1 Every detergent product contains one or more types of surfactant such as fatty alcohols, condensation products of fatty alcohols and ethylene oxides, taurine derivatives, alkylbenzenes and linear alkylbenzenes. The alkylbenzenes (ABS) and the linear alkylbenzenes (LABS) are homologs of benzene. The ABS have largely fallen out of favour in the manufacture of detergents because of their partial bio-degradation. Concerns pertaining to the use of LAB on human health and the environment have been evaluated by the European Council Regulation (EC) 1488/94 report which concluded the use of LAB as being safe2. Growth in household detergents is driving demand for linear alkylbenzene produced form kerosene-derived normal paraffins.3
Benzene is industrially produced from the refining of
petroleum from the catalytic reformer using Rhenium and Platinum on an alumina
support at a temperature between 450-550oC, at a pressure greater
that 10 atmospheres maintained by a stream of hydrogen gas.4
Dehydrogenation (aromatization) and ring formation (cyclization) reactions as
shown below yields benzene
Linear alkylbenzene is produced via aromatic electrophylic substitution of benzene. Linear alkylbenze is a family of organic compounds with the formula C6H5CnH2n+1. Typically n lies between C10 - C16, although generally supplied as a tighter cut, such as C12-C15, C12-C13 and C10-C13 for detergent use.5 The alkyl portion in LAB molecule being usually a straight chain kerosene or a suitable olefin. Since the 1960s LAB has emerged as the dominant precursor of biodegradable detergents.6 Given the large scale application of LAB-derived detergents, a variety of routes have been developed to produce linear alkylbenzene.7 The paraffins are usually chlorinated, the monochloro derivatives being desirable, the yield of this ensured by maintaining a high concentration of the hydrocarbon and not allowing the concentration of the chloroparaffin to rise above 20% weight in the continuous type of reactor used for this process. The monochloro paraffin derivatives are ultimately attached to the benzene rings by Friedel-Crafts alkylation which uses either AlCl3 or HF as catalyst as shown, using dodecane in the reactions below.
Sulphonation of the LAB produced the linear alkylbenzene sulphonic acid in which the ortho- and para- products are favoured. However, owing to the nature of the substituent on the benzene ring, a bulky alkyl group, the para- product predominates because of steric hinderance at the ortho- position.8
Which, upon neutralization with sodium hydroxide gives the sodium salt, the AI in the degreaser.
Experimental section:
Sulphonation. In the sulphonation of LAB, the presence of water brings about a reversible reaction. The absence of water in the LAB was confirmed by measuring 100 ml which was shaken with a few crystal of potassium permanganate. The absence of faint purple colouraton indicated that there was no water in the sample. 500ml of LAB was measured into a three-neck round bottom flask to which a thermometer, a dropping funnel and a stirrer were fitted, each via a cork. The flask was mounted in a freezing mixture of ice/NaCl for temperature control (the reaction being exothermic), the temperature was allowed to stabilize at -10oC in a fume cupboard. Oleum (65%) was gradually added via the funnel with constant stirring, ensuring that the temperature do not exceed 60oC. With the addition of Oleum the colourless LAB gradually turned dark and increased in viscousity. At regular intervals of 5 minutes from the start of reaction, 2 mls of the sulphonation product was withdrawn and neutralized. At points with volume of oleum less than 140 ml the neutralized product showed free oil floating on top of water, indicating incomplete sulphonation. With oleum addition at 140 ml, the neutralized product showed good colour, satisfactory foaming and absence of free oil. At points with oleum addition exceeding 140 mls the neutralized product became too soluble – an indication of over-sulphonation (presence of di- or tri- sulphonic acid groups on the LAB. There was less foaming of this product in comparison with that of used oleum at 140 ml, when 2ml of the products was mixed separately and shaken with 100 ml of water. The sulphonation was repeated using conc. sulphuric acid.
Neutralization. The neutralization of LAB sulphonic acid is exothermic and temperature control is necessary for good appearance (colour) of the product. LAB sulphonic acid (100 ml) was placed in a beaker and NaOH (2M) was gradually added, with vigorous stirring and cooling under the tap. As the addition of NaOH progressed a pale yellow paste of the sodium salt started appearing. At complete neutralization after 5 minutes at a pH of 7 checked with a calibrated pH meter, the product had low viscousity and the colour was unsatisfactory. The process was repeated with 6M NaOH which yielded a product brighter in colour but too viscous. Neutralization using 4M NaOH gave a product with good colour and satisfactory viscousity. 100 ml of 4M NaOH neutralized 70 ml of LAB sulphonic acid at pH of 7. Apart from the main equation of neutralization given above, free H2SO4 from oleum in solution with LAB sulphonic acid was neutralized as shown the reaction below.
The process of sulphonation with oleum and subsequent neutralization has yielded Na2SO4, (equation 8) a builder, into the degreaser. Addition of Na2SO4 as a builder from external source was necessary only for the degreaser obtained from sulphonation using H2SO4 (98%).
The table below shows the volumetric relationship between the LAB and oleum (65%) and H2SO4 (98%) and between LAB sulphonic acid and NaOH (4M) at pH values of 7, 9 and 11.
Table 1
|
Process 1: Sulphonation with Oleum (65% SO3) and neutralization |
|||
|
pH |
LAB sulphonic acid (cm3) |
Oleum (cm3) |
4M NaOH (cm3) |
|
7 9 11 |
500 500 500 |
140 140 140 |
715 758 806 |
|
Process 2: Sulphonation with H2SO4(98%) and neutralization |
|||
|
pH |
LAB sulphonic acid (cm3) |
H2SO4(98%) (cm3) |
4M NaOH (cm3) |
|
7 9 11 |
500 500 500 |
555 555 555 |
465 476 488 |
The foam booster/stabilizer was prepared by grating the fleshy mesocarp of eight coconut fruits and soaking in water for 24 hours. The oil and water was squeezed out. The water/oil mixture was evaporated to remove the water. 34ml of coconut oil recovered was saponified with 60 ml of DEA (diethanolamine), ratio 2:1 to give N,N-bis (2-hydoxyethyl) lauramide (equation 9).
Citronella perfume extracted from the Eucalyptus Citronella plant by steam distillation was added to the formulation to mask the soapy odour to give it better appeal.
The degreaser formulation had the following composition by weight %: sodium LAB sulphonate (AI) 95.00% (1751.09g), stabilizer/foam booster - N,N-bis (2-hydoxyethyl) lauramide 1.93% (35.6g), EDTA 0.75% (13.82g) sodium oxide 1.08% (20.0g), potassium silicate 1.08% (20.0g) and citronella fragrance 0.18% (3.36g). A performance test carried out revealed that the formulation was very effective in removing soils from wares, fabric and surfaces and in comparison was not inferior to imported products.
CONCLUSION:
The sulphonation of LAB and subsequent neutralization of the resultant sulphonic acid is a fast chemical reaction requiring strict temperature control because of the highly exothermic nature of the reaction. The linear alkylbenzene sulphonate (AI), depending on the intended end use and form in which it is desired, could be formulated into liquid detergent, degreaser, powder or flakes. With the availability of LAB from the Kaduna petrochemical plant and a very functional oleum/sulphuric acid plants at Agbara industrial estate in Ogun state, the stage is set for a potent detergent industry in Nigeria.
REFERENCES
1. Harris, J C (1980). Soap and synthetic detergents in Riegel’s handbook of Industrial Chemistry, edited by Kent J, 1980. p383-395
2. European Council Regulations, (EC) 1488/94.
3. http//www.uop.com/processing-solution/petrochemical/ detergents. Retrieved 10/06/11
4. Nigerian National Petroleum Corporaton (NNPC). Catalytic Reforming.Training nanuals, 1980, p4-10
5. Ashford,s Dictionary of Industrial Chemicals, third edition. p3858.
6. Kurt, K (2005). “Surfactants” in Ullman’s Encyclopedia of industrial Chemistry, Wiler-VCH, Weinbeim. Doi 10.1002/ 14356007.925 747.
7. Linear alkylbenzene 07/08-87 Report, Chemsystems, February 2009.
8. Finar, I L (1973). Organic Chemistry Vol. 1. Continental Printing Co., Hong Kong. p157.
Received on 08.07.2011 Modified on 03.08.2011
Accepted on 14.08.2011 © AJRC All right reserved
Asian J. Research Chem. 4(12): Dec., 2011; Page 1833-1835