Process for the preparation of a low viscosity alkyl toluene or alkyl xylene sulfonate

A process for the preparation of a low viscosity aqueous alkyl toluene or alkyl xylene sulfonate which comprises neutralizing alkyl toluene or alkyl xylene sulfonic acid with aqueous sodium hydroxide in the presence of sufficient sodium chloride to lower the viscosity of the sulfonate salt produced. Alternatively, the sodium chloride may be added subsequent to neutralization of the sulfonic acid.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for the preparation of a low 
viscosity alkyl toluene or alkyl xylene sulfonate. 
Alkyl toluene and alkyl xylene sulfonates have utility as surfactants for 
use in enhanced oil recovery. However, these sulfonates are often highly 
viscous and therefore can be difficult to handle and transport except in 
highly dilute form. Since the selection of a particular surfactant which 
can be utilized in petroleum recovery techniques is based in part upon 
economic considerations, it would be advantageous to have a method for 
obtaining a low viscosity alkyl toluene or alkyl xylene sulfonate. 
U.S. Pat. No. 3,957,671 describes a low viscosity detergent acid mix 
containing alkyl benzene sulfonic acid which is prepared by sulfonating 
alkyl benzene in the presence of benzoic acid. 
SUMMARY OF THE INVENTION 
The present invention provides a process for the preparation of a low 
viscosity aqueous alkyl toluene or alkyl xylene sulfonate from the alkyl 
toluene or alkyl xylene sulfonic acid obtained by the sulfur trioxide 
sulfonation of alkyl toluene or alkyl xylene having an average molecular 
weight of about 300 to 365 and a straight or branched alkyl side chain 
ranging from about C.sub.12 to C.sub.24 which comprises neutralizing the 
alkyl toluene or alkyl xylene sulfonic acid with aqueous sodium hydroxide 
in the presence of sufficient sodium chloride to lower the viscosity of 
the aqueous sodium alkyl toluene or alkyl xylene sulfonate produced to 
less than about 600 centipoise (cp), while maintaining a homogeneous 
mixture. 
In an alternate embodiment of the present invention, the sodium chloride is 
added subsequent to neutralization of the sulfonic acid to provide the low 
viscosity sulfonate. 
Among other factors, the present invention is based on the discovery that 
the viscosity of the sodium alkyl toluene or alkyl xylene sulfonate 
produced by the sulfur trioxide sulfonation and caustic neutralization of 
alkyl toluene or alkyl xylene can be substantially lowered by the addition 
of sodium chloride during or subsequent to the neutralization. This is 
particularly surprising in view of the known teaching that salt water 
increases the viscosity of petroleum sulfonates. See, for example, U.S. 
Pat. No. 3,587,737. 
DETAILED DESCRIPTION OF THE INVENTION 
The alkyl toluene or alkyl xylene employed in the process of the present 
invention is, in general, a broad-range alkyl toluene or alkyl xylene 
having an average molecular weight of about 300 to 365, preferably about 
310 to 355, and an alkyl side chain ranging from about C.sub.12 to 
C.sub.24, preferably from about C.sub.15 -C.sub.20. The alkyl toluene or 
alkyl xylene is normally prepared by the alkylation of toluene or xylene 
with an appropriate olefin. The alkylate so produced is then sulfonated 
and neutralized in accordance with the present process. 
The alkyl side chain on the toluene or xylene may be straight, i.e., 
linear, or branched chain in structure and will generally contain from 
about 12 to about 24 carbon atoms, preferably from about 15 to about 20 
carbon atoms. These side chains are derived from corresponding straight or 
branched chain olefins. Straight chain olefins may be obtained by various 
procedures known to the art, such as thermal cracking of paraffin waxes 
and the ethylene growth process. Branched chain olefins are normally 
obtained by the oligomerization of low molecular weight olefins such as 
propylene and butylene. Preferred branched chain olefins are propylene 
oligomers in the C.sub.12 to C.sub.24 range. The straight and branched 
chain olefins are then employed to alkylate the toluene or xylene, using a 
variety of catalysts known to the art. 
The aromatic compound alkylated may be either toluene or xylene. When 
xylene is employed, any of the three ortho, meta and para isomers of 
xylene may be utilized, although a mixed xylene is generally preferred. 
The alkyl toluene or alkyl xylene is then prepared by alkylating toluene or 
xylene with the desired olefin in the presence of a Friedel-Crafts 
catalyst, such as hydrogen fluoride or aluminum chloride. Other 
Friedel-Crafts catalysts which may be used include sulfuric acid, 
phosphoric acid, boron trifluoride, and the like. The temperature for the 
alkylation will ordinarily be in the range of about 0.degree. C. to 
60.degree. C. Generally, about 2 to 10 moles, and preferably 5 to 7 moles, 
of toluene or xylene may be employed per mole of olefin. The alkylate 
product is isolated by separating the hydrocarbon phase, washing it and 
distilling out excess toluene or xylene and low molecular weight alkylate 
to obtain a bottoms product. In the alkylate so produced, the alkyl group 
may be found in any position on the aromatic ring. 
The alkyl toluene or alkyl xylene is then sulfonated with sulfur trioxide 
to give the corresponding alkyl toluene or alkyl xylene sulfonic acid. The 
sulfonation is generally accomplished using thin-film dilution techniques, 
although other types of sulfonation reactors may be used with equivalent 
results. These include low temperature solvent systems, jet impact and 
hydrocarbon diluent techniques. Basically the procedure in a film reactor 
comprises introducing the sulfonate precursor at the top of a reaction 
vessel such that a thin film is formed on the walls of the vessel. The 
film is continuously exposed to a gaseous sulfonating agent as the film 
moves along the surface of the reaction vessel. The sulfonating agent may 
be sulfur trioxide or sulfur trioxide diluted with a gas which is inert in 
the process. Preferably, the sulfonation is carried out with sulfur 
trioxide, using air or nitrogen as a carrier gas. 
The alkyl toluene or alkyl xylene sulfonic acid is subsequently neutralized 
to the sodium salt with aqueous sodium hydroxide in the presence of 
sufficient sodium chloride to lower the viscosity of the sulfonate 
produced. In general, about 2 to 10, preferably 3 to 6, weight percent 
aqueous sodium hydroxide is suitable for neutralizing the sulfonic acid. 
Alternatively, the sodium chloride can be added to the aqueous sulfonate 
after neutralization of the acid. 
In order to obtain optimum fluidity, the viscosity of the aqueous sulfonate 
should be maintained below about 600 cp. In the case of an aqueous 
sulfonate which is about 22% active, that is, 22 weight percent sulfonate, 
the viscosity of the sulfonate can be lowered to the desired level by 
carrying out the neutralization in the presence of an amount of sodium 
chloride ranging from above about 3% to below about 5%, preferably about 
4%, based on weight of sulfonate. At sodium chloride levels of about 3% or 
below, the aqueous sulfonate is highly viscous and flows poorly. At sodium 
chloride levels above about 5%, the aqueous sulfonate normally separates 
into two layers, which is undesirable. In carrying out the invention, it 
is preferable to maintain a homogeneous mixture.

The following examples are provided to illustrate the invention in 
accordance with the principles of the invention but are not to be 
construed as limiting the invention in any way, except as indicated by the 
appended claims. In the examples, viscosity was measured by a Brookfield 
Viscometer at 70.degree. F. 
EXAMPLES 
Example 1 
Preparation of Polypropylene Toluene Sulfonic Acid 
A polypropylene toluene having an average molecular weight of about 316 and 
an average side chain length of about 16 carbon atoms was sulfonated 
continuously in a falling film sulfonator using 1.12 moles of sulfur 
trioxide per mole of alkylate. The alkylate was fed at 6.4 ml/min., and 
liquid sulfur trioxide (1.00 ml/min.) was vaporized by heating in a stream 
of nitrogen at 7 l/min. This sulfur trioxide-nitrogen stream was further 
diluted with nitrogen at 10 l/min. before contacting the alkylate. The 
reaction was carried out at about 60.degree. C. 
Example 2 
This example demonstrates the neutralization of polypropylene toluene 
sulfonic acid in the absence of sodium chloride. To 163 g of water was 
added 10.3 g of 50 weight percent aqueous sodium hydroxide. A high-shear 
Eppenbach mixer was immersed in this solution at room temperature. The 
polypropylene sulfonic acid of Example 1 was added slowly while stirring 
at as high a speed as possible without ejecting the contents from the 
beaker. After 41.6 g of the acid had been added (about 85% of the acid 
required to neutralize the NaOH present), the resulting slurry, about 19% 
sulfonate, was too viscous to stir. 
Example 3 
To 162.5 g of water was added 0.5 g of sodium chloride (1% of sulfonate) 
and 10.3 g of 50 weight percent sodium hydroxide. Fifty (50) grams of 
polypropylene toluene sulfonic acid from Example 1 were added following 
the procedure of Example 2, until a pH of about 8 was reached. The 
resulting slurry, about 22% sulfonate, was difficult to stir. 
Example 4 
The procedure of Example 3 was repeated, except that 1.0 g of sodium 
chloride (2% of sulfonate) was employed. The resulting slurry was 
difficult to stir. 
Example 5 
The procedure of Example 3 was repeated, except that 1.5 g of sodium 
chloride (3% of sulfonate) was employed. The resulting slurry was easily 
mixed. 
Example 6 
The procedure of Example 3 was repeated, except that 2.0 g of sodium 
chloride (4% of sulfonate) was employed. The resulting slurry was very 
fluid. 
Example 7 
The procedure of Example 3 was repeated, except that 2.5 g of sodium 
chloride (5% of sulfonate) was employed. The resulting slurry was very 
fluid, but separated into two layers on standing. 
Viscosity measurements for Examples 2 to 7 are provided in Table I. 
TABLE I 
______________________________________ 
Sulfo- NaCl, Brookfield 
Ex- nate, Wt. % of Viscosity,.sup.1 
ample Wt. % Sulfonate cp (70.degree. F.) 
Remarks 
______________________________________ 
2 19 0 &gt;500,000 Too viscous 
to stir 
3 22 1 &gt;500,000 Difficult to 
stir 
4 22 2 428,000 Difficult to 
stir 
5 22 3 48,000 Easily stirred 
6 22 4 250 Very fluid 
7 22 5 400 Fluid, but 
separated into 
2 layers. 
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.sup.1 Spindle No. SC4231 for Examples 2 to 5; 
Spindle No. SC418 for Examples 6 and 7 
Example 8 
This example demonstrates the addition of sodium chloride subsequent to 
neutralization of the polypropylene toluene sulfonic acid with aqueous 
sodium hydroxide. 
A 24% active slurry of sodium polypropylene toluene sulfonate prepared as 
in Example 2 was highly viscous and very difficult to mix. To 100 g of 
this slurry was added 3.6 g of a 20 wt % solution of sodium chloride in 
water. The resulting 23.3% active slurry, containing 3 wt % sodium 
chloride based on active sulfonate, was easily mixed. The Brookfield 
viscosity was found to be 19,750 cp at 70.degree. F., using Spindle No. 
SC4-231. 
Example 9 
A polypropylene xylene having an average molecular weight of about 333 and 
an average side chain length of about 16 carbon atoms was sulfonated using 
substantially the same procedure as in Example 1. The resulting 
polypropylene xylene sulfonic acid was neutralized with 50 weight percent 
aqueous sodium hydroxide to produce a 24.5% sodium polypropylene xylene 
sulfonate slurry. 
Several aliquots of differing sodium chloride concentrations were prepared 
by adding a 10 percent aqueous sodium chloride solution and varying 
portions of water to the above 24.5% sodium polypropylene xylene sulfonate 
slurry. Resulting slurries of about 17 weight percent and 22 weight 
percent sulfonate were obtained. The Brookfield viscosity of these 
slurries was measured at 70.degree. F., using Spindle No. SC4-231. The 
results are shown in Table II. 
TABLE II 
______________________________________ 
NaCl, Brookfield 
Run Sulfonate 
Wt. % of Viscosity, 
No. Wt. % Sulfonate cp (70.degree. F.) 
______________________________________ 
1 17 0 23,700 
2 22 0 92,000 
3 22 1 33,300 
4 22 2 18,700 
5 22 3 4,000 
6 22 4 540 
7 22 5 -- (separated into 
two layers) 
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Example 10 
A linear alkyl toluene having a linear alkyl side chain of 15 to 18 carbon 
atoms was sulfonated using substantially the same procedures as in Example 
1. The resulting linear alkyl toluene sulfonic acid was neutralized with 
50 weight percent aqueous sodium hydroxide to produce a 19.5% sodium 
linear alkyl toluene sulfonate slurry. 
Several aliquots of differing sodium chloride concentrations were prepared 
by adding a 20 percent aqueous sodium chloride solution and varying 
portions of water to the above 19.5% sodium linear alkyl toluene sulfonate 
slurry. The Brookfield viscosity of the resulting slurries was measured at 
70.degree. F., using Spindle No. SC4-231. The results are shown in Table 
II. 
TABLE III 
______________________________________ 
NaCl Brookfield 
Run Sulfonate, Wt. % of Viscosity, 
No. Wt. % Sulfonate 
cp (70.degree. F.) 
______________________________________ 
1 19.5 0 700 
2 19.2 2 228 
3 19.0 3 136 
4 18.8 4 87 
5 18.6 5 62 
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