Process for removing paraffins from their mixtures with paraffinsulphonic acids

Mixtures of C.sub.12 -C.sub.18 n-paraffins with paraffinsulphonic acids having the same number of carbon atoms, water and sulphuric acid, and obtained by sulphoxidation of said paraffins with SO.sub.2 and O.sub.2 in the presence of water and UV radiation are stripped of their excess SO.sub.2 and decanted to separate most of the paraffins, and obtain a residual mixture. The residual mixture is dehydrated according to the invention until a two-phase system forms or at least until the mixture becomes turbid, and the dehydrated mixture either as such or after separating the heavier phase consisting of water and sulphuric acid is extracted with supercritical CO.sub.2, which removes with it the n-paraffins, these being reused in the sulphoxidation process.

This invention relates to a process for removing n-paraffins from their 
mixtures with paraffinsulphonic acids. Paraffinsulphonic acids containing 
between 12 and 18 carbon atoms are generally prepared by sulphoxidation of 
C.sub.12 -C.sub.18 paraffins with SO.sub.2 and O.sub.2 using UV radiation 
for reaction initiation. The reaction product obtained form the 
sulphoxidation reactor consists of a mixture containing small percentages 
of paraffinsulphonic acids, water and sulphuric acid, but mostly unreacted 
n-paraffins. 
Most of the n-paraffins can be easily separated from said mixture, but a 
substantial fraction of them remains together with the sulphuric acid, the 
water and the paraffinsulphonic acids. It is important to note that the 
n-paraffins must be separated to the maximum possible extent not only for 
obvious economic reasons, but also because their presence in 
paraffinsulphonic acids is undesirable. 
The known art gives suggestions for separating n-paraffins from the rest of 
the sulphuric acid, paraffinsulphonic acid and water mixture, one of these 
suggestions being contained in European patent application No. 131913, in 
particular in Example 1, according to which the mixture containing 
paraffinsulphonic acids, unreacted n-paraffins, water and sulphuric acid 
is treated with isopropanol in a quantity of 15%, to separate the mixture 
into three distinct phases, the upper one essentially consisting of 
n-paraffins, the lower one consisting of water, sulphuric acid and 
isopropanol, and the intermediate one containing paraffinsulphonic acids, 
sulphuric acid, water, n-paraffins and isopropanol. The intermediate phase 
is then mixed with methylene chloride to separate an aqueous sulphuric 
acid phase containing isopropanol and a little methylene chloride from a 
phase containing paraffinsulphonic acids, n-paraffins, water, methylene 
chloride and sulphuric acid, this being neutralised with soda and 
concentrated, and finally heated to a temperature of 200.degree. C. to 
distill off the n-paraffins. 
This procedure for removing the n-paraffins is obviously complicated, and 
notwithstanding its various extraction stages it is still necesary to use 
high-temperature vaporisation at the end, which in all cases damages the 
product obtained. With the known process it is therefore not possible to 
prepare free paraffinsulphonic acids or their salts with weak bases, as 
these are unstable at high temperature. 
It has been surprisingly found that the previously described drawbacks of 
the known art regarding the separation of n-paraffins can be obviated in a 
very simple manner by dehydrating the mixture (partial removal of the 
water present) of C.sub.12 -C.sub.18 n-paraffins, paraffinsulphonic acids, 
water and sulphuric acid, and then subjecting the dehydrated mixture to 
extraction with supercritical CO.sub.2, this removing all or substantially 
all the n-paraffins. 
The present invention provides a process for removing n-paraffins 
containing between 12 and 18 carbon atoms from mixtures of said 
n-paraffins with paraffinsulphonic acids having the same number of carbon 
atoms, water and sulphuric acid, where said mixtures have been obtained by 
sulphoxidation of C.sub.12 -C.sub.18 n-paraffin mixtures at a temperature 
of between 25.degree. and 50.degree. C. with SO.sub.2 and O.sub.2 in the 
presence of water and UV radiation, comprising removing excess SO.sub.2, 
if present, from the reaction mixture originating from the 
paraffinsulphonic acid synthesis reactor, and decanting the mixture to 
remove most of the C.sub.12 -C.sub.18 n-paraffins, said process being 
characterised in that the residual mixture obtained after removing the 
SO.sub.2 and the decanted paraffins is dehydrated until a two-phase system 
forms, or at least until the mixture becomes turbid, the dehydrated 
mixture then being extracted with supercritical CO.sub.2, which removes 
all or substantially all the residual n-paraffins. 
With regard to dehydration of the residual mixture, it should be noted that 
this must be continued at least until it becomes turbid, this being a sign 
of commencement of the formation of a two-phase system. The dehydration 
can be conducted until 85% of the water initially present in the mixture 
is removed. If dehydration is conducted beyond the formation of mixture 
turbidity, a two-phase system forms in which the lower heavier phase 
consists of water and sulphuric acid. The upper or supernatant phase is 
subjected to extraction with supercritical CO.sub.2, and the lower phase 
(water+H.sub.2 SO.sub.4) is removed. 
Dehydration can be conducted with any medium which does not interfere with 
the system, and thus absorption systems can be used if they have high 
selectivity only towards water. However, the preferred system consists of 
controlled evaporation at a temperature less than 100.degree. C., and 
preferably under vacuum at a temperature of 50.degree. C. or less. 
With regard to the conditions under which the dehydrated mixture is 
extracted with supercritical CO.sub.2, these are as follows: 
extraction temperature: between 32.degree. C. and 80.degree. C. 
extraction pressure: between 75 and 350 bar 
weight ratio of CO.sub.2 used for extraction to paraffinsulphonic acids 
present in the dehydrated mixture: between 1:1 and 50:1. 
The paraffinsulphonic acid mixture resulting from the process according to 
the present invention is then generally neutralised in known manner using 
chosen bases, to thus obtain paraffin sulphonates of any desired type. 
The sulphuric acid contained in the mixture resulting from the process of 
the present invention can be separated, if required, by methods known in 
the art, such as mixing with suitable substances or precipitation to form 
insoluble salts. 
An example is given hereinafter to better illustrate the invention, but 
without intending to limit the invention thereto or thereby. 
EXAMPLE 
200 g of a crude mixture (free of SO.sub.2 and naturally decanted 
paraffins) of paraffinsulphonic acids, obtained by sulphoxidation of 
C.sub.12 -C.sub.18 n-paraffins and having the following composition: 
paraffinsulphonic acids: 24.74% by weight 
C.sub.12 -C.sub.18 n-paraffins: 26.46% by weight 
water: 40.94% by weight 
sulphuric acid: 7.86% by weight 
were placed in the flask of a rotary evaporator. 
Maintaining the temperature in the evaporation flask at less than 
45.degree. C. and operating under vacuum, water was distilled from this 
mixture until turbidity appeared in the evaporation flask. At this point, 
38.5 g of water had been evaporated. Distillation was continued, and a 
further 7.5 g of water were evaporated. The residue in the flask consisted 
of two liquid phases. The lower phase, consisting of water and sulphuric 
acid, was separated (7.7 g). The upper phase (146.3 g) contained all the 
fed paraffinsulphonic acids and paraffins, and smaller quantities of water 
and sulphuric acid. 
106.5 g of this mixture were fed into the extractor of the laboratory 
extraction apparatus described hereinafter, and were extracted with 
CO.sub.2 under supercritical conditions. 
The extraction temperature was maintained at 45.degree. C., the extraction 
pressure at 150 bar and the CO.sub.2 throughput at 1.72 kg/h. After two 
hours of extraction, the CO.sub.2 feed was halted and the product 
contained in the extractor was discharged and analysed. Its composition 
was as follows: 
paraffinsulphonic acids: 58.91% by weight 
C.sub.12 -C.sub.18 n-paraffins: 0.03% by weight 
water: 28.90% by weight 
sulphuric acid: 12.16% by weight 
The extracted paraffins, collected in the separator, were found to be pure 
and could be recycled to the sulphoxidation reactor without any treatment. 
The extraction apparatus used in the example is shown in FIGURE.

The CO.sub.2 containing the products extracted from the crude mixture fed 
into 4 passes through 6 and leaves the supercritical field in the 
separator 7, where the CO.sub.2 evaporates and is condensed in 8 to then 
return to the already described cycle, whereas the extract remains in the 
separator. Any required make-up CO.sub.2 is fed through 9. 
The separator 7 is provided with two diametrically opposite sight glasses 
for visually checking the level. 
This is kept constant by adjusting the temperature of the water originating 
from a second temperature-controlled bath. The pressure in 7 is kept 
constant by a pressure switch which operates the refrigeration cycle. A 
cylindrical vessel with its top and base of porous sintered steel can be 
arranged inside the extractor 4, to receive the feed of crude product to 
be extracted. In the preferred embodiment, the extractor is filled with 
stainless steel packing held down by a demister. 
A second pump 10 is used for continuous operation to feed the crude product 
to be extracted. In this case, the refined product is discharged through 
the valve 11.