the anionic surfactant slurries to be treated according to the present invention are those obtained from sulfonation or sulfation of organic starting materials such as olefins having 10 to 22 carbon atoms , paraffins having 10 to 22 carbon atoms , long chain aliphatic alcohols having 8 to 22 carbon atoms , and alkylbenzenes having an alkyl group with 8 to 16 carbon atoms , followed by neutralization . typical examples of the anionic surfactants are alkali metal salts , alkaline earth metal salts , ammonium salts , and alkanol amine salts of internal olefin sulfonic acids , alpha - olefin sulfonic acids , paraffin sulfonic acids , and alkylbenzene sulfonic acids . these sulfonates may be contained , alone or in any mixture thereof , in the anionic surfactant slurries . the anionic surfactant slurries used in the present invention generally contain 10 % to 50 % by weight of the above - mentioned anionic surfactants and 5 parts to 50 parts by weight of the unreacted oil based on 100 parts by weight of the surfactants . furthermore , the anionic surfactants may optionally contain inorganic salts ( i . e ., by - products ), chelating agents such as ethylenediaminetetraacetic acid ( i . e ., edta ), citric acid , and the salts thereof , ph buffers such as benzoic acid , antibacterial agents , and other conventional ingredients . it should be noted that , of these anionic surfactant slurries , the present invention can be especially effective when applied to anionic surfactant slurries of internal olefin sulfonates and paraffin sulfonates , which are less reactive during sulfonation and which contain unreacted oil in a large amount , e . g ., 5 % to 30 % by weight based on the surfactant . the internal olefin sulfonates are those obtained from conventional sulfonation of c 10 to c 22 olefins having a double bond in a non - terminal portion of the carbon chain thereof , followed by neutralization and hydrolysis . the internal olefin sulfonates generally contain 10 % to 50 % by weight of alkene sulfonates , 90 % to 50 % by weight of hydroxyalkane sulfonates , and 0 % to 25 % by weight of disulfonates . according to the present invention , the anionic surfactant slurries should be contained in a pressure - resistant vessel or container and should be maintained under a pressure of 5 kg / cm 2 or more . in order to create a high pressure in the vessel , it is desirable to heat and / or to introduce steam into the vessel . accordingly , the use of pressure - resistant vessels capable of being outwardly heated by , for example , electric heating or steam heating is desirable . in the practice of the present invention , the anionic surfactant slurries are desirably preheated near to an operation temperature before feeding the slurries into the pressure vessel , from the viewpoints of steam consumption and vessel volume . furthermore , the anionic surfactant slurries may be allowed to stand , after preheating , to separate the slurries into an upper layer ( i . e ., unreacted oil ) and a lower layer ( i . e ., a mixture of unreacted oil and the surfactant ) and , then , the resultant lower layer may be subjected to the present process after removing the upper layer therefrom . the steam fed into the anionic surfactant slurries is , for example , saturated steam having a temperature of 130 ° c . to 250 ° c . although the amount of steam fed into the anionic surfactant slurries can be appropriately determined depending upon the pressure , the steam is desirably used in an amount of 5 to 80 times by weight , especially 15 to 60 times by weight , of the unreacted oil in view of the treatment efficiency . if the amount of the steam is less than 5 times by weight of the unreacted oil , a sufficient removal efficiency of the unreacted oil cannot be obtained . contrary to this , if the amount of the steam is more than 80 times by weight of the unreacted oil , the removal efficiency is not increased with the increase in the amount of steam so that it is not desirable from the economical point of view . in order to increase a gas - liquid contact efficiency of the steam and the slurry , raschig rings , stationary type mixing devices , or other similar mixing means can be desirably placed or equipped in the gas - liquid region to economically decrease the feed amount of the steam . the steam is continuously introduced into the anionic surfactant slurry under a high pressure of 5 kg / cm 2 or more , preferably 7 to 50 kg / cm 2 . the desirable gas - liquid contact time of the steam and the slurry under the high pressure is about 5 minutes or more . the removal efficiency of the unreacted oil increases as the contact time becomes long . however , since too long a gas - liquid contact time tends to result in deterioration of the recovered unreacted oil and the surfactant slurries , the gas - liquid contact time is preferably about 30 minutes or less . although the pressure in the discharge zone is sufficient if less than the above - mentioned high pressure , the surfactant slurry is flashed off under an atmospheric pressure . the flashed gas is recovered as a condensate in a heat exchanger and the unreacted oil and water are readily separated by a settling separation . the recovered unreacted oil can be recycled to a sulfonation or sulfation step directly or after being purified by a dewatering treatment or an activated clay treatment . the removal of unreacted oil from a surfactant slurry according to the present invention can be carried out in , for example , an apparatus as shown in fig1 . an anionic surfactant slurry containing unreacted oil is quantitatively fed via a line 1 by means of a feed pump ( not shown ) into a pressure resistant vessel ( resistant up to 100 kg / cm 2 g ) 4 provided with a jacket and packed with raschig rings . on the other hand , saturated steam having a temperature of about 130 ° c . to about 250 ° c . is continuously fed via a line 2 into the vessel 4 , while maintaining the pressure within the vessel 4 to 5 kg / cm 2 or more by a pressure control valve 5 provided at the outside of the vessel 4 . thus , the gas - liquid contact is thoroughly effected in the vessel 4 . then , the gas - liquid mixture is flashed , under an atmospheric pressure , in a cyclone type gas - liquid separator 6 . the pressure vessel 4 is desirably kept warm or heated by passing steam from a portion 3 through the jacket . the flashed unreacted oil and steam are condensed in a condenser 7 and the condensate is separated in a settling separator 8 . the separated unreacted oil is recovered from a line 10 and the separated water is recovered from a line 11 . the anionic surfactant slurry is obtained as an aqueous slurry from a bottom 9 of the gas - liquid separator 6 , without evaporating upon flashing . according to the present invention , unreacted oil is effectively recovered from an anionic surfactant slurry as mentioned above . especially , according to the present invention , the following advantages can be obtained : ( 1 ) since the removal of the unreacted oil is effected under a high pressure of 5 kg / cm 2 or more , undesirable foaming due to the presence of the surfactant can be readily prevented and , therefore the removal efficiency of the unreacted oil is remarkably increased ; and ( 2 ) since saturated steam having a high temperature of 130 ° c . to 250 ° c . is used , a molar fraction of an oil component in the distilled or flashed vapor becomes large and the steam consumption required for the recovery of the unreacted oil becomes very small . the present invention now will be further illustrated by , but is by no means limited to , the following examples , in which all percentages are expressed on a weight basis unless otherwise specified . olefins having an internal double bond and having 13 and 14 carbon atoms ( c 13 : 55 %, c 14 : 45 %; positions of double bonds 1 - position 0 %, 2 - position 27 %, 3 - position 21 %, 4 - position 20 %, and 5 to 7 positions 32 %) were sulfonated by using a continuous thin - film type sulfonator and , then , the sulfonated product was neutralized and hydrolyzed in a conventional manner . thus , an aqueous slurry of sodium internal olefin sulfonates having a surfactant content ( i . e ., &# 34 ; ai &# 34 ;) of 30 % and a unreacted oil content of 25 % based on ai was obtained . the aqueous anionic surfactant slurry thus obtained was treated by using an apparatus shown in fig1 . the anionic surfactant slurry was quantitatively fed via a line 1 into a pressure vessel 4 at a rate of 10 kg / hr , while saturated steam having a pressure of 13 kg / cm 2 g ( gauge ) was introduced , via a line 2 , into the pressure vessel 4 . the pressure vessel 4 having a capacity of 10 liters was packed with raschig rings and was kept warm or heated by passing steam having a pressure of 13 kg / cm 2 g through a jacket of the vessel 4 . the gas - liquid contact was effected in the vessel 4 by changing the feed amounts of the steam and by controlling the system pressures by means of a pressure control valve 5 . thus , the mixture of the aqueous surfactant slurry and the steam was flashed off under an atmospheric pressure to recover a surfactant slurry from the bottom 9 of a separator 6 and unreacted oil from a line 10 . the results thus obtained and the operation conditions are shown in table 1 . table 1______________________________________run nos . 1 *. sup . 3 2 *. sup . 3 3 4 5 6______________________________________conditionssteam feed amount *. sup . 1 0 40 60 40 30 15system pressure ( kg / cm . sup . 2 g ) 10 2 7 7 10 10resultsurfactant slurry ai (%) 33 25 26 26 28 29surfactant unreacted oil 22 . 7 11 . 3 1 . 6 2 . 1 2 . 6 3 . 0 (%)*. sup . 2removal efficiency of 92 55 94 92 90 88unreacted oil (%) ______________________________________ *. sup . 1 times by weight based on unreacted oil *. sup . 2 based on ai *. sup . 3 comparative examples unreacted oil was removed from various aqueous surfactant slurries listed in table 2 in the same manner as in example 1 except that 5 kg / hr of slurry was fed and saturated steam having a pressure of 45 kg / cm 2 g was used as the steam fed into the slurry and as the jacket steam . table 2______________________________________kind of unreactedsurfactant ai (%) oil (%)*. sup . 1 carbon distribution______________________________________sodium internal 35 35 c . sub . 14 : 15 %, c . sub . 16 : 50 %, olefin sulfonate c . sub . 18 : 35 %( ios - na ) sodium paraffin 15 50 c . sub . 13 or less : 18 %, c . sub . 14 : sulfonate ( ps - na ) 25 %, c . sub . 15 : 25 %, c . sub . 16 : 18 %, c . sub . 17 or more : 14 % potassium alkyl 15 7 c . sub . 12 : 21 %, c . sub . 13 : 29 %, sulfate ester c . sub . 14 : 33 %, c . sub . 15 : 17 %( as - k ) sodium alkyl - 45 5 c . sub . 10 : 12 %, c . sub . 11 : 31 %, benzene sulfonate c . sub . 12 : 27 %, c . sub . 13 : 22 %, c . sub . 14 :( las - na ) 8 % ______________________________________ *. sup . 1 based on ai table 3______________________________________ las - kind of surfactant ios - na ps - na as - k na______________________________________conditionsteam feed rate *. sup . 1 80 40 50 50 40system pressure ( kg / cm . sup . 2 g ) 10 30 20 20 40resultsurfactant slurry ai (%) 30 31 9 9 40surfactant unreacted oil *. sup . 2 2 . 1 2 . 9 6 . 7 0 . 7 0 . 5removal efficiency of 94 92 87 90 90unreacted oil (%) ______________________________________ *. sup . 1 times by weight based on unreacted oil *. sup . 2 based on ai