STABLE FORMS OF DIALKYLAROMATIC SULPHONATES

Abstract: Polyalkyl aromatic sulphonates, and particularly dialky­ laromatic sulphonates, useful as surfactants in steam recov­ ery methods for enhancing oil recovery from subterranean formations, have been found to comprise essentially mix­ tures of meta- and para-isomers obtained by alkylating alkylaromatics, where the alkyl group has from 1 to 4 carbon atoms, with a C₁₄⁻₂₄ olefin. It has further been found that when the ratio of para-isomer to meta-isomer is increased in this mixture, a significantly more hydrolytically, thermally stable surfactant under steam recovery operating conditions is obtained.

Description: STABLZ FORMS OF POLYALKYXAROMATIC SULPHONATtS This invention relates to improved surfactants useful in the recovery of oil, and to methods and compositions employing the same. More particularly, it relates to hydrolytically stable forms of polyalkylaromatic sulphonates which may be used with team in enhancing recovery of subterranean oil. The use of aqueous flooding techniques, with or without the addition of various reagents such as surfactnts, water thickeners and the like. to recover crude oil left pehind in formations after the "primary" oil has jee withdrawn s well established in the art. These dispiacement methods have been improved by the aforesaid surfactants and the like in both secondary and tertiary processes, as where a formation has already been water flooded at least once. Representative of the prior art compositions and methods described above are those taught in US-A 3,348,611 to Reisburg; US-A 3,885,626 to Gale et al; US-A 3,901,317 to Plummer et al; US-A 3,994,342 to Healy et al; and US-A 4,295,980 to Motz, all cf which teach aqueous flooding techniques with at least one surfactant, and in some cases, with viscosity modifiers, co-surfactants or the like. Amongst the more preferred surfactants employed have been the alkyl sulphonates, and particularly the polyalkyl sulphonates such as those derived by the alkylation of toluene, xylene, and the like. Of these, the dialkyl sulphonates are most preferred. In addition to the aforementioned aqueous flooding techniques, the art has also employed steam for secondary and ertiary oil recovery, utilizing the effect of heat to obtain heavy oil from the formations in which it is found. See, for example, US-A 3,357,487 and US-A 3,994,345. The mechanism and effects of surfactants under these high temperatures and diverse formation conditions retain unclear, and thus make it impossible to predict from a knowledge of the effects of aqueous surfactant systems which surfactants, if any, can advantageously be employed in these steam recovery conditions. However, it is known that over a period of time these surfactants dc become deactIvated as a result of the loss of their sulphonate groups because of the high temperatures and other crerat ing conditions of the steam rcovery methods. It is, therefore, an object of this invention to provide surfactants, and partisularly polyalkyiaromatic sulphonates, which are ore stable under the operating conditions of steam recovery methods than those of the prior art. In accordance with te present Invention it has been found that polyalkylaromatic sulphonates obtained by conventional alkylation and sulphonation processes which are well known in the art actually comprise mixtures of meta- and para-isomers of said polyalkyl compounds, and tat surprisingly, when the amount of the para-isomers In the mixture is increased, a significantly more hydrolytically stable sulphonate is obtained which Is resistant to deactivation over longer periods of time Thus the invention provides a method of enhancing the recovery of oil from subterranean formations wherein a polyalkylaromatic sulphonate surfactant is employed in a steam recovary system in which one of the alkyl groups contains 14 to 24 carbon atoms. and the other alkyl group contains 1 to 4 carbon atoms, and wheerin the plyalkylaromatis sulphonate comprises a mixture og para- and meta isomers of @@@@ polyalkylaromatic sulphonates, characterised in that the saic para-isomer is increased in the mixture relative to the amount of said meta-isomer in amounts sufficient t increase the hydrolytic stability cf saId isomeric mixture. This improved sulphonate composition may be used alone or in combination with co-surfactants, viscosity modifiers, hydrotropes or other additives known to those skilled in the art. The polyalkylaromatic sulphonates of te pricr art are generally prepared, as stated above, by first alkylating an alkylaromatisc compound, such as toluene or xylenen, with a long chain olefin or mixture of asuch olefins in the presence of an alkylating catalyst. This reaction, it is not known, actually provides a mixture of meta- and paraisomers of the resulting dialkyl- or trialkylaromatic compound in which the amount of meta-isomer exceeds that-ofthe para-isomer. This mixture is then sulphonated to provide the desired surfactant composition. Since it is now recognized for the first time, in accordance with this invention, than y changing the ratios of these isomers to increase the ar"ount of para-isomer there is obtained a more stable fcrr. of surfactant compo sit on to te usec -n steam recovery methods, it will be recognized Zhat tis desired result may be achieved either by alkylation z.et..ocs which selectively increase the amount of para-isomer, or by adding concentrated or pure paraisomer to an alkylate obtained by conventIonal means. In terms of percentages of te respec ive isomers in the alkylate mixture, it has been form that conventional alkylates prepared by reacting â @@@@-chain olefin with an alkylaromatic starting material generally contain about 35 to 40% para-isomer and 60 to 65% meta-isomer by weight. When this amount cf para-isomer is increased Uy t least bout 5-10 percent, i.e., is at least about 45 weight percent, and desirably as much feasible up to, ideally 100 percent, the effective lifetime of the resulting sulphonate is significantly increased under steam recovery operating conditions, thereby providing increased oil recovery at lower cost. Amongst the polyalkylaromatic compounds which may be employed in the me@n@ds and composition of this innvention are most preferably the dialkylaromatics wherein one alkyl group contains 1 to 4 carbon atoms, and the other is a longer chain moiety containing up to 24 carbon atoms. These dialkyl compounds are generally obtained by the alkylation of such alkylaromatics as toluene, ethyl benzene, cumene and the like. The long chain alkyl moiety of the dialkylaromatic sulphonate (which may be branched or straight-chain) should desirably have from 12 to 24 carbon atoms, and most preferably an average of about 16 to 18 carbon atoms. The term "average" is thus meant to signify that mIxtures of hydrocarbons may be employed wherein the weighted average Is from 16 to 18 carbon atoms even though sorter or longer chain iengths may be present. Alternatively, pure olefins in t;.is range nay also be employed. Thus, in one embodiment cf the invention, the alkyl moiety may be derived from a mixed C14-18 a-olefin source in which the molecular weight distribution is such that the resultant alkylate side cain has 16 carbon atoms, even though lesser amounts og somewhat shorter or longer chain lengts may be present. One preferred alkylate, having an average number of carbon atoms cf about 16.2, may be derived fror: a wax- cracked C14-18 0-clefin, and has the following weight distributiorl: Carbon Atoms in Side Chain eight Distribution (%) C14 2 C15 30 C16 30 C17 28 C18 10 Alternatively, the olefin may be a C14-18 mixture derived from the polymerization of ethylene in a known manner, wherein the average alkyl group is 16.0, and wherein the mixture is further characterized by alkyl groups having even-numbered carbon atoms only. A typical weight distribution of such a mixture is as follows: Carbon Atoms in Side Cahin Weight Distribution (%) C14 25 50 '18 25 Conventional alkylation methods leading to a mixture of dialkylaromatic isomers, generally in the ratio of about 40:60 of para:meta, are well-known in the art and need not be described in detail here. However, it has been found that one method for accomplishing the objectives of this invention, i.e., 'o increase the ratio of para- to mataisomer in the a;:yiate, is to modify the operating temperautres in, for example, an HF alkylation process. Thus, it has been found that when the temperature of a known HF alkylation process is reduced from about 75 to 100 C. down to about 0 to 25 C., there is obtained in the product mixture a ratio of about 70:30 of para:n-tta isomers. Other methods, sut as alkylation using annsr. tetrachloride, are a Ise known in the art for increasing the ratio of the para-isomer, as for example the procedure of N.M. Cullinane et al. described in J. Chem. Soc., 1954., at page 2942. Also, as stated above, if desired, this ratio can be increased by simply adding more para-isomer to the alkylate, or less desirably, separating and removing as much of the meta-isomer from a conventional alkylate as is feasible. after the desired ratio of para- to meta-isomer is obtained, te alkylate may then e sulphonated by methods well-known in the art, and the resulting more highly stable form of polyalkylaromatic sulphonate used in the process of this Invention. he unexpected superior hydrolytic stability of the para-isomer of dialkylsulphonates is illustrated by the data in Example 1. EXAMPLE 1 A series of sulphonate decomposition reactions was carried out in a 300-ml Parr stainless steel reactor equiped with a sampling tube, pressure relief valve, pressure gauge and thermowell. The reactor was heated via an external proportionating heater, ar: sales were withdrawn through coiled 3.2 mm (1/8-inch) stainless steel tube immersed i an ice-beth thereby providing only condensed samples. r:is system was purgec between samples. The reactor was chrged with 200-220 mis of 1% (wt.) aqueous surfactant solution and the en+. fre system swept wit nitrogen. sulphonate solutions were prepared in deionized water; samples were analyzed in triplicate for surfactant by HPLC. Following the above procedure, the rate cf ces'lphon- at ion of p-2-hexadecyl toluene sulphonate was ccred with m-2-hexadecyl toluene sulphonate at 299 c and buffered at pH-4. The following results were obtained. TABLE 1 2-m-Tolyhexadecane 2-p-Tolyhexadecane Time (hrs.) Activity (%) Tie (hrs.) Actlvitv (%) 0 0.759 0 .13 1 0.707 1 1.14 10.05 0.517 3.0 .02 35.50 0.440 5.0 0.98 59.33 0.310 84.5 1.13 65.36 80.211 113.9 1.11 156.8 1.09 280.3 1-.05 Thus, it is seen that the para-isomer possesses greater stability against desulphonation than does the meta-isomer. EXAMPLE 2 A commercially prepared C14 -8 alkyltoluene sulphonate mixture in which the orientation of the alkyl groups was 60% meta-isomer and 40% para-isomer was subjected to the desulphonation conditions described in the previous example. After 42 hours, the reaction was stopped and the hydrocarbon layer arising from the desulphonation reaction was isolated and analyzed by capillary gas chromatography. This material was more than 90% of the meta-oriented alkyltoluene. Thus, the more rapid hydrolysis of the meta-dialkyl apromatic sulphonate isomer in a commercial mixture is estabilished When a similar experiment is carried out using a mixture of dialkyl sulphonates having a predominate para- isomer composition, the tire required to attain the save degree of hydrosis is always greater than when the metaisomer is the principal component, therebly allowing the surfactant greater lifetim- in the reservoir, resulting in better oil or overise.

Claims: CLAIMS: 1. A method of enhancing the recovery of oil from subterranean formations wherein a polyalkylaromatic sulphonate surfactant is employed in steam recovery system in which one of the alkyl groups contain 14 to 24 carbon atoms, and the other alkyl group contains 1 to 4 carbon atoms, and wherein the polyalkylaromatic sulphonate comprises a mixture of para- and meta-isomers of said polyalkylaromatic sulptonates, characterised in that the said para-isomer is increased in the mixture relative to the amount of said meta-isomer In amounts sufficient to increase the hydrolytic stability of said isomeric mixture. 2. A method according to Claim 1, wherein, the polyalkylaromatic sulphonate is a dialkylaromatic sulphonate. 3. A method according to Claim 2, wherein the dialkylaro- matic sulphonate an alkyltoluene sulphonate, said alkyl group having from 14 to 24 carbon atoms. 4. A method according to Claim 3, wherein the dialkyl aromatic sulphonate is a C14-18 alkyltoluene sulphonate, said C 18 alkyl group having an average of about 16 carbon atoms. 5. h method according to any of Claims 1 to 4, wherein the weight percent of the para-isomer of the poly yakyl- aromatIc sulphonate is at least 45 percent. 6. A method according to any of claims ' to 5. wherein the surfactant is accompanied by a consurfactant, viscosity modifier, a hydrotrope, or mixtures ;r the same.

Inventors: ANGSTADT, HOWARD P.
Applicants: SUN REFINING AND MARKETING COMPANY
Application year: 1985
Main classification: E21B43
IPC codes: C07C301, C07C67, C09K8, E21B43, C07C309