PROCESS FOR THE HANDLING OF DIALKYL SULPHOSUCCINATES

Abstract: C₄-C₁₆ dialkyl sulphosuccinates are prepared as 30-50% by weight aqueous compositions at reaction temperatures above 85°C. In order to prevent a sudden large viscosity rise on cooling below 75°C, urea (10 to 30% by weight based on the dialkyl sulphosuccinate) is added to the reaction mixture as it cools.

Description: PROCESS FOR THE HANDLING OF DIALKYL SULPHOSUCCINATES The present invention relates to the preparation of salts of dialkyl esters of sulphosuccinic acid, hereinafter referred to as dialkyl sulphosuccinates. These materials are useful inter alia as detergent-active agents. Dialkyl sulphosuccinates are materials of the general formula I. EMI1.1 wherein R1 and R2 are straight-chain or branched-chain alkyl groups, and may be the same or different, and X is a monovalent cation or 1/m of an m-valent cation. For detergent activity, the alkyl groups R1 and R2, which may be the same or different, generally have 4 to 12 carbon atoms, and X is a solubilising cation, for example, alkali metal, ammonium, substituted ammonium or magnesium. The synthesis of dialkyl sulphosuccinates is well documented in the literature, for example in US 2 028 091 and GB 760 121 (American Cyanamid), DD 75075 (Weigner), GB 1 576 019 (BASF), GB 1 215 561 (belle Bezons), and GB 1 527.020 (Chemische Fabrik Pfersee). The preferred method for making these materials is by bisuiphite addition to the corresponding dialkyi maleates and/or fumarates. The reaction is generally carried out in an aqueous medium, optionally in the presence of ethanol, at elevated temperatures above 85"C. The sulphiting agent is generally a water-soluble sulphite-ion-generating salt, for example, an alkali metal or ammonium sulphite, bisulphite or metabisulphite. The present invention is especially concerned with the preparation of dialkyl sulphosuccinates for use in liquid detergent compositions. For this end-use, the reaction may conveniently be carried out in relatively large quantities of water, to give a final aqueous product having a concentration of about 30 to 50% by weight. If desired, small amounts of ethanol may also be present. After the reaction is complete the mixture is cooled from the relatively high reaction temperature above 85"C to a desired temperature for further processing or storage. The product mixture is a non-Newtonian pseudo-plastic liquid and during this cooling stage an unexpected problem has been encountered in that as the temperature falls the viscosity rises sharply so that the reaction mixture becomes a highly viscous mass which is very difficult to handle. The highly viscous mass cannot readily be cooled further using conventional cooling equipment because of poor heat transfer and poor fluid flow properties. The tendency to form a highly viscous mass during cooling is especially marked when dialkyl sulphosuccinates of more than one alkyl chain length are present. Various measures have been tried in an attempt to alleviate this problem. Varying the electrolyte content has been found to be ineffective, as has the addition of other detergent-active materials, for example, alkyl ether sulphates. The problem can be circumvented by working at lower concentrations or by using large amounts of ethanol, but the final product is then no longer tailored to end-user requirements. Large amounts of ethanol give products of unacceptably low viscosity. It has now been found, according to the present invention, that in the presence of relatively low amounts of ethanol the addition of urea in a particular amount at or near the beginning of the cooling stage is highly effective in preventing a steep rise in viscosity. This is surprising because above about 750C the decomposition of urea into ammonia and carbon dioxide starts to become significant, yet in the process of the invention it is generally necessary to add it to the reaction mixture at temperatures not significantly below this figure. The presence of urea in the final product at the sort of levels in question is also advantageous because, as is well known in the art, urea is a useful hydrotrope and formulation aid in liquid detergent compositions. The present invention accordingly provides a process for the preparation of an aqueous composition containing from 30 to 50% by weight of at least one C4-C16 dialkyl ester of sulphosuccinic acid, which comprises the steps of: (a) chemically synthesising one or more C4-C16 dialkyl esters of sulphosuccinic acid in an aqueous reaction mixture at a concentration or from 30 to 50% by weight at a temperature above 850C, (b) cooling the mixture, in the presence of from 2 to 20% by weight of ethanol, to a temperature below 750C, preferably below 700C, at which the mixture is still fluid, (c) adding to the cooled reaction mixture from 10 to 30% by weight of urea, based on the dialkyl sulphosuccinate; and (d) cooling the mixture further to a desired temperature for storage or further processing. Preferably step (b) comprises cooling the mixture to a temperature at which its viscosity does not exceed 50 poise, and more preferably does not exceed 20 poise, at a shear rate of 110 The dialkyl sulphosuccinates with which the invention is concerned preferably have alkyl chain lengths within the range of from C4 to C10, more preferably C6 to C8. Dialkyl sulphosuccinates of this chain length are especially suitable for use in high foaming light duty liquid products. If desired, mixtures of dialkyl sulphosuccinates of different chain lengths may be prepared by the process of the invention. In such mixtures, the individual dialkyl sulphosuccinates may be either symmetrical (both alkyl groups the same) or unsymmetrical (with two different alkyl groups). Of especial interest are mixed dialkyl sulphosuccinates derived from mixtures of two or more alcohols, notably the mixtures described and claimed in GB 2 108 520 (Unilever) and British Patent Application No. 84 01449 (Unilever) An example of the former type of product is the C6/C8 mixed system derived from a mixture of C6 and C8 alcohols and containing the symmetrical dihexyl and dioctyl sulphosuccinates as well as the unsymmetrical hexyl octyl sulphosuccinate. The latter material is described and claimed in GB 2 105 325 (Unilever). Mixed C7/C8 and C6/C7/C8 systems derived from mixtures of the corresponding alcohols are described and claimed in the aforementioned British Patent Application No. 84 01449 and are also highly preferred in the context of the present invention. The synthesis of the dialkyl sulphosuccinate in step (a) may be carried out by any method suitable for operation under aqueous conditions to give a final product having a concentration of 30 to 50% by weight, preferably 35 to 40% by weight, and which requires a reaction temperature above 85"C. As previously indicated, the normal and most convenient synthetic route is by way of bisulphite addition to the corresponding dialkyl maleate and/or fumarate. These in turn may be prepared by esterification of the corresponding alcohol or mixture of alcohols with maleic anhydride or maleic acid, preferably maleic anhydride. The sulphitation process is well known in the art and details are given, for example, in the patent specifications mentioned previously. Thus according to a preferred embodiment of the invention step (a) comprises reacting together at least one C4-C16 dialkyl maleate and/or fumarate and a water-soluble sulphite-ion-generating material. The sulphiting agent may be any material that yields sulphite.ions in aqueous solution. Suitable materials include the alkali metal and ammonium sulphites, bisulphites and metabisulphites. Preferred materials are sodium metabisulphite and sodium sulphite. As previously mentioned, the reaction is carried out in a relatively large volume of water, the concentration of the starting materials being chosen so that the final product has a concentration suitable for its intended end-use. In general the conversion of maleate/fumarate to sulphosuccinate is highly efficient (95-100%) and the yield of sulphosuccinate is of the order of 98% of the theoretical yield, so little or no correction for loss during the reaction is required in choosing the initial concentration. The reaction is generally carried out under reflux conditions under ambient or elevated pressure. The reaction temperature will thus exceed 850C, and will generally exceed 1000C. Typically the temperature will be in the range of from 85 to 1300C. At the end of the reaction the mixture will be at a relatively high temperature and may then be cooled. Cooling is clearly desirable in order to reach a convenient handling temperature, and is also important in order to minimise hydrolysis of the product. - It is during this stage of the process that the sudden increase in viscosity takes place that makes further cooling and handling so difficult. With the C6/C8 dialkyl sulphosuccinate mix the referred to earlier, the viscosity begins to rise steeply at temperatures around 70 to 800C. According to the present invention urea is added during the cooling stage, in time to prevent this dramatic viscosity increase. The addition of urea must not be made too soon, because of its tendency to start to decompose at a significant rate at temperatures above 750C, but on the other hand it must be added before the viscosity has rise to a level at which further cooling and handling become difficult. The lowest temperature at which the urea can be added depends on the rheology of the particular material or materials present. For the C6/C8 mixture, this lower limit will generally be around 600C, and the addition of urea should be carried out at a temperature in the 60 to 700C range, preferably at about 650C. Once urea has been added, the rheology of the mixture changes completely, the viscosity typically falling by a factor of 10 and then increasing gradually as the temperature is reduced further. The urea is added in an amount of from 10 to 30%, more preferably 15 to 25% by weight, based on the dialkyl sulphosuccinate present. At a 40% dialkyl sulphosuccinate level the optimum urea level of about 20% by weight is equivalent to about 8% by weight based on the total composition. The urea is preferably added in the form of a solid, as powder or granules, conveniently in the form of prills. It is essential that some lower alcohol, preferably ethanol, be present during the cooling stage. If alcohol has not been present during the manufacturing step (a), it may be introduced at the end of the reaction before cooling. At least 2% by weight of alcohol, preferably 3 to 6% by weight, should be present during cooling, the percentages being based on the total reaction mixture. Amounts of alcohol exceeding 20% by weight are undesirable for product formulation reasons. The product, having a dialkyl sulphosuccinate level of 30 to 50% by weight, preferably 35 to 40% by weight, and a urea level preferably in the 6 to 10% by weight range, can conveniently be used for formulating a range of liquid detergent products. The invention will now be illustrated by the following non-limiting Examples. Example 1 An aqueous composition containing about 399 by weight (in total) of the mixed C6 and C8 dip alkyl sulphosuccinates described in GB 2 108 520 (Unilever), was prepared by reacting 24 parts C6/C8 dialkyl maleates with 8.7 parts of sodium metabisulphite in the presence of an emulsifying mix of 43.6 parts water, 3.2 parts industrial ethanol and 20 parts of a 40% C6/C8 dialkyl sulphosuccinate mixture (product from a previous batch). The reaction was carried out at 90-950C, in a stirred reactor fitted with a torque measuring device. After 5 hours, the reaction was essentially complete with final mixture containing 39.2% dialkyl sulphosuccinate and only 0.002% dialkyl maleate. At the end of the reaction, the net torque exerted by the stirrer on the liquid was about 1.0 Nm. On cooling to 620C, the net torque rose to about 12 Nm indicating about a 10 fold increase in viscosity. 8 parts of urea were then added, and the net torque fell immediately to about 1.5 Nm. Further cooling was then readily accomplished, during which the net torque rose slowly to reach a maximum of about 9.7 Nm at 300C before falling again rapidly as the temperature was further reduced. The stirrer torque is related linearly to the viscosity, but the relationship is complex and it is not possible to deduce the actual viscosity figures from the torque values. These do, however, show how the viscosity changed on cooling and on the addition of urea. Example 2 Samples of the dialkyl sulphosuccinate mixture prepared as in Example 1, at a concentration of 40% by weight and containing 3% by weight of ethanol, were heated to various temperatures as detailed below in the presence of various amounts of urea, and their viscosities at a shear rate of 110 s 1 were measured by means of a Haake viscometer. The results were as shown in the Table below, the urea percentages being based on the dialkyl sulphosuccinate. Urea Viscosity (poise) at temperature ("C) of level (%) 60 50 45 40 35 30 0 40 35 28 18 9 3 0 40 35 28 18 9 3 7.5 23 30 22 15 10 7 15 1 31 27 21 20 21 20 0.6 0.9 4.5 26 28 1.5 It will be seen that with this particular dialkyl sulphosuccinate system and at this particular concentration level, a 7.5% urea level is clearly inadequate over the whole temperature range and a 15% urea level is unsatisfactory at the lower end of the range. The 20% level is good over the whole range, except for a narrow viscosity peak at 35 to 400C.

Claims: CLAIMS 1. A process for the preparation of an aqueous composition containing from 30 to 50% by weight of at least one salt of a C4-C16 dialkyl ester of sulphosuccinic acid, characterised in that it comprises the steps of: (a) chemically synthesising one or more C4-C16 dialkyl esters of sulphosuccinic acid in an aqueous reaction mixture at a concentration or from 30 to 50% by weight at a temperature above 850C, (b) cooling the mixture, in the presence of from 2 to 20% by weight of a lower alcohol, to a temperature below 750C at which the mixture is still fluid, (c) adding to the cooled reaction mixture from 10 to 305 by weight of urea, based on the dialkyl sulphosuccinate; and (d) cooling the mixture further to a desired temperature for storage or further processing. 2. A process according to claim 1, characterised in that step (b) comprises cooling the mixture to a temperature below 700C at which the mixture is still fluid. 3. A process according to claim 1, characterised in that step (b) comprises cooling the mixture to a temperature at which the viscosity does not exceed -1 50 poise at a shear rate of 110 s 4. A process according to claim 3, characterised in that step (b) comprises cooling the mixture to a temperature at which the viscosity does not exceed 20 poise at a shear rate of 110 5. A process according to any one'of claims 1 to 4, characterised in that the dialkyl sulphosuccinate has a chain length within the range of from C4 to C10. 6. A process according to claim 5, characterised in that the dialkyl sulphosuccinate has a chain length within the range of from C6 to C8. 7. A process according to any one of claims 1 to 6, characterised in that the dialkyl sulphosuccinate include material of more than one chain length. 8. A process according to claim 7, characterised in that the dialkyl sulphosuccinate comprises a mixture of dioctyl, dihexyl and hexyl octyl sulphosuccinates. 9. A process according to any one of claims 1 to 8, characterised in that the reaction mixture at the end of step (a) has a dialkyl sulphosuccinate concentration of from 35 to 40% by weight. 10. A process according to any one of claims 1 to 9, characterised in that step (b) is carried out in the presence of from 3 to 6% by weight of the lower alcohol. llr A process according to any one of claims 1 to 10, characterised in that the lower alcohol comprises ethanol. 12. A process according to any one of claims 1 to 11, characterised in that in step (c) the amount of urea added is within the range of from 15 to 25% by weight, based on the dialkyl sulphosuccinate. 13. A process according to any one of claims 1 to 12, characterised in that the urea is added at a temperature within the range of from 60 to 700C. 14. A process according to anyone of claims 1 to 13, characterised in that step (a) comprises reacting together at least one C4-C16 dialkyl maleate and/or fumarate and a water-soluble sulphite-ion-generating material. 15. An aqueous composition comprising from 30 to 50% by weight of C4-C16 dialkyl sulphosuccinate, whenever prepared by a process according to any one of claims 1 to 14.

Inventors: RAND, JOHN ARTHUR, STANLEY, CHRISTOPHER PAUL
Applicants: UNILEVER NV
Application year: 1984
Main classification: C07C143
IPC codes: C11D3, C07C67, C07C303, C11D1, C07C309, C11D11, C07C301