The process is especially suitable for bleaching alkylarylsulfonic acids with 4 to 12 carbon atoms in the alkyl group and one or two benzene rings, the alkali salt of these compounds, alkyl sulfonic acids with l2 to 20 carbon atoms and .the alkali salts of the latter compounds prepared on a technical scale.
The principal object of this invention is to produce an alkyl aryl sulfonic acid having a materially improved color. Another object of this invention is to retain the benefit of the low-color, bleached sulfonic acid by stabilization, including neutralization thereof, to provide an alkyl aryl sulfonate which is substantially white. Still another object of this invention is to effect dry neutralization of the bleached alkyl aryl sulfonic acid with solid, pulverulent, anhydrous, alkali metal salts with or without the presence of detergent builder salts, to directly produce a high-active detergent composition. Further objects and advantages of this invention will be apparent from the following description and appended claims.
Critical control of the temperature of the sulfonic acid while in the presence of hydrogen peroxide has been found to be essential. A temperature range of from about 40 to about 60 C. can be employed, but even temperatures above about 55 C. often cause erratic results and bring about reversion of the bleached sulfonic acid to a higher color. Accordingly, the bleaching process is preferably carried out between about 40 to about 55 C. and more preferably between about 40 and about 45 C. To avoid local overheating of the sulfonic acid in the presence of the hydrogen peroxide it is necessary to maintain suitable agitation to effect adequate heat-transfer during the bleaching operation.
Hydrogen peroxide is commercially available in a number of grades as solutions containing varying amounts of hydrogen peroxide such as 3%, 6%, 27.5%, 30%, 35%, 50%, 90% and 99-l-%. The high-strength materials are too active for direct addition to the sulfonic acid since they cause degradation of the acid. Whereas the dilute solutions can be employed the additional Water introduced therein may limit the use of the bleached sulfonic acid in the dry neutralization process for the preparation of detergent compositions. The preferred concentration of hydrogen peroxide is 30%, but equivalent amounts of medium-strength solutions can be employed. The quantity of 30% hydrogen peroxide necessary to effectively bleach the sulfonic acid may range up to about 5 percent by weight of the acid, but preferably ranges from about 1 to about 3 percent thereof. It is desirable to avoid the use of excess hydrogen peroxide since its presence may ultimately cause degradation of the alkylbenzene sulfonic acid if it is subject to relatively high temperature during storage and transit. If the maximum temperature to which the bleached sulfonic acid is subjected does not exceed about 25 to 30 C. the reversion does not present any serious problem. When the storage and transit temperatures are in doubt it is desirable to treat the bleached sulfonic acid with from about 1 to about 2 percent by volume of a saturated solution of sodium bisulfite to stabilize the treated acid. Also the use of excess hydrogen peroxide imparts a fruity estertype odor to the sulfonic acid which is undesirable in detergent compositions produced therefrom.
Before: Bleach or acid soak?
Answer: Acid; however, container needs to be clearly labeled.