Chemistry and kinetics of LAS acid thermal decomposition

Abstract

The emission of sulfur dioxide (SO 2 ) from linear alkylbenzene sulfonate (LAS) acid (LASH) at high temperatures has been studied. Rate constants and Arrhenius parameters have been determined, enabling estimation of the amount of SO 2 evolved under any time/temperature combination for risk assessment purposes. Further analysis of the kinetic data and comparison with earlier molecular modeling work on the mechanism of sulfonation of linear alkyl benzene (LAB) to make LASH provide insight into the reaction pathway of SO 2 formation by thermal decomposition of LASH. For risk assessment purposes, the calculation is as follows: Estimate k from k = 3.9 × 10 7 ·e −13,000/(273+T) where T is in degrees C and k is in s −1 . Estimate N(SO 2 ,t), the number of moles of SO 2 evolved when N(LASH 0 ) moles of LASH are heated for t s at T°C, from:Paper no. S1254 in JSD 5, 111-115 (April 2002).KEY WORDS: Color formation, sulfonation, sulfur dioxide, sulfur trioxide.When working with linear alkylbenzene sulfonate (LAS) acid (LASH) we have often observed an odor of sulfur dioxide (SO 2 ), particularly at high temperatures. Formation of SO 2 from LASH does not appear to have been investigated previously. We therefore carried out kinetic studies to understand the nature of the chemical reactions involved and to enable the prediction of the SO 2 emission for any LASH heating situation.In the present work a series of experiments was carried out to measure the amounts of SO 2 released on heating LASH at temperatures between 170 and 220°C. MATERIALS AND METHODSLASH was obtained from the sulfonation plant at the Lever Fabergé factory in Port Sunlight (Wirral, United Kingdom). LASH (ca. 3.5 g) was heated in a two-necked flask at a fixed temperature (ranging from 180 to 220°C). A continuous stream of nitrogen was passed into the flask, and the exiting gas was passed through a Drechsel bottle containing 100 mL 0.1 M NaOH, to collect any SO 2 and convert it to sodium sulfite. At various time intervals the Drechsel bottle was replaced and the contents analyzed for sodium sulfite by addition of excess iodine followed by back-titration with sodium thiosulfate solution. RESULTSThe results from kinetic experiments in which LASH was heated at temperatures ranging from 180 to 220°C are presented in Table 1.The nature of the organic reactions was not known when the work started. The two most likely possibilities were:NMR and IR spectra of the nonvolatile residue after the reaction showed no evidence of phenolic OH groups and indicated that the major component was LAB, i.e., the reaction occurring is shown in Equation 1, desulfonation.First-order kinetic analysis. The simplest way to analyze data of the type shown in Table 1 is by first-order rate plots, for which in this case ln(100 − %SO 2 ) is the appropriate function to be plotted against time. These plots give reasonably straight lines whose slopes are the first-order or pseudo firstorder rate constants k obs . Figure 1 shows one of these plots (for the run at 200°C), and Table 2 lists the k obs ...

Coloration Process in the Sulfonation of Fatty Acid Methyl Ester with Sulfur Trioxide

“…Sperling reacted cyclohexane with fuming sulfuric acid, and discovered the generation of alkene and SO 2 . Roberts also reported that SO 2 was generated in the production of linear alkyl benzene sulfonate (LAS) [14]. On the other hand, the colored species in the ME reaction mixture was suggested to have a sulfonated polyolefin structure with conjugated double bonds [9], but there has been no report on the gas generated in the course of ME sulfonation.…”

Alkylaromatics in Detergents Manufacture: Modeling and Optimizing Linear Alkylbenzene Sulfonation

“…Linear alkylbenzene (LAB) is one of the most common organic feedstocks used in the detergent industry. Linear alkylbenzene sulfonic acids (ASA) of high molecular weight (315–335) are the anionic surfactants used in all ranges of household detergent formulation, especially in heavy‐duty laundry products, sometimes in combination with nonionic alcohol sulfates from tallow and soaps (Roberts, ; Roberts & Lejeune, ; Shukla, Arnipally, Dagaonkar, & Joshi, ; Wang et al, ; Yamane, ). The ASA technology has almost completely replaced the older technologies for surfactant production because of improved biodegradability and cost effectiveness.…”