Sulfonation of Petroleum Feedstocks In a Wiped Film Reactor
Authors: Ashcraft T.L. , Saunders R.K. 
Published: March 2010

This paper summarizes the yields of broad-spectrum sulfonates obtained from the sulfonation of selected petroleum fractions using gaseous SO3 in a wiped film reactor. Sulfonation is selective toward molecules having more than two aromatic rings. SO3-to-feed ratios well in excess of 1.0 mole SO3/mole feed aromatics are required to achieve aromatics conversions in excess of 50–70%. Sulfonic acid decomposition with concomitant formation of SO2 can significantly reduce sulfonates yield. Sulfonic acid decomposition, which can- be minimized by rapid neutralization of the acid product, is an important consideration in the design of a sulfonation process.

Introduction

Sulfonates produced from tube-boiling-range petroleum-fractions are potentially important as tertiary oil recovery surfactants(1). This type of broad-spectrum sulfonate can be produced from one of several processes which utilize either oleum or SO3 as the primary sulfonating agent. Hydrocarbon sulfonates are a major component in many micellar formulations. Both the yield of hydrocarbon sulfonate per unit feedstock and the type and distribution of sulfonation by-products will strongly influence projected surfactant manufacturing costs and the properties of the resulting surfactant.

The objective of this study was to investigate the sulfonation of selected lube-boiling-range petroleum fractions under a variety of reaction conditions utilizing a wiped film reactor and gaseous SO3. Product distributions and, yields are correlated against feed molecular weight and type, SO3-to-feed ratio, elapsed time between sulfonation and neutralization, and reactor effluent temperature.

Chemistry

The formation of broad-spectrum petroleum sulfonates occurs primarily through reaction of SO3 with molecules in the oil which contain at least one aromatic ring(2, 3, 4), followed by neutralization of the resulting free acid.

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The aromatic portion of the molecule may contain either a single ring (e.g., alkyl benzene) or two or more condensed rings (e.g., alkyl naphthalene). In addition to the primary sulfonation reaction, contact between the complex mixture of molecules comprising a petroleum oil and gaseous, SO3 can produce a variety of by-products, which include polysulfonates, anhydrides, sulfones, sulfinic acids, H2SO4 and SO2(5). Desulfonation of the free sulfonic acid is an important side reaction and can occur through formation of an unstable sulfinic acid(6).

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Reactions (3) and (4) are important because they can significantly reduce yields and produce SO2, an undesirable by-product. Direct SO3, oxidation of the feed can produce both SO2 and sulfuric acid as by-products.

After neutralization, the inorganic salt fraction of the neutralized sulfonation product contains of salts of both sulfuric and sulfurous acids.

In addition to the aromatics, nonaromatics which contain a reactive site within their structures can also react with SO3). Olefins and molecules containing heteroatoms (sulfur, oxygen, etc.) are potential candidates. Data obtained in this study show that the contribution of nonaromatic compounds to the sulfonates product is relatively small compared to that of the aromatics fraction.

Sulfone formation is another typical side reaction which consumes sulfonic acid groups:

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