Distribution Of Sulfur Compounds In Arab Crudes

Abstract

Abstract The chemistry of sulfur and sulfur compounds present in petroleum is of vital interest to petroleum present in petroleum is of vital interest to petroleum technologists. This paper describes the results of an analytical study of four Arabian crude oil distillates for the type of sulfur compounds present in them. Each crude oil sample was distilled up to 350 deg. C to separate it into various fractions. The concentration of sulfur compound groups present in each fraction was determined. Introduction Sulfur is among the thirteen most abundant elements making up the crust of the earth. It occurs free in the elemental state, with other elements as minerals, and as a vital constituent in plants and animal tissues. Petroleum and petroleum science is directly concerned with all three forms of sulfur. The chemistry of sulfur is of interest for two main reasons: firstly from a practical point of view, this interest seems principally from the deleterious effects of sulfur compounds on the metals used in processing crude oils and on the undesirable processing crude oils and on the undesirable characteristics which sulfur compounds impart to the products derived from the crude oil and secondly from products derived from the crude oil and secondly from the academic or theoretical point of view, the interest of sulfur in petroleum arises because of the possible bearing which sulfur and its compounds have upon the origin, composition and the geochemical and geological history of petroleum. Crude oils vary in sulfur content from less than 0.05 to more than 14% although relatively few produced crude oils contain more than 4% sulfur. Most mid-east crude oils contain 1 to 3% sulfur. Sulfur compounds found in crude petroleum are commonly considered undesirable in finished oils because of their actual or potential corrosiveness, disagreeable odor, deleterious effect on color or color stability, and unfavorable influence on antiknock and oxidation characteristics. Sulfur and sulfur compounds present in petroleum have previously been studied and the subject comprehensively reviewed by several workers including Dean and Whitehead, Rall et al, Zobell, Challenger and Orr. Drushel has reviewed the types of sulfur present in petroleum with emphasis on the methods used present in petroleum with emphasis on the methods used in their analysis. However, the bulk of the work done has dealt with U.S. crude oils and relatively little has been reported on mid-eastern or Saudi crude oils. Recently we have reported the results of a study of sulfur compounds present in light Arabian and Kuwait crude oils. The present work is concerned with the study of the sulfur compounds found in the distillates up to 350 deg. C of the four Saudi crude oils, namely, Arab Berri, Arab light, Arab medium and Arab heavy. These are the four marketable qualities of Saudi Arabian crude oils. The Berri is a high API gravity, comparatively low sulfur, crude oil. The API gravity for other oils decreases from Arab Light to Arab Heavy. The sulfur content varies from 1.1 for Berri to 2.9 for Arab Heavy. To determine the types and quantity of sulfur compounds present in the crude oils and to enable inter-comparison of these data, separation of these crude oils into uniform boiling ranges is essential. For this study each crude oil was distilled under controlled identical conditions in an all glass apparatus and six distillate cuts prepared up to 350 deg. C were analysed for the types and quantity of sulfur compounds present. present. EXPERIMENTAL Preparation of Cuts: Preparation of Cuts:The crude oil samples were obtained from ARAMCO (Arabian American Oil Company). The apparatus used for crude fractionation was semi-cal series 3650 serial 298 made by Podbielniak Inc., Illinois, U.S.A. and the method adopted was ASTM D2892-78. A weighed sample of about 2.5 litres of stabilized crude petroleum was distilled in a vacuum jacketed fractionating petroleum was distilled in a vacuum jacketed fractionating column of 25-mm diameter, and 1-m length with an efficiency at the total reflux of about 16 theoretical plates. Reflux ratio of 5:1 was maintained at all plates. Reflux ratio of 5:1 was maintained at all operating pressures. Six distillate fractions, the first one up to 100 deg. C and the other five fractions at 50 deg. C intervals up to 350 deg. C were collected. Methods of Analysis: P. 51