Change in composition of deasphalted oils by type of solvent deasphalting for various vacuum residues.

Fundamental relationship of yield and properties of deasphalted oil(DAO), versus factors such as composition of the feedstock, kind of solvent used and extracting conditions were studied for three different vacuum residues using a SDA (solvent deasphalting) pilot plant (2l/h) (Fig. 1).<br>Specially devised interfacial levelmeters between the phases of asphalt and solvent at the bottom of the extractor were installed in the packed column extractor and this made stable operations possible (Fig. 2).<br>The vacuum residues of Arabian Light (A/L), Arabian Heavy (A/H) and Sumatran Light (S/L) were used as feedstocks (Table 1). The above-mentioned feedstocks differ in their compositions as to saturates, aromatics, resins and asphaltens contents. For all feedstocks, metals V and Ni, and nitrogen are mainly found in resins and asphaltens, although their distribution differs among feedstocks. Sulfur is mainly found in aromatics, resins and asphaltens, although their distribution differs among feedstocks (Fig. 3).<br>Five different solvents, Propane (C₃), butane (C₄), n-pentane (nC₅) and two different mixtures of C₄ and nC₅ were studied on their respective features in this work.<br>The effects of operating conditioins, mainly extraction temperature and solvent ratio, were studied and it was found that the top of extractor temperature is very important factor to determine the yield of DAO (Fig. 4). It was found also that the yield depends on the solvent type, while DAO quality is improved with the increased solvent ratio (Fig. 5).<br>From these studies, it was determined that the optimum conditions for the maximum DAO yield are: at the lowest extractor top temperature, solvent ratio 9.0 for C₃ solvent, and 5.0 for C₄ or nC₅ solvent.<br>From experiments involving all the aforementioned feedstocks, it can be seen that metals (V, Ni) content in DAO using C₃ solvent was very low, in the range of 1.0-1.5ppm, while metals and nitrogen content and carbon residues in DAO increased, in cases of using C₄ and nC₅ solvent (Table 2). Further, results showed that C₃ solvent extracts saturates and some parts of aromatics, C₄ solvent extracts saturates, aromatics, and some parts of resins, and nC₅ solvent extracts saturates, aromatics, resins and a small parts of asphaltenes (Fig. 6).<br>Since, almost one-half of the total metals were originally contained in the resin part of the feedstocks (Fig. 3), it was found that higher the resin content of DAO the higher was the metal content (Fig. 6). Further, as high molecular weight resins and asphaltens contain more metals, DAO with a balanced yield and metals content can be obtained with C₄-nC₅ mixture solvent (Fig. 7).<br>Relationships between the removal of elements such as metals, sulfur, nitrogen and carbon residues, and DAO yield (Fig. 8) can be explained by the elements distribution in composition of each feedstock and variations in composition of DAO effected through each extracting operation. Removal of sulur, nitrogen and carbon residues decreased with increase in DAO yield, almost linearly, while removal of metals decreased suddenly when high molecular weight resins were extracted.<br>Almost identical tendencies were observed for all the feedstocks studied, pertaining to changes in composition (Fig. 9).