Abstract

Fractionation of wax from heavy petroleum fractions of different geological origins and their characterization by DSC and HTGC

Author(s): Manoj Kumar Sarmah, Arun Borthakur, Aradhana Dutta

Four north east indian crude oils having different geological origins namely DK (Eocene), SL (Barail), JN (Tipam) and KMC(Girujan) were collected fromwells of different locations. The crude oils were distilled up to 300oC at atmospheric pressure. Waxes from the heavy fractions (3000C+) were separated by solvent extraction method using methyl isobutyl ketone (MIBK) as solvent at different temperatures (40-00C). n-Alkanes and isoand cyclo- alkanes were separated from the wax fractions by urea adduction method. The separated wax and iso- and cyclo- alkane fractions were then analyzed by high temperature gas chromatography (HTGC) for nalkane carbon no. distribution and different non n-alkane compounds present in different wax fractions and differential scanning calorimetry (DSC) for solid-liquid transition temperatures. Clear differenceswere observed for the above parameters in the different fractions. On increasing the temperature of dewaxing there is an increase in average carbon number, peak carbon number and also the molecular weight of the separated wax. In all the crude oilsmaximumwax separation temperature was found to be 300C.At 400C negligible amount ofwaxwas obtained.Major portion of the separated waxes have alkane carbon number from17-25 followed by 26-35 alkane carbon number. DK, SLand JN contain significant amount of C30 and above hopanes whereas KMC contains very insignificant quantities of hopanes. The concentration of C18 isoprenoid, pristane and phytane are more in DK and JN than that of SL and KMC. The solid-liquid transition of waxes increases with increase of separation temperature of the wax. At 00C both solid-solid as well as solid-liquid transition state of wax was observed. But at higher wax separation temperature only one transition i. e. solid-liquid state was observed.