Enhancement of the Physical and Molecular Properties of Sudanese Crude Oil (Rawat) Using Solvent Dewaxing Process

Abstract

This study was conducted to treat the Sudanese crude oil from Rawat area southwest of Kosti which has a high wax content of 26.3% by weight and pour point 54°C, in order to remove the wax and to reduce the pour point and enhance the physical and molecular properties of the treated oil using organic solvent de-waxing technology. The physical and molecular properties of crude oil and the oils produced from the treatments were obtained using American Society for Testing and Materials (ASTM) methods and materials. Methyl Ethyl Ketone (MEK)- Methyl Isobutyl Ketone (MIBK)- Butyl Acetate (BA)- Methyl Tert-butyl Ether (MTBE) were used as de-waxing solvents. The de-waxing temperatures at -5, -10, -15 and -20°C and solvent feed ratio of 10:1, 8:1, 6:1, and 4:1 with constant washing ratio 2:1 and crystallization time 6, 12 and 24 hours. MEK recorded as the best oil production, at 10:1 S/F ratio which is 16.81% with pour point equal 2°C at de-waxing temperature -10°C, while MIBK recorded 29.14% of yield, pour point 5°C at 10:1 S/F and e-waxing temperature -10°C, Due to high cost of this ketone is very expensive, so it has been excluded and also MEK has low yield as a single solvent and requires a companion solvent such as toluene to increase the solubility. Recovery of mixed solvents is not desirable due to the differentiation in their boiling points range, and it is too hard to separate the two solvents upon making distillation and it is recovery for another de-waxing step. When using butyl acetate, the yield was 36% and the pour point was 5°C. Therefore, this represents the best result compared to the previous solvents. Methyl tertiary butyl ether recorded a high yield 68.19% but also a high pour point 28°C because a high percentage of wax was soluble in solvent, the percentage of wax in the oil produced was equal to 18.8%, so the solvent was excluded. Butyl acetate was selected to remove wax from crude oil and solvent ratios were used 10:1, 8:1, 6:1 and 4:1 and the best ratio was 10:1 and de-waxing temperatures were -5, -10, -15 and -20°C and the best one was -10 degrees, crystallization times are 6 -12 -24 hours and the best time is 24 hours because the size of the crystals is larger and the removal efficiency is higher. Thus, it can be concluded that the process of de-waxing at crystallization time of 24hrs would be suitable and is the one selected for de-waxing of Sudanese crude oil using Butyl Acetate at dilution solvent ratio of 10:1 and at de-waxing temperature of −10°C.