Treatment and Recovery of Oil-Based Sludge Using Solvent Extraction

Abstract

Abstract Oil-based sludge is a common by-product of petroleum processing, storage, and transport. It is currently treated to a minor extent before it is disposed of in a landfill. However, as energy costs rise, and environmental impacts become of greater concern, there is increased interest in developing a means to reduce the amount and toxicity of this waste, and to recover useful materials. Solvent extraction was used to treat oil-based sludge from oil tankers. Methyl ethyl ketone (MEK) and LPG condensate were among the solvents used. Different solvent-to-waste ratios by weight were used to determine the optimum process. The mixture was then filtered, and solvent was recovered from the filtrate through distillation. The extraction and filtration steps were at ambient temperature. The recovered fuel oil was analyzed for fuel charactistics. The maximum recovery of fuel oil occurred with a four-to-one ratio of MEK to sludge. Thirty-nine percent of the sludge mass was recovered as fuel oil using this system. On analysis, the recovered fuel oil was similar to typical fuel oils, except for elevated levels of carbon residue and sulfur. This solvent extraction process can be implemented as a continuous process to reduce the amounts of waste oil-based sludge, while recovering valuable fuel oil. Introduction Petroleum refining industries generate relatively large amounts of waste from various sources including waste water, tank bottoms, slop oil emulsion solids and various sludges from oil/water/solids separation. The accumulation of crude storage tank bottoms is a comparatively serious problem experienced by most refineries worldwide. The settling out of sand, rust and heavy fractions of crude oil results in a loss of ullage in the refinery crude storage tanks and can ultimately cause refinery problems when sludge is introduced into the plant. It can cause below-optimal crude throughputs and fouling of heat exchangers. And when solids or emulsions pass from one area to another, an increase in production down-time can result. Since sludge has previously been disposed of at landfill sites and lagoons, valuable hydrocarbons have been lost, which has both environmental and financial implications. As this method of disposal becomes widely unacceptable, alternative solutions providing oil recovery, re-use and recycling are essential.