Prevention of Refinery Plugging by Residual Oil Gellant Chemicals in Crude-Optimization of Phosphonate Ester Oil Gellants

Abstract

Abstract Previous research(1, 2) described refinery plugging caused by volatile phosphorus components originating from phosphate ester oil gellants. Also documented were two successful field trials of new phosphonate ester oil gellants used to address this problem. In this paper, results of additional field testing are presented as a final step to broad field application. The objectives of this additional work were to optimize cost and performance, investigate any remaining questions, and establish quality control specifications based on both performance testing and NMR compositional analysis. The synthesis methodology of this new molecule has been refined as a means to reducing final production costs. One objective of the additional field testing was to ensure both operational performance and the ability to control volatile phosphorus while continuing to meet the standards of the first two field trials. Several questions also needed further investigation. One issue was the ability of phosphonate esters to control volatile phosphorus at higher temperatures. Distillations used to evaluate volatile phosphorus to date have had a 250 °C end point. This temperature was chosen because it represents the approximate temperature experienced at the distillation tower trays where plugging has been observed from components condensing from the gas phase. However, the actual peak temperature in the tower bottom is closer to 350 °C. This higher temperature is the actual temperature at which decomposition or volatilization will occur. Therefore, to more fully understand our ability to control volatile phosphorus, distillations were conducted with a 350 °C end point. Volatile and total phosphorus to both 250 °C and 350 °C end points are reported. Another continuing area of concern has been organic halide formation under distillation tower conditions. Although no organic halides were detected in either of the two initial field trials, further testing was conducted during the additional field trials reported in this paper. Finally, quality control methods have been established based on both performance testing and compositional analysis determined using NMR. Overall conclusions are drawn in preparation for broad field implementation regarding:Ability to control volatile and total phosphorus;Ability to prevent organic halide formation;Cost and availability;Rheology and CO2 compatibility;Temperature stability;Field handling and typical concentration ranges; and,Quality control specifications based on performance testing and NMR analysis. Theory Free-radical addition of dimethyl phosphite to an alpha olefin can result in a mixture of isomers. The desired 1 ° product arises from addition to the terminal carbon of the double bond, but some addition of the double bond results in formation of the 2 ° isomer (Figure 1). Depending on the reaction conditions, this byproduct can account for as much as 20% of the product. Both of these isomers are carried through the subsequent dealkylation reaction, again resulting in a mixture of isomers (Figure 2). To obtain a successful product, two characteristics are required: low volatility to prevent distillation tower fouling and the ability to form a good gel. Gelation results from metal complexation with the phosphonate monoester.