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

Abstract Previous research1,2 described refinery plugging caused by volatilephosphorus components originating from phosphateester oil gellants. Also documented were two successful field trials of new phosphonate ester oilgellants 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, andestablish 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 volatilephosphorus at higher temperatures.Distillations used to evaluate volatile phosphorus to date have had a 250 ° Cend point. This temperature was chosen because it represents the approximatetemperature experienced at the distillation tower trays where plugging has beenobserved from components condensing from the gas phase. However, the actualpeak 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 wereconducted with a 350 ° C end point. Volatile andtotal phosphorus to both 250 ° C and 350 ° C end points are reported. Another continuing area of concern has been organic halide formation underdistillation tower conditions. Although no organic halides were detected ineither of the two initial fieldtrials, 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.Quality control specifications based on performance testing and NMR analysis. Theory Free-radical addition of dimethyl phosphite to an alpha olefin can result in amixture of isomers. The desired 1 ° productarises from addition to the terminalcarbon of the double bond, but some addition of the double bond results information of the2 ° isomer (Fig. 1). Depending on the reaction conditions, this by product can account for as much as 20% of the product. Both of these isomersare carried through the subsequent dealkylation reaction, again resulting in amixture of isomers (Fig. 2). To obtain a successful product, two characteristics are required: low volatility to prevent distillation towerfouling and the ability to form a good gel. Gelation results from metal complexation with the phosphonate monoester. The poorer performance of themonoester product resulting from alkylation at the 2 ° carbon can be explainedby greater steric effects compared to the less-hindered primary isomer.

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