Heat-transfer analogy for wax deposition from paraffinic mixtures

Wax deposition from mixtures of a paraffinic wax (C-20-C-40) dissolved in n-dodecane (C-12) was investigated. A novel batch apparatus was developed, in which the flow of a "hot" wax-C-12 mixture was accomplished with an axial flow propeller while the solid deposition took place on the inner "cold" surface of a draft tube. The effects of mixture composition, shear rate, residence time, and temperature on solid deposition were studied at pseudo-steady state. Predictions from a steady-state heat-transfer model were in good agreement with experimental data, which confirmed the wax deposition process to be controlled primarily by heat transfer. A temperature difference ratio corresponding to the fractional temperature difference across the deposit layer was related to the amount of deposited solids. GC analyses of the deposited solids were used to study compositional changes within the liquid and solid phases.