CRYSTALLIZATION OF NORMAL-DOTRIACONTANE FROM HYDROCARBON SOLUTION WITH POLYMERIC ADDITIVES

A fuel oil is simulated with n-dotriacontane (n-C32H66), a normal alkane present in a typical middle range wax, dissolved in m-xylene. Physical properties and crystal growth rates are reported for a range of temperatures and concentrations, with and without fumarate vinyl acetate (FVA) copolymers present. Solubility, which obeys the Van 't Hoff equation, increases in the presence of copolymer additive provided that the alkyl side chain length of the additive is close to that of the solute. Diffusivity, {reversed tilde}5X10-6cm2 s-1, decreases by an order of magnitude in the presence of additive, regardless of the side chain length. The crystal growth rate in the (110) direction varies from {reversed tilde}1 to 3 μm s-1 at 14.5°C over the relative supersaturation range 1.0< σ <1.5. The copolymer concentrations at which wax crystal growth is completely arrested, exhibit a step-change on passing from C14FVA (105 ppm) to C16FVA (103 ppm). Crystal habits also depend strongly on additive side chain length. Lattice matching between the additive and solute structures is shown to be critical importance. © 1990.