Denormal oils

In this study, C16-C32 wax distillate is separated into n-paraffin and denormal oil fractions by vapor phase contacting with type 5A molecular sieves. 2,2,4-Trimethylpentane (isooctane), 2,2-dimethylbutane, and 2-methylpentane are each used as the supercritical fluid. Recovery of n-paraffins from the molecular sieves is accomplished by contacting with nitrogen or ammonia gas. 

The denormal oils recovered from the experiments were separated from the solvent by batch distillation. Vacuum and nitrogen stripping were applied towards the end, stopping when the oil temperature in the reboiler reached 473 K. Cloud and pour points were determined on the oil products. 

A test was made with 2,3-dimethylbutane as the supercritical solvent it has a lower critical temperature than 2,2,4-trimethyl-pentane. Operating at a temperature of 508-512 K, a pressure of 4.10-4.37 MPa, a molecular sieve/oil ratio of 6.39, and a solvent/ oil ratio of 21.3, the molecular sieve capacity attained is 5.73 g/100 g of molecular sieves (as compared to 3.2 g/100 g of molecular sieves with 2,2,4-trimethylpentane at 550 K). The n-paraffin content of the wax distillate was reduced by 88% to a level of 2 wt %, giving a pour point of 266 K. The yield of denormal oil was lower (63%) and the n-paraffin content of the desorbate was lower (44%) at this lower temperature level. This is probably due to increased capillary condensation. Conversely, operation at temperatures greater than 550 K should produce less capillary condensation and purer n-paraffin product. It would be interesting to try supercritical solvents with critical temperatures in the 600-670 K range. 

The oil yields calculated from the analyses of the denormal products in Table III are plotted versus denormal product pour point in Figure 12. It is seen that 60% of the ii-paraffins must be removed before the pour point begins to decrease. Further extraction of the ti-paraffins to 88% of the theoretical (maximum) yield of 16.7 wt % n-paraffins then reduces the pour point from 294 K to 266 K. It appears that extraction of the remaining n-paraffins may lower the pour point to the desirable range of 261-255 K. It would be interesting to determine the effect of pour point depressants on the denormal oil product. 

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