Vacuum potstill distillation: How to get fractions with TBP cut points

The continuity of the data obtained for crude oils evaluations requires to link the results acquired by different distillations techniques and conside ring that those results have to,be referred to the same reference. The True Boiling Point concept (TBP) is the only reference recognized for any fract ionation by distillation. The ASTM D 2892 distillation method accomplish th is approach to obtain cuts up to 400 degrees C. Beyond this temperature, th e Vacuum Potstill distillation referred ASTM D 5236 with one theoretical pl ate, allows to obtain the required cuts to achieve a complete crude evaluat ion. In the present study a new methodology for vacuum Potstill distillatio n is proposed, in order to obtain fractions with cut points equivalent to a TBP fractionation. A comparison with results obtained with the current pro cedure described in ASTM D5236 is presented. For this purpose, an atmospher ic residue was fractionated both by the current ASTM D 5236 standard method and this proposed method "by volume". This new methodology is based on the conversion to TBP of previous ASTM D 1160 distillation data of the atmosph eric residue. Comparison of the True Boiling Points calculated for the frac tions by both procedures, permitted to conclude that the proposed methodolo gy "by Volume" affords fractions according to the expected nominal cut poin ts, while the distillation cuts obtained following ASTM D 5236 have cut poi nts noticeable lower than the nominal boiling range required.