HDO product
CP reduction: 7˚C
255˚C
n-C n-C 270˚C 287˚C 302˚C 317˚C n-C
n-C n-C 270˚C 287˚C 302˚C 317˚C n-C
255˚C
n-C
n-C
n-C
n-C
Boiling point
Boiling point
CP reduction: 38˚C
Hydro-isomerised product
255˚C
n-C n-C 270˚C 287˚C 302˚C 317˚C n-C
255˚C
n-C n-C 270˚C 287˚C 302˚C 317˚C n-C
n-C
n-C
n-C
n-C
Boiling point
Boiling point
Figure 4a GCxGC traces of HDO product and hydroisomerised products with different degrees of isomerisation
Hydroisomerisation Once a stream of n-paraffins has been produced in the HDO step, the required reduction in boiling point range and freezing point must be achieved via isomerisation and selective cracking. The GCxGC traces of a typical HDO product and products from an HI reactor with increasing degrees of isomerisation and decreasing cloud point are presented in Figure 4 . In these traces, each dot represents the concentration of a single molecular compound with a unique combination of boiling point (on the x-axis) and polarity (on the y-axis). Starting from a mixture of linear paraffins (a single dot for C15, C16, and so on n-paraffins, as shown
in the top-left trace), isomerisation results in the formation of single and double branched isomers with a lower boiling point compared to the parent n-paraffin (top-right trace). Further increasing the degree of isomerisation results in the formation of triple-branched isomers (bottom-left trace) and a complete removal of n-paraffins (bottom-right trace). This process significantly reduces the cloud point, boiling point distribution, and density of the product. The objective is to achieve deep isomerisation while preventing the unselective cracking of branched paraffins, which would result in excessive yield loss, a significant exotherm, and higher H2 consumption.
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