Process for production of high quality gasoline with low aromatic content

#The present invention relates to a process for the production of high quality gasoline with reduced content of aromatic compounds. In particular, the invention is a catalytic two stage isomerisation process of C4-C12 paraffinic hydrocarbons to multi-branched hydrocarbons.

#Multi-branched paraffins are ideal gasoline blending components possessing high octane numbers. For environmental reasons there is also a need to find substitutes for aromatic components in gasoline. Therefore, there is an incentive to develop a process for increasing octane number of the C4-C12 cuts. While C5/C6 paraffin isomerisation is a common refinery process, commercialisation of processes including higher fractions (C7+ hydrocarbons) meets significant difficulties given by high degree of cracking to gas and low octane number of the once-through products. The present invention relates to a catalytic process, where combinations of given steps allow sufficient yields of products with high octane numbers also for the C7+ hydrocarbon fraction. The process can thus convert the complete C4-C12 cut, or it can solely be designed for the C7+ fraction.

#The C7+ fraction is difficult to isomerise because of several reasons. Unlike the C5/C6 paraffins, mono-branched C7+ isomers possess too low octane number. Octane number is around 50 for methylhexanes, and linear molecules have RON equal to zero or even negative when blended with other hydrocarbons. Only multi-branched paraffins are valuable blending components, but their concentration is limited by thermodynamics. A maximum of 40% of multi-branched C7 isomers can be formed by passing n-heptane once-through over an isomerisation catalyst at 230° C. This number increases to 50% at 150° C. All mono-branched and linear isomers have to be removed from the product and recycled with close to 100% selectivity. Although separation of linear isomers is a common technology, no efficient and economical process to separate mono-branched from multi-branched isomers is operational.

#In order to illustrate the invention an example is now given to describe a process configuration capable of producing high RON gasoline with a high liquid yield.

#Zirconium oxide is prepared by adding diluted ammonia to a water solution of zirconyl nitrate and adjusting pH to 11. The mixture is refluxed for 4 days. The white solid is filtered and dried overnight at 120° C. 30 wt % of ammonium metatugstate is added to the zirconia support by incipient wetness impregnation and the sample is calcined for 3 hours at 750° C. 0.3% Pd is introduced to the catalyst by cation exchange and the catalyst is calcined at 350° C. before being put into the reactor.

#The feed used in the reaction is a C7 cut consisting of 32 wt % cycloparaffins, 3 wt % toluene and 65% of heptanes. The detail composition is shown in Table 1. The reaction is performed in a fixed bed reactor at 190° C. with LHSV=1 h−1 at the total pressure 6 bar, and the feed consisting of a hydrocarbons:hydrogen mixture with the ratio of 1:2. The detail feed and product compositions are shown in Table 1. 1 TABLE 1 Feed and product compositions referring to the first reaction step Feed [wt %] Product [wt %] Propane — 0.7 Isobutane — 0.9 Isopentane — — Isohexanes — — 2,2-dimethylpentane — 4.0 2,4-dimethylpentane 0.6 4.5 2,2,3-trimethylbutane — 0.5 3,3-dimethylpentane — 1.0 2-methylhexane 13.5 17.2 2,3-dimethylpentane 0.5 4.4 3-methylhexane 11.4 15.9 3-ethylpentane 1.2 1.1 n-heptane 37.6 15.5 Cycloheptanes 32.2 34.2 Toluene 3 — RON-calculated 49.5 64.8