Process for production of high quality gasoline with low aromatic content

Abstract

This patent presents a two-stage process for production of high-octane gasoline from a hydrocarbon stream comprising C 4 -C 12 hydrocarbon mixtures of paraffins, optionally including cycloalkanes, aromatics and olefins. During the first step linear molecules are activated and converted predominantly to mono-branched isomers. Present cyclic molecules and olefins are hydrogenated, but conversion must be sufficiently low to avoid ring opening. Only such (low) amount of multi-branched isomers is formed in the first reaction zone that extent of cracking is still acceptable. Concentration of multi-branched isomers is consecutively increased in the second step. Reaction of mono-branched isomers requires lower activation energy than cracking and isomerisation of linear molecules. Monomethyl-paraffins readily react to their multi-branched counterparts with a high selectivity under mild reaction conditions with catalysts having a Hammet acidity value lower than −10 at temperature of maximum 100° C. and at least 50° C. lower than in the first step. These are the conditions effectively isomerising hydrocarbon molecules containing tertiary carbon, while other feed components are little effected. The combination of both steps utilising different catalysts and conditions is essential to achieve a high selectivity. Both reaction steps can be combined with separation of low octane number paraffin molecules by a suitable separation process.

1 . A process for production of high-octane gasoline from a hydrocarbon feed stream comprising of C 4 -C 12  hydrocarbon cuts or intermediate cuts of linear paraffins and naphtenes, aromates and olefins comprising 
 two isomerisation steps in series by subjecting the feedstock in a first isomerisation step to a first isomerisation reaction in presence of a first catalyst in form of a solid acid containing noble metal being effective in converting the linear paraffins to mono-branched isomers and saturation of aromatics to saturated cyclic hydrocarbons; and    in a second isomerisation step increasing concentration of multi-branched isomers in effluent from the first step by converting the mono-branched isomers contained in the effluent to the multi-branched isomers in presence of a second catalyst having a Hammet acidity value lower than −10, and at reaction temperature of up to 100° C. and at least 50° C. lower than the temperature in the first step.    
     
     
         2 . Process of  claim 1 , further comprising a first separation step for separation of the linear paraffins contained in the effluent from the first isomerisation step and/or a second separation step for separation of the linear paraffins and mono-branched isomers contained in the effluent from the second isomerisation step.  
     
     
         3 . Process according to  claim 1 , wherein the first catalyst comprises a solid, shape selective molecular sieve, and/or a mesoporous, acidic catalyst and the second catalyst comprises a liquid super acid.  
     
     
         4 . Process according to  claim 1 , wherein the first catalyst comprises an acidic, shape selective molecular sieve with a pore diameter of 4 to 7 Å, further containing at least one noble metal of palladium and platinum in an amount of 0.01 to 5 wt %.  
     
     
         5 . Process of  claim 3 , wherein the mesoporous, acidic catalyst is tungsten oxide supported on zirconia, titania, hafnia or tin oxide with a tungsten content of between 5 to 50 wt %.  
     
     
         6 . Process of  claim 1 , wherein the first isomerisation step is carried out at a temperature of between 100° C. and 400° C. in presence of hydrogen under total pressures between 1 to 40 bar with hydrogen to hydrocarbon ratio between 1 to 10.  
     
     
         7 . Process of  claim 1 , wherein the second isomerisation catalyst comprises any fluorinated alkanesulphonic acid, hydrofluoric acid; sulphuric acid or mixtures thereof and/or an ionic liquid based on complexes of metal halogenides with quaternary ammonium salts.  
     
     
         8 . Process of  claim 3 , wherein the liquid catalyst is grafted on inorganic solid support.  
     
     
         9 . Process wherein the effluent from the first isomerisation reactor is passed directly to the liquid isomerisation process.