Process for the production of hydrocarbons with a high octane number starting from mixtures of n-butane/isobutane such as field butanes

Abstract

A process is described for the production of hydrocarbons with a high octane number starting from mixtures essentially consisting of n-butane and isobutane (such as for example field butanes) comprising a skeleton isomerization section, a dehydrogenation section of paraffins, a selective hydrogenation section of butadiene, two conversion sections of olefins, in which the isobutene is firstly selectively transformed by means of dimerization and/or etherification, followed by the linear butenes by means of alkylation, in order to obtain, by joining the products of the two conversion sections, a product having excellent motoristic properties (octane number, volatility and distillation curve).

1 . A process for the production of hydrocarbons with a high octane number starting from mixtures essentially consisting of n-butane and isobutane characterized in that it comprises a skeleton isomerization section, a dehydrogenation section of paraffins, a selective hydrogenation section of butadiene, two conversion sections of olefins, in which the isobutene is firstly selectively transformed by means of dimerization and/or etherification, followed by the linear butenes by means of alkylation, in order to obtain, by joining the products of the two conversion sections, a mixture of hydrocarbons with a high octane number.  
     
     
         2 . The process according to  claim 1 , comprising the following steps: 
 a) feeding a part of the mixture essentially consisting of n-butane and isobutane, a stream of hydrogen and a stream consisting of recycled n-butane, to a skeleton isomerization section;    b) joining the product leaving the skeleton isomerization section with the remaining part of the mixture essentially consisting of n-butane and isobutane and sending the mixture thus obtained to a dehydrogenation section of paraffins;    c) sending the stream leaving the dehydrogenation to a selective hydrogenation of butadiene;    d) sending the stream leaving the selective hydrogenation section to a first conversion section in which the isobutene is reacted by means of dimerization and/or etherification, separating the dimerized and/or etherified product from the non-reacted C 4  hydrocarbon stream, mainly consisting of isobutane, n-butane and linear butenes, and subjecting said product, only if it has been dimerized, to hydrogenation, obtaining a hydrocarbon stream mainly containing iso-octane;    e) sending the C 4  hydrocarbon stream leaving the first conversion section, mainly consisting of isobutane, n-butane and linear butenes, to a second conversion section in which all the linear butenes are reacted by means of alkylation obtaining a stream of saturated hydrocarbons;    f) sending the non-reacted butanes in the second conversion section to a first separation column (deisobutanizing column) from whose head a stream essentially consisting of propane and isobutane is recovered and from whose bottom n-butane is recovered to be recycled to the skeleton isomerization section;    g) sending the stream at the head of the first separation column (deisobutanizing column) to a second separation column (depropanizing column) from whose head the light products are recovered and from whose bottom the isobutane is recovered, which is recycled to the second conversion section and/or to the first conversion section and/or to the selective hydrogenation section.    
     
     
         3 . The process according to  claim 1  or  2 , wherein the mixtures substantially consisting of n-butane and isobutane are mixtures of field butanes.  
     
     
         4 . The process according to  claim 2 , wherein the isobutane recovered from the bottom of the second separation column (depropanizing column) is sent to the second conversion section.  
     
     
         5 . The process according to  claim 2 , wherein the isobutene is dimerized in the first conversion section.  
     
     
         6 . The process according to  claim 1  or  2 , wherein the mixtures substantially consisting of n-butane and isobutane have an n-butane/isobutane ratio ranging from 1/5 to 5/1.  
     
     
         7 . The process according to  claim 6 , wherein the mixtures substantially consisting of n-butane and isobutane have an n-butane/isobutane ratio ranging from 1/1 to 5/1.  
     
     
         8 . A mixture of hydrocarbons with a high octane number, substantially containing saturated hydrocarbons with from 5 to 16 carbon atoms and in which at least 50% by weight are saturated C 8  hydrocarbons, obtained by means of the process according to  claim 1  or  2  and by joining the hydrocarbon stream containing iso-octane produced in the first conversion step and the stream of saturated hydrocarbons produced in the second conversion step.  
     
     
         9 . The mixture according to claims  8  and  5 , wherein at least 60% by weight are saturated C 8  hydrocarbons.