Process for the Separation of C5 Hydrocarbons Present in Streams Prevalently Containing C4 Products Used for the Production of Highoctane Hydrocarbon Compounds By the Se-Lective Dimerization of Isobutene

Abstract

A process is described for the separation of C 5 hydrocarbons present, in a quantity ranging from 0.2 to 20% by weight, in streams prevalently containing C 4 products used for the production of high-octane hydrocarbon compounds, by the selective dimerization of isobutene, characterized in that the dimerization reaction is carried out in the presence of linear and branched alcohols and alkyl ethers in a quantity which is such as to have a molar ratio alcohols/alkyl ethers/isobutene in the feeding higher than 0.01.

1 : A process for the separation of C 5  hydrocarbons present, in a quantity ranging from 0.2 to 20% by weight, in hydrocarbon streams prevalently containing C 4  products used for the production of high-octane hydrocarbon compounds, by the selective dimerization of isobutene, characterized in that the dimerization reaction is carried out in the presence of linear and branched alcohols and-alkyl ethers in such a quantity as to have a molar ratio alcohols+alkyl ethers/isobutene in the feeding higher than 0.01, being the separation of C 5 /branched alcohol azeotropic product effected using traditional fractionation columns. 
   
   
       2 : The process according to  claim 1 , wherein the molar ratio alcohols+alkyl ethers/isobutene is lower than 0.7. 
   
   
       3 : The process according to  claim 1 , wherein the reaction is carried out at a temperature ranging from 30 to 120° C., at a pressure lower than 5 MPa and at feeding space velocities lower than 30 h −1 . 
   
   
       4 : The process according to  claim 1  wherein the feeding space velocities range from 1 to 15 h −1 . 
   
   
       5 : The process according to  claim 1 , wherein the linear-alcohol has a number of carbon atoms ranging from 1 to 6. 
   
   
       6 : The process according to  claim 5 , wherein the linear alcohol is selected from methanol and/or ethanol. 
   
   
       7 : The process according to  claim 1 , wherein the branched alcohol has a number of carbon atoms ranging from 4 to 7. 
   
   
       8 : The process according to  claim 7 , wherein the branched alcohol is selected from tert-butyl alcohol or tert-amyl alcohol. 
   
   
       9 : The process according to  claim 1 , wherein the alkyl ether has a number of carbon atoms ranging from 5 to 10. 
   
   
       10 : The process according to  claim 9 , wherein the alkyl ether is selected from MTBE, ETBE, MSBE, ESBE, TAME, TAEE or mixtures thereof. 
   
   
       11 : The process according to  claim 1 , wherein other possible olefins present in the charge react to form high octane products. 
   
   
       12 : The process according to  claim 1 , wherein isobutene content in the charge is modified by dilution with C 4 -C 7  streams. 
   
   
       13 : The process according to  claim 1  comprising the following essential steps:
 a) feeding the C 4 -C 5  hydrocarbon cut containing isobutene, together with one or more streams containing oxygenated products, linear and branched alcohols, ethers and water, to one or more reaction steps, consisting of one or more reactors;   b) separating the C 4 /linear alcohol azeotropic product and possibly the C 4  products from the C 5  hydrocarbons, from the remaining oxygenated products and from the hydrocarbon product, in one or more distillation columns;   c) recovering the linear alcohol from the azeotropic mixture with the C 4  products by means of conventional processes such as washing with water or absorption on inorganic solids;   d) separating the C 5  hydrocarbons, as an azeotropic compound with the branched alcohol, from the remaining oxygenated products and from the reaction product, in one or more fractionation columns, in order to obtain three streams with the desired purity;   e) recycling the streams containing the oxygenated products, branched alcohol and ether, and the linear alcohol recovered, to the two reaction steps;   f) feeding linear alcohol and water, which forms the branched alcohol in the reactors by reaction with the tertiary olefin, to the reaction steps to compensate the losses of linear alcohol, which can react with the dimers and linear C 4  olefins, and branched alcohol which, on the contrary, leaves the plant together with the C 5  products;   g) recycling part of the C 4  products, with or without linear alcohol, to the reaction steps in order to maximize the isobutene conversion.   
   
   
       14 : The process according to  claim 1 , wherein the separation of the C 5 /branched alcohol azeotropic product can be carried out starting from blends of:
 a) C 5 —oxygenated′ products, ethers and branched alcohols, 7—reaction product, wherein the C 5  hydrocarbons are recovered as an azeotropic compound with the branched alcohol as head effluent using a scheme based on a column, with recovery of the remaining oxygenated products as side cut, or two fractionation columns;   b) C 5 —oxygenated products, ethers and branched alcohols,—dimers, wherein the C 5  hydrocarbons are recovered as an, azeotropic compound with the branched alcohol as head effluent of a fractionation column;   c) C 4 -C 5 —oxygenated products, ethers and branched alcohols,—reaction product, effluent from a reaction step, wherein the C 5  hydrocarbons are recovered as an azeotropic compound with the branched alcohol as side cut of a fractionation column from whose head the C 4 /linear alcohol azeotropic product and possibly the C 4  products are recovered, whereas a mixture containing the oxygenated products and the reaction product is recovered at the bottom;   d) C 4 -C 5 —oxygenated products, linear and branched alcohols, wherein the C 5  hydrocarbons are recovered as an azeotropic compound with the branched alcohol as bottom effluent of a fractionation column from whose head the C 4 /linear alcohol azeotropic product, and possibly the C 4  products are recovered.   
   
   
       15 : The process according to  claim 1 , wherein the C 5 /branched alcohol azeotropic mixture is joined to the reaction product. 
   
   
       16 : The process according to  claim 1 , wherein the dimerization reaction is carried out in one or more fixed bed, tubular and/or adiabatic reactors. 
   
   
       17 : The process according to  claim 13 , wherein the C 5  hydrocarbons are present in streams prevalently containing C 4  products in a quantity ranging from 0.5 to 10% by weight.