Method for improved production of cyclohexenyl and alkenyl aromatic compounds

Abstract

Disclosed is an improvement in a process of preparing cyclohexenyl and alkenyl aromatic compounds, such as styrene, that enables economical and convenient removal of nitrogen compounds. The nitrogen compounds can be stabilizers or neutralizers or derived from stabilizers or neutralizers added to prevent styrene homopolymerization. The nitrogen compounds are removed from, in the case of styrene production, the benzene fraction that results from dehydrogenation of ethylbenzene. Because of the preferential solubility of nitrogen compounds in water, a majority of such compounds can be removed by intimately contacting the benzene fraction with sufficient water, at an appropriate point in the process, and then removing most or all of the water with the entrained nitrogen compounds.

1 . A process for preparing cyclohexenyl or alkenyl aromatic compounds comprising alkylation of a cyclohexane or aromatic compound; dehydrogenation of the alkylated cyclohexane or aromatic compound to form a process stream including a cyclohexenyl or alkenyl aromatic compound; and separating the process stream into a cyclohexenyl or alkenyl aromatic compound rich fraction and a cyclohexane or aromatic compound rich fraction, wherein the process further comprises adding nitrogen-containing compounds at one point in the process and using water to extract the nitrogen-containing compounds or, break down products of the nitrogen-containing compounds, from the cyclohexane or aromatic compound rich fraction at another point in the process.  
     
     
         2 . A process for preparing styrene comprising alkylating benzene to form ethylbenzene, dehydrogenating ethylbenzene to form a process stream containing styrene, unreacted ethylbenzene, benzene and toluene products, separating the process streams into styrene, benzene and toluene fractions, and recycling the benzene fraction back into the process wherein the process further comprises adding a nitrogen-containing compound at one point in the process and using water to extract the nitrogen-containing compounds, or break down products of the nitrogen-containing compounds, from the benzene fraction at another point in the process.  
     
     
         3 . The process of  claim 2  wherein the nitrogen-containing compounds, or break down products of the nitrogen-containing compounds, are extracted by intimately contacting the benzene fraction with water in an amount of from about 0.1 percent to about 10 percent by weight of benzene.  
     
     
         4 . The process of  claim 3  further comprising removing the water containing nitrogen compounds, or break down products of the nitrogen-containing compounds, from the benzene fraction such that no more than about 900 ppm water remains, prior to or after mixing the recycled benzene fraction with fresh benzene prior to alkylation.  
     
     
         5 . The process of  claim 2  wherein the benzene fraction is contacted with water in an amount of from about 0.5 percent to about 4 percent by weight of benzene.  
     
     
         6 . The method of  claim 2  wherein the water is introduced immediately after separation of the benzene, styrene and toluene fractions.  
     
     
         7 . The method of  claim 2  wherein the water is introduced into the system as water entrained in feedstocks to the process.  
     
     
         8 . The process of  claim 6  wherein the water is removed as a liquid via drying or distillation.  
     
     
         9 . The process of  claim 7  wherein the water is removed as a liquid via drying or distillation.  
     
     
         10 . The process of  claim 2  wherein the water is introduced concurrent with the mixing of fresh and recycled benzene and the water is removed after alkylation in a drying column.  
     
     
         11 . The process of  claim 2  wherein the nitrogen-containing compounds are stabilizers or neutralizers or break down products of these compounds.  
     
     
         12 . In a process for preparing cyclohexenyl or alkenyl aromatic compounds, wherein the process includes an alkylation of a cyclohexane or aromatic compound; a dehydrogenation of the alkylated cyclohexane or aromatic compound to form a process stream; and a separation of the process stream into a cyclohexenyl or alkenyl aromatic compound rich component and a cyclohexane or aromatic compound rich component; and the process also includes the use of nitrogen-containing compounds, the improvement comprising using water to extract the nitrogen-containing compounds from the cyclohexane or aromatic compound rich component.  
     
     
         13 . The process of  claim 12  wherein the nitrogen-containing compounds, or break down products of the nitrogen-containing compounds, are extracted by intimately contacting the cyclohexane or aromatic compound rich component with water in an amount of from about 0.1 percent to about 10 percent by weight of the cyclohexane or aromatic compound rich component.  
     
     
         14 . The process of  claim 13  wherein the cyclohexane or aromatic compound rich component is contacted with water in an amount of from about 0.5 percent to about 4 percent by weight of the cyclohexane or aromatic compound rich component.  
     
     
         15 . The process of  claim 13  further comprising removing the water containing nitrogen compounds, or break down products of the nitrogen-containing compounds, from the benzene fraction such that no more than about 900 ppm water remains, prior to or after mixing the recycled benzene fraction with fresh benzene prior to alkylation.  
     
     
         16 . The process of  claim 12  wherein the cyclohexenyl or alkenyl aromatic compound is styrene.