Thermal separating process for removing at least one stream containing enriched (meth)acrylic monomers

Abstract

A thermal separating process for removing a stream containing enriched (meth)acrylic monomers from a mixture containing (meth)acrylic monomers, in which the liquid phases retained in the separating space at high temperature and high (meth)acrylic monomer content are minimized.

1 . A thermal separating process for removing at least one stream containing enriched (meth)acrylic monomers from a mixture containing (meth)acrylic monomers, comprising the continuous steady-state operation of at least one thermal separating apparatus which comprises at least one separating space with or without separating internals, into which at least one stream containing (meth)acrylic monomers is conducted and out of which at least one stream containing (meth)acrylic monomers is conducted, with the proviso that 
 the stream which is conducted overall into the separating space and is obtained in a theoretical sense by adding the individual streams conducted into the separating space contains X % by weight of constituents other than (meth)acrylic monomers,    the stream which is conducted out of the separating space with the highest proportion by weight of (meth)acrylic monomers contains Y % by weight of constituents other than (meth)acrylic monomers,    the X:Y ratio is ≧5,    the separating space, except at the stream inlet and at the stream outlet points, is bounded by a solid phase and comprises at least one circulation heat exchanger, and    the total volume filled with liquid phase in the separating space is ≧1 m 3 , and the temperature of the liquid phase, at least in places, is ≧80° C., wherein,    in the case that the separating space is divided into n individual volume elements and the highest and the lowest temperatures of the liquid phase disposed in an individual volume element do not differ by more than 2° C. and the volume element is continuous within the separating space,    the overall residence time t ort ,                t   ort     =       ∑     i   =   1     n     ⁢           ⁢         m   si         m   .     i       ·     2   A           ,           is ≦20 h,    where    A=(T i −T o )/10° C.,    T o =100° C.,    T i =the arithmetic mean of the highest and lowest temperature existing in the liquid phase of the volume element i in ° C.,    m si =the total amount of (meth)acrylic monomers present in the volume of the liquid phase present in the volume element i,    {dot over (m)} i =the total amount of liquid phase stream conducted out of the volume element i, and                ∑     i   =   1     n     ⁢           ⁢     =     the   ⁢           ⁢   sum   ⁢           ⁢   over   ⁢           ⁢   all   ⁢           ⁢   volume   ⁢           ⁢   elements   ⁢           ⁢   i         ,           with the proviso that the sum over all volume elements i includes neither volume elements i having a liquid phase mass m i  present therein and m i /{dot over (m)} i  ≧100 h, as deadspace volume elements, nor volume elements i which have no liquid phase, and the total amount of the liquid phase present in the deadspace volume elements is not more than 5% by weight of the overall liquid phase present in the separating space.    
     
     
         2 . A process as claimed in  claim 1 , wherein X:Y is ≧8.  
     
     
         3 . A process as claimed in either of claims  1  or  2 , wherein the total volume filled with liquid phase in the separating space is ≧5 m 3 .  
     
     
         4 . A process as claimed in any of  claims 1  to  3 , wherein the temperature of the liquid phase in the separating space is, at least in places, ≧100° C.  
     
     
         5 . A process as claimed in any of  claims 1  to  4 , wherein the at least one (meth)acrylic monomer is selected from the group consisting of acrolein, methacrolein, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, glycidyl acrylate, glycidyl methacrylate, methyl acrylate, methyl methacrylate, n-butyl acrylate, isobutyl acrylate, isobutyl methacrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, N,N-dimethylaminoethyl methacrylate and N,N-dimethylaminoethyl acrylate.  
     
     
         6 . A process as claimed in any of  claims 1  to  5 , wherein t ort  is ≦15 h.  
     
     
         7 . A process as claimed in any of  claims 1  to  6 , wherein t ort  is ≦10 h.  
     
     
         8 . A process as claimed in any of  claims 1  to  7 , wherein the separating space comprises a separating column having mass transfer trays as separating internals.  
     
     
         9 . A process as claimed in any of  claims 1  to  8 , wherein the circulation heat exchanger is a circulation evaporator.  
     
     
         10 . A process as claimed in any of  claims 1  to  9 , wherein the circulation heat exchanger is a direct circulation evaporator.  
     
     
         11 . A process as claimed in any of  claims 1  to  10 , wherein the thermal separating process is the fractional condensation of the product gas mixture of a heterogeneously catalyzed partial gas phase oxidation of propene and/or propane to acrylic acid.  
     
     
         12 . A process as claimed in any of  claims 1  to  11 , wherein tort is ≦10 h, the mixture comprising (meth)acrylic monomers is the product gas mixture of a heterogeneously catalyzed partial gas phase oxidation of propene and/or propane to acrylic acid and has an acrylic acid content of from 5 to 15% by weight, and the stream which is conducted out of the separating space with the highest proportion by weight of (meth)acrylic monomers is crude acrylic acid having an acrylic acid content of ≧95% by weight.  
     
     
         13 . A process as claimed in  claim 8 , wherein the mass transfer trays of the separating column, from bottom to top, are initially dual-flow trays, then hydraulically sealed crossflow trays and finally valve trays.