Patent GB-725598-A (GB)
Title: Improvements in or relating to the separation of mixtures of organic compounds
Inventor: GARNER PHILIP JAMES
Filed: 1953-04-15
Abstract: In the process described in the parent Specification of separating a mixture of organic compounds having a hydrocarbon radical of at least six carbon atoms by treatment with aqueous urea in the presence of a wetting agent and of an ionising water-soluble salt, a higher concentration of water-soluble salt is employed when separating the urea complexes from the other p  components of the mixture or when separating the urea solution from compounds with straight-chain hydrocarbon radicals after decomposing the complexes than when forming the complexes.  An auxiliary solvent as in the parent Specification is, preferably, also present.  While removal of the salt from the solution before it is used for treating fresh feed may be effected, for example, by precipitation or selective solvent action, it is preferred to use a volatile salt, e.g. ammonium carbonate, and a closed gas cycle with passage of gas through the solution; after separating straight-chain compounds, to strip ammonium carbonate, and passage of gas, after forming urea complexes, to cause the mixture to absorb ammonium carbonate.  The concentration of auxiliary solvent will also be varied in this method and, since a low concentration thereof is not always desirable during complex formation, means for returning part of the solvent withdrawn with the volatile salt are provided.  This return of solvent may be combined with elimination of ammonium carbonate from the urea solution necessitated by the formation of ammonium carbonate from hydrolysis of urea.  The period wherein the urea solution is held above 50 DEG C. is made as short as possible and, immediately after decomposition of the urea complexes at about -70 DEG , the mixture is cooled below 50 DEG  for separation of straight-chain compounds to take place. The stripping of ammonium carbonate preferably takes place just below 50 DEG  C.  A continuous process using a plurality of reactors is described, the mixture from the last reactor being fed down a column against a stream of air saturated with vapours of ammonium carbonate and auxiliary solvent at a temperature above that of the mixture whereby the vapours are absorbed.  After separation of the urea complexes and their decomposition, the urea solution is stripped with air at about 45 DEG  C. and recycled while the vapour saturated air is fed to the above-mentioned absorber column.  Part of this air passes to a solvent recovery column containing active carbon and is then vented with its ammonium carbonate content.  In an example, a cracked distillate is treated with a urea solution containing isopropanol, ammonium carbonate, potassium chromate, and C8-C11 secondary alkyl sulphates of sodium.ALSO:In the process described in the parent Specification of separating a mixture of organic compounds having a hydrocarbon radical of at least six carbon atoms by treatment with aqueous urea in the presence of a wetting agent and of an ionizing water-soluble salt, a higher concentration of water-soluble salt is employed when separating the urea complexes from the other components of the mixture or when separating the urea solution from compounds with straight-chain hydrocarbon radicals after decomposing the complexes than when forming the complexes.  An auxiliary solvent as in the parent Specification is, preferably, also present.  While removal of the salt from the solution before it is used for treating fresh feed may be effected, for example, by precipitation or selective solvent action, it is preferred to use a volatile salt, e.g., ammonium carbonate, and a closed gas cycle with passage of gas through the solution, after separating straight-chain compounds, to strip ammonium carbonate, and passage of gas, after forming urea complexes, to cause the mixture to absorb ammonium carbonate.  The concentration of auxiliary solvent will also be varied in this method and, since a low concentration thereof is not always desirable during complex formation, means for returning part of the solvent withdrawn with the volatile salt are provided.  This return of solvent may be combined with elimination of ammonium carbonate from the urea solution necessitated by the formation of ammonium carbonate from hydrolyses of urea.  The period wherein the urea solution is held above 50 DEG  C. is made as short as possible and, immediately after decomposition of the urea complexes at about 70 DEG , the mixture is cooled below 50 DEG  C. for separation of straight-chain compounds to take place.  The stripping of ammonium carbonate preferably takes place just below 50 DEG  C.  A continuous process using a plurality p  of reactors is described, the mixture from the last reactor being fed down a column against a stream of air saturated with vapours of ammonium carbonate and auxiliary solvent at a temperature above that of the mixture whereby the vapours are absorbed.  After separation of the urea complexes and their decomposition, the urea solution is stripped with air at about 45 DEG C. and recycled while the vapour saturated air is fed to the above-mentioned absorbed column.  Part of this air passes to a solvent recovery column containing active carbon and is then vented with its ammonium carbonate content.  In an example, a cracked distillate is treated with a urea solution containing isopropanol, ammonium carbonate, potassium chromate, and C8C11 secondary alkyl sulphates of sodium.