The Study On The Separation Process Of Alkali Fusion Product In The Production Of P-Cresol And Determination Of Related Solubility Data

P-cresol,an important organic intermediate,is extremely valuable for the production of pesticides,medicines,spices,dyes and cosmetics.Although there are some other processes to produce p-cresol,the main industrial process to produce p-cresol is sulfonation-alkali fusion process.It includes four steps:sulfonation,neutralization,alkali fusion and acidification.Excess sodium hydroxide is used in the alkali fusion step and the reaction yield of it is only 70%.Meanwhile,there are too many side reactions in this step.All these reasons above cause that there is a lot of NaOH in the reaction residue,leading to the waste of NaOH.Therefore,the solubilitiesofsodiump-toluenesulfonate?NaPTS?,Na₂SO₃ and sodium p-methylphenoxide?NaCRS?in aqueous NaOH solutions were measured by a dynamic method over the temperature range from 277 to 341 K at atmospheric pressure in this work.According to the determined solubility data,the post process pf alkali fusion was improved.The NaOH recycling process was discussed and the optimized process parameters were suggested.The experimental results showed that the solubilities of NaPTS,Na₂SO₃ and NaCRS in aqueous NaOH solutions decreased distinctly with the solute-free mass fraction of NaOH?w₄⁰?.Besides,there were obvious transition points in the solubility-temperature curves of NaPTS and Na₂SO₃ in aqueous NaOH solutions and the transition points shifted to lower temperature as w₄⁰ rose.The forming of transition point was due to the different equilibrium solid phase,which was revealed by characterization of the equilibrium solid phase.As the temperature rose,the solubilities of NaPTS and NaCRS in aqueous NaOH solutions increased,while the solubilities of Na₂SO₃ increased at first and then decreased after the transition points in aqueous NaOH solutions.The determined experimental data were correlated with the electrolyte non-random two-liquid?E-NRTL?model and Apelblat model.The parameters and root-mean-square deviations of the SLE temperature were determined simultaneously.The root-mean-square deviations in E-NRTL model of NaPTS,Na₂SO₃ and NaCRS in aqueous NaOH solutions vary from?0.19 to 1.14?K,?0.50 to 0.91?K and?0.60 to1.27?K,respectively.The correlated results showed good agreement with the experiment data.Based on the solubility difference between Na₂SO₃ and NaCRS,a new process for reusing the NaOH in the alkali fusion reaction residue was proposed.Na₂SO₃ and NaCRS were separated from the reaction residue by multiple concentration-filtration.After the filtration of Na₂SO₃,the filtrate is concentrated and filtrated twice to recycle the NaOH in the filtrate which can be used in the neutralization 2 step.Process parameters were optimized and determined by experiment.w₄⁰ of the filtration 1,2and 3 are 0.15,0.18 and 0.25 respectively.The purity and yield of obtained Na₂SO₃were 0.9774 and 0.9028,where the total purity and yield of NaCRS?H₂O were 0.9172and 0.9169 respectively.0.78 mass fraction of NaOH can be recovered.