| With the large scale exploitation of natural gas,the newly appearing problems of NG were the high acidity,the high contents of hydrogen sulfide and the high contents of odorous mercaptans.In order to meet the demands of environmental protection and production,natural gas sweetening attracts more attention.Currently,the main industrial method for natural gas sweetening is caustic washing,which shows the weakness in sweetening efficiency and renewability.It is suggested that a similar technology Merox sweetening process for LPG,which is widely used in refineries,will be the future solution for natural gas sweetening.Nevertheless,the phthalocyanine cobalt catalyst used in this method aggregates easily,which affects its sweetening efficiency.In this paper,an alkali-soluble,well dispersed,and with highly sweetening efficiency of metal phthalocyanine was designed and synthesized,which provides the possibility to its application in the field of natural gas sweetening.To improve the solubility of the metal phthalocyanine catalyst,a novel metal phthalocyanine with 8 carboxyl groups was designed,which is named tetra-(3,5-dicarboxylphenoxy)phthalocyanine(metal).Firstly,4-(3,5-dicarboxylphenoxy)phthalonitrile was synthesized with 4-nitrophthalonitrile and 5-hydroxy isophthalic acid as raw materials,followed by the purification with column chromatography.The purified product was characterized by IR and ~1H-NMR.Afterwards,tetra-(3,5-dicarboxylphenoxy)phthalocyanine as well as four novel metal phthalocyanines were synthesized through DBU liquid phase catalysis.The synthesized tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt,tetra-(3,5-dicarboxylphenoxy)phthalocyanine copper,tetra-(3,5-dicarboxylphenoxy)phthalocyanine zinc and tetra-(3,5-dicarboxylphenoxy)phthalocyanine nickel were characterized by IR,UV-Vis,mass spectrometry and XRD.Metal phthalocyanine compounds aggregate easily in polar solvents(solutions),resulting in the reduction of its performance for the oxidation of the sodium mercaptides.UV-vis spectroscopy and fluorescence spectroscopy were employed to study the aggregation of designed phthalocyanine and metal phthalocyanine complexes.The results indicated that tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt shows better stability than other four compounds,which provides a chioce for the design of stable metal phthalocyanine catalyst in sweetening.Solubility of tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt in three different polar solvents(solutions),i.e.10wt%NaOH,water and DMF was studied.As the polarity of the solvents increasing,the solubility of the tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt gradually increases,indicating that tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt has strong polarity.Compared with the solubility of three industrial catalysts in 10wt%NaOH,tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt is found to have better alkali solubility.Tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt shows good catalytic performance in the oxidation of sodium thioethylate,sodium propanethiolate and sodium butanethiolate,and the catalytic activity varies with the structures of the sodium mercaptides.In contrast with the three industrial catalysts,tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt shows better catalytic performance,with both higher initial conversion rates and final conversion rate of sodium mercaptides.In conclusion,tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt is a very promising sweetening catalyst.The stabilizing mechanism of tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt in sodium hydroxide solution was explained.It is suggested that the combination of hydrogen bond,solvation and steric effect prevent the aggregating of tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt,which makes it stable in the polar solvents(solutions).The catalyzing mechanism of tetra-(3,5-dicarboxylphenoxy)phthalocyanine cobalt was investigated,which provides a theoretical support for its future industrial application. |
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