Effective adsorption of sulfate ions with poly(m-phenylenediamine) in aqueous solution and its adsorption mechanism

Sulfate adsorption by poly（m-phenylenediamine）s（PmPDs） with various oxidation states synthesized through chemically oxidative polymerization was investigated.Series of sorption experiments were conducted,and the adsorption mechanism and the relationship between oxidation state and adsorption performance were studied with the characterization of Fourier transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,pH tracking and energy calculation.The results show that the adsorption performance in acidic solution is improved with the decrease of oxidation state of poly（m-phenylenediamine）（PmPD）.The rate constant is as high as 425.5 mg/（g·min） in the short equilibrium time of 30 min.The estimated highest adsorptivity of sulfate ions is 95.1%.According to the Langmuir equation,the adsorbance is 108.5 mg/g.The sulfate desorption efficiency is about 95% and the accumulative adsorbance is up to 487.95 mg/g in 5 cycles.

Synthesis of poly(m-phenylenediamine) with improved properties and superior prospect for Cr(VI) removal

Chemically oxidative polymerization of m-phenylenediamine was improved through adding the weak alkaline, Na2CO3. Results show that the poly （m-phenylenediamine） （PmPD） possesses a weak solubility in acidic solution according to total organic carbon （TOC） that the TOC is less than 8 mg/L, which is much lower than the discharge standard （20 mg/L）. The TOC of the PmPD synthesized with NaOH can be as high as 120.9 mg/L. This very weak solubility of PmPD synthesized with Na2CO3 facilitates its application in water purification. The oxidation state of PmPD is decreased and the yield is increased with a maximum of 84%, promoting the concentration of Na2CO3 in the synthesis. Moreover, the Cr（VI） performance of PmPD was marvelously enhanced with Na2CO3 to improve the synthesis. The largest Cr（VI） adsorbance can reach as high as 666.8 mg/g, which is far more than the performance of other common adsorbents.

Effects of the Supports on Activity of Supported Nickel Catalysts for Hydrogenation of m-Dinitrobenzene to m-Phenylenediamine

The hydrogenation of m-dinitrobenzene to m-phenylenediamine in liquid phase was studied with the nickel catalysts supported on SiO2, TiO2, γ-Al2O3, MgO and diatomite carders. Based on the experiments of X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, temperature-programmed reduction （TPR）, temperature-programmed desorption of hydrogen （H2-TPD） and activity evaluation, the physico-chemical and catalytic properties of the catalysts were investigated. Among the catalysts tested, the SiO2 supported nickel catalyst showed the highest activity and selectivity towards m-phenylenediamine, over which 97.3% m-dinitrobenzene conversion and 95.1% m-phenylenediamine yield were obtained at 373K under hydrogen pressure of 2.6MPa after reaction for 6 h when using ethanol as solvent. Although TiO2 and diatomite supported nickel catalysts also presented high activity, they had lower selectivity towards m-phenylenediamine. As for γ-Al2O3 and MgO supported catalysts were almost inactive for the object reaction. It was shown that both the activity and selectivity of the catalysts were strongly depended on the interaction between nickel and the support. The higher activities of Ni/SiO2, Ni/TiO2 and Ni/diatomite could be attributed to the weaker metal-support interaction, on which Ni species presented as crystallized Ni metal particles. On the other hand, there existed strong metal-support interaction in Ni/MgO and Ni γ-Al2O3, which causes these catalysts more difficult to be reduced and the availability of Ni active sites decreased, resulting in their low catalytic activity.

Determination and correlation solubility of m-phenylenediamine in (methanol, ethanol, acetonitrile and water) and their binary solvents from 278.15 K to 313.15 K

In this study, the solubility of m-phenylenediamine in four pure solvents(methanol, ethanol, acetonitrile and water) and three binary solvent(methanol + water),(ethanol + water) and(acetonitrile + water) systems were determined in the temperature ranging from 278.15 K to 313.15 K by using the gravimetric method under atmospheric pressure. In the temperature range of 278.15 K to 313.15 K, the mole fraction solubility values of m-phenylenediamine in water, methanol, ethanol, and acetonitrile are 0.0093–0.1533, 0.1668–0.5589,0.1072–0.5356, and 0.1717–0.6438, respectively. At constant temperature and solvent composition, the mole fraction solubility of o-phenylenediamine in four pure solvents was increased as the following order:water b ethanol b methanol b acetonitrile;and in the three binary solvent mixtures could be ranked as follows:(ethanol + water) b(methanol + water) b(acetonitrile + water). The relationship between the experimental temperature and the solubility of m-phenylenediamine was revealed as follows: the solubility of mphenylenediamine in pure and binary solvents could be increased with the increase of temperature. The experimental values were correlated with the Jouyban–Acree model, van’t Hoff–Jouyban–Acree model, modified Apelblat–Jouyban–Acree model, Sun model and Ma model. The standard dissolution enthalpy, standard dissolution entropy and the Gibbs energy were calculated based on the experimental solubility data. In the binary solvent mixtures, the dissolution of m-phenylenediamine could be an endothermic process. The solubility data,correlation equations and thermodynamic property obtained from this study would be invoked as basic data and models regarding the purification and crystallization process of m-phenylenediamine.

A Novel Catalyst for Liquid Phase Hydrogenation of m-Dinitrobenzene to m-Phenylenediamine

A novel lanthana-promoted nickel catalyst supported on silica for the liquid phase hydrogenation of m-dinitrobenzene to m-phenylenediamine was prepared by an incipient wetness sequential impregnation method. It was found that Ni-La/SiO2 catalyst exhibited high activity and stability for m-dinitrobenzene hydrogenation. Over this catalyst, the conversion of m-dinitrobenzene and the yield of m-phenylenediamine were up to 97.1% and 93.5%, respectively, at 373 K and 2.6 MPa hydrogen pressure after reaction for 1 h.

Effects of preparation methods of support on the properties of nickel catalyst for hydrogenation of m-dinitrobenzene

Using tetraethyl orthosilicate(TEOS)as the pre-cursor of silica,the silica aerogel and xerogel,which were used as supports of nickel-based catalysts for liquid hydroge-nation of m-dinitrobenzene to m-phenylenediamine,were prepared by the sol-gel method combined with supercritical drying(SCD)and conventional drying,respectively.Then,a series of nickel-based catalyst samples supported on these supports were prepared by the incipient wetness impregna-tion method with an aqueous solution of nickel nitrate as well as lanthanum nitrate as impregnation liquids.Based on the characterization results of nitrogen adsorption-desorption(BET),X-ray diffraction(XRD),temperature programmed reduction(TPR),temperature-programmed desorption of hydrogen(H2-TPD),and catalytic activity evaluation,the physico-chemical properties and catalytic performances of the catalysts were investigated.The results show that the nickel crystallites on the binary nickel catalyst using silica aerogel as support are of smaller particle size.However,com-pared with the sample supported on silica xerogel,the nickel catalyst supported on the silica aerogel exhibits lower activity and selectivity for the hydrogenation of m-dinitrobenzene because it has a lesser amount of active sites and weaker absorption ability to reactants caused by sintering of the nickel crystallites.The addition of promoter La2O3 could increase the activity and selectivity of the catalysts.Among all the nickel-based catalyst samples prepared,the La2O3 promoted ternary nickel-based catalyst supported on silica xerogel exhibits the highest activity and selectivity for the hydrogenation of m-dinitrobenzene to m-phenylenediamine,which could be attributed to its highest active surface area and appropriate absorption strength to reactants.Over this prom-ising catalyst,the conversion of m-dinitrobenzene and the yield of m-phenylenediamine could reach 97.0%and 93.1%,respectively,under proper reaction conditions of hydrogen pressure 2.6 MPa,temperature 373 K,and reaction time 1 h.