Preparation Of Alginate And Their Catalytic Activities For Phenol Hydroxylation

As a naturally occurring biopolymer, alginates have attracted much attention due to their wide applications, such as metallurgy, chemical engineering, food industry and so on. Recently, the alginates have been utilized as metal supports because of their high adsorbabilities of metals. Two kinds of alginate catalysts were prepared. The inner structure, outside morphology, physical and chemical properties were well characterized by many analyze techniques. Their catalytic activities for phenol hydroxylation were investigated, and the influence of different reaction conditions was studied. Some new and interesting results are as following:1. A series of ion-cross-linked Cu-ALG dry beads and powder were synthesized through ion exchange. They were characterized by UV-vis diffuse reflectance spectra, Fourier transform infrared, Inductively coupled plasma atomic emission spectroscopy, X-ray photoelectron spectroscopy, Scanning electron microscope equipped with an EDX system and nitrogen adsorption/desorption measurement. The results showed that the Cu ions were corsslinked on the alginate successfully, and the contents of metals in catalysts were associated with the concentration of the CuCl2in the raw materials, but the corsslinked contents of metals could be saturated.The results of phenol hydroxylation illustrated that the conversions of phenol were associated with the immobilized content of the Cu2+ions. The effects of reaction temperature, solvents, reaction time, initial pH value, molar ratio of phenol/H2O2and the amount of catalysts were investigated. The reusability of catalysts illustrated that they have high catalytic stability.2. A series of ion-cross-linked Cu-Pd-ALG dry beads catalysts were synthesized through ion exchange. They were characterized by UV-vis diffuse reflectance spectra, Fourier transform infrared, Inductively coupled plasma atomic emission spectroscopy, X-ray photoelectron spectroscopy, Scanning electron microscope equipped with an EDX system and nitrogen adsorption/desorption measurement. The results showed that the Cu and Pd ions were corsslinked on the alginate successfully, and the contents of metals in catalysts were associated with the concentration of the CuCl2and PdCl2in the raw materials, but the corsslinked contents of metals could be saturated.The results of phenol hydroxylation illustrated that the conversions of phenol were associated with the immobilized content of the Cu2+ions, as well the selectivities to dihydroxybenzene were determined by the immobilized content of the Pd2+ions. Compared with the Cu-ALG, the activities of Cu-Pd-ALG were better. Cause the introduction of Pd2+ions could reduce the selectivity to BQ effectively. The effects of reaction temperature, solvents, reaction time, initial pH value, molar ratio of phenol/H2O2and the amount of catalysts were investigated. The reusability of catalysts illustrated that they have high catalytic stability.3. The fixed-bed reactor was utilitied to investigate the effect of the actual industrial production of the prepared catalysts. The obtained catalysts were mixed with Al2O3with the weight ratio of3:7, and extrudated to form the cloverleaf pattern. The formed catalysts were prepared for hydroxylation of phenol in fixed-bed reactor. And the reaction conditions, such as molar ratio of phenol/H2O2, reaction temperature, weight hourly space velocity, solution and weight ratio of water/phenol, which played important roles in this reaction were evaluated. The optimum reaction condition: temperature70℃, molar ratio of phenol/H2O23:1, weight hourly space velocity4.0h-1, solution water, weight ratio of water/phenol4.5. Under the optimum reaction conditions,17.1%phenol conversion was obtained with selectivities to catechol and hydroquinone being67.7%and31.4%, respectively. The long-run catalytic test for36h confirmed the excellent catalytic activity of the catalyst and there was no metals leaching out from the catalyst.