Shuixia Chen

CO2 Capture by Polyethylenimine-Modified Fibrous Adsorbent

This work focuses on developing a novel adsorbent for CO2 capture, by coating polyethylenimine (PEI) on glass fiber matrix and using epichlorohydrin (ECH) as cross-linking agent. The physicochemical properties of the fibrous adsorbent were characterized. The CO2 adsorption capacity was evaluated. Factors that affect the adsorption capacity of the fibrous adsorbent were studied. The experimental results show that this fibrous PEI adsorbent exhibits a much higher adsorption capacity for CO2 compared with another PEI fiber prepared in our previous work, which employed epoxy resin as the cross-linking agent. A CO2 adsorption capacity as high as 4.12 mmol CO2/g of adsorbent was obtained for this fibrous PEI adsorbent at 30 degrees C, equal to 13.56 mmol CO2/g of PEI, with a PEI/ECH ratio of 20:1. The adsorbent can be completely regenerated at 120 degrees C.

Effect of activated carbon fiber anode structure and electrolysis conditions on electrochemical degradation of dye wastewater

The alizarin red S (ARS) in simulated dye wastewater was electrochemically oxidized using an activated carbon fiber (ACF) felt as an anode. The influence of electrolytic conditions and anode structure on the dye degradation was investigated. The results indicated that initial pH, current density and supporting electrolyte type all played an important role in the dye degradation. The chemical oxygen demand (COD) removal efficiency of dye solution in neutral or alkaline medium was about 74% after 60 min of electrolysis, which was higher than that in acidic medium. Increasing current density would lead to a corresponding increase in the dye removal. The addition of NaCl could also improve the treatment effect by enhancing the COD removal efficiency 10.3%. For ACF anodes, larger specific surface area and higher mesopore percentage could ensure more effective electrochemical degradation of dye. The data showed that the color removal efficiency increased from 54.2 to 83.9% with the specific surface area of ACF anodes increasing correspondingly from 894 to 1,682 m(2)/g.

Preparation of amine group-containing chelating fiber for thorough removal of mercury ions.

An aminated chelating fiber (AF) with high adsorption capacity for mercury ions was prepared by grafting copolymerization of acrylonitrile onto polypropylene fiber, followed by aminating with chelating molecule diethylenetriamine. Effects of reaction conditions such as temperature, reaction time, bath ratio and dosage of catalyst on the grafting yield were studied. Chemical structure, tensile strength and thermal stability of AF were characterized. The adsorption performances for mercury were evaluated by batch adsorption experiments and kinetic experiments. The results show that AF is effective for the removal of mercury over a wide range of pH. The chelating fiber also shows much higher adsorption capacities for mercury, the equilibrium adsorption amount could be as high as 657.9 mg/g for mercury. The high adsorption capacity of Hg(2+) on AF is resulted from the strong chelating interaction between amine groups and mercury ions. Two amine groups coordinate with one mercury ion could be speculated from the adsorption capacity and amine group content on AF. The kinetic adsorption results indicate that the adsorption rates of AF for mercury are very rapid. Furthermore, the residual concentration was less than 1 microg/L with feed concentration of mercury below 1mg/L, which can meet the criterion of drinking water, which indicates that the chelating fiber prepared in this study could be applied to low-level Hg contaminated drinking water purification.

Preparation of an ion-imprinted fiber for the selective removal of Cu2+.

A novel Cu(2+)-imprinted fiber (IIF) was prepared by grafting acrylic acid (AA) onto the surface of a polypropylene (PP) fiber and subsequently modified with polyethylenimine (PEI). An examination by infrared spectroscopy and scanning electron microscopy confirmed that the ion-imprinted polymer was successfully introduced onto the surface of a PP fiber. The modification of PP fibers with AA was beneficial to the grafting of PEI onto the fibers. The highest grafting degree of PEI could reach 120 wt % under optimal grafting conditions. This IIF showed excellent tensile and chemical stability in acid solution, which qualified the IIF for practical applications. Besides having a high adsorption capacity for Cu(2+) (120 mg/g), the IIF adsorbent showed a high selectivity for Cu(2+) as compared with that of the non-ion-imprinted fiber (NIF). The dynamic adsorption results indicated that IIF can thoroughly remove Cu(2+) from the solution in a relatively short contact time. The effective treatment volume was about 910 bed volumes. The selectivity coefficient of IIF for Cu(2+) with respect to Zn(2+) could reach 76.4. IIF also has good regeneration performance and could maintain almost the same adsorption capacity for copper ions after 10 adsorption-desorption cycles.

Preparation and Characterization of a Solid Amine Adsorbent for Capturing CO2 by Grafting Allylamine onto PAN Fiber

Solid amine adsorbents using synthetic fibers instead of silica as the matrix are expected to offer more benefits for the adsorption of CO(2) because of high external surface area, low pressure drops, and flexibility of the matrix fibers. A novel kind of solid amine-containing fibrous adsorbent (PAN-AF) was prepared by preirradiation grafting copolymerization of allylamine onto polyacrylonitrile (PAN) fiber, using the redox system of (NH(4))(2)S(2)O(8)/NaHSO(3) as initiator. The effects of the reaction conditions such as reaction time, temperature, monomer concentration, amount of the initiator on grafting degree were studied. The results showed that the optimal conditions for the grafting copolymerization were using 50% allylamine monomer (V/V) and 1.5% (W/V) initiator and reacting at 100 degrees C for 10 h. FTIR was employed to characterize the corresponding changes on the surface chemical structure of PAN and PAN-AF. Thermal gravimetric analysis was used to evaluate the thermal stability of the materials. Equilibrium adsorption capacities for CO(2) and regeneration behaviors of PAN-AF were determined. Adsorption capacity for CO(2) of PAN-AF with 60.0 wt % grafting degree was 6.22 mmol CO(2)/g PAN-AF. PAN-AF could be completely regenerated by heating in boiling water for 30 min. The CO(2) adsorption performance of the regenerated PAN-AF was almost the same as that of the fresh adsorbent after several cycles, which revealed that PAN-AF exhibited good regenerating stability. The high speed and effective regeneration process proves that PAN-AF has great potential in industrial applications for CO(2) capture.

Preparation and characterization of a strong basic anion exchanger by radiation-induced grafting of styrene onto poly(tetrafluoroethylene) fiber.

A novel anion-exchange fiber with strong basic groups has been prepared by grafting styrene onto poly(tetrafluoroethylene) fibers via irradiation. Experiments were carried out to analyze the effects of synthesis conditions on the grafting degree and to characterize the physicochemical properties of the anion-exchange fibers. The experimental results showed that preirradiation grafting styrene onto poly(tetrafluoroethylene) fiber could significantly reduce the waste of raw material and the formation of homopolymer, although the grafting degree was relatively low. The grafting reaction could be effectively enhanced through the addition of magnesium powder into the reaction system. The optimal temperature and time for preirradiation grafting were 80 degrees C and 6 h, respectively. The experimental results also showed that the anion-exchange fibers had excellent mechanical properties and thermal stability at a temperature up to 420 degrees C. The fibers were stable in acidic, alkali, and oxidative solutions. The static ion-exchange capacity of the fibers was as high as 6.08 mmol/g. The static adsorption capacities for Cr(2)O(2-)(7) and MnO(-)(4) ions were 214.08 and 290.98 mg/g, respectively.

Surface molecular imprinting on polypropylene fibers for rhodamine B selective adsorption.

A surface molecular imprinted fiber (MIF-B) for rhodamine B (RhB) was prepared by bonding polyethylenimine (PEI) onto polypropylene (PP) fibers and subsequently cross-linking with epichlorohydrin (ECH) in the presence of RhB. The chemical structures of composites in each synthetic step were traced by FTIR analyses. The MIF-B exhibited excellent static and dynamic adsorption properties for RhB. Its adsorption isotherm for RhB followed Langmuir model. The competitive adsorption results indicated that the MIF-B had much higher selectivity for RhB over a structural analog (rhodamine 6G) with a selectivity coefficient (K(c)) of 74.1. The MIF-B proved to be a pH-sensitive material. Poly(acrylic acid) (PAA) and PEI chains grafted on PP would stretch or shrink in response to pH, resulting in the change in size and shape of binding sites of the MIF-B. Basic condition could induce the lightly cross-linked MIF-B to swell and expand its surface area, thus providing more memory cavities and internal binding sites constructed by imprinting process and ultimately leading to higher binding capacity and better RhB recognition.

Structure design of a hyperbranched polyamine adsorbent for CO2 adsorption

An amino-terminated hyperbranched polymer (HBP-NH2) has been prepared through the Michael addition reaction between amines and methyl acrylate (MA) at 0 °C, followed by self-condensation of the addition reaction products at 100 °C and 140 °C. A novel CO2-“imprinted” hyperbranched polymeric adsorbent (IHBPA) with a high amino density was conveniently prepared by using glutaraldehyde to crosslink HBP-NH2 which had pre-adsorbed CO2. Through comparing the adsorption capacities of the IHBPA with HBPA, which was prepared with a similar procedure to that of IHBPA but without CO2 pre-adsorption, it could be found that the pre-adsorbed CO2 on HBP-NH2 would occupy the reactive sites of amino groups, and play the role of “imprinting” in the preparation of the adsorbent. The adsorption capacity of the IHBPA could thus be improved. After reducing the imino groups of the IHBPA to alkyl amine by NaBH4, the adsorption capacity of the reducing solid amine adsorbent (IHBPA-R) can be further improved. The prepared solid amine adsorbents also showed promising regeneration performance, which could maintain almost the same adsorption capacity for CO2 after 10 adsorption and desorption recycles. The high CO2 adsorption capacity (7.65 mmol g−1) of IHBPA-R can be attributed to its high amino density, terminal amine and hyper-branched structures.

Synthesis of porous polymer based solid amine adsorbent: Effect of pore size and amine loading on CO2 adsorption

A series of porous polymers was synthesized by a suspension polymerization of divinylbenzene (DVB) and ethylene glycol dimethyl acrylate (EGDMA), which was further functionalized with polyethyleneimine (PEI) for CO2 capture. The results showed that the synthesized DVB and EGDMA (DE) copolymers were an effective support for loading PEI because of its larger pore size and specific surfaces area. It was found that DE (30, 10) loaded with 30wt% PEI exhibited a higher CO2 adsorption amount of 3.28mmol/g at 25°C under dry condition. The CO2 adsorption capacity would decline gradually as the temperature continuously raised, for the reaction between CO2 and amine groups was an exothermic reaction. The kinetics study showed that Avrami kinetic model could accurately describe the whole CO2 adsorption process, suggesting that both physical adsorption and chemical adsorption were involved with the CO2 adsorption process. The intraparticle diffusion and Boyds film diffusion models were applied to investigate the CO2 diffusion mechanism, the intraparticle diffusion model could well distinguish the rate-limiting step during CO2 adsorption process. This solid amine adsorbent could be regenerated with nitrogen stream at 75°C, and it kept stable CO2 adsorption capacity after eight adsorption-desorption cycles. All these features indicated that this porous polymer based adsorbent has a high potential for CO2 capture and separation from flue gas.

The use of ZnCl2 activation to prepare low-cost porous carbons coated on glass fibers using mixtures of Novolac, polyethylene glycol and furfural as carbon precursors

Abstract Using ZnCl 2 as an activation agent, low-cost porous carbons were prepared using mixtures of Novolac, polyethylene glycol (PEG) and furfural in alcohol as carbon precursors that were coated onto glass fiber mats. The morphology, microcrystalline structure, pore structure, surface chemistry, mechanical strength and adsorption properties of the porous carbons were characterized. Results show that the addition of furfural and PEG to the carbon precursors greatly improves pore development. The specific surface area of the porous carbons is as high as 2023 m 2 /g when PEG and furfural are added, otherwise it is only 404 m 2 /g. It is found that the addition of PEG to the precursors can increase the solubility of ZnCl 2 in alcohol, and thus facilitate the activation of the carbon precursors. The formation of a crosslinked structure of furfural with Novolac is responsible for the improvement in the thermal stability of the precursors and the increase in the carbon yield, which favors the increase in the surface area and the reduction of the production cost. The porous carbons have similar adsorption performance and microcrystalline structure to conventional activated carbon fibers.