A New Microporous Adsorbent Of Ultra-Fine Activated Carbon Fiber And Adsorption Behavior For Indoor Formaldehyde Thereof

Formaldehyde (HCHO), one of the simplest carbonyl compounds, is colorless volatile gas. HCHO exists in many products for home use, such as wood products, paint, insulation materials. Even if the concentration of HCHO is less than 0.1ppm, it could cause vomit, chest tightness, shortness of breath, skin rashes, allergic reactions and other symptoms. Moreover, formaldehyde is a potential carcinogen. As modern living facilities and construction enter into the house, the formaldehyde concentration in indoor air is increasing year by year and exceeds the national standard. Removal of indoor formaldehyde is the strong desire of the residents, and is also one of the important research directions for environmental researcher.Currently, the technology that could be used to deal with indoor formaldehyde included adsorption, thermal destruction, absorption, photocatalysis, photochemical oxidation method, etc. Among them, adsorption is most widely used because of the relatively lower cost, simpler operation, higher removal efficiency and other advantages. The common adsorbent has poor formaldehyde adsorption capacity and need to be desorbed or replaced after work time.Thereforc, the development and application of new efficient adsorbents for indoor formaldehyde and to solve the saturated problem of adsorbent became the research focus for indoor air purification.Ultra-fine activated carbon fiber (UFACF) is a special form of carbon fiber, the biggest difference between UFACF and ordinary carbon fiber is the fiber diameter. UFACF has much smaller fiber diameter and fiber mesh. UFACF has many adsorption advantages such as large surface area, large pore volume and fast adsorption. Because the distinct advantage in filtration and adsorption, UFACF can be used as a potential adsorbent material for formaldehyde.In this paper, polyacrylonitriles (PAN) with different molecular weight were polymerized. Taking the PAN as a material, the electrospinning technology, pre-oxidation, carbonization heat treatment technology, steam activation technology were applied for the preparation of UFACF, which was a new microporous adsorbent for indoor formaldehyde removal; And taking the indoor formaldehyde as target, the formaldehyde adsorption behaviors of UFACF were studied in different conditions; In addition, through the introduction of photochemical oxidation, the effect of adsorption-photochemical oxidation coupling technology on formaldehyde removal was studied too.The research purpose of paper was to prepare the UFACF which was nice for indoor formaldehyde adsorption and find out optimization of preparation conditions of UFACF, and the influence factors for the application of formaldehyde adsorption of UFACF were investigated in the paper too. The optimization research results of preparation conditions for UFACF could be useful to the preparation of carbon adsorbent material; the influence factors for the application of formaldehyde adsorption of UFACF could provide reference for practical application of UFACF and open a new way for air purification. This paper was consisted with several parts, which included:the preparation of electrospinning UFFM from PAN; pre-oxidation and carbonization study of UFFM; study on the preparation of UFACF; formaldehyde static adsorption of UFACF; formaldehyde dynamic adsorption behavior study of UFACF; the formaldehyde remove study of adsorption-pHotochemical oxidation technology.In the research for the preparation of UFFM, five kinds of PAN with different molecular weight were polymerized via DMSO/H2O mixed solvent method, and the PAN was dissolved into the spinning solution with DMF as solvent and electrospun into UFFM. The polymerization results showed that viscosity average molecular weight and conversion rate of PAN would increase with higher H2O ratio in mixed solvent in the same monomer concentration and environment conditions. From the TG analysis, dramatic weight loss zone would appear and the weight loss ratio would larger with PAN molecular weight increasing. Electrospinning results showed that the spinning solution could not be electrospun into ultra-fine fiber if the molecular weight of PAN was too high, and the higher electrospinning voltage was favorable for finer fiber diameter but cause larger dispersion of fiber diameter distribution with the electrospinning stability decreasing.UFFM-1,UFFM-2,UFFM-3 were taken as materials to prepare UFCFM in the research of pre-oxidation and carbonization, the purpose of the experiments was to determine the raw material for the preparation of UFACF. The results of the pre-oxidation experiments showed that the UFPFM could be made from UFFM after pre-oxidation process, and which was a nice steam adsorbent. In the process of pre-oxidation and carbonization, the mass of the fibers reduced, many complex chemical reactions occurred and UFFM fiber structure and element content significantly changed. From the analysis of fiber bundles tensile properties, UFCFM-3 had high mechanical strength and could be taken as the raw material for the preparation of UFACF.In the preparation research of UFACF, two kinds of UFACF (UFACF (D) and UFACF (W)) were separately made via electric heating orthogonal activation experiments and microwave heating orthogonal activation experiments. From measuring and characterization, the optimal conditions for UFACF preparation were analyzed. Where, the maximum specific surface area of UFACF (D) reached 1075.1 m2/g and the maximum specific surface area of UFACF (W) reached 1107.4 m2/g. From the pore size distribution and infrared spectra characterization of UFACF which were made from the different heating methods were explored. To be specified, the cost and efficiency of UFACF (W) preparation were advantage than UFACF (D)In the research for static formaldehyde adsorption of UFACF, the formaldehyde adsorption performance of UFACF (D)-7 and UFACF (W)-5 were tested at same relative humidity. And automatic surface area and pore size distribution analyzer was used to investigate the micropore size distribution. From the test results, both UFACF (D)-7 and UFACF (W)-5 had nice formaldehyde adsorption properties because there were a large number of ultramicropore existing in them. But in the case of similar surface area and micropore size distribution, formaldehyde adsorption performance of UFACF (D)-7 was better than UFACF (W)-5, the presence of the oxygen groups in the UFACF (D)-7 explained the reason. Where, on the condition of relative humidity 40%, formaldehyde equilibrium adsorption capacity of UFACF (D)-7 and UFACF (W)-5 was separately 0.50mg/g and 0.36mg/g.In the research for dynamic adsorption behavior of UFACF, some experiments results were get:on the condition of same initial concentration of formaldehyde and the gas flow, larger relative humidity caused worse formaldehyde adsorption performance; on the condition of same initial concentration of formaldehyde and relative humidity, with the gas flow increasing, formaldehyde effective amount of adsorption and equilibrium adsorption were decreasing. Where, on the condition of relative humidity 70% and 30% with same gas flow rate, formaldehyde equilibrium adsorption capacity were 0.31 mg/g and 0.41 mg/g. and on the condition of gas flow rate 1.0 L/min and 0.6 L/min with relative humidity 50%, the formaldehyde equilibrium adsorption capacity were 0.23 mg/g and 0.50 mg/g. According to Wheeler-Jonas equation' modeling and prediction for dynamic adsorption process, the simulation curves of Wheeler-Jonas equation were similarity with experimental data curve between breakthrough time and saturation time, and adsorption equilibrium time and equilibrium adsorption capacitance were close to the actual experimental data, but the breakthrough time of adsorption, the effective adsorption and adsorption band length were quite different with the actual experimental data.From the research of adsorption-photochemical oxidation coupling technology, the photooxidation of low-pressure mercury light in air could produce hydroxyl radicals, and the formaldehyde removal efficiency of adsorption-photochemical oxidation coupling technology was better than single absorption process or single photochemical oxidation process. Where, on the condition of relative humidity 50%, at 90 min, the formaldehyde removal efficiency of the single photochemical oxidation technology, the single adsorption process and the adsorption-photochemical oxidation coupling process were 68.8%,37.0% and 95.2%. Adsorption-photochemical oxidation technology was a new air purifying technology, which could solve the problem of secondary photochemical pollution and adsorbent saturation. The technology was one of directions for improving indoor air quality.The innovative research results of this paper were summarized as follows:1) With the literature search results from the sciencedirect, the preparation of UFACF was a relatively new research field, and that UFACF was applied to the adsorption of formaldehyde was rarely reported. This research projects was advanced.2) In the research of preparation of UFCFM, the influence of the PAN molecular weight to UFCFM product performance were discussed, the related analysis could provide reference for improving the mechanical properties of UFACF or carbon fiber.3) The research about the preparation of UFACF via microwave heating was rarely reported, the related experiment conclusions could be valuable for the choice of heating method of porous carbon materials preparation.4) From the Wheeler-Jonas equation simulation and prediction results about the dynamic adsorption behavior of formaldehyde, the simulated breakthrough time of adsorption, the effective adsorption and adsorption band length were quite different with the actual experimental data, which verified the wheeler-Jonas equation was limited for predicting gas dynamic adsorption behavior of UFACF. The conclusion could be useful to the adsorption applications of UFACF.5) The adsorption-photochemical oxidation coupling technology was studied in this paper. And the conception of the fixed position desorption of adsorbent and the fixed position degradation of adsorbate were proposed. From the experiment results, the coupling technology was advantage for the formaldehyde remove and had potentiality for air purification.