Abstract
Zeolite with CHA structure is kind of important miorporous materials as gas adsorbent and selective catalytic reaction (SCR) catalyst. Coal fly ash was selected as low cost silicon and aluminum source for CHA zeolite synthesis.
1. Introduction
Coal is the main energy source of China and the main solid waste of coal fire plant is fly ash. The emissions and accumulation of coal fly ash caused serious environmental problems [1] .The coal fly ash pulled up at random, not only take up a lot of land, but also damage the environment. Properly handle the fly ash can convert waste into valuable source and improve the environment. Currently, the utilization of fly ash are mainly concentrated in building materials, such as fly ash brick, cement and concrete, these materials are low value product and the utilization rate of less than 50%. Recently, using fly ash as silicon and aluminum source to synthesis high value- added zeolite has attracted more attention [2].
Zeolite are hydrate, microporous aluminosilicates structured into three-dimensional network tetrahedra joined at the corners by oxygen atoms. This structural configuration means zeolites have a significant number of intermolecular cavities and channels, with molecular dimensions that allow the transfer of matter between intercrystalline spaces [3]. Zeolite has a unique internal hole structure and crystal chemistry, which can be widely used in industry, such as sorbents for the removal of ions in liquid and gaseous effluents[4], mercury removal from flue gases[5-8], dryer[9], adsorption separation agent, catalyst, deodorant, and also as material for capturing carbon dioxide[10-11]. Zeolite CHA is a kind of useful molecular sieve, which has high surface area and pore volume and can be used for gas separation [12]. After ion exchange, zeolite CHA can also used as catalyst in various catalytic reaction[13].The particles of fly ash possess the similar chemical component as zeolite. Herein, we investigate using fly ash as raw materials for zeolite CHA synthesis.
2. Method
2.1. Materials
The coal fly ash used in this study was from Shenhua Group, China, and the content of the fly ash components as shown in table 1. KOH (AR), Aluminum powder (AR), silica hydrated (99.8%) template agent (25%) and Distilled water were used as chemicals for zeolite synthesis.
Table 1. Chemical composition of Coal Fly Ash
2.2. Characterization Methods
The major element chemical analyses were performed on pressed powder pellets using X-ray fluorescence spectrometry (XRF; S4 Pioneer, AXS). The mineralogical composition was determined by powder X-ray diffraction (XRD; D/MAX-2500). The data collections were performed in the 20 range 5-60˚with scanning speed of 10˚/min. The morphological features of the starting and aged materials were observed using a field emission scanning electron microscope (SEM, Nanosem 430). Elemental analyses were performed with an energy-dispersive X-ray spectrometer (EDS, S-4800).
2.3. Synthetic experiment
Aqueous alkali performed with 0.17g of KOH in 26ml deionized water, then 0.036 g aluminium powder added into the solution and then stirring for 30-60 mins. After aluminum powder dissolved 0.126 g coal fly ash was added into the solution with stirring 30-60 mins. And then then the organic template was added into the mixture.After stirring at room temperature for 30 mins,1.2 g white carbon black was added into the solution and stirred for 1h. The final mixture was placed into the Teflon-lined stainless steel autoclave and transferred into the oven at 160? for 3- 7 days .After crystallization, the reaction mixture was cooled to room temperature, and the solid phase was separated from the liquid phase by filtration. The solid product was washed thoroughly with distilled water, and it was dried overnight at 100?.
3. Results and Discussion
Fig 1. XRD pattern of coal fly ash (CFA) and (inset) its SEM image
Figure 1 Shows the characteristic morphology of the coal fly ash (CFA). The major phases were quartz and mullite. Presence of amorphous glassy phase can be observed by a broad hump in the region between 20 and 40˚. Quartz and mullite present in the coal fly ash are the source of silicon and aluminum.
Fig 2. XRD pattern of CHA synthesized with aluminite powder
Figure 2 shows the effect of different crystallizing time on the formation of resultant zeolites and their crystallinity. It can be seen from the XRD plot that the complete formation of pure phase was formatted, proving that the zeolite CHA was synthesized. There was slight decrease in degree of crystallinity of the zeolite with increase in time of crystallization. So the optimal crystallization time was found to be 6d.
Fig 3. SEM image of CHA synthesized with different crystallization time(A:6d,B:8d).
Figure 3 shows the morphology of CHA. The SEM image of the synthesized zeolites showed a different grain size. There was clearly decrease in degree of crystallinity of the zeolite with increase in time of crystallization, but the impurities were rising. So we further determine the best crystallization time is 6 days.
Table 2. Chemical composition of CHA(6d)
Table 3. Chemical composition of CHA(8d)
Table 2 and 3 show the effect of crystallization time on the formation of Si/Al. It can be seen from the table 2 and3 that the Si/Al (8d) >Si/Al (6d), and the ratio is 8.2 and 6.3 respectively. This proves that with the extension of the crystallization time, the Si/Al is increasing.
Fig 4. XRD pattern of CHA synthesized from the aluminite powder and coal fly ash (6d)
Figure 4 shows the effect of adding coal fly ash on the formation of resultant zeolites and their crystallinity. It be seen from the XRD plot that the complete formation was formatted, but the crystallinity decreased due to the peak change to wider. There may be a small amount of impurities.
4. Conclusion
We have successfully synthesized CHA zeolite by adding coal fly ash as low cost raw materials. The optimal crystallization time was found to be 6 days, there was clearly decrease in degree of crystallinity of the zeolite with increase in time of crystallization, but the impurities were rising.
Acknowledgements
This research was financially supported by the National Natural Science Fund of China (grant no. 21406165), Natural Science Fund of Tianjin and Special fund of State Key Laboratory of Engines.
Source: Xiaotong Jina, Na Ji, Chunfeng Songa, Degang Ma, Guoping Yan, Qingling Liu
a Tianjin Key Laboratory of Indoor Air Environmental Quality Control, School of Environmental Science and Engineering, Tianjin University,
Tianjin 300072, China
b State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China
c Department of Material Science and Engineering, Wuhan Institute of Technology Material Science and Engineering, Wuhan 430074, China
Advertisement
The 10 largest coal producers and exporters in Indonesia:
- Bumi Resouces
- Adaro Energy
- Indo Tambangraya Megah
- Bukit Asam
- Baramulti Sukses Sarana
- Harum Energy
- Mitrabara Adiperdana
- Samindo Resources
- United Tractors
- Berau Coal
