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Continuous synthesis of mesoporous molecular sieves thick mesoporous molecular sieve synthesis

Author: WangAiHua
Tutor: GuoYiQun
School: Zhengzhou University
Course: Physical and chemical
Keywords: mesoporous molecular sieve continuous synthesis hydrothermal stability thick pore wall MCM-41 mesoporous molecular sieve double template characteristic
CLC: TQ424.25
Type: Master's thesis
Year: 2007
Downloads: 135
Quote: 1
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Abstract


Mesoporous molecular sieves, since the discovery of MCM-41, have resulted in a worldwild resuigence. This novel mesoporous solid represents a new class of mesoporous materials with the special characteristics of large internal surface area and favorable uniformity but controllable size of the pore. Special attention have been given to the mesoporous silicate molecular sieves because of their potential for use in areas of catalysis, immobilization of ativeenzyme, prepration of functional materials, soption and separations of bulky molecules.The most commonly studied mesoporous phase is MCM-41, which contains hexaonally ordered mesopores with diameter form 1.5 to over 10nm.The mesoporous molecular sieve has been synthesized under the mild conditions, in which crystallizing temprature is 100℃for 1~5d and the mol-ratio of the slurry mixture is SiO2: Na2O: CTMAB: H2SO4: H2O=7: 2.13: (0.7~3.5): (1~1.36): (350~546), using industrial water glass and C16H33 (CH33NBr (CTMAB) as original materials, H2SO4 as an adjustable agent of pH value of the slurry. The characterization of its pore structure is carried out by XRD and pore distributing measurment.Quaternary ammonium cationic surfactants (cetyltrimethylammonium-chloride (CTMAB)) have an important effect on the synthesis of mesoporous molecular sieves MCM-41. But quaternary ammonium cationic surfactants are very expensive. The cost account for 90% of raw materials, even more than 90%. In fact, its utilization factor is about 50%, the other remain in mother solution. If discarding mother solution result to serious waste. There is no report about continuous synthesis process of mesoporous molecular sieves MCM-41. We measure the contents of cetyltrimethylammoniumchloride in mother solution by spectrophotometry. The mesoporous molecular sieve is synthesized by adding appropriate industrial raw material to the mother solution under the above conditions. In the process of composing, we have to add appropriate cetyltrimethylammoniumchloride. The characterization of its pore structure is carried out by XRD and measurement of pore distributing. It is important to the industrialization of mesoporous molecular sieves.The research works in improving hydrothermal stability of mesoporous molecular sieves in recent years were reviewed in this paper. In the application of the mesoporous molecular sieve, it is possible to carry through for modification, catalytic reaction, and adsorption/separation in hot water, but hydrothermal stability of mesoporous molecular sieves is required. So how to enhance hydrothermal stability of mesoporous molecular sieves have resulted in a worldwild resurfence. One method of increasing its high thermal and hydrothermal stability is increse the pore wall thickness of MCM-41. Preliminary attempts made in the improvement of the pore wall thickness of MCM-41. The meaning of the equation calculating MCM-41’s inorganic pore wall thickness has been show based on its special porous structure and the principle of XRD’s characterization. The synthesized samples were characterized by XRD, N2 adsorption-desorption measurements. The hydrothermal stability of the samples was investigated in boiling water. The results show that the inorganic pore wall thickness is an important factor to determine the thermal and hydrothermal stabilities of MCM-41. The thickness the inorganic pore wall was, the more stable the MCM-41 was.It shows that the thermal and hydrothermal stabilities of the MCM-41 materials were improved.We study the modification of MCM-41 mesoporous molecular sieve in sake of increasing the pore wall thick, and we adopt two measurements. Mesoporous MCM-41 materials were prepared by post-synthesis modification of a purely siliceous MCM-41 that before Calcining. The post-synthesis salt treatment for an MCM-41 sample obtained by the second sythesis procedure.The sample of MCM-41 that synthesized as silicon source was carried recrystally. We synthesize MCM-41 mesoporous molecular with double templates. The frist procedure used a sodium silicate water as silicate source, cetytrimethammonium bromide and diethyl amine as the surfactants. The frist procedure used sodium silicate water as silicate source, cetytrimethammonium bromide and tetramethylammonium bromide as the surfactants. A serial of mesoporous molecular sieves MCM-41 were characterized using XRD and pore distributing measurment techniques. The influnce of kinds of concentration of small molecule template on pore wall thickness and structure was examined. The results show that tthe thermal and hydrothermal stabilities of the MCM-41 materials synthesized by mixed surfactant were improved. It was not obvious that the thermal and hydrothermal stabilities of the MCM-41 materials synthesized by post-synthesis treatmen were improved.

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CLC: > Industrial Technology > Chemical Industry > Reagents and the production of pure chemicals > Adsorbent > Inorganic adsorbent > Used as artificial silicate adsorbent
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