本文選題：silicalite-1 + 形貌　； 參考：《浙江大學(xué)》2015年碩士論文

【摘要】：MFI型分子篩由于其獨(dú)特的交叉孔道結(jié)構(gòu)、較高的機(jī)械強(qiáng)度和水熱穩(wěn)定性以及親油疏水能力,在催化和分離等多種領(lǐng)域有著十分廣泛的應(yīng)用。其中,全硅型MFI分子篩(silicalite-1)由于其骨架結(jié)構(gòu)中不含鋁,具有疏水性,特別適用于有機(jī)物提純等應(yīng)用。眾所周知,silicalite-1晶體的形貌和粒徑對(duì)其性能有較大的影響,所以其形貌和性能的研究一直是分子篩領(lǐng)域的一大熱點(diǎn)。但是,目前調(diào)控的范圍大多集中在納米級(jí)顆粒,鮮有文獻(xiàn)報(bào)道關(guān)于微米級(jí)范圍內(nèi)晶體粒徑的調(diào)節(jié),而且大多數(shù)需要苛刻的合成條件與昂貴的有機(jī)模板劑(如多聚四丙基銨,TPAOH等)和原料(如正硅酸乙酯),合成過(guò)程復(fù)雜,這些問(wèn)題限制了它們?cè)诠I(yè)生產(chǎn)中的實(shí)際應(yīng)用。因此,根據(jù)特定的需要(如制備分子篩膜用晶種),利用價(jià)格低廉的原料并通過(guò)簡(jiǎn)單的合成過(guò)程實(shí)現(xiàn)對(duì)微米或亞微米silicalite-1晶體的調(diào)控具有十分重要的意義。本文基于在大孔氧化鋁管上制備MFI型分子篩膜的晶種出發(fā),實(shí)現(xiàn)silicalite-1粒徑大小和形貌的調(diào)控,探討不同晶種對(duì)于MFI分子篩膜結(jié)構(gòu)和醇水分離性能的影響。主要研究?jī)?nèi)容和結(jié)果如下：1. Silicalite-1晶體形貌和粒徑的調(diào)控在傳統(tǒng)水熱合成體系中,以廉價(jià)氣相二氧化硅為硅源,TPABr為模板劑,采用電子顯微鏡(SEM)、X光衍射(XRD)和激光粒度儀(LLS)等技術(shù)對(duì)分子篩晶體的形貌和粒徑進(jìn)行表征,分別采用一步法和兩步變溫法實(shí)現(xiàn)分子篩形貌和粒徑的調(diào)控。一步合成法：考察了合成液的水量、堿度、模板劑含量、晶化條件和攪拌方式對(duì)晶體粒徑和形貌的影響。研究發(fā)現(xiàn),增大合成液的水量可以使晶體由球形轉(zhuǎn)變?yōu)楣仔?提高堿度則可以促使晶體向球形轉(zhuǎn)變,且隨著堿度的增加,晶體粒徑逐漸減小。增大模板劑的含量和縮短晶化時(shí)間均可以在不影響分子篩產(chǎn)率的情況下實(shí)現(xiàn)較小粒徑silicalite-1晶體的制備。在晶化過(guò)程中轉(zhuǎn)動(dòng)式合成能夠得到粒徑較為均一的晶體,而攪拌式合成能得到粒徑分布較廣的晶體,粒徑相對(duì)較小。兩步變溫合成法：研究低溫預(yù)晶化和高溫晶化的兩步變溫法制備silicalite-1晶體的規(guī)律。低溫預(yù)晶化溫度控制在40-80℃,時(shí)間3-81 h；控制高溫晶化溫度在130℃,時(shí)間3-120 h。研究發(fā)現(xiàn),預(yù)晶化溫度在50-60℃時(shí)晶體粒徑較小,而在40℃和80℃時(shí)粒徑較大。隨著預(yù)晶化時(shí)間的延長(zhǎng),晶體的粒徑逐漸減小,但超過(guò)24 h時(shí),晶體粒徑下降速率較為緩慢,且進(jìn)一步延長(zhǎng)預(yù)晶化時(shí)間,晶體的產(chǎn)率有所下降。當(dāng)晶化時(shí)間為3h時(shí),即可制備出較高產(chǎn)率(68.6%)的0.5μm左右的silicalite-1晶體,進(jìn)一步延長(zhǎng)晶化時(shí)間,晶體粒徑基本不發(fā)生變化。在較優(yōu)合成條件(在60℃預(yù)晶化24 h,130℃晶化3h)下可以制備出產(chǎn)率約為70%的0.5μm左右的silicalite-1晶體。與傳統(tǒng)的一步法相比,兩步變溫法在同等條件下可制備出粒徑遠(yuǎn)小于一步法的晶體；晶體的產(chǎn)率較一步法提高了約15%；大大縮短了制備分子篩所需的晶化時(shí)間,節(jié)約能源。2.不同晶種對(duì)MFI分子篩膜的結(jié)構(gòu)和分離性能的影響以不同形貌、硅鋁比、粒徑分布及Na+含量的MFI型分子篩為晶種,在一定條件下在大孔氧化鋁管表面合成MFI分子篩膜,并通過(guò)SEM觀測(cè)膜層形貌,采用滲透汽化測(cè)試其對(duì)60℃下5 wt%乙醇/水混合溶液的分離性能。研究發(fā)現(xiàn),不同形貌的晶種制備的分子篩膜有著不同的膜層結(jié)構(gòu),隨著晶種形態(tài)由單晶(棺形)向多晶(帶孿晶的棺形和球形)變化,所得膜層表面的孿晶也逐漸增加。同時(shí),多晶形貌的晶種相對(duì)于單晶形貌更容易制備出致密的膜層。且當(dāng)膜層均致密時(shí),含孿晶的棺形晶種制備的膜層分離性能略高,在合成液中TPAOH/TEOS=0.005時(shí),其分離因子高達(dá)114。比較了不同硅鋁比的MFI晶種成膜的性能,發(fā)現(xiàn)少量Al的存在并不會(huì)影響分子篩膜的性能,甚至當(dāng)TPAOH/TEOS=0.05時(shí),以ZSM-5(140)為晶種制備膜層的分離因子可達(dá)103。同時(shí),研究發(fā)現(xiàn),球磨有助于增大晶種的粒徑分布,球磨后晶種制備的膜層分離因子提高約10。晶種中Na+的含量對(duì)于其成膜性能有影響,Na+含量越高,所制備膜層分離乙醇/水的性能越低。
[Abstract]:MFI type molecular sieves are widely used in many fields, such as catalysis and separation because of their unique cross channel structure, high mechanical strength, hydrothermal stability and hydrophobicity and hydrophobicity. Among them, all silicon MFI molecular sieves (silicalite-1) are hydrophobic and are especially suitable for organic purification because of their skeleton structure without aluminum. It is well known that the morphology and particle size of silicalite-1 crystals have a great influence on their properties, so the study of their morphology and properties has been a hot spot in the field of molecular sieves. However, the scope of the current regulation is mostly concentrated in nanoscale particles. There are few reports about the regulation of crystal size in the micron range, and most of them have been reported. A number of demanding synthetic conditions and expensive organic templates, such as poly (four propyl ammonium, TPAOH, etc.) and raw materials (such as ethyl orthosilicate), are complex, which limit their practical applications in industrial production. The realization of the single synthesis process is very important for the regulation of the micrometer or submicron silicalite-1 crystal. Based on the preparation of the MFI type molecular sieve membrane on the macroporous alumina tube, the size and morphology of the silicalite-1 particle size and morphology are controlled. The effects of different crystal species on the structure of the MFI molecular sieve membrane and the separation performance of alcohol and water are discussed. The main contents and results are as follows: 1. Silicalite-1 crystal morphology and particle size are regulated in the traditional hydrothermal synthesis system, using cheap gas phase silica as the silicon source, TPABr as a template, using electron microscope (SEM), X light diffraction (XRD) and laser particle size analyzer (LLS) to characterize the morphology and particle size of the molecular sieve crystal. One step method and two step temperature change method are used to control the morphology and particle size of molecular sieves. One step synthesis method: the effect of water quantity, alkalinity, template content, crystallization condition and stirring mode on the particle size and morphology of the synthetic liquid. With the increase of basicity, the particle size of crystal gradually decreases with the increase of alkalinity. Increasing the content of the template and shortening the crystallization time can achieve the preparation of the smaller size silicalite-1 crystal without affecting the molecular sieve yield. The crystal with a wide particle size distribution can be obtained with a relatively small particle size distribution. The two step temperature synthesis method: the study on the preparation of silicalite-1 crystals at low temperature precrystallization and high temperature crystallization by two step temperature variation method. The temperature precrystallization temperature is controlled at 40-80, 3-81 h, and the crystallization temperature is controlled at 130 and 3-120 h. at high temperature. The grain size of the crystal is smaller at 50-60 C, and the particle size is larger at 40 and 80. As the precrystallization time prolongs, the particle size of the crystal gradually decreases, but the grain diameter decreases more slowly than 24 h, and further prolongs the precrystallization time and the crystal yield decreases. When the crystallization time is 3h, the grain size can be prepared. The silicalite-1 crystal with high yield (68.6%) of about 0.5 m, further prolongs the crystallization time, and the crystal size does not change basically. Under the better synthesis condition (precrystallization 24 h at 60, 130 C 3H), the silicalite-1 crystal with about 0.5 mu m production rate can be prepared. Compared with the traditional one step method, the two step temperature method is equal. The crystal yield is far less than one step, the yield of crystal can be increased by about 15% compared with one step method; the crystallization time required for the preparation of molecular sieves is shortened, and the effects of different crystal species on the structure and separation performance of MFI molecular sieve membrane are reduced by different morphologies, silicon aluminum ratio, particle size distribution and Na+ content of MFI type molecules. The MFI molecular sieve membrane was synthesized on the surface of a large pore oxide tube under certain conditions, and the morphology of the membrane was observed by SEM. The separation performance of the mixed solution of 5 wt% ethanol / water at 60 C was measured by pervaporation. As the crystal (coffin) changes to polycrystalline (with twin coffin and spherical), the twin crystals on the surface of the membrane also increase gradually. At the same time, the crystal species of the polycrystalline morphology is more likely to produce a compact membrane than the single crystal morphology. And when the film is dense, the separation performance of the film with twin crystal coffin crystals is slightly higher, and when TPAOH/TEOS=0.005 is in the synthetic liquid. The separation factor is up to 114. to compare the properties of MFI seed formation with different Si / Al ratio. It is found that the presence of a small amount of Al does not affect the performance of the molecular sieve membrane. Even when TPAOH/TEOS=0.05, the separation factor of the film prepared by ZSM-5 (140) is up to 103.. The ball milling helps to increase the particle size distribution and after ball milling. The membrane separation factor prepared by the crystal seed increases the content of Na+ in about 10. crystals, and the higher the content of Na+, the lower the performance of the preparation of the membrane to separate ethanol / water.

【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TQ051.893

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本文編號(hào)：1828385