銅基水滑石催化劑制備及氫解高濃度纖維素性能
發(fā)布時間：2018-10-05 18:20
【摘要】：由于石油、煤炭等化石燃料資源的緊缺,以及日益加重的溫室效應(yīng),探索和發(fā)展可再生能源的利用迫在眉睫。在對眾多非常規(guī)能源的探索中,生物質(zhì)轉(zhuǎn)化不僅可以緩解能源短缺帶來的瓶頸,同時也可以減輕化石資源的利用所引起的環(huán)境問題。而纖維素作為一種廣泛存在的生物質(zhì)資源,其可以轉(zhuǎn)化為多種化學(xué)品原料,具有很高的利用價值。其中,纖維素通過氫解獲得的一系列低碳多元醇類化合物,如乙二醇(EG)、丙二醇(PD)等,是工業(yè)上合成聚酯、纖維等聚合物的重要原料,應(yīng)用范圍十分廣泛。因此,纖維素氫解制備低碳多元醇是一條十分有潛質(zhì)的生物質(zhì)轉(zhuǎn)化路線。采用堿性的水滑石材料作為前體,制備了一系列Cu基催化劑,并應(yīng)用于高濃度的纖維素氫解反應(yīng)。通過共沉淀法合成不同Cu/Mg/Al摩爾比的水滑石前體,通過焙燒制備不同金屬含量的催化劑,系統(tǒng)的研究金屬配比、焙燒和還原條件對催化劑晶相結(jié)構(gòu)以及物理化學(xué)性質(zhì)上的影響。采用CO2-TPD以及N20化學(xué)吸附分別對催化劑的堿性以及活性位含量進(jìn)行測定,結(jié)果顯示,Mg含量的降低會嚴(yán)重導(dǎo)致催化劑堿性下降,而Cu的含量不僅可以控制堿性,同時影響催化劑表面的活性位含量。結(jié)合纖維素氫解反應(yīng)結(jié)果發(fā)現(xiàn),堿性的增強(qiáng)有利于纖維素的轉(zhuǎn)化,同時促進(jìn)C-C鍵斷裂,而Cu含量的提高則會對產(chǎn)物中EG和1,2-PD具有較好的選擇性。因此,可以通過選擇性的控制催化劑的堿性以及活性位的含量,以此優(yōu)化纖維素的轉(zhuǎn)化率以及多元醇的收率。此外,通過控制水滑石前體的焙燒溫度,獲得不同晶相結(jié)構(gòu)的催化劑。討論焙燒溫度引起的催化劑結(jié)構(gòu)變化,同時探究了催化劑結(jié)構(gòu)的轉(zhuǎn)變對其堿性和表面活性位含量的影響。揭示出催化劑在晶相轉(zhuǎn)變的過程中,結(jié)構(gòu)中的O2-存在形式是影響其堿性強(qiáng)弱的主要因素。采用N20化學(xué)吸附表征發(fā)現(xiàn)不同結(jié)構(gòu)的Cu物種顯著影響催化劑的活性表面的含量。在高濃度纖維素氫解反應(yīng)中,揭示出催化劑的堿性位與活性表面在催化反應(yīng)中的協(xié)同作用。結(jié)果顯示催化劑的堿性不僅促進(jìn)纖維素的水解,而且促進(jìn)反應(yīng)中逆羥醛縮合過程的進(jìn)行,從而有利于低碳多元醇的獲得,而催化劑表面的活性Cu是氫解反應(yīng)的主要活性位,其不僅可以促進(jìn)纖維素水解產(chǎn)物的進(jìn)一步氫解,同時也可以影響氫解反應(yīng)速率來控制產(chǎn)物分布。同時,在此基礎(chǔ)上,進(jìn)一步優(yōu)化了氫解反應(yīng)的操作條件,分別考察了反應(yīng)溫度、反應(yīng)壓力以及纖維素濃度的影響。值得注意的是,在高達(dá)18 wt%濃度下的纖維素,反應(yīng)沒有發(fā)生任何結(jié)焦現(xiàn)象,表明了催化劑具有很強(qiáng)的氫解高濃度纖維素的能力。
[Abstract]:Because of the shortage of fossil fuel resources such as oil, coal, and the increasing Greenhouse Effect, it is urgent to explore and develop renewable energy. In the exploration of many unconventional energy sources, biomass conversion can not only alleviate the bottleneck caused by the shortage of energy, but also alleviate the environmental problems caused by the utilization of fossil resources. Cellulose, as a widely existing biomass resource, can be converted into a variety of chemical raw materials and has high utilization value. Among them, a series of low carbon polyols obtained by hydrogenolysis of cellulose, such as ethylene glycol (EG), propylene glycol (PD), are important raw materials for the industrial synthesis of polyester, fiber and other polymers. Therefore, the preparation of low-carbon polyols by hydrogenolysis of cellulose is a potential biomass conversion route. A series of Cu based catalysts were prepared by using basic hydrotalcite as precursor and applied to the hydrogenolysis of cellulose at high concentration. The precursors of hydrotalcite with different Cu/Mg/Al molar ratio were synthesized by coprecipitation method. Catalysts with different metal contents were prepared by calcination. The effects of metal ratio, calcination and reduction conditions on the crystal structure and physicochemical properties of the catalysts were systematically studied. The alkalinity and active site content of the catalyst were determined by CO2-TPD and N20 chemisorption, respectively. The results showed that the decrease of mg content would lead to the decrease of the alkalinity of the catalyst, while the content of Cu could not only control the alkalinity. At the same time, the active site content on the catalyst surface was affected. Combined with the hydrogenolysis of cellulose, it was found that the enhancement of alkalinity was beneficial to the conversion of cellulose and the cleavage of C-C bond, while the increase of Cu content had a good selectivity for EG and 1b2-PD in the product. Therefore, the conversion of cellulose and the yield of polyol can be optimized by selectively controlling the alkalinity and active site content of the catalyst. In addition, catalysts with different crystal structure were obtained by controlling the calcination temperature of hydrotalcite precursors. The change of catalyst structure caused by calcination temperature was discussed, and the influence of the change of catalyst structure on its alkalinity and surface active site content was also discussed. It is revealed that the existence of O _ 2-in the structure is the main factor affecting the alkalinity of the catalyst during the process of crystal phase transition. N20 chemisorption characterization showed that Cu species with different structures significantly affected the active surface content of the catalyst. In the hydrogenolysis of high concentration cellulose, the synergism between the basic potential of the catalyst and the active surface in the catalytic reaction was revealed. The results showed that the alkalinity of the catalyst not only promoted the hydrolysis of cellulose, but also promoted the reverse condensation of hydroxyaldehydes in the reaction, which was beneficial to the obtaining of low carbon polyols. The active Cu on the surface of the catalyst was the main active site in the hydrogenolysis reaction. It can not only promote the further hydrogenation of cellulose hydrolysates, but also influence the reaction rate to control the distribution of the products. At the same time, the operation conditions of hydrogenolysis reaction were optimized, and the effects of reaction temperature, reaction pressure and cellulose concentration were investigated. It is worth noting that at the concentration of up to 18 wt%, there is no coking in the reaction, which indicates that the catalyst has a strong ability of hydrogenation of high concentration cellulose.
【學(xué)位授予單位】：大連理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：O643.36
本文編號：2254395
[Abstract]:Because of the shortage of fossil fuel resources such as oil, coal, and the increasing Greenhouse Effect, it is urgent to explore and develop renewable energy. In the exploration of many unconventional energy sources, biomass conversion can not only alleviate the bottleneck caused by the shortage of energy, but also alleviate the environmental problems caused by the utilization of fossil resources. Cellulose, as a widely existing biomass resource, can be converted into a variety of chemical raw materials and has high utilization value. Among them, a series of low carbon polyols obtained by hydrogenolysis of cellulose, such as ethylene glycol (EG), propylene glycol (PD), are important raw materials for the industrial synthesis of polyester, fiber and other polymers. Therefore, the preparation of low-carbon polyols by hydrogenolysis of cellulose is a potential biomass conversion route. A series of Cu based catalysts were prepared by using basic hydrotalcite as precursor and applied to the hydrogenolysis of cellulose at high concentration. The precursors of hydrotalcite with different Cu/Mg/Al molar ratio were synthesized by coprecipitation method. Catalysts with different metal contents were prepared by calcination. The effects of metal ratio, calcination and reduction conditions on the crystal structure and physicochemical properties of the catalysts were systematically studied. The alkalinity and active site content of the catalyst were determined by CO2-TPD and N20 chemisorption, respectively. The results showed that the decrease of mg content would lead to the decrease of the alkalinity of the catalyst, while the content of Cu could not only control the alkalinity. At the same time, the active site content on the catalyst surface was affected. Combined with the hydrogenolysis of cellulose, it was found that the enhancement of alkalinity was beneficial to the conversion of cellulose and the cleavage of C-C bond, while the increase of Cu content had a good selectivity for EG and 1b2-PD in the product. Therefore, the conversion of cellulose and the yield of polyol can be optimized by selectively controlling the alkalinity and active site content of the catalyst. In addition, catalysts with different crystal structure were obtained by controlling the calcination temperature of hydrotalcite precursors. The change of catalyst structure caused by calcination temperature was discussed, and the influence of the change of catalyst structure on its alkalinity and surface active site content was also discussed. It is revealed that the existence of O _ 2-in the structure is the main factor affecting the alkalinity of the catalyst during the process of crystal phase transition. N20 chemisorption characterization showed that Cu species with different structures significantly affected the active surface content of the catalyst. In the hydrogenolysis of high concentration cellulose, the synergism between the basic potential of the catalyst and the active surface in the catalytic reaction was revealed. The results showed that the alkalinity of the catalyst not only promoted the hydrolysis of cellulose, but also promoted the reverse condensation of hydroxyaldehydes in the reaction, which was beneficial to the obtaining of low carbon polyols. The active Cu on the surface of the catalyst was the main active site in the hydrogenolysis reaction. It can not only promote the further hydrogenation of cellulose hydrolysates, but also influence the reaction rate to control the distribution of the products. At the same time, the operation conditions of hydrogenolysis reaction were optimized, and the effects of reaction temperature, reaction pressure and cellulose concentration were investigated. It is worth noting that at the concentration of up to 18 wt%, there is no coking in the reaction, which indicates that the catalyst has a strong ability of hydrogenation of high concentration cellulose.
【學(xué)位授予單位】：大連理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：O643.36
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相關(guān)期刊論文 前3條
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2 曹月領(lǐng);王軍威;李其峰;殷寧;劉振民;亢茂青;朱玉雷;;Ni-WO_3/SBA-15催化劑上纖維素的水解加氫[J];燃料化學(xué)學(xué)報;2013年08期
3 彭楠楠;李凝;鄧明海;韋立寧;蔣武;;制備方法對NiCoPrLa類水滑石及其衍生復(fù)合氧化物結(jié)構(gòu)及催化性能的影響[J];分子催化;2012年05期
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