離子液體溶解生物質(zhì)的分子模擬研究
發(fā)布時(shí)間：2018-08-19 20:30
【摘要】：木質(zhì)纖維素生物質(zhì)是地球上儲(chǔ)量最豐富的可再生資源,其開(kāi)發(fā)利用是未來(lái)能源的重要發(fā)展方向。它主要由纖維素、木質(zhì)素和半纖維素組成,其中,纖維素是含量最高的部分,由于其結(jié)構(gòu)的穩(wěn)固性,需要經(jīng)過(guò)溶解等預(yù)處理過(guò)程,才能進(jìn)行開(kāi)發(fā)利用。離子液體是近年來(lái)纖維素預(yù)處理中的"明星溶劑",具有優(yōu)良的溶解性和穩(wěn)定性。然而,離子液體為何能夠溶解纖維素是當(dāng)今的難點(diǎn)問(wèn)題,目前仍然缺乏系統(tǒng)性解釋。本文構(gòu)建了纖維素微絲體系,通過(guò)大規(guī)模分子動(dòng)力學(xué)模擬獲得完整的溶解過(guò)程,揭示了不同種類(lèi)離子液體對(duì)纖維素的作用機(jī)制。并且研究了陽(yáng)離子飽和性對(duì)離子液體溶解纖維素的影響機(jī)制,探索了軟木木質(zhì)素與離子液體的相互作用。本文的研究將為認(rèn)識(shí)微觀溶解過(guò)程和開(kāi)發(fā)新型離子液體溶劑提供理論依據(jù)。論文的主要內(nèi)容及結(jié)論如下:(1)離子液體溶解纖維素束的模擬研究。針對(duì)7*8(7根纖維素單鏈,聚合度為8)纖維素束,在4種溶劑([Emim][Cl],[Emim][OAc],[Bmim][Cl]和H2O)中進(jìn)行長(zhǎng)時(shí)間的分子動(dòng)力學(xué)模擬。研究發(fā)現(xiàn),離子液體溶解纖維素的速度快慢順序是[Emim][OAc][Emim][Cl][Bmim][Cl],與實(shí)驗(yàn)相符。通過(guò)氫鍵分析,發(fā)現(xiàn)[OAc]-能夠在纖維素鏈之間形成特定的氫鍵構(gòu)象,這種構(gòu)象能有效地分開(kāi)相鄰纖維素鏈,從而加速溶解過(guò)程。另外,提出了陰陽(yáng)離子是以協(xié)同的方式溶解纖維素:陰離子首先插入纖維素表面的外層鏈之間,與周?chē)牧u基形成氫鍵,隨著陰離子與纖維素束的充分接觸,更多的陰離子與內(nèi)部的羥基形成氫鍵,陽(yáng)離子由于陰離子負(fù)電荷的吸引以及與糖環(huán)的范德華相互作用,也進(jìn)入微絲之中,進(jìn)而剝離出纖維素單鏈。(2)離子液體溶解纖維素微絲的模擬研究。針對(duì)36*40的纖維素微絲(36根纖維素單鏈,聚合度為40)體系,在[Emim][OAc]中進(jìn)行長(zhǎng)時(shí)間(3μs)的模擬。分析了纖維素微絲在溶解過(guò)程中的結(jié)構(gòu)變化,發(fā)現(xiàn)了逆時(shí)針的扭曲,且扭曲發(fā)生在溶解過(guò)程之前。考察了微絲的溶解方式,發(fā)現(xiàn)微絲是以單根鏈剝離的形式逐漸溶解于離子液體中,且微絲中親疏水面交界處的鏈最先剝離,另外剝離從還原性末端開(kāi)始。最后對(duì)陰陽(yáng)離子和纖維素的相對(duì)位置進(jìn)行分析,提出離子液體與纖維素的作用模式,[OAc]-陰離子主要在與纖維素鏈平行的方向上,和纖維素的羥基形成大量的氫鍵,而[Emim]+陽(yáng)離子更多地分布在疏水面上,與纖維素之間主要為范德華作用。(3)陽(yáng)離子飽和性對(duì)離子液體溶解纖維素的控制機(jī)理。模擬了7*8纖維素束在四種離子液體([Bmim][OAc],[Bpyr][OAc],[Bpy][OAc]和[Bpip][OAc])中的變化過(guò)程,最終纖維素只能溶解在陽(yáng)離子含不飽和雜環(huán)的離子液體[Bmim][OAc]和[Bpy][OAc]中,與實(shí)驗(yàn)相吻合。通過(guò)動(dòng)力學(xué)模擬研究了陽(yáng)離子和纖維素的相互作用,通過(guò)量化分析研究了不飽和雜環(huán)的影響,另外考察了體系傳質(zhì)性質(zhì)對(duì)溶解的影響規(guī)律。研究發(fā)現(xiàn),不飽和雜環(huán)的作用機(jī)制主要包括結(jié)構(gòu)和傳質(zhì)兩方面:首先,不飽和雜環(huán)由于π電子離域,能夠增強(qiáng)陽(yáng)離子與纖維素的作用,也能穩(wěn)定陰離子與纖維素形成的氫鍵,且含不飽和雜環(huán)的陽(yáng)離子體積較小,在溶解過(guò)程中更容易進(jìn)入纖維素內(nèi)部;另外,不飽和的[Bmim][OAc]和[Bpy][OAc]相比于飽和的[Bpyr][OAc]和[Bpip][OAc],具有更快的傳質(zhì)特性,陰陽(yáng)離子能更充分地與纖維素發(fā)生相互作用,進(jìn)而促進(jìn)溶解。(4)離子液體和木質(zhì)素的作用機(jī)理及其界面結(jié)構(gòu)。針對(duì)軟木木質(zhì)素建立了一條長(zhǎng)鏈模型,研究其與[Emim][Cl],[Bmim][Cl],[Emim][OAc],[Choline][OAc],[Choline][Gly]五種離子液體的相互作用。研究發(fā)現(xiàn),離子液體能夠在木質(zhì)素周?chē)纬上鄬?duì)穩(wěn)定的結(jié)構(gòu),陰離子分布在第一溶劑化層,與木質(zhì)素有較強(qiáng)的靜電相互作用;陽(yáng)離子分布在第二溶劑化層,與木質(zhì)素有較強(qiáng)的范德華作用。陰陽(yáng)離子作用于木質(zhì)素不同的位置,共同溶解木質(zhì)素。[OAc]-與木質(zhì)素形成較多的氫鍵,[Gly]-與木質(zhì)素形成更多高氫鍵構(gòu)象,因此,[Emim][OAc],[Choline][OAc]和[Choline][Gly]對(duì)木質(zhì)素的溶解效果要強(qiáng)于[Emim][Cl]和[Bmim][Cl]。
[Abstract]:Lignocellulose biomass is the most abundant renewable resource on the earth, and its development and utilization is an important development direction of energy in the future. It mainly consists of cellulose, lignin and hemicellulose. Cellulose is the most abundant part of lignocellulose. Because of its structural stability, lignocellulose needs to be dissolved and other pretreatment processes before it can be developed. Ionic liquids (ILs) are the "star solvents" in cellulose pretreatment in recent years, which have excellent solubility and stability. However, it is still a difficult problem to explain why ILs can dissolve cellulose. A cellulose microfilament system has been constructed in this paper, which is integrated by large-scale molecular dynamics simulation. The dissolution process reveals the mechanism of different kinds of ionic liquids on cellulose. The influence mechanism of cationic saturation on the dissolution of cellulose by ionic liquids is studied. The interaction between cork lignin and ionic liquids is explored. This study will provide a basis for understanding the micro-dissolution process and developing new ionic liquids solvents. The main contents and conclusions of this paper are as follows: (1) Simulation of cellulose beam dissolution by ionic liquids. For 7*8 (7 cellulose single chains, degree of polymerization 8) cellulose beam, long-term molecular dynamics simulations were carried out in four solvents ([Emim] [Cl], [Emim] [OAc], [Bmim] [Cl] and H2O). It was found that the dissolution rate of cellulose by ionic liquids was high. The order of speed is [Emim] [OAc] [Emim] [Cl] [Bmim] [Cl] [Cl] [Cl] [Cl], which agrees with the experiment. Through hydrogen bond analysis, it is found that [OAc] - can form a specific hydrogen bond conformation between cellulose chains. This conformation can effectively separate adjacent cellulose chains, thus speeding up the dissolution process. Firstly, the outer chains of the cellulose surface were inserted to form hydrogen bonds with the surrounding hydroxyl groups. With the full contact between the anions and the cellulose bundles, more anions formed hydrogen bonds with the inner hydroxyl groups. (2) Simulation of dissolving cellulosic microfilaments in ionic liquids. A long-term simulation of cellulosic microfilaments (36 cellulose single chains, degree of polymerization 40) in [Emim] [OAc] was carried out. Structural changes of cellulosic microfilaments during dissolution were analyzed and counterclockwise distortion was found. Previously, the dissolution of microfilaments was investigated. It was found that the microfilaments were gradually dissolved in ionic liquids in the form of a single strand peeling. The chain at the junction of hydrophilic and hydrophobic surfaces was first peeled off, and the peeling started at the reductive end. In the model, [OAc] - anions mainly form hydrogen bonds with the hydroxyl groups of cellulose in the direction parallel to the cellulose chain, while [Emim]+ cations are more distributed on the hydrophobic surface and mainly van der Waals interaction with cellulose. The changes of four ionic liquids ([Bmim] [OAc], [Bpyr] [OAc], [Bpy] [OAc] and [Bpip] [OAc]) were studied. The cellulose could only be dissolved in cationic ionic liquids containing unsaturated heterocycles [Bmim] [OAc] and [Bpy] [OAc], which were in agreement with the experiment. The interaction between cations and cellulose was studied by kinetic simulation, and the quantitative analysis was carried out. The mechanism of unsaturated heterocycles mainly includes structure and mass transfer. Firstly, unsaturated heterocycles can enhance the interaction between cations and cellulose and stabilize the hydrogen formed by anions and cellulose because of the delocalization of PI electrons. In addition, unsaturated [Bmim] [OAc] and [Bpy] [OAc] have faster mass transfer characteristics than saturated [Bpyr] [OAc] and [Bpip] [OAc], and anions and cations can interact more fully with cellulose, thus promoting dissolution. A long chain model of cork lignin was established to study the interaction between cork lignin and five ionic liquids, namely [Emim] [Cl], [Bmim] [Cl], [Emim] [OAc], [Choline] [OAc], [Choline] [Gly]. The cations are distributed in the second solvation layer and have a strong van der Waals effect on lignin. The anions and cations act on different positions of lignin to dissolve lignin together. [OAc] - Form more hydrogen bonds with lignin, [Gly] - Form more hydrogen bonds with lignin. Thus, [Emim] [OAc], [Choline] [OAc] and [Choline] [Gly] are more effective in dissolving lignin than [Emim] [Cl] and [Bmim] [Cl].
【學(xué)位授予單位】：中國(guó)科學(xué)院大學(xué)(中國(guó)科學(xué)院過(guò)程工程研究所)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TQ413.2
[Abstract]:Lignocellulose biomass is the most abundant renewable resource on the earth, and its development and utilization is an important development direction of energy in the future. It mainly consists of cellulose, lignin and hemicellulose. Cellulose is the most abundant part of lignocellulose. Because of its structural stability, lignocellulose needs to be dissolved and other pretreatment processes before it can be developed. Ionic liquids (ILs) are the "star solvents" in cellulose pretreatment in recent years, which have excellent solubility and stability. However, it is still a difficult problem to explain why ILs can dissolve cellulose. A cellulose microfilament system has been constructed in this paper, which is integrated by large-scale molecular dynamics simulation. The dissolution process reveals the mechanism of different kinds of ionic liquids on cellulose. The influence mechanism of cationic saturation on the dissolution of cellulose by ionic liquids is studied. The interaction between cork lignin and ionic liquids is explored. This study will provide a basis for understanding the micro-dissolution process and developing new ionic liquids solvents. The main contents and conclusions of this paper are as follows: (1) Simulation of cellulose beam dissolution by ionic liquids. For 7*8 (7 cellulose single chains, degree of polymerization 8) cellulose beam, long-term molecular dynamics simulations were carried out in four solvents ([Emim] [Cl], [Emim] [OAc], [Bmim] [Cl] and H2O). It was found that the dissolution rate of cellulose by ionic liquids was high. The order of speed is [Emim] [OAc] [Emim] [Cl] [Bmim] [Cl] [Cl] [Cl] [Cl], which agrees with the experiment. Through hydrogen bond analysis, it is found that [OAc] - can form a specific hydrogen bond conformation between cellulose chains. This conformation can effectively separate adjacent cellulose chains, thus speeding up the dissolution process. Firstly, the outer chains of the cellulose surface were inserted to form hydrogen bonds with the surrounding hydroxyl groups. With the full contact between the anions and the cellulose bundles, more anions formed hydrogen bonds with the inner hydroxyl groups. (2) Simulation of dissolving cellulosic microfilaments in ionic liquids. A long-term simulation of cellulosic microfilaments (36 cellulose single chains, degree of polymerization 40) in [Emim] [OAc] was carried out. Structural changes of cellulosic microfilaments during dissolution were analyzed and counterclockwise distortion was found. Previously, the dissolution of microfilaments was investigated. It was found that the microfilaments were gradually dissolved in ionic liquids in the form of a single strand peeling. The chain at the junction of hydrophilic and hydrophobic surfaces was first peeled off, and the peeling started at the reductive end. In the model, [OAc] - anions mainly form hydrogen bonds with the hydroxyl groups of cellulose in the direction parallel to the cellulose chain, while [Emim]+ cations are more distributed on the hydrophobic surface and mainly van der Waals interaction with cellulose. The changes of four ionic liquids ([Bmim] [OAc], [Bpyr] [OAc], [Bpy] [OAc] and [Bpip] [OAc]) were studied. The cellulose could only be dissolved in cationic ionic liquids containing unsaturated heterocycles [Bmim] [OAc] and [Bpy] [OAc], which were in agreement with the experiment. The interaction between cations and cellulose was studied by kinetic simulation, and the quantitative analysis was carried out. The mechanism of unsaturated heterocycles mainly includes structure and mass transfer. Firstly, unsaturated heterocycles can enhance the interaction between cations and cellulose and stabilize the hydrogen formed by anions and cellulose because of the delocalization of PI electrons. In addition, unsaturated [Bmim] [OAc] and [Bpy] [OAc] have faster mass transfer characteristics than saturated [Bpyr] [OAc] and [Bpip] [OAc], and anions and cations can interact more fully with cellulose, thus promoting dissolution. A long chain model of cork lignin was established to study the interaction between cork lignin and five ionic liquids, namely [Emim] [Cl], [Bmim] [Cl], [Emim] [OAc], [Choline] [OAc], [Choline] [Gly]. The cations are distributed in the second solvation layer and have a strong van der Waals effect on lignin. The anions and cations act on different positions of lignin to dissolve lignin together. [OAc] - Form more hydrogen bonds with lignin, [Gly] - Form more hydrogen bonds with lignin. Thus, [Emim] [OAc], [Choline] [OAc] and [Choline] [Gly] are more effective in dissolving lignin than [Emim] [Cl] and [Bmim] [Cl].
【學(xué)位授予單位】：中國(guó)科學(xué)院大學(xué)(中國(guó)科學(xué)院過(guò)程工程研究所)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TQ413.2
【參考文獻(xiàn)】
相關(guān)期刊論文 前3條
1 姚瑩瑩;李W，
本文編號(hào)：2192749
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