聞芯君,賈宏葛
自具微孔聚酰亞胺氣體分離膜的研究進展
聞芯君1,賈宏葛2,3
(齊齊哈爾大學(xué) 1. 化學(xué)與化學(xué)工程學(xué)院,2. 材料科學(xué)與工程學(xué)院,3. 黑龍江省聚合物基復(fù)合材料重點實驗室,黑龍江 齊齊哈爾 161006)
概述了近年來自具微孔聚酰亞胺不同致孔基元,通過比較不同致孔基元間表現(xiàn)的氣體分離性能,選取制備自具微孔聚酰亞胺氣體分離膜的最佳結(jié)構(gòu).主要有5類致孔基元:螺吲哚(SBI)單元、螺雙芴(SBF)單元、三蝶烯(Trip)、亞乙基蒽(EA)和特勒格堿(TB).在綜合比較中發(fā)現(xiàn),Trip的高自由體積(IFV)的剛性Y形結(jié)構(gòu)的致孔基元和EA的橋接雙環(huán)結(jié)構(gòu)均可以為聚合物提供高度形狀持久性結(jié)構(gòu),確保微孔性.由于SBI中有一定程度的構(gòu)象靈活性,會損害聚合物主鏈的剛性,導(dǎo)致整體的氣體分離性能不高.SBF為致孔基元的聚酰亞胺,在5類致孔基元中的氣體分離性能處于中等.所以Trip和EA結(jié)構(gòu)在未來制備自具微孔聚酰亞胺氣體分離膜方面更具發(fā)展?jié)摿Γ?/p>
自具微孔聚酰亞胺;氣體分離膜;致孔基元;氣體分離性能
基于聚合物膜的氣體分離技術(shù)具有占地面積小、操作簡單、成本效益高等優(yōu)點而受到越來越多的關(guān)注,在未來的碳中和目標中發(fā)揮重要作用[1].分離膜技術(shù)廣泛應(yīng)用于天然氣脫硫、CO2捕獲和儲存、制氮和制氫領(lǐng)域[2-3].工業(yè)過程中最具挑戰(zhàn)性的是具有高滲透性,還需兼顧選擇性和穩(wěn)定性的高效膜[4-5].氣體分離性能是否突破Robeson上限是衡量氣體分離膜性能優(yōu)劣的重要依據(jù)[6].通過分子設(shè)計,目前已開發(fā)出多種類型的氣體分離膜,如聚烯烴、聚酰亞胺、聚砜、纖維素、聚碳酸酯等[7].
聚酰亞胺具有優(yōu)越的綜合性能,相對于其它芳雜環(huán)高分子比較容易合成.大多數(shù)線性聚酰亞胺因其分子鏈具有一定的柔性,分子鏈相互緊密地纏結(jié)在一起,自由體積小,所以一般不具微孔結(jié)構(gòu).為了提高其分離性能,在線性聚酰亞胺的結(jié)構(gòu)中引入剛性的扭曲結(jié)構(gòu),可以有效抑制亞胺鍵的旋轉(zhuǎn),阻礙分子鏈構(gòu)象轉(zhuǎn)變,破壞線性分子對稱性,阻礙有效的鏈堆積和鏈間作用,增加其分子鏈的自由體積[8-9],從而制備出自具微孔聚酰亞胺材料(PIM-PI).
自具微孔聚酰亞胺(PIM)材料的核心概念是合理設(shè)計具有高剛性和扭曲結(jié)構(gòu)的聚合物,從而產(chǎn)生梯狀大分子形狀并能夠高效阻礙聚合物鏈堆積[10-11].微孔構(gòu)成需要引入剛性、橋接和非平面脂環(huán)鏈段致孔基元[12]4147,主要有5類:螺吲哚(SBI)單元[13]、螺雙芴(SBF)單元、三蝶烯(Trip)、亞乙基蒽(EA)和特勒格堿(TB)[14-15].因為致孔基元的扭曲結(jié)構(gòu)中含有剛性和橋聯(lián)節(jié)點,在PIM骨架中提供橋聯(lián)作用和成孔位點,扭曲結(jié)構(gòu)位點造成聚合物空間結(jié)構(gòu)的無效堆積,并且在鏈間產(chǎn)生自由體積.這些致孔基元扭曲結(jié)構(gòu)使聚合物分子鏈在聚集態(tài)時不能形成致密堆砌,導(dǎo)致大量微孔產(chǎn)生,為氣體傳輸提供一定的選擇性分離通道[16].
2009年有文獻報道了以螺雙辛烷基二酐和一系列二胺反應(yīng)制得PIM-PIs[17],在聚合物骨架中引入SBI的扭曲結(jié)構(gòu),通過固定酰亞胺環(huán)中的C-N旋轉(zhuǎn)鍵,螺中心單元(即2個環(huán)共享的單個四面體碳原子)結(jié)構(gòu)不能沿聚合物鏈旋轉(zhuǎn),或由于空間位阻對旋轉(zhuǎn)的阻礙限制,以避免構(gòu)象變化,從而幫助聚合物堆疊成孔.在提高透氣性和選擇性方面具有優(yōu)勢[18-19].
SBI致孔基元是剛性強的橋連雙環(huán),系統(tǒng)性提高對各種氣體對的選擇性[20].通過改變二胺,制備出PIM-PI系列自具微孔聚酰亞胺膜,其對O2/N2組分的分離中,O2具體透過量范圍在23.8~98 Barrer,選擇性在3.7~4.6,并且接近1991年上限,多數(shù)聚酰亞胺氣體分離性能接近1991年Robeson曲線;CO2/CH4組分中,CO2具體透過量范圍在119~2 180 Barrer,選擇性在12.8~35,多數(shù)聚酰亞胺氣體分離性能在1991年Robeson曲線上方.
對于使用SBI作為扭曲位點的基本PIM-PI系列,因為SBI中具有一定程度的構(gòu)象靈活性,即會損害聚合物主鏈的剛性,導(dǎo)致整體的氣體分離性能不高.為了提高其氣體分離性能,對于引入了SBF或TB結(jié)構(gòu)的SPDA-HSBF、SBI-HTB微孔膜的氣體選擇透過性都有較大的改善,在SBI基礎(chǔ)上引入SBF或TB結(jié)構(gòu)使氣體分離膜的分離性能達到最佳狀態(tài).未來在氣體分離方面,合成含有SBI致孔基元的自具微孔聚酰亞胺膜還具有很大的改進空間,引入更強剛性結(jié)構(gòu)或者引入較大側(cè)基,增大分子間作用力,提高氣體分離性能是一個潛在的方向.
在SBF中,2個芴環(huán)正交排列并通過四面體鍵合碳原子,即螺中心連接,聚合物鏈上形成以每個螺環(huán)為中心90°角周期性的鋸齒形[21].這種結(jié)構(gòu)特征可最大限度地減少鏈間的相互作用,并限制聚合物鏈的緊密堆積,聚合物主鏈的剛性將被保留[22].
含有SBF致孔結(jié)構(gòu)的PI膜整體上的氣體分離性能中等[23].在O2/N2組分中,O2透過量主要集中在35.1~243 Barrer,選擇性在3.5~4.5的范圍;CO2/CH4組分透過量主要集中在182~1 340 Barrer,選擇性在13.1~28.4的范圍(見表1).其中含有龐大結(jié)構(gòu)的3,3-二甲基萘二胺(DMN)與含有SBF酸酐反應(yīng)制備的SBFDA-DMN膜,氣體分離性能達到2008年Robeson曲線的上限,由于其扭曲的剛性結(jié)構(gòu)導(dǎo)致其比表面積、聚合物滲透性均顯著提高.
表1 氣體選擇透過性
由于SBF中溴的引入,氣體滲透量增加,因為溴阻礙鍵旋轉(zhuǎn)而提高的剛度導(dǎo)致比表面積和氣體選擇性小幅降低.未來通過調(diào)整結(jié)構(gòu)、引入大分子單元等方法提高氣體分離性能,有望用于空氣中的氧富集.
Trip是高性能微孔聚合物的獨特結(jié)構(gòu)單元,因為其三角雙錐(D3h)對稱性,具有剛性Y形結(jié)構(gòu),內(nèi)部自由體積(IFV)較高,其中包含[2,2,2]辛三烯橋頭的芳烴單元.因為鏈間堆積不好導(dǎo)致自由體積進一步增加.2011年,Cho[44]等將三維剛性的內(nèi)部具有高自由體積的Trip引入PI結(jié)構(gòu)中,得到了高分子量、高自由體積的微孔PI.
含有Trip結(jié)構(gòu)的自具微孔聚酰亞胺膜在CO2/CH4,O2/N2組分的分離性能非常出色,部分材料甚至突破2008年上限,總的來看,都在1991年上限和2008年上限之間.在一系列Trip聚合物中,9,10-橋頭上取代的烷基可調(diào)整比表面積以增強氣體吸附.通過調(diào)控Trip扭曲節(jié)點9,10-橋頭上的烷基鏈長和幾何構(gòu)型,發(fā)現(xiàn)最短甲基鏈擁有最高的比表面積,而擁有最長的烷基鏈的聚合物的比表面積卻最低.在CO2/CH4組分中,橋頭甲基取代的TDA1-DMN(CO2透過量達到3 700 Barrer)比含有異丙基側(cè)鏈的KAUST-PIs膜(膜的CO2透過量達到2 389 Barrer)具有更高的氣體透過性和略低的選擇性.將含異丙基的Trip扭曲中心引入酸二酐單體后,相對于無側(cè)鏈PI膜的氣體分離性能也得到了極大的提升.整體上看,9,10-橋頭取代基對PI氣體透過性影響規(guī)律為:甲基>異丙基>無側(cè)鏈.
未來通過調(diào)整Trip內(nèi)部IFV和鏈間自由體積的方法提升氣體分離總體性能,也可以通過選擇橋頭取代基種類,影響Trip衍生聚合物的氣體滲透性能.
在TB獨特結(jié)構(gòu)特征中的二氮雜辛橋會產(chǎn)生類似裂縫的形狀,具有剛性V形橋接雙環(huán)連接基團,使其在分子識別和超分子化學(xué)中的應(yīng)用非常具有吸引力[45].提供高度剛性的扭曲位點來阻礙鏈間堆積,從而導(dǎo)致這種剛性框架在具有微孔的各種聚合物(PIM)中得到廣泛應(yīng)用[46].Lee[12]等以Tr?ger′s Base構(gòu)型單體為扭曲節(jié)點,并在其扭曲節(jié)點上增加甲基數(shù)量來限制酰亞胺鍵的構(gòu)象自由度,以此來提高氣體分離能力.
含有TB結(jié)構(gòu)的致孔基元在CO2/CH4組分中主要集中在1991年和2008年Robeson曲線之間.6FDA-HTB的高滲透選擇性主要是由于其含有羥基質(zhì)子和Troger堿叔胺中氮原子之間的氫鍵(O-H…N)所產(chǎn)生的強大尺寸篩分特性,從而產(chǎn)生了異常的分離選擇性.Trip和EA結(jié)構(gòu)在制備更高氣體分離性能PIM-PI膜上更具有優(yōu)勢.
未來可以考慮通過引入功能性側(cè)基或者形成氫鍵等改性方式,提高含有TB結(jié)構(gòu)致孔基元的聚酰亞胺氣體分離性能.
橋接雙環(huán)EA是高度不靈活的,可以為聚合物提供高度形狀持久性結(jié)構(gòu),確保微孔性,相對于其它致孔單元,EA結(jié)構(gòu)在氣體分離性方面最具優(yōu)勢.基于EA制備的具有微孔氣體分離膜的O2/N2氣體分離性能位于2008年Robeson上限之上.PIM-PI-EA的氣體分離性能主要受EA的結(jié)構(gòu)影響,與PIM中常用的SBI相比,EA二酐產(chǎn)生了比螺環(huán)二酐更好的選擇性和滲透性.
龐大的3,3-二甲基萘二胺(DMN)單元與橋環(huán)酸酐制備的自具微孔聚酰亞胺中,含EA結(jié)構(gòu)(PIM-PI-EA)氣體分離性能最佳,有更高的透過性,其中CO2透過量從948 Barrer增長到7 340 Barrer,相應(yīng)的O2透過量從320 Barrer增長到1 380 Barrer,相比其它結(jié)構(gòu),選擇性變化不大.
未來可以通過優(yōu)化選擇性,提高整體性能.EA結(jié)構(gòu)是目前報道的作為微孔膜材料研究的最佳致孔單元.
用于工業(yè)氣體分離裝置的氣體分離膜應(yīng)具有足夠好的機械性能和成膜性能,具有良好的化學(xué)和熱穩(wěn)定性,還應(yīng)具有足夠的抗塑化性和不老化性.在氣體分離應(yīng)用中,滲透率和選擇性滲透率之間通常存在權(quán)衡,尋找超過Robeson上限的膜材料一直是重要目標.
自PIM-1發(fā)明以來,開發(fā)了數(shù)百種新的PIM-PI,它們具有不同類型的致孔基元,作為空間位阻扭曲位點.用于商業(yè)可用微孔膜材料PIM設(shè)計的5個最核心致孔基元中:Trip,EA,TB可以增大比表面積、增加微孔,具有相同的120扭結(jié)結(jié)構(gòu),在高氣體分離性材料領(lǐng)域,擁有巨大的研究潛力.在這5種致孔結(jié)構(gòu)中,SBI的氣體分離性能沒有其它幾種優(yōu)異.因為SBI中有一定程度的構(gòu)象靈活性,即會損害聚合物主鏈的剛性,導(dǎo)致整體的氣體分離性能不高.Trip和EA的氣體分離性能較優(yōu)異,突破2008年上限,未來在制備新型微孔結(jié)構(gòu)上潛力巨大.微孔的發(fā)展在很大程度上取決于扭曲中心抵抗分子變形和維持破壞鏈堆積的分子內(nèi)剛性的能力.剛性和超微孔的結(jié)合,通過使用橋聯(lián)雙環(huán)結(jié)構(gòu)進行微調(diào),合成高滲透性和低自由體積的聚合物,能夠彌補商用材料的不足.
自具微孔聚酰亞胺材料在氣體分離領(lǐng)域具有非常大的應(yīng)用前景,在今后的研究中還需不斷突破現(xiàn)有領(lǐng)域,擴大應(yīng)用范圍,主要從3個方面入手:(1)尋找新的致孔結(jié)構(gòu)和連接方式,制備選擇性和滲透性都好的氣體分離膜;(2)設(shè)計并合成滿足剛性結(jié)構(gòu)、功能化和廉價性的構(gòu)筑單體,豐富構(gòu)筑單體的種類;(3)簡化實驗條件并探索新的有效合成途徑,使實驗制備從精細化和微量化發(fā)展到常規(guī)化和量產(chǎn)化.
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Research progress of polymers of intrinsic microporosity gas separation membranes
WEN Xinjun1,JIA Hongge2,3
(1. School of Chemistry and Chemical Engineering,2. School of Materials Science and Engineering,3. Heilongjiang Province Key Laboratory of Polymer Matrix Composites,Qiqihar University,Qiqihar 161006,China)
Overview the different pore forming elements of polymers of intrinsic microporosity in reserent years.In gas separation,the best structure of polymers of intrinsic microporosity gas separation membrane was selected by comparing the gas separation performance of different pore forming units.Five kinds of polymers of intrinsic microporosity pore forming units,including spiro indole(SBI)unit,spiro difluorinate(SBF)unit,triphene(Trip),ethyleneanthracene(EA)and terzag base(TB)were summarized.In a comprehensive comparison,among the porogens with polymers of intrinsic microporosity gas separation performance,Trip has a rigid Y-shaped structure with high free volume(IFV)and a bridged bicyclic structure of EA,both of which can provide a high shape persistence structure for polymers to ensure microporosity.Due to a certain degree of conformational flexibility in SBI,the rigidity of the polymer backbone will be damaged,resulting in low overall gas separation performance.Polyimide with SBF as porogen has medium gas separation performance among the five kinds of porogen.Therefore,Trip and EA structures have more development potential in the preparation of polymers of intrinsic microporosity gas separation membranes in the future.
polymers of intrinsic microporosity;gas separation membrane;pore forming elements;gas separation performance
1007-9831(2022)11-0057-06
O69
A
10.3969/j.issn.1007-9831.2022.11.011
2022-06-03
黑龍江省重點研發(fā)計劃指導(dǎo)類項目(GZ20210034);黑龍江省領(lǐng)軍人才梯隊后備帶頭人資助項目(黑人社函2019(278)號)
聞芯君(1996-),女,黑龍江黑河人,在讀碩士研究生,從事聚酰亞胺氣體分離膜研究.E-mail:1748259983@qq.com
賈宏葛(1978-),黑龍江大慶人,教授,博士,從事聚酰亞胺氣體分離膜、過渡金屬催化劑研究.E-mail:jiahongge@qqhru.edu.cn