溫敏性離子液體氯化N-丁基吡啶雙水相體系相圖的測定及關(guān)聯(lián)

李宇亮, 楊思語, 張文杉

(長安大學(xué) 環(huán)境科學(xué)與工程學(xué)院, 陜西 西安 710064)

溫敏性離子液體氯化N-丁基吡啶雙水相體系相圖的測定及關(guān)聯(lián)

李宇亮, 楊思語, 張文杉

(長安大學(xué) 環(huán)境科學(xué)與工程學(xué)院, 陜西 西安 710064)

利用濁點法測定了氯化N-丁基吡啶([Epy]Cl)-磷酸氫二鉀(K2HPO4·3H2O)-水(H2O)雙水相體系在常壓和308.15、318.15、328.15 K三個溫度下的雙節(jié)線數(shù)據(jù)，并通過matlab編程驗證測定數(shù)據(jù)的準(zhǔn)確性，繪制相圖探討溫度對雙水相形成的影響。利用經(jīng)驗公式對得到的雙節(jié)線和系線數(shù)據(jù)進行關(guān)聯(lián)，得到的相關(guān)性良好。研究表明：溫度對該體系的分相能力影響不大。研究結(jié)果即可以作為雙水相體系應(yīng)用于萃取分離的分相基礎(chǔ)，又可作為從雙水相回收離子液體的依據(jù)。

氯化N-丁基吡啶；磷酸氫二鉀；液液相平衡；雙水相體系；溫度

1 前 言

雙水相系統(tǒng)(ATPS)是一種由兩相組合在一起高于臨界值時形成的互不相溶的水相系統(tǒng)，其組成可以是結(jié)構(gòu)不同的聚合物[1]，一種聚合物和一種鹽[2]，離子液體和一種鹽[3]，或小分子有機溶劑和一種鹽[4]。與傳統(tǒng)的分離萃取方法相比，雙水相具有反應(yīng)時間短、耗能低等優(yōu)點，并且現(xiàn)已廣泛地應(yīng)用于分離萃取DNA[5]、抗體[6]、蛋白質(zhì)[7]等，具有良好的研究潛力。

Gutowski等人提出了一種新的雙水相體系—離子液體-鹽[8]。對于離子液體的定義是由特定的陽離子和陰離子組成的具有不易揮發(fā)、不易燃等優(yōu)點的低溫熔鹽。近年來，在蛋白質(zhì)、抗生素、氨基酸等生物分離分析中得到了廣泛地研究與應(yīng)用[9～11]。目前離子液體雙水相體系主要集中于咪唑類離子液[12,13]，針對于吡啶類離子液體雙水相體系的報道較少。研究表明，吡啶類離子液體在既能形成雙水相體系的同時也具有良好的萃取分離性能[14～16]。此外，離子液體存在價格昂貴的缺點，尋找便宜、高效的離子液體是目前研究關(guān)注的焦點與熱點。氯鹽離子液體具有獨特的性質(zhì)且價格低廉，常用作改性離子液體的基質(zhì)，氯化N-丁基吡啶雙水相體系的研究尚未見報到。同時，磷酸氫二鉀作為雙水相體系中常用的鹽，具有良好的分離性能，易于形成雙水相體系。離子液體-鹽雙水相體系組成不同，對于溫度的響應(yīng)規(guī)律也不同。

本文將離子液體氯化N-丁基吡啶和磷酸氫二鉀相結(jié)合，形成了三元雙水相體系，并利用濁點法在308.15、318.15、328.15 K三個溫度下測定雙節(jié)線數(shù)據(jù)和液液相平衡數(shù)據(jù)，采用經(jīng)驗方程進行擬合，并研究溫度對該體系相平衡的影響，得到的結(jié)果有助于對離子液體的應(yīng)用進行工業(yè)化推廣。

2 實驗部分

2.1 主要儀器與試劑

分析天平(塞多利斯科學(xué)儀器(北京)有限公司)；101-1A型超級恒溫水浴鍋(南京多助科技發(fā)展有限公司)，氯化N-丁基吡啶[Epy]Cl(上海成捷化學(xué)有限公司)純度≥99.9%，磷酸氫二鉀[K2HPO4·3H2O](國藥集團化學(xué)試劑有限公司)，純度≥99.0%。所有試劑使用時均無需進行進一步純化。實驗用水為二次蒸餾水。

2.2 實驗方法

雙節(jié)線曲線利用濁點滴定法測定[17,18]。把已知質(zhì)量分?jǐn)?shù)的離子液體[Epy]Cl溶液放在比色管中，向里滴加一定質(zhì)量分?jǐn)?shù)的鹽溶液[K2HPO4·3H2O]直到混合溶液出現(xiàn)濁點。然后滴加一定量的水直到濁點剛好澄清，算出此時各個組分的質(zhì)量百分含量。然后繼續(xù)滴加鹽溶液直到下一個濁點出現(xiàn)。反復(fù)操作。實驗過程中質(zhì)量用分析天平測量，比色管分別在溫度為308.15、318.15、328.15 K的恒溫水浴鍋內(nèi)操作。

雙水相系線的測定：同樣在溫度為308.15、318.15、328.15 K的恒溫水浴鍋內(nèi)進行，一定量的離子液體[Epy]Cl，鹽[K2HPO4·3H2O]和水加入到離心管中，然后以2000 r·min-1的速度離心操作10 min，再將離心管放置在水浴中恒溫靜置24 h，保證雙水相完全形成。上下相中離子液體是通過液相色譜測定陽離子得到，鹽的濃度通過原子吸收測定鉀離子含量得到，水通過質(zhì)量守恒定律相減得到[19,20]。

系線的校對：達(dá)到相平衡后的雙水相體系，準(zhǔn)確分離上下相，并分別精確稱量上下相的質(zhì)量。根據(jù)雙水相體系的總組成，利用杠桿原理，通過軟件MATLAB可快速計算出離子液體雙水相體系液液相平衡(ILATPS)上相和下相中的離子液體[Epy]Cl和鹽[K2HPO4·3H2O]的含量[21～23]。系線長度TLL，系線斜率S利用如下公式而得：

其中w1t，w1b，w2t，w2b分別為離子液體[Epy]Cl上相，下相，鹽[K2HPO4·3H2O]上相，下相的質(zhì)量百分?jǐn)?shù)。

3 結(jié)果與討論

3.1 雙節(jié)線數(shù)據(jù)的關(guān)聯(lián)

對三元系統(tǒng)氯化N-丁基吡啶([Epy]Cl)+ 磷酸氫二鉀(K2HPO4·3H2O)+ 水(H2O)雙水相體系在T=308.15、318.15、328.15 K三個溫度下的雙節(jié)線和系線數(shù)據(jù)繪制圖見圖1，并采用Merchuk方程[24]對雙節(jié)線數(shù)據(jù)進行關(guān)聯(lián)，方程如下所示：

式中w1、w2分別代表離子液體[Epy]Cl和鹽K2HPO4·3H2O的質(zhì)量分?jǐn)?shù)，方程(3)擬合得到的a，b，c，R2和相對標(biāo)準(zhǔn)偏差sd在表1中給出。

圖1 [Epy]Cl + K2HPO4·3H2O + H2O體系在溫度為308.15K、318.15K和328.15K下的雙節(jié)線數(shù)據(jù)和系線數(shù)據(jù)Fig.1 Binodal curves and tie lines of [Epy]Cl + K2HPO4·3H2O + H2O ATPSs at 308.15, 318.15 and 328.15 K

為了提高精確度，采用另外兩個非線性方程對雙節(jié)線進行擬合：

同樣，由方程(4)擬合得到的參數(shù)a，b，c，d，R2，sd和方程(5)擬合得到的參數(shù)a1，b1，a2，b2，c，R2，sd分別在表2和表3中給出從表1，表2和表3可以看出，三個經(jīng)驗方程對所研究體系均具有良好的擬合效果。通過比較三個方程的線性相關(guān)系數(shù)R2和相對標(biāo)準(zhǔn)偏差(sd)可以看出方程(3)的擬合效果最好。表明Merchuk方程在離子液體雙水相體系的擬合過程中具有更好的適用性[25]。

表1 [Epy]Cl-K2HPO4·3H2O-H2O三元體系關(guān)于方程(3)的參數(shù)結(jié)果及標(biāo)準(zhǔn)偏差Table 1 Parameters of Eq.(3) andsddata for the [Epy]Cl-K2HPO4·3H2O-H2O systems

表2 [Epy]Cl-KHPO·3HO-HO三元體系關(guān)于方程(4)的參數(shù)結(jié)果及標(biāo)準(zhǔn)偏差2422Table 2 Parameters of Eq.(4) andsddata for the [Epy]Cl-K2HPO4·3H2O-H2O systems

3.2 溫度對雙節(jié)線的影響

三元系統(tǒng)氯化N-丁基

吡啶([Epy]Cl)+磷酸氫二鉀(K2HPO4·3H2O)+ 水(H2O)雙水相體系在T= 308.15、318.15 、328.15 K三個溫度下的溫度對比圖如圖2所示。由圖中可以看出三條雙節(jié)線軌跡相互重疊，表明了溫度對該體系分相能力沒有影響。這與[C4mim][Br]+K2HPO4+H2O體系隨溫度基本沒有變化相同[26]，但與氨基酸咪唑鹽離子液體雙水相隨溫度下降成相能力增強的規(guī)律不同[27]，也不同于[C4mim][BF4] + Na3C6H5O7/(NH4)3C6H5O7+ H2O體系和經(jīng)典的聚合物雙水相體系隨溫度的變化規(guī)律[28]。

3.3 液液相平衡數(shù)據(jù)的關(guān)聯(lián)

表3 [Epy]Cl-K2HPO4·3H2O-H2O三元體系關(guān)于方程（5）的參數(shù)結(jié)果及標(biāo)準(zhǔn)偏差Table 3 Parameters of Eq.(5) andsddata for the [Epy]Cl-K2HPO4·3H2O-H2O systems

圖2 溫度對[Epy]Cl-K2HPO4·3H2O-H2O雙水相體系的影響Fig.2 Effect of temperature on binodal curves for the [Epy]Cl-K2HPO4·3H2O-H2O aqueous two-phase system■ 308.15 K ○ 318.15 K △ 328.15 K

氯化N-丁基吡啶([Epy]Cl)+磷酸氫二鉀(K2HPO4·3H2O)+水(H2O)雙水相體系在T=308.15、318.15、328.15 K三個溫度下的液液相平衡數(shù)據(jù)、系線的長度及斜率如表4所示。

表4 [Epy]Cl-K2HPO4·3H2O-H2O三元體系在三個溫度下的液液相平衡數(shù)據(jù)、系線長度及斜率Table 4 Liquid–liquid equilibrium data， tie-line TLL and S for the [Epy]Cl-K2HPO4·3H2O-H2O systems at different temperatures

采用Setschenow-type 方程(6)[29]和另外一個由兩個參數(shù)組成的方程(7)進行關(guān)聯(lián)：

其中c1，c2，kIL，ks分別代表離子液體摩爾濃度、鹽摩爾濃度、離子液體活度系數(shù)和鹽析常數(shù)。上標(biāo)t，b分別代表離子液體相和鹽相。所得相關(guān)系數(shù)(R2)和標(biāo)準(zhǔn)偏差(sd)如表5所示。w1、w2分別代表離子液體[Epy]Cl和鹽K2HPO4·3H2O的質(zhì)量分?jǐn)?shù)，β，k分別代表鹽析常數(shù)和活度系數(shù)。所得的相關(guān)系數(shù)(R2)和標(biāo)準(zhǔn)偏差(sd)列于表6。

表5 [Epy]Cl-K2HPO4·3H2O-H2O三元體系關(guān)于方程(6)的參數(shù)結(jié)果及標(biāo)準(zhǔn)偏差Table 5 Parameters of Eq(6) andsddata for the [Epy]Cl-K2HPO4·3H2O-H2O systems

表6 [Epy]Cl-K2HPO4·3H2O-H2O三元體系關(guān)于方程(7)的參數(shù)結(jié)果及標(biāo)準(zhǔn)偏差Table 6 Parameters of Eq.(7) andsddata for the [Epy]Cl-K2HPO4·3H2O-H2O systems

從表中可以看出，利用方程(6)、(7)對所研究的離子液體雙水相體系進行關(guān)聯(lián)，結(jié)果令人滿意。方程(7)的擬合精度更高一些。

4 結(jié) 論

離子液體氯化N-丁基吡啶([Epy]Cl)可以和磷酸氫二鉀(K2HPO4·3H2O)在水溶液中形成雙水相體系。采用常見的經(jīng)驗公式對得到的液液相平衡數(shù)據(jù)進行擬合，Merchuk方程對于雙節(jié)線的擬合精度更高。相圖表明該體系上下相組成服從杠桿原理。由于不同離子液體對溫度的敏感程度不同，對于本體系的離子液體，溫度對體系的分相能力影響不明顯。從相圖得到的規(guī)律為萃取分離提供分相基礎(chǔ)，同時加入鹽有助于離子液體從水溶液中析出，可作為離子液體回收再利用的理論依據(jù)。

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Measurement and Correlation of Phase Diagram of the Thermosensitive Ionic Liquid ( [Epy]Cl ) Aqueous Two-Phase System

LI Yu-liang, YANG Si-yu, ZHANG Wen-shan
（School of Environmental Science and Engineering, Chang’an University, Xi'an 710064, China）

Binodal data of the [Epy]Cl + K2HPO4·3H2O + H2O aqueous two-phase system was determined by cloud-point method under atmospheric pressure and T = 308.15, 318.15 and 328.15 K, respectively. The tie-line data was measured and verified with Matlab, and the effect of temperature on phase forming was studied via phase diagram. Empirical equations were used to correlate the binodal and tie-line data, which show good agreement with experimental data. The results demonstrate that the phase forming ability is maintained with temperature variation, which is important in the applications of antibiotic separation and ionic liquid recovery.

[Epy]Cl； K2HPO4·3H2O； liquid–liquid equilibrium； aqueous two-phase system；temperature

O642.42

A

10.3969/j.issn.1003-9015.2016.06.029

1003-9015(2016)06-1445-06

2016-04-06；

2016-06-27。

國家大學(xué)生創(chuàng)新創(chuàng)業(yè)項目(201610710078，201610710069)；長安大學(xué)中央高?；净?310829153507，310829161112，310829161013)。

李宇亮(1983-)，男，山西偏關(guān)人，長安大學(xué)副教授，博士。

李宇亮，E-mail：yulianglee175@chd.edu.cn