張學(xué)楊,徐浩亮,戴歡濤,游新秀,韋趙龍,曹苓玉

微波輻照木質(zhì)素浸漬生物炭吸附CO2性能

張學(xué)楊*,徐浩亮,戴歡濤,游新秀,韋趙龍,曹苓玉

(徐州工程學(xué)院環(huán)境工程學(xué)院,江蘇 徐州 221018)

以木質(zhì)素鈣為前驅(qū)體浸漬生物炭并進(jìn)行微波輻照活化獲得浸漬生物炭.利用比表面積分析儀、SEM、FTIR、Raman等對生物炭進(jìn)行表征,而后考察了生物炭吸附CO2的性能.結(jié)果表明,浸漬生物炭的比表面積和微孔體積均隨浸漬比的降低呈現(xiàn)先上升后下降的趨勢,浸漬比過高會導(dǎo)致木質(zhì)素鈣團(tuán)聚并堵塞生物炭孔隙,而少量木質(zhì)素鈣浸漬后會調(diào)變生物炭孔隙改善微孔結(jié)構(gòu).浸漬生物炭對CO2的吸附量可達(dá)123.11mg/g,相關(guān)性分析表明比表面積和微孔體積是影響CO2吸附的主要因素.動力學(xué)擬合結(jié)果顯示吸附過程符合Avrami模型,表明CO2吸附過程由物理吸附和化學(xué)吸附共同作用.等溫線擬合結(jié)果顯示當(dāng)木質(zhì)素鈣浸漬量較少時吸附過程符合Langmuir模型,而提高浸漬比后則更符合Freundlich模型,表明適量木質(zhì)素鈣浸漬可以在生物炭表面形成更均勻的微孔吸附點位.循環(huán)實驗發(fā)現(xiàn),浸漬生物炭經(jīng)10次連續(xù)吸附-脫附后仍保持98.22%～98.98%的吸附能力,表明其具有良好的重復(fù)使用性能.綜上,微波輻照木質(zhì)素鈣浸漬生物炭是一種具有潛力的CO2吸附劑.

生物炭；CO2吸附；微波輻照；木質(zhì)素；浸漬

CO2等溫室氣體排放量逐年增加,引發(fā)了氣候變暖、海平面上升等一系列的生態(tài)環(huán)境問題[1].找到一種有效控制CO2排放的方法對保護(hù)人類生存環(huán)境至關(guān)重要.CO2捕集方法主要有吸附法、吸收法、膜分離法等[2],其中吸附法因其高效、低能耗和操作簡便等優(yōu)勢在氣體吸附和碳捕集等領(lǐng)域得到廣泛應(yīng)用[3-4].常見的吸附劑有活性炭、沸石分子篩、硅膠、MOFs等材料,除此之外,生物炭因為造價低廉、吸附性能好等優(yōu)點,近年來在吸附領(lǐng)域受到越來越多的關(guān)注[5-7].孔結(jié)構(gòu)和表面化學(xué)性質(zhì)是影響吸附劑性能的主要因素.由于微孔可以增強CO2分子與吸附劑之間的范德華力[8],因此提高生物炭微孔結(jié)構(gòu)可增強對CO2的吸附效果.生物炭的堿度對CO2吸附性能也有巨大影響.作為一種路易斯酸性氣體,CO2可以被堿性的吸附劑捕獲[9].KOH活化、超聲處理、浸漬、配位體同化等方法都可以有效改善生物炭的理化性質(zhì)[8-10],其中浸漬法因不產(chǎn)生二次污染且能耗低,更加綠色節(jié)能而獲得了廣泛關(guān)注.常用的浸漬劑有金屬鹽、銨鹽、有機(jī)酸鹽、樹脂、瀝青、硅烷以及水溶性有機(jī)物[6-11-12].作為一種儲量巨大的可再生資源,木質(zhì)素也是一種具有應(yīng)用潛力的浸漬劑.木質(zhì)素是由苯丙烷單元通過醚鍵和碳-碳鍵連接而成的具有三維網(wǎng)狀結(jié)構(gòu)的無定形聚合物,其自然儲量僅次于纖維素.目前,全球造紙工業(yè)每年從各種植物中提取約1.4億t天然纖維,同時產(chǎn)生約5000萬t木質(zhì)素副產(chǎn)物[13],預(yù)計到2030年木質(zhì)素年產(chǎn)量將達(dá)到2.25億t[14].然而,目前木質(zhì)素利用率和利用水平較低,超過95%的木質(zhì)素被直接排放到河流或集中燃燒[13].拓展木質(zhì)素利用途徑、提高利用水平,將有助于提高木質(zhì)素價值.

制備方法對生物炭的性能影響巨大,微波輻照加熱是通過電磁波傳遞能量的加熱方式,具有高效、選擇性、快速啟閉、非接觸加熱等優(yōu)點[15].微波輻照可以促進(jìn)生物質(zhì)中有機(jī)物揮發(fā),從而獲得更加規(guī)整有序的微孔結(jié)構(gòu),因此微波輻照制備的生物炭相較于傳統(tǒng)熱解生物炭具有更發(fā)達(dá)的微孔結(jié)構(gòu)[16].以木質(zhì)素為浸漬劑改性生物炭時,若對浸漬于生物炭的木質(zhì)素進(jìn)行熱解,則可產(chǎn)生更加豐富的孔隙.借助微波加熱的優(yōu)點以及生物炭良好的微波吸收能力,可采用微波輻照提高浸漬生物的制備效率和性能.為制備高性能、低成本CO2吸附劑,同時實現(xiàn)生物質(zhì)資源高效利用,本文以大豆秸稈為載體生物炭,木質(zhì)素鈣為浸漬劑,通過浸漬法將木質(zhì)素鈣填充至生物炭較大孔隙,而后利用微波輻照法活化浸漬生物炭,提高生物炭微孔結(jié)構(gòu),并研究該浸漬生物炭對CO2的吸附性能和機(jī)理.

1 材料與方法

1.1 材料、試劑與儀器

大豆秸稈采集于徐州農(nóng)田,木質(zhì)素鈣(LCa)購買自合肥巴斯夫生物科技有限公司;高純N2和CO2氣體購買自徐州特種氣體廠.微波實驗儀(MG08S-2B,南京匯研)用于活化浸漬生物炭;同步熱分析儀(TGA/DSC3+,梅特勒-托利多)用于測量生物炭熱穩(wěn)定性、灰分與CO2吸附實驗;生物炭表面官能團(tuán)利用傅立葉變換紅外光譜儀(iS10,賽默飛世爾)采用KBr壓片法檢測;N2吸附脫附曲線由比表面積分析儀(X1000,北京彼奧德)測試;生物炭孔隙結(jié)構(gòu)根據(jù)BET方程和DFT(密度泛函理論)方法分析,P/P0相對壓力取值范圍為0.05～0.35;元素成分(C、N、S、H)由德國元素分析儀(Elementar Vario MICRO cube)測試;拉曼光譜通過拉曼透鏡(DXR2,賽默飛世爾)測量;生物炭表面形態(tài)由掃描電子顯微鏡(Hitachi S-3400N,日立公司)測試.

1.2 生物炭制備

將大豆秸稈洗凈、切斷、干燥后在馬弗爐中600oC下熱解5h,熱解得到的大豆秸稈產(chǎn)率為27.97%.將熱解完成的大豆秸稈切斷粉碎過篩,獲得40～100目的顆粒,將顆粒水洗后放在真空冷凍干燥機(jī)中干燥24h,獲得大豆秸稈生物炭,命名為SS.將木質(zhì)素鈣LCa與SS按照質(zhì)量比1:1、1:3、1:5、1:10、1:15分別稱重混合,取混合物2g溶于50mL去離子水,置于磁力攪拌器室溫攪拌24h后水浴加熱蒸干水分.將干燥的混合物放入150mL帶蓋石英罐中,在600W功率下微波輻照20min,獲得微波輻照木質(zhì)素浸漬生物炭,根據(jù)浸漬比命名為SS-LCa,=1, 3, 5, 10, 15.

1.3 吸附試驗

吸附動力學(xué)實驗使用同步熱分析儀采用重力法測試,取樣品約10mg在150℃下干燥20min脫去水蒸氣等雜質(zhì),待生物炭降溫至吸附溫度(25℃、45℃、65℃)后通入高純CO2氣體進(jìn)行吸附實驗,生物炭增加的重量為CO2吸附量.

CO2吸附等溫線通過比表面積分析儀測得,取樣品約100mg在200℃真空干燥2h,隨后在0℃恒溫水浴條件下注入高純CO2氣體進(jìn)行吸附等溫線測試.

1.4 吸附/脫附實驗

CO2吸附/脫附循環(huán)實驗在同步熱分析儀上進(jìn)行,取樣品約10mg在200℃脫去雜質(zhì),降溫至25℃后通入高純CO2氣體進(jìn)行吸附30min.而后以15℃/min自25℃升溫至200℃進(jìn)行脫附,完成一次循環(huán).上述過程連續(xù)重復(fù)10次完成CO2吸附脫附循環(huán)實驗.

2 結(jié)果與分析

2.1 生物炭理化特征

掃描電鏡照片(圖1)顯示,生物炭載體SS的表面較為光滑存在大量孔隙;木質(zhì)素鈣浸漬較多時,樣品SS1-LCa和SS3-LCa的孔隙被嚴(yán)重堵塞,隨著浸漬比的降低,越來越多的木質(zhì)素鈣填充進(jìn)載體的較大孔隙,有效減小了SS的孔徑,在SS10-LCa和SS15- LCa上形成了豐富的微孔結(jié)構(gòu).

浸漬生物炭的比表面積為41.10～303.71m2/g(表1),當(dāng)浸漬比從1:1減小至1:10,比表面積逐漸增大,浸漬比為1:10時SS10-LCa具有最大值303.71m2/g,進(jìn)一步減小浸漬比至1:15時比表面積反而有所下降(231.25m2/g).木質(zhì)素鈣是一種大分子有機(jī)物,其分子質(zhì)量達(dá)到5000～60000g/mol,因此浸漬的木質(zhì)素鈣會進(jìn)入生物炭大孔和介孔,卻難以進(jìn)入微孔[6].當(dāng)木質(zhì)素鈣進(jìn)入生物炭較大孔隙后,生物炭原有大孔隙將被調(diào)變?yōu)楠M窄的微孔,從而增大比表面積.另外,生物炭能夠吸收微波并將微波能轉(zhuǎn)化為熱能,浸漬到生物炭中的木質(zhì)素鈣在微波轉(zhuǎn)化的熱能作用下被熱解碳化[17],從而使浸漬到生物炭的木質(zhì)素鈣產(chǎn)生大量微孔,進(jìn)一步增大生物炭比表面積[6].然而,當(dāng)浸漬比過高時大量的木質(zhì)素鈣不僅會填充生物炭孔隙,還會在生物炭表面發(fā)生團(tuán)聚、堵塞生物炭原始孔隙,使其比表面積下降.隨著浸漬比下降,木質(zhì)素鈣團(tuán)聚和堵塞生物炭孔隙的概率下降,比表面積逐漸增大.然而,當(dāng)浸漬比過低木質(zhì)素鈣相對較少時,生物炭大孔隙不能得到充分填充和改造,因此木質(zhì)素調(diào)變孔隙的促進(jìn)作用有所減弱,比表面積會有所下降.生物炭的總孔體積為0.094～0.248cm3/g,微孔體積為0.019～0.135cm3/g,生物炭孔體積隨浸漬比的變化規(guī)律與比表面積相似,均呈出先增長后下降的趨勢.生物炭平均孔徑為1.22～5.52nm,其中浸漬比為1:1時平均孔徑最大,表明過量木質(zhì)素鈣會在生物炭顆粒表面團(tuán)聚堵塞原有狹窄孔道并形成較大的堆積孔道導(dǎo)致孔徑變大.少量木質(zhì)素鈣浸漬和微波輻照活化作用下,原始生物炭孔隙結(jié)構(gòu)得到提升,當(dāng)浸漬比為1:10時,比表面積和微孔體積相比原始生物炭分別提高1.96倍和2.08倍,為最佳浸漬比.

圖1 生物炭SEM圖

浸漬生物炭的灰分含量為8.13%～14.32%(表1),高于原始生物炭(7.49%).木質(zhì)素鈣是利用亞硫酸鹽法制漿、濃縮、發(fā)酵脫糖及噴霧干燥等工序制備的,因此含有大量金屬無機(jī)鹽,導(dǎo)致生物炭浸漬后灰分含量升高.浸漬生物炭的碳含量為65.22%～84.17%,氮含量為0.65%～1.33%(表1),碳、氮含量均隨浸漬比下降呈增長趨勢,這與載體SS中的碳、氮含量均高于木質(zhì)素鈣有關(guān).大豆秸稈可以與根瘤菌共存,并通過根瘤菌從大氣中固定氮元素,從而使大豆秸稈生物炭具有較高的碳和氮含量[5].Li等[18]發(fā)現(xiàn),碳含量高的木屑基生物炭具有更佳的介電性能,因此轉(zhuǎn)化微波為熱能的效率更高升溫速率更快.載體SS的碳含量高達(dá)82.68%,具有良好的微波吸收和轉(zhuǎn)化能力,因此采用微波活化浸漬于SS的木質(zhì)素鈣成為可能.浸漬生物炭的氫含量為1.15%～2.52%,硫含量為0.39%～8.61%(表1),隨浸漬比降低總體呈現(xiàn)下降趨勢.木質(zhì)素鈣浸漬過多時,載體生物炭的含量相對較少,因此吸收微波并轉(zhuǎn)化為熱量的能力有所減弱,導(dǎo)致木質(zhì)素鈣被熱解和碳化不充分,木質(zhì)素鈣中的磺酸鹽和氫鍵沒有被充分熱解[19-20].因此,高浸漬比生物炭(SS1-LCa)的氫含量高于原始生物炭(1.79%),浸漬比過高時(浸漬比1:1、1:3、1:5)其硫含量也遠(yuǎn)高于原始生物炭(0.24%).木質(zhì)素鈣浸漬比過高導(dǎo)致微波熱解不充分可被拉曼光譜分析進(jìn)一步證實.

表1 生物炭理化性質(zhì)

圖2 生物炭表征測試圖

生物炭的拉曼光譜(圖2(b))中D峰和G峰分別代表生物炭中不定型碳和有序碳,AD/AG(D峰與G峰的積分面積比值)可反映生物炭石墨化程度[21], AD/AG比值越低說明生物炭的熱解和碳化越充分、石墨碳含量越高[22].浸漬生物炭的AD/AG為1.88～ 3.22,且隨著浸漬比的降低而逐漸變小,表明木質(zhì)素鈣浸漬量越少,微波輻照后其熱解和碳化程度越高.SS15-LCa相較其他生物炭具有最高的石墨化程度(AD/AG=1.88),與KOH和CO2活化改性的生物炭(AD/AG=1.81)相接近[22].相反,當(dāng)浸漬比過高時, SS1-LCa的AD/AG比值為3.22甚至高于SS(2.71),表明木質(zhì)素鈣浸漬過多時碳化不徹底.損失角正切值是反映材料將微波能轉(zhuǎn)化為熱能的參數(shù),生物質(zhì)損失角正切值較低,微波吸收能力弱[23].為了提高生物質(zhì)的微波熱解效率,往往需要增加多孔活性炭、金屬等催化劑加速反應(yīng)[24].本實驗熱解木質(zhì)素鈣所需的熱量,來自于載體SS吸收微波并轉(zhuǎn)化成的熱能.微波輻照時,載體SS表面的木質(zhì)素鈣最易被熱解炭化.因此,隨著浸漬比降低,木質(zhì)素鈣更加均勻地填充在生物炭的孔隙中,可以更加充分地被熱解炭化;然而,當(dāng)木質(zhì)素鈣過量時,距離生物炭較遠(yuǎn)的外層木質(zhì)素鈣難以獲得足夠的熱量,無法被充分熱解.此外,微波對載體生物炭還會造成二次熱解,當(dāng)過量的微波被載體吸收后,會造成孔道坍塌的風(fēng)險[25],而此時所浸漬的木質(zhì)素鈣除了調(diào)變孔結(jié)構(gòu),還能起到支撐孔道防止坍塌的作用.

熱重曲線(圖2(c))顯示,生物炭浸漬比過高時,有大量的有機(jī)質(zhì)未被充分熱解,從而產(chǎn)生了較多的失重,SS1-LCa在200～700℃損失了近50%質(zhì)量.Kim等[26]制備木屑生物炭,發(fā)現(xiàn)當(dāng)熱解溫度提高到700℃時,生物炭中木質(zhì)素被充分熱解.由此可見,浸漬生物炭的失重主要是由于木質(zhì)素鈣不能充分熱解造成的,因此,浸漬比越高未被充分熱解的木質(zhì)素鈣越多,從而導(dǎo)致浸漬生物炭失重增加.

紅外光譜(圖2(d))中,在3427cm-1,2921cm-1, 1609cm-1和1107cm-1的振動分別為-OH伸縮振動、-CH2伸縮振動、偶氮伸縮振動以及酮類.浸漬比過高時(1:1),木質(zhì)素鈣被熱解碳化程度較低,其中所含的大量有機(jī)質(zhì)被保留下來,因此,SS1-LCa的官能團(tuán)更加豐富.而隨著浸漬比下降,浸漬生物炭中的官基團(tuán)振動峰逐漸變?nèi)?表明微波熱解導(dǎo)致木質(zhì)素鈣中的有機(jī)成分被熱解碳化.

2.2 吸附性能

生物炭對CO2的吸附量如圖3所示,隨著吸附溫度的升高而逐漸下降,在0oC浸漬生物炭對CO2的吸附量最高.除浸漬比為1:1的SS1-LCa吸附量(66.73mg/g)小于原始生物炭SS(105.36mg/g)外,其他浸漬生物炭(109.40～123.11mg/g)均高于SS,表明木質(zhì)素浸漬后可有效提升生物炭對CO2的捕集能力.另外,該微波活化的浸漬生物炭對CO2的吸附量,明顯高于部分文獻(xiàn)報道的吸附劑,如氮摻雜改性海藻生物炭(26.53～45.85mg/g, 25℃)[27],鐵摻雜球磨改性生物炭(52.0mg/g, 25℃)[28]和木質(zhì)素浸漬生物炭(102.88mg/g, 0℃)[6].當(dāng)吸附溫度從0℃上升至65℃吸附量下降了72.63%～79.50%,表明提高溫度不利于生物炭對CO2的吸附[29].這主要是因為升高溫度加劇了CO2分子的布朗運動破壞了吸附平衡,導(dǎo)致吸附量下降.此外CO2吸附量下降幅度與浸漬比有關(guān),木質(zhì)素鈣浸漬量越大,升溫時其CO2吸附量降幅也越大,說明熱解后木質(zhì)素鈣在CO2吸附過程中對溫度更敏感.

圖3 生物炭CO2吸附容量

多孔材料對CO2的吸附與其孔隙結(jié)構(gòu)密切相關(guān),將CO2吸附量與比表面積、總孔體積、微孔體積、平均孔徑進(jìn)行線性相關(guān)分析,發(fā)現(xiàn)2分別為0.9309、0.3132、0.9222、0.7913(圖4).比表面積與CO2吸附量關(guān)系最為密切,這主要是由于大的比表面積為CO2提供了更多的吸附位點[30].總孔體積與吸附量之間沒有顯著的線性關(guān)系,然而微孔體積與吸附量之間存在著顯著的線性關(guān)系,Zhang等[6]同樣發(fā)現(xiàn)微孔體積相較于總孔體積與吸附量之間線性關(guān)系更顯著,表明CO2主要被吸附于微孔而非介孔或大孔.此外,平均孔徑與吸附量存在線性負(fù)相關(guān),進(jìn)一步表明CO2吸附主要發(fā)生在孔徑較小的微孔中.

圖4 CO2吸附量與孔隙結(jié)構(gòu)參數(shù)相關(guān)分析

2.3 吸附機(jī)理

圖5 CO2吸附前后生物炭紅外光譜

對比生物炭吸附CO2前后的紅外光譜(圖5),發(fā)現(xiàn)吸附CO2后生物炭在2340cm-1處出現(xiàn)了C=O伸縮振動形成的CO2的紅外吸收特征峰,表明CO2被生物炭捕獲.除該峰外生物炭紅外光譜無其他明顯差異,表明吸附中CO2與生物炭未能通過化學(xué)反應(yīng)形成大量新官能團(tuán),因此該吸附過程主要受物理吸附控制,即生物炭利用范德華力將CO2分子吸附在表面[31].通過動力學(xué)擬合以及活化能計算可以進(jìn)一步揭示吸附機(jī)理.

采用偽一級、偽二級動力學(xué)和Avrami模型擬合生物炭對CO2的吸附過程,R2分別為0.897～ 0.937、0.882～0.945和0.922～0.948(圖6,表2),除SS1-LCa更符合偽二級動力學(xué)模型外,其他生物炭采用Avrami模型的擬合結(jié)果最佳.偽一級動力學(xué)模型用于描述純物理吸附過程[32],偽二級動力學(xué)模型適用于化學(xué)吸附過程[33],而Avrami模型主要用于描述晶體生長過程,可用于描述物理吸附和化學(xué)吸附共存的吸附過程[34].木質(zhì)素鈣是一種路易斯堿性物質(zhì)[6],木質(zhì)素鈣浸漬量最多的SS1-LCa,其堿度較高且孔隙不發(fā)達(dá),因此對酸性氣體CO2表現(xiàn)出較多化學(xué)吸附.而其他生物炭均具有更為發(fā)達(dá)的孔隙結(jié)構(gòu),可通過孔隙填充的物理吸附大量捕集CO2;與此同時,浸漬的少量木質(zhì)素鈣以及大豆秸稈生物炭上的堿性基團(tuán),均可通過路易斯酸堿反應(yīng)捕集CO2,因此在吸附過程中表現(xiàn)為物理和化學(xué)吸附共存.另外,Avrami模型的速率常數(shù)KA隨著溫度升高而不斷增大,說明升高溫度能加速生物炭對CO2的吸附,這與提高溫度加劇了CO2分子的布朗運動有關(guān)[35].

利用阿侖尼烏斯方程計算生物炭對CO2的吸附活化能[36-37].物理吸附的作用力是范德華力吸附活化能較低,而化學(xué)吸附則需要更高的活化能[38-39].本實驗SS1-LCa對CO2的吸附活化能為10.99kJ/mol,高于其他生物炭(3.46～4.28kJ/mol),表明有化學(xué)吸附參與了該過程.

圖6 生物炭CO2吸附動力學(xué)

表2 生物炭吸附CO2動力學(xué)參數(shù)

續(xù)表2

圖7 生物炭吸附CO2等溫線(0℃)

吸附等溫線實驗(圖7,表3)表明,木質(zhì)素鈣浸漬較多時,SS1-LCa、SS3-LCa、SS5-LCa對CO2的吸附更符合Freundlich等溫線,這是由于過多的木質(zhì)素鈣會在生物炭表面發(fā)生團(tuán)聚從而形成較多的不規(guī)則吸附點位,使吸附傾向于多分子層吸附[40];而當(dāng)木質(zhì)素鈣浸漬較少時,SS10-LCa和SS15-LCa更符合Langmuir等溫線,這是由于少量木質(zhì)素鈣浸漬可以通過填充的方式將生物炭較大孔隙調(diào)變?yōu)楦泳鶆虻奈⒖?從而使吸附更傾向于單分子層吸附[41].

表3 生物炭吸附CO2等溫線參數(shù)(0℃)

2.4 重復(fù)使用性

吸附-脫附實驗(圖8)顯示經(jīng)10次連續(xù)的吸附脫附后,浸漬生物炭對CO2的重復(fù)利用率高達(dá)98.22%～98.98%.僅有少量的CO2未被脫附,這可能是由于CO2分子與生物炭的堿性吸附點位形成不可逆的化學(xué)吸附所致[42].經(jīng)微波活化的木質(zhì)素浸漬生物炭的可重復(fù)使用性明顯高于原始生物炭SS(94.05%),表明該浸漬生物炭在CO2吸附中具有良好的應(yīng)用潛力.

圖8 CO2吸附-脫附實驗

3 結(jié)論

3.1 木質(zhì)素鈣浸漬生物炭后進(jìn)行微波輻照活化可以改善生物炭的微孔結(jié)構(gòu),增大比表面積、總孔體積和微孔體積.然而過多的木質(zhì)素鈣浸漬會由于團(tuán)聚堵塞生物炭孔隙和熱解不充分而影響微孔發(fā)育,浸漬比為1:10為最優(yōu)浸漬比.

3.2 生物炭對CO2的吸附為放熱反應(yīng),降低溫度有利于提高吸附量,在0℃吸附量可達(dá)123.11mg/g.相關(guān)性分析表明比表面積和微孔體積是影響CO2吸附性能的主要因素.Avrami模型可更好地擬合CO2吸附過程,表明同時存在物理和化學(xué)吸附.吸附等溫線擬合結(jié)果表明少量的木質(zhì)素鈣浸漬可以在生物炭表面形成更均勻的吸附點位符合Langmuir等溫線.

3.3 經(jīng)10次吸附-脫附循環(huán)實驗,浸漬生物炭仍具有高達(dá)98.22%～98.98%的重復(fù)使用率,表明微波輻照木質(zhì)素浸漬生物炭是一種良好的CO2吸附劑.

[1] 劉清濤. PEI改性生物炭的制備及對CO2吸附性能的評價[J]. 環(huán)境科學(xué)學(xué)報, 2021,41(3):932-939.Liu Q T. Preparation of PEI-modified biochar and evaluation of its CO2adsorption performance [J]. Acta Scientiae Circumstantiae, 2021,41(3):932-939.

[2] 孟 園,林 莉,陳哲紅,等.樹脂基固態(tài)胺吸附材料的選擇性CO2吸附性能[J]. 中國環(huán)境科學(xué), 2022,42(9):4343-4350.Meng Y, Lin L, Chen Z H, et al. Selective CO2adsorption performance of resin-based solid amine adsorbents [J]. China Environmental Science, 2022,42(9):4343-4350.

[3] Hussin F, Aroua M K. Recent trends in the development of adsorption technologies for carbon dioxide capture: A brief literature and patent reviews (2014–2018) [J]. Journal of Cleaner Production, 2020,253: 119707.

[4] 雷 婷,喻樹楠,周昶安,等.吸附法碳捕集固體胺吸附劑成型技術(shù)研究進(jìn)展[J]. 化工進(jìn)展, 2022,41(12):6213-6225.Lei T, Yu S N, Zhou C A, et al. Research progress on the shaping technology of solid amine adsorbents for CO2capture by adsorption method [J]. Chemical Industry and Engineering Progress, 2022,41(12): 6213-6225.

[5] Cao L, Zhang X, Xu Y, et al. Straw and wood based biochar for CO2capture: Adsorption performance and governing mechanisms [J]. Separation and Purification Technology, 2022,287:120592.

[6] Zhang X, Cao L, Xiang W, et al. Preparation and evaluation of fine-tuned micropore biochar by lignin impregnation for CO2and VOCs adsorption [J]. Separation and Purification Technology, 2022, 295:121295.

[7] 張欣穎,石國亮.二氧化碳固體堿吸附劑改性研究進(jìn)展[J]. 現(xiàn)代化工, 2022,42(8):50-53. Zhang X Y, Shi G L. Research progress in modification of solid alkali adsorbent for carbon dioxide [J]. Modern Chemical Industry, 2022, 42(8):50-53.

[8] Igalavithana A D, Choi S W, Shang J, et al. Carbon dioxide capture in biochar produced from pine sawdust and paper mill sludge: Effect of porous structure and surface chemistry [J]. Science of the Total Environment, 2020,739:139845.

[9] Gao W, Lin Z, Chen H, et al. A review on N-doped biochar for enhanced water treatment and emerging applications [J]. Fuel Processing Technology, 2022,237:107468.

[10] Petrovic B, Gorbounov M, Soltani S M. Influence of surface modification on selective CO2adsorption: A technical review on mechanisms and methods [J]. Microporous and Mesoporous Materials, 2021,312:110751.

[11] Shao J, Zhang J, Zhang X, et al. Enhance SO2adsorption performance of biochar modified by CO2activation and amine impregnation [J]. Fuel, 2018,224:138-146.

[12] Zubbri N A, Mohamed A R, Kamiuchi N, et al. Enhancement of CO2adsorption on biochar sorbent modified by metal incorporation [J]. Environmental Science and Pollution Research, 2020,27(11):11809-11829.

[13] Chio C, Sain M, Qin W. Lignin utilization: A review of lignin depolymerization from various aspects [J]. Renewable and Sustainable Energy Reviews, 2019,107:232-249.

[14] Bajwa D S, Pourhashem G, Ullah A H, et al. A concise review of current lignin production, applications, products and their environmental impact [J]. Industrial Crops and Products, 2019,139:111526.

[15] Zhang X, Xiang W, Miao X, et al. Microwave biochars produced with activated carbon catalyst: Characterization and sorption of volatile organic compounds (VOCs) [J]. Science of the Total Environment, 2022,827:153996.

[16] Leng L, Xiong Q, Yang L, et al. An overview on engineering the surface area and porosity of biochar [J]. Science of the total Environment, 2021,763:144204.

[17] Lin J, Sun S, Xu D, et al. Microwave directional pyrolysis and heat transfer mechanisms based on multiphysics field stimulation: Design porous biochar structure via controlling hotspots formation [J]. Chemical Engineering Journal, 2022,429:132195.

[18] Li H, Li J, Fan X, et al. Insights into the synergetic effect for co- pyrolysis of oil sands and biomass using microwave irradiation [J]. Fuel, 2019,239:219-229.

[19] Devi P, Saroha A K. Effect of pyrolysis temperature on polycyclic aromatic hydrocarbons toxicity and sorption behaviour of biochars prepared by pyrolysis of paper mill effluent treatment plant sludge [J]. Bioresource Technology, 2015,192:312-320.

[20] Zhang J, Liu J, Liu R. Effects of pyrolysis temperature and heating time on biochar obtained from the pyrolysis of straw and lignosulfonate [J]. Bioresource Technology, 2015,176:288-291.

[21] 黃 婷,張 山,蘇明雪,等.污泥基生物炭結(jié)構(gòu)的共焦顯微拉曼技術(shù)應(yīng)用[J]. 中國環(huán)境科學(xué), 2022,42(7):3378-3384.Huang T, Zhang S, Su M X, et al. Application of confocal Raman microscopy on the structure of sludge-based biochar [J]. China Environmental Science, 2022,42(7):3378-3384.

[22] Dissanayake P D, Choi S W, Igalavithana A D, et al. Sustainable gasification biochar as a high efficiency adsorbent for CO2capture: A facile method to designer biochar fabrication [J]. Renewable and Sustainable Energy Reviews, 2020,124:109785.

[23] Durán-Jiménez G, Stevens L A, Kostas E T, et al. Rapid, simple and sustainable synthesis of ultra-microporous carbons with high performance for CO2uptake, via microwave heating [J]. Chemical Engineering Journal, 2020,388:124309.

[24] 張學(xué)楊,曹苓玉,徐 悅,等.微波生物炭對陰、陽離子型染料的吸附特性[J]. 安全與環(huán)境學(xué)報, 2022,22(6):3464-3472. Zhang X Y, Cao L Y, Xu Y, et al. Adsorption properties of anionic and cationic dye on biochar produced by microwave irradiation [J]. Journal of Safety and Environment, 2022,22(6):3464-3472.

[25] Atinafu D G, Yun B Y, Kim Y U, et al. Introduction of eicosane into biochar derived from softwood and wheat straw: Influence of porous structure and surface chemistry [J]. Chemical Engineering Journal, 2021,415:128887.

[26] Kim H-B, Kim J-G, Kim T, et al. Mobility of arsenic in soil amended with biochar derived from biomass with different lignin contents: Relationships between lignin content and dissolved organic matter leaching [J]. Chemical Engineering Journal, 2020,393:124687.

[27] Yang X, Jiang D, Cheng X, et al. Adsorption properties of seaweed- based biochar with the greenhouse gases (CO2, CH4, N2O) through density functional theory (DFT) [J]. Biomass and Bioenergy, 2022, 163:106519.

[28] Xu X, Xu Z, Gao B, et al. New insights into CO2sorption on biochar/Fe oxyhydroxide composites: Kinetics, mechanisms, and in situ characterization [J]. Chemical Engineering Journal, 2020,384:123289.

[29] 梁文俊,楊 嵐,張 艷,等.改性赤泥吸附劑吸附低濃度CO2研究[J]. 中國環(huán)境科學(xué), 2023,43(6):2798-2805.Liang W J, Yang L, Zhang Y, et al. Adsorption of low concentration CO2with modified red mud [J]. China Environmental Science, 2023, 43(6):2798-2805.

[30] Chen Y-D, Liu F, Ren N-Q, et al. Revolutions in algal biochar for different applications: State-of-the-art techniques and future scenarios [J]. Chinese Chemical Letters, 2020,31(10):2591-2602.

[31] Zhang J, Huang D, Shao J, et al. A new nitrogen-enriched biochar modified by ZIF-8 grafting and annealing for enhancing CO2adsorption [J]. Fuel Processing Technology, 2022,231:107250.

[32] Kamran U, Park S-J. Hybrid biochar supported transition metal doped MnO2composites: Efficient contenders for lithium adsorption and recovery from aqueous solutions [J]. Desalination, 2022,522:115387.

[33] Yang X, Zhang X, Wang Z, et al. Mechanistic insights into removal of norfloxacin from water using different natural iron ore – biochar composites: more rich free radicals derived from natural pyrite- biochar composites than hematite-biochar composites [J]. Applied Catalysis B: Environmental, 2019,255:117752.

[34] Krounbi L, Enders A, Anderton C R, et al. Sequential ammonia and carbon dioxide adsorption on pyrolyzed biomass to recover waste stream nutrients [J]. ACS Sustainable Chemistry & Engineering, 2020, 8(18):7121-7131.

[35] Raganati F, Alfe M, Gargiulo V, et al. Kinetic study and breakthrough analysis of the hybrid physical/chemical CO2adsorption/desorption behavior of a magnetite-based sorbent [J]. Chemical Engineering Journal, 2019,372:526-535.

[36] Jung S, Park Y K, Kwon E E. Strategic use of biochar for CO2capture and sequestration [J]. Journal of CO2Utilization, 2019,32:128-139.

[37] Mukherjee A, Borugadda V B, Dynes J J, et al. Carbon dioxide capture from flue gas in biochar produced from spent coffee grounds: Effect of surface chemistry and porous structure [J]. Journal of Environmental Chemical Engineering, 2021,9(5):106049.

[38] Creamer A E, Gao B, Zhang M. Carbon dioxide capture using biochar produced from sugarcane bagasse and hickory wood [J]. Chemical Engineering Journal, 2014,249:174-179.

[39] Lahijani P, Mohammadi M, Mohamed A R. Metal incorporated biochar as a potential adsorbent for high capacity CO2capture at ambient condition [J]. Journal of CO2Utilization, 2018,26:281-293.

[40] Rahman S, Navarathna C M, Krishna Das N, et al. High capacity aqueous phosphate reclamation using Fe/Mg-layered double hydroxide (LDH) dispersed on biochar [J]. Journal of Colloid and Interface Science, 2021,597:182-195.

[41] Sewu D D, Woo S H, Lee D S. Biochar from the co-pyrolysis of Saccharina japonica and goethite as an adsorbent for basic blue 41removal from aqueous solution [J]. Science of The Total Environment, 2021,797:149160.

[42] Abd A A, Naji S Z, Hashim A S, et al. Carbon dioxide removal through physical adsorption using carbonaceous and non-carbonaceous adsorbents: a review [J]. Journal of Environmental Chemical Engineering, 2020,8(5):104142.

Adsorption performance of CO2on lignin impregnated biochar activated by microwave irradiation.

ZHANG Xue-yang*, XU Hao-liang, DAI Huan-tao, YOU Xin-xiu, WEI Zhao-long, CAO Ling-yu

(School of Environmental Engineering, Xuzhou University of Technology, Xuzhou 221018, China)., 2023,43(8)：4427～4436

Calcium lignosulphonate was selected as precursor to impregnate the biochar and followed by the microwave irradiation to activate the impregnated biochar. The obtained impregnated biochar was characterized by surface area analyzer, SEM, FTIR and Raman, and then its CO2adsorption ability was investigated. The results showed that both specific surface area and micropore volume of impregnated biochar increased with the decrease of impregnation ratio and then decreased. That was because too much lignin impregnation would block the original pores of biochar, while appropriate small amount of lignin impregnation would modulate and improve the micropore structure of biochar by entering its large size pores. The adsorption capacity of CO2on impregnated biochar could reach 123.11mg/g, and correlation analysis demonstrated that it was influenced by both specific surface area and micropore volume. Kinetic study showed that the Avrami model fitted CO2adsorption on biochar more accurately, indicating this adsorption process was dominated by physical adsorption and chemical adsorption. Adsorption isotherm fitting showed that Langmuir model fitted the CO2adsorption well for the biochar with less lignin impregnation, while Freundlich model fitted the biochar with more lignin impregnation better. This indicated that appropriate small amount of lignin impregnation facilitated the formation of more uniform micropore adsorption sites on biochar. Reusability experiment showed that the adsorption capacity of impregnated biochar remained 98.22%～98.98% after 10 consecutive adsorptions-desorption cycles, indicating that it had excellent reusability. In a word, lignin impregnated biochar assisted with microwave irradiation could be a potential CO2adsorbent.

biochar；CO2capture；microwave irradiation；lignin；impregnation

X511

A

1000-6923(2023)08-4427-10

張學(xué)楊(1982-),男,山東濟(jì)南人,教授,博士,主要從事生物質(zhì)資源化與氣態(tài)污染物控制.發(fā)表論文60余篇.zhaxuy@163.com.

張學(xué)楊,徐浩亮,戴歡濤,等.微波輻照木質(zhì)素浸漬生物炭吸附CO2性能 [J]. 中國環(huán)境科學(xué), 2023,43(8):4427-4436.

Zhang X Y, Xu H L, Dai H T, et al. Adsorption performance of CO2on lignin impregnated biochar activated by microwave irradiation [J]. China Environmental Science, 2023,43(8):4427-4436.

2023-01-11

江蘇省自然科學(xué)基金資助項目(BK20201151);徐州市科技計劃項目(KC21288)

* 責(zé)任作者, 教授, zhaxuy@163.com