史 瑞,張付申

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堿催化水熱氧化法處理廢棄雙氯芬酸鈉類藥物

史 瑞1,2,張付申1,2*

(1.中國(guó)科學(xué)院生態(tài)環(huán)境研究中心固體廢棄物處理與資源化實(shí)驗(yàn)室,北京 100085；2.中國(guó)科學(xué)院大學(xué),北京 100049)

針對(duì)廢棄藥物綠色處理技術(shù)匱乏的實(shí)際問(wèn)題,以雙氯芬酸鈉(DS)藥物為研究對(duì)象,探討了堿催化水熱氧化法對(duì)其的無(wú)害化處理效果,確定了相應(yīng)的操作方法并優(yōu)化了反應(yīng)參數(shù).利用單因素實(shí)驗(yàn)確定了適宜的實(shí)驗(yàn)因素水平,通過(guò)響應(yīng)面分析法進(jìn)一步解析優(yōu)化了多因素交互作用下的反應(yīng)條件.結(jié)果表明,堿催化水熱氧化法能有效通過(guò)脫氯過(guò)程實(shí)現(xiàn)DS的無(wú)害化處理,最佳反應(yīng)參數(shù)為:H2O2:DS 0.3mL/mg、反應(yīng)時(shí)間98min、反應(yīng)溫度196℃,脫氯效率優(yōu)化值為99.6%,實(shí)測(cè)值為98.9%,相對(duì)誤差0.70%.通過(guò)降解產(chǎn)物測(cè)定和解析,發(fā)現(xiàn)堿催化水熱氧化處理DS存在2個(gè)反應(yīng)路徑:(1)苯環(huán)之間C-N鍵斷裂,然后氧化開環(huán)脫氯;(2)苯環(huán)上直接羥基化,然后氧化開環(huán)脫氯.本研究為廢棄DS類藥物的無(wú)害化處理提供了一條綠色環(huán)保的新途徑.

雙氯芬酸鈉；水熱氧化；響應(yīng)面分析；脫氯效率

近年來(lái),由于藥物的大量使用和不當(dāng)管理,導(dǎo)致大量過(guò)期藥物的產(chǎn)生,僅我國(guó)每年產(chǎn)生的過(guò)期藥物就超過(guò)1500萬(wàn)kg[1].大量研究表明[2-4],過(guò)期藥物會(huì)引起潛在性環(huán)境污染問(wèn)題,即使微量的藥物分子遷移進(jìn)入環(huán)境中也會(huì)對(duì)生態(tài)系統(tǒng)的穩(wěn)定運(yùn)行和人體健康構(gòu)成嚴(yán)重威脅.因此,必須對(duì)其進(jìn)行安全妥善的處理.目前,國(guó)內(nèi)外關(guān)于過(guò)期藥物的處理現(xiàn)狀主要包括[5]:焚燒、混入生活垃圾共處理、按照危險(xiǎn)廢棄物進(jìn)行填埋等.非甾體抗炎藥物(NSAIDs)是目前使用最多的藥物,全球每天大約有3000萬(wàn)人使用該類藥物[6],由其引起的環(huán)境污染問(wèn)題受到越來(lái)越多關(guān)注[7-8].雙氯芬酸是一種典型的非甾體抗炎藥物,主要以鈉鹽形式存在,我國(guó)每年雙氯芬酸鈉(DS)原料的產(chǎn)量達(dá)上千t[9].雙氯芬酸類物質(zhì)具有很強(qiáng)的環(huán)境污染性,大量研究[10-13]證實(shí)其持續(xù)輸入環(huán)境中會(huì)對(duì)水生物造成嚴(yán)重的毒害作用,通過(guò)食物鏈積累會(huì)對(duì)其它生物和人體健康構(gòu)成巨大威脅.早在2000年歐盟就將雙氯芬酸列為環(huán)境中的優(yōu)先控制污染物[14]

迄今關(guān)于水中雙氯芬酸類物質(zhì)降解的研究報(bào)道包括物理吸附法[15]、高級(jí)氧化法(光催化氧化[16]、電化學(xué)氧化[17]、芬頓氧化[18]、臭氧氧化[19]等)以及生物處理法[20].這些研究表明不同方法對(duì)低濃度雙氯芬酸類物質(zhì)的降解效果較好,但是對(duì)降解過(guò)程產(chǎn)生的氯代中間產(chǎn)物進(jìn)一步降解關(guān)注較少.與本體相比,這些氯代中間產(chǎn)物的毒害性可能會(huì)高于其母體本身,一般認(rèn)為含氯有機(jī)物發(fā)生脫氯反應(yīng),即能說(shuō)明含氯有機(jī)物毒性降低[21].因此,以脫氯效率來(lái)評(píng)價(jià)DS處理過(guò)程的無(wú)害化程度更加合理.水熱氧化(HTO)是一種非常高效的化學(xué)氧化技術(shù),特別適合水溶液中高濃度有毒有害污染物的處理,該技術(shù)在鹵代有機(jī)物污染物脫鹵領(lǐng)域受到廣泛關(guān)注[22-23].HTO技術(shù)已應(yīng)用在高濃度制藥廢水處理中[24],但目前還未見(jiàn)該技術(shù)用于廢棄藥物處理的報(bào)道.

本研究以脫氯效率作為無(wú)害化處理效果的評(píng)價(jià)指標(biāo),采用HTO技術(shù)對(duì)廢棄DS藥物進(jìn)行無(wú)害化降解處理,研究了堿加入對(duì)DS脫氯效果的影響,通過(guò)單因素實(shí)驗(yàn)和響應(yīng)面實(shí)驗(yàn)分析,得到堿催化水熱氧化DS脫氯效果的最佳反應(yīng)條件,并分析了不同實(shí)驗(yàn)因素對(duì)DS脫氯效率影響的交互作用,同時(shí)提出了堿催化水熱氧化DS的反應(yīng)路徑,以期為廢棄DS藥物的綠色無(wú)害化處理提供理論依據(jù)和技術(shù)支持.

1 實(shí)驗(yàn)材料與方法

1.1 材料

雙氯芬酸鈉(C14H10Cl2NNaO2,由河南東泰制藥有限公司提供);過(guò)氧化氫(H2O2,30.wt%);氫氧化鈉(NaOH,優(yōu)級(jí)純);聚四氟乙烯水熱反應(yīng)釜;超純水(電阻率>18MΩ×cm, Merck Millipore超純水儀);離子色譜(ICS-2000,DIONEX公司);氣相色譜聯(lián)用GC-MS(7890A/5975C,Agilent公司).

1.2 實(shí)驗(yàn)部分

1.2.1 實(shí)驗(yàn)流程 稱取50mgDS固體粉末,放入聚四氟乙烯水熱反應(yīng)釜中,加入不同量的NaOH和H2O2,之后加入一定體積的超純水,保證反應(yīng)體系總體積均為40mL,擰緊密封好反應(yīng)釜.烘箱提前預(yù)熱到反應(yīng)溫度,將反應(yīng)釜放入烘箱中并開始計(jì)時(shí).

1.2.2 反應(yīng)體系篩選實(shí)驗(yàn) 本研究首先對(duì)不同的反應(yīng)體系進(jìn)行了篩選,開展4組對(duì)照實(shí)驗(yàn):未加入NaOH和H2O2組(空白組)、單獨(dú)加入15mLH2O2組、單獨(dú)加入10mgNaOH組及同時(shí)加入10mgNaOH和15mLH2O2組.確定NaOH-H2O2體系作為單因素實(shí)驗(yàn)的反應(yīng)體系.

1.2.3 單因素實(shí)驗(yàn) 分別選取H2O2:DS、NaOH加入量、反應(yīng)時(shí)間、反應(yīng)溫度作為實(shí)驗(yàn)考察因素.

1.2.4 響應(yīng)面優(yōu)化實(shí)驗(yàn)設(shè)計(jì) 為進(jìn)一步考察不同因素之間的交互作用,得到最優(yōu)的實(shí)驗(yàn)因素水平組合,設(shè)計(jì)了響應(yīng)面優(yōu)化實(shí)驗(yàn).選取單因素實(shí)驗(yàn)中對(duì)脫氯效率影響最大的3個(gè)因素(H2O2:DS、反應(yīng)溫度、反應(yīng)時(shí)間)設(shè)計(jì)3因素3水平的響應(yīng)面分析,利用Design -Expert軟件進(jìn)行實(shí)驗(yàn)設(shè)計(jì)和數(shù)據(jù)分析,得到3個(gè)因素交互作用下的最優(yōu)反應(yīng)條件.

1.3 處理效果評(píng)價(jià)方法

將收集的液體產(chǎn)物定容至100mL,稀釋后經(jīng)微孔濾膜過(guò)濾除去雜質(zhì),利用離子色譜定量分析Cl-濃度,脫氯效率通過(guò)式(1)進(jìn)行計(jì)算:

1.4 產(chǎn)物分析方法

收集不同反應(yīng)時(shí)間處理后的液體產(chǎn)物,利用二氯甲烷萃取,除水后通過(guò)GC-MS分析產(chǎn)物成分.GC-MS分析條件:60℃保持1min,以10℃/min升溫至200℃保持2min,以5℃/min升溫至280 ℃保持2min.進(jìn)樣口溫度280℃,不分流,進(jìn)樣量為1μL,電離方式為EI源,產(chǎn)物通過(guò)標(biāo)準(zhǔn)NIST譜庫(kù)比對(duì)確定.

2 結(jié)果與討論

2.1 反應(yīng)體系的篩選

如圖1所示,單獨(dú)加入H2O2體系以及同時(shí)加入NaOH和H2O2體系(NaOH-H2O2體系)均能促進(jìn)DS在水熱條件下脫氯,但單獨(dú)加入NaOH并未有效促進(jìn)水熱氧化DS的脫氯過(guò)程.在NaOH-H2O2體系下脫氯效率是單獨(dú)加入H2O2體系下的2倍,這主要是由于在堿性條件下, H2O2更加活躍,容易分解產(chǎn)生更多的×OH[25],促進(jìn)氧化脫氯過(guò)程發(fā)生.故選擇NaOH-H2O2體系開展后續(xù)單因素實(shí)驗(yàn).

2.2 DS脫氯效率單因素實(shí)驗(yàn)結(jié)果

2.2.1 H2O2:DS對(duì)DS脫氯效率的影響 如圖2(a)所示,脫氯效率隨著H2O2:DS的增大而增大,在H2O2:DS為0.3mL/mg時(shí)達(dá)到最大,之后緩慢降低,確定適宜的H2O2:DS為0.3mL/mg.H2O2對(duì)水熱降解DS脫氯的影響存在兩面性,低濃度的H2O2有利于×OH的生成,但當(dāng)H2O2加入量過(guò)高時(shí),會(huì)對(duì)×OH產(chǎn)生抑制作用,發(fā)生的抑制反應(yīng)如下[26]:

×OH +×OH→H2O2(2)

×OH +×OOH→H2O+O2(3)

×OH +H2O2→×OOH +H2O (4)

2.2.2 NaOH加入量對(duì)DS脫氯效率的影響 如圖2(b)所示,脫氯效率隨著NaOH加入量的增大而增大后維持穩(wěn)定,NaOH加入量超過(guò)10mg,脫氯效率維持在90%左右.相關(guān)研究表明[27]加入過(guò)量的堿會(huì)對(duì)H2O2分解生成×OH產(chǎn)生抑制作用,故確定適宜的NaOH加入量為10mg.

2.2.3 反應(yīng)時(shí)間對(duì)DS脫氯降解效果的影響 如圖2(c)所示,脫氯效率隨著反應(yīng)時(shí)間的延長(zhǎng)而增大,在反應(yīng)時(shí)間為120min時(shí)達(dá)到最大值,之后維持不變.實(shí)驗(yàn)結(jié)果表明在反應(yīng)時(shí)間120min內(nèi)DS脫氯完全,確定適宜的反應(yīng)時(shí)間為120min.

2.2.4 反應(yīng)溫度對(duì)DS脫氯降解效果的影響 如圖2(d)所示,脫氯效率隨著反應(yīng)溫度的升高而增大,在反應(yīng)溫度180℃時(shí)達(dá)到最大,之后不再增加.隨著反應(yīng)溫度升高,H2O2產(chǎn)生×OH速率加快,促進(jìn)DS的氧化脫氯反應(yīng),確定適宜的反應(yīng)溫度為180℃.

2.3 響應(yīng)面法優(yōu)化分析

利用Design-Expert軟件進(jìn)行優(yōu)化實(shí)驗(yàn)設(shè)計(jì),實(shí)驗(yàn)設(shè)計(jì)和數(shù)據(jù)處理結(jié)果如表1和圖3(脫氯效率3D響應(yīng)曲面圖)所示.

表1 響應(yīng)面實(shí)驗(yàn)設(shè)計(jì)及響應(yīng)值

2.3.1 二次響應(yīng)面回歸模型的建立與分析 利用Design-Expert軟件進(jìn)行回歸分析,使用二次項(xiàng)模型進(jìn)行數(shù)值模擬.如表2所示,模型的值為0.0017<0.05,說(shuō)明該模型具有顯著性;響應(yīng)度充足精確度為12.754>4,說(shuō)明該模型滿足信號(hào)互相干擾要求,能夠用于精確的預(yù)測(cè).由表2可知、2、2的值<0.05,說(shuō)明H2O2:DS、反應(yīng)時(shí)間、反應(yīng)溫度以及兩兩因素之間交互作用對(duì)脫氯效率的影響是顯著的.回歸分析得到擬合公式:

式中:為H2O2:DS,mL/mg;為反應(yīng)時(shí)間,min;為反應(yīng)溫度,℃.

表2 二次多項(xiàng)模型方差分析

2.3.2 各因素交互作用對(duì)DS脫氯效率影響的分析 圖3(a)~(c)直觀地反映了各實(shí)驗(yàn)因素對(duì)脫氯效率的影響,比較圖3中的3組圖可知,反應(yīng)溫度()對(duì)脫氯效率的影響最為顯著,表現(xiàn)為其曲線曲率較高;而H2O2:DS()對(duì)脫氯效率影響的顯著程度次之;反應(yīng)時(shí)間()相對(duì)于的表現(xiàn)為曲線曲率較小.

通過(guò)軟件分析得到的堿催化水熱氧化降解DS的最佳實(shí)驗(yàn)條件為H2O2:DS 0.3mL/mg、反應(yīng)時(shí)間98min、反應(yīng)溫度196℃,脫氯效率預(yù)測(cè)值為99.6%.在此條件下,重復(fù)實(shí)驗(yàn)3次,脫氯效率平均為98.9%,與預(yù)測(cè)值相比,相對(duì)誤差為0.70%.重復(fù)性較好,說(shuō)明優(yōu)化結(jié)果可靠.

2.4 DS降解反應(yīng)路徑解析

利用GC-MS分析不同反應(yīng)時(shí)間所得降解產(chǎn)物,結(jié)合不同研究提出的DS降解路徑,推斷出堿催化水熱氧化處理DS的反應(yīng)路徑.DS的降解產(chǎn)物信息如表3所示.

表3 GC-MS分析降解產(chǎn)物

將不同反應(yīng)時(shí)間下得到的降解產(chǎn)物的峰面積進(jìn)行歸一化處理,總結(jié)不同降解產(chǎn)物隨反應(yīng)時(shí)間的變化趨勢(shì),如圖4所示.

由圖4可知,反應(yīng)15min后具有內(nèi)酰胺結(jié)構(gòu)的雙氯芬酸脫水產(chǎn)物1-(2,6-二氯苯基)-1,3-二氫-2H-吲哚-2-酮大量增加,其含量隨著反應(yīng)時(shí)間的延長(zhǎng)而逐漸降低,雙氯芬酸和雙氯芬酸脫水產(chǎn)物的峰面積分別在放入60和75min之后消失.在反應(yīng)初期DS發(fā)生部分水解生成雙氯芬酸,DS和雙氯芬酸隨后發(fā)生分子內(nèi)脫水反應(yīng)生成具有內(nèi)酰胺結(jié)構(gòu)的環(huán)化產(chǎn)物,該環(huán)化脫水產(chǎn)物是DS降解過(guò)程中的重要中間產(chǎn)物[18,28].同時(shí)加熱過(guò)程也能促進(jìn)內(nèi)酰胺結(jié)構(gòu)環(huán)化產(chǎn)物的生成[29].

反應(yīng)15min后二氯苯胺和二氯苯酚的峰面積逐漸增大,45min后達(dá)到最大值,之后逐漸減小,90min后二者的峰消失.二氯苯胺的出現(xiàn)說(shuō)明DS在降解過(guò)程中發(fā)生了苯環(huán)之間C-N鍵的斷裂[30],推斷這是主要的反應(yīng)路徑.二氯苯酚峰面積增加滯后于二氯苯胺,表明二氯苯酚是由二氯苯胺的-NH2在×OH的攻擊下被取代而生成.

反應(yīng)30min后檢測(cè)到具有氯胺結(jié)構(gòu)的羥基化產(chǎn)物,60min后達(dá)到最大峰面積,之后降低,105min后峰消失.具有氯胺結(jié)構(gòu)的羥基化產(chǎn)物和二氯苯酚出現(xiàn)峰面積最大值的時(shí)間相同,表明二氯苯酚和具有氯胺結(jié)構(gòu)的羥基化產(chǎn)物是同時(shí)通過(guò)二氯苯胺與×OH反應(yīng)生成,之后具有氯胺結(jié)構(gòu)的羥基化產(chǎn)物再進(jìn)一步經(jīng)過(guò)×OH氧化形成小分子產(chǎn)物[31].

反應(yīng)30min內(nèi)檢測(cè)出甲基咔唑,該產(chǎn)物在DS的光降解過(guò)程中出現(xiàn)[32].同時(shí)也檢測(cè)出含雙氯芬酸骨架結(jié)構(gòu)的羥基化產(chǎn)物,在超聲輻照降解DS的研究中檢測(cè)出該產(chǎn)物[33].含雙氯芬酸骨架結(jié)構(gòu)的羥基化產(chǎn)物和甲基咔唑產(chǎn)物的峰面積要低于檢測(cè)到的其他產(chǎn)物,同時(shí)這兩種產(chǎn)物均含有苯環(huán)之間的C-N鍵,表明除主反應(yīng)路徑之外,還存在不發(fā)生C-N鍵斷裂而直接在DS分子上發(fā)生羥基化反應(yīng)的副反應(yīng)路徑.甲基咔唑產(chǎn)物是由DS直接羥基化得到含有雙氯芬酸骨架結(jié)構(gòu)的羥基化產(chǎn)物,經(jīng)過(guò)脫羧基、分子間脫氯反應(yīng)生成[16].反應(yīng)105和120min之后未檢測(cè)出產(chǎn)物峰,表明此時(shí)DS脫氯反應(yīng)完全,沒(méi)有含氯產(chǎn)物生成,有機(jī)氯完全轉(zhuǎn)化為無(wú)機(jī)氯.

綜合上述分析,可以推斷堿催化水熱氧化降解DS包括2個(gè)反應(yīng)路徑:(1)首先發(fā)生DS中2個(gè)苯環(huán)之間C-N鍵斷裂,之后生成二氯苯胺、二氯苯酚等含苯環(huán)中間產(chǎn)物;(2)DS苯環(huán)上直接發(fā)生羥基化,之后發(fā)生脫羧基、脫氯反應(yīng)生成甲基咔唑中間產(chǎn)物.這些含苯環(huán)結(jié)構(gòu)的中間產(chǎn)物進(jìn)一步在×OH的氧化下發(fā)生開環(huán)反應(yīng)生成小分子有機(jī)酸和醇類,最終完全氧化為CO2和HCl. DS中的有機(jī)氯完全轉(zhuǎn)化為無(wú)機(jī)氯,從而實(shí)現(xiàn)DS的無(wú)害化處理,反應(yīng)路徑如圖5所示:

3 結(jié)論

3.1 建立了堿催化水熱氧化無(wú)害化處理廢棄DS藥物的新方法.堿的加入可以提高水熱氧化DS的脫氯效率,單因素實(shí)驗(yàn)和響應(yīng)面優(yōu)化實(shí)驗(yàn)表明H2O2:DS、反應(yīng)時(shí)間、反應(yīng)溫度是對(duì)堿催化水熱氧化降解DS脫氯效率影響最大的3個(gè)因素,最佳反應(yīng)條件為:H2O2:DS為0.3mL/mg、反應(yīng)時(shí)間為98min、反應(yīng)溫度為196℃,脫氯效率達(dá)到98.9%.

3.2 整個(gè)處理過(guò)程包括2個(gè)反應(yīng)路徑:(1)苯環(huán)之間的C-N鍵首先發(fā)生斷裂,之后發(fā)生氧化開環(huán)反應(yīng);(2)苯環(huán)上直接羥基化,之后發(fā)生氧化開環(huán)反應(yīng).隨后生成小分子有機(jī)酸和醇類,最終完全礦化為CO2和HCl.

3.3 本研究證明了堿催化水熱氧化法可以有效地?zé)o害化處理固體形式的非甾體抗炎藥物.

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Treatment of waste diclofenac sodium medicine by base-catalyzed hydrothermal oxidation method.

SHI Rui1,2, ZHANG Fu-Shen1,2*

(1.Department of Solid Waste Treatment and Recycling, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China；2.University of Chinese Academy of Sciences, Beijing 100049, China).

Aiming at the problem of lacking of green treatment technologies for pharmaceutical wastes, the current study was carried out to investigate the detoxification effect of base-catalyzed hydrothermal oxidation on diclofenac sodium (DS) medicine. The corresponding operation method was established and the reaction parameters were optimized. The suitable experimental levels were determined by single-factor design, and response surface methodology (RSM) was carried out to further establish the optimum conditions under multi-factor interaction. The results showed that base-catalyzed hydrothermal oxidation was an efficient approach for the detoxification of DS by dechlorination. The optimal parameters were, H2O2: DS 0.3mL/mg, reaction time 98min, reaction temperature 196℃, respectively. It was noted that the determined value was 98.9% and the predicted value was 99.6% with a relative error of 0.70%. Determination and analysis of the degradation products showed that there were two different reaction pathways for the degradation of DS by base-catalyzed hydrothermal oxidation: (1) the C-N bond between the two benzene rings cleaved, followed by benzene rings opened and dechlorinated through oxidation; (2) the benzene rings directly hydroxylated, followed by benzene rings opened and dechlorinated through oxidation. This study provides a green and environmentally benign approach for the detoxification of waste DS medicine.

diclofenac sodium；hydrothermal oxidation；response surface methodology；dechlorination efficiency

X703.5

A

1000-6923(2017)04-1386-08

2016-09-12

國(guó)家自然科學(xué)基金資助項(xiàng)目(21477151);國(guó)家水體污染控制與治理重大專項(xiàng)資助項(xiàng)目(2012ZX07202-005)

史 瑞(1991-),男,四川成都人,中國(guó)科學(xué)院生態(tài)環(huán)境研究中心博士研究生,主要從事固體廢棄物資源化利用研究.

* 責(zé)任作者, 研究員, fszhang@rcees.ac.cn

, 2017,37(4)：1386~1393