馬洪亭,王明輝,王芳超,郝夙?xiàng)?,楊國利,張于峰,?娜
(天津大學(xué)環(huán)境科學(xué)與工程學(xué)院,天津 300072)
典型廢舊家電印刷線路板熱失重特性和熱解動力學(xué)模型
馬洪亭,王明輝,王芳超,郝夙?xiàng)鳎瑮顕?,張于峰,?娜
(天津大學(xué)環(huán)境科學(xué)與工程學(xué)院,天津 300072)
用熱重法研究了廢舊電視機(jī)、電腦、手機(jī)和洗衣機(jī)4種典型家電印刷線路板的熱解特性,發(fā)現(xiàn)在相同條件下不同印刷線路板的熱解起始溫度、終止溫度、最大失重速率、峰溫和反應(yīng)時間隨升溫速率的變化規(guī)律一致,但總失重率存在著較大差異. 建立了不定溫條件下非均相反應(yīng)的熱解動力學(xué)模型,用Kissinger法和形狀因子法求解了4種典型家用電器印刷線路板的表觀動力學(xué)參數(shù)E、A和n. 彩電:E=103.09,kJ/mol,A=8.17×108,/min,n=1.73;洗衣機(jī):E=98.15,kJ/mol,A=1.50×108,/min,n=2.73;手機(jī):E=78.79,kJ/mol,A=2.48×106/min,n=3.56;電腦:E=101.31,kJ/mol,A=2.96×108,/min,n=1.77. 由動力學(xué)模型計算出的轉(zhuǎn)化率與實(shí)驗(yàn)值之間能夠較好地吻合.
典型廢舊家電;熱失重特性;印刷線路板;動力學(xué)模型
隨著電視機(jī)、洗衣機(jī)、電腦、手機(jī)等家用電器的普及和更新速度的加快,產(chǎn)生的廢舊家電越來越多.由于其中的印刷線路板(printed circuit boards, PCBs)含有大量可回收利用的銅、錫、鉛、金、玻璃纖維等金屬和非金屬,其處理技術(shù)和處理方法的研究越來越受重視[1-3].火法冶金、濕法冶金和機(jī)械物理法[4-7]等處理方法,雖然技術(shù)比較成熟,但在處理過程中會產(chǎn)生嚴(yán)重的二次污染,而且金屬回收率低、非金屬材料無法回收,所以應(yīng)用受到限制.熱解法由于具有處理工藝簡單、處理過程比較環(huán)保、金屬和非金屬回收率高等優(yōu)勢,近年來已成為廢舊印刷線路板回收技術(shù)研究的熱點(diǎn)[8-11].文獻(xiàn)[12-15]研究了未經(jīng)使用的印刷線路板基材的熱失重特性與動力學(xué)規(guī)律.筆者以彩電、電腦、手機(jī)和洗衣機(jī)4種典型廢舊家電印刷線路板為研究對象,用差熱-熱重聯(lián)用分析儀進(jìn)行了熱失重實(shí)驗(yàn),研究了熱解特性,并在此基礎(chǔ)上建立了熱解動力學(xué)模型,用Kissinger法和形狀因子法求解了4種典型家用電器印刷線路板的表觀動力學(xué)參數(shù)E、A和n.
1.1 實(shí)驗(yàn)樣品
實(shí)驗(yàn)用印刷線路板是從市場上收購的廢舊彩電、電腦、手機(jī)和洗衣機(jī)經(jīng)拆解獲得.熱失重實(shí)驗(yàn)時,為消除物料內(nèi)外溫差和傳熱傳質(zhì)的影響,實(shí)驗(yàn)前將各種線路板分割成3,mm×3,mm大小左右的小顆粒,每次實(shí)驗(yàn)的樣品質(zhì)量在25~33,mg之間不等.
1.2 實(shí)驗(yàn)儀器和實(shí)驗(yàn)方法
熱失重實(shí)驗(yàn)是在日本島津公司生產(chǎn)的DTG-60H型差熱-熱重聯(lián)用分析儀中完成的,儀器的測溫范圍是室溫至1 500,℃,溫度分辨力為0.1,℃.電子天平的靈敏度為±0.001,mg,量程為±500,mg,測量精度為±1%.用于盛放實(shí)驗(yàn)樣品和參比物的坩堝由耐高溫的Al2O3材料制成,參比物為高純度的Al2O3白色粉末.為保證熱解過程中爐內(nèi)的絕氧條件,實(shí)驗(yàn)過程中一直向設(shè)備中通入壓力為0.3,MPa的高純度的N2,N2流量為30,L/min.升溫速率分別控制在10,℃/min、20,℃/min、30,℃/min和40,℃/min,熱解終溫統(tǒng)一設(shè)定為800,℃.實(shí)驗(yàn)基本參數(shù)、熱失重曲線和差熱曲線被自動記錄和保存在電腦中.
為研究廢舊彩電、洗衣機(jī)、電腦和手機(jī)4種典型家電印刷線路板的熱解特性,在升溫速率β分別為10,℃/min、20,℃/min、30,℃/min和40 ℃/min的條件下進(jìn)行熱失重實(shí)驗(yàn),并對獲得的TG曲線和DTG 曲線進(jìn)行分析,得到表征4種典型家電印刷線路板熱解特性的起始溫度t0、終止溫度tf、最大失重速率峰溫tp和反應(yīng)時間τ 等參數(shù),見表1.
從表中數(shù)據(jù)可以看出,彩電和手機(jī)印刷線路板的熱解過程為2步反應(yīng),有2個峰溫.電腦和洗衣機(jī)的熱解過程為單步反應(yīng),有1個峰溫;由于不同家電線路板的組成成分不同,熱解后總的熱失重率有比較大的差異;在扣除線路板中不參與熱解的金屬成分后,廢舊彩電印刷線路板的熱失重率最大,為67.77%,廢舊手機(jī)印刷線路板的熱失重率最小,為26.82%.
表1 不同印刷線路板熱解特性參數(shù)Tab.1 Thermogravimetric characteristics parameters of different PCBs
廢舊印刷線路板的熱解過程比較復(fù)雜,一般包括解聚反應(yīng)(拉鏈降解)、無規(guī)斷裂和低分子物質(zhì)的脫除等,甚至還伴隨著裂解后分子的重整.根據(jù)文獻(xiàn)[16],該過程可看成是不定溫、非均相反應(yīng),其動力學(xué)方程可表示為
式中:α為轉(zhuǎn)化份額,%;T為熱力學(xué)溫度,K;k( T)為反應(yīng)速率常數(shù),是溫度的函數(shù).根據(jù)Arrhenius方程,k( T)=Aexp(?E/ RT);f(α)為反應(yīng)機(jī)理函數(shù),對于固體熱分解反應(yīng),一般認(rèn)為反應(yīng)速率與反應(yīng)物濃度成正比,即f(α)=(1?α)n.因此,可得熱解反應(yīng)動力學(xué)微分方程為
式中:E為反應(yīng)活化能,kJ/mol;A為指前因子,min-1;R為摩爾氣體常數(shù),8.314,J/(mol·K);n為反應(yīng)級數(shù).
熱解動力學(xué)研究的目的在于求解描述熱解反應(yīng)的上述方程中的“動力學(xué)三因子”(kinetic triplet)E、A和n.
對方程(3)兩邊取對數(shù),可得Kissinger方程
通過對圖1~圖4中的4條直線進(jìn)行最小二乘法回歸,可以得到相應(yīng)的直線方程,根據(jù)直線的截距(intercept)和斜率(slope)可以求出相應(yīng)的活化能E、指前因子A和相關(guān)系數(shù)r,見表2.
彩電、手機(jī)、電腦和洗衣機(jī)4種典型廢舊家電印刷線路板的表觀動力學(xué)參數(shù)E、A、n及相關(guān)系數(shù)r,匯總于表2中.
圖1 廢舊彩電印刷線路板lnFig.1for waste color TV PCBs
圖2 廢舊手機(jī)印刷線路板lnFig.2for waste mobile phones PCBs
圖3 廢舊洗衣機(jī)線路板lnFig.3for waste washing mathions PCBs
圖4 廢舊電腦線路板lnFig.4for waste computures PCBs
表2 不同廢舊家電印刷線路板熱解反應(yīng)動力學(xué)參數(shù)值匯總Tab.2 Thermogravimetric reaction kinetic parameters data summary on PCBs from different waste life electro-equipments
計算結(jié)果表明,不同家電的印刷線路板,由于組成成分和生產(chǎn)工藝不同,其熱解過程的表觀動力學(xué)參數(shù)不同;同一種線路板的不同失重階段,由于熱解成分不同,熱解的難易程度不同,導(dǎo)致其表觀動力學(xué)參數(shù)也不相同.一般第2步熱解要比第1步熱解更為困難,需要消耗更多的能量,因此,彩電和手機(jī)第2步熱解的活化能大于第1步熱解的活化能.
對方程(4)進(jìn)行整理,兩側(cè)在0~α和0T~T之間積分,得
從圖中可以看出,彩電和電腦印刷線路板的熱解動力學(xué)模型計算值與實(shí)驗(yàn)值之間吻合得比較好,說明本文所選的熱解機(jī)理函數(shù)與熱解動力學(xué)規(guī)律一致,是最概然函數(shù).由熱重實(shí)驗(yàn)數(shù)據(jù)和形狀因子法計算出的表觀動力學(xué)參數(shù)反映了熱解過程的真實(shí)情況.
圖5 彩電線路板熱解動力學(xué)模型與實(shí)驗(yàn)值對比Fig.5 Comparison between experimental data and kinetic model prediction from color TV PCBs
圖6 電腦線路板熱解動力學(xué)模型與實(shí)驗(yàn)值對比Fig.6 Comparison between experimental data and kinetic model prediction from computures PCBs
(1)彩電、洗衣機(jī)、手機(jī)和電腦4種典型廢舊家電印刷線路板的熱解起始溫度、終止溫度、最大失重速率、反應(yīng)時間、峰溫隨升溫速率的變化規(guī)律相似,但總失重率之間存在著較大的差異.
(2)用Kissinger和形狀因子法求出了動力學(xué)三因子,分別為,彩電:E=103.09,kJ/mol,A=8.17× 108,/min,n=1.73;洗衣機(jī):E=98.15,kJ/mol,A=1.50×108,/min,n=2.73;手機(jī):E=78.79,kJ/mol,A=2.48×106/min,n=3.56;電腦:E=101.31,kJ/mol,A=2.96×108,/min,n=1.77.而且由動力學(xué)模型計算出的轉(zhuǎn)化率與實(shí)驗(yàn)值之間吻合較好.
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Thermogravimetric Characteristics and Kinetic Modes of Printed Circuit Boards from Typical Waste Life Electro-Equipments
MA Hong-ting,WANG Ming-hui,WANG Fang-chao,HAO Su-feng,YANG Guo-li,ZHANG Yu-feng,DENG Na
(School of Environmental Science and Technology,Tianjin University,Tianjin 300072,China)
The thermogravimetric characteristics of printed circuit boards(PCBs)from waste color televisions,computers,mobile phones,and washing machines were studied using thermogravimetry in strict pyrolyisis conditions. The results indicated that the variations of initial temperature,finial temperature,maximum weight loss ratios,peak temperature,and reaction time with heating rate are similar for different printed circuit boards. However,the total weight loss ratios have an obvious difference for different printed circuit boards in the same conditions. Based on the assumptions of non-isothermal and heterogeneous reactions,a kinetic mode was established,and the apparent kinetic parameters for different printed circuit boards were obtained with Kissinger method and shape index method. The activation energy E,the pre-exponential factor A,and the reaction order n were:103.09,kJ/mol,8.17×108/min,and 1.73 for color television PCB,98.15,kJ/mol,1.50×108,/min,and 2.73 for washing machine PCB,78.79,kJ/mol,2.48×106,/min,and 3.56 for mobile phone PCB,101.31,k/mol,2.96×108,/min,and 1.77 for computer PCB,respectively. The conversion calculated agreed quite well with the experimental data.
typical waste life electro-equipment;thermogravimetric characteristics;printed circuit board;kinetic mode
O621.259
A
0493-2137(2011)07-0602-05
2010-04-12;
2010-10-12.
天津市自然科學(xué)基金資助項(xiàng)目(09JCYBJC08100);天津市濱海新區(qū)“十大戰(zhàn)役”重大科技支撐項(xiàng)目(2010-Bk140002);天津市科技創(chuàng)新專項(xiàng)資金資助項(xiàng)目(07FDIDH0400).
馬洪亭(1964— ),男,博士,副教授.
馬洪亭,mht116@tju.edu.cn.