國際純化學與應(ying)用化學學會(IUPAC)將活性(xing)(xing)(xing) 炭(tan)(tan)的(de)孔(kong)(kong)(kong)(kong)分(fen)為大(da)孔(kong)(kong)(kong)(kong)(>50 nm)、中(zhong)(zhong)孔(kong)(kong)(kong)(kong)(2~50 nm)及微(wei) 孔(kong)(kong)(kong)(kong)(<2 nm)3 類,在(zai)改(gai)性(xing)(xing)(xing)過程(cheng)中(zhong)(zhong),碳原子一直被消 耗,煤(mei)(mei)(mei)基(ji)活性(xing)(xing)(xing)炭(tan)(tan)孔(kong)(kong)(kong)(kong)隙(xi)進一步發育,生成(cheng)(cheng)更多微(wei)孔(kong)(kong)(kong)(kong). 甲(jia)(jia)烷在(zai)煤(mei)(mei)(mei)體中(zhong)(zhong)的(de)吸(xi)(xi)(xi)附(fu)(fu)(fu)(fu)與擴散(san)主要發生在(zai)微(wei)孔(kong)(kong)(kong)(kong)中(zhong)(zhong), 而微(wei)孔(kong)(kong)(kong)(kong)屬于納米級孔(kong)(kong)(kong)(kong)徑,所以(yi)煤(mei)(mei)(mei)對(dui)甲(jia)(jia)烷的(de)吸(xi)(xi)(xi)附(fu)(fu)(fu)(fu)能 力與納米級孔(kong)(kong)(kong)(kong)隙(xi)結(jie)構(gou)密切相關. 結(jie)合圖 1 和表(biao)(biao) 1, 對(dui)比(bi)(bi)分(fen)析煤(mei)(mei)(mei)基(ji)活性(xing)(xing)(xing)炭(tan)(tan)孔(kong)(kong)(kong)(kong)隙(xi)結(jie)構(gou)的(de)改(gai)變(bian)(bian)對(dui)于甲(jia)(jia)烷吸(xi)(xi)(xi) 附(fu)(fu)(fu)(fu)的(de)影響,可(ke)知:酸式(shi)改(gai)性(xing)(xing)(xing)后(hou),煤(mei)(mei)(mei)基(ji)活性(xing)(xing)(xing)炭(tan)(tan) BET 比(bi)(bi)表(biao)(biao)面(mian)(mian)積(ji)、總(zong)孔(kong)(kong)(kong)(kong)容與微(wei)孔(kong)(kong)(kong)(kong)孔(kong)(kong)(kong)(kong)容均有明顯(xian)增加,而甲(jia)(jia) 烷吸(xi)(xi)(xi)附(fu)(fu)(fu)(fu)量卻明顯(xian)下(xia)降(jiang);堿(jian)式(shi)改(gai)性(xing)(xing)(xing)后(hou),煤(mei)(mei)(mei)基(ji)活性(xing)(xing)(xing)炭(tan)(tan) BET 比(bi)(bi)表(biao)(biao)面(mian)(mian)積(ji)、總(zong)孔(kong)(kong)(kong)(kong)容與微(wei)孔(kong)(kong)(kong)(kong)孔(kong)(kong)(kong)(kong)容均減少,而甲(jia)(jia)烷 吸(xi)(xi)(xi)附(fu)(fu)(fu)(fu)量卻有所增加 ;聯(lian)合改(gai)性(xing)(xing)(xing)后(hou) ,煤(mei)(mei)(mei)基(ji)活性(xing)(xing)(xing) 炭(tan)(tan) BET 比(bi)(bi)表(biao)(biao)面(mian)(mian)積(ji)、總(zong)孔(kong)(kong)(kong)(kong)容與微(wei)孔(kong)(kong)(kong)(kong)孔(kong)(kong)(kong)(kong)容均減少,甲(jia)(jia)烷吸(xi)(xi)(xi) 附(fu)(fu)(fu)(fu)量卻明顯(xian)增加. 分(fen)析以(yi)上結(jie)果可(ke)以(yi)得出,存在(zai)其(qi) 他(ta)因素(su)的(de)改(gai)變(bian)(bian)造成(cheng)(cheng)了對(dui)甲(jia)(jia)烷吸(xi)(xi)(xi)附(fu)(fu)(fu)(fu)的(de)抑(yi)制(zhi)作(zuo)用,且 在(zai)一定條件(jian)下(xia)這種抑(yi)制(zhi)作(zuo)用要強(qiang)于孔(kong)(kong)(kong)(kong)隙(xi)增加對(dui)甲(jia)(jia) 烷吸(xi)(xi)(xi)附(fu)(fu)(fu)(fu)能力的(de)促進作(zuo)用.
表面官能團對甲烷吸附的影響
由于煤基活性炭本身孔隙結構改變,處于開
放狀態,導致在改性過程中煤基活性炭表面生成
了更多含氧官能團,其總量多于改性后的原生結
構煤基活性炭.
酸式改性后,含氧官能團對甲烷的影響要大
于孔隙結構與比表面積的作用. 紅外光譜結果表
明,改性后煤基活性炭表面極性官能團數量明顯
增加,不利于非極性氣體甲烷的吸附. 結合甲烷吸
附量變化可發現,羧基與羥基對甲烷吸附的抑制
作用最明顯. 郇璇[27] 研究表明,酸性含氧官能團
為吸電子基團,表面含量增加后,活性炭與吸附質
之間作用降低,甲烷的有效吸附位降低,會造成吸
附量降低,與本研究結果一致.
堿性改性雖然造成塌孔和堵塞,微孔和中孔
的數量均下降,比表面積相應減少,但煤基活性炭
表面酸性官能團減少,表面極性基團減少. 這種改
變抵消了孔隙變化的抑制作用,因此對于甲烷的
吸附整體表現為促進作用. 可以看出,改性后官能
團的變化對甲烷吸附的影響要大于孔隙結構改變
的作用.
在聯合改性過程中,酸式改性使得煤基活性
炭表面孔隙增加,對甲烷吸附有一定的促進作用.
隨后堿式改性使得煤基活性炭表面極性降低,煤基活性炭表面非極性相對增大,甲烷吸附量明顯
增加. 故聯合改性后,煤基活性炭比表面積和微孔
都增大了,且表面非極性基團數量也相對較少,對
甲烷吸附整體表現為促進作用.
結論 (1)酸(suan)(suan)式改(gai)性(xing)(xing)(xing)后(hou)的(de)(de)煤基活性(xing)(xing)(xing)炭表(biao)(biao)面極性(xing)(xing)(xing)增(zeng)(zeng)強(qiang); 堿式改(gai)性(xing)(xing)(xing)后(hou)的(de)(de)煤基活性(xing)(xing)(xing)炭,酸(suan)(suan)性(xing)(xing)(xing)基團(tuan)含量(liang)減少,表(biao)(biao) 面非(fei)極性(xing)(xing)(xing)增(zeng)(zeng)強(qiang). (2)聯合改(gai)性(xing)(xing)(xing)后(hou)的(de)(de)煤基活性(xing)(xing)(xing)炭比表(biao)(biao)面積(ji)和(he)孔(kong) 容均明顯增(zeng)(zeng)大,其(qi)中比表(biao)(biao)面積(ji)增(zeng)(zeng)大 66.66%,總(zong)孔(kong)容 增(zeng)(zeng)大 30.89%;非(fei)極性(xing)(xing)(xing)官能(neng)團(tuan)增(zeng)(zeng)加,甲烷(wan)吸(xi)附(fu)(fu)量(liang)顯著 增(zeng)(zeng)加,相較于改(gai)性(xing)(xing)(xing)前提升 25.686%,且吸(xi)附(fu)(fu)量(liang)大于 單一的(de)(de)酸(suan)(suan)式改(gai)性(xing)(xing)(xing)或堿式改(gai)性(xing)(xing)(xing)的(de)(de)煤基活性(xing)(xing)(xing)炭. (3)孔(kong)隙結構和(he)表(biao)(biao)面官能(neng)團(tuan)共(gong)同決定了煤基 活性(xing)(xing)(xing)炭對甲烷(wan)的(de)(de)吸(xi)附(fu)(fu)作(zuo)用,其(qi)中表(biao)(biao)面官能(neng)團(tuan)的(de)(de)種 類和(he)數量(liang)是影響主要(yao)原因(yin),孔(kong)隙結構是次要(yao)原因(yin).
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