胺類處理之二氧化矽或碳氣凝膠於二氧化碳捕捉之應用

Amine-treated Silica or Carbon Aerogels for Applications on Carbon Dioxide Capture

莊承翰(Cheng-Han Chuang)

指導教授 ： 呂世源

國立清華大學/工學院/化學工程學系/碩士(2011年)

https://doi.org/10.6843/NTHU.2011.00630

摘要

近年來，全世界消耗大量的化石能源，提供工業生產或交通所需的動力來源，使得大氣中二氧化碳濃度大幅增加，因而造成全球暖化效應。為了減緩溫室效應的惡化，最主要的課題即是減少二氧化碳的排放量。目前，最常見的減碳方法是利用捕捉劑將二氧化碳捕捉下來並與其他氣體分離，減少其排放到大氣的量。
捕捉劑的種類有很多，最常見也最實用的是固體吸附材，因為分離過程簡單也不需要消耗太多能量。目前有很多研究是著重在利用介面活性劑和模板(template)合成的矽材，如SBA-15、MCM-41等等，這些材料的共同優勢是具有很高的比表面積，因此經過胺類處理以後便可以製備成二氧化碳吸附材。
本實驗室之前成功以溶膠-凝膠法(sol-gel)合成出高比表面積和孔洞體積的二氧化矽氣凝膠(silica aerogel)，其比表面積可高達1,051 m2/g左右。就我們所知，高比表面積的矽材中似乎還沒看到二氧化矽氣凝膠被報導過，因此我們以此為基材，經過胺類浸漬或是改質的處理，變成一種可再利用式的固體二氧化碳捕捉材。從以前實驗到現在的經驗，我們發現胺類浸漬過後的二氧化矽氣凝膠，其二氧化碳捕捉效率非常不理想，但若是經過胺類改質的二氧化矽氣凝膠，效率提升了不少，也因此二氧化矽氣凝膠後來的研究便著重在胺類改質的部分。我們考量到未來此類型的吸附材可能會應用在非純二氧化碳的環境下，因此檢測的時候我們設定吸附材樣品在二氧化碳佔了和氮氣混合的氣體5%(v/v)的環境下測定其二氧化碳的捕捉效率。在此條件下，我們所合出之無水改質的樣品，在25℃下二氧化碳的吸附量最高可達64 mg-CO2/g-sorbent左右，而有水改質的樣品在25℃下二氧化碳的吸附量最高可達61.6 mg-CO2/g-sorbent左右。另外，我們發現此材料吸附二氧化碳的速率很快，而且在吸脫附循環的穩定度表現也很可觀，甚至到了6次循環以後材料對二氧化碳的吸附量依舊沒有明顯的減少，換句話說，在混合氣體環境下，此材料在二氧化碳捕捉方面很具有優勢。
同時，我們也發現有許多文獻積極在研究以碳為基材的二氧化碳吸附材，如奈米碳管，這些碳材的共同特性為具有高比表面積的孔洞材料。就目前我們所知，似乎還沒有有關碳氣凝膠應用在二氧化碳捕捉的文獻被報導過，有鑑於此，我們嘗試利用高比表面積的碳氣凝膠作為基材，進行胺類浸漬或改質的處理使之成為二氧化碳捕捉材。但我們也發現此類材料在混合氣體環境時，二氧化碳的吸附量並不理想，這也意味著若將此吸附材應用在混合氣體下，對二氧化碳選擇性的問題可能會成為不可忽略的隱憂。

關鍵字

氣凝膠 ； 二氧化碳捕捉 ； 胺類處理 ； 改質 ； 浸漬

並列摘要

Currently, with a large amount of fossil fuel consumption throughout the world, most of which are required for industry and transportation, the carbon dioxide (CO2) concentration of the atmosphere has been increasing to harmful levels, resulting in devastating global warming. Thus, the key to mitigating the acceleration of global warming is to reduce CO2 emission to atmosphere. Currently, the most common way to decrease the emission of CO2 is using adsorbents to capture CO2, thus separating it from other gases.
Owing to the simple separation process that costs moderate energy, solid adsorbents are the most practical choice among a variety of adsorbents. Many current researches focus on silica materials, synthesized with surfactant and template such as SBA-15, MCM-41, etc., which possess high specific surface areas as their common advantage. These materials can serve as effective CO2 adsorbents after amine treatment.
In our lab, we have successfully synthesized silica aerogels through sol-gel methods, featuring high specific surface areas and large pore volumes. To the best of our knowledge, research efforts have not yet been made on the utilization of silica aerogels for CO2 capture. Hence, we use silica aerogels as the basic material and transform it into a recyclable solid CO2 adsorbent through either amine-impregnation or amine-modification process. From our results, amine-impregnated silica aerogels were ineffective in CO2-capture, but the CO2 capture efficiency improved significantly for amine-modified silica aerogels. Hence, we focus on the amine-modification process for silica aerogels in our work, with the understanding that the possible application of this material is in an environment of gas mixtures. Therefore, in measuring the CO2 capacity, we set the environment as 5% CO2 (v/v). The highest CO2 capacity obtained was 64 mg-CO2/g-sorbent at 25℃ for none-water-treated samples and 61.6 mg-CO2/g-sorbent at 25℃ for water treated samples. Besides, we observed that this material showed a high rate of CO2 capture and a great stability in the adsorption-desorption cycle manifested with an excellent CO2 capacity even at the 6th cycle. In other words, this material has a great potential for CO2 capture.
Meanwhile, many researches on CO2 adsorbents focus on carbon-based materials such as carbon nano-tubes, which are known for their high specific surface areas. We also tried to turn carbon aerogels with high specific surface areas into CO2 adsorbents with the amine-impregnation or amine-modification process. However, the CO2 capacity of this type of adsorbent becomes worse in gas mixture environments. It is essential to improve the CO2 selectivity of this adsorbent so that it may prove suitable for applications in gas mixture environments.

參考文獻

洪錦德, “氣膠法合成之中孔洞矽值材料特性分析及其空氣汙染應用”, 國立交通大學環境工程研究所博士論文 (2009)

林佑勳, “含氧化錳複合氣凝膠在超級電容器之應用”, 國立清華大學化學工程研究所碩士論文 (2009)

徐米君, “製備較高比表面積之矽酸鋰(Li4SiO4)於二氧化碳捕捉之應用”, 國立清華大學化學工程研究所碩士論文 (2008)

魏得育, “二氧化矽氣凝膠與複合氣凝膠之製備與物理性質探討”, 國立清學化學工程研究所碩士論文 (2006)

Al-Muhtaseb, S.A., and Ritter, J.A., "Preparation and properties of resorcinol-formaldehyde organic and carbon gels," Adv Mater. 15, 101 (2003)