鉬基多孔性觸媒應用於合成氣產製烷類及醇類之研究

Production of Alkanes and Alcohols from Syngas over Porous Mo-based Catalyst

劉冠郁(Kuan-Yu Liu)

指導教授 ： 張慶源

國立臺灣大學/工學院/環境工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.02722

摘要

因應我國能源自給之困難，本研究以高溫高壓觸媒床合成氣(CO及H2)重組反應產製液體燃料，以期未來能應用於生質物氣化產品合成氣之進一部利用，除了可解決能源問題外亦可降低環境之汙染。
本研究之實驗使用連續式高壓觸媒填充床(high pressure catalytic packed bed, HPCPB)將合成氣轉化為液體燃料。以自製比表面積達800 m2/g中孔性分子篩SBA-15(Santa Barbara amorphous-15)做為觸媒之擔體，批覆Mo2C觸媒於顆粒表面後，將使原本SBA-15之晶型結構稍微掩蓋，另觸媒表面鉬含量達20 wt.%仍具500 m2/g之高比表面積。研究結果顯示：觸媒床反應器中進行只填充SBA-15，並未產生合成氣之重組反應；而填充觸媒Mo2C/SBA-15後即有提高CO轉化之效果，且醇類產物之選擇性(selectivity, S)亦高。研究中探討鉬含量對合成氣重組之影響，結果顯示當鉬含量提升時，CO之轉化率(conversion of CO, XCO)可大幅之上升。另外亦針對其他重要操作參數之影響進行探討，包括：反應器溫度(T)，壓力(P)及氣體流量(QG)。參考條件為：T = 523 K, P = 450 psi, QG = 60 mL min-1, 20% Mo2C/SBA-15觸媒量(mS) = 5 g，觸媒體積(VS) = 3.76 mL。實驗結果得知，反應溫度由473 K提升至573 K，XCO由10.76% 提高至59.75%，增加48.99%，但醇類產物之選擇性(SOH) 由92.32% 下降至13.81%，降低78.51%。而壓力參數設定由250 psi增高至450 psi時，並無顯著之影響，唯乙醇之産率(yield of ethanol (EtOH), YEtOH)由1.18%提高至1.52%，有些微之增加。合成氣之進氣流量影響氣體之空間流速(gas hourly space velocity, GHSV = QG/VS)，GHSV之倒數即氣體在反應器中與觸媒之接觸時間。當QG由90降低至30 mL min-1時，XCO雖可由24.82% 提高至49.15%，但會使高碳數之醇類分解為低碳數之烷類及醇類，因而高碳數醇類產物之選擇性由5.32%降低至3.34%。故在氣體流量之選擇上，須考慮目標產物為何，進而對其做一適切之選擇。另本實驗之觸媒失活試驗結果顯示，觸媒之使用時間在96小時內仍可維持其80%以上之活性。且由使用前後觸媒之掃描式電子顯微鏡(scanning electronic microscope, SEM)觀察結果，可知觸媒之失活原因在於觸媒表面之積碳所致。

關鍵字

合成氣 ； 液體燃料 ； 連續式高壓觸媒填充床 ； SBA-15 ； Mo2C ； 合成氣重組反應 ； 失活試驗

並列摘要

In order to reduce the stress of energy demand and pollution, reforming of syngas (CO and H2), which may be obtained from biomass gasification process, can produce liquid fuel and reduce green house gases (GHGs) emission.
This study examined the feasibility and operation performance of reforming of syngas via high pressure catalytic packed bed (HPCPB) process. Mesoporously molecular sieves of Santa Barbara amorphous-15 (SBA-15), which has small paticle size of 31.75 μm and high BET (Brunauer- Emmett- Teller) suffice area of 800 m2/g was used as the support of catalyst. Catalytic species of Mo2C was well dispersed on the support. The blank experiment indicated no reavtion between SBA-15 and syngas. The Mo2C catalyst containg Mo 20 wt.% exhibits significant conversion of CO (XCO). Main system parameters investigated include temperature (T), pressure (P) and the influent gas flow rate (QG). In addition to XCO, the production rate, selectivity and yield were also elucidated. The T and QG have more significant influences on the system performance than P. The result shows a higher T gives higher XCO, while lower selectivity of alcohols. A low QG, which means gas has long contact time with catalyst, improves the XCO, however it can cause the decomposition of butnol to low carbon content products. To select suitable QG, one should consider which alcohol product is the target. The increase of pressure from 250 to 450 psi examined in this study has no obvious enhancing effect as compared to other operation parameters. The catalytic deactivation test shows that the catalyst can maintain 80% activity after 96 hr. The SEM observation indicated the carbon accumulation on the catalyst surface, which may thus cause the deactivation.

並列關鍵字

Syngas ； liquid fuel ； high pressure catalytic packed bed ； SBA-15 ； Mo2C ； deactivation

參考文獻

37.杜文凱 (2009). "以高週波電漿及觸媒催化程序熱處理稻稈生質廢棄物之研究." 臺灣大學環境工程學研究所博士學位論文(2009 年).

38.楊宇傑 (2007). "生質廢棄物電漿熱裂解之研究." 臺灣大學環境工程學研究所碩士學位論文(2007 年): 1-135.

1.Bwoker, M. (1992). "On the mechanism of ethanol synthesis on rhodium." Catalysis today 15(1): 77-100.

2.Cherubini, F., N. D. Bird, A. Cowie, G. Jungmeier, B. Schlamadinger and S. Woess-Gallasch (2009). "Energy-and greenhouse gas-based LCA of biofuel and bioenergy systems: Key issues, ranges and recommendations." Resources, Conservation and Recycling 53(8): 434-447.

4.Egbebi, A. and J. J. Spivey (2008). "Effect of H2/CO ratio and temperature on methane selectivity in the synthesis of ethanol on Rh-based catalysts." Catalysis Communications 9(14): 2308-2311.