Pyrolysis and catalytic upgrading of Citrus unshiu peel

다국어 초록 (Multilingual Abstract)

In this study, the pyrolysis of Citrus unshiu peel and catalytic upgrading of its pyrolyzates were carried out. Thermal property of Citrus unshiu peel was investigated using a thermogravimetric analysis (TGA). Thermogravimetric (TG) curves at heating rate of 10, 20, and 30°C/min showed that the pyrolysis of Citrus unshiu peel was happened mainly between 150-590°C. Differential thermogravimetric (DTG) analysis curves illustrated that the pyrolysis of mandarin peel has a multi-step process, consisting of water desorption, the decomposition of pectin, hemicellulose, cellulose and lignin, and stabilization of the residual char. The apparent activation energies analyzed by a model free kinetic analysis method were ranged between 119 and 406 kJ/mol, depending on the pyrolytic conversion (x).
Non-isothermal evolved gas analysis-MS (EGA-MS) also revealed five evolved gas emission temperature zones which consisted with the vaporization of water and limonene, pyrolysis of pectin, hemicellulose, and cellulose, and char stabilization.
Multi shot-GC/MS revealed the specific pyrolysis products of each component of Citrus unshiu peel. Limonene was vaporized with water below 140°C. Large amounts of methanol, acetic acid, 5-hydroxymethylfurfural, 3,5-dihydroxy-6-methyl-2,3-dihydro-4H-pyran-one, and p-vinylguaiacol were produced between 140 and 280°C, at which temperature range pectin and hemicellulose decomposed. The specific pyrolyzates of cellulose formed between 211 and 360°C, and a small amount of lignin pyrolyzates were also detected over a wide temperature range, 141-360°C. At temperatures higher than 360°C, small amounts of aromatics were produced as the by-products of char stabilization.
For the catalytic upgrading of Citrus unshiu peel, a tandem μ-reactor-GC/MS which consists of sequential two furnaces, 1st furnace for pyrolysis and 2nd furnace for catalytic upgrading of pyrolyzates, was used. Pyrolyzates of Citrus unshiu peel such as alcohols, ketones, furans, were upgraded to aromatic hydrocarbons by the use of catalysts such as HZSM-5 (SiO2/Al2O3: 23, 50), HBETA (SiO2/Al2O3: 25), HY (SiO2/Al2O3: 30), and Al-MCM-41 (SiO2/Al2O3: 20). Compare to wood powder, pyrolyzates of Citrus unshiu peel produced higher amounts of aromatic hydrocarbons over HZSM-5(23). Among various catalysts, HZSM-5(23) and HBETA(25) showed highest aromatic yields, 6.78 C% and 9.69 C% respectively, however, HBETA(25) produced large amounts of undesirable PAHs (3.59%) such as naphthalene and methylnaphthalene. During the sequential catalytic upgrading test, monocyclic aromatic BTEXs (benzene, toluene, ethylbenzene, xylenes) yields over HBETA(25) were reduced faster than over HZSM-5(23) due to the faster deactivation of HBETA(25) and this indicates that HZSM-5(23) is the more stable catalyst for the production of monocyclic aromatics.

국문 초록 (Abstract)

본 연구에서는 감귤껍질의 열분해 및 촉매 개질화를 수행하였다. 열중량 분석기를 이용한 열분해 특성 분석 결과, 감귤껍질은 150-590°C 사이에서 주로 분해되었으며, 펙틴, 헤미셀룰로오스, 셀룰로오스, 리그닌 분해구간과 촤의 안정화 구간이 존재하였다. 동역학 분석을 통해 얻은 활성화 에너지는 전환율에 따라 119-406 kJ/mol 의 분포를 가졌다.
비등온 휘발가스분석(EGA) 분석 결과에 의하면 수분과 리모넨 휘발 구간, 펙틴, 헤미셀룰로오스, 셀룰로오스 분해구간과 촤의 안정화에 이르는 총 5개의 휘발가스 생성 온도 구간이 존재하였다. 멀티샷-GC/MS분석을 통해 감귤껍질의 열분해 온도 구간별 생성 화합물을 확인한 결과, 리모넨은 140°C 이전에 물과 함께 휘발되었으며 메탄올, 아세트산, 하이드록시메틸퓨란, 비닐 구아이아콜과 같은 성분이 펙틴과 헤미셀룰로오스가 분해되는 140-280°C 사이에서 생성되었다. 211-360°C 사이에는 셀룰로오스의 분해 산물이 주로 분포하였으며 소량이지만 리그닌 분해 산물은 141-360oC에 이르는 넓은 온도 범위에서 생성되었다. 360°C 보다 높은 열분해 온도 구간에서는 촤 생성 과정의 부산물인 방향족 화합물이 소량 생성되었다.
감귤껍질 열분해 산물의 촉매 개질화를 위해 열분해와 촉매 개질화 및 반응 생성물 분석을 한 시스템에서 수행할 수 있도록 고안된 텐덤 마이크로 반응기- GC/MS를 사용하였다. 알코올, 케톤, 퓨란류를 다량 함유하고 있는 감귤껍질 열분해 산물은 HZSM-5 (SiO2/Al2O3: 23, 50), HBETA (SiO2/Al2O3: 25), HY (SiO2/Al2O3: 30), 그리고 Al-MCM-41 (SiO2/Al2O3: 40)과 같은 촉매에 의해 방향족 화합물로 전환되었다. 또한 HZSM-5(23) 촉매 하에서 방향족 화합물 생성량을 비교해 본 결과, 나무에 비해 감귤껍질이 더 많은 양의 방향족 화합물을 생성하였다. 본 연구에서 사용된 촉매 가운데 HZSM-5(23)과 HBETA(25)가 많은 양의 방향족 화합물 생성량(각각 6.78 탄소%, 9.69 탄소%)을 보였으나HBETA(25)의 경우에는 나프탈렌과 같은 다환방향족화합물의 생성량(3.59 탄소%) 또한 많았다.
연속 촉매 개질화 실험을 통해 촉매 반응의 비활성화를 확인한 결과, HZSM-5(23) 보다 HBETA(25)에서BTEX(벤젠, 톨루엔, 에틸벤젠, 자일렌) 수율의 감소가 더 빠르게 진행되었고 연속 실험 후 생성된 코크(coke)의 양 또한 HBETA(25)가 현저하게 많은 것으로 보아 본 실험에서 사용된 촉매 중 HZSM-5(23)가 BTEX 생산을 위한 가장 안정된 촉매임을 확인할 수 있었다.

목차 (Table of Contents)

• Chapter Ⅰ. Introduction 1
• Ⅰ-1. Research background 1
• Ⅰ-2. Research purpose 3
• Ⅰ-3. Expected effects and application 4
• Ⅰ-4. Scope of present work 4
• Chapter Ⅱ. Literature review 6
• Ⅱ-1. Biomass resources 6
• Ⅱ-2. Citrus unshiu peel 8
• Ⅱ-3. Biomass conversion technologies and pyrolysis 9
• Ⅱ-4. Biomass pyrolysis 10
• Ⅱ-5. Catalyst 16
• Ⅱ-6. Catalytic upgrading of biomass pyrolysis oil 17
• Ⅱ-7. Kinetic analysis 20
• Ⅱ-7-1. Friedman method 21
• Ⅱ-7-2. Ozawa method 22
• Ⅱ-7-3. Kissenger method 24
• Ⅱ-8. Analytical pyrolysis 26
• Ⅱ-9. Analytical catalytic pyrolysis 28
• Chapter Ⅲ. Experimental methods 31
• Ⅲ-1. Physico-chemical properties of Citrus unshiu peel 31
• Ⅲ-1-1. Samples 31
• Ⅲ-1-2. Proximate, ultimate analysis, heating value measurement 31
• Ⅲ-1-3. Lignocellulosic composition analysis 32
• Ⅲ-2. Kinetic analysis 32
• Ⅲ-2-1. Thermogravimetric analysis and Ozawa method 32
• Ⅲ-3. Non-isothermal pyrolysis of Citrus unshiu peel 33
• Ⅲ-3-1. EGA-MS analysis 33
• Ⅲ-3-2. Multi shot-GC/MS analysis 35
• Ⅲ-4. Catalytic upgrading of Citrus unshiu peel thermal products 35
• Ⅲ-4-1. Catalyst preparation 35
• Ⅲ-4-2. Tandem μ-reactor-GC/MS analysis 39
• Chapter Ⅳ. Results and discussion 43
• Ⅳ-1. Physico-Chemical properties of Citrus unshiu peel 43
• Ⅳ-2. Kinetic analysis 46
• Ⅳ-3. Non-isothermal pyrolysis of Citrus unshiu peel 59
• Ⅳ-3-1. EGA-MS Analysis 59
• Ⅳ-3-2. Multi-shot GC/MS Analysis 62
• Ⅳ-4. Catalytic upgrading of Citrus unshiu peel 69
• Ⅳ-4-1. Pyrolysis without any catalyst 69
• Ⅳ-4-2. Catalytic upgrading of pyrolyzates over zeolites 71
• Ⅳ-4-3. Gas, oil, char, and coke yield 78
• Ⅳ-4-4. The effect of catalyst bed temperature over HZSM-5(23) 80
• Ⅳ-4-5. Deactivation of HZSM-5(23) and HBETA(25) during catalytic upgrading of Citrus unshiu peel pyrolyzates 83
• Chapter Ⅴ. Conclusion 87
• References 92
• Summary (in Korean) 105