Study on conversion of glucose and xylose to furan derivatives using the modified solid acid catalysts

Abstract

퓨란계 화합물은 차세대 바이오연료 및 화학물질로써 그 활용 가치가 높아 주목 받고 있다. 특히 Ethoxymethyl furfural (EMF)과 alkoxymethyl furan은 바이오에탄올과 비교했을 때 (6.1 kWh/l, 20 MJ/kg)높은 연료 물성을 띄어 주목 받고 있다 (EMF: 8.7 kWh/l, alkoxymethyl furan: 27 MJ/kg). 본 연구에서는 글루코오스와 자일로오스의 one-pot 전환 반응을 통해 각각 EMF, alkoxymethyl furan을 생산하였다. 촉매로는 Brønsted acid인 Amberlyst 15와 주석 첨가를 통해 Lewis acid를 띈 제올라이트 베타를 사용하였다. 제올라이트 베타는 알루미늄 제거 반응과 주석 첨가 반응을 통해 개질 되어 Sn-BEA로 명명하였다. 개질된 제올라이트의 mesopores는 그대로 유지되었으며 알루미늄 제거로 인해 Si/Al 비율은 38에서 520까지 증가하였다. X-ray diffraction 결과 제올라이트 개질 이후에도 제올라이트의 결정 구조는 크게 바뀌지 않은 것을 확인하였다. 제올라이트와 Amberlyst 15의 산 촉매 특성은 NH3-Temperature programmed desorption을 통해 측정되었으며 제올라이트 개질에 따라 Brønsted 특성이 감소하는 것으로 확인되었다. 글루코오스로부터 EMF로의 One-pot 전환 반응의 반응조건은 반응온도 180-200℃, 반응시간 10-30분 촉매는 Sn-BEA (0.025 g)+Amberlyst 15 (0.025 g), Amberlyst 15 (0.05 g), Sn-BEA (0.05 g)을 사용하였다. EMF의 최대 생산 수율은 반응온도 190℃, 반응시간 10분, Sn-BEA+Amberlyst 15 조건에서 29.37%를 달성하였다. 상기 조건에서 촉매 비율을 달리하여 실험한 결과 Sn-BEA와 Amberlyst 15의 질량비가 1:1일 때 EMF의 수율이 가장 높은 것으로 확인되었다. 자일로오스로부터 alkoxymethyl furan으로의 one-pot 전환 반응의 조건은 반응온도 170-190℃, 반응시간은 10분으로 설정되었고 촉매는 앞선 글루코오스의 전환 조건과 동일하게 설정되었다. 실험 결과 propylene, lactate와 같은 경쟁 산물의 발생으로 alkoxymethyl furan의 생산이 확인되지 않았다. 촉매의 재사용 실험은 furfural로부터 alkoxymethyl furan의 전환 반응을 통해 평가되었고 두 번째 사용까지는 활성이 유지되었으나 세 번째부터 활성이 약간 감소하였음이 확인되었다.

Furan derivatives is considered as value added-chemical due to its high valorization to chemical or biofuel. Especially, Ethoxymethl furfural (EMF) and Alkoxymethyl furan are considered as promising biofuel due to its high fuel properties (EMF: 8.7 kWh/l, alkoxymethyl furan: 27 MJ/kg) compared to bioethanol (6.1 kWh/l, 20 MJ/kg). In this study, one-pot conversions from glucose to EMF and xylose to alkoxymethyl furan were conducted. Brønsted acid Amberlyst 15 and Lewis acid tin impregnated zeolite beta (Sn-BEA) were adopted in one-pot conversion reaction. Zeolite beta (NH4-BEA) was modified to Sn-BEA by dealumination followed by tin impregnation. By zeolite modification, micropores surface area increased, while mesopores area, pore volume, and pore diameter remained. By XRF analysis, Si/Al ratio increased after dealumination process from 38 to 520. X-ray diffraction pattern was remained constantly after zeolite modification process. Acidic properties of solid acid catalysts (zeolite, Amberlyst 15) were measured by Temperature-programmed desorption analysis. NH3 molecules were used for probe molecule, indicating that Brønsted acidity of zeolite decreased by modification process. One-pot conversion of glucose to EMF conducted at reaction temperature from 180 to 200℃, reaction time from 10 to 30 min. Sn-BEA (0.025 g) with Amberlyst 15 (0.025 g), Amberlyst 15 (0.05 g), and Sn-BEA (0.05 g) used as catalysts. Maximum yield of EMF (29.37%) achieved by 190℃ of reaction temperature, 10 min of reaction time, and Sn-BEA with Amberlyst 15 as a catalyst. Lewis/Brønsted acidity ratio was changed in 190℃ of reaction temperature and 10 min of reaction time. As a result, Sn-BEA (0.025 g) with Amberlyst 15 (0.025 g) performed highest EMF yield. Alkoxymethyl furan conversion from furfural conducted at reaction temperature from 170 to 190℃, 10 min of reaction time, and Sn-BEA (0.05 g) as a catalyst. Highest alkoxymethyl furan yield (36.73%) achieved at 190℃ of reaction temperature. One-pot conversion of xylose to alkoxymethyl furan conducted at reaction temperature from 170 to 190℃, 10 min of reaction time, and Sn-BEA (0.025 g) with Amberlyst 15, Amberlyst 15 (0.05 g) and Sn-BEA (0.05 g) used as catalysts. The results showed that there was no alkoxymethyl production from xylose in one-pot conversion reaction in all reaction condition due to formation of propylene and lactate. Reusability of Sn-BEA conducted by estimating activity of furfural to alkoxymethyl furan conversion. Catalytic activity remained until two time uses, and slightly decreased in three time uses.