Hydrodeoxygenation of pyrolysis oils derived from kraft lignin using - PDF document

1 Hydrodeoxygenation of pyrolysis oils der
Hydrodeoxygenation of pyrolysis oils derived from kraft lignin using noble metal catalysts in a continuous flow reactor Jinho Lee 1 , Jeong - Myeong Ha 1 , Dong Jin Suh 1 , Jungho Jae 2 * 1 Korea Institute of Science and Technology, Seoul 02792, Republic of Korea 2 School of Chemical and Biomolecular Engineering, Pusan National University, Busan 46241 , Republic of Korea *jh.jae@pusan.ac.kr Introduction The hydrodeoxygenation (HDO) of pyrolysis oils derived from lignin is considered to be the most effective method f or improving the quality of oil by selectively removing oxygen functionalities [1]. Although the effectiveness of noble metal - b ased catalysts such as Pd, Ru, RuRe or PdFe for the HDO of lignin model compounds (e.g., phenols ) are demonstrated, HDO studies w ith real pyrolysis oil are relatively unexplored [2 - 3]. Due to its complex composition and mineral impurities such as sulfur, the activity and stability of the catalysts for the HDO of pyrolysis oil would be significantly different from those for the model compounds. In this work, HDO of pyrolysis - oils derived from kraft lignin over carbon - supported noble metal catalysts (i.e., Ru, Pd , RuRe ) was studied using a continuous flow trickle bed reactor system. The effects of reaction temperature and space velocit y were investigated, and a detailed analysis of the reaction products were performed to understand the fundamental reaction chemistry. The spent RuRe/C catalysts were also studied to elucidate the main cause of catalyst deactivation. Materials and Methods Pyrolysis oil was obtained from fast pyrolysis of kraft lignin at 500 ° C in a bench - scale fixed bed reactor. 5 wt% Pd/C and 5 wt% Ru/C were purchased from Alfa Aesar. Bimetallic RuRe catalysts with 4 wt% Ru and 3.64 wt% Re content were prepared by success ive impregnation with an aqueous solution of RuCl 3 and NH 4 ReO 4 . This metal loading was found to be the optimal composition of the RuRe catalyst in our previous study [2]. HDO of lignin pyrolysis oil was performed in a fixed bed reactor, and the size of the reactor tube was 18 mm ID and 14 cm in length. For a typical run, a reactor was loaded with a RuRe/C catalyst of 4 - 8 g and treated with hydrogen at 350 ° C for 2 h. The reactor was then pressurized to 100 bar , and the pyrolysis - oil/tetrahydrofuran mixture (50:50 vol%) was fed to the reactor with H 2 . Results and Discussion Catalyst screening results revealed that rhenium - promoted Ru/C catalyst exhibited considerably higher deoxygenation activity compared to unprompted Ru and Pd. Thus, RuRe/C was selected as the model catalyst for parameter study. The yield of liquid product and the degree of deoxygenation of pyrolysis - oil were strongly dependent on the reaction temperature and weight hourly space velocity (WHSV). At 300 ° C, the liquid yield was very low, and the majority of carbon was deposited on the surface of the catalyst, indicating that strong adsorption of phenolics on active sites makes catalyst deactivation more severe at lower reaction temperature. In contrast, at 350 ° C or above, the liquid products were biphasic mixtures composed of an organic phase and aqueous phase , and the organic phase primarily consisted of cyclic alkanes (naphthenes) ranging from C6 to C20 as evidenced by GCxGC - MS and 2D - HSQC NMR analyses of the organic phase. Although higher temperature (i.e, 400 ° C) leaded to an enhanced deoxygenation of pyrolysis - oils (i.e., lower O/C ratio), the organic phase yield decreased due to the cracking of oils to light gases (C2 - C6). Low WHSV (0.2 h - 1 ) was also crucial to achieve a high degree of deoxygenation of pyrolysis - oil and prolong the catalyst lifetime. Catalyst deactivation and reactor plugging by tar formation were observed at high WHSV (~1.0 h - 1 ) even after ~10 h TOS. The characterization of spent Ru Re/C catalyst with ICP and HR - TEM reve aled the existence of sulfur species on the catalyst surface due to the high sulfur impurities in the lignin oil . XPS analysis confirmed the formation of RuS 2 and ReS 2 phase s in the catalyst . In addition , TGA analysis revealed the presence of high amount o f coke on the spent catalyst. Overall, this study suggests that the catalyst stability is the main issue in the HDO of real lignin oils rather than catalyst activity for practical application. Figure 1. GCxGC - MS analysis of liquid products obtained from HDO of lignin oils at different WHSV. Significance This study re ports on the hydrodeoxygenation (HDO) results of pyrolysis oils derived from kraft lignin over several noble metal catalysts (i.e., Pd, Ru, RuRe) using a continuous flow reactor. Although car bon - supported RuRe catalyst exhibited considerably high activity for the HDO of real lignin oils, severe deactivation was observed even after 20 h time - on - stream due to sulfur poisoning and coking. References 1. Saidi, M., Samimi, F., Karimipourfard, D., Nim manwudipong, T., Gates, B.C., Rahimpour, M. R., Energy Environ. Sci. 7 103 (2014) 2. Kim, M., Ha, J. - M., Lee, K. - Y., Jae, J., Catal. Commun. 86 113 (2016) 3. Jung, K.B., Lee, J., Ha, J. - M., Lee, H., Suh, D.J., Jun, C. - H., Jae, J., Catal. Today 303 130 (2018)