The Influence of Active Phase Loading on the Hydrodeoxygenation (HDO) of Ethylene Glycol over Promoted MoS2/MgAl2O4 Catalysts

Abstract

The hydrodeoxygenation (HDO) of ethylene glycol over MgAl2O4 supported NiMo and CoMo catalysts with around 0.8 and 3 wt% Mo loading was studied in a continuous flow reactor setup operated at 27 bar H2 and 400 °C. A cofeed of H2S of typically 550 ppm was beneficial for both deoxygenation and hydrogenation and for enhancing catalyst stability. With 2.8-3.3 wt% Mo, a total carbon based gas yield of 80-100 % was obtained with an ethane yield of 36-50 % at up to 118 h on stream. No ethylene was detected. A moderate selectivity towards HDO was obtained, but cracking and HDO were generally catalyzed to the same extent by the active phase. Thus, the C2/C1 ratio of gaseous products was 1.1-1.5 for all prepared catalysts independent on Mo loading (0.8-3.3 wt%), but higher yields of C1-C3 gas products were obtained with higher loading catalysts. Similar activities were obtained from Ni and Co promoted catalysts. For the low loading catalysts (0.83-0.88 wt% Mo), a slightly higher hydrogenation activity was observed over NiMo compared to CoMo, giving a relatively higher yield of ethane compared to ethylene. Addition of 30 wt% water to the ethylene glycol feed did not result in significant deactivation. Instead, the main source of deactivation was carbon deposition, which was favored at limited hydrogenation activity and thus, was more severe for the low loading catalysts.

Hydrodeoxygenation (HDO) of Aliphatic Oxygenates and Phenol over NiMo/MgAl2O4: Reactivity, Inhibition, and Catalyst Reactivation

“…The amount of carbon deposited strongly depends on the time on stream (Figure 8). In line with previous reports [18,19], this is probably the main cause of deactivation. The severe carbon deposition is partly caused by a very high space velocity, which was chosen to facilitate steady state activity with a conversion below 100%.…”

“…TEM (Figure S8) indicated that the deposited carbon was present throughout the spent catalysts, which is in agreement with previous findings [41]. The carbon appeared crystalline in agreement with Raman spectroscopy data on similar catalysts [18]. The lattice distances were analyzed by performing fast Fourier transforms of several crystalline areas in the TEM images of spent catalysts, which showed the presence of the MgAl2O4 support, and indicated the presence of crystalline carbon as well.…”

“…The severe carbon deposition is partly caused by a very high space velocity, which was chosen to facilitate steady state activity with a conversion below 100%. If the liquid hourly space velocity (LHSV) is decreased to obtain full conversion, the carbon deposition is expected to occur at a lower rate than observed here, based on the results from previous work [18]. The high amount of carbon (13.6 wt %) deposited on the catalyst from the experiment with the cyclohexanol/ethylene glycol mixture, was affected by the lack of N 2 flushing at reaction temperature, as the experiment was terminated abruptly due to equipment malfunction.…”

“…Phenol, which was fed in a mixture with ethylene glycol, was not converted at the applied conditions over the sulfided NiMo catalyst. The only products detected in low yields from phenol were alkyl substituted phenols and coupling products (primarily 2-ethylphenol, 3-methylphenol, and benzofuran), which were ascribed to the catalytic activity of the support acid sites [18]. These non-deoxygenated coupling products were mainly formed during the first 30 h on stream at a total phenol-based carbon yield of up to 12%.…”

“…CO 2 can form from the water gas shift (WGS) reaction. The MgAl 2 O 4 support catalyzes dehydration and alcohol condensation reactions [18].…”