Role of water on attenuating HZSM-5 zeolite catalyst deactivation in low-pressure ethylene oligomerization

• Role of water in low pressure ethylene oligomerization at 275–375 °C. • Temperature-dependent interplay between water and acidity on reaction pathways. • At 375 °C, water limits the formation of C 7 (aromatic) hydrocarbons. • Water addition attenuates the extent of secondary reactions and coke formation. • The mesoporous matrix of HZSM-5 favors the diffusion of coke precursors-oligomers. This work focuses on the in-line low-pressure oligomerization of ethylene coming from sustainable sources (i.e. biomass, wastes or CO 2 ), where the presence of water in the reaction medium will play a key role. The experiments were performed in a fixed-bed reactor under the following operating conditions: 275–375 °C; 1.5 bar; space time, 5.4 g catalyst h mol C -1 ; ethylene flow rate of 37 cm 3 min −1 containing 10 vol% of H 2 O; time on stream, 5 h. Temperature was found to play an important role on product distribution and on the extent and nature of coke deposition. At low temperature (275 °C), water strongly competed with ethylene for Brönsted acid sites, suppressing oligomer condensation and thus, reducing total coke content. At intermediate temperature (325 °C), water favored hydrogen transfer and aromatization reactions to some extent, leading to a decrease in soft/hard coke distribution without altering the overall coke content. At high temperature (375 °C), although competitive adsorption of water was less pronounced, the moderation of strong acid sites suppressed aromatization (limiting the formation of hydrocarbons up to C 7 ). These results suggest the interest in co-feeding H 2 O with the aim of controlling the product distribution and coke deactivation, showing promising prospects for process scale-up.