Ethylene production via catalytic dehydration of diluted bioethanol: A step towards an integrated biorefinery

Abstract

After a preliminary thermodynamic investigation, proper operating conditions have been selected to maximise ethylene productivity by ethanol dehydration and limit side products such as coke and higher olefins or oxygenates. We focused on the possibility to operate with a diluted bioethanol solution (ca. 50 wt%), which represents a promising and convenient raw material, obtainable by simple flash concentration of the fermentation broth. Furthermore, water addition to the ethanol dehydration reactor may help preventing catalyst coking and diethyl ether formation, although affecting the thermodynamic products distribution. A proof of concept for an ethanol dehydration process using diluted ethanol is also provided through process simulation. Catalysts based on a BEA zeolite have been compared, characterised by different acidity imparted by dealumination treatments. Ni addition in variable loading helped suppressing undesired byproducts, difficult to separate from ethylene. For instance, no trace of diethyl ether nor acetaldehyde has been observed for the Ni-loaded samples under optimised working conditions. Catalyst characterisation by FT IR allowed correlating a high selectivity to ethylene with the acid sites nature of the catalyst, whereas the presence of extraframework Lewis acidic sites induced faster coke formation. Durability was finally checked on the most active and selective catalyst evidencing stable operation for 80 h-on-stream and without evidence of coke deposition, as determined after characterisation of the spent samples. A γ-Al2O3 catalyst has been tested as benchmark under the same conditions

Process Simulation for the Design and Scale Up of Heterogeneous Catalytic Process: Kinetic Modelling Issues

“…As the complexity of the reactions carried out in the process increases, this becomes one of the key issues to be settled prior to process design. In the following, we will consider the emblematic case of ethanol valorization into hydrogen or ethylene, as a pathway to the biorefinery exploitation [18][19][20][21]. In this view, a biomass-derived raw material is used to provide important chemicals/fuels in a more sustainable way.…”

Insight into Three‐Coordinate Aluminum Species on Ethanol‐to‐Olefin Conversion over ZSM‐5 Zeolites

“…The main difference between HZ‐1 and HZ‐2 zeolites is the presence of larger amounts of three‐coordinate Al 3+ species in HZ‐2 zeolite as described above. In the catalytic dehydration of ethanol at high temperature, previous work reported that BAS are active sites, while the presence of EFAl species induces the side‐reaction such as aromatics formation . However, the introduction of the dominant Al 3+ species into zeolite in this research showed the extremely high selectivity to ethylene and nearly no unsteady‐state period.…”

“…For comparison, the formation of aromatics ( δ 13C =127–135 ppm) on HZ‐1, was only observed after 2 h reaction, which having almost twice more BAS for oligomerization and aromatization. This is in agreement with a previously report on H‐ZSM‐5 that the presence of strong LAS in high content can facilitate the formation of aromatics . The formation aromatics are widely accepted as carbon pool intermediates to promote the generation of carbenium ions.…”

Recent research progress on bio‐oil conversion into bio‐fuels and raw chemicals: a review

“…A wide range of fuels and raw chemicals conventionally produced from petroleum can be obtained from these raw materials. Bio‐ethanol is well‐known for its potential as an alternative fuel, and also noteworthy is the technological development of bio‐ethanol conversion into hydrocarbons, chemical platforms, and H 2 (via steam reforming) . However, bio‐ethanol valorization is limited by the availability of fermentable biomass, given that sugars production from lignocellulosic biomass (which would not interfere with the human and animal feed chain) is still under development …”