Green Ethylene Catalytic Production from Oat Hulls Alcohol and Its Downstream Conditioning
Resent progress in synthesis of highly valuable PE-carbon nanotubes composite materials has stimulated search for small-scale ethylene production from renewable non-edible resources. Lignocellulosic biomasses, such as wheat straw, oat hulls and other agricultural residues are attractive materials for bioethanol (bioEtOH) production, due to its worldwide availability and low cost. Generally, the bioEtOHbased “green” C2H4 can be produced in four steps: biomass fermentation to a crude bioEtOH; rectification to purify the EtOH; catalytic dehydration of EtOH; treatment of the crude C2H4 and production of the target-grade C2H4. Results of catalytic conversion of crude and purified bioEtOH on specially designed and prepared
alumina catalysts, followed by conditioning of the crude C2H4 to the grade appropriate for synthesis of functional polymer-nanocarbon composites are discussed in this paper. The crude bioEtOH that was synthesized from oat hulls in IPCET SB RAS (Russia, Biysk) had been rectified and used in the dehydration process as 96 % bioEtOH. On an anhydrous EtOH, mass concentration of organic impurities in bioEtOH was 0.02-11 g/L, primarily as acetaldehyde and propanol. If their content is more than 0.02 g/L, this reduces selectivity to C2H4 in bioEtOH dehydration, and subsequently, increases content of oxygenates in the crude C2H4 which complicates C2H4 conditioning. In ethylene intended for PE-based composite materials synthesis, the content of oxygen-containing substances should not exceed 6.5…700 ppm. Among them, CO and H2O contents are the most strictly limited, to 1…50 ppm and 3…300 ppm, respectively. The crude ethylene produced on the pilot setup by catalytic dehydration of EtOH contained (mol. %, ave.): 45 % C2H4, 53 % H2O, 1.4 % oxygenates (aldehydes, ethers, alcohols), 0.3 % alkenes and H2, 0.1 % olefins, and 0.03 % COx. For downstream conditioning of C2H4, water condensation at 283 K, cryogenic cooling at 270-233 K, catalytic CO oxidation and final adsorption of H2O, VOCs and CO2 have been used. Catalytic dehydration process, in conjunction with downstream ethylene conditioning was studied; the optimal operation conditions for C2H4 production of the target quality were developed.