Design and operation of integrated pilot-scale dimethyl ether synthesis system via pyrolysis/gasification of corncob

The integrated pilot-scale dimethyl ether (DME) synthesis system from corncob was demonstrated for modernizing utilization of biomass residues. The raw bio-syngas was obtained by the pyrolyzer/gasifier at the yield rate of 40-45 Nm³/h. The content of tar in the raw bio-syngas was decreased to less than 20 mg/Nm³ by high temperature gasification of the pyrolysates under O₂-rich air. More than 70% CO₂ in the raw bio-syngas was removed by pressure-swing adsorption unit (PSA). The bio-syngas (H₂/CO ≈ 1) was catalytically converted to DME in the fixed-bed tubular reactor directly over Cu/Zn/Al/HZSM-5 catalysts. CO conversion and space-time yield of DME were in the range of 82.0-73.6% and 124.3-203.8 kg/m_cat³/h, respectively, with a similar DME selectivity when gas hourly space velocity (GHSV, volumetric flow rate of syngas at STP divided by the volume of catalyst) increased from 650 h⁻¹ to 1500 h⁻¹ at 260 °C and 4.3 MPa. And the selectivity to methanol and products was less than 0.65% under typical synthesis condition. The thermal energy conversion efficiency was ca. 32.0% and about 16.4% carbon in dried corncob was essentially converted to DME with the production cost of ca. ¥ 3737/ton DME. Cu (1 1 1) was assumed to be the active phase for DME synthesis, confirmed by X-ray diffraction (XRD) characterization.