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Feasibility and energy assessment of green methanol production via catalytic hydrogenation of carbon oxides from biomass gasification
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School of Engineering |
Master's thesis
Electronic archive copy is available via Aalto Thesis Database.
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en
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61
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Abstract
Waste woodchips are an abundant, low-value residue with few high-grade uses beyond combustion or mulch. Converting this distributed resource into methanol, which is a liquid energy carrier to be used as fuel, could offer a route to store renewable energy and reduce reliance on fossil-derived feedstock without relying on natural-gas reforming. Realizing this sustainably at a modular scale is non-trivial: biomass syngas must be clean and near-stoichiometric for synthesis, compression and separations must be right-sized, and heat must be recycled to keep specific energy low. This thesis addresses these constraints by pairing a biomass-to-syngas system (XyloGas) with homogeneous-catalysis, liquid-phase methanol synthesis at mild conditions, targeting a compact, heat-integrated pathway suitable for stranded feedstock sites.
The work combines actual plant data and Aspen Plus models to evaluate two operating modes. First, a lab-scale homogeneous-catalysis gas-liquid contactor for producing 0.1 kg MeOH h⁻¹ with CO₂-free, dry syngas and H₂ to CO ratio of SN = 2. Second, an integrated case matched to the XyloGas syngas production of 10.6 Nm³ h⁻¹ yielding 4.2 kg MeOH h⁻¹. Key Energy Performance Indices (EPIs) are quantified: Specific Electrical Energy Consumption (SECelec), Specific Thermal Energy Consumption (SECₜₕ), syngas to MeOH energy capture, primary-energy intensity, and carbon intensity.
Results show that from the XyloGas measurements, the waste-woodchip to products conversion exceeds 65% on an energy basis (useful syngas + biochar), establishing a credible renewable feed platform. On the methanol reactor side, the CO to MeOH conversion is taken as 100% at SN = 2, and the reaction exotherm being sufficient to drive the flash separation, pushing SECₜₕ close to 0 when recovered. Electrical auxiliaries yield a relatively high SECelec at lab scale but decrease with appropriately sized equipment and increasing scale. In the integrated analysis, durable biochar sequestration drives the pathway’s carbon intensity to near-zero or net-negative per kg MeOH. While the approach cannot leverage mega-scale economies, the results show that a small, heat-integrated biomass-to-methanol system is technically feasible, energetically competitive per kilogram, and environmentally advantageous where waste woodchips are locally available.