Tandem Cu/ZnO/ZrO2-SAPO-34 System for Dimethyl Ether Synthesis from CO2 and H2: Catalyst Optimization, Techno-Economic, and Carbon-Footprint Analyses

Abstract

To alleviate detrimental effects associated with anthropogenic emissions, the use of CO₂ and H₂ as feedstocks for their conversion to dimethyl ether (DME) with tandem catalysts is an attractive and sustainable route. First, we investigated the catalytic activity of bifunctional admixtures of Cu-ZnO-ZrO₂ (CZZ) and a silicoaluminophosphate, SAPO-34, for CO₂ hydrogenation to DME and optimized their reactivity with an emphasis on identifying optimum synthesis conditions for CZZ including Cu:Zn:Zr molar ratio and aging and calcination temperatures. The highest methanol (MeOH) productivity (10.8 mol kg_cat^–1 h^–1) was observed for CZZ-611 aged at 40 °C and calcined at 500 °C. When coupled with SAPO-34, CZZ/SAPO-34 reached 20% CO₂ conversion and 56% DME selectivity at optimized conditions (260 °C, 500 psig, and 2000 mL g_CZZ^–1 h^–1) and was stable for 50 h time-on-stream, with a slight reduction in activity. Next, we performed kinetic modeling to translate lab-scale findings to industrial packed-bed reactors followed by a techno-economic analysis (TEA) with cradle-to-gate environmental footprint evaluation to evaluate its industrial applicability. A TEA of a 20,000 tpy DME plant revealed raw material costs as the main operating cost drivers (H₂ cost comprises 47% of total cost). Considering green H₂ ($4/kg H₂) and captured CO₂ as feed, the minimum DME selling price (MDSP) was $3.21/kg, ∼2.7× higher than the market price ($1.2/kg). MDSP drops to $1.99/kg with gray H₂ ($1/kg H₂) and fluctuates ±$0.14 with changes in CAPEX (±30%) and other economic factors. The plant’s carbon footprint was mainly affected by the H₂ source. Green and gray H₂ resulted in emissions of 0.21 and 4.4 kg CO₂ eq/kg DME, respectively. Importantly, a negative carbon footprint can be achieved by using green H₂ and CO₂ captured directly from air. Overall, our work shows tandem catalysis as a promising approach toward sustainable DME production and identifies the pathway toward making it cost-competitive with fossil fuels.