Direct dimethyl carbonate synthesis from CO₂ and methanol catalyzed by CeO₂ and assisted by 2-cyanopyridine: a cradle-to-gate greenhouse gas emission study

Abstract

Rigorous process simulation helps in the qualification of direct CO2 to DMC conversion co-assisted by a catalyst and dehydration agent in GHG emission reduction.

Ceria-Based Materials for Thermocatalytic and Photocatalytic Organic Synthesis

“…CeO 2 -based catalysts (e.g., Al 2 O 3 /CeO 2 , spindle-like CeO 2 ) with unique acid–base properties are well-known as effective heterogeneous catalysts for the activation of alcohol and CO 2 to produce DMC (Figure a), but the yields without the addition of dehydrating agents were very low (≤5% based on methanol) because of the thermodynamic equilibrium limitations. ,, In addition, as water is the only byproduct in the organic synthesis of carbonates, the chemical equilibrium can be shifted to the carbonate side in the presence of an excess amount of dehydrating agents to react with the produced water. Several dehydrating agents (e.g., acetonitrile, benzonitrile, 2-cyanopyridine) have been widely used for increasing the yields of DMC over CeO 2 catalysts from alcohols and relatively low CO 2 pressure, whereas the adsorption of the side products benzamide, acetamide or 2-picolinamide on CeO 2 can lead to gradually decreased reaction rates of DMC formation with increasing reaction time. − For example, Tomishige et al investigated the catalytic performance of DMC formation over CeO 2 with various nitriles (e.g., 2-cyanopyrimidine, 3-cyanopyrimidine, 4-cyanopyrimidine, pyrrole-2-carbonitrile, methyl aminoacetonitrile, acetonitrile, benzonitrile) as dehydrating agents using stoichiometric amounts, demonstrating that 2-cyanopyridine and pyrazine-2-carbonitrile were effective with a DMC yield of 94% and 91%, respectively . The recyclable utilization of the dehydrating agent 2-cyanopyridine was achieved via the dehydration of 2-picolinamide to form 2-cyanopyridine again catalyzed by Na 2 O/SiO 2 .…”

“…Urakawa et al reported the continuous DMC synthesis from CO 2 and methanol over CeO 2 + 2-cyanopyridine system, which exhibited outstanding methanol conversion of >95% and >99% selectivity toward dimethyl carbonate with much shorter reaction time in a continuous flow fixed-bed reactor than in batch operation . Later, the continuous synthesis of DMC from CO 2 and methanol with excellent yields in a fixed bed has been widely adopted via optimizing the catalyst composition and morphology, the catalyst amount, CO 2 pressure, reaction temperature, and residence time. ,, Concerning catalyst composition and morphology, it has been reported that the adsorption and activation of CO 2 for the synthesis of DMC is significantly affected by the surface oxygen vacancy sites and acid–base properties of the catalysts. , As a result, several strategies have been adopted to increase the number of surface oxygen vacancy sites and acid–base sites of CeO 2 -based catalysts for the synthesis of DMC via tuning the morphology, structure and composition, such as Ti x Ce 1– x O 2 nanocomposites, , surface modification of CeO 2 by rare earth metal, Zr-doped CeO 2 nanorods, MgO-CeO 2 , CeO 2 nanomaterials with differently exposed planes . For example, Urakawa et al reported that the addition of rare earth metals (La, Gd, and Pr) can effectively enhance the catalyst stability by improving the methoxy species adsorption strength while preventing the adsorption of 2-picolinamide-like species, as shown in Figure c .…”

“…305 Later, the continuous synthesis of DMC from CO 2 and methanol with excellent yields in a fixed bed has been widely adopted via optimizing the catalyst composition and morphology, the catalyst amount, CO 2 pressure, reaction temperature, and residence time. 303,306,307 Concerning catalyst composition and morphology, it has been reported that the adsorption and activation of CO 2 for the synthesis of DMC is significantly affected by the surface oxygen vacancy sites and acid−base properties of the catalysts. 308,309 As a result, several strategies have been adopted to increase the number of surface oxygen vacancy sites and acid−base sites of CeO 2 -based catalysts for the synthesis of DMC via tuning the morphology, structure and composition, such as Ti x Ce 1−x O 2 nanocomposites, 306,310 surface modification of CeO 2 by rare earth metal, 307 Zr-doped CeO 2 nanorods, 311 MgO-CeO 2 , 312 CeO 2 nanomaterials with differently exposed planes.…”

Enhanced transformation of CO2 over microporous Ce-doped Zr metal–organic frameworks

“…Firstly, the catalytic activities of the MOF samples were measured by converting CO 2 and methanol in the presence of 2-cyanopyridine (2-CY, dehydrating agent, shown in Scheme 1) at 150 C under 2.6 MPa CO 2 pressure for 6 hours (see Experimental section for details) with DMC as the target product. 14,44 The catalytic methanol conversion, DMC yield and TOF of the MOF composites are displayed in Fig. 2(a).…”

Catalytic processes for the direct synthesis of dimethyl carbonate from CO2 and methanol: a review

“…Recently, Ohno et al investigated the regeneration of 2-CP by process simulation of the direct synthesis of DMC from CO 2 and methanol using CeO 2 as a catalyst combined with 2-CP as a dehydrating agent. 180 The simulated process includes a reaction zone (DMC synthesis and 2-CP hydration), a separation zone (separation of unreacted gas phase CO 2 and methanol and of the formed liquid phase containing DMC and 2-picolinamide (hydration product of 2-CP) through two distillation columns) and a recycling loop (where 2-CP is regenerated by dehydrating 2-picolinamide). The whole process achieved 99.4% DMC yield and total net greenhouse gas emissions of 0.39 kg CO 2 equivalent per kg DMC, which are much lower than that in conventional commercial processes (the least impacting one emits 2.12 kg CO 2 equivalent per kg DMC).…”