Novel Process for Conversion of CO₂ to Dimethyl Carbonate using Catalytic Membrane Reactors

Dimethyl carbonate (DMC) receives much attention due to its versatile use, low toxicity and fast biodegradability. Various ‘green’ production routes are explored and developed to replace the classic and rather toxic synthesis of DMC via phosgene. The direct DMC synthesis route – from CO2 and methanol – is one of the most interesting options for the chemical industry, but this is hindered by the limited chemical equilibrium. This work describes the simulation of a novel process for DMC using PSE and PI methods. A membrane reactor plays the central role, as it continuously removes the water by-product, in order to overcome the equilibrium limitations. Aspen Plus simulations were carried out for a DMC process (20 kt/yr) and over 99 wt% purity of the DMC product. Due to the incomplete conversion in the membrane reactor, the DMC concentration in the reactor effluent is rather low hence the purification of this diluted stream leads to large recycles and requires large size equipment and a considerable amount of energy

Highly selective amino acid salt solutions as absorption liquid for CO2 capture in gas-liquid membrane contactors

\u3cp\u3eThe strong anthropogenic increase in the emission of CO\u3csub\u3e2\u3c/sub\u3e and the related environmental impact force the developments towards sustainability and carbon capture and storage (CCS). In the present work, we combine the high product yields and selectivities of CO\u3csub\u3e2\u3c/sub\u3e absorption processes with the advantages of membrane technology in a membrane contactor for the separation of CO\u3csub\u3e2\u3c/sub\u3e from CH\u3csub\u3e4\u3c/sub\u3e using amino acid salt solutions as competitive absorption liquid to alkanol amine solutions. Amino acids, such as sarcosine, have the same functionality as alkanol amines (e.g., monoethanolamine=MEA), but in contrast, they exhibit a better oxidative stability and resistance to degradation. In addition, they can be made nonvolatile by adding a salt functionality, which significantly reduces the liquid loss due to evaporation at elevated temperatures in the desorber. Membrane contactor experiments using CO\u3csub\u3e2\u3c/sub\u3e/CH\u3csub\u3e4\u3c/sub\u3e feed mixtures to evaluate the overall process performance, including a full absorption/desorption cycle show that even without a temperature difference between absorber and desorber, a CO\u3csub\u3e2\u3c/sub\u3e/CH\u3csub\u3e4\u3c/sub\u3e selectivity of over 70 can be easily achieved with the sarcosine salt solution as absorption liquid. This selectivity reaches values of 120 at a temperature difference between absorber and desorber of 35°C, compared to a value of only 60 for MEA under the same conditions. Although CO\u3csub\u3e2\u3c/sub\u3e permeance values are somewhat lower than the values obtained for MEA, the results clearly show the potential of amino acid salt solutions as competitive absorption liquids for the energy efficient removal of CO\u3csub\u3e2\u3c/sub\u3e. In addition, due to the low absorption of CH\u3csub\u3e4\u3c/sub\u3e in sarcosine compared to MEA, the loss of CH\u3csub\u3e4\u3c/sub\u3e is reduced and significantly higher CH\u3csub\u3e4\u3c/sub\u3e product yields can be obtained.\u3c/p\u3

On the isolation of single acidic amino acids for biorefinery applications using electrodialysis

\u3cp\u3eElectrodialysis using commercially available ion exchange membranes was applied for the isolation of l-glutamic acid (Glu) and l-aspartic acid (Asp) from a mixture of amino acids. Based on the differences in their isoelectric points, Glu and Asp, being negatively charged at neutral pH, can be separated from neutral and basic amino acids. Outstanding recoveries for Glu and Asp of around 90% and 83%, respectively, were obtained. The further separation of Glu from Asp with electrodialysis is enabled with an enzymatic modification step where Glu is converted into γ-aminobutyric acid (GABA) with the enzyme glutamic acid α-decarboxylase (GAD) as the catalyst. Negatively charged Asp is separated from uncharged GABA at neutral pH conditions with a current efficiency of 70% and a recovery of 90%. Higher current efficiencies and lower energy consumption can be obtained when adjusting the current in time. This opens the route to successful isolation of amino acids for biorefinery applications using an integrated process of enzymatic conversion and separation with electrodialysis.\u3c/p\u3

Kinetics of CO2 absorption in aqueous sarcosine salt solutions:Influence of concentration, temperature, and CO2 loading

\u3cp\u3eAmino acid salt solutions are a promising alternative to alkanolamines (e.g., MEA) as absorption liquid for CO\u3csub\u3e2\u3c/sub\u3e removal due to their ionic nature, their low evaporative losses, and their assumed higher oxidative and thermal stability. Sarcosine is a promising candidate because of its relatively high CO\u3csub\u3e2\u3c/sub\u3e loading capacity and reactivity. In this work, CO \u3csub\u3e2\u3c/sub\u3e absorption experiments in the so-called pseudo-first-order regime were carried out to determine the reaction rate expression and reaction rate constant of CO\u3csub\u3e2\u3c/sub\u3e absorption in aqueous sarcosine salt solutions. Next to the influence of the sarcosine concentration (0.5-3.8 M) and the temperature (298-308 K) on the rate of reaction, the reaction rate constants for partially loaded sarcosinate solutions were investigated. Compared to MEA, very high reaction rate constants for the carbamate formation were obtained for aqueous sarcosine salt solutions. The reaction order in CO\u3csub\u3e2\u3c/sub\u3e was found to be equal to 1, which is in accordance with the literature, and for potassium sarcosinate an (apparent) reaction order of 1.66 was found. The activation energy was found to be approximately 26 kJ/mol. The apparent rate of the reaction strongly decreases with increasing partial loading of the solution with CO\u3csub\u3e2\u3c/sub\u3e and was found to be directly related to the decrease in free amine concentration in the solution. This observation is especially relevant for cyclic absorption processes such as gas-liquid membrane contactors, where incomplete solvent regeneration occurs.\u3c/p\u3

Techno-economic evaluation of the direct conversion of CO₂ to dimethyl carbonate using catalytic membrane reactors

The production of dimethyl carbonate (DMC) caught more interest in the past decades due to its versatile use (e.g. as fuel additive), low toxicity and fast biodegradability. Different 'green' production routes are being developed to replace the conventional and rather toxic production of DMC via phosgene. The direct conversion of CO2 and methanol toward DMC is an environmental and economically interesting production route for the chemical industry.This work describes the process design of the direct conversion of CO2 to dimethyl carbonate, providing a valuable insight and a better understanding of the process limitations. In this design, membrane reactors are used for continuous removal of water by-product, in order to overcome the equilibrium limitations. The rigorous Aspen Plus simulations show that even when using an excess of methanol, the attainable conversion is low and the DMC concentration in the reactor effluent is less than 1.5mol%. Purifying this diluted stream to the desired concentrations demands large size equipment and a substantial amount of energy (13.61kWh/kg DMC) resulting in high investment and utility costs, thus making the process not profitable. The focus for new membrane reactors could be on the selective removal of DMC (instead of water) from the reaction area to allow for a more concentrated DMC stream

Techno-economic evaluation of the direct conversion of CO\u3csub\u3e2\u3c/sub\u3e to dimethyl carbonate using catalytic membrane reactors

\u3cp\u3eThe production of dimethyl carbonate (DMC) caught more interest in the past decades due to its versatile use (e.g. as fuel additive), low toxicity and fast biodegradability. Different 'green' production routes are being developed to replace the conventional and rather toxic production of DMC via phosgene. The direct conversion of CO\u3csub\u3e2\u3c/sub\u3e and methanol toward DMC is an environmental and economically interesting production route for the chemical industry.This work describes the process design of the direct conversion of CO\u3csub\u3e2\u3c/sub\u3e to dimethyl carbonate, providing a valuable insight and a better understanding of the process limitations. In this design, membrane reactors are used for continuous removal of water by-product, in order to overcome the equilibrium limitations. The rigorous Aspen Plus simulations show that even when using an excess of methanol, the attainable conversion is low and the DMC concentration in the reactor effluent is less than 1.5mol%. Purifying this diluted stream to the desired concentrations demands large size equipment and a substantial amount of energy (13.61kWh/kg DMC) resulting in high investment and utility costs, thus making the process not profitable. The focus for new membrane reactors could be on the selective removal of DMC (instead of water) from the reaction area to allow for a more concentrated DMC stream.\u3c/p\u3