CO2-based Process Research Articles

Feasibility and Advantages of Continuous Synthesis of Bioinspired Silica Using CO2 as an Acidifying Agent.

In this work, we present a method for the continuous synthesis of bioinspired porous silica (BIS) particles using carbon dioxide (CO2) as an acidifying agent. Typical BIS synthesis uses strong mineral acids (e.g., HCl) to initiate the hydrolysis and subsequent condensation reactions. The use of strong acids leads to challenges in controlling the reaction pH. The synthesis approach proposed in this work offers for the first time CO2 as an attractive alternative for the synthesis of BIS and demonstrates the continuous process. The developed method leverages the mild acidic and the self-buffering nature of the CO2 combined with additional options for controlling mass transfer rates to facilitate enhanced control of pH, which is crucial for controlling the properties of synthesized BIS. Proof of concept experiments conducted in continuous mode demonstrated a yield of over 70% and a surface area exceeding 500 m2/g. These results indicate the successful synthesis of BIS using CO2 with properties in the desired range. The enhanced pH control offered by this CO2-based process will facilitate the implementation of a sustainable and robust continuous process for BIS synthesis.

Evaluation of alternative processes of methanol production from CO2: Design, optimization, control, techno-economic, and environmental analysis

Converting carbon dioxide (CO2) to methanol via direct hydrogenation has been regarded as an essential part of the pursuit of a decarbonized energy economy. This study first explored and evaluated alternative processes for converting CO2 to methanol, in which six schemes based on adiabatic and/or non-adiabatic fixed-bed reactors were focused. The research scope includes rigorous process design, optimization, techno-economic and environmental assessment, and control. The generated results indicate that the two-reactor system (Scheme 5), which employs a non-adiabatic one as the first stage and a adiabatic one follows, has the lowest production cost. This process reveals great potential for decarbonization (i.e. CO2-e = −1.314 Ton-CO2/Ton-MeOH), whereas less economic attractiveness (i.e. minimum required selling price (MRSP) of methanol = 998 USD/Ton, average market price = 378 USD/Ton). Correspondingly, the maximum allowable CO2 emission from utilizing hydrogen (MACEH2) was found to be 6.554 Ton-CO2/Ton-H2. This indicated that using hydrogen produced from steam methane reforming (SMR) with carbon capture on both syngas and flue gas (i.e. 5.7 Ton-CO2/Ton-H2) leads to net decarbonization. Furthermore, if the emission associated with the CO2 feed (specific energy = 2.8 GJ/Ton-CO2) is also considered, net decarbonation would be achieved by using hydrogen produced from biomass gasification (i.e. 3.1 Ton-CO2/Ton-H2). A more comprehensive comparison between various CO2 utilization processes, in terms of the decarbonization ability and economics, was performed. Through this, it is concluded that there has been no existing CO2-based process that is attractive in both aspects. Finally, a suitable control strategy was proposed for the selected scheme, which suitably handles the throughput and composition disturbances.

CO2-solvated liquefaction of polyethylene glycol (PEG): A novel, green process for the preparation of drug-excipient composites at low temperatures

Polyethylene glycol (PEG), MW = 1500 D, a solid excipient approved by the US FDA, is commonly used in organic solvent as well as hot melt-based, pharmaceutical processes with importance in increasing the solubility of hydrophobic drugs for processing. We demonstrate here, for the first time, a novel use of this benign excipient in a near-ambient temperature, CO2-based process to produce drug-excipient composites. We show that PEG 1500 undergoes deliquescence in contact with gaseous CO2 at 40 bar eventually forming a biphasic liquid system that allows homogeneous mixing of an active pharmaceutical ingredient (API). Acetone- and CO2-processed composites of PEG with two model drug systems, viz., paracetamol and aspirin, were prepared, characterized, and drug release kinetics reported. Release kinetics from these composites resemble those of composites prepared using acetone. The results demonstrate a new, green, near-ambient temperature pharmaceutical process eliminating the use of organic solvents and compatible with thermally labile drugs, unlike thermal processing methods.

New trends in bioprocesses for lignocellulosic biomass and CO2 utilization

Innovation and technology are seen today as key points in the transition to a greener and more sustainable economy. In this sense, the development of new processes able to result in reduced emissions and levels of CO2 in the atmosphere has been considered essential to support this transition and, at the same time, promote economic growth. Several techno-economic and life cycle assessment studies have shown promising data when sugars derived from lignocellulosic biomass are used as carbon source for fermentation processes. The use of CO2 as carbon source for fermentation is another smart concept for reusing this molecule while minimizing its emissions to the atmosphere. However, the large-scale implementation of biomass-based and CO2-based processes still require significant research efforts to result in robust and cost-competitive technologies. This paper discusses some promising approaches able to advance this research area including potential strategies for process intensification (enzymatic hydrolysis using high solid loading, simultaneous saccharification and fermentation, fermentation with downstream process integration), robust microbial strains for application in biomass-based and CO2-based bioprocesses, microbial co-cultivation systems, greener technologies for lignocellulosic biomass fractionation, among others. A critical evaluation of sustainability aspects including techno-economic and life cycle assessment is also provided. Overall, this study contributes with information on innovative trends able to advance the development of greener bioprocesses.

Supercritical carbon dioxide combined with high power ultrasound as innovate drying process for chicken breast

This work explores the feasibility to apply supercritical CO2 (SC−CO2) drying alone or in combination with High-Power Ultrasounds (SC−CO2+HPU) to improve the shelf life and safety of raw chicken meat. SC−CO2+HPU drying process revealed the fastest water removal and higher rehydration capacity. A complete inactivation (6 log CFU/g) of mesophilic bacteria and yeasts and moulds was achieved with both the SC−CO2 processes, while oven drying at 75 °C, used as control, showed only a limited inactivation (4 log CFU/g). The SC−CO2 processes were efficient also for the inactivation of inoculated Salmonella. The retention of Vitamins B1, B2, B3 and B12 after the SC−CO2 drying demonstrated the preservation of fresh like properties in terms of nutrients. Colour analysis showed a change in colour comparable to traditional cooking techniques. Results demonstrate that SC−CO2-based processes may be used as innovative technologies to dry chicken and make it microbiologically safe, while maintaining nutritional properties.

Hierarchically Porous Calcium Carbonate Scaffolds for Bone Tissue Engineering.

Hierarchically porous CaCO3 scaffolds comprised of micro- (diameter = 2.0 ± 0.3 μm) and nano-sized (diameter = 50.4 ± 14.4 nm) pores were fabricated on silicon substrates using a supercritical CO2-based process. Differentiated human THP-1 monocytes exposed to the CaCO3 scaffolds produced negligible levels of the inflammatory cytokine tumor necrosis factor-alpha (TNF-α), confirming the lack of immunogenicity of the scaffolds. Extracellular matrix (ECM) proteins, vitronectin and fibronectin, displayed enhanced adsorption to the scaffolds compared to the silicon controls. ECM protein-coated CaCO3 scaffolds promoted adhesion, growth, and proliferation of osteoblast MC3T3 cells. MC3T3 cells grown on the CaCO3 scaffolds produced substantially higher levels of transforming growth factor-beta and vascular endothelial growth factor A, which regulate osteoblast differentiation, and exhibited markedly increased alkaline phosphatase activity, a marker of early osteoblast differentiation, compared to controls. Moreover, the CaCO3 scaffolds stimulated matrix mineralization (calcium deposition), an end point of advanced osteoblast differentiation and an important biomarker for bone tissue formation. Taken together, these results demonstrate the significant potential of the hierarchically porous CaCO3 scaffolds for bone tissue engineering applications.

Techno-economic evaluation of different CO2-based processes for dimethyl carbonate production

In this work, several chemical processes for production of dimethyl carbonate (DMC) based on CO2 utilization are evaluated. Four CO2-based processes for production of DMC are considered: (1) direct synthesis from CO2 and methanol; (2) synthesis from urea; (3) synthesis from propylene carbonate; and (4) synthesis from ethylene carbonate. The processes avoid the use of toxic chemicals such as phosgene, CO and NO that are required in conventional DMC production processes. From preliminary thermodynamic analysis, the yields of DMC are found to have the following order (higher to lower): ethylene carbonate route>urea route>propylene carbonate route>direct synthesis from CO2. Therefore, only the urea and ethylene carbonate routes are further investigated by comparing their performances with the commercial BAYER process on the basis of kg of DMC produced at a specific purity. The ethylene carbonate route is found to give the best performance in terms of energy consumption (11.4% improvement), net CO2 emission (13.4% improvement), in global warming potential (58.6% improvement) and in human toxicity-carcinogenic (99.9% improvement) compared to the BAYER process. Also, the ethylene carbonate option produces ethylene glycol as a valuable by-product. Based on the above and other performance criteria, the ethylene carbonate route is found to be a highly promising green process for DMC production.

CO 2-based methanol and DME – Efficient technologies for industrial scale production

The conversion of CO 2 with H 2 to methanol (MeOH) over a commercial Cu/ZnO catalyst (Süd-Chemie, Germany) was studied under process conditions. The obtained results showed a good stability of the catalytic system and a large potential for a CO 2 emission reduction with simultaneous production of MeOH or dimethyl ether (DME) as bulk chemicals or alternative fuels. If H 2 is obtained from renewable or CO 2-neutral sources (e.g. biomass, solar, wind or nuclear energy), respectively, a potentially CO 2-neutral cycle is possible. Compared to the conventional synthesis gas based technologies like the Lurgi MegaMethanol ® process, the CO 2-based process shows lower productivities. However, since the overall reaction is less exothermic, lower temperature peaks and lower byproduct contents are found at similar process conditions. The higher purity is beneficial for further chemical conversions, like the DME synthesis. In the Lurgi MegaDME ® technology, DME is produced efficiently in terms of costs and energy demand and can be used as alternative fuel for diesel engines. The MegaDME technology, based on the Lurgi MegaMethanol ® process, allows overall capacities of up to 1.5 Mio t a −1 DME in a single process train from syngas generation via Methanol synthesis, to DME synthesis and product purification without parallelized equipment.

Cleaning up with catalysts

The conversion of CO2 with H2 to methanol (MeOH) over a commercial Cu/ZnO catalyst (Süd-Chemie, Germany) was studied under process conditions. The obtained results showed a good stability of the catalytic system and a large potential for a CO2 emission reduction with simultaneous production of MeOH or dimethyl ether (DME) as bulk chemicals or alternative fuels. If H2 is obtained from renewable or CO2-neutral sources (e.g. biomass, solar, wind or nuclear energy), respectively, a potentially CO2-neutral cycle is possible. Compared to the conventional synthesis gas based technologies like the Lurgi MegaMethanol® process, the CO2-based process shows lower productivities. However, since the overall reaction is less exothermic, lower temperature peaks and lower byproduct contents are found at similar process conditions. The higher purity is beneficial for further chemical conversions, like the DME synthesis. In the Lurgi MegaDME® technology, DME is produced efficiently in terms of costs and energy demand and can be used as alternative fuel for diesel engines. The MegaDME technology, based on the Lurgi MegaMethanol® process, allows overall capacities of up to 1.5 Mio t a−1 DME in a single process train from syngas generation via Methanol synthesis, to DME synthesis and product purification without parallelized equipment.

Non-fluorous polymers with very high solubility in supercritical CO2 down to low pressures

Liquid and supercritical carbon dioxide have attracted much interest as environmentally benign solvents, but their practical use has been limited by the need for high CO2 pressures to dissolve even small amounts of polar, amphiphilic, organometallic, or high-molecular-mass compounds. So-called 'CO2-philes' efficiently transport insoluble or poorly soluble materials into CO2 solvent, resulting in the development of a broad range of CO2-based processes, including homogeneous and heterogeneous polymerization, extraction of proteins and metals, and homogeneous catalysis. But as the most effective CO2-philes are expensive fluorocarbons, such as poly(perfluoroether), the commercialization of otherwise promising CO2-based processes has met with only limited success. Here we show that copolymers can act as efficient, non-fluorous CO2-philes if their constituent monomers are chosen to optimize the balance between the enthalpy and entropy of solute-copolymer and copolymer-copolymer interactions. Guided by heuristic rules regarding these interactions, we have used inexpensive propylene and CO2 to synthesize a series of poly(ether-carbonate) copolymers that readily dissolve in CO2 at low pressures. Even though non-fluorous polymers are generally assumed to be CO2-phobic, we expect that our design principles can be used to create a wide range of non-fluorous CO2-philes from low-cost raw materials, thus rendering a variety of CO2-based processes economically favourable, particularly in cases where recycling of CO2-philes is difficult.

Synthesis of phenolic/furfural gel microspheres in supercritical CO 2

Phenolic/furfural (P/F) gel microspheres have been successfully produced by a new supercritical CO 2-based process. CO 2-soluble poly(dimethylsiloxane) (PDMS) was used as the stabilizer in this system. The spherical morphology of the gel microspheres was confirmed by scanning electron microscopy. The particle size and particle size distribution of the P/F gel microspheres can be modified upon variation of the solids content and the stabilizer content. The resultant P/F microspheres have an average particle size in the range of 1–6 μm. The structure of the P/F gel microspheres was revealed by IR analysis.