MPa CO2 Pressure Research Articles

A Green Chemo-Enzymatic Approach for CO2 Capture and Transformation into Bis(cyclic carbonate) Esters in Solvent-Free Media.

A sustainable approach for CO2 capture and chemo-enzymatic transformation into bis(cyclic carbonate) esters from CO2, glycidol, and organic anhydrides under solvent-free conditions has been demonstrated. The chemo-enzymatic process is based on two consecutive catalytic steps, which can be executed through separated operations or within a one-pot combo system, taking advantage of the synergic effects that emerge from integrating ionic liquid (IL) technologies and biocatalysts. In a first step, lipase-catalyzed transesterification and esterification reactions of different diacyl donors (e.g., glutaric anhydride, succinic anhydride, dimethyl succinate, etc.) with glycidol in solvent-free under mild reaction conditions (70 °C, 6 h) produce the corresponding diglycidyl ester derivatives in up to 41% yield. By a second step, the synthesis of bis(cyclic carbonate) esters was carried out as a result of the cycloaddition reaction of CO2 (from an exhausted gas source, 15% CO2 purity) on these diglycidyl esters, catalyzed by the covalently attached 1-decyl-2-methylimidazolium IL (supported ionic liquid-like phase, SILLP), in solvent-free condition, leading up to 65% yield after 8 h at 45 °C and 1 MPa CO2 pressure. Both key elements of the reaction system (biocatalyst and SILLP) were successfully recovered and reused for at least 5 operational cycles. Finally, different metrics have been applied to assess the greenness of the solvent-free chemo-enzymatic synthesis of bis(cyclic carbonate) esters here reported.

Incorporation of Mg/Al metal oxide into ionic liquids for CO2 capture and conversion into cyclic carbonate under solvent-free conditions: Effect of coordination ability, recyclability, and catalytic study

The direct conversion of carbon dioxide (CO2) and propylene oxide (PO) into propylene carbonate (PC) offers a green way to utilize anthropogenic CO2. However, this reaction is limited by low conversion of PO and harsh reaction conditions. In this study, we solve this problem using ionic liquids (ILs)/metal oxide composites (ILs@MAO). The catalytic activity of MAO-500 (500 = annealing temperature) is poor evidenced by its low conversion of PO (24.94%). However, ILs@MAO-500 has a high conversion of PO (97.54%) under similar reaction conditions (2 h at 1.5 MPa CO2 pressure, 90 °C, and 0.85 g catalyst). The ILs consist of imidazolium cation with weak coordinated [NTf2]– anion leading to outward movement of anion resulting in the formation of “heterodinuclear complex”. This complex generates an amorphous-crystalline intermediate with balanced acid-base sites that activate PO and stabilize the catalytic intermediate. In large part, the high PO conversion is theorized to be primarily due to the abundant reactive sites in the ILs that are covalently immobilized on the MAO-500 carrier. Furthermore, even after multiple recycling, ILs@MAO-500 remains stable and exhibits high yield and selectivity. The proposed solvent-free catalytic system is mild, kinetically fast, and naturally safe for coupling CO2 and PO into PC synthesis.

Interfacial properties of CO2 and liquid sulfur in high-sulfur gas fields: Molecular simulations on carbonate mineral surfaces

As the global energy landscape transforms, the development of high-sulfur natural gas has become increasingly critical. However, sulfur deposition during these gas field developments significantly affects operational efficiency. This study employed molecular dynamics simulation to explore the effectiveness of CO2 in alleviating sulfur deposition on carbonate rock reservoirs. Specifically, it examined the interfacial tension between liquid sulfur and CO2, the wettability of sulfur on carbonate rock mineral surfaces, and the kinetics of CO2 displacing liquid sulfur. Results show that as CO2 pressure increases from 10 MPa to 60 MPa, the interfacial tension between liquid sulfur and CO2 decreases by 84 %, from 35.54 mN/m to 5.53 mN/m. The contact angles of sulfur droplets on calcite and dolomite surfaces stabilize at 41.82° ± 2.10° and 44.33° ± 3.27°, respectively, indicating greater sulfur spread on calcite surfaces. With higher CO2 pressures, sulfur deposition on mineral surfaces and interfacial tension both decrease significantly, while the wetting angle of liquid sulfur increases, particularly on dolomite. At 60 MPa CO2 pressure, the adsorption energy of dolomite for liquid sulfur drops from 364.56 kcal/mol to 25.46 kcal/mol, a 93 % reduction, suggesting CO2′s dual role in displacing sulfur and promoting its desorption from mineral surfaces. Furthermore, the efficiency of sulfur deposition alleviation in carbonate rock slit structures improves and stabilizes at around 40 MPa CO2 pressure. This study presents a potential environmentally friendly approach for efficiently developing high-sulfur gas fields, and its findings provide practical insights for optimizing CO2 injection strategies to mitigate sulfur deposition.

Vinyl-containing covalent organic frameworks co-polymerized with imidazolium ionic liquids for the efficient cycloaddition of CO2 with epoxides

The chemical fixation of CO2 into high value-added cyclic carbonates over metal- and cocatalyst-free heterogeneous catalyst has attracted considerable attention and is still a challenge. Rationally integrating multifunctional units into porous materials has been regarded as a promising strategy to enhance catalytic efficiency. In this study, the poly (ionic liquid)-hierarchical covalent organic framework (R-PIL-COF, R refers to CH2NH2/CH2OH/COOH/CH3) hybrids were successfully fabricated via in situ copolymerization of vinyl-containing covalent organic framework and hydrogen bond donors (HBDs)-functionalized imidazolium ionic liquids. Among, CH2NH2-PIL-COF hybrid bearing acidic and basic sites possess moderate CO2 adsorption ability and hierarchical pore structure which promoted the activation of CO2 and epichlorohydrin. Furthermore, the influence on the catalytic activity of various HBD groups and grafting amounts of poly (ionic liquid)s were systematically investigated, and CH2NH2-PIL–COF–45 % exhibited an exceptional catalytic performance under mild conditions (100 °C and 1 MPa CO2 pressure). Additionally, CH2NH2-PIL–COF–45 % had broad substrate tolerance and excellent stability. Finally, a synergistic catalytic mechanism was proposed based on the experimental and characterization results. The strategy of co-polymerizing ionic liquids to COF provides a new way to develop efficient COF-based hybrids by the integration of nucleophilic units into the COF skeleton for CO2 fixation under cocatalyst-free and mild conditions.

Nitrogen-rich covalent-organic-framework as a recyclable heterogenous catalyst for the efficient cycloaddition of carbon dioxide with epoxides

Carbon dioxide (CO2) can be chemically converted into high-value products, which is not only helps to ease the environmental problems instigated by global warming and has an optimistic effect on economies around the planet. The production of cyclic carbonates is regarded as a promising approach to convert CO2 through the cycloaddition of CO2 with epoxides. However, a major obstacle in this process is the synthesis of environmentally friendly and highly effective heterogeneous catalysts. Here, a novel nitrogen-rich covalent organic framework (CP-COF) was firstly synthesized through a polymerization method of piperazine and cyanuric chloride with 1, 4‐dioxane and used for the aforesaid reaction. A number of analytical methods were employed to verify the chemical composition and the structure of the catalyst. The CP-COF catalyst possessed a significant amount of active nitrogen sites and hydrogen bond donors in it, resulting in a high level of reactivity for the cycloaddition reaction of CO2 with epichlorohydrin in the absence of any solvent and metals, and the yield of chloropropene carbonate (CPC) reached 99 % at 110 ℃, 6 h and 1 MPa CO2 pressure. The CP-COF sample exhibited commendable activity towards a range of epoxides. Moreover, it showed high reusability for the reaction without any loss in the catalytic efficiency.

A dual-ionic hyper-crosslinked polymer for efficient CO2 fixation and conversion

It is of great significance for reducing carbon emissions and protecting the environment to convert carbon dioxide (CO2) into high-value chemicals. The cycloaddition of CO2 with epoxides to prepare cyclic carbonates is a very attractive and potential approach. However, due to the inherent chemical inertness of CO2, the development of highly efficient, metal-free, solvent-free, and co-catalyst-free heterogeneous catalysts is crucial. Herein, a dual-ionic system hyper-cross-linked polymer (HIP-COOH-TMG) was synthesized by a post-synthetic strategy. HIP-COOH-TMG with multiple active sites was characterized by FT-IR, XPS and other characterizations. HIP-COOH-TMG exhibited the excellent catalytic activity than HIP-COOH for the CO2 cycloaddition, the yield and selectivity of chloropropene carbonate (CC) reached 99 % within 8 h at 110 °C under 1 MPa CO2 pressure. In addition, HIP-COOH-TMG is easily separated from the product, has good recyclability and structural stability, and exhibits high activity towards a series of epoxides. Finally, density functional theory (DFT) calculations reveal the synergistic catalytic mechanism of hydrogen bond donors (HBDs) groups = NH2+ sites and N sites activation of HIP-COOH-TMG, providing a reference for the design of metal-free, co-catalyst-free, and solvent-free heterogeneous catalysts.

Transformation of glycerol and CO2 to glycerol carbonate over ionic liquids-composite catalysts: Activity, stability, and effect of Li/Al metal oxide

The direct conversion of glycerol and carbon dioxide (CO2) into glycerol carbonate (GC) provides a green pathway for utilizing both the waste glycerol and CO2. However, this reaction is hampered by low CO2 absorbency and H2O generation. Currently, high pressure and H2O trapping agents are employed to elucidate these problems. Our objective is to design a spongy metal oxide/ionic liquids (ILs) blended composite that can solve both limitations under moderate conditions. We created a glycol-modified biphasic cation with various anions aided ILs in combination with electrospin Li/Al nanofibers-500 (LANS-500). It achieved 98.40 % selectivity and 11.45 mmol g−1 cat., GC yield in 6 h at 4 MPa CO2 pressure, 140 °C, and 1.10 g catalyst. Furthermore, even after numerous recyclings, the catalyst yield or selectivity remain unaffected. Also, the LANS-500 catalyst has a porous nature which results in the formation of a strong “adduct” with CO2, as shown by Bode plot, FT-IR, and TGA analysis. ILs, conversely, are acidic, excellent thermal stability, low vapor pressure, and less viscosity. As a result, LANS-500 may be easily incorporated into ILs to produce a highly permeable network with high ratios of surface to volume to create a coordination structure that can absorb more CO2.

Effects of chain composition of PBAT on the supercritical CO2 foaming and degradation behavior

Poly (butylene adipate-co-butylene terephthalate) (PBAT) with different copolymer compositions and molecular weights exhibits unique foaming behavior and dimensional stability when supercritical CO2 is used as a blowing agent. With an increase in the content of butylene glycol terephthalate (BT) from 43% to 61%, the melting point and crystallinity of PBAT increase. Consequently, the foaming temperature range of PBAT shifts toward a narrower, higher temperature zone, i.e., from 70 – 120 °C to 135 –160 °C under 13 MPa CO2 pressure. Additionally, CO2 solubility and desorption rate decrease, while PBAT exhibits a higher compression modulus and better foam dimensional stability. For similar BT contents, an increase in the molecular weight of PBAT widened the foaming temperature window and increased the cell density of the foam. It is noteworthy that increasing the BT content of PBAT to 52% not only ensures good dimensional stability of the PBAT foams, but also good biodegradability of PBAT. In addition, the effect of foam structure on degradation behavior was investigated. It was found that the PBAT foams with a higher volume expansion, larger cell size, and lower cell density degrade faster.

Rational engineering of multifunctional ionic covalent organic frameworks for metal-free and efficient chemical fixation of CO2 under mild conditions

The transformation of CO2 into high value-added chemicals such as cyclic carbonates provide a promising technology to solve the exceeding CO2 emission. In the absence of solvent and co-catalyst, the development of highly efficient and recyclable metal-free catalyst with excellent performance under mild conditions still remains a great challenge. Herein, a series of multifunctional ionic covalent organic frameworks (COFs) was synthesized via post-synthesis modification strategy of covalently grafting functionalized imidazole on triazine-based COF skeleton. The influence of bridged alkyl chain, imidazole functional group, nucleophile and grafting amount on catalytic activity was investigated in the cycloaddition of CO2 with epichlorohydrin. Remarkably, IM-COF-Br-Vinyl could afford 96.49% yield and > 99% selectivity with a turnover frequency (TOF) value of 5434 h−1 at 0.5 MPa CO2 pressure and 100 ℃ for 6 h, which was superior to other reported COF catalysts. The excellent catalytic performance was mainly ascribed to its excellent CO2 adsorption capacity and the synergistic effect of CO2-philic basic sites, hydrogen bond donors and nucleophilic anions. Additionally, the reusability and versatility of the catalyst was considered and the proposal catalytic mechanism was speculated according to the above conclusions. This strategy not only avoided the environmental pollution caused by catalytic system itself but also ensured the safety and low-energy consumption by realizing highly efficient catalytic conversion of CO2 under mild conditions. This provides an effective avenue for the design and synthesis of ionic liquid functionalized COF catalysts and the development of CO2 activation and utilization.

The characterization and mechanism of carbonated steel slag and its products under low CO2 pressure

Steel slag can be applied as a promising carbon fixing material. This paper mainly explored the characterization and carbonation mechanism of steel slag and its products at relatively low CO2 pressure. The experimental conditions were pure CO2 gas, 0.02 MPa CO2 pressure and 24 h carbonation time. The carbonation reaction degree of samples was evaluated by numerical carbonation rate. The phase composition and microstructure of samples were analyzed by XRD, FTIR, TG and SEM. The mechanical properties of carbonated steel slag bricks were evaluated by flexural strength. The results show that the average flexural strength of carbonated steel slag bricks (CSSB) reaches 15.9 MPa, and the carbonation rate reaches 33.9 %, which has a good carbonation degree. Low pressure and short time operation methods were adopted in this research, which provides ideas for reducing cost and simplifying carbon dioxide storage process in steel slag carbonation industry.

Metalloporphyrin and triazine integrated nitrogen-rich frameworks as high-performance platform for CO2 adsorption and conversion under ambient pressure

The development of multi-site integrated nanomaterials with remarkable properties and their application to selective CO2 capture and utilization have attracted extensive research interest. In this study, several metalloporphyrin and triazine integrated nitrogen-rich frameworks (M ⊂ PPTFs; where “M” stands for metal) were constructed and structurally characterized. These frameworks’ tendency to adsorb CO2 and their catalytic performance in the conversion of CO2 to cyclic carbonates were then investigated. The cycloaddition between CO2 and epichlorohydrin to produce chloropropene carbonate was selected as model reaction to screen the various catalysts and optimize the reaction conditions. The recycling performance and substrate scope were also evaluated. Evidence indicated that Zn ⊂ PPTF15 has dual functions: CO2 adsorption and its synergistic conversion. The CO2 adsorption capacity reached values of 2315 μmol/g and 1883 μmol/g at 273 K and 298 K, respectively. Under conditions of synergistic catalysis with tetrabutylammonium bromide (TBAB), Zn ⊂ PPTF15 afforded 96% yield of chloropropene carbonate with 99% selectivity at 60 °C and 0.1 MPa CO2 pressure for 15 h. The catalytic conditions and activity were investigated by comparison with reported triazinyl-based polymers. Notably, the catalytic system also displayed satisfactory applicability to other epoxides. Furthermore, Zn ⊂ PPTF15 was easily recyclable and did not become deactivated after repeated use. Based on the multi-site structure of the catalyst and the experimental results, a possible mechanism was proposed for the cycloaddition reaction.

A Biomass‐Ligand‐Based Ru(III) Complex as a Catalyst for Cycloaddition of CO2 and Epoxides to Cyclic Carbonates and a Study of the Mechanism

AbstractAiming highly efficient conversion of greenhouse gas CO2 to cyclic carbonates, a biomass Ru(III) Schiff base complex catalyst (SalRu) was constructed by employing a derivative of Lignin degradation (5‐aldehyde vanillin). The SalRu catalyst had a remarkable conversion for epoxides into corresponding cyclic carbonates even at atmospheric pressure of CO2 without the presence of co‐catalyst. As the condition at 120 °C and 2 MPa CO2 the conversion reached to 94 % with selectivity at 99 % after 8 h. 32 % cyclic carbonate production was obtained even under 0.2 MPa CO2 pressure. The epoxide activation and ring opening, CO2 insertion and cyclic carbonate formation were illuminated explicitly through the of characteristic absorption peaks changing, which further providing direct and visual evidence for the mechanism proposing. This study has important theoretical significance for the comprehensive utilization of environmental pollutants and energy.

Bismuth nanosheets with rich grain boundaries for efficient electroreduction of CO2 to formate under high pressures

AbstractElectrochemical CO2 reduction reaction (CO2RR) driven by sustainable energy has emerged as an attractive route to achieve the target of carbon neutral. Formate is one of the most economically viable products, and electrocatalytic CO2RR to formate is a promising technology. High-pressure H-cell electrolyzer is easy to operate and allows high CO2 solubility for realizing high current density, but the design of highly efficient catalysts for working under high CO2 pressures remains challenging. Bismuth-based catalysts exhibit high formate selectivity, but suffer from limited activity. Here, we report a high-performance catalyst, which is derived from BiPO4 nanopolyhedrons during electrocatalytic CO2RR to formate in neutral solution under high CO2 pressures. A high partial current density of formate (534 mA cm−2) and formate formation rate (9.9 mmol h−1 cm−2) with a formate Faradaic efficiency of 90% have been achieved over BiPO4-derived catalyst at an applied potential of −0.81 V vs. RHE under 3.0 MPa CO2 pressure. We discover that BiPO4 nanopolyhedrons evolve into metallic Bi nanosheets with rich grain boundaries in electrocatalytic CO2RR under high CO2 pressures, and the grain boundaries of the BiPO4-derived catalyst play a vital role in promoting electrocatalytic CO2RR to formate. Our theoretical studies reveal that the charge redistribution occurs at the grain boundaries of Bi surface, and this promotes CO2 activation and increases HCOO* intermediate stability, thus making the pathway for CO2RR to formate more selective and energy-favorable. This work not only demonstrates a highly efficient catalyst for CO2RR to formate but also discovers a unique feature of catalyst evolution under high CO2 pressures.

Hydroxyl-Imidazolium Ionic Liquid-Functionalized MIL-101(Cr): A Bifunctional and Highly Efficient Catalyst for the Conversion of CO2 to Styrene Carbonate.

Considerable attention has been focused on the development of catalysts for the coupling reaction of carbon dioxide (CO2) and epoxides due to the distinct advantages and importance of this reaction. To develop high-performance and easy-to-recycle catalyst is still a hot topic, especially for candidates with excellent activity under moderate conditions. A new heterogeneous catalyst, MIL-101-ImEtOH, is reported by post-synthesis modification, in which 2-(1-imidazol-1-yl) ethanol (Im-EtOH) is immobilized on MIL-101(Cr). In the absence of solvent and co-catalyst, MIL-101-ImEtOH exhibits high activity for the cycloaddition of CO2 and styrene oxide. A 95.6% yield is achieved under 0.5 MPa CO2 pressure and 90 °C by utilization of 50 mg of catalyst for 3 h. Moreover, MIL-101-ImEtOH is easily separated from the catalytic system by simple filtration. To elucidate the influence of hydroxyl group and porous structure on catalysis, other two supported ionic liquids, MIL-101-EtIm and PS-ImEtOH, are prepared and used to catalyze the title reaction under the same conditions. The contribution of each active component is determined by density functional theory along with noncovalent interaction analysis.

Rational design of Lewis acid-base bifunctional nanopolymers with high performance on CO2/epoxide cycloaddition without a cocatalyst

Based on the Schiff base reaction and post-modification strategy, novel nanocomposites of pyridine-zinc-based ionic porous organic polymers (Py-Zn@IPOPX, X = Br, I, Ac) were constructed and structurally characterized. Various Py-Zn@IPOPX were applied to the transformation of CO2 and epoxides into cyclic carbonates, and their catalytic activities were studied and discussed in detail. The results showed that Py-Zn@IPOPI possesses Lewis acid-base bifunctional features, and also modified with superior nucleophilic active groups, which exerted an important synergistic effect on activation of CO2 and epoxide, and ring-opening of epoxide. Under co-catalyst/solvent-free conditions, Py-Zn@IPOPI could afford 96 % PC yield and 99 % selectivity at 120 °C and 2.0 MPa CO2 pressure for 6 h, and turnover frequency (TOF) was high to 230 h−1. Moreover, the reusability and versatility of the catalyst were examined, and the catalytic mechanism was speculated according to the obtained results. Compared with previously reported porous polymer catalysts, Py-Zn@IPOPI requires much greener and milder reaction conditions while avoids the use of a co-catalyst, displaying bright prospects for the design and synthesis of ionic porous organic polymers for CO2 activation and utilization.

Tribological investigation of advanced coatings subjected to Venusian environment of 2.4 MPa CO2 pressure and 462 °C

Mechanical components in future missions to Venus will encounter high pressure (HP) and high temperature (HT) CO2 harsh conditions. Herein, the surface of Inconel 718 (INC 718), a HT nickel-based alloy was modified by applying advanced coatings by different deposition techniques. Three commercial coatings, namely Nedox PF-F™ (nickel-phosphorous alloy, referred as Nedox), Cera Tough™ (titanium-doped molybdenum disulfide alloy, referred as TiMoS2), and Balinit® DLC (amorphous hydrogenated diamond-like carbon, DLC) were coupled with PS400, a NASA-developed HT alloy, and slid against each other under HPHT Venusian-simulated environment. It was found that modifying one of the contacting surfaces (metal-on-coating) via PS400-deposition reduced the friction by 25%, whereas the wear increased significantly, compared to metal-on-metal contact. Sliding of the three coatings against PS400 coating (coating-on-coating) enhanced the frictional and wear performance significantly, in particular for PS400 vs. TiMoS2, attributed to the high wear resistance of the coating and the formation of beneficial oxide particles. The coefficient of friction (COF) was reduced by 38 and 43%, for PS400 vs. TiMoS2, and PS400 vs. DLC tribo-pairs, respectively compared to INC 718 vs. INC 718. In addition, the total wear rate decreased up to ten times, compared to metal-on-metal sliding.

Cobalt-based MOF nanoribbons with abundant O/N species for cycloaddition of carbon dioxide to epoxides

Chemical fixation of CO2 with epoxides is an effective option to achieve sustainable synthesis of cyclic organic carbonates. Although metal–organic frameworks (MOFs) are promising catalysts for this reaction, their low stability in aqueous solutions makes this application infeasible. In an effort to overcome this limitation, cobalt-based metal–organic framework (Co(II)MOF) nanoribbons have been prepared by coordinating the Co(II) ions with a new ligand (C16H12N4O4) full of oxygen and nitrogen moieties. Strong chemical interactions occur between the adsorbed CO2 and oxygen/nitrogen atoms in this porous MOF structure. Co(II)-MOF nanoribbons with tetra-n-butylammonium bromide acted as cocatalysts with ∼97% yield of cyclic carbonate (reaction kinetic rate of 14.7 × 106 µmol g-1 h−1) upon the cycloaddition of epichlorohydrin (ECH) to CO2 (>99% reaction selectivity under solvent-free reaction condition at 80 °C, 3 h and 1 MPa CO2 pressure). This work may open a new avenue for chemical fixation of CO2 by rational design of the components and morphology of MOF-based catalysts.

SBA-15 supported pyrazolium ionic liquid efficient fixation of carbon dioxide into cyclic carbonate under mild conditions: The synergistic contribution of SBA-15 and pyrazolium ionic liquid

Immobilized ionic liquids are one of the most popular catalysts for the cycloaddition of carbon dioxide (CO2) and epoxides with some distinguished advantages. However, the harsh reaction condition, especially for the high reaction pressure, is still the obstacle for its large-scale application. A series of amino-functionalized pyrazolium ionic liquids are grafted on SBA-15 in this work. Among them, SBA-15-APMPzBr(20) exhibits the best catalytic activity achieving 97.6% product yield under 0.5 MPa CO2 pressure at 100 °C by using 100 mg SBA-15-APMPzBr(20) for 10 h. No solvent is added in the catalytic system. Moreover, SBA-15-APMPzBr(20) exhibits the good recyclability and generality. Its excellent catalytic performance is attributed to the contribution from both immobilized ionic liquids and the SBA-15 supporter. Besides the mesoporous feature, the hydroxyl groups in SBA-15 promote the ring-opening of substrate, which is testified by the experimental measurements and density functional theory calculations.

Effective synthesis of cyclic carbonates from CO2 and epoxides catalyzed by acetylcholine bromide-based deep eutectic solvents

Fixing CO2 into cyclic carbonates is urgently required under green and eco-friendly conditions. Herein, we synthesized a series of bio-based deep eutectic solvents (DESs) for catalyzing cycloaddition reaction of CO2 with epoxides. Notably, AcChBr-LMA (2:1) formed by acetylcholine bromide (AcChBr) and L-malic acid (LMA) shows the best catalytic activity (up to 98% yield) and excellent recyclability under mild conditions (0.1 MPa CO2 pressure, 80 °C and 2 h). Mechanism studies have shown that there is a synergistic catalytic effect between the hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD).

Combination strategy of CO2 pressurization and ultrasound: To improve the freezing quality of fresh-cut honeydew melon

The effects of CO2 pressurization combined with ultrasound-assisted immersion freezing (CO2USIF) on improving the freezing quality of honeydew melon were studied. The cut melon samples were first subjected to 0.2, 0.5 and 0.8 MPa CO2 pressure for 2 h respectively, and then frozen by an ultrasound-assisted freezing device. The results indicated that the CO2 pressurization affected the water state and reduced the freezable water content. Cryo-observed results showed the ice crystal area of the 0.5CO2USIF sample was 66.6% smaller than that of the SF, and 60.8% smaller than that of the IF. The drip loss of 0.5CO2USIF sample was 58.2% lower than that of SF. The indexes of vitamin C, flavor, texture and color of CO2USIF samples were kept better. The SEM results showed that the cell structures of CO2USIF samples were better maintained. These demonstrated that CO2USIF technology has application potential in improving the quality of frozen food.