In situ infrared study of the effect of amine density on the nature of adsorbed CO2 on amine-functionalized solid sorbents.

In situ Fourier transform infrared spectroscopy was used to determine the nature of adsorbed CO2 on class I (amine-impregnated) and class II (amine-grafted) sorbents with different amine densities. Adsorbed CO2 on amine sorbents exists in the form of carbamate-ammonium ion pairs, carbamate-ammonium zwitterions, and carbamic acid. The adsorbed CO2 on high-amine density sorbents showed that the formation of ammonium ions correlates with the suppression of CH stretching intensities. An HCl probing technique was used to resolve the characteristic infrared bands of ammonium ions, clarifying that the band observed around 1498 cm(-1) is a combination of the deformation vibration of ammonium ion (NH3(+)) at 1508 and 1469 cm(-1) and the deformation vibration of NH in carbamate (NHCOO(-)) at 1480 cm(-1). Carbamate and carbamic acid on sorbents with low amine density desorbed at a rate faster than those on sorbents with high amine density after switching the flow from CO2 to Ar at 55 °C. Evaluation of the desorption temperature profiles showed that the temperature required to achieve the maximal desorption of CO2 (Tmax. des) increases with amine density. The adsorbed CO2 on sorbents with high amine density is stabilized via hydrogen bonding interactions with adjacent amine sites. These sorbents require higher temperature to desorb CO2 than those with low amine density.

Ex Situ CO2 capture by carbonation of steelmaking slag coupled with metalworking wastewater in a rotating packed bed.

Both basic oxygen furnace (BOF) slag and cold-rolling wastewater (CRW) exhibiting highly alkaline characteristics require stabilization and neutralization prior to utilization and/or final disposal. Using CO2 from flue gases as the stabilizing and neutralizing agents could also diminish CO2 emissions. In this investigation, ex situ hot stove gas containing 30 vol% CO2 in the steelmaking process was captured by accelerated carbonation of BOF slag coupled with CRW in a rotating packed bed (RPB). The developed RPB process exhibits superior results, with significant CO2 removal efficiency (η) of 96-99% in flue gas achieved within a short reaction time of 1 min at 25 °C and 1 atm. Calcite (CaCO3) was identified as the main product according to XRD and SEM-XEDS observations. In addition, the elimination of lime and Ca(OH)2 in the BOF slag during carbonation is beneficial to its further use as construction material. Consequently, the developed RPB process could capture the CO2 from the flue gas, neutralize the CRW, and demonstrate the utilization potential for BOF slag. It was also concluded that carbonation of BOF slag coupled with CRW in an RPB is a viable method for CO2 capture due to its higher mass transfer rate and CO2 removal efficiency in a short reaction time.

Chemical fluid deposition of monometallic and bimetallic nanoparticles on ordered mesoporous silica as hydrogenation catalysts.

A simple and green method of depositing monometallic (Ru, Rh, Pd) and bimetallic nanoparticles (Ru-Rh, Ru-Pd and Rh-Pd) on an ordered mesoporous silica support (MCM-41) in supercritical carbon dioxide (scCO2) is described. Metal acetylacetonates were used in the experiments as CO2-soluble metal precursors. Suitable temperature and pressure conditions for synthesizing each kind of nanoparticles were applied in this study. The characterizations of these nanocomposites were performed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The nanoparticles had average sizes varying from 2 nm to 8 nm. The Ru nanoparticles were clearly shown to be inside the mesopores of MCM-41 from the TEM image. These nanocomposites used as catalysts for hydrogenation was demonstrated. The efficiency of the scCO2 prepared Ru/MCM-41 catalyst was nearly 8 times than that of a Ru/MCM-41 catalyst prepared by conventional impregnation method.

Facile synthesis of silver nanoparticles in CO2-expanded liquids from silver isostearate precursor.

This approach provides a new technique to synthesize silver nanoparticles (AgNPs) using CO(2)-expanded liquids (CXLs) as the processing medium. A soluble form of silver carboxylate, silver isostearate (AgISt), was synthesized and characterized. The XRD and DSC analyses indicated that the methylated branched alky chains in AgISt exhibited a steric hindrance to impede the growth of layered structure of AgISt molecules, which led to the high solubility of AgISt in nonpolar solvents. By using AgISt as silver precursor, AgNPs of 2.64 +/- 0.51 nm in diameter were synthesized in CO(2)-expanded heptane with H(2) as the reducing agent. The ATR-FTIR analysis showed that the produced AgNPs were capped with isostearic acid, which was derived from the reduction of AgISt. Hence, the isostearic acid capped AgNPs were well-dispersed in heptane to form a stable silver organosol.

Hydrogenation of High Molecular Weight Bisphenol A Type Epoxy Resin BE503 in a Functional and Greener Solvent Mixture Using a Rh Catalyst Supported on Carbon Black.

A functional greener solvent mixture containing water, isopropyl alcohol (IPA) and ethyl acetate with the ratio 10:20:70 (wt%) was found to accelerate hydrogenation of bisphenol A type epoxy resin BE503 with a molecular weight of 1500 through an on-water mechanism, and led to an increased H2 availability, due to high solubility of H2 in IPA. Different carbon-based supports were tested and VulcanXC72 was found as the best support among the tested carbon-based ones as it possessed the highest amount of electron deficient promoter, RhOx. The catalyst, Rh5/VulcanXC72-polyol, synthesized by the microwave assisted polyol method, yielded a 100% hydrogenation of aromatic rings with an epoxy ring opening below 20.0% at 50 °C and a H2 pressure of 1000 psi in 2.25 h. Intrinsic activation energies for the hydrogenation of aromatic rings and epoxy ring opening were experimentally estimated and a mechanism for the hydrogenation of BE503 was proposed, wherein the hydrogenation of aromatic rings and epoxy ring opening in BE503 proceeded simultaneously in parallel and in-series with parallel being the major pathway.

Purification of Polybutylene Terephthalate by Oligomer Removal Using a Compressed CO2 Antisolvent.

In this study, the cyclic oligomers in the highly chemically resistant polyester polybutylene terephthalate (PBT) were effectively removed using a compressed CO2 antisolvent technique in which 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) was used as the solvent. In addition to the oligomers, tetrahydrofuran was completely removed because of its low molecular weight and liquid state. The effects of the operating variables, including temperature, pressure, and the PBT concentration in HFIP, on the degree of removal of the oligomers were systematically studied using experimental design and the response surface methodology. The most appropriate operating conditions for the purification of PBT were 8.3 MPa and 23.4 °C when using 4.5 wt % PBT in HFIP. Under these conditions, the cyclic trimers and dimers could be removed by up to 81.4% and 95.7%, respectively, in a very short operating time.

Optimization of continuous lipid extraction from Chlorella vulgaris by CO2-expanded methanol for biodiesel production.

CO2-expanded methanol (CXM) was used to extract lipids from the microalgae Chlorella vulgaris (a total lipid content of 20.7% was determined by Soxhlet extraction with methanol at 373 K for 96 h) in a continuous mode. The CXM was found to be a superior solvent to methanol, ethanol, pressurized methanol and ethanol, and CO2-expanded ethanol for lipid extraction. The effects of operation variables including temperature, pressure and CO2 flow rate on extraction performance were examined using the response surface and contour plot methodologies. The optimal operating conditions were at a pressure of 5.5 MPa, a temperature of 358 K, a methanol flow rate of 1 mL/min and a CO2 flow rate of 3.0 mL/min, providing an extracted lipid yield of 84.8 wt% over an extraction period of 30 min. Compared with propane methanol mixture, CXM was safer and more energy efficient for lipid extraction from C. vulgaris.

Continuous extraction of lipids from Schizochytrium sp. by CO2-expanded ethanol.

CO2-expanded ethanol (CXE) was used to extract DHA-containing lipids from Schizochytrium sp. with a 35.7 wt% lipid content of dry biomass in a continuous mode. The effects of operation variables such as temperature, pressure, ethanol flow rate and CO2 flow rate on extraction performance were investigated. Based on a 2(4)-central composite design and response surface methodology, the optimal operating conditions were determined to be a pressure of 6.9 MPa, a temperature of 313 K, an ethanol flow rate of 1 mL/min and a CO2 flow rate of 6.0 mL/min, providing an extracted lipid yield of 87 wt% over an extraction period of 30 min. Not only the lipid yield obtained using CXE was observed to be significantly greater than those using ethanol and pressurized ethanol as the solvents, but also a lower amount of ethanol and less time were required to achieve the same extraction yield by using CXE.

Innovative pretreatment of sugarcane bagasse using supercritical CO2 followed by alkaline hydrogen peroxide.

An innovative method for pretreatment of sugarcane bagasse using sequential combination of supercritical CO2 (scCO2) and alkaline hydrogen peroxide (H2O2) at mild conditions is proposed. This method was found to be superior to the individual pretreatment with scCO2, ultrasound, or H2O2 and the sequential combination of scCO2 and ultrasound regarding the yield of cellulose and hemicellulose, almost twice the yield was observed. Pretreatment with scCO2 could obtain higher amount of cellulose and hemicellulose but also acid-insoluble lignin. Pretreatment with ultrasound or H2O2 could partly depolymerize lignin, however, could not separate cellulose from lignin. The analysis of liquid products via enzymatic hydrolysis by HPLC and the characterization of the solid residues by SEM revealed strong synergetic effects in the sequential combination of scCO2 and H2O2.

CO2 uptake performance and life cycle assessment of CaO-based sorbents prepared from waste oyster shells blended with PMMA nanosphere scaffolds.

In this paper, we demonstrate a means of simultaneously solving two serious environmental issues by reutilization of calcinated mixture of pulverized waste oyster shells blending with poly(methyl methacrylate) (PMMA) nanospheres to prepare CaO-based sorbents for CO2 capture. After 10 cycles of isothermal carbonation/calcination at 750°C, the greatest CO2 uptake (0.19 g CO2/g sorbent) was that for the sorbent featuring 70 wt% of PMMA, which was almost three times higher than that (0.07 g CO2/g sorbent) of untreated waste oyster shell. The greater CO2 uptake was likely a result of particle size reduction and afterwards surface basicity enhancement and an increase in the volume of mesopores and macropores. Following simplified life cycle assessment, whose all input values were collected from our experimental results, suggested that a significant CO2 emission reduction along with lesser human health and ecosystems impacts would be achieved immediately once waste is reutilized. Most importantly, the CO2 uptake efficiency must be greater than 20% or sorbents prepared from limestone mining would eventually produce a net positive CO2 emission.

Catalytic hydrodechlorination of dioxins over palladium nanoparticles in supercritical CO2 swollen microcellular polymers.

In this study, palladium nanoparticles embedded in monolithic microcellular high density polyethylene supports are synthesized as heterogeneous catalysts for remediation of 1,6-dichlorodibenzo-p-dioxin and 2,8-dichlorodibenzofuran in 200 atm of supercritical carbon dioxide containing 10 atm of hydrogen gas and at 50-90°C. Stepwise removal of chlorine atoms takes place first, followed by saturation of two benzene rings with slower reaction rates. The pseudo first order rate constant of initial hydrodechlorination for 2,8-dichlorodibenzofuran is 4.3 times greater than that for 1,6-dichlorodibenzo-p-dioxin at 78°C. The catalysts are easily separated from products and can be recyclable and reusable without complicated recovery and cleaning procedures.

Accelerated carbonation of steelmaking slags in a high-gravity rotating packed bed.

Carbon dioxide (CO(2)) sequestration using the accelerated carbonation of basic oxygen furnace (BOF) slag in a high-gravity rotating packed bed (RPB) under various operational conditions was investigated. The effects of reaction time, reaction temperature, rotation speed and slurry flow rate on the CO(2) sequestration process were evaluated. The samples of reacted slurry were analyzed quantitatively using thermogravimetric analysis (TGA) and atomic absorption spectrometry (AAS) and qualitatively using X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), and transmission electron microscopy (TEM). The sequestration experiments were performed at a liquid-to-solid ratio of 20:1 with a flow rate of 2.5 L min(-1) of a pure CO(2) stream under atmospheric temperature and pressure. The results show that a maximum conversion of BOF slag was 93.5% at a reaction time of 30 min and a rotation speed of 750 rpm at 65°C. The experimental data were utilized to determine the rate-limiting mechanism based on the shrinking core model (SCM), which was validated by the observations of SEM and TEM. Accelerated carbonation in a RPB was confirmed to be a viable method due to its higher mass-transfer rate.

Evaluation of alkanolamine solutions for carbon dioxide removal in cross-flow rotating packed beds.

The removal of CO(2) from a 10 vol% CO(2) gas by chemical absorption with 30 wt% alkanolamine solutions containing monoethanolamine (MEA), piperazine (PZ), and 2-amino-2-methyl-1-propanol (AMP) in the cross-flow rotating packed bed (RPB) was investigated. The CO(2) removal efficiency increased with rotor speed, liquid flow rate and inlet liquid temperature. However, the CO(2) removal efficiency decreased with gas flow rate. Also, the CO(2) removal efficiency was independent of inlet gas temperature. The 30 wt% alkanolamine solutions containing PZ with MEA were the appropriate absorbents compared with the single alkanolamine (MEA, AMP) and the mixed alkanolamine solutions containing AMP with MEA. A higher portion of PZ in alkanolamine solutions was more favorable to CO(2) removal. Owing to less contact time in the cross-flow RPB, alkanolamines having high reaction rates with CO(2) are suggested to be used. For the mixed alkanolamine solution containing 12 wt% PZ and 18 wt% MEA, the highest gas flow rate allowed to achieve the CO(2) removal efficiency more than 90% at a liquid flow rate of 0.54 L/min was of 29 L/min. The corresponding height of a transfer unit (HTU) was found to be less than 5.0 cm, lower than that in the conventional packed bed.

Supercritical CO2 desorption of activated carbon loaded with 2,2,3,3-tetrafluoro-1-propanol in a rotating packed bed.

Desorption of activated carbon loaded with 2,2,3,3-tetrafluoro-1-propanol (TFP) by supercritical carbon dioxide in a rotating packed bed was investigated in this study. The experimental data show that the time required to achieve complete desorption of TFP from activated carbon in a rotating packed bed was much lower than that in a static packed bed. The reduction of desorption time is attributed to the presence of centrifugal force. The supercritical CO2 desorption efficiency in a rotating packed bed was observed to increase with increasing rotation speed, pressure, and C02 flow rate. To enhance desorption efficiency, a smaller activated carbon particle size was suggested. At low operating pressures such as 8.96 and 11.72 MPa, a better desorption efficiency was found to occur at lower temperatures in a temperature range of 305-335 K. However, at high operating pressures such as 15.86 MPa, a temperature of 315 K was found to be more appropriate for desorption, as compared to other temperatures. Due to a reduction of packed bed volume and an increase in desorption efficiency, supercritical CO2 desorption in a rotating packed bed is suggested for recovering TFP from the exhaust gases.