Phase equilibria of poly(methyl methacrylate) in supercritical mixtures of carbon dioxide and chlorodifluoromethane

Phase behavior data are presented for poly(methyl methacrylate) (PMMA: M_w= 15,000, 120,000) in supercritical solvent mixtures of carbon dioxide (CO₂) and chlorodifluoromethane (HCFC-22). Experimental cloud point curves, which were the phase boundaries between single and liquid-liquid phases, were measured by using a high-pressure equilibrium apparatus equipped with a variable-volume view cell at various CO₂ compositions up to about 63 wt% (on a polymer-free basis) and at temperatures up to about 100 °C. The cloud point curves exhibited the characteristics of a lower critical solution temperature phase behavior. As the CO₂ content in the solvent mixture increased, the cloud point pressure at a fixed temperature increased significantly. Addition of CO₂ to HCFC-22 caused a lowering of the dissolving power of the mixed solvent due to the decrease of the solvent polarity. The cloud point pressure increased with increasing the molecular weight of PMMA.     

High molecular weight graft stabilisers for dispersion polymerisation of vinylidene fluoride in supercritical carbon dioxide: the effect of architecture

A group of high molecular weight graft stabilisers, both fluorinated and non-fluorinated, were synthesised by thermal ring-opening esterification of anhydride copolymers. These included poly(methyl vinyl ether-alt-maleic anhydride) and poly(maleic anhydride-octadecene) and were reacted with alcohols, including 1H,1H,2H,2H-perfluorooctanol, 1H,1H,2H,2H-perfluoro-dodecanol and 1-octanol. The stabilisers were fully characterised by ¹H, ¹⁹F and ¹³C nuclear magnetic resonance, diffuse reflectance Fourier transform infrared spectroscopy, and thermal analysis. Their phase behaviour in supercritical carbon dioxide (scCO₂), vinylidene fluoride (VDF), and a mixture of scCO₂/VDF was also studied using a variable volume view cell. Each stabiliser was tested for the dispersion polymerisation of VDF in scCO₂. The effect of the stabiliser architecture on the molecular weight and morphology of the poly(vinylidene fluoride) (PVDF) polymer product was investigated. Steric stabilisation effects were observed. Gel permeation chromatography and scanning electron microscopy were used for the characterisation of the molecular weight and morphology of PVDF polymers.     

Kinetics of carbon dioxide absorption in aqueous solution of diethylenetriamine (DETA)

A string of discs contactor was used to measure the kinetics CO₂ absorption in unloaded aqueous solution with the diethylenetriamine (DETA) concentrations ranging between 1.0 and 2.9 kmol m⁻³ and at temperatures ranging between 298.1 and 332.3 K. The reaction rates strongly increase as the increasing the concentrations and temperatures. Both the termolecular and the zwitterion models were applied to interpret the experimental data and gave identical results for all practical purposes. The reaction order with respect to the DETA concentration is found to vary slightly with temperature between 1.71 and 1.76 with an average of about 1.73. Both DETA and water contribute as a base in carbamate formation. It was found that fitting of experimental data to the termolecular mechanism gave statistically more robust results than fitting to the zwitterion mechanism.     

Direct synthesis of poly(l-lactic acid) in supercritical carbon dioxide with dicyclohexyldimethylcarbodiimide and 4-dimethylaminopyridine

The direct synthesis of poly(l-lactic acid) (PLLA) from an l-lactic acid oligomer has been performed in supercritical carbon dioxide (scCO₂) using an esterification promoting agent, dicyclohexyldimethylcarbodiimide (DCC), and 4-dimethylaminopyridine (DMAP) as a catalyst. PLLA within M_n of 13,500 g/mol was synthesised in 90% yield at 3500 psi and 80 °C after 24 h. The molecular weight distribution of the products was narrower than PLLA prepared with melt-solid phase polymerisation under conventional conditions. Both DCC and DMAP showed high solubility in scCO₂ (DCC: 7.6 wt% (1.63×10⁻² mol/mol CO₂) at 80 °C, 3385 psi, DMAP: 4.5 wt% (1.62×10⁻²mol/mol CO₂) at 80 °C, 3386 psi) and supercritical fluid extraction was found to be effective at removing excess DMAP and DCC after the polymerisation was complete. We show that DCC and DMAP are effective esterification promoting reagents with further applications for condensation polymerisations in scCO₂.     

Kinetics study of carbon dioxide absorption in aqueous solutions of 1,6-hexamethyldiamine (HMDA) and 1,6-hexamethyldiamine, N,N′ di-methyl (HMDA, N,N′)

A study towards the kinetics of CO₂ in aqueous solutions of 1,6-hexamethyl diamine (HMDA) and 1,6-hexamethyl diamine, N,N′ di-methyl (HMDA, N,N′) was performed at concentrations ranging from 0.5 to 2.5 mol/L and temperatures from 283 up to 303 K. The kinetics data were determined by CO₂ absorption experiments using a stirred cell reactor with a flat interface between gas and liquid. These new CO₂ solvents were identified in earlier work for their high CO₂ capacity and limited corrosiveness. The experimental technique was validated using kinetic experiments for a 2.5 mol/L monoethanolamine solution. In view of double amine functionality and the six carbon chain between the amine groups, attention was paid to whether the amine groups acted independently and whether or not internal cyclisation would affect the carbamate forming mechanism. The reaction order with respect to HMDA was found to vary from 1.4 to 1.8 with increasing temperature. Absorption experiments in an equimolar solution of HMDA with HCl showed that the two amine groups react independently from each other towards CO₂. The reactivity of both diamines was more than five times larger than for monoethanolamine. The secondary diamine HMDA, N,N′ was found to be even more reactive towards CO₂. Additionally, the effect of CO₂ loading on the kinetics was studied for 0.5 mol/L aqueous solutions of HMDA and HMDA, N,N′ at 293 K. Both solvents are from absorption kinetics point of view good candidates for further evaluation as solvent (-component) for CO₂ capture.     

Kinetics of carbon dioxide absorption into aqueous amine amino acid salt: 3-(methylamino)propylamine/sarcosine solution

A string of discs contactor apparatus was used to measure the CO₂ absorption kinetics into an unloaded aqueous amine amino acid salt, 3-(methylamino)propylamine/sarcosine, SARMAPA solution. The solution was prepared by mixing equinormal proportions of sarcosine, SAR and 3-(methylamino)propylamine, MAPA. Experiments were carried out for the concentration range 1.0–5.0 kmol m⁻³ and for temperatures 25–62 °C. The termolecular mechanism was applied to interpret the experimental data after correcting for non-idealities from the ionic strength using an ionic correction factor. A model correlation without the ionic strength correction was found not to give a good fit to the experimental data. The reaction rate constant for aqueous SARMAPA was determined and found to be comparable to values for amines. It increases significantly with temperature and concentration. The reaction rate constant for water is higher in the SARMAPA system than in amine systems indicating that water contributes significantly to the overall absorption rate and more than in amine systems. The reaction order with respect to the amino acid salt, SARMAPA, concentration varies from 1.06 to 1.43 with an average value of 1.21. A simplified approach applied to the complex speciation chemistry of the amine amino acid salt, AAAS, system gave a good representation of the experimentally observed kinetic rate constant.     

Solubility in the binary and ternary system for poly(alkyl acrylate)-supercritical solvent mixtures

Experimental cloud-point data to 210 ‡C and 2,200 bar are presented for binary and ternary mixtures of poly(methyl acrylate)-CO₂-methy acrylate and poly(ethyl acrylate)-CO₂, propylene, and 1-butene-ethyl aerylate systems. The accuracy of the experimental apparatus was tested by comparing the measured pressure-temperature phase behavior data of the poly(ethyl acrylate)-CO₂ system obtained in this study with those of Rindfleisch et al. [1995]. The phase behaviors for the system poly(methyl acrylate)-CO₂-methyl acrylate were measured in changes of pressure-temperature slope, and with cosolvent concentrations of 0, 5.0, 13.7, 25.3, and 43.3 wt%, respectively. With 48.3 wt% methyl acrylate to the poly(methyl acrylate)-CO₂ solution significantly changes, the phase behavior curve takes on the appearance of a typical lower critical solution temperature (LCST) boundary. The impact of ethyl acrylate on the cloud-point for the poly(ethyl acrylate)-CO₂ system shows the change of slope of the phase behavior curves from negative to positive with ethyl acrylate concentration of 0, 8.2, and 25.0 wt%. The cloud-point behavior for the poly(ethyl acrylate)-CO₂-39.5 wt% ethyl acrylate system shows an LCST curve. The solubility curve to ∼150 ‡C and 1,650 bar for poly(ethyl acrylate)-propylene-ethyl acrylate system shows the change of pressure-temperature diagram and with ethyl acrylate concentration of 0, 7.2 and 21.0 wt%. Also, when 41.1 wt% ethyl acrylate was added to the poly(ethyl acrylate)-propylene solution, the phase behavior curve showed the LCST region. The high pressure phase behavior of poly(ethyl acrylate)-1-butene-0, 3.1, 8.1, 18.5 and 30.7 wt% ethyl acrylate system presented the change of pressure-temperature curve from the UCST region to U-LCST region as the ethyl acrylate concentration increased.     

Cloud-point measurement of the biodegradable poly(d,l-lactide-co-glycolide) solution in supercritical fluid solvents

Experimental data of high pressure phase behavior between 35 °C and 105 °C and pressures up to 2,200 bar is presented for poly(d,l-lactic acid)(d,l-PLA) and poly(lactide-co-glycolide)₁₅ (PLGA₁₅), PLGA₂₅, and PLGA₅₀ in supercritical carbon dioxide, trifluoromethane (CHF₃), chlorodifluoromethane (CHClF₂), dichloromethane (CH₂Cl₂), and chloroform (CHCl₃). d,l-PLA dissolves in carbon dioxide at pressures of 1,250 bar, in CHF₃ at pressures of 500 to 750 bar, and in CHClF₂ at pressures of 30–145 bar. As glycolic acid (glycolide) is added to the backbone of PLGA, the cloud point pressure increases by 36 bar/(mol GA) in carbon dioxide, 27 bar/(mol GA) in CHF₃, and by only 3.9 bar/(mol GA) in CHClF₂. PLGA₅₀ does not dissolve in carbon dioxide at pressures of 2,800 bar, whereas it is readily soluble in CHClF₂ at pressures as low as 95 bar at 40 °C. Cloud point behavior of d,l-PLA, PLGA₁₅, and PLGA₂₅ in supercritical carbon dioxide shows the effect of glycolide content between 35 °C and 108 °C. Also, the phase behavior for poly(lactic acid) — carbon dioxide-CHClF₂ mixture shows the changes of pressure-temperature slope, and with CHClF₂ concentration of 6 wt%, 19 wt%, 36 wt% and 65 wt%. The cloud-point behavior shows the impact of glycolide content on the phase behavior of PLA, PLGA₁₅, PLGA₂₅ and PLGA₅₀ in supercritical CHClF₂. A comparison was made between the phase behaviors of d,l-PLA and poly(l-lactide)(l-PLA) in supercritical CHF₃. The phase behavior of CHF₃ as a cosolvent for 5 wt% d,l-PLA-supercritical carbon dioxide system is presented for the effect being added 10 wt% and 29 wt% to CHF₃ content.     

A food grade approach for the isolation of major alkylresorcinols (ARs) from rye bran applying tailored supercritical carbon dioxide (scCO2) extraction combined with HPLC

Tailored supercritical carbon dioxide (scCO₂) extraction of alkylresorcinols (ARs) from rye bran resulting in pre-purification of ARs already during extraction process. The pre-purification was achieved by splitting the extraction process in 2 steps._. In both steps, the CO₂ pressure was set at 25 MPa with a flow rate of 10 g/min. The first step was carried out at 70 °C, 0.06% of ethanolic co-solvent for 2 h, followed by the second step at 45 °C using 10% of ethanolic co-solvent for 4 h, resulting in a pre-purified ARs extract. From the pre-purified scCO₂ extract, chromatographed on C8 column, were obtained pure ARs homologues of C17, C19 and C21 (68% of total) eluting separately in a linear gradient of ethanol. Additionally, a rapid method for the isolation of high purified pools of ARs homologues using a disposable solid phase extraction SPE-C18 column and a step gradient of ethanol was developed.     

Kinetics of absorption of carbon dioxide into aqueous blends of 2-(1-piperazinyl)-ethylamine and N-methyldiethanolamine

The kinetics absorption of CO₂ into aqueous blends of 2-(1-piperazinyl)-ethylamine (PZEA) and N-methyldiethanolamine (MDEA) were studied at 303, 313, and 323 K using a wetted wall column absorber. The PZEA concentrations in the blends with MDEA varied from 0 to to see the effect of PZEA as an activator in the blends with two different total amine concentrations (1.0 and ). Based on the pseudo-first-order condition for the CO₂ absorption, the overall second-order reaction rate constants were determined from the kinetic measurements. The kinetic rate parameters were calculated and presented at each experimental condition.     

Foaming strategies for bioabsorbable polymers in supercritical fluid mixtures. Part I. Miscibility and foaming of poly(l-lactic acid) in carbon dioxide + acetone binary fluid mixtures

Miscibility and foaming of poly(l-lactic acid) (PLLA) in carbon dioxide + acetone mixtures have been explored over the temperature and pressure ranges from 60 to 180 °C and 14 to 61 MPa. Liquid-liquid phase boundaries were determined in a variable-volume view-cell for polymer concentrations up to 25 wt% PLLA and fluid mixtures containing 67-93 wt% CO₂ over a temperature range from 60 to 180 °C. Even though not soluble in carbon dioxide at pressures tested, the polymer could be completely solubilized in mixtures of carbon dioxide and acetone at modest pressures.Foaming experiments were carried out in different modes. Free-expansions were carried out by exposure and swelling in pure carbon dioxide in a view-cell followed by depressurization. Foaming experiments were also carried out within the confinement of specially designed molds with porous metal surfaces as boundaries to direct the fluid escape path and to generate foams with controlled overall shape and dimensions. These experiments were conducted in pure carbon dioxide and also in carbon dioxide + acetone fluid mixtures over a wide range of temperatures and pressures. Foaming in carbon dioxide + acetone mixtures was limited to 1 and 4 wt% acetone cases. Microstructures were examined using an environmental scanning electron microscope (ESEM). Depending upon the conditions employed, pore diameters ranging from 5 to 400 μm were generated. At a given temperature, smaller pores were promoted when foaming was carried out by depressurization from higher pressures. At a given pressure, smaller pores were generated from expansions at lower temperatures. Foams with larger pores were produced in mixtures of carbon dioxide with acetone.