High Pressure Phase Equilibria of the Related Substances in the Limonene Oxidation in Supercritical CO 2 (original) (raw)
Related papers
Phase equilibrium and kinetics of O2-oxidation of limonene in high pressure carbon dioxide
The Journal of Supercritical Fluids, 2012
The effect of phase equilibrium on the kinetics of O 2-oxidation of limonene was studied. Vapour-liquid equilibrium measurements of the system (CO 2 + O 2 + limonene) were performed at 328 K and 8, 10, 10.7 and 11 MPa. In an attempt to establish a relation between vapour-liquid equilibrium data and the kinetics of limonene oxidation, different reactions were performed at 328 K and at different CO 2 total pressures of 9.3 MPa, 10 MPa and 10.3 MPa (with the reaction mixture being biphasic) and at 12.2 MPa (in a single supercritical phase). The volumetric concentration of O 2 in the liquid phase increased as CO 2 was added to the system, although this behaviour was only observed close to the critical region. Kinetics of oxidation reactions performed at biphasic conditions, suggests that is the volumetric concentration of O 2 in the liquid phase that is controlling the reaction rates.
Effect of Flow Rate of a Biphasic Reaction Mixture on Limonene Hydrogenation in High Pressure CO 2
Industrial & Engineering Chemistry Research, 2009
In this work the effect of the overall flow rate of the biphasic reaction mixture on hydrogenation distribution products is reported. As it was already presented by us, the reaction rate strongly correlates with the phase equilibrium existing in the system. On the other hand, carbon dioxide is nonreactive; nevertheless by its presence it changes the energy balance. The catalytic performance in four kinds of overall flow rate conditions (1.3, 3.3, 5.3, and 7.3 mL/min) was compared under fixed hydrogen (2.5 MPa) and total pressure (12.5 MPa). The appearance of isomers of limonene and partially hydrogenated products significantly rely upon the flow rate used in the reaction. The 1% Pd SCN catalyst used in the reaction gave the final products trans-and cis-p-menthane in a 2 / 3 to 1 / 3 molar ratio.
Modelling High-Pressure Vapor-Liquid Equilibrium of Limonene, Linalool and CO2 Systems
Journal of Supercritical Fluids The
The research reported in this study is focused on modeling high-pressure phase behavior for CO 2-limonene and CO 2-linalool. A modified Peng-Robinson equation of state was applied to calculate vapor-liquid equilibrium using five different mixing rules obtained by incorporating activity coefficient models. The methodologies proposed by Heidemann-Kokal, Wong-Sandler and LCVM were used coupled with NRTL, UNIQUAC and UNIFAC models. A comparative analysis of the generated models was done for the binary systems and the best model was chosen to describe phase behavior of the system CO 2-limonene-linalool. An isothermal flash calculation was applied to investigate selectivity and yield simultaneously for this ternary system in order to understand better the process parameters governing supercritical CO 2 deterpenation of citrus peel oil. The results showed that to obtain good separation between limonene and linalool at 50°C and pressures from 80 to 90 bar a high CO 2 /oil ratio is needed. As this ratio decreases, the process can be operated at 60 and 70°C over the same pressure range with equivalent performance.
Modeling high-pressure vapor–liquid equilibrium of limonene, linalool and carbon dioxide systems
The Journal of Supercritical Fluids, 1999
The research reported in this study is focused on modeling high-pressure phase behavior for CO 2 -limonene and CO 2 -linalool. A modified Peng-Robinson equation of state was applied to calculate vapor-liquid equilibrium using five different mixing rules obtained by incorporating activity coefficient models. The methodologies proposed by Heidemann-Kokal, Wong-Sandler and LCVM were used coupled with NRTL, UNIQUAC and UNIFAC models. A comparative analysis of the generated models was done for the binary systems and the best model was chosen to describe phase behavior of the system CO 2 -limonene-linalool. An isothermal flash calculation was applied to investigate selectivity and yield simultaneously for this ternary system in order to understand better the process parameters governing supercritical CO 2 deterpenation of citrus peel oil. The results showed that to obtain good separation between limonene and linalool at 50°C and pressures from 80 to 90 bar a high CO 2 /oil ratio is needed. As this ratio decreases, the process can be operated at 60 and 70°C over the same pressure range with equivalent performance.
Applied Catalysis A: General, 2006
The selective oxidation of benzyl alcohol to benzaldehyde with molecular oxygen in supercritical carbon dioxide over a commercial 0.5 wt.% Pd/Al 2 O 3 catalyst was studied under continuous-flow conditions using toluene as a co-solvent. The whole range from neat CO 2 , toluene-modified CO 2 , CO 2 -expanded toluene to neat toluene was investigated. Adding a small amount of toluene to the feed (molar ratio toluene/alcohol of 1/1) resulted in a strikingly higher reaction rate than in neat CO 2 . The turnover frequency reached 2500 h À1 compared to 1500 h À1 without toluene. A too high toluene concentration led to a biphasic reaction mixture and to a remarkably lower catalytic activity (TOF 130 h À1 at a toluene/benzyl alcohol/O 2 /CO 2 molar ratio of 16/0.8/0.4/82.8). In all cases, a strong dependence of the reaction rate on the pressure was found, which was closely related to the phase behaviour. The best catalytic activity could be achieved under monophasic conditions due to the elimination of the gas/liquid interface as uncovered by video monitoring combined with ATR-IR spectroscopy. Additional in situ infrared spectroscopic investigations showed that toluene was fully dissolved already at low pressure (120 bar), whereas higher pressure was required (150 bar) to dissolve benzyl alcohol and thus to reach a single phase. Using a higher amount of toluene (five times more toluene than alcohol) led to complete dissolution of the benzyl alcohol in the CO 2 /toluene mixture at 130 bar and thus to a higher catalytic activity in this region of lower pressure. #
The Journal of Supercritical Fluids, 2005
The high-pressure phase behavior of the ternary system carbon dioxide + limonene + linalool was determined experimentally by a synthetic method. All the experiments were carried out in an approximately constant molar concentration of carbon dioxide equal to 98.00%. The ratio of limonene to linalool was varied from 0 to 1 through 12 different concentrations. Under these conditions, no liquid-liquid immiscibility was observed for this system. The data included bubble points, critical points and dew points within a temperature and pressure range of 293-349 K and 5-14 MPa, respectively. The results were compared with ternary data of ethane + limonene + linalool at similar conditions of constant supercritical fluid concentration and varying limonene to linalool ratios. The results indicated that supercritical extraction of citrus oils could be carried out at lower pressures if ethane is used instead of carbon dioxide.
Computation
Studies of phase transition kinetics are important for such supercritical processes as supercritical drying, adsorption, micronization, etc. In supercritical technologies, “organic solvent—CO2” systems are often formed, the properties of which strongly depend on the system parameters. In this article, the kinetic curves of phase transitions in the “2-propanol—CO2” system were investigated experimentally and theoretically. Experimental studies were carried out in a 250 mL high-pressure apparatus at temperatures of 313 and 333 K and pressures of 6.3 and 7.8 MPa with and without the addition of alginate porous gel. Theoretical studies were carried out using the mass transfer equation, the Peng-Robinson equation of state, and the Van der Waals mixing rules, with Python being used for the calculations. The mass transfer coefficients and equilibrium concentrations of CO2 in the liquid phase were determined using the BFGS optimization method.
Selective oxidation of benzyl alcohol in dense CO2: Insight by phase behavior modeling
The Journal of Supercritical Fluids, 2012
Catalytic reactions in pressurized CO 2 are often strongly affected by the phase behavior. Knowledge on phase behavior is therefore desirable for optimizing the reaction conditions but often requires considerable experimental effort. Here, a previously established thermodynamic model for complex systems, based on the Cubic Plus Association (CPA) equation of state, is utilized in order to gain insight into the phase behavior during the palladium-catalyzed selective oxidation of benzyl alcohol to benzaldehyde. The catalytic reaction was studied in a tubular continuous reactor both under biphasic and single phase conditions at different flow rates, compositions and oxygen concentrations. In general, biphasic conditions resulted in the highest reaction rate which was also found when running the reaction in a batch reactor. On transition to a single phase a gradual deactivation of the catalyst was observed. Hence, the model predictions can be beneficially applied in order to find optimal reaction conditions. In the continuous reactor under biphasic conditions, the substrate was found to accumulate in the reactor due to segregation. The study indicates that a direct comparison between the catalytic performance observed in the continuous flow system and batch reactor under biphasic conditions requires knowledge on the influence of the segregation on flow conditions and mass transfer, which is often ignored in the literature.
Journal of Catalysis, 2006
Cinnamyl alcohol was oxidized to cinnamaldehyde in a continuous fixed-bed reactor with molecular oxygen over an alumina-supported palladium catalyst in supercritical carbon dioxide modified with toluene. A strong dependence of the reaction performance on pressure and oxygen concentration in the feed was found. Optimization of the reaction conditions resulted in a higher catalytic activity than in the liquid phase. At 120 bar, 80 • C, and double stoichiometric oxygen concentration, a turnover frequency of 400 h −1 at a selectivity of 60% to cinnamaldehyde was achieved. Spectroscopic investigations and the knowledge of the selectivity pattern turned out to be crucial for a deeper understanding of the reaction allowing a rational optimization. Under almost all experimental conditions (even at high oxygen concentration) hydrogenated byproducts, stemming from internal hydrogen transfer reactions, were detected in the effluent. This indicated that alcohol dehydrogenation was the first reaction step; this finding was further confirmed by spectroscopic investigations. In situ XANES and EXAFS revealed that in the entire experimental range investigated, the palladium constituent was mainly in a reduced state, and its surface could be oxidized only in the absence of cinnamyl alcohol in the feed. Bulk-phase behavior studies and investigations at the catalyst-fluid interface, performed by visual inspection and combined transmission and ATR-IR spectroscopy, demonstrated that the reaction performed best in the biphasic region. Moreover, cinnamaldehyde and carbon dioxide, but hardly any toluene and cinnamyl alcohol, were detected inside the porous catalyst, indicating a significantly different product composition inside the porous catalyst compared with the bulk phase. (J.-D. Grunwaldt).
Fluid Phase Equilibria, 2011
Cellulose is a natural, abundant, renewable and environmental friendly resource from which it is possible to obtain multiple of different substances with a high added value, as sugars, ethanol, lactic acid or aromatics. Increasing the use of cellulose as a raw matter can mean a reduction of the use of fossil fuels. Nevertheless, due to its structure, cellulose is not soluble in water soluble nor in other conventional solvents, therefore it is difficult to process. Thus, finding an environmentally friendly solvent for cellulose is a very important step in order to use this material. In the last years the interest in ionic liquids as cellulose solvents has increased. The number of articles published in the field of ionic liquids have increased exponentially, see Figure 1, this means that more than 64000 papers were published in the current decade. In addition, more than 70 patents have been published in the biomaterials processing topic since 2005. Chapter 2: Determination of density, viscosity and vapor pressures of mixtures of dimethyl sulfoxide + 1allyl-3-methylimidazolium chloride at atmospheric