Thermodynamic Equilibrium of Xylene Isomerization in the Liquid Phase

This study deals with the thermodynamic equilibrium for xylene isomerization. Experiments performed by several researchers to calculate the equilibrium in the gas phase in the 1990s led to the conclusion that the earlier available thermodynamic data for xylenes, which were mainly based on experimental work performed in the 1940s, were in error. In this work a similar procedure was followed to determine the thermodynamic equilibrium for xylene isomerization in the liquid phase. By means of the thermodynamic functions at saturated conditions presented by the previously mentioned studies, the standard free energies of formation were calculated between 250 K and 550 K. Three different expressions were developed to calculate the equilibrium constants as a function of temperature

Isobaric Vapor–Liquid Equilibrium for Binary Systems of 2,2,4-Trimethylpentane with <i>o</i>‑Xylene, <i>m</i>‑Xylene, <i>p</i>‑Xylene, and Ethylbenzene at 250 kPa

Isobaric vapor–liquid equilibrium (VLE) data were determined at the pressure of 250 kPa for the four binary mixtures composed of 2,2,4-trimethylpentane (isooctane) + <i>para</i>-, <i>ortho</i>-, or <i>meta</i>-xylene and ethylbenzene (EB) by using a circulation-type apparatus, in which both vapor and liquid phases are recirculated. The vapor- and liquid-phase compositions were analyzed by gas chromatography. All of the data were found to be thermodynamically consistent according to the Herington, van Ness, infinite dilution, and pure component consistency tests. The experimental data were regressed with Aspen Plus 7.3, and binary interaction parameters were reported for the most frequently used activity coefficient models: the nonrandom two-liquid (NRTL) and the universal quasichemical activity coefficient (UNIQUAC) models, respectively. All of the calculated values with these models showed good agreement with the experimental data, as well as with available isobaric and isothermal data from the literature

Octane Upgrading of C₅/C₆ Light Naphtha by Layered Pressure Swing Adsorption

The performance of a layered pressure swing adsorption (PSA) process for the separation of high research octane number (HRON) paraffins from a C₅/C₆ light naphtha fraction is simulated with a detailed, adiabatic single column PSA model. A zeolite 5A layer is used for selective adsorption of the low RON linear paraffins, while a zeolite beta-layer is used to separate the intermediate RON 3MP from the HRON fraction. The effects of various independent process variables (zeolite 5A to zeolite beta ratio, purge to feed ratio, cycle time, operating temperature, and depressurization mode) on the key dependent process variables (product RON, HRON species recovery, HRON purity, and adsorbent productivity) are evaluated. It is demonstrated that an optimal zeolite 5A to zeolite beta ratio can improve the product average RON up to 1.0 point as compared to existing processes using zeolite 5A only. Moreover, process simulations demonstrated that increasing the operating temperature from 523 to 543 K results in an octane gain of 0.2 RON

Flavor Engineering–A Methodology To Predict Sensory Qualities of Flavored Products

A simple methodology able to predict the sensory quality of flavored products based on their gas phase composition together with psychophysical models and olfactory descriptors is proposed. Fruit juices (lemon, peach, pineapple, apple, and mango) were studied as an example of flavored products. The gas phase composition of each pure fruit juice was assessed using headspace and chromatographic techniques. Results revealed that the proposed methodology can be applied for the evaluation of the dominant olfactive families of pure fruit juices, as well as for binary and ternary fruit juices mixtures. The validation of this technique was performed through a sensorial evaluation (consumers), and a good agreement was achieved when compared their findings with those of the theoretical data

Modeling Fragrance Components Release from a Simplified Matrix Used in Toiletries and Household Products

A new methodology based on Henry’s law is proposed for modeling the release of fragrances from a simplified matrix commonly used in consumer products’ formulations. For that purpose, different mixtures were formulated containing one, two, three, or four fragrance ingredients diluted in dipropylene glycol (simplified matrix). Headspace concentrations were measured to estimate Henry’s constants (<i>H</i>) for each fragrance component in all mixtures. The individual Henry’s constants for multicomponent fragrance mixtures were also predicted from the ones measured for each single compound diluted in the matrix. Furthermore, we used a model that combines the UNIFAC group-contribution method with the modified Raoult’s law and the psychophysicals Stevens’ power law and strongest component model to predict the perceived odor intensity and character, respectively. Results showed a strong linear relationship between experimental <i>H</i> for single fragrances and experimental <i>H</i> for binary (<i>r</i>² = 0.998), ternary (<i>r</i>² = 0.997), and quaternary (<i>r</i>² = 0.996) fragrance mixtures. This new approach can bring a relevant advantage to the preformulation process by reducing time and cost associated with trial-and-error experiments

Reaction Kinetics and Thermodynamic Equilibrium for Butyl Acrylate Synthesis from <i>n</i>‑Butanol and Acrylic Acid

The esterification reaction of <i>n</i>-butanol with acrylic acid in the presence of a commercial ion-exchange resin, Amberlyst 15-wet, was carried out in a batch reactor. The reactions were performed at different temperatures (50 to 90 °C), different <i>n</i>-butanol/acrylic acid molar ratios (2 and 3), and different catalyst amounts (1 wt % to 3.5 wt %). Different reaction rate expressions were evaluated. A simplified Langmuir–Hinshelwood–Hougen–Watson kinetic model was found to be the best model to describe the experimental results. This model is given by the following expression: <i>r</i> = <i>K</i>_c·((<i>a</i>₁·<i>a</i>₂ – (<i>a</i>₃·<i>a</i>₄)/<i>K</i>_eq)/(1 + <i>K</i>₄·<i>a</i>₄)²), with <i>k</i>_c (mol·<i>g</i>_cat^–1·min^–1) = 1.52 × 10⁷ – 66 988/(<i>RT</i>) and <i>K</i>₄ = 1.589. Also equilibrium experiments were carried out. The proposed equilibrium equation was <i>K</i>_eq = exp((−(1490 ± 577)/<i>T</i> + (7.21 ± 1.67)). From this equation, it was possible to determine the reaction standard enthalpy and entropy values: Δ<i>H</i>° = 12.39 ± 4.80 [kJ/mol] and Δ<i>S</i>° = 59.98 ± 13.87 [J/mol·K]

Improving the Performance of a Simulated Moving Bed Reactor for the Synthesis of Solketal by Implementing Multifeed Strategy

The simulated moving bed reactor (SMBR) is a sorption-enhanced reactive technology that has been successfully applied to the synthesis of several organic compounds, due to its ability to overcome the thermodynamic limitations associated with reversible reactions. This work proposes the implementation of an innovative multifeed strategy that can considerably improve the performance of the SMBR, particularly for systems in which none of the reactants can be used as desorbent. A systematic design methodology based on the so-called “reactive-separation volumes” is developed and applied for the first time, and the results for the multifeed SMBR are compared to those obtained in a conventional SMBR. Due to its industrial relevance, the synthesis of solketal through the ketalization of glycerol and acetone was selected as a case study. The results demonstrated that the new SMBR operating mode can produce solketal with a purity of 97%, reaching a productivity of over 10 kgSolk LAds–1 day –1, while for a conventional unit this is barely possible. Moreover, it led to a reduction in desorbent consumption of 85%

Xylene Isomerization over Beta Zeolites in Liquid Phase

An experimental study of xylene isomers interconversion (isomerization) kinetics was conducted to gain a deeper insight into the field. Two beta zeolites with SiO₂/Al₂O₃ ratio of 35 (BEA35) and 38 (BEA38) were used as catalysts for the performed experiments. The isomerization reactions were carried out under the following conditions: 513, 493, 473, and 453 K at 2.1 MPa in liquid phase. It was verified that all reactions were in the kinetic-controlled regime. Kinetic constants were estimated with four different models; two of them were based on the xylene isomerization thermodynamic equilibrium from the literature. The linear reaction scheme, which does not consider the direct conversion between <i>p-</i> and <i>o-</i>xylene, presented a better fit to the experimental values. Higher conversion of <i>p-</i>xylene was observed when compared with the conversion of the other two isomers. This may be attributed to its smaller molecular size. BEA35 presented better performance due to its higher amount of Brønsted acid sites. Finally, activation energies over the two catalysts, estimated through Arrhenius equation, presented similar values

Predicting Vapor-Phase Concentrations for the Assessment of the Odor Perception of Fragrance Chemicals Diluted in Mineral Oil

In this study, the Henry’s law methodology is applied to predict the release of odorants present in single and multicomponent fragrance mixtures diluted in mineral oil, a simplified matrix used in cosmetic products. To attain this goal, the experimental Henry’s law constant (<i>H</i>) of each odorant in each studied fragrance system (containing one, two, three, or four odorants) was first evaluated by plotting their liquid phase and experimental vapor phase concentrations assessed by headspace gas chromatography. From that point, the <i>H</i> value of each odorant in the multicomponent fragrance system was predicted from its corresponding <i>H</i>^exp in the single fragrance component system. The theoretical vapor-phase concentrations were also calculated using the activity coefficients for vapor–liquid equilibria by applying the thermodynamic UNIFAC model. The odor intensity and character of the studied fragrance systems were assessed through the Stevens’s power law and Strongest Component models (psychophysical models). This study confirmed that the headspace concentrations and odor intensity of each odorant present in a multicomponent fragrance mixture dissolved in mineral oil can be efficiently predicted from its corresponding <i>H</i> determined when present alone in the simplified matrix, for low concentrations. Also, comparing both methodologies, UNIFAC and Henry’s law, it was concluded that Henry’s law is a better predictive model for the vapor–liquid equilibria, showing lower deviations from the experimental data. Therefore, the proposed predictive mathematical model can be attractive for the assessment of sensory quality of multicomponent fragrance systems in early formulation stages

Accurate Model for Predicting Adsorption of Olefins and Paraffins on MOFs with Open Metal Sites

Metal–organic frameworks (MOFs) have shown tremendous potential for challenging gas separation applications, an example of which is the separation of olefins from paraffins. Some of the most promising MOFs show enhanced selectivity for the olefins due to the presence of coordinatively unsaturated metal sites, but accurate predictive models for such systems are still lacking. In this paper, we present results of a combined experimental and theoretical study on adsorption of propane, propylene, ethane, and ethylene in CuBTC, a MOF with open metal sites. We first propose a simple procedure to correct for impurities present in real materials, which in most cases makes experimental data from different sources consistent with each other and with molecular simulation results. By applying a novel molecular modeling approach based on a combination of quantum mechanical density functional theory and classical grand canonical Monte Carlo simulations, we are able to achieve excellent predictions of olefin adsorption, in much better agreement with experiment than traditional, mostly empirical, molecular models. Such an improvement in predictive ability relies on a correct representation of the attractive energy of the unsaturated metal for the carbon–carbon double bond present in alkenes. This approach has the potential to be generally applicable to other gas separations that involve specific coordination-type bonds between adsorbates and adsorbents