The paper reports on experimental data on the extraction of caffeine, coffee oil and chlorogenic acids from green coffee beans using pure supercritical CO2 and supercritical CO2 modified with ethanol (5% w/w) and isopropyl alcohol (5% w/w) at 50 and 60ºC and 15.2 24.8 e 35.2 MPa. In this study extraction kinetics were obtained for all assays i.e. samples were collected at several time intervals for each solvent and mixed solvent. When pure CO2 and CO2-ethanol mixed solvent were used, an increase in pressure resulted in an increase in the amount of oil extracted. When CO2 was modified with isopropyl alcohol, the amount of coffee oil extracted also increased with pressure. Caffeine extraction initially increased and subsequently decreased with pressure. Chlorogenic acids were only extracted when isopropyl alcohol was used as a co-solvent. An increase in extraction temperature resulted in a decrease of caffeine and oil extraction (retrograde condensation) when only CO2 was used as solvent. With the use of co-solvent this retrograde behavior was no longer observed and the increase in temperature resulted in the increase in the extracted amounts of caffeine, coffee oil and chlorogenic acids

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A static analytical equilibrium method was used to measure the binary and ternary solubilities of anthracene and p-terphenyl in subcritical water between 393 and 473 K and at 50 and 150 bar. Temperature was found to have the most significant effect on the solubility of polycyclic aromatic hydrocarbons (PAHs) in subcritical water. The effect of pressure, and the combined effect of temperature and pressure on solubility were found to be insignificant, particularly when the range of pressure considered is relatively small. The solubilities of PAHs were found to be governed primarily by sublimation pressure, and only secondarily by the dielectric constant of water. The Peng−Robinson equation of state was used to correlate the aqueous solubilities of PAHs under subcritical conditions, with good agreement between experimental and calculated values obtained for binary systems.

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Purpose -The purpose of this paper is to analyze mathematical aspects of the q-Weibull model and explore the influence of the parameter q. Design/methodology/approach -The paper uses analytical developments with graph illustrations and an application to a practical example. Findings -The q-Weibull distribution function is able to reproduce the bathtub shape curve for the failure rate function with a single set of parameters. Moments of the distribution are also presented. Practical implications -The generalized q-Weibull distribution unifies various possible descriptions for the failure rate function: monotonically decreasing, monotonically increasing, unimodal and U-shaped (bathtub) curves. It recovers the usual Weibull distribution as a particular case. It represents a unification of models usually found in reliability analysis. Q-Weibull model has its inspiration in nonextensive statistics, used to describe complex systems with long-range interactions and/or long-term memory. This theoretical background may help the understanding of the underlying mechanisms for failure events in engineering problems. Originality/value -Q-Weibull model has already been introduced in the literature, but it was not realized that it is able to reproduce a bathtub curve using a unique set of parameters. The paper brings a mapping of the parameters, showing the range of the parameters that should be used for each type of curve.

This study aims to evaluate the performance of the four most known screening methods used to predict the risk of asphaltene precipitation in crude oil employing a large database from the literature. The selection of these methods was based on the amount of property data required for their application. Most methods reported in the literature use saturate, aromatic, resin, and asphaltene (SARA) analysis as the property to monitor the stability of the oil with respect to asphaltene precipitation. Other methods require the temperature, pressure, and oil density data to indicate the risk of asphaltene precipitation. Results showed inconsistency for two of the four screening methods selected, and improvements were proposed and successfully validated.

The transesterification of waste frying oil (WFO) with methanol and ethanol was studied in a batch reactor using a zinc aluminate catalyst prepared by the combustion reaction method. The reaction runs were carried out for 2 hours, using alcohol:oil molar ratio of 40:1, temperature range of 60-200°C, catalyst ratio of 1-10% wt., under 700 rpm stirring. The catalyst was characterized by XRD, EDX, TG, FTIR, N 2 physisorption, NH 3and CO 2-TPD. The catalyst showed a normal spinel structure and acid character (Lewis acid), in spite of the presence of both strong acid and base sites. Methyl and ethyl esters yields higher than 95% were obtained at 150 and 200°C and the catalyst was recovered and reused in 3 reaction cycles, without significant loss of activity.