PET and aluminum recycling from multilayer food packaging using supercritical ethanol

Different properties, such as barriers to gas, light, flavor and water vapor, as well as flexibility, are necessary for the production of food packages. These properties may be obtained by combining different polymers. In spite of the advantages achieved with the use of multilayer films, the recycling process of such material is a challenging task. This study presents an alternative for recycling of a quite common food packaging kind, which contains polyethylene (PE), aluminum and poly(ethylene terephthalate) (PET) as a multilayer film. The multilayer packages were delaminated with acetone. PET was depolymerized by ethanol in supercritical conditions. The diethyl terephthalate (DET) was obtained as the main product, presenting high purity and yield of 80%. Also, metallic aluminum was obtained by the PET-depolymerizing process. The optimal reaction time was 120 min. The products were characterized by FTIR, ¹H NMR and ¹³C NMR spectroscopies, DSC and TGA.     

现代食品工业中的超临界流体萃取技术

因为食物中的营养成分具有不稳定性和易被破坏的性质 ,故在其分离和富集过程中需要一些特殊的分离手段。介绍一种适宜在食品工业中应用的新型分离手段——超临界流体萃取     

Determination of sudan dyes in food samples using supercritical fluid extraction-capillary liquid chromatography

Determination of sudan dyes (Sudan I, Sudan II, Sudan III and Sudan IV) in food samples has been developed by several and different methods. However, sample treatment continues being the most important problem to determine these compounds in real samples. A rapid, sensitive and selective method for the extraction, separation and quantification of sudan dyes in commercial food samples has been developed. The method is based on the combination of a supercritical fluid extraction (SFE) procedure, followed by the analysis of the extracted plug by capillary liquid chromatography (CLC) with diode array detection (DAD). The entire procedure was optimized for the extraction of the samples, separation and detection of the analytes. For the SFE, the effect of CO₂ flow rate, extraction pressure, extraction temperature, equilibration and extraction time and methanol modifier content were studied. Linear responses in the range from 50 to 1000 ng mL⁻¹ with average relative standard deviation lower than 11.6, and detection limits ranging from 23.2 to 42.0 ng mL⁻¹ were obtained for the different sudan dyes. The recoveries were in the range of 91-109% for dyes powder samples.     

Near critical and supercritical impregnation and kinetic release of thymol in LLDPE films used for food packaging

The impregnation of organic compounds in polymeric materials using supercritical carbon dioxide (scCO₂) is a well-known technique, which is currently used in drug/polymer formulation. In this work, near critical and supercritical impregnation of thymol in linear low-density polyethylene (LLDPE) films was done in order to develop a new technique for preparation of active polymers to be used as food packages. The properties of thymol as a natural antimicrobial and antioxidant agent have motivated this study about the assessment of its migration from the polymer to different food simulant. Impregnation assays of thymol in LLDPE films were done in a high-pressure cell, where pure thymol was solubilized in supercritical carbon dioxide at 313 K and pressures varying from 7 to 12 MPa. This procedure allowed the preparation of plastic films with thymol concentrations ranged between 5100 and 13,200 ppm. Migration tests showed that the pressure applied during the impregnation procedure is a key parameter that affects the content of the active compound into the polymer, since thymol solubility in scCO₂ and absorption phenomena in the polymer increased with the pressure. The correlation between experimental data and a phenomenological transfer model allowed the estimation of the diffusion coefficient of thymol in LLDPE, which was ranged from 7.5 × 10⁻¹³ to 3.0 × 10⁻¹² m² s⁻¹.     

Kinetics of oxidation of food wastes with H2O2 in supercritical water

In this study, supercritical water oxidation (SCWO) of carrots and beef suet was carried out in a batch reactor system with an H₂O₂ oxidant, at a temperature between 400 and 450°C and reaction times from 10 s to 10 min. The results showed that the oxidative decomposition of carrots and beef suet proceeded rapidly and a high total organic carbon (TOC) decomposition of up to 97.5% was obtained within 3 min at 420°C for carrots and within 5 min at 450°C for beef suet when there was a sufficient supply of oxygen. It was also found that the oxidation reaction for both carrots and beef suet might be separated into a fast reaction at the early stage and a slow reaction at the later stage. In the later stage following the early stage reaction, acetic acid, which is a fairly stable product of the early stage reaction, is the reactant and the rate of overall oxidation reaction for complete decomposition is dominated by the later stage reaction. Global kinetic analysis based on the model described above showed that the early stage oxidative reaction of beef suet could be considered as a first-order reaction with respect to the concentration of organic carbon. The activation energy was 37.3 kJ mol⁻¹. Oxidation of acetic acid could also be expressed as a first-order reaction, and the activation energy was 106.5 kJ mol⁻¹. The early stage oxidation reaction of carrots was too fast to be analyzed. On the basis of intermediate products identified, reaction pathways were discussed. For carrots, polysaccharides may first be hydrolyzed to glucose and then oxidation of the glucose may take place. For beef suet, glyceride is first hydrolyzed to glycerin and carboxylic acids corresponding to the components of glyceride, followed by consecutive reactions for oxidative decomposition.     

Synthesis of biodiesel in supercritical alcohols and supercritical carbon dioxide

Biodiesel was synthesized in supercritical fluids by two routes: non-catalytically in supercritical alcohols and by enzyme catalysis in supercritical carbon dioxide. Two oils, sesame oil and mustard oil, and two alcohols, methanol and ethanol, were used for the synthesis. Complete conversion was observed for synthesis in supercritical alcohols whereas only a maximum of 70% conversion was observed for the enzymatic synthesis in supercritical carbon dioxide. For the synthesis in supercritical alcohols, the activation energies and pseudo-first order rate constants were determined. For the reactions in supercritical carbon dioxide, a mechanism based on ping pong bi-bi was proposed and the kinetic parameters were determined.     

Distribution of solutes between polymer and supercritical fluid by inverse supercritical fluid chromatography

Two methods of inverse supercritical fluid chromatography (ISFC), frontal analysis supercritical fluid chromatography (SFC) and elution SFC, have been compared for the determination of distribution coefficients of solutes between a polymer and a supercritical CO₂. The logarithm of the distribution coefficient showed monotonic decrease with the density of the supercritical fluid (SF). The abnormal-maximum behavior of solute sorption in the polymer phase was explained by the fluid and solute properties, ϕ₂P/P ₂ ^sat . Interesting open-elliptic shapes of sorption and volume-fraction curves were obtained and explained with the fugacity coefficient. Correction to the capacity factor was employed to eliminate the retention due to the adsorption on the surface of the silica support. A model based on the Flory equation and the Peng-Robinson equation of state (EOS) successfully predicted the phase behavior of the ternary solutesupercritical fluid-polymer systems using only interaction parameters obtained from the binary systems. The solute distribution coefficient at infinite dilution was used to calculate the phase equilibrium at finite concentration using a ternary-phase diagram.     

Preparative-scale supercritical fluid extraction/supercritical fluid chromatography of corn bran

A preparative-scale supercritical fluid extraction/supercritical fluid chromatography (SFE/SFC) procedure has been developed for the removal of oil from corn bran to obtain fractions enriched with free sterols and ferulate-phytosterol esters (FPE). Operational parameters from an analytical-scale supercritical fluid fractionation technique were translated to and optimized on a home-built, preparatory-scale SFE/SFC apparatus. SFE was performed at 34.5 MPa and 40°C using supercritical carbon dioxide. These conditions did not result in exhaustive extraction of the corn bran, but yielded about 96% of the available oil. SFC was conducted in three steps, followed by reconditioning of the sorbent bed. Preparative-scale SFE/SFC of corn bran produced a fraction enriched greater than fourfold in free sterols and 10-fold in FPE, suggesting that such a scheme could be used industrially to produce a functional food ingredient.     

Glycerol in subcritical and supercritical solvents

Glycerol conversion to added value chemicals is a research avenue that has attracted significant interest in recent years. The utilization of critical solvents such as water and organic solvents in critical conditions as well as subcritical conditions (or hot compressed solvent) and supercritical conditions can offer several advantages to batch processes and in continuous flow systems in view of their potential implementation in industry. This review has been aimed to highlight most recent key processes for glycerol valorization to valuable products using different types of catalysts and processes. © 2016 Society of Chemical Industry     

Extraction and processing with supercritical fluids

OVERVIEW: Extraction and processing with supercritical fluids (SCF) is increasingly gaining importance in the food, pharmaceutical and chemical industries. Supercritical fluid extraction (SCFE) using carbon dioxide (CO₂) as a solvent has emerged as a highly popular technology today over the conventional techniques for extraction of natural products for rapid, contamination‐free, tailor‐made extracts having superior quality and shelf‐life and high potency of active ingredients. IMPACT: The importance of SCFE is on the rise due to consumers' preferences for ‘natural’ as opposed to synthetic substances and, impending regulations for environmental protection, safety, nutritive and toxicity levels. APPLICATIONS: Newer applications of SCFs include separation and purification of chemicals, cleaning, coating, particle formation, textile dyeing, aerogel drying, reactions with separation and food preservation. Some fundamental aspects of SCFs, various processing technologies with SCFs, and a few newer potential applications are presented in this article. Copyright © 2008 Society of Chemical Industry     

Biodiesel production from supercritical carbon dioxide extracted Jatropha oil using subcritical hydrolysis and supercritical methylation

This study investigates supercritical carbon dioxide (SC-CO₂) extraction of triglycerides from powdered Jatropha curcas kernels followed by subcritical hydrolysis and supercritical methylation of the extracted SC-CO₂ oil to obtain a 98.5% purity level of biodiesel. Effects of the reaction temperature, the reaction time and the solvent to feed ratio on free fatty acids in the hydrolyzed oil and fatty acid esters in the methylated oil via two experimental designs were also examined. Supercritical methylation of the hydrolyzed oil following subcritical hydrolysis of the SC-CO₂ extract yielded a methylation reaction conversion of 99%. The activation energy of hydrolysis and trans-esterified reactions were 68.5 and 45.2 kJ/mole, respectively. This study demonstrates that supercritical methylation preceded by subcritical hydrolysis of the SC-CO₂ oil is a feasible two-step process in producing biodiesel from powdered Jatropha kernels.     

Extraction with supercritical gases

Extraction with compressed fluids in the critical region is discussed in terms of the marked effect on solvent properties that can be brought about by small changes in pressure or temperature. The theoretical background and experimental data are described, including the classification of the phase behaviour of binary systems. A number of application studies are quoted, and comparison is made with liquid solvent extraction and distillation. Apart from such topics as the breaking of azeotropes, the main area of study is in performing separations on the basis of volatility where the general level of volatility is low. In the field of natural products these include the removal of undesirable substances such as caffeine and nicotine and the isolation of valuable constituents such as food essences and drugs. For fossil fuels, applications are described in enhanced oil recovery, fractionation of heavy petroleum liquids and extraction of liquids from coal.     

Synthesis of biodiesel from edible and non-edible oils in supercritical alcohols and enzymatic synthesis in supercritical carbon dioxide

Biodiesel is an attractive alternative fuel because it is environmentally friendly and can be synthesized from edible and non-edible oils. The synthesis of biodiesel from edible oils like palm oil and groundnut oil and from crude non-edible oils like Pongamia pinnata and Jatropha curcas was investigated in supercritical methanol and ethanol without using any catalyst from 200 to 400 °C at 200 bar. The variables affecting the conversion during transesterification, such as molar ratio of alcohol to oil, temperature and time were investigated in supercritical methanol and ethanol. Biodiesel was also synthesized enzymatically with Novozym-435 lipase in presence of supercritical carbon dioxide. The effect of reaction variables such as temperature, molar ratio, enzyme loading and kinetics of the reaction was investigated for enzymatic synthesis in supercritical carbon dioxide. Very high conversions (>80%) were obtained within 10 min and nearly complete conversions were obtained at within 40 min for the synthesis of biodiesel in supercritical alcohols. However, conversions of only 60–70% were obtained in the enzymatic synthesis even after 8 h.     

超临界流体萃取原理及应用

本文论述了超临界流体的性质、超临界流体萃取法的分类,以及超临界流体萃取工艺在食品、医药、化学、化妆品香料等工业领域中的应用,并阐述了超临界流体萃取工艺中存在的不足,同时对今后的发展方向进行了展望.     

Study of supercritical three-phase methanol synthesis with n-hexane at supercritical state

A process of supercritical three-phase methanol synthesis on a Cu-based catalyst C302-2, which has high activity at low temperature and low pressure, has been carried out in a mechanically agitated slurry reactor with paraffin as the inert liquid medium and n-hexane as the supercritical medium. The reaction conditions are as follows: pressure ranging from 6.0 to , temperature ranging from 235 to and mass space velocity from 450 to . The influences of these conditions on the conversion of CO and the outlet methanol mole fraction have been investigated in detail. The results show that both the conversion of CO and outlet methanol mole fraction decreased when the mass space velocity and the temperature were increased under the condition of supercritical n-hexane. In addition, we compared the three-phase slurry bed methanol synthesis with and without supercritical medium. The results show that the conversion of CO, CO₂ and H₂ as well as outlet methanol mole fraction of supercritical three-phase methanol synthesis are obviously higher than those chemical equilibrium values of gas-solid reaction under the corresponding experimental condition. That is to say, the process of supercritical three-phase methanol synthesis with n-hexane at supercritical state can remove the limitation of chemical reaction balance of the reversible exothermic methanol synthesis reaction on the conversion of reactants by introducing a supercritical medium that plays an important role in the reaction-separation coupling process in methanol synthesis, by which the conversion of reactants and outlet methanol mole fraction at supercritical condition are increased greatly. Therefore, they are higher than those of three-phase methanol synthesis without supercritical n-hexane. The advantage of supercritical three-phase methanol synthesis is self-evident. Our present study provides an experimental foundation for further engineering exploitation research on the three-phase methanol synthesis process with supercritical medium in three-phase slurry reactors.