Carlos A. V. Costa

Fenton oxidation of cork cooking wastewater—overall kinetic analysis

In the present work, the possibility of using chemical oxidation through Fentons reagent for the pre-treatment of cork cooking wastewaters was exploited. Aiming both the selection of the best operating conditions (pH, Fe2+:H2O2 ratio and initial H2O2 concentration) and the evaluation of the overall reaction kinetics, trials were performed in a batch reactor. Operating at pH = 3.2, H2O2 concentration = 10.6 g/L and Fe2+:H2O2 ratio = 1:5 (by weight), about 66.4% of total organic carbon (TOC), 87.3% of chemical oxygen demand (COD) and 70.2% of biochemical oxygen demand (BOD5) were removed and an increase of the BOD5/COD ratio from 0.27 to 0.63 was achieved. In the temperature range 20-50 degrees C, the best performance was obtained at 30 degrees C. The kinetic study was undertaken at different initial TOC concentrations and temperatures. Overall kinetics can be described by a second-order followed by a zero-order rate equation and the apparent kinetic constants at 30 degrees C are k = 2.3 x 10(-4) L/mg min and k0 = 26.0 mg/L min, respectively. The experiments performed at different temperatures confirmed the global kinetic model and allowed to calculate the global activation energy for the second-order reaction (70.7 kJ/mol).

Intraparticle diffusion of phenol in macroreticular adsorbents: Modelling and experimental study of batch and CSTR adsorbers

Intraparticle diffusivity of phenol in macroreticular adsorbents was studied by considering different models for particle structure: homogeneous, pore diffusion, “parallel” and series model. Numerical solution of model equations was achieved by using collocation methods. Models were tested by carrying out experiments in batch adsorbers. In the working range the pore diffusion model represents well our system. The value of effective diffusivity of phenol in Duolite ES861 (Dpe = 7.7 × 10−10 m2/s) were successfully used to predict the outlet concentration as a function of time in CSTR adsorbers.

Removal of acetone, ethyl acetate and ethanol vapors from air using a hollow fiber PDMS membrane module

Abstract Polyetherimide (PEI) membranes coated with polydimethylsiloxane (PDMS) are frequently used for removing volatile organic compounds (VOCs) from air. An experimental and theoretical study was performed to evaluate the effects of the feed flow rate, feed VOC composition, feed and permeate total pressure using a hollow fiber membrane module for separating acetone, ethyl acetate and ethanol from air. The results are discussed on a basis of permeate flux and permeate VOC concentration. It was found that the hollow fiber module provides good separation capabilities, in spite of the observed PEI sub-layer mass transport resistance, and the proposed model fits the experimental results fairly well.

On the determination of diffusivity and sorption coefficients using different time-lag models

Abstract Different models have been proposed to fit experimental permeation data in order to obtain membrane transport parameters (sorption capacity and solute diffusivity) when using the time-lag method. Depending on the assumptions, their complexity can vary from a simple linear equation to a more complex non-linear partial differential equation. The applicability, limitations and inaccuracies of these different models are discussed. A numerical procedure to solve the time-lag equation in a membrane slab considering permeate pressure build up is presented. This procedure involves the numerical computation of an inverse Laplace transform using a fast Fourier transform. This is applicable to the full range of the experimental permeation data, provided that both sorption and diffusivity coefficients are constant within the experimental pressure range. Due to its simplicity, the linear time-lag equation is the most commonly used model. However, it does not account for permeate pressure build up. It is shown that this leads to errors in the determination of the permeation parameters which increase with the capacitance parameter (related with the volume available for permeation). For values above a certain threshold ( η >0.05) these errors are above 5%. Emphasis is put on providing a simple and straight forward way to minimise them.

Oxygen separation from air by PSA: modelling and experimental results: Part I: isothermal operation

This work presents an experimental and simulation study of a pressure swing adsorption (PSA) unit running a traditional Skarstrom cycle and a Skarstrom cycle with co-current equalisation for the oxygen separation from air using a 5A zeolite. The effects of production pressure, purge and product flowrates, and production step duration on the product purity and recovery are studied for both cycles and compared. The Skarstrom cycle with co-current equalisation proved to perform better than the traditional Skarstrom cycle, e.g. for the same operating conditions it gives better product purities and recoveries. Nevertheless, both cycles present the same general trend as a function of the operating conditions. The PSA/LDF-DG model is employed to simulate both PSA cycles. This model considers a linear driving force representation of the dusty gas intraparticle mass transport model. Within the range of tested conditions, it was found that the model can predict reasonably well the product concentration time evolution for the cyclic steady state and for the unsteady state, for both cycles.

Hysteresis in the cyclic adsorption of acetone, ethanol and ethyl acetate on activated carbon

This paper describes the adsorption behaviour of three solvents (ethyl acetate, ethanol and acetone) on BASF activated carbon at various temperatures (15–80°C). The adsorption isotherms show hysteresis which persists to very low pressures (Low Pressure Hysteresis, LPH). After prolonged outgassing (<10−2 mbar) at 473–523 K we found that LPH still remains. This LPH is more pronounced for ethyl acetate at higher temperatures. Due to its importance on Pressure Swing Adsorption (PSA) units design and operation we discuss the adsorption behaviour when adsorption/desorption cycles are applied. We concluded that after approximately five cycles the system reaches what we called ‘limiting isotherm’ where adsorption and desorption branches cannot be distinguished within experimental error. This isotherm is independent of system history if a sufficiently low pressure and/or a sufficiently high pressure is used for cycling and in these conditions the adsorbent has higher capacity than when fresh. Also the Langmuir equation correlates quite well with the limiting isotherms.

Modelling the environmental impact of an aluminium pressure die casting plant and options for control

This study describes a model (MIKADO) to analyse options to reduce the environmental impact of aluminium die casting. This model will take a company perspective, so that it can be used as a decision-support tool for the environmental management of a plant. MIKADO can be used to perform scenario analyses to analyse the impact on the environment of different strategies, while taking into account both economical and ecological consequences of decision-making. The MIKADO approach is based on relevant parts of Life Cycle Assessment, environmental systems management and Multi-criteria Analysis. One of the strengths of MIKADO is the integrated approach that it takes in analysing, simultaneously, a set of eight environmental problems, including: human toxicity, abiotic depletion, global warming, solid waste production, acidification, terrestrial ecotoxicity, photochemical ozone formation and aquatic toxicity, caused by the aluminium die casting plant. The model is developed for and applied to a specific aluminium die casting plant supplying car manufacturers with aluminium die casting products. We present model results for a reference case, indicating that most of the environmental impact of the plant is associated with releases of compounds during the melting and casting of alloy, as well as with the use of natural gas. Finally, we present results of a partial sensitivity analysis, indicating the sensitivity of the model to changes in parameter values.

Characteristics of p-hydroxybenzoic acid oxidation using Fenton's reagent.

Abstract The objective of this work was to investigate the oxidation of p-hydroxybenzoic acid by the Fentons reagent. Batch experiments were carried out to investigate the influence of the most important process variables: hydrogen peroxide and ferrous salt concentrations, pH, and temperature. The optimal results obtained indicate that p-hydroxybenzoic acid can be effectively degraded using Fentons oxidation within 10-min reaction time by using a molar ratio H2O2: p-hydroxybenzoic acid of 4:1 and H2O2:Fe2+ of 15:1, at 30°C and pH = 3.0. The behavior of ORP and pH along the reaction time for different values of R (molar ratio H2O2: p-hydroxybenzoic acid) was also discussed. A pseudo-first order model was applied to describe the oxidation kinetics of p-hydroxybenzoic acid by Fentons reagent.

Life Cycle Assessment of Different Reuse Percentages for Glass Beer Bottles

Life cycle assessment (LCA) is increasingly becoming an important tool for ecological evaluation of products or processes. In this study the environmental impacts associated with the returnable and the non-returnable glass beer bottles were assessed in order to compare different reuse percentages. The inventory analysis is performed with data obtained from two Portuguese companies (a glass bottles producer and a brewery) and completed with the BUWAL database. It includes all operations associated with the bottles’ manufacture, the brewery and the wastewater treatment plant. The environmental impact assessment considers both the potential ecological and ecotoxicological effects of the emissions. The environmental impact categories included and discussed in this study are the contribution to ecological and human health, global warming, stratospheric ozone depletion, acidification, eutrophication and photochemical ozone creation. The first category is divided into three subcategories that are human toxicity, critical air volume and critical water volume. This study was performed for several reuse percentages and returnable bottle cycles, and is comprised of a sensitivity analysis. The general output is that the relative importance of the impacts associated with the use of returnable and/or non-returnable bottles depends on the number of cycles performed by the returnable bottles. According to the impact index defined in this study, the most significant impacts are the eutrophication and the final solid wastes generated, and the least significant impact is the ozone depletion.

Studies on the impregnation step of the Merox process

Abstract Laboratory studies for the determination of equilibrium data and effective diffusivities of Merox solutions in activated carbon were carried out in batch, CSTR and fixed-bed adsorbers. Simulation of the impregnation step of an industrial Merox unit was then performed. The fixed-bed plant was modelled by a heterogeneous model with pore diffusion in particles and was solved numerically either by using the package PDECOL or the method of characteristics.