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Experimental and theoretical study of VOC removal by adsorption onto activated carbon in a fixed bed column.
No full textIn this work, an experimental and theoretical study on the adsorption of vapors of volatile organic compounds (VOCs) in a fixed bed column is presented and developed; the analyzed system is composed by three kinds of VOCs, that is dimethoxy-ethane (DME), isopropyl alcohol (IPA) and methyl-tertbutyl-ether (MTBE) and a commercial activated carbon as adsorbent material.
Nowadays VOC are widely used as dissolving and cleaning agents in many industrial processes such as printing, manufacturing of magnetic tapes, electronic chips, pharmaceutical and cosmetic synthesis and are therefore frequently present in the gaseous industrial effluents.
Unfortunately VOC are a class of hazardous pollutants, due to their harmful effects of human and animal health and the environments. It is well documented that VOC inhalation and longterm exposure can cause serious health effects; moreover they are included in the “ozone precursor substances”, that means substances which contribute to the formation of ground-level ozone. Therefore, control of VOC emission is mandatory for the industries, according to the environmental regulations issued world-wide.
Different techniques are available to destroy VOC by different types of thermal, catalytic or biological oxidation or to remove VOC from gaseous effluents by absorption, adsorption or membrane separation. Among the last type of technologies, adsorption is one of the most extensively used, because of the high selectivity and capacity of the adsorbent material, the ease of operation, the low capital and operating costs, and the compactness of equipment; due to its high separation efficiency even at low concentrations and at low operating costs, adsorption is also employed after one or more previous treatment processes, which operate a more gross separation to reduce pollutant’s concentrations to low levels. Furthermore, adsorption in fixed bed columns is suitable to treat effluents of variable composition and can tackle the problem of accidental increases of pollutant concentration without compromising the effluent quality, but at the expense of a reduction of the column’s useful life.
Several adsorbent materials can be used to adsorb VOCs: activated carbon, zeolite, silica gel, MOF, carbon molecular sieve. In particular, activated carbon is a good adsorbent with high adsorption capacities towards polar and non-polar compounds; it can be produced by a great variety of raw materials, such as hazelnut shell, rubber-seed shell, palm kernel shell, coconut shell, rice husk, wood; this large availability of waste material makes the activated carbon relatively cheap and available. However, its removal efficiency can be negatively affected by gas relative humidity, competitive adsorption of different contaminants and slow mass transfer rate. In particular, in the pharmaceutical industry in which the production is predominantly in batch mode, the gaseous streams contain several VOCs and competitive adsorption usually occurs. Furthermore, the gaseous composition can vary periodically in relation to the planning of production.
The effluent is treated in a fixed bed column packed with activated carbon before its release into the atmosphere; it is clear that it is difficult to study the column behavior, and hence, to predict its life time in such operating conditions. Indeed, as mentioned before, when a column is fed with a multicomponent stream, the competitive adsorption for the adsorbent sites usually occurs; moreover, because of the discontinuity nature of the feeding stream, the column is
subjected to adsorption and desorption phases which take place along the bed until its break occurs.
Therefore, the development of a fixed-bed mathematical model able to describe the complex system behavior is crucial if you want to predict the performance of such separation process; to this aim an adequate understanding of both equilibrium and kinetics of adsorption and desorption is essential. In order to obtain this information, the experimental response must be matched with the theoretical response, calculated from the dynamic model of the system. On
the other hand, from the perspective of the fixed-bed column design, the model can represent a useful tool to predict the dynamic behavior of the column in a wide range of operating conditions, without recourse to extensive experimentation.
Single VOC removal by adsorption process is widely analyzed in the literature, where a variety of VOCs as well as kinds of models to describe their adsorption in several adsorbent materials can be found; far fewer studies focusing on the adsorption of multicomponent mixtures in dynamic conditions are instead available and even fewer studies on the desorption phase have been carried out.
In this research work, adsorption and desorption of the three aforementioned organic solvents, widely used in pharmaceutical industries, on a commercial activated carbon are experimentally and theoretically studied in a fixed bed column
Isopropyl alcohol vapour removal from diluted gaseous stream by adsorption: Experimental results and dynamic model
Full text linkThe gas phase adsorption of isopropyl alcohol (IPA) onto a commercial activated carbon at 30°C was
investigated under different operating conditions. Fixed-bed experiments were performed to obtain equilibrium
and kinetic data for IPA adsorption. The equilibrium data were fitted by means of the Langmuir equation and
isotherm parameters were determined. A dynamic, isothermal, dilute solution adsorption model, based on the
linear driving force (LDF) approximation, was developed to describe the kinetic adsorption behavior. A very
good agreement between experimental and model results was found when a LDF mass-transfer-rate
coefficient dependent on the gas concentration was used
Pressure swing adsorption for biogas upgrading. A new process configuration for the separation of biomethane and carbon dioxide
No full textPressure swing adsorption (PSA) is an interesting technology for biogas upgrading, due to compactness of the equipment, low energy requirements, low capital cost, and safety and simplicity of operation. Unfortunately, some shortcomings penalize its diffusion in comparison with other technologies; in particular, conventional PSA has a low methane recovery and cannot compete in this field with other processes such as amine scrubbing; furthermore, it produces an off gas stream with a significant methane content, which requires further treatment to avoid the emission of residual methane into the atmosphere. In this framework, this study focuses on the feasibility of a PSA based separation process able to obtain a biomethane stream suitable to be injected in the natural gas grid (CO2 99%). The proposed process uses Zeolite 5A as adsorbent material in two PSA units; the biogas is fed to the first unit which produces biomethane; the off gas of the first unit is sent to a second PSA unit which separates carbon dioxide from a residual gas stream, recycled to the first to enhance methane recovery. A dynamic non-isothermal model, based on the linear driving force approximation, is employed to demonstrate the technological feasibility of the separation units and to assess the performance of the whole process. In particular a methane recovery greater than 99% can be obtained with energy consumption of about 1250 kJ per kg of biomethane
Phase equilibria and thermodynamic modeling of systems CO2 – bergamot oil and CO2 – linalyl acetate
No full textIn this paper experimental equilibrium data of the system CO2– bergamot essential oil are reported at323 K and 343 K, in the pressure range 7.8–13.1 MPa. Furthermore equilibrium data for the subsystemCO2– linalyl acetate at 323 K are reported in the pressure range 7.0–10.3 MPa. The equilibrium data arepredicted by means of two thermodynamic models based on Peng – Robinson and PC-SAFT equations ofstate. In particular the bergamot essential oil is described as a mixture of four components: limonene,linalool, linalyl acetate and beta-caryophyllene. In the models regression parameters are calculated fromdata of binary subsystems, CO2– limonene, CO2– linalool and CO2-beta-caryophyllene, and CO2– linalylacetate. Therefore both of the models are predictive with regard to the bergamot oil and show quite agood agreement (especially the Peng Robinson one) with respect to the experimental data
PLA recycling by hydrolysis at high temperature
No full textIn this work the process of PLA hydrolysis at high temperature was studied, in order to evaluate the possibility of chemical recycling of this polymer bio-based. In particular, the possibility to obtain the monomer of lactic acid from PLA
degradation was investigated. The results of some preliminary tests, performed in a laboratory batch reactor at high temperature, are presented: the experimental results show that the complete degradation of PLA can be obtained in relatively
low reaction times
How does radial convection influence the performance of membrane module for gas separation processes?
Full text linkA two-dimensional axial-symmetric isothermal model, based on full coupling between mass and momentum transport, has been developed to describe the separation of a binary gaseous mixture in a packed bed membrane module. Steady-state conditions have been studied. The gaseous mixture to be separated enters an annular gap between two co-axial cylinders. The inner wall of the outer cylinder is impermeable to both components, whereas a membrane, with infinite selectivity towards one of the components, is supported onto the outer wall of the inner cylinder. A radial flux of the permeating components is therefore present. The main focus was on the determination of the influence of radial convection on the performance of the separator, which has been analysed in terms of three dimensionless groups. Different transport regimes could be identified, corresponding to different values of the dimensionless groups. The impact of radial convection has been assessed by comparing model predictions with those of a fully uncoupled one-dimensional model. A discrepancy up to 20% of the recovery has been observed in industrially relevant ranges of the parameters
Production and purification of hydrogen-methane mixtures utilized in internal combustion engines
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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