Pervaporation-based hybrid process: a review of process design,applications and economics

Pervaporation is one of the developing membrane technologies that can be used for various industrial applications but for a predefined task, the optimal process design is unlikely to consist solely of pervaporation. Often the optimised solution becomes a hybrid process combining pervaporation with one or more other separation technologies. A distinction will be made between hybrid and integrated processes. Hybrid processes are important and consequently need to be considered in process design. This paper focuses on pervaporation–based hybrid processes that have been realised on an industrial scale. Both present and future prospects of applying these process combinations will be reviewed. The emphasis of this paper is, therefore, on pervaporation combined with distillation and with chemical reactors. The economic potential of these hybrid processes is evaluated, for various applications, by cost comparisons between the pervaporation-based hybrid processes and alternative separation processes. Pervaporation-based processes for waste water treatment and biotechnology applications involve other types of pervaporation based hybrid processes and have been excluded from this review.     

Cost Comparisons of Some Separation Processes

Abstract

There are many separation methods in use today in the chenical inaustriesl. In the last 50 years or there about, the common and dominant separation prooesses have been the conventional processes of distillation, liquid-liquid extraction, gas absorption, leaching, crystallization, evaporation, e.t.c. This is so because of advantages of using these processes among which are the technical know-how on the design, construction, control and operation of these processes. Naturally, manfacturers are usually reluctant to venture into new areas. But in recent years, attention is being focussed on newer separation processes which are sometimes referred to as the “Novel Separaation Processes (NSP)”. These are usually seen as alternatives to conventional processes. Example of such novel processes include the membrane processes (like the Ultrafiltration (UF), Electrodialysis (ED), Reverse Osmosis (RO), etc.), adsorption, ion exchang and gas or liquid chromatography.     

Improved ultrafiltration processes by partial recycle of ultrafiltrate

The economics of ultrafiltration processes may be improved in certain situations by partially recycling the ultrafiltrate. These situations include purification processes involving the use of additives in the makeup stream or processes where a recoverable product is present in the ultrafiltrate. A mathematical solution to this approach has been obtained to calculate the number of stages required as a function of the purification desired, the rejection coefficient of the species being removed, and the number of diavolumes. Some economic comparisons have been performed for multiple-stage ultrafiltration processes and compared with conventional single-stage diafiltration processes.     

Recent advances in electrochemical water technologies for the treatment of antibiotics: A short review

This short review presents a critical overview of the most recent works published in the literature related to the use of electrochemical advanced oxidation processes (EAOPs) for the treatment of antibiotics present in synthetic and real wastewaters. The first section focuses on novelties within the traditional EAOPs, including electrochemical oxidation and electrochemical Fenton-based processes. The second section is devoted to new electrochemical technologies, including heterogeneous electro-Fenton, electrochemically activated persulfate processes, and combined processes. Future perspectives about these processes are also presented to aid the continuous evolution of research in the area.     

Design of catalytic processes based on studies of elementary processes

In the first part of the review, the personal reminiscences of the development period of organometallic chemistry are described referring to the unexpected discoveries of late transition metal alkyls through the effort of finding an active species involved in catalysis. The isolation and examination of the behavior of these transition metal complexes led to findings of elementary processes important in catalysis. In the second part of the account, applications of the newly found elementary processes to organic syntheses are described, with emphasis on the recent development of environmentally benign catalytic processes utilizing the concept of the C-O bond cleavage in carboxylic acid derivatives combined with other elementary processes. The recently developed catalytic processes include conversion of carboxylic anhydrides and acids into aldehydes, ketones, perfluoroketones, benzylation of olefins, and conversion of allylic formates into unsaturated carboxylic acids.     

Inelastic collision processes of low-energy protons in liquid water

Production probabilities of ions and excited particle species along the proton beam track in liquid water are estimated around the Bragg peak region, taking into account charge-changing processes and energetic secondary electron (δ-ray) behavior. Ionization and excitation processes are divided into two categories in this study: primary processes associated with direct proton (or hydrogen) interaction and secondary processes arising from the electrons ejected by the primary process. We show that the number of events in the secondary processes producing ions and excited particles is larger than that of the primary processes around the Bragg peak while neutralized protons (i.e., hydrogen) with low energy have a large contribution to direct ionization. Effects of charge-changing processes on ionization and excitation are also discussed.     

Analysis of the efficiency of liquid membranes in extraction processes

Calculations were made to study the processes of purification of substances in a series of extraction and stripping columns or in a battery of mixer-settlers using a combination of free and supported liquid membranes. It was found that the efficiency of recovery or separation of substances in processes using liquid membranes exceeds that in conventional processes even after breaking up a series of columns or a battery of mixer-settlers into as few as two extractant-circulation loops. Investigation of the dependence of the purification processes on various parameters showed that the maximal effect on the processes is exerted by the distribution coefficients of substances at the stripping stage.     

A comparison of rheokinetics on static and shear crosslinking processes of xanthan gum

The crosslinking process of xanthan gum was studied under static and shear conditions. Conventional rotational rheometer was adopted to study the shear crosslinking process, and the static crosslinking process was monitored using an optical microrheometer without physical contact between the instrument and the sample. Both experiment and numerical simulation were adopted to compare the two gelation processes at different temperatures. The results showed that the effects of temperature on static and shear crosslinking processes of xanthan gum have the same trend and the rheological curves of the two gelation processes are similar in shape. The same rheokinetics equations were established to describe the two gelation processes and the simulated values are in good agreement with the experimental data. The changes of the model parameters with respect to temperature are quite similar for both the gelation processes, which verifies the feasibility of the microrheology method for measuring the static crosslinking reaction.     

Mechanistic implications of the equality of compensation temperatures in chromatography

A common interpretation of the observation that two processes exhibit similar compensation temperatures in an enthalpy-entropy plot is that the two processes occur via the same "mechanism". We show that this interpretation is not rigorously allowed. In fact, the only thing that can be concluded from the observation of identical compensation temperatures is that the relative contributions of enthalpy and entropy to the overall free energy are the same in the two processes. Since it is possible that two processes occur via different mechanisms that, by chance, result in the same relative blends of enthalpy and entropy, the observation of identical compensation temperatures cannot be used as evidence for mechanistic identity. If two processes exhibit different compensation temperatures, however, it can logically be concluded that the two processes are mechanistically distinct.     

Photooxidative treatment of sulfurous water for its potabilization

The feasibility of potabilization of sulfurous water was investigated by photochemical oxidation processes using a batch photoreactor and a continuous-flow photoreactor, equipped with UV lamps of 1000 W and 1500 W, respectively. Additionally, two advanced processes of oxidation were applied i.e. with a use of a UV light/H2O2/air and UV light/H2O2/O3/air. These two processes were compared for their efficiency to the direct oxidation process where ozone is used in the absence of UV light. Results obtained for both advanced processes showed better oxidation than takes place by ozone in the absence of UV light. After the photooxidation processes, different processes for the absorption or precipitation of sulfates were investigated to comply with the World Health Organization (WHO) norm that demands a limit of < or =250 mg L(-1) of SO4(2-) in drinking water. Additionally, reverse osmosis was simulated using Osmonics Inc. software to predict the feasibility of lowering the salt concentration below WHO limits.     

The special features of heat conversion into work in solar cell energy reemission

The absorption of radiant energy in solar cells is divided into parallel reversible and irreversible circular processes. Their fractions correlate with the known thermodynamic limits of the efficiency of heat conversion into work provided the conversion of solar energy is divided into antenna and work processes. (An analogue of antenna processes is the selective absorption of solar radiation by pigment molecules of plant cells, and an example of work processes is the work of chlorophyll molecules in plant photosynthesis.) It is shown that an efficiency of solar cells close to limiting cannot be achieved without reversible antenna processes.     

Mechanism of electrochemical reactions of polyaniline films formed under the conditions of cathodic oxygen reduction

Polyaniline films (further, CPANI) were obtained under the conditions of oxygen cathodic reduction in the aniline-containing solution on the electrodes of mixed indium tin oxide (ITO), graphite, and gold. CPANI films are characterized by redox processes in the potential ranges of 0.1–0.2 V and ～0.4 V (SCE). These processes are caused by the polymer chain fragments of different structure and the ratio between the peaks corresponding to these processes varies significantly as dependent on the synthesis conditions (electrode material, stirring, etc). The mechanism of electrode processes on CPANI is studied using the methods of cyclic voltammetry and quartz microgravimetry. It is found that only hydrogen cations and supporting electrolyte anions participate in the electrode process at the potentials of 0.1–0.2 V. The mechanism of redox processes on the obtained polymer films is discussed.     

Comparison of the water change characteristics between the formation and dissociation of methane hydrate and the freezing and thawing of ice in sand

Hydrate formation and dissociation processes are always accompanied by water migration in porous media, which is similar to the ice. In our study, a novel pF-meter sensor which could detect the changes of water content inside sand was first applied to hydrate formation and dissociation processes. It also can study the water change characteristics in the core scale of a partially saturated silica sand sample and compare the differences of water changes between the processes of formation and dissociation of methane hydrate and freezing and thawing of ice. The experimental results showed that the water changes in the processes of formation and dissociation of methane hydrate were basically similar to that of the freezing and thawing of ice in sand. When methane hydrate or ice was formed, water changes showed the decrease in water content on the whole and the pF values rose following the formation processes. However, there were very obvious differences between the ice thawing and hydrate dissociation.     

An economic and environmental comparison of a biochemical and a thermochemical lignocellulosic ethanol conversion processes

With the world’s focus on rapidly deploying second generation biofuels technologies, there exists today a good deal of interest in how yields, economics, and environmental impacts of the various conversion processes of lignocellulosic biomass to transportation fuels compare. Although there is a good deal of information regarding these conversion processes, this information is typically very difficult to use on a comparison basis because different underlying assumptions, such as feedstock costs, plant size, co-product credits or assumed state of technology, have been utilized. In this study, a rigorous comparison of different biomass to transportation fuels conversion processes was performed with standard underlying economic and environmental assumptions so that exact comparisons can be made. This study looked at promising second-generation conversion processes utilizing biochemical and thermochemical gasification technologies on both a current and an achievable state of technology in 2012. The fundamental finding of this study is that although the biochemical and thermochemical processes to ethanol analyzed have their individual strengths and weaknesses, the two processes have very comparable yields, economics, and environmental impacts. Hence, this study concludes that based on this analysis there is not a distinct economic or environmental impact difference between biochemical and thermochemical gasification processes for second generation ethanol production.     

Reorganization of enynes catalyzed by platinum salts

Activation of alkynes with platinum salts allows their reaction with alkenes, giving rise to a myriad of interesting processes like cyclizations, formation of cyclopropanes, or metathesis. Weak nucleophiles can also participate in the processes leading to alkoxycyclizations. There are intriguing mechanistic aspects of these processes in which subtle variations of the reaction conditions and/or substrate structures can lead to completely different products.     

Comparison of plasma and plasma-solution modifications of polymer materials in the liquid phase

The capabilities of atmospheric-pressure gas-discharge plasma and plasma-solution systems as applied to enhancement of industrial processes in solutions, such as flax bleaching and wood delignification, were analyzed. It was shown that the set of active species generated in the plasma systems corresponds to that required for the processes in question. According to estimates, the efficiency of plasma-solution systems is higher than that of cold atmospheric-pressure plasma. A kinetic scheme for the bleaching processes activated in the plasma-solution systems is discussed.     

Initial crystallization mechanism of isotactic polystyrene from different States

The isothermal crystallization processes of isotactic polystyrene at 160 degrees C from different initial states (quenched glassy state and melt state), i.e., cold- and melt-crystallization processes, have been investigated by infrared (IR) and generalized two-dimensional (2D) IR correlation spectroscopy. It has been found that not only the crystallization kinetics and crystallinity but also the sequential changes of the amorphous and crystalline sensitive bands are quite different for the cold- and melt-crystallization processes. This leads to the conclusion that the physical origins for spinodal decomposition prior to polymer crystallization may be different for different crystallization processes.     

Comparative study of dielectric,mechanical, and nuclear magnetic relaxations of linear polyethylene. I. Broad-line NMR investigation of the fine structure of the α and γ loss bands observed by dielectric and mechanical measurements

Detailed investigation of the linewidth, second moment, and mobile fraction by straightline decomposition of NMR spectra of linear polyethylene from ca. ?160 to ca. 100°C reveals five molecular processes denoted γ₁, γ₂, β, α′, and α. Relaxation maps show that the γ₁, γ₂, and β processes correspond to the dielectric and mechanical relaxations given the same names, while the α and α′ processes correspond respectively to the mechanical α₂ process due to molecular motion in the interior of crystals and to the dielectric α process. Close relations are found between the mass fractions of protons for the γ₁ and β processes and also between those for the γ₂ and α′ processes. From the effects of diluent on these processes and the annealing-time dependence of mass fractions of protons, the γ₁, and β processes are attributed to two modes of molecular motion in an interlamellar amorphous region, while the γ₂ and α′ processes are attributed to motions in the lamellar surface layers. The surface-layer thickness obtained by applying the two-phase model for the data on mobile fraction agrees quite well with that reported in the literature. The Bergmann–Nawotki three-component analysis of NMR spectra and symmetric-line decomposition for determining mobile fraction are shown to be unsuitable for studying the fine structure of the α and γ loss bands.     

Simulation of nonstationary processes in solid electrolyte electrochemical cells for the pulsed mode of gas composition variations

Studying processes that occur in solid electrolyte electrochemical cells when the working electrode is subjected to an impact of the reactive gas medium are of interest for both their practical application and the understanding of mechanisms of these processes. There are grounds to assume that the methods of studying the processes on electrodes by subjecting the latter to chemical pulses provide more information as compared with the conventional methods based on electric perturbations. A computer simulation of nonstationary processes in a solid electrolyte electrochemical cell of the flow-through kind is carried out. The model of these processes takes into account the transport of electrochemically active components in the gas phase, the kinetics and statics of adsorption of these substances on the gas/electrode interface, and the kinetics of electrode reactions including chemical and charge-transfer stages. Time dependences of concentration fields are calculated as well as the integral characteristics of flows, namely, the oxygen flow from the gas phase to the electrode, the oxygen flow from the electrode to the solid electrolyte, and the flow of the electrochemically active component at the cell outlet.