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Papers by Tiina Leppäjärvi

Periodica Polytechnica Chemical Engineering, 2015

Pervaporation of binary ethanol/water solutions of 5-10 wt.% ethanol was studied experimentally t... more Pervaporation of binary ethanol/water solutions of 5-10 wt.% ethanol was studied experimentally through a thin supported high-silica MFI zeolite membrane of hydrophobic character in the temperature range of 30-70 °C. The fluxes obtained were very high, 2-14 kg m-2 h-1 with ethanol/water separation factors of 4-7. The loss of effective driving force was significant in the supporting layers, which limited the membrane performance. The correlation between the experimental data and three different semi-empirical mass-transfer models was examined. The correlation was good especially when the driving force for mass-transfer was determined based solely on bulk feed, or the bulk feed and permeate conditions together. Somewhat lower correlation was observed when the driving force was corrected with the effect of support resistance. This was most likely due to the inaccuracies of the used mass transfer parameters in the support. The investigated semi-empirical models can be applied for initial stage process design purposes.

SID Symposium Digest of Technical Papers

The production of liquid transportation fuels such as bioethanol and more recently also biobutano... more The production of liquid transportation fuels such as bioethanol and more recently also biobutanol from renewable resources has received considerable attention. In the production of bio-based alcohols, the separation steps are expensive as the mixtures to be separated are dilute. As an energy-efficient separation technology, pervaporation is considered to be a potential process in biofuel purification. One of the main constraints in the commercialization of pervaporation has been low membrane fluxes, and the consequent high costs due to the high membrane area needed. In order to obtain high fluxes, the membranes should be as thin as possible. In this thesis, the performance of ultrathin zeolite membranes in pervaporation was investigated. Binary ethanol/water and n-butanol/ water mixtures were studied using both hydrophobic and hydrophilic zeolite membranes for alcohol concentration, as well as dehydration. The development of pervaporation membranes and processes has been mainly emp...

Journal of Membrane Science, 2012

ABSTRACT Discrete Faujasite zeolite nanocrystals with an average size of about 60 nm were attache... more ABSTRACT Discrete Faujasite zeolite nanocrystals with an average size of about 60 nm were attached as a well-defined monolayer on the surface of porous graded alumina supports. Ultrathin zeolite X films with a total thickness of about 1 mu m were grown from the seed monolayers by hydrothermal treatment in clear synthesis solutions. One of the membranes showed a total flux of 3.37 +/- 0.08 kg m(-2) h(-1) and a separation factor of 296 +/- 4 for dehydration of a 90/10 wt.% ethanol/water mixture by pervaporation at 65 degrees C. Moreover, the membranes displayed stable performance during pervaporation for 5.5 h operation. A mathematical model indicated that the flux and selectivity of the membranes were limited by pressure drop in the supports. Therefore, in order to obtain higher flux, the permeability of the support must be improved. (c) 2012 Elsevier B.V. All rights reserved.

Industrial & Engineering Chemistry Research, 2014

ABSTRACT The pervaporative mass transfer of pure ethanol and water through a thin (0.5 μm) suppor... more ABSTRACT The pervaporative mass transfer of pure ethanol and water through a thin (0.5 μm) supported high-silica MFI membrane was studied experimentally at 30–70 °C, and modeled on the basis of the Maxwell–Stefan formalism. The temperature dependency of adsorption was described with the temperature dependency of pure component saturated vapor pressure. Two scenarios of coverage dependency, i.e., coverage-dependent and coverage-independent Maxwell–Stefan diffusivity, were applied in the modeling of the mass transfer through the zeolite film. In addition, the mass-transfer resistance of the support layers was taken into account. The derived unary models provided good representations of ethanol and water pervaporation flux. The study illustrates that pure component steady-state pervaporation flux measurements at different conditions offer a feasible basis for determining diffusion coefficients. Basically, pure component adsorption isotherms and derived diffusivities can be used in the modeling of pervaporative mass transfer of mixtures using zeolite membranes.

Chemical Engineering Science, 2012

In this study, the feasibility of utilizing pure component saturated vapour pressure P i sat in r... more In this study, the feasibility of utilizing pure component saturated vapour pressure P i sat in representing the temperature-dependency of physisorption of vapours on zeolites is examined. Adsorption data of water, alcohols and aromatic compounds both on hydrophilic on and hydrophobic zeolites has been collected from the literature and represented as a function of P/P i sat. It is found that the temperaturedependency of adsorption of a component can be described by the saturated vapour pressure, especially for water adsorption on zeolites. For systems where chemisorption also plays an important role, such as aromatics adsorption on zeolites, P i sat alone is not capable of predicting the temperaturedependency accurately enough. It is also observed that contrary to common practice, the maximum adsorption loading q i sat on zeolite should be considered independent of temperature. The proposed approach can be used in the modelling and design of industrial processes exploiting adsorption, such as in zeolite membrane systems, where separation is based on both adsorption and diffusion phenomena.

Chemical Engineering Science, 2013

Journal of Membrane Science, 2013

MFI membranes with a thickness of 0.5 mm prepared on a graded a-alumina support were evaluated fo... more MFI membranes with a thickness of 0.5 mm prepared on a graded a-alumina support were evaluated for separation of feed mixtures of 3 wt% n-butanol/water and 10 wt% ethanol/water by pervaporation. The membranes were selective to n-butanol and ethanol. The flux observed in the present work was about 100 times higher than that previously reported for n-butanol/water separation by pervaporation and about 5 times higher than that for ethanol/water separation by pervaporation. At 60 1C, the observed n-butanol/water flux was about 4 kg m À 2 h À 1 and the n-butanol/water separation factor was about 10 for the best membrane. At the same temperature, the membrane displayed an ethanol/water flux of ca. 9 kg m À 2 h À 1 and an ethanol/water separation factor of ca. 5. A mathematical model indicated significant mass transfer resistance in the support, which reduced the flux and the selectivity of the membranes. & 2012 Elsevier B.V. All rights reserved. was observed by Kuhn et al. [5] for all-silica DDR membranes. Over the past decade, production of renewable biofuels has received considerable attention due to the limited oil resources and the rising concern about the environment. So-called bioethanol produced by fermentation of sugars released from biomass is Contents lists available at SciVerse ScienceDirect

Periodica Polytechnica Chemical Engineering, 2015

Pervaporation of binary ethanol/water solutions of 5-10 wt.% ethanol was studied experimentally t... more Pervaporation of binary ethanol/water solutions of 5-10 wt.% ethanol was studied experimentally through a thin supported high-silica MFI zeolite membrane of hydrophobic character in the temperature range of 30-70 °C. The fluxes obtained were very high, 2-14 kg m-2 h-1 with ethanol/water separation factors of 4-7. The loss of effective driving force was significant in the supporting layers, which limited the membrane performance. The correlation between the experimental data and three different semi-empirical mass-transfer models was examined. The correlation was good especially when the driving force for mass-transfer was determined based solely on bulk feed, or the bulk feed and permeate conditions together. Somewhat lower correlation was observed when the driving force was corrected with the effect of support resistance. This was most likely due to the inaccuracies of the used mass transfer parameters in the support. The investigated semi-empirical models can be applied for initial stage process design purposes.

SID Symposium Digest of Technical Papers

The production of liquid transportation fuels such as bioethanol and more recently also biobutano... more The production of liquid transportation fuels such as bioethanol and more recently also biobutanol from renewable resources has received considerable attention. In the production of bio-based alcohols, the separation steps are expensive as the mixtures to be separated are dilute. As an energy-efficient separation technology, pervaporation is considered to be a potential process in biofuel purification. One of the main constraints in the commercialization of pervaporation has been low membrane fluxes, and the consequent high costs due to the high membrane area needed. In order to obtain high fluxes, the membranes should be as thin as possible. In this thesis, the performance of ultrathin zeolite membranes in pervaporation was investigated. Binary ethanol/water and n-butanol/ water mixtures were studied using both hydrophobic and hydrophilic zeolite membranes for alcohol concentration, as well as dehydration. The development of pervaporation membranes and processes has been mainly emp...

Journal of Membrane Science, 2012

ABSTRACT Discrete Faujasite zeolite nanocrystals with an average size of about 60 nm were attache... more ABSTRACT Discrete Faujasite zeolite nanocrystals with an average size of about 60 nm were attached as a well-defined monolayer on the surface of porous graded alumina supports. Ultrathin zeolite X films with a total thickness of about 1 mu m were grown from the seed monolayers by hydrothermal treatment in clear synthesis solutions. One of the membranes showed a total flux of 3.37 +/- 0.08 kg m(-2) h(-1) and a separation factor of 296 +/- 4 for dehydration of a 90/10 wt.% ethanol/water mixture by pervaporation at 65 degrees C. Moreover, the membranes displayed stable performance during pervaporation for 5.5 h operation. A mathematical model indicated that the flux and selectivity of the membranes were limited by pressure drop in the supports. Therefore, in order to obtain higher flux, the permeability of the support must be improved. (c) 2012 Elsevier B.V. All rights reserved.

Industrial & Engineering Chemistry Research, 2014

ABSTRACT The pervaporative mass transfer of pure ethanol and water through a thin (0.5 μm) suppor... more ABSTRACT The pervaporative mass transfer of pure ethanol and water through a thin (0.5 μm) supported high-silica MFI membrane was studied experimentally at 30–70 °C, and modeled on the basis of the Maxwell–Stefan formalism. The temperature dependency of adsorption was described with the temperature dependency of pure component saturated vapor pressure. Two scenarios of coverage dependency, i.e., coverage-dependent and coverage-independent Maxwell–Stefan diffusivity, were applied in the modeling of the mass transfer through the zeolite film. In addition, the mass-transfer resistance of the support layers was taken into account. The derived unary models provided good representations of ethanol and water pervaporation flux. The study illustrates that pure component steady-state pervaporation flux measurements at different conditions offer a feasible basis for determining diffusion coefficients. Basically, pure component adsorption isotherms and derived diffusivities can be used in the modeling of pervaporative mass transfer of mixtures using zeolite membranes.

Chemical Engineering Science, 2012

In this study, the feasibility of utilizing pure component saturated vapour pressure P i sat in r... more In this study, the feasibility of utilizing pure component saturated vapour pressure P i sat in representing the temperature-dependency of physisorption of vapours on zeolites is examined. Adsorption data of water, alcohols and aromatic compounds both on hydrophilic on and hydrophobic zeolites has been collected from the literature and represented as a function of P/P i sat. It is found that the temperaturedependency of adsorption of a component can be described by the saturated vapour pressure, especially for water adsorption on zeolites. For systems where chemisorption also plays an important role, such as aromatics adsorption on zeolites, P i sat alone is not capable of predicting the temperaturedependency accurately enough. It is also observed that contrary to common practice, the maximum adsorption loading q i sat on zeolite should be considered independent of temperature. The proposed approach can be used in the modelling and design of industrial processes exploiting adsorption, such as in zeolite membrane systems, where separation is based on both adsorption and diffusion phenomena.

Chemical Engineering Science, 2013

Journal of Membrane Science, 2013

MFI membranes with a thickness of 0.5 mm prepared on a graded a-alumina support were evaluated fo... more MFI membranes with a thickness of 0.5 mm prepared on a graded a-alumina support were evaluated for separation of feed mixtures of 3 wt% n-butanol/water and 10 wt% ethanol/water by pervaporation. The membranes were selective to n-butanol and ethanol. The flux observed in the present work was about 100 times higher than that previously reported for n-butanol/water separation by pervaporation and about 5 times higher than that for ethanol/water separation by pervaporation. At 60 1C, the observed n-butanol/water flux was about 4 kg m À 2 h À 1 and the n-butanol/water separation factor was about 10 for the best membrane. At the same temperature, the membrane displayed an ethanol/water flux of ca. 9 kg m À 2 h À 1 and an ethanol/water separation factor of ca. 5. A mathematical model indicated significant mass transfer resistance in the support, which reduced the flux and the selectivity of the membranes. & 2012 Elsevier B.V. All rights reserved. was observed by Kuhn et al. [5] for all-silica DDR membranes. Over the past decade, production of renewable biofuels has received considerable attention due to the limited oil resources and the rising concern about the environment. So-called bioethanol produced by fermentation of sugars released from biomass is Contents lists available at SciVerse ScienceDirect