title: The Use of Solubility Parameters to Select Membrane Materials for Pervaporation of Organic Mixtures

authors: Buckley-Smith, Marion

subjects: pervaporation

abstract: Pevaporation is a method for separating volatile components from liquid mixtures at ambient temperatures. The paint processing industry uses Hansen solubility parameters (HSP) to indicate polymer solubility. The potential of this method to predict solvent-polymer affinity was investigated for screening potential membrane materials for the pervaporation of a model solution containing linalool and linalyl acetate (major components of lavender essential oil), in ethanol. 

Published HSP values were collated for various polymers, and statistically analysed to determine variations in HSP values for polymer species. An investigation of published research into pervaporation of organic/organic binary solutions separated by homogeneous membranes indicated that the solvent whose HSP value was closest to that of the polymer would preferentially permeate. This relationship did not always hold for halogenated solvents or aqueous/organic solutions. Conflicting literature regarding the relationship between solvent uptake by polymers and HSP relative energy differences was resolved using a logarithmic relationship between these two parameters. 

The following membranes were selected, using their HSP to indicate their potential to interact with lavender oil components: Polyamide (PA: 26.9 micro;m), Polycarbonate (PC: 20.5 micro;m), Poly(ether imide) (PEI: 29.2 micro;m), Poly(ether sulphone) (PES: 27.6 micro;m), Polyethylene (HDPE: 10 micro;m, LDPE: 13-30 micro;m), Polyimide (PI: 30.0 micro;m), Poly(methyl methacrylate) (PMMA: 50 micro;m), Polypropylene (PP: 15.9 micro;m), and Poly(tetrafluoro ethylene) (PTFE: 26.7 micro;m). The HSP (dispersive, polar  hydrogen bonding components) for each membrane were calculated using the mean value obtained from swelling experiments, group contribution (calculated using Hoftyzer-Van Krevelen, Hoy and Beerbower methods), refractive indices (dispersive component), dielectric constants (polar component), and published HSP values. 

Pervaporation experiments investigated the effect of membrane thickness, process temperature, permeate pressure, impinging jet heights, feed flow rates and concentrations, and pre-soaking the membrane; on flow rate and selectivity in a polyethylene membrane. Membrane thickness was the dominant factor in membrane selectivity; the thinnest membranes (11.3-14.8 micro;m) had much poorer selectivity than membranes gt;24.7 micro;m. Temperatures between 22-34ordm;C, permeate pressure lt;10 kPa, impinging jet heights between 0.36-3.36 mm, feed flow rates between 541-1328 mL/min and concentrations between 1.78-6.01 % v/v of linalool and linalyl acetate in ethanol did not significantly affect selectivity. Flow rates increased with operating temperature, permeate pressure, and impinging jet heights. However, feed flow rate and concentration had no effect on membrane flux rate. Pre-soaking the membrane reduced the time to reach steady-state. 

Selected membranes were further investigated under standard operating conditions (permeate temperature 30ordm;C, permeate pressure lt;10 kPa, impinging jet height 1.36 mm, feed flow rate 804 mL/min and feed concentration of 5% v/v of linalool and linalyl acetate in ethanol). PMMA completely disintegrated in feed solution, and PC was too brittle to make an effective homogeneous membrane. PA, PC, PEI and PTFE had the highest efficiency (selectivity x flow rate) in their homogeneous form. However, PEI, PI and PTFE had the greatest selectivity, thus further trials should be done to improve stability and flow rates through these membranes. 

Pervaporation selectivity did not always follow trends predicted by HSP. Although polymers such as PA, PEI, PES, and PI preferentially permeated linalool as predicted, PC, PP and PTFE did not preferentially permeate linalyl acetate. This may have been due to the difference in size and diffusivity of these molecules (linalyl acetate, the larger molecule, did not follow the sorption selectivity predictions), or reliability of literature HSP values and those calculated by group contribution. 

This research shows that HSP is a good screening method for pervaporation membranes, especially where the molecules being separated are of comparable size. Polymers that have HSP close to the desired component and not to other components tend to have the best selectivity and flux characteristics. However, diffusion is an important factor, and is not completely accounted for by HSP. 

Recommendations for further research include: carrying out pervaporation analyses of selected polymers using pure lavender essential oil; modifying polymers to form asymmetric or composite membranes with improved permeation characteristics; and potential use of thin channel inverse gas chromatography to determine a more accurate HSP which includes diffusivity.

text: The Use of Solubility Parameters to Select Membrane Materials for Pervaporation of Organic Mixtures Pevaporation is a method for separating volatile components from liquid mixtures at ambient temperatures. The paint processing industry uses Hansen solubility parameters (HSP) to indicate polymer solubility. The potential of this method to predict solvent-polymer affinity was investigated for screening potential membrane materials for the pervaporation of a model solution containing linalool and linalyl acetate (major components of lavender essential oil), in ethanol. 

Published HSP values were collated for various polymers, and statistically analysed to determine variations in HSP values for polymer species. An investigation of published research into pervaporation of organic/organic binary solutions separated by homogeneous membranes indicated that the solvent whose HSP value was closest to that of the polymer would preferentially permeate. This relationship did not always hold for halogenated solvents or aqueous/organic solutions. Conflicting literature regarding the relationship between solvent uptake by polymers and HSP relative energy differences was resolved using a logarithmic relationship between these two parameters. 

The following membranes were selected, using their HSP to indicate their potential to interact with lavender oil components: Polyamide (PA: 26.9 micro;m), Polycarbonate (PC: 20.5 micro;m), Poly(ether imide) (PEI: 29.2 micro;m), Poly(ether sulphone) (PES: 27.6 micro;m), Polyethylene (HDPE: 10 micro;m, LDPE: 13-30 micro;m), Polyimide (PI: 30.0 micro;m), Poly(methyl methacrylate) (PMMA: 50 micro;m), Polypropylene (PP: 15.9 micro;m), and Poly(tetrafluoro ethylene) (PTFE: 26.7 micro;m). The HSP (dispersive, polar  hydrogen bonding components) for each membrane were calculated using the mean value obtained from swelling experiments, group contribution (calculated using Hoftyzer-Van Krevelen, Hoy and Beerbower methods), refractive indices (dispersive component), dielectric constants (polar component), and published HSP values. 

Pervaporation experiments investigated the effect of membrane thickness, process temperature, permeate pressure, impinging jet heights, feed flow rates and concentrations, and pre-soaking the membrane; on flow rate and selectivity in a polyethylene membrane. Membrane thickness was the dominant factor in membrane selectivity; the thinnest membranes (11.3-14.8 micro;m) had much poorer selectivity than membranes gt;24.7 micro;m. Temperatures between 22-34ordm;C, permeate pressure lt;10 kPa, impinging jet heights between 0.36-3.36 mm, feed flow rates between 541-1328 mL/min and concentrations between 1.78-6.01 % v/v of linalool and linalyl acetate in ethanol did not significantly affect selectivity. Flow rates increased with operating temperature, permeate pressure, and impinging jet heights. However, feed flow rate and concentration had no effect on membrane flux rate. Pre-soaking the membrane reduced the time to reach steady-state. 

Selected membranes were further investigated under standard operating conditions (permeate temperature 30ordm;C, permeate pressure lt;10 kPa, impinging jet height 1.36 mm, feed flow rate 804 mL/min and feed concentration of 5% v/v of linalool and linalyl acetate in ethanol). PMMA completely disintegrated in feed solution, and PC was too brittle to make an effective homogeneous membrane. PA, PC, PEI and PTFE had the highest efficiency (selectivity x flow rate) in their homogeneous form. However, PEI, PI and PTFE had the greatest selectivity, thus further trials should be done to improve stability and flow rates through these membranes. 

Pervaporation selectivity did not always follow trends predicted by HSP. Although polymers such as PA, PEI, PES, and PI preferentially permeated linalool as predicted, PC, PP and PTFE did not preferentially permeate linalyl acetate. This may have been due to the difference in size and diffusivity of these molecules (linalyl acetate, the larger molecule, did not follow the sorption selectivity predictions), or reliability of literature HSP values and those calculated by group contribution. 

This research shows that HSP is a good screening method for pervaporation membranes, especially where the molecules being separated are of comparable size. Polymers that have HSP close to the desired component and not to other components tend to have the best selectivity and flux characteristics. However, diffusion is an important factor, and is not completely accounted for by HSP. 

Recommendations for further research include: carrying out pervaporation analyses of selected polymers using pure lavender essential oil; modifying polymers to form asymmetric or composite membranes with improved permeation characteristics; and potential use of thin channel inverse gas chromatography to determine a more accurate HSP which includes diffusivity.

year: 2006

title: Where have all the children gone? Experiences of children, parents and teachers in a changing early childhood education service

authors: Hawkes, Kathryn Frances

subjects: Early childhood education

abstract: This study analyses the experiences of children, parents and teachers in a changing early childhood education (ECE) service in New Zealand. This thesis derived from the researcher’s growing awareness of neo-liberal politics and the institutionalisation of children resulting from social, economic and cultural changes. The researcher’s interest in connecting children within ECE services to the local community outside of the ECE service’s gate was also explored. The study revealed experiences and perspectives from children, families and teachers within one independent, community based, not for profit ECE service that recently underwent changes.
Drawing from literature, the thesis acknowledges the changes that have taken place within ECE in New Zealand over the past 20 years. The changes identified within the literature are identified within the historical, economic and social context. The changes include marketisation, competition, the increase of hours and days that young children are placed within ECE services and the government support of families to return to work. 
The study was based on a social constructionist framework that used a qualitative inquiry research methodology. Perspectives and views were gathered from the head teacher, parents and children at the ECE service utilising the Mosaic approach. The methodological tools included semi structured interviews, walking interviews, a diary of outings collated by the head teacher, children’s auto photography and interviews with the children while viewing their learning journals.
The collected data was analysed in relation to the study’s social constructionist framework. The patterns and themes that emerged included marketisation, intrinsic and extrinsic pressures on children, parents and teachers, leadership, changes to the operational structure of the service and curriculum experiences for parents, teachers and children. 
Foundational to the study are the rights of the child and need for children to have their perspective heard. The Mosaic approach to the methodology utilised within the study raises the perspectives and views of the child giving equitable value to their contribution within the study. The outcome of the study is to propose an ideological framework that could assist in ensuring the child is heard within ECE and that the child is represented within all matters affecting them. This ideological framework aspires to be an underpinning framework that is utilised by ECE leaders and teachers when making decisions on all matters relating to children, their families and the ECE service.

text: Where have all the children gone? Experiences of children, parents and teachers in a changing early childhood education service This study analyses the experiences of children, parents and teachers in a changing early childhood education (ECE) service in New Zealand. This thesis derived from the researcher’s growing awareness of neo-liberal politics and the institutionalisation of children resulting from social, economic and cultural changes. The researcher’s interest in connecting children within ECE services to the local community outside of the ECE service’s gate was also explored. The study revealed experiences and perspectives from children, families and teachers within one independent, community based, not for profit ECE service that recently underwent changes.
Drawing from literature, the thesis acknowledges the changes that have taken place within ECE in New Zealand over the past 20 years. The changes identified within the literature are identified within the historical, economic and social context. The changes include marketisation, competition, the increase of hours and days that young children are placed within ECE services and the government support of families to return to work. 
The study was based on a social constructionist framework that used a qualitative inquiry research methodology. Perspectives and views were gathered from the head teacher, parents and children at the ECE service utilising the Mosaic approach. The methodological tools included semi structured interviews, walking interviews, a diary of outings collated by the head teacher, children’s auto photography and interviews with the children while viewing their learning journals.
The collected data was analysed in relation to the study’s social constructionist framework. The patterns and themes that emerged included marketisation, intrinsic and extrinsic pressures on children, parents and teachers, leadership, changes to the operational structure of the service and curriculum experiences for parents, teachers and children. 
Foundational to the study are the rights of the child and need for children to have their perspective heard. The Mosaic approach to the methodology utilised within the study raises the perspectives and views of the child giving equitable value to their contribution within the study. The outcome of the study is to propose an ideological framework that could assist in ensuring the child is heard within ECE and that the child is represented within all matters affecting them. This ideological framework aspires to be an underpinning framework that is utilised by ECE leaders and teachers when making decisions on all matters relating to children, their families and the ECE service.

year: 2014

title: Imagining our own approaches

authors: Smith, Linda Tuhiwai

abstract: I spent some formative years of my life either in the back of museums or their basements helping my father, a scholar of Māori Studies, and keeping myself out of trouble. In the late 1960s I had one small job in the library basement of the Peabody Museum in Salem, Massachusetts, typing new labels for the captains’ log books of ships that were sailing during the American Revolution. I read most of those journals that consisted of pages and pages of wind directions with the rare glimpse of an encounter with another ship or a list of supplies. Why were we there in Salem when we came from Aotearoa, New Zealand? We were there because Salem was the home base for ships that sailed into the Pacific and returned home with collections of materials from the various Pacific Islands countries they visited. My father was studying elaborately carved items from the Marquesa Islands that looked very much like Māori designs.

text: Imagining our own approaches I spent some formative years of my life either in the back of museums or their basements helping my father, a scholar of Māori Studies, and keeping myself out of trouble. In the late 1960s I had one small job in the library basement of the Peabody Museum in Salem, Massachusetts, typing new labels for the captains’ log books of ships that were sailing during the American Revolution. I read most of those journals that consisted of pages and pages of wind directions with the rare glimpse of an encounter with another ship or a list of supplies. Why were we there in Salem when we came from Aotearoa, New Zealand? We were there because Salem was the home base for ships that sailed into the Pacific and returned home with collections of materials from the various Pacific Islands countries they visited. My father was studying elaborately carved items from the Marquesa Islands that looked very much like Māori designs.

year: 2015