Pervaporation and vapour permeation of methanol – dimethyl carbonate mixtures

through PIM-1 membranesPetr Číhal1, Ondřej Vopička1,*, Tereza-Markéta Durďáková1, Peter M. Budd2, Wayne Harrison2, Karel Friess1

1 Department of Physical Chemistry, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic2 School of Chemistry, The University of Manchester, Manchester M13 9PL, United Kingdom* Corresponding author: vopickao@vscht.czKeywords: PIM-1, organophilic pervaporation, vapour permeation, sorption, swelling

AbstractThe separation of dimethyl carbonate (DMC) from its mixtures with methanol was studied using pervaporation (PV) and vapour permeation (VP) through thick (~0.5 mm) PIM-1 membranes; PV characteristics of PDMS and PTMSP membranes are provided for comparison. DMC is a “green” chemical with numerous applications in chemistry, but its production is energy- and cost-intensive. As their azeotrope contains 82 mol.% of methanol at 40 °C, DMC-selective rather than common methanol-selective membranes can allow for energy efficient separation and thus production of this “green chemical”. PV of the azeotropic mixture through the PIM-1 membrane showed a separation factor of 2.3, which is comparable to that observed for PV through the PDMS membrane; the PTMSP membrane showed practically no separation. The total PV fluxes followed the order: PTMSP >> PIM-1 > PDMS. When the PIM-1 membrane was operated in the VP mode, a separation factor of up to 5.1 was reached for the vapours having the azeotropic composition, while total fluxes dropped ca 50-times compared to PV. The highest observed separation factor of 6.5 was found for VP of DMC-rich vapour mixtures highly diluted with inert gas. To our knowledge, VP through PIM-1 membranes enables to date the most selective membrane-based removal of DMC from its azeotrope with methanol.

1 IntroductionPIM-1, the archetypal member of the class of polymers of intrinsic microporosity, is an amorphous glassy polymer having a high fraction of free volume [1]. Because of its high permeability and considerable selectivity, it has frequently been used to produce selective layers of gas separation and PV membranes, the latter of which have so far been used for the separations of phenol, alcohols and other organic compounds from water [1-9]. In this context, the use of PIM-1 for Organic Solvent Nanofiltration membranes has been extensively studied [10-12].

Dimethyl carbonate (DMC) is a biodegradable and practically non-toxic solvent, fuel additive and chemical feedstock which can replace phosgene and other harmful agents [13-15]. As this compound is produced from methanol (MeOH), energy efficient breaking of the azeotrope (82 mol.% of methanol at 40 °C) is vital for the economical production and, in turn, exploitation of DMC [13, 14, 16, 17]. Since classical methods such as high-pressure distillation [18] or extractive and azeotropic distillation [19, 20] are energy intensive, hybrid processes combining rectification and membrane separation offer an economically viable alternative [18, 21-24] provided that permeable, selective and reliable membranes are available.

Pervaporation (PV) is probably the most common membrane technique used for the separation of liquid methanol–DMC mixtures. Mainly methanol-selective membranes were reported in the literature as these allow for very high separation factors [18, 25-30]. However, the principal drawback of the methanol-selective membranes is the necessity to pass excessive amounts of methanol through the membrane, while retaining the minor component of the azeotrope, DMC, in the retentate. This drawback can be eliminated by using DMC-selective (organophilic) membranes, which are typically based on cross-linked polydimethylsiloxane (PDMS). These membranes, however, exhibit rather limited separation factors of approximately 2-4 at the composition of the azeotrope [31-35]. The situation is similar for mixtures of methyl acetate, an analogue of DMC, and methanol [36-38]. This limitation most probably originates from the competition between the fast diffusion of small molecules of methanol and high sorption of the more condensable molecules of DMC [39, 40].

Besides PV, vapour permeation (VP) can be used for the separation of methanol-DMC mixtures, either with methanol- or DMC-selective membranes [35, 41]. Clearly, VP is well suited to the processing of the head streams, such as volatile azeotropes from distillation columns, as no phase transition is required. In contrast to the PV setup, a vapour mixture is fed to the membrane, thereby avoiding the intensive heat exchange through the membrane occurring in PV [21, 23]. Moreover, the mixture of vapours can be fed to the membrane at any pressure and temperature provided that the pressure is lower than that of the dew point. Thus, there are at least three straightforward ways of manipulating the feed pressure: i) depressurization of the saturated vapour, ii) elevation of the dew point pressure in the vapour permeation module by maintaining it at higher temperature than the saturated vapour, iii) the addition of inert gas to the saturated vapour mixture. The addition of an inert gas seems convenient on the laboratory scale, as it enables the overall feed mixture to be kept at atmospheric pressure, while manipulation of the feed pressure and/or membrane module temperature are presumably more convenient on larger scales. However, if the same temperatures and pressures of the individual vapours in the feed are adjusted in either way, comparable membrane performances can be expected.

As follows from earlier studies, VP enables a better control over the driving forces, plasticization of membranes and, in turn, over the flux and separation factor [22, 35, 41-46] than PV. This better control then enables the enhancement of separation factors, which appear to be limited for DMC-selective membranes when compared to the methanol-selective

ones [41]. We thus limit ourselves here to the challenging search for efficient DMC-selective membranes and report the characteristics of PIM-1 membranes for VP and PV. Moreover, sorption and swelling of PIM-1 membranes in single component vapours were studied as they provide a better insight into the transport mechanisms [47-49] and allow for the modelling of the volume changes necessarily occurring in a real VP module.

2 Experimental2.1 Materials

The synthesis of PIM-1 was based on the procedure described in detail in the literature [50]. To characterize the product, Gel Permeation Chromatography (GPC) measurements were carried out using a Viscotek GPC max VE 2001 instrument with two PL mixed B columns and a Viscotek TDA 302 Triple Detector Array: Mw = 127 000 g/mol, Mw/Mn = 2.0, Mp = 94 000 g/mol, that is weight-average molecular weight, polydispersity and molecular weight at the maximum in the GPC peak.

PIM-1 was dissolved in chloroform (min. 99.83%, Lach–ner) and filtered. Solution containing ca 3 wt.% of PIM-1 was cast on a glass Petri dish; evaporation took 6 days under ambient conditions. The films were then exposed to an excess of liquid methanol for 1 day to remove the residual solvent and rejuvenate the physical structure of the polymer [51-53], the density of PIM-1 was taken from the literature [54]. PDMS and poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes were prepared by solution-casting onto glass Petri dishes as described elsewhere [40, 55], raw materials were obtained from Dow Corning (Sylgard 184) and Gelest. The PTMSP membrane was soaked in excess of methanol for 1 day prior to its use [56, 57]. Thicknesses of the membranes were: 632 μm (PIM-1 membrane for VP), 663 μm (PIM-1 membrane for PV), 655 μm (PDMS membrane) and 476 μm (PTMSP membrane).

Methanol (min. 99.8%, Penta) and DMC (99+ %, Acros Organics) were used as received; their physical properties were taken from the literature [58, 59]. Hydrogen (Siad Czech, 5.5), helium (Siad Czech, 4.8) nitrogen (Siad Czech, 4.0) and liquid nitrogen (Siad Czech) were used as received.

2.2 Sorption and swelling of PIM-1

Sorption isotherms can be correlated with the Guggenheim-Anderson-De Boer (GAB) model of multilayer adsorption [60, 61] in the form:

v=vm h f a

(1−f a ) (1−f a+h f a )(1)

where v represents the amount of sorbate in the sorbent, vm stands for the capacity of the (first) adsorption monolayer of the sorbent, h is the ratio between the strength of binding of the molecules to the surface in the first layer and higher layers, f is a parameter representing

the ratio of the pressure of saturated vapours and reference pressure, and a represents activity:

a= ppsat .

Sorption of vapours in PIM-1 was measured at 40 °C using a gravimetric sorption apparatus [62, 63] equipped with McBain’s spiral balances. The previously evacuated (< 1 Pa) cell with the membrane was filled with vapours of a studied compound; elongation of the spiral was followed in real time until equilibrium was reached. While methanol desorbed readily from PIM-1 upon applying vacuum at 40 °C, DMC remained entrapped and did not fully desorb even if exposed to vacuum for several days. Despite that, all points of the sorption isotherms were reproducible as these were, in the case of DMC, higher than the entrapped amount. The entrapped amount was roughly 2 mmol(DMC)g(PIM-1)-1 and was completely removable upon soaking the membrane in an excess of liquid methanol (1 day) and drying in vacuum. Therefore, sorption of methanol vapours was measured prior to that of DMC. The maximum relative uncertainty of the individual sorption uptakes was 5%.

As polymers generally swell upon their exposure to low molecular mass compounds, the assessment of the volume of the swollen polymer is vital for the construction of separation membranes and membrane modules. Swelling is expressed here as relative change of volume in the form:

ΔV rel=V Ø−V 0

V 0 =aØ bØ lØ−a0b0l0

a0 b0 l0 , (2)

where V Ø is the equilibrium volume of the swollen membrane, V 0 is the initial volume of the membrane cleared of volatile compounds by soaking in methanol and desorption in the stream of hydrogen. Volumes V Ø and V 0 were calculated from the respective directly measured perpendicular proportions of the sample (a, b) and its thickness (l).

Swelling of PIM-1 membranes exposed to methanol and DMC vapours was measured in a cell equipped with a glass window allowing for the optical observation of the membrane and maintained at 40 °C. The membrane was consecutively exposed to the continuous streams of gaseous mixtures of hydrogen with methanol or DMC. Partial pressures of methanol and DMC vapours were assured by passing controlled streams of hydrogen gas (50 cm3(STP)min-1, Aalborg GFC) through a saturator filled with the liquid (methanol or DMC) and maintained at a matching temperature (Julabo F12-MA and Testo 735-2/Pt 100). Two approximately square pieces having dimensions of ca 0.277 millimetres were cut from the PIM-1 membrane. Their thicknesses and two perpendicular dimensions of the area proportions were independently observed with two optical microscopes Dino-Lite (AM7013MZT and AM7013MZT4) with magnifications of 20x (area) and 460x (thickness). Once the membrane was exposed to the vapour, its proportions were measured until they remained constant and were compared to those of the membrane equilibrated with pure hydrogen. Maximum uncertainty of the individual points was (Vrel) = 0.03.

2.3 Pervaporation and vapour permeation

The separation performance of PV and VP units can be expressed based on the molar fractions of the respective components in the feed and permeate stream by a separation factor:

β=

xDMCperm

x MeOHperm

xDMCfeed

x MeOHfeed

. (3)

As the above quantity does not solely depend on the properties of the membrane but also on the actual experimental setup, gas permeability is also used here as it allows for consistent comparisons of the PIM-1 membranes when used either in the PV or VP mode [64]:

ji=Pi

l (γ i 0L x i 0

L pi 0sat−pil ) (4a)

ji=Pi

l ( p i0−p il)(4b)

where ji stands for the flux of component i, Pi for its (gas) permeability, γ i 0L and x i 0

L for its activity coefficient and molar fraction in the liquid feed mixture, pi 0

sat for its saturated vapour pressure, pi 0 and pil for its partial pressures at the feed (0) and permeate (l) faces of the membrane having the thickness l. Activity coefficients experimentally determined at isothermal conditions (40 °C) were taken from the literature [16]. As separation factor reflects not only material properties of the membrane but also of the entire experimental setup, material properties of different membranes can be well compared using selectivity [64]:

¿PDMC

PMeOH. (5)

Pervaporation (PV) experiments were conducted using the previously published apparatus [29, 65], in which hydrogen at 100 cm3 (STP) min−1 was used to sweep the permeate side of the membrane. The feed tank with a circulator having the volume of ca 150 cm3 was filled with liquid mixture of composition xMeOH

feed . The tank and the entire PV cell were maintained at 40 °C, both feed and permeate compartments were open to the atmosphere and the effective area of the membrane was 3.1 cm2. Permeate was collected in a cryogenic liquid nitrogen trap and weighed with an Ohaus DV215CD balance. Feed and permeate were then evaporated into a previously evacuated chamber connected to a Nicolet iS10 FTIR spectrometer equipped with a gas phase cuvette and analysed as described elsewhere [40]. The evolution of flux over time was observed to identify the steady state conditions, which were in all cases safely reached within two (PDMS, PTMSP) and

three (PIM-1) hours of operation. Maximum relative uncertainties of the PV fluxes of the individual components were 5% (PIM-1), 10% (PTMSP), 10% (PDMS).

H2 MFC

cryogenic trap

balance~

vent

feed tankand circulating pump

FTIR

membrane

Fig. 1: Schematic drawing of the pervaporation setup. MFC stands for mass flow controller.

Measurements of the permeation of vapour mixtures were performed at 40 °C and at atmospheric pressure using a previously reported apparatus [35, 66] having the active area of the membrane of 5.0 cm2. Hydrogen was used as a sweep gas and as an inert gas diluting the vapours fed to the membrane. The mixtures of sweep gas with permeate were analysed with a Perkin Elmer Clarus 500 GC-MS. The molar fraction of methanol in the condensable part of the overall feed mixture composed of methanol, DMC and hydrogen (xMeOH

feed in methanol-

DMC vapour mixture) and partial pressures of the vapours in the overall feed were adjusted by passing controlled streams of the inert gas through two saturators, each filled with methanol or DMC and maintained at a matching temperature. Thus, the series of experiments was conducted at fixed ratios of the partial pressure of the vapours with respect to the dew point pressure, the latter of which was calculated based on the literature data [16, 58, 59]. Similar to the PV measurements, the evolution of flux over time was observed to identify the steady state conditions, which were in all cases safely reached within 5 hours of operation. Maximum relative uncertainty of the VP fluxes of the individual components was 10%.

MFC

saturator

heating

H2

vent

ventSL GC - MS

vent

membrane

MFC

MFC

MFC

MFC

saturator

Fig. 2: Schematic drawing of the vapour permeation setup. MFC stands for mass flow controller.

3 Results and discussion3.1 Sorption and swelling of PIM-1

Sorption isotherms of methanol and DMC vapours in PIM-1 membranes at 40 °C were of type II according to IUPAC [67] (Fig. 3). Isotherms of similar shapes were earlier observed also for other compounds in PIM-1 as well as in other glassy polymers, such as for DMC in PTMSP or methanol and DMC in cellulose triacetate (CTA) [61, 68, 69]. Despite the fact that PIM-1 membranes were earlier found to be organophilic [1, 8], the sorption uptakes of methanol were not negligible compared to those of DMC. Thus, based just on these data and assuming the solution-diffusion mode of transport [70], PIM-1 is either diffusion selective towards heavier compounds or strong co-sorption effects occur. Similar to the earlier observations for PTMSP, which shows light gas rejection, competitive adsorption and surface diffusion can be expected to be the main mechanisms [71].

0.0 0.2 0.4 0.6 0.8 1.0

0

2

4

6

8

10

12

14 MeOH DMC GAB MeOH GAB DMC

v / [

mm

ol g

-1]

a / [-]

Fig. 3: Sorption isotherms of methanol and DMC vapours in PIM-1 at 40 °C. Curves represent the GAB model – Eq. (1).

The values of vm (Tab. 1) can be recalculated so that either 2.6 moles of methanol or 1.6 mole of DMC can be adsorbed in the first layer on one mole of mer units of PIM-1 (MmerPIM-

1 = 460.5 gmol-1). The specific surface area of PIM-1 can be estimated based on Hill’s equation for the surface occupied by one adsorbed molecule  = 6.354 (Tc/pc)2/3 [61, 72], yielding 721 m2g-1 for methanol and 670 m2g-1 for DMC. These specific areas compare well to the value of 850 m2g-1 obtained using nitrogen BET analysis [73].

The parameter f equalled roughly 0.6 for both components in PIM-1. As this parameter is related [60, 61] to the saturated vapour pressure of the free sorptive and reference pressure for

the sorbate f = psat

pref , it follows that the reference pressure is approx. 1.6 times higher than the

saturated vapour pressure. Hence, by assuming the Kelvin equation it follows that the sorbate has the nature of localized adsorbed droplets.

The molecules of DMC bind ten times more strongly to the surface of PIM-1 than those of methanol, that is hDMC  10  hMeOH (Tab. 1). This is consistent with with the steep initial increase of the sorption uptakes at low activities of DMC vapour; see Fig. 3 and Eq. (1). Besides that, DMC binds four times more strongly to PIM-1 than to PTMSP (hDMC

PTMSP=25.1) [61]. Clearly, PIM-1 adsorbs the molecules of DMC more strongly than PTMSP. Since PTMSP shows blockage of the permeation of light gases by condensable gases [55, 74, 75], which was explained in the literature to be a result of the capillary condensation of the heavier component in the inner pores of the polymer, similar blockage of the permeation of methanol by the molecules of the heavier DMC can be expected to occur also in PIM-1.

Tab. 1: GAB parameters, Eq. (1), for sorption of methanol and DMC vapours in PIM-1 at 40 °C

methanol DMCvm / [mmolg-1] 5.55 vm / [mmolg-1] 3.45h / [-] 10.4 h / [-] 98.9f / [-] 0.62 f / [-] 0.63

The relative changes in the volume of the PIM-1 membrane differed markedly from those predicted by assuming volume additivity of the polymer and liquid sorbate. The measured relative changes of volume showed linear dependences on concentration with intercepts at non-zero concentrations (Fig. 4A). The slopes of these lines were comparable to those calculated based on the ideal additivity of the volumes of liquid sorbate and the polymer, which naturally showed zero intercepts. As follows from the intercepts at non-zero concentrations, PIM-1 membrane did not swell at methanol vapour activities below 0.12, which corresponds to the sorption uptake of 2.7 mmolg-1, and at DMC vapour activities below 0.013, which corresponds to the sorption uptake of 1.6 mmolg-1 (Fig. 4B). Clearly, swelling occurred when the first adsorption monolayer was saturated to approximately one half of its capacity (vm) regardless of the chemical composition of the sorbate (Tab. 2). The internal structure of PIM-1 can thus withstand a certain amount of a sorptive, 0.5vm. By assuming that the sorptive condenses to a liquid and that the density of the polymer equals 1.06 gcm-3 [54], PIM-1 begins to swell when containing more than 0.11 cm3(MeOH)g-

1(PIM-1) or 0.14 cm3(DMC)g-1(PIM-1), that is, when 12-15 % of the apparent volume of the polymer is occupied. This fraction of the available free volume compares well with a fractional free volume exceeding 20 % (from the literature [76]).

A) B)

0 2 4 6 8 10 120.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Vrel=0.03946vMeOH-0.10602

MeOH DMC

Vre

l / [-

]

nsorb/mpol / [mmol g-1]

Vrel=0.10026vDMC-0.17411

0.0 0.2 0.4 0.6 0.8 1.00.0

0.1

0.2

0.3

0.4

0.5

0.6 MeOH DMC

V

rel /

[-]

a / [-]

Fig. 4: Relative change of volume of PIM-1 membrane exposed to methanol and DMC vapours at 40 °C. A: Lines with zero intercept represent ideal behaviour assuming the additivity of volumes of the polymer and the liquid sorbate, lines with non-zero intercept represent the correlation of measured data. B: Curves represent the model based on correlations of measured data from figure A and Eq. (1).

3.2 Pervaporation and vapour permeation

Soon after its invention, PIM-1 was found to form membranes which can selectively remove a highly condensable phenol from water by PV [1, 8]. A very similar behaviour was found for the separation of highly condensable gases from the less condensable ones by PTMSP membranes [71]. In analogy to these well-known observations, PV through a PIM-1 membrane showed the separation of DMC from its solution with methanol (Fig. 5) provided that the DMC content in the liquid feed did not exceed 60 mol.%. A similar behaviour was found also for PTMSP and PDMS membranes. The loss of separation most likely occurs due to the loss of sorption selectivity connected to the solubilisation of methanol by the already sorbed DMC; this phenomenon has so far been identified in the case of PDMS and PTMSP membranes [32, 40, 55]. Overall, membranes from PIM-1 and PDMS showed comparable separation of the methanol-DMC mixtures while PTMSP showed almost no separation in the PV mode. In all cases, PV and VP through PIM-1, PDMS and PTMSP membranes preferentially removed DMC from the feed. In contrast to that, methanol preferentially evaporates from the free liquid (feed). The VLE data are thus located above the diagonal in the “x-y” diagram, while VP and PV data are located under the diagonal (Fig. 5A). In all cases, crossing the diagonal implies the loss of separation.

In the VP setup, the PIM-1 membrane was exposed to continuous streams of mixtures of vapours of given compositions at atmospheric pressure and at 40 °C. These mixtures were accordingly diluted by hydrogen so that the pressure of the vapours reached 282, 493 and 633 % of the dew point pressure; the uncertainties originated from those of the temperatures and hydrogen flow rates. Separation factors of 5.1, 4.0 and 3.3 were observed

for the feeds having the azeotropic composition; a separation factor of 2.3 was observed for PV (Fig. 5). Clearly, the dilution of the feed vapour mixture enhanced separation factors at all the feed compositions studied. Interestingly, in the VP mode, the PIM-1 membrane did not show the loss of separation for the DMC-rich feeds that occurred in the PV mode. On the contrary, separation factors up to 6.5 were observed. Hence, VP through PIM-1 membranes can be an effective way of removing heavier compounds even from mixtures having small concentrations of methanol (or other alcohols). This is the case of most binary azeotropes of methanol occurring at pressures close to atmospheric, such as those with methylal [77, 78], acetone [79], methyl acetate [80, 81], methyl formate [82], halogenated hydrocarbons [83, 84] or trimethoxysilane [85].

The increase of the separation factor and selectivity with DMC concentration in the feed was more pronounced at high dilutions, that is, at the feed pressures set here to 28 % of the dew point pressure. Clearly, low vapour activities in these feed mixtures (e.g. aMeOH = 0.24, aDMC = 0.13 at xMeOH = 0.82) approximately correspond to the equilibrium sorption uptakes that are comparable to the monolayer capacity of PIM-1 for the individual components (Fig. 3) and, in turn, to low swelling of the membrane (Fig. 5B). The highest DMC-selectivity of PIM-1 membranes can thus be expected when the membrane is not significantly swollen, when most penetrating molecules are strongly adsorbed in the first layer rather than weakly adsorbed in multilayers and, in turn, when the capacity of the internal voids of PIM-1 are preferentially occupied by the adsorbed molecules of DMC. The use of inert gas can be expected to be equivalent to feed depressurization, as sorption of methanol and DMC vapours in PDMS and PTMSP was earlier shown to be independent of the presence of hydrogen as an inert gas [40, 55].

A) B)

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

y MeO

H, x

perm

MeO

H /

[-]

xMeOH, xfeedMeOH / [-]

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

2

4

6

8

10 VP 28 % p(d.p) VP 49 % p(d.p) VP 63 % p(d.p) PV (PIM-1) PV (PDMS) PV (PTMSP)

[

-]

xfeedMeOH / [-]

Fig. 5: The “y-x” diagram for the VP through the PIM-1 membrane, PV through the PIM-1, PDMS and PTMSP membranes and VLE [16], all at 40 °C (A). Separation factor for the VP

through the PIM-1 membrane, PV through the PIM-1, PDMS and PTMSP membranes at 40 °C (B). Dashed curves are guides for the eye, solid curve represents Wilson model [16], x and y are molar fractions, xMeOH

feed is methanol molar fraction in the feed vapour (VP) and liquid (PV). Colours in (A) have the same meaning as in (B); pentagons refer to VLE, circles for VP at age 1, triangles for age 2, diamonds for age 3 and squares for PV.

The influence of the ageing of the PIM-1 membranes on the measured characteristics was limited by using relatively thick films (632 μm for VP and 663 μm for PV), which were soaked in methanol prior to the first measurement [51, 53, 86]. In the case of PV, no effect of ageing was observed as all measurements were conducted during six days after the methanol treatment (eight days for PTMSP). In the case of VP, the effect of ageing was followed so that each experiment was repeated with a time span of ca 30 days; the repetitions are denoted here as age 1, age 2 and age 3. It should be noted that the individual measurements were discontinuous, that is, the membrane was cleared of the volatile compounds by purging the apparatus with hydrogen after each measurement. While the effect of the membrane ageing on the VP separation was very limited (Fig. 5A), the permeabilities of the individual components dropped by 7-30 % of the initial value after ca 60 days (Fig. A1), while bigger drops of permeability were observed for the more saturated feeds. Therefore, averages calculated from results of three measurements (referred to as Age 1 to 3 in Fig. A1) are presented for VP in figures Fig. 5B to 7 and in Fig. 9. The use of thick membranes thus enabled us to limit the influence of time on the measured characteristics, thereby reducing the number of independent variables to composition and, in the case of VP, the total pressure of vapours. This simplification is vital as ageing is influenced not only by time and membrane thickness but also by the feed composition and mode of operation of VP (continuous, discontinuous) [86]. Hence, the reported characteristics refer to non-aged membranes.

The total PV permeate fluxes of the three studied membranes followed the expected order: PTMSP >> PIM-1 > PDMS and showed mild dependences on the feed concentration (Fig. 6B), which was, in the case of PIM-1, mainly influenced by the concentration dependence of the DMC flux.

The total VP permeate fluxes observed for the PIM-1 membrane  (Fig. 6A) reached ca 2-7% of those observed for PV (Fig. 6B); similar drops of total permeate flux with respect to PV were earlier found also for PDMS and PTMSP membranes [35]. In the case of PIM-1, the total permeate fluxes increased, as expected, with increasing pressure of the vapours in the feed. The dependence of the total flux on the feed mixture composition was dominated, at all feed dilutions, by the respective dependences of the fluxes of the individual components. Clear blocking of methanol transport was found for feeds containing minor concentrations of DMC (Figs. 7B and 8). Hence the strongly sorbing molecules of DMC likely block the sorption centres of PIM-1 for methanol sorption and transport.

A) B)

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0

0.4

0.8

1.2

4.4

4.8

5.2

MeOH (PIM1) DMC (PIM1) total (PIM1) total (PDMS) total (PTMSP)

F / [

KM

H]

xfeedMeOH / [-]

Fig. 6: Dependences of the total VP flux through the 632 μm PIM-1 membrane (A) and of the total PV fluxes through the 663 μm PIM-1, 655 μm PDMS and 476 μm PTMSP membranes (B) on the feed composition at 40 °C. Solid and dashed curves are guides for the eye, xMeOH

feed is methanol molar fraction in the feed vapour (VP) and liquid (PV).

Permeabilities of PIM-1 for methanol and DMC, as calculated based on Eq. (4a) and Eq. (4b) for PV and VP, differed by ca one order of magnitude. It may thus be concluded that diffusion fluxes occurring in highly swollen PIM-1, in which most of the compounds are sorbed in the form of adsorption multilayers, can be generally expected to be higher. In both modes of operation, methanol permeability increased abruptly when the feed did not contain DMC. Thus, the permeation of methanol through PIM-1 membranes appears to be blocked by even low concentrations of DMC in the feed liquid and vapour mixtures.

The DMC permeability showed a strong dependence on the mode of operation and on the DMC activity in the feed (Figs. 7A and 8). Clearly, the PIM-1 membrane became more permeable for DMC at low DMC activities in the VP mode, which corresponds with the observed enhancement of DMC-selectivity at low pressures of the feed vapour mixtures. In the PV-mode, the permeabilities of the PIM-1 and PTMSP membranes for DMC showed maxima for the feeds having the azeotropic composition (PIM-1) and for DMC-rich mixtures (PTMSP), that is, at the DMC activities of 0.50 and 0.70 (Fig. 8). This presumably reflects a trade-off between swelling of these glassy polymers and pore blocking. The permeabilities of the PIM-1 and PTMSP membranes for methanol increased with increasing methanol activity in the feed, thus reducing their separation performance. In contrast, the methanol permeability in PDMS decreased and the DMC permeability increased with the increasing activities of these compounds, both of which positively influences the separation. Overall, the PIM-1 membranes showed comparable performances to those from PDMS when operated in the PV mode, while they showed superior performance compared to PDMS and PTMSP when used in the VP mode.

Selectivity of the PIM-1 membranes operated in the VP and PV mode is shown in Fig. 9. Clearly, selectivity approximately equals separation factor for VP as relatively thick membranes were intentionally used; selectivity generally approaches VP separation factor as pil becomes negligible. Moreover, from Eq. (4a) it follows that while the PV-operated PIM-1 membrane still shows good selectivity, its separation factor is reduced as the result of the thermodynamic non-ideality of the liquid feed. Hence, membranes operated in the VP mode not only show higher selectivity but also higher practical separation factors when used with diluted feed vapours. Naturally, the thermodynamic non-ideality of the liquid feed influences its evaporation, which necessarily precedes vapour permeation.

Selectivity of the PIM-1 membrane clearly obeys a rule of thumb that the more concentrated the feed vapour mixture is, the smaller selectivity is observed; the smallest selectivity is consequently observed for pervaporation. The membranes from PIM-1, PTMSP and PDMS membranes operated in the PV mode showed similar selectivities but differed in their concentration dependences. While the selectivity of the PDMS membrane was almost independent of the feed concentration, the selectivities of the PTMSP and PIM-1 membranes decreased with increasing concentration of methanol in the feed. From the separation factors (Fig. 5B) and selectivities (Fig. 9) of the PIM-1, PTMSP and PDMS membranes operated in the PV mode, it appears that the (practical) separation factor becomes progressively reduced by the thermodynamic non-ideality of the liquid feed, while the membranes themselves are, in most cases, still well selective.

A) B)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

4.0x104

4.5x104

5.0x104

5.5x104

6.0x104

6.5x104

7.0x104

7.5x104

82 mol.% MeOH 55 mol.% MeOH 30 mol.% MeOH pure DMC

PD

MC /

[Bar

rer]

afeedDMC / [-]

0.0 0.2 0.4 0.65.0x103

1.0x104

1.5x104

4x104

5x104

6x104

7x104

8x104

82 mol.% MeOH 55 mol.% MeOH 30 mol.% MeOH 100 mol.% MeOH

PM

eOH /

[Bar

rer]

afeedMeOH / [-]

Fig. 7: Individual permeabilities of the PIM-1 membrane for DMC (A) and methanol (B) plotted against activities of the respective compounds in the feed vapour mixture at 40 °C. Dashed curves and lines are guides for the eye.

Fig. 8: Permeability of the PIM-1, PTMSP and PDMS membranes for methanol and DMC plotted against the activities of the respective compounds in the liquid feed (PV) at 40 °C. Dashed curves are guides for the eye.

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

2

4

6

8

10 VP 28 % p(d.p) VP 49 % p(d.p) VP 63 % p(d.p) PV (PIM-1) PV (PDMS) PV (PTMSP)

[

-]

xfeedMeOH / [-]

Fig. 9: Selectivity of the PIM-1, PTMSP and PDMS membranes for methanol and DMC plotted against the feed mixture composition at 40 °C. Dashed curves are guides for the eye, xMeOH

feed is methanol molar fraction in the feed vapour (VP) and liquid (PV).

4 ConclusionWhen operated in the vapour permeation (VP) mode, the membrane from PIM-1 has shown so far the most selective removal of dimethyl carbonate (DMC) from its mixtures with methanol. The separation factor progressively increased with the dilution of the feed vapour mixtures and with the content of DMC. At pressures equal to 28% of the dew point pressure, separation factors of 5.1 and 6.5 were observed for the feed having the azeotropic composition and for a DMC-rich feed, that is, for feeds which correspond to the saturation of the first adsorption layer and minor swelling of the membrane.

Comparison of the separation factor and selectivity of PIM-1 membranes operated in the VP and PV modes shows that, despite this material having good selectivity in both modes of operation, the (practical) separation factor becomes progressively reduced in the PV mode due to the thermodynamic non-ideality of the liquid feed.

The PIM-1 membrane showed a similar separation factor (2.3) but higher total fluxes than the PDMS membrane when used as a pervaporation (PV) membrane. This contrasts sharply with the fact that another polymer with a high fraction of free volume, PTMSP, showed almost no separation when used as a PV membrane. The likely explanation results from the analysis of vapour sorption isotherms with the GAB model of multilayer adsorption, which showed that DMC adsorbs four times more strongly to PIM-1 than to PTMSP. In the near future, we intend to study in detail the sorption of methanol-DMC vapour mixtures in PIM-1.

The analysis of the swelling of PIM-1 in single component vapours showed that the polymer does not swell until one half of the capacity of its monolayer is depleted by sorbing compounds, which corresponds to the vapour activities of 0.12 for methanol and 0.013 for DMC. The probable main mechanism responsible for the DMC-selectivity of PIM-1 is blocking of the diffusion pathways for methanol by DMC. This beneficial mechanism appears, however, to be weakened if the membrane is exposed to more saturated vapours (VP) or even to liquids (PV), that is, at conditions which correspond to the multilayer regime of sorption and extensive swelling.

AcknowledgementFinancial support obtained partly from the Czech Science Foundation, projects 13-32829P and 18-08389S, and from specific university research (MSMT No 21-SVV/2018 and 21-SVV/2019) is gratefully acknowledged. Wayne Harrison was funded by the UK Engineering and Physical Sciences Research Council (EPSRC grant EP/K016946/1).

Appendix AThe permeability of the PIM-1 membrane for methanol and DMC vapours decreased with time due to the polymer ageing. The kinetics is shown for vapour mixtures having azeotropic composition and pressures of 28, 49 and 63 % of that of the dew point (Fig. A1). Clearly, ageing was more pronounced for more saturated feed vapour mixtures.

Fig. A1: Permeabilities of the 632 μm thick PIM-1 membrane for methanol and DMC vapours having the azeotropic composition and variable pressure to dew point pressure ratio at 40 °C. Dashed lines are guides for the eye.

References[1] Budd, P. M.; Makhseed, S. M.; Ghanem, B. S.; Msayib, K. J.; Tattershall, C. E.;

McKeown, N. B., Microporous polymeric materials. Materials Today 2004, 7 (4), 40-46.

[2] Gao, L.; Alberto, M.; Gorgojo, P.; Szekely, G.; Budd, P. M., High-flux PIM-1/PVDF thin film composite membranes for 1-butanol/water pervaporation. Journal of Membrane Science 2017, 529, 207-214.

[3] Žák, M.; Klepic, M.; Štastná, L. Č.; Sedláková, Z.; Vychodilová, H.; Hovorka, Š.; Friess, K.; Randová, A.; Brožová, L.; Jansen, J. C.; Khdhayyer, M. R.; Budd, P. M.; Izák, P., Selective removal of butanol from aqueous solution by pervaporation with a PIM-1 membrane and membrane aging. Separation and Purification Technology 2015, 151, 108-114.

[4] Salehian, P.; Yong, W. F.; Chung, T.-S., Development of high performance carboxylated PIM-1/P84 blend membranes for pervaporation dehydration of isopropanol and CO2/CH4 separation. Journal of Membrane Science 2016, 518, 110-119.

[5] Adymkanov, S. V.; Yampol’skii, Y. P.; Polyakov, A. M.; Budd, P. M.; Reynolds, K. J.; McKeown, N. B.; Msayib, K. J., Pervaporation of alcohols through highly permeable PIM-1 polymer films. Polymer Science Series A 2008, 50 (4), 444-450.

[6] Wu, X. M.; Guo, H.; Soyekwo, F.; Zhang, Q. G.; Lin, C. X.; Liu, Q. L.; Zhu, A. M., Pervaporation Purification of Ethylene Glycol Using the Highly Permeable PIM-1 Membrane. Journal of Chemical & Engineering Data 2016, 61 (1), 579-586.

[7] Wu, X. M.; Zhang, Q. G.; Soyekwo, F.; Liu, Q. L.; Zhu, A. M., Pervaporation removal of volatile organic compounds from aqueous solutions using the highly permeable PIM-1 membrane. AIChE Journal 2015, 62 (3), 842-851.

[8] McKeown, N. B.; Budd, P. M.; Msayib, K. J.; Ghanem, B. S.; Kingston, H. J.; Tattershall, C. E.; Makhseed, S.; Reynolds, K. J.; Fritsch, D., Polymers of Intrinsic

Microporosity (PIMs): Bridging the Void between Microporous and Polymeric Materials. Chemistry – A European Journal 2005, 11 (9), 2610-2620.

[9] Alberto, M.; Bhavsar, R.; Luque-Alled, J. M.; Prestat, E.; Gao, L.; Budd, P. M.; Vijayaraghavan, A.; Szekely, G.; Holmes, S. M.; Gorgojo, P., Study on the formation of thin film nanocomposite (TFN) membranes of polymers of intrinsic microporosity and graphene-like fillers: Effect of lateral flake size and chemical functionalization. Journal of Membrane Science 2018, 565, 390-401.

[10] Cook, M.; Gaffney, P. R. J.; Peeva, L. G.; Livingston, A. G., Roll-to-roll dip coating of three different PIMs for Organic Solvent Nanofiltration. Journal of Membrane Science 2018, 558, 52-63.

[11] Ignacz, G.; Fei, F.; Szekely, G., Ion-Stabilized Membranes for Demanding Environments Fabricated from Polybenzimidazole and Its Blends with Polymers of Intrinsic Microporosity. ACS Applied Nano Materials 2018, 1 (11), 6349-6356.

[12] Anokhina, T. S.; Yushkin, A. A.; Budd, P. M.; Volkov, A. V., Application of PIM-1 for solvent swing adsorption and solvent recovery by nanofiltration. Separation and Purification Technology 2015, 156, 683-690.

[13] Delledonne, D.; Rivetti, F.; Romano, U., Developments in the production and application of dimethylcarbonate. Applied Catalysis A: General 2001, 221 (1–2), 241-251.

[14] Pacheco, M. A.; Marshall, C. L., Review of Dimethyl Carbonate (DMC) Manufacture and Its Characteristics as a Fuel Additive. Energy & Fuels 1997, 11 (1), 2-29.

[15] Ein-Eli, Y., Dimethyl carbonate (DMC) electrolytes – the effect of solvent purity on Li–ion intercalation into graphite anodes. Electrochemistry Communications 2002, 4 (8), 644-648.

[16] Comelli, F., Isothermal Vapor−Liquid Equilibria Measurements, Excess Molar Enthalpies, and Excess Molar Volumes of Dimethyl Carbonate + Methanol, + Ethanol, and + Propan-1-ol at 313.15 K. J. Chem. Eng. Data 1997, 42 (4), 705-709.

[17] Švec, P.; Cattey, H.; Růžičková, Z.; Holub, J.; Růžička, A.; Plasseraud, L., Triorganotin(iv) cation-promoted dimethyl carbonate synthesis from CO2 and methanol: solution and solid-state characterization of an unexpected diorganotin(iv)-oxo cluster. New Journal of Chemistry 2018, 42 (10), 8253-8260.

[18] Shah, V. M.; Bartels, C. R.; Pasternak, M.; Reale, J., Opportunities for membranes in the production of octane enhancers. AIChE Symposium Series 1989, 85 (272), 93-97.

[19] Hsu, K.-Y.; Hsiao, Y.-C.; Chien, I. L., Design and Control of Dimethyl Carbonate−Methanol Separation via Extractive Distillation in the Dimethyl Carbonate Reactive-Distillation Process. Industrial & Engineering Chemistry Research 2010, 49 (2), 735-749.

[20] Blahut, A.; Dohnal, V., Ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate: An efficient entrainer to separate methanol + dimethyl carbonate azeotropic mixture. Fluid Phase Equilibria 2016, 423, 120-127.

[21] Néel, J., Chapter 5 Pervaporation. In Membrane Science and Technology, Richard, D. N.; Stern, S. A., Eds. Elsevier: 1995; Vol. Volume 2, pp 143-211.

[22] Cen, Y.; Lichtenthaler, R. N., Chapter 3 Vapor permeation. In Membrane Science and Technology, Noble, R. D.; Stern, S. A., Eds. Elsevier: 1995; Vol. 2, pp 85-112.

[23] Baker, R. W.; Low, B. T., Gas Separation Membrane Materials: A Perspective. Macromolecules 2014, 47 (20), 6999-7013.

[24] Rautenbach, R.; Vier, J., Aufbereitung von Methanol/Dimethylcarbonat-Strömen durch Kombination von Pervaporation und Rektifikation. Chemie Ingenieur Technik 1995, 67 (11), 1498-1501.

[25] Tsuru, T.; Sasaki, A.; Kanezashi, M.; Yoshioka, T., Pervaporation of methanol/dimethyl carbonate using SiO2 membranes with nano-tuned pore sizes and surface chemistry. AIChE Journal 2010, 57 (8), 2079-2089.

[26] Rynkowska, E.; Kujawa, J.; Chappey, C.; Fatyeyeva, K.; Karpenko-Jereb, L.; Kelterer, A.-M.; Marais, S.; Kujawski, W., Effect of the polar–nonpolar liquid mixtures on pervaporative behavior of perfluorinated sulfonic membranes in lithium form. Journal of Membrane Science 2016, 518, 313-327.

[27] Lang, W.-Z.; Niu, H.-Y.; Liu, Y.-X.; Liu, C.-X.; Guo, Y.-J., Pervaporation separation of dimethyl carbonate/methanol mixtures with regenerated perfluoro-ion-exchange membranes in chlor-alkali industry. Journal of Applied Polymer Science 2013, 129 (6), 3473-3481.

[28] Wang, L.; Li, J.; Lin, Y.; Chen, C., Separation of dimethyl carbonate/methanol mixtures by pervaporation with poly(acrylic acid)/poly(vinyl alcohol) blend membranes. Journal of Membrane Science 2007, 305 (1), 238-246.

[29] Kludský, M.; Vopička, O.; Matějka, P.; Hovorka, Š.; Friess, K., Nafion® modified with primary amines: chemical structure, sorption properties and pervaporative separation of methanol-dimethyl carbonate mixtures. European Polymer Journal 2018, 99, 268-276.

[30] Li, W.; Galiano, F.; Estager, J.; Monbaliu, J.-C. M.; Debecker, D. P.; Figoli, A.; Luis, P., Sorption and pervaporation study of methanol/dimethyl carbonate mixture with poly(etheretherketone) (PEEK-WC) membrane. Journal of Membrane Science 2018, 567, 303-310.

[31] Hung, P. D.; Masawaki, T.; Tone, S., Separation of Dimethylcarbonate from Dimethylcarbonate-Methanol Mixture by Pervaporation. KAGAKU KOGAKU RONBUNSHU 1997, 23 (5), 733-737.

[32] Wang, L.; Han, X.; Li, J.; Zhan, X.; Chen, J., Separation of Azeotropic Dimethylcarbonate/Methanol Mixtures by Pervaporation: Sorption and Diffusion Behaviors in the Pure and Nano Silica Filled PDMS Membranes. Separation Science and Technology 2011, 46 (9), 1396-1405.

[33] Wang, L.; Han, X.; Li, J.; Zheng, D.; Qin, L., Modified MCM-41 silica spheres filled polydimethylsiloxane membrane for dimethylcarbonate/methanol separation via pervaporation. Journal of Applied Polymer Science 2012, 127 (6), 4662-4671.

[34] Zhou, H.; Lv, L.; Liu, G.; Jin, W.; Xing, W., PDMS/PVDF composite pervaporation membrane for the separation of dimethyl carbonate from a methanol solution. Journal of Membrane Science 2014, 471, 47-55.

[35] Vopička, O.; Pilnáček, K.; Friess, K., Separation of methanol-dimethyl carbonate vapour mixtures with PDMS and PTMSP membranes. Separation and Purification Technology 2017, 174, 1-11.

[36] Lux, S.; Winkler, T.; Körbler, M.; Siebenhofer, M., Assessment of pervaporative separation of methyl acetate and methanol using organophilic membranes. Chemical Engineering Science 2017, 158, 500-508.

[37] Genduso, G.; Farrokhzad, H.; Latré, Y.; Darvishmanesh, S.; Luis, P.; Van der Bruggen, B., Polyvinylidene fluoride dense membrane for the pervaporation of methyl acetate–methanol mixtures. Journal of Membrane Science 2015, 482, 128-136.

[38] Penkova, A. V.; Polotskaya, G. A.; Toikka, A. M., Separation of acetic acid–methanol–methyl acetate–water reactive mixture. Chemical Engineering Science 2013, 101, 586-592.

[39] Vopička, O.; Randová, A.; Friess, K., Sorption of vapours and liquids in PDMS: novel data and analysis with the GAB model of multilayer adsorption. European Polymer Journal 2014, 60, 49-57.

[40] Vopička, O.; Radotínský, D.; Friess, K., Sorption of vapour mixtures of methanol and dimethyl carbonate in PDMS: Experimental study. European Polymer Journal 2015, 73, 480-486.

[41] Wang, M.; Li, M.; Chang, N.; Gao, L.; Wang, M.; Zhang, Y., Vapor separation of methanol-dimethyl carbonate mixture on SAPO-34 zeolite membrane. Journal of Membrane Science 2018, 565 (1), 311-321.

[42] Will, B.; Lichtenthaler, R. N., Comparison of the separation of mixtures by vapor permeation and by pervaporation using PVA composite membranes. I. Binary alcohol-water systems. Journal of Membrane Science 1992, 68 (1), 119-125.

[43] Holtbruegge, J.; Wierschem, M.; Steinruecken, S.; Voss, D.; Parhomenko, L.; Lutze, P., Experimental investigation, modeling and scale-up of hydrophilic vapor permeation membranes: Separation of azeotropic dimethyl carbonate/methanol mixtures. Separation and Purification Technology 2013, 118, 862-878.

[44] Dytrych, P.; Vajglová, Z.; Morávková, L.; Jandová, V.; Izák, P.; Petrusová, Z., Minimization of the Theoretical Error of Input Parameters for a Vapor Permeation Apparatus. Chemical Engineering & Technology 2018, 41 (9), 1727-1736.

[45] Bowen, T. C.; Noble, R. D.; Falconer, J. L., Fundamentals and applications of pervaporation through zeolite membranes. Journal of Membrane Science 2004, 245 (1), 1-33.

[46] Flanders, C. L.; Tuan, V. A.; Noble, R. D.; Falconer, J. L., Separation of C6 isomers by vapor permeation and pervaporation through ZSM-5 membranes. Journal of Membrane Science 2000, 176 (1), 43-53.

[47] Hölck, O.; Siegert, M. R.; Heuchel, M.; Böhning, M., CO2 Sorption Induced Dilation in Polysulfone:  Comparative Analysis of Experimental and Molecular Modeling Results. Macromolecules 2006, 39 (26), 9590-9604.

[48] Hölck, O.; Böhning, M.; Heuchel, M.; Siegert, M. R.; Hofmann, D., Gas sorption isotherms in swelling glassy polymers—Detailed atomistic simulations. Journal of Membrane Science 2013, 428, 523-532.

[49] Ogieglo, W.; Rahimi, K.; Rauer, S. B.; Ghanem, B.; Ma, X.; Pinnau, I.; Wessling, M., How Do Organic Vapors Swell Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1? The Journal of Physical Chemistry B 2017, 121 (29), 7210-7220.

[50] Du, N.; Robertson, G. P.; Song, J.; Pinnau, I.; Thomas, S.; Guiver, M. D., Polymers of Intrinsic Microporosity Containing Trifluoromethyl and Phenylsulfone Groups as Materials for Membrane Gas Separation. Macromolecules 2008, 41 (24), 9656-9662.

[51] Low, Z.-X.; Budd, P. M.; McKeown, N. B.; Patterson, D. A., Gas Permeation Properties, Physical Aging, and Its Mitigation in High Free Volume Glassy Polymers. Chemical Reviews 2018, 118 (12), 5871-5911.

[52] Budd, P. M.; McKeown, N. B.; Ghanem, B. S.; Msayib, K. J.; Fritsch, D.; Starannikova, L.; Belov, N.; Sanfirova, O.; Yampolskii, Y.; Shantarovich, V., Gas permeation parameters and other physicochemical properties of a polymer of intrinsic microporosity: Polybenzodioxane PIM-1. Journal of Membrane Science 2008, 325 (2), 851-860.

[53] Tiwari, R. R.; Jin, J.; Freeman, B. D.; Paul, D. R., Physical aging, CO2 sorption and plasticization in thin films of polymer with intrinsic microporosity (PIM-1). Journal of Membrane Science 2017, 537, 362-371.

[54] Song, Q.; Cao, S.; Pritchard, R. H.; Ghalei, B.; Al-Muhtaseb, S. A.; Terentjev, E. M.; Cheetham, A. K.; Sivaniah, E., Controlled thermal oxidative crosslinking of polymers

of intrinsic microporosity towards tunable molecular sieve membranes. Nature Communications 2014, 5, 4813.

[55] Vopička, O.; Radotínský, D.; Friess, K., Sorption of vapour mixtures of methanol and dimethyl carbonate in PTMSP: Cooperative and competitive sorption in one system. European Polymer Journal 2016, 75, 243-250.

[56] Nagai, K.; Higuchi, A.; Nakagawa, T., Gas permeability and stability of poly(1-trimethylsilyl-1-propyne-co-1-phenyl-1-propyne) membranes. Journal of Polymer Science Part B: Polymer Physics 1995, 33 (2), 289-298.

[57] Hill, A. J.; Pas, S. J.; Bastow, T. J.; Burgar, M. I.; Nagai, K.; Toy, L. G.; Freeman, B. D., Influence of methanol conditioning and physical aging on carbon spin-lattice relaxation times of poly(1-trimethylsilyl-1-propyne). Journal of Membrane Science 2004, 243 (1), 37-44.

[58] Design Institute for Physical Properties, S. b. A., DIPPR Project 801 - Full Version. Design Institute for Physical Property Research/AIChE.

[59] Pokorný, V.; Štejfa, V.; Fulem, M.; Červinka, C.; Růžička, K., Vapor Pressures and Thermophysical Properties of Dimethyl Carbonate, Diethyl Carbonate, and Dipropyl Carbonate. Journal of Chemical & Engineering Data 2017, 62 (10), 3206-3215.

[60] Guggenheim, E. A., In Application of Statistical Mechanics, Clarendon Press: Oxford, 1966; pp 186-207.

[61] Vopička, O.; Pilnáček, K.; Číhal, P.; Friess, K., Sorption of methanol, dimethyl carbonate, methyl acetate, and acetone vapors in CTA and PTMSP: General findings from the GAB Analysis. Journal of Polymer Science Part B: Polymer Physics 2016, 54 (5), 561-569.

[62] Vopička, O.; Hynek, V.; Zgažar, M.; Friess, K.; Šípek, M., A new sorption model with a dynamic correction for the determination of diffusion coefficients. Journal of Membrane Science 2009, 330 (1), 51-56.

[63] Vopička, O.; Hynek, V.; Friess, K.; Šípek, M.; Sysel, P., A device for determination of vapour sorption in polymers (EN); Aparatura pro stanovení sorpce par v polymerech (CZ). Chemické listy 2009, 103 (4), 310-314.

[64] Baker, R. W.; Wijmans, J. G.; Huang, Y., Permeability, permeance and selectivity: A preferred way of reporting pervaporation performance data. Journal of Membrane Science 2010, 348 (1), 346-352.

[65] Číhal, P.; Vopička, O.; Lanč, M.; Kludský, M.; Velas, J.; Hrdlička, Z.; Michalcová, A.; Dendisová, M.; Friess, K., Poly(butylene succinate)-cellulose triacetate blends: permeation, pervaporation, sorption and physical structure. Polymer Testing 2018, 65, 468-479.

[66] Vopička, O.; Hynek, V.; Rabová, V., Measuring the transient diffusion of vapor mixtures through dense membranes. Journal of Membrane Science 2010, 350 (1), 217-225.

[67] Sing, K. S. W., Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984). In Pure and Applied Chemistry, 1985; Vol. 57, p 603.

[68] Witchey-Lakshmanan, L. C.; Hopfenberg, H. B.; Chern, R. T., Sorption and transport of organic vapors in poly[1-(trimethylsilyl)-1-propyne]. Journal of Membrane Science 1990, 48 (2), 321-331.

[69] Vopička, O.; Friess, K.; Hynek, V.; Sysel, P.; Zgažar, M.; Šípek, M.; Pilnáček, K.; Lanč, M.; Jansen, J. C.; Mason, C. R.; Budd, P. M., Equilibrium and transient sorption of vapours and gases in the polymer of intrinsic microporosity PIM-1. Journal of Membrane Science 2013, 434, 148-160.

[70] Wijmans, J. G.; Baker, R. W., The solution-diffusion model: a review. Journal of Membrane Science 1995, 107 (1), 1-21.

[71] Srinivasan, R.; Auvil, S. R.; Burban, P. M., Elucidating the mechanism(s) of gas transport in poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes. Journal of Membrane Science 1994, 86 (1), 67-86.

[72] Hill, T. L., Statistical Mechanics of Multimolecular Adsorption. IV. The Statistical Analog of the BET Constant a1b2/b1a2. Hindered Rotation of a Symmetrical Diatomic Molecule Near a Surface. The Journal of Chemical Physics 1948, 16 (3), 181-189.

[73] Budd, P. M.; Ghanem, B. S.; Makhseed, S.; McKeown, N. B.; Msayib, K. J.; Tattershall, C. E., Polymers of intrinsic microporosity (PIMs): robust, solution-processable, organic nanoporous materials. Chemical Communications 2004, (2), 230-231.

[74] Rutherford, S. W., Mechanism of Sorption and Diffusion in a High Free-Volume Polymer. Industrial & Engineering Chemistry Research 2001, 40 (5), 1370-1376.

[75] Baker, R. W., Membrane Transport Theory. In Membrane Technology and Applications, 2004.

[76] Emmler, T.; Heinrich, K.; Fritsch, D.; Budd, P. M.; Chaukura, N.; Ehlers, D.; Rätzke, K.; Faupel, F., Free Volume Investigation of Polymers of Intrinsic Microporosity (PIMs): PIM-1 and PIM1 Copolymers Incorporating Ethanoanthracene Units. Macromolecules 2010, 43 (14), 6075-6084.

[77] Weidert, J.-O.; Burger, J.; Renner, M.; Blagov, S.; Hasse, H., Development of an Integrated Reaction–Distillation Process for the Production of Methylal. Industrial & Engineering Chemistry Research 2017, 56 (2), 575-582.

[78] Dong, Y.; Dai, C.; Lei, Z., Extractive distillation of methylal/methanol mixture using ethylene glycol as entrainer. Fluid Phase Equilibria 2018, 462, 172-180.

[79] Li, W.; Du, Y.; Li, J.; Chen, X.; Guo, S.; Zhang, T., Isobaric vapor-liquid equilibrium for acetone + methanol system containing different ionic liquids at 101.3 kPa. Fluid Phase Equilibria 2018, 459, 10-17.

[80] Bernatová, S.; Aim, K.; Wichterle, I., Isothermal vapour–liquid equilibrium with chemical reaction in the quaternary water+methanol+acetic acid+methyl acetate system, and in five binary subsystems. Fluid Phase Equilibria 2006, 247 (1), 96-101.

[81] Shang, W.; Cui, X.; Yu, X.; Zhang, Y.; Feng, T.; He, J.; Zhang, X.; Wang, J., Isobaric vapor-liquid equilibrium for methanol + methyl acetate with ionic liquids [OMMIM][Tf2N] and [OMIM][Tf2N] as entrainers at 101.3 kPa. Fluid Phase Equilibria 2018, 473, 90-97.

[82] Sundberg, A. T.; Uusi-Kyyny, P.; Pakkanen, M.; Alopaeus, V., Vapor−Liquid Equilibrium for Methoxymethane + Methyl Formate, Methoxymethane + Hexane, and Methyl Formate + Methanol. Journal of Chemical & Engineering Data 2011, 56 (5), 2634-2640.

[83] Vrbka, P.; Dohnal, V., Limiting activity coefficient measurements in binary mixtures of dichloromethane and 1-alkanols (C1–C4). Fluid Phase Equilibria 2016, 411, 59-65.

[84] Řehák, K.; Klajmon, M.; Strejc, M.; Morávek, P., Isothermal Vapor–Liquid Equilibria for Binary Mixtures of Methyl Nonafluorobutyl Ether + Acetone, Cyclopentyl Methyl Ether, Ethyl Acetate, n-Heptane, Methanol, and Toluene. Journal of Chemical & Engineering Data 2017, 62 (11), 3878-3888.

[85] Luyben, W. L., Control of a Heat-Integrated Pressure-Swing Distillation Process for the Separation of a Maximum-Boiling Azeotrope. Industrial & Engineering Chemistry Research 2014, 53 (46), 18042-18053.

[86] Pilnáček, K.; Vopička, O.; Lanč, M.; Dendisová, M.; Zgažar, M.; Budd, P. M.; Carta, M.; Malpass-Evans, R.; McKeown, N. B.; Friess, K., Aging of polymers of intrinsic microporosity tracked by methanol vapour permeation. Journal of Membrane Science 2016, 520, 895-906.