## 2 Materials and Methods
### Vacuum Pervaporation  
The transport and separation properties of PHeptMS, PDecMS, and commercial MDK-3 membranes were studied in the mode of vacuum pervaporation when separating the ABE-fermentation broth at 30-60 \({}^{\circ}\)C.  
Figure 2 shows the scheme of the vacuum pervaporation setup. From a thermostatically controlled container of 1 L with a stirrer (1), by means of an MV-Z gear pump (Ismatec, Zurich, Switzerland) (2), the initial separated mixture (flow I) is directed through the heat exchanger (3) to the membrane module (4) and then returns back to the container (1) by flow II. The effective membrane area in the membrane module is 13.5 cm\({}^{2}\) and the volume flow rate of the separated mixture is 350 mL/min. The permeate passing through the membrane (flow III) in the vapor phase is condensed in glass traps (5) that are placed in Dewar flasks with liquid nitrogen (\(-\)196 \({}^{\circ}\)C). To achieve continuity of the pervaporation separation, the traps are arranged in parallel and operated alternately throughout the experiment. The LOIP LT-100 liquid thermostat (St. Petersburg, Russia) (6) ensures a constant temperature of the separated mixture with an accuracy of \(\pm\)0.1 \({}^{\circ}\)C. Creation and maintenance of the difference of partial pressures of the mixture vapor was provided by vacuumization of the sub-membrane space using an Ebara PDV-250 vacuum pump (EBARA Corporation, Tokyo, Japan) (7). A safety trap (8) prevents permeate vapors from entering the vacuum pump. Concentration of the initial solution, as well as retentate and permeate, was determined by gas chromatography on a Crystallux-4000M chromatograph (RPC \"META-CHROM\", Co., Ltd., Yoshkar-Ola, Russia) equipped with a flame ionization detector. Analysis was performed using the following parameters: evaporation temperature--200 \({}^{\circ}\)C, column temperature--120 \({}^{\circ}\)C, and detector temperature--150 \({}^{\circ}\)C. A Phenomenex Zebron ZB-FFAP (Phenomenex, Torrance, CA, USA) capillary column (length 50 m, diameter 0.32 mm, phase thickness 0.50 \(\upmu\)m) was used with the following phase composition: polymeric ester of 2-nitroerephthalatic acid and polyethylene glycol. Water was added during the permeate analysis to homogenize the sample. Total permeate flux \(J\), kg/(m\({}^{2}\cdot\)h), was determined using the weight method according to Formula (1):  
\[J=\frac{m}{S\cdot t}, \tag{1}\]  
Figure 2: Scheme of the vacuum pervaporation setup: 1—a container with a mixing device; 2—a gear pump; 3—a heat exchanger; 4—a membrane module; 5—traps for collecting permeate, placed in Dewar vessels with liquid nitrogen; 6—thermostat; 7—vacuum pump; 8—safety trap; I—initial separable mixture; II—retentate; III—permeate; IV—coolant. where \(m\) is the total mass of permeate (kg) permeated through the membrane of area \(S\) (m\({}^{2}\)) in time \(t\), h.  
The separation factor \(\beta\) was determined using Formula (2):  
\[\beta=\frac{y_{o}\cdot x_{w}}{y_{w}\cdot x_{o}}, \tag{2}\]  
where \(x_{o}\) and \(x_{w}\) are the mass fractions of the organic component and water in the separated mixture, and \(y_{o}\) and \(y_{w}\) are the mass fractions of the organic component and water in the permeate. Mass fluxes of components in the permeate were determined as:  
\[J_{i}=J\cdot y_{o}, \tag{3}\]  
To describe the balance between permeability and selectivity of separation, a criterion of membrane quality was introduced--pervaporation separation index (_PSI_):  
\[PSI=J\big{(}\beta_{ij}-1\big{)}, \tag{4}\]  
The permeability (\(P\), mol/(m\({}^{2}\cdot\)h\(\cdot\) kPa)) for component \(i\) was calculated according to Equation (5):  
\[P_{i}=\frac{J_{i}}{\Big{(}P_{i}^{f}-P_{i}^{p}\Big{)}}, \tag{5}\]  
where \(p_{i}^{f}\) and \(p_{i}^{p}\) are the vapor pressure of component \(i\) in the initial mixture and permeate (kPa), respectively.