## 3 Results
### Dynamics of Contamination of the PHeptMS Membrane during Separation of ABE-Fermentation Broth  
Based on the results obtained above, the composite PHeptMS membrane was of the greatest interest, since it demonstrated not only a high separation ability of the ABE broth, but also was least susceptible to fouling. Nevertheless, it is interesting to trace the dynamics of changes in the transport and separation characteristics of this membrane in the process of preparation of the real ABE-fermentation broth under conditions of continuous contact of the PHeptMS membrane with the medium to be separated. Between experiments of the separation of the real ABE broth, the membrane was in the module under a layer of broth. Pervaporation separation of ABE-fermentation broth was carried out at 30 \({}^{\circ}\)C. The data obtained are shown in Figure 13.  
When separating the real ABE-fermentation broth for 6 h, the total permeate flux decreased from 0.203 to 0.175 kg/(m\({}^{2}\cdot\)h) and continued to decrease during the first 24 h of membrane operation. This behavior appears to be related to the beginning of the precipitation of protein on the membrane surface. This is also evidenced by the increased selectivity of the membrane for acetone. As shown earlier, clogging of the membrane surface with proteins leads to an increase in the contact wetting angle by acetone and leads to an increase in the selectivity of its transport across membranes. Figure 13a shows that the performance of the PHeptMS composite membrane in separating the ABE-fermentation mixture from 28 to 150 h was generally stable, and this membrane exhibited a high and constant total flux average of 0.162 kg/(m\({}^{2}\cdot\)h) and average separation factors of 49.5, 44.8, and 6.3 for acetone, butanol, and ethanol, respectively. After 150 h of continuous contact  
Figure 12: Temperature dependences of selectivity for PHeptMS (**a**), PDecMS (**b**), and MDK-3 (**c**). of the membrane with the fermentation broth, a drop in the membrane selectivity for n-butanol and acetone was observed. This decrease is caused by a decrease in membrane permeability to n-butanol and acetone, as well as a slight increase in water permeability through the membrane. For ethanol, no noticeable changes in transport were observed. Apparently, after 150 h of contact, there is a significant increase in the thickness of the sludge layer, which directly affects the transport and separation characteristics of the membrane. Nevertheless, the values obtained exceed the characteristics of the PDMS/PVDF membrane studied for 100 h of separation of the ABE-fermentation broth. Thus, it was shown in [67] that the PDMS-PVDF composite membrane exhibited an average total flux of 0.1105 kg/(m\({}^{2}\cdot\)h) and average separation factors of 21.8, 19.1, and 5.2 for acetone, butanol, and ethanol, respectively. In [68], PDMS- and POMS-based membranes were used to separate the ABE-fermentation broth. For the PDMS membrane, the separation factors for acetone, butanol, and acetone at 37 \({}^{\circ}\)C were 21.6, 18.8, and 8.9, respectively. The POMS-based membrane at 32 \({}^{\circ}\)C showed separation factors for acetone, butanol, and ethanol of 27.2, 19.7, and 7.8, respectively. The dynamics of the effect of the contact time of the membrane with the fermentation medium on its transport properties were not studied. The PHeptMS membrane obtained in this work before contact with the broth in the separation of the ABE-fermentation broth showed better separation factor values for butanol and acetone, being 46.3 for butanol, 35.9 for acetone, and 6.0 for ethanol. The value of the total permeate flux for the PHeptMS membrane during the first 2 h of the experiment was 0.203 kg/(m\({}^{2}\cdot\)h). After 216 h of separation of the ABE-fermentation mixture, the value of the total permeate flux decreased to 0.158 kg/(m\({}^{2}\cdot\)h).