## 1 Introduction
This material allows selective extraction of n-butanol from a mixture with water due to increased sorption of n-butanol. [PERSON] et al. [37] measured the sorption of water and butanol by PDMS membranes at 37 \({}^{\circ}\)C. The sorption of water was 0.6 g/g, whereas the sorption of butanol was 16.3 g/g, indicating that the more hydrophobic substance penetrates the PDMS membrane more easily and causes its swelling. Due to this effect, the polymer chains become more flexible and the transport of substances through the siloxane membrane increases. In [38] it was shown that when separating the ABE-fermentation broth through a PDMS membrane at 37 \({}^{\circ}\)C, the butanol-water separation factor reaches a value of 16.6. [PERSON] et al. [39] investigated the separation of the fermentation broth through a ceramic tubular membrane with an inner selective layer of PDMS and it was shown that at 37 \({}^{\circ}\)C the butanol/water separation factor is 24.7. The selectivity of membranes for biobutanol is a key factor influencing the economics of its extraction from fermentation mixtures. Accordingly, the task of developing pervaporation membranes based on polymers with increased selectivity for n-butanol is relevant. Chemical modification of the polysiloxane chain allows improving the separation properties of pervaporation membranes [40]. The main approaches to such modifications are the introduction of functional groups into the main or side chain, as well as chemical cross-linking. For example, the use of trifunctional cross-linking agents in the synthesis of PDMS to create composite PDMS/PVDF membranes made it possible to increase the butanol/water separation factor to a value of 51 [41]. A wide range of functional polysiloxanes has been synthesized and studied in the process of the pervaporation separation of organic substances from water [42]. In particular, it was demonstrated that the introduction of 10% tridecyl substituents into the side chain leads to an almost twofold increase in the methyl isobutyl ketone/water separation factor. Functionalized membranes in comparison with PDMS show an increase in sorption of organic substances and a decrease in sorption of water [42]. The introduction of alkyl side substituents having a length of 7-10 carbon atoms into the siloxane chain makes it possible to increase the selectivity of the membrane for organic components. The polyheptylmethylsiloxane-based membrane (PHeptMS) exhibits a record separation factor of n-butanol-water binary mixture of 97, which is almost three times higher than the separation factor of PDMS [43]. Increasing the hydrophobicity of the membrane selective layer makes it possible to reduce water transfer and thus increase the concentration of n-butanol in the permeate. For example, it was shown in [44] that butanol/water selectivity for the PDecMS/MFFK-1 membrane was 3-7 times higher than that for commercial membranes. At a selective layer thickness of the PDecMS/MFFK-1 composite membrane of about 4.5 \(\upmu\)m, the 1-butanol permeability comparable to that of commercial composite membranes (5.2 mol\(\cdot\)m\({}^{-2}\cdot\)h\({}^{-1}\cdot\)kaPa\({}^{-1}\)) can be achieved. Nevertheless, in addition to a high separation capacity, the membrane must demonstrate stable performance during the pervaporation process. During the separation of butanol from the ABE-fermentation mixture, membrane clogging by components of the fermentation mixture is observed, resulting in reduced transport and separation capacity of the membrane. [PERSON] et al. [45] reported a threefold decrease in the butanol selectivity of the PDMS membrane during pervaporation separation of the ABE-fermentation broth compared with the model mixture. The researchers attributed the decrease in the transport characteristics of the PDMS membrane mainly to the activity of active microbial cells from the fermentation medium, which are adsorbed on the membrane surface [46].