**2. Experimental Methods**

#### *2.1. Experimental and Operating Conditions*

The pilot plant presented in Figure 1 was used in the study of the separation of succinic acid by the NF technique. The exploited system was equipped with two membrane modules, whereas all research was carried out on the only one of them. The used membrane module was equipped with a tubular ceramic mono-channel membrane (TiO2 active layer, TAMI Industries, Nyons, France) with a cut-o ff of 450 Da, support mean porosity 38.5 mm2, membrane mean porosity 3 μm, open porosity 30–40%, external diameter 10 mm, channel diameter and filtration area per 0.6 m tube equal to 0.0125 m<sup>2</sup> [51]. The transmembrane pressure (TMP) was set to 1.5 MPa. The process temperature for all experiments was fixed to 300 ± 2.0 K. The system was operated in a continuous mode, which means that the permeate and retentate were recirculated to the feeding tank continuously. The total volume of each investigated solution was equal to 12 L.

After each experiment, the ceramic membrane was cleaned to recover its initial permeance according to the procedure described in details elsewhere [51]. All cleaning steps were carried out at a flow system, the deionized water was filtered for 60 min, and the resulting flux was compared to the initial water flux. The decline in water flux after cleaning was not observed.

**Figure 1.** Pilot installation of the NF process: 1—feed tank; 2—rotameter; 3—heat exchanger; 4—pump; 5—membrane module; 6—temperature and flow rate controller; 7—permeate measuring cylinder; 8—pressure gauge; 9—heater.
