Abstract-This research was carried out to determine the predominant fouling mechanism during the pretreatment of an aqueous pectin solution by cross-flow microfiltration with membrane with nominal size of 0.44 m, at different values of transmembrane pressure, temperature, and pectin concentration. To evaluate the predominant resistive mechanism was used series resistance and permeate flux model analysis. The rejection coefficient for pectin varied from 93.4 to 97.9%. The maximum flux observed was 238.69 ± 6.48 kg m -2 h -1 at transmembrane pressure of 0.12 MPa, temperature of 50 °C and initial pectin of 1.0 g kg -1 . The dominant restrictive mechanism observed was the cake layer formation, for all assay evaluated.Index Terms-Pectin, microfiltration, permeate flux, fouling.
I. INTRODUCTIONPectin is a family of complex polysaccharides constituted of galacturonic acid units linked by (1→4) glycoside bonds.It also presents esterified regions with methylic groups and branches constituted of neutral sugars. The structure of the lateral chain and the degree of esterification characterize the capacity of gelling, solubilization, and aggregation of pectin in solutions. Due to its gelling characteristic, pectin is a very important raw material in the jelly, sweet, and preserve industries [1]- [3]. In the production of pectin, the most costly step is the purification process, which requires large amounts of ethanol to precipitate pectin from the extraction solution. The ethanol solution is later evaporated by vacuum [4], [5].The porous membrane separation process has been widely used in the food industry, especially in the clarification of juices. The traditional macromolecular fractioning processes that are frequently used in the industry can be optimized with the implementation of membrane separation steps [6]-[8]. According with Moresi [9], the implementation of a microfiltration step before the precipitation with ethanol results in the successful concentration of the extraction solution, reducing the volume of ethanol required to precipitate pectin, and consequently, reducing the energy spent in the evaporation step. Cho et al. [10] incorporated a system of cross-flow microfiltration with a 0.2-m cellulose membrane to a purification step in the extraction of pectin. With the microfiltration system, was achieved a reduction of 75% of the volume of ethanol required.However, the reduction in the permeate flow is a restriction of membrane processes. Pectin is undesirable in the fruit and vegetable juice clarification process, as the typical concentrations of 1 % mass precipitate on the membrane surface as a viscous gel, increasing the resistance to permeation [11]-[13]. The polarization layer is the concentration boundary layer adjacent to the membrane surface, formed in the beginning of process, resulting in a sharp flux decrease, which is stabilized by the renewal surface effect promoted by the crossflow flux [14]. However, a gradual decrease in flux is also observed due to physical and chemical interactions of pect...