Porous hollow fiber membrane

A hollow fiber porous membrane comprising polyethersulfone or polysulfone, wherein

• the hollow fiber porous membrane has an inner diameter from 300 to 600 μm and a thickness from 70 to 200 μm;
• the hollow fiber porous membrane has a molecular weight cut-off of 10000 or lower;
• the hollow fiber porous membrane has a plurality of pores having a pore diameter from 0.1 to 0.5 μm throughout an outer surface of the hollow fiber porous membrane;
• and
• the hollow fiber porous membrane has a bulging rate of less than 5%, the bulging rate being defined below:
• Bulging Rate (%):
• for 20 or more hollow fiber porous membranes, after a membrane thickness in a cross section of each one of the hollow fiber porous membranes in a width direction is measured at randomly selected 10 or more locations, an average membrane thickness is calculated based on 200 or more locations in total, and the bulging rate is calculated by a formula below:
• Bulging Rate (%)=(location numbers where the membrane thickness as measured exceeded 1.3 times the average membrane thickness)/(membrane thickness measurement numbers)×100;
• wherein the bulging rate is calculated by cutting the 20 or more hollow fiber porous membranes randomly at 10 locations, observing each cross section using a scanning electron microscope, and measuring the membrane thickness;
• wherein the hollow fiber porous membrane has a five-layer structure comprising sequentially from inside to outside an inner surface dense layer, an inner void layer, an interlayer, an outer void layer, and an outer surface dense layer;
• wherein the hollow fiber porous membrane contains a humectant, the humectant being uniformly present in the outer surface dense layer and the inner surface dense layer.