Patent ID: 8900458

Claim:
A method of fractionating or isolating a target substance using a membrane, the method comprising: in a diafiltration process including supplying a membrane separation apparatus with a treating liquid containing multiple target substances and extracting a target substance into a permeate liquid supplied from the membrane separation apparatus to fractionate or isolate the target substance from other target substances remaining in a residual liquid, using a separation status index which quantizes a separation state of the membrane separation apparatus in a separating operation and which is used as a target value of the separating operation, and a progress index which quantizes a degree of progress of the separating operation; controlling an operating parameter such that a measurement value of the separation status index is in a predetermined range of a first set value which is preset as the separation status index before the separating operation based on the separation status index and the progress index of the separating operation; changing the first set value of the separation status index to a third set value which is preset when a measurement value of the progress index of the separating operation is in a predetermined range of a second set value which is preset as the progress index of the separating operation before the separating operation; and controlling the operating parameter such that a measurement value of the separation status index is in a predetermined range of the third set value in the changing step, wherein: the separation status index is selected from at least one of a flow rate of the permeate liquid, a saccharide content of the permeate liquid, a saccharide content ratio provided by the saccharide content of permeate liquid being divided by the saccharide content of the circulating liquid, refractive index of the permeate liquid, density of the permeate liquid, and light transmission of the permeate liquid; the progress index is selected from at least one of an elapsed time of the separation, a cumulative amount of the permeate liquid, a cumulative amount of the supplied cleaning liquid, an amount of the circulating liquid, an amount of a liquid in the circulation tank, separating result index from concentration of the residual liquid, separating result index from concentration of the permeate liquid, separating result index from concentration of the unfiltered liquid, a saccharide content, a viscosity, an electric conductivity, a measurement value, a pH, an analytical value that is based on the selected progress index, and a calculated value that is based on the selected progress index; and the operating parameter is selected from at least one of an operating pressure of the membrane separation apparatus, a temperature of the membrane separation apparatus, a concentration of the circulating liquid, and an amount of the circulating liquid.