Saccharified solution production method using porous membrane

1. A method for producing a saccharified solution, comprising the following steps:

a liquefaction step of adding an enzyme to liquid starch to partially degrade the starch and obtain a sugar-containing liquefied product;

a saccharification step of adding a saccharifying enzyme to the obtained sugar-containing liquefied product to further degrade the sugar and obtain a saccharified solution composition containing a saccharified solution and an insoluble component;

a filtration step of passing the saccharified solution composition through a porous membrane composed of a resin having a three-dimensional network structure to separate the saccharified solution from the insoluble component; and

a cleaning step of passing or soaking the porous membrane into a cleaning solution to clean/remove an insoluble matter attached to the surface or inside of the porous membrane; wherein

on an SEM image of a membrane cross-section in the membrane thickness direction perpendicular to an inner surface of the porous membrane, in each region of a total of 4 visual fields with a visual field including the inner surface, a visual field including an outer surface of the membrane, and two visual fields photographed at regular intervals between those visual fields, the total of areas of resin parts having an area of 1 μm 2 or less is 70% or more relative to the total area of resin parts, and

the cleaning solution is an aqueous solution containing from 0.1 to 4 wt % of sodium hydroxide and from 0.01 to 0.5 wt % of sodium hypochlorite.

2. A method for producing a saccharified solution, comprising the following steps:

a liquefaction step of adding an enzyme to liquid starch to partially degrade the starch and obtain a sugar-containing liquefied product;

a saccharification step of adding a saccharifying enzyme to the obtained sugar-containing liquefied product to further degrade the sugar and obtain a saccharified solution composition containing a saccharified solution and an insoluble component;

a filtration step of passing the saccharified solution composition through a porous membrane composed of a resin having a three-dimensional network structure to separate the saccharified solution from the insoluble component; and

a cleaning step of passing or soaking the porous membrane into a cleaning solution to clean/remove an insoluble matter attached to the surface or inside of the porous membrane; wherein

on an SEM image of a membrane cross-section in the membrane thickness direction perpendicular to an inner surface of the porous membrane, in each region of a total of 4 visual fields with a visual field including the inner surface, a visual field including an outer surface of the membrane, and two visual fields photographed at regular intervals between those visual fields, the total of areas of resin parts having an area of 10 μm 2 or more is 15% or less relative to the total area of resin parts, and

the cleaning solution is an aqueous solution containing from 0.1 to 4 wt % of sodium hydroxide and from 0.01 to 0.5 wt % of sodium hypochlorite.

3. A method for producing a saccharified solution, comprising the following steps:

a liquefaction step of adding an enzyme to liquid starch to partially degrade the starch and obtain a sugar-containing liquefied product;

a saccharification step of adding a saccharifying enzyme to the obtained sugar-containing liquefied product to further degrade the sugar and obtain a saccharified solution composition containing a saccharified solution and an insoluble component;

a filtration step of passing the saccharified solution composition through a porous membrane composed of a resin having a three-dimensional network structure to separate the saccharified solution from the insoluble component; and

a cleaning step of passing or soaking the porous membrane into a cleaning solution to clean/remove an insoluble matter attached to the surface or inside of the porous membrane; wherein

on an SEM image of a membrane cross-section in the membrane thickness direction perpendicular to an inner surface of the porous membrane, in each region of a total of 4 visual fields with a visual field including the inner surface, a visual field including an outer surface of the membrane, and two visual fields photographed at regular intervals between those visual fields, the total of areas of resin parts having an area of 1 μm 2 or less is 70% or more relative to the total area of resin parts, and the total of areas of resin parts having an area of 10 μm 2 or more is 15% or less relative to the total area of resin parts, and

the cleaning solution is an aqueous solution containing from 0.1 to 4 wt % of sodium hydroxide and from 0.01 to 0.5 wt % of sodium hypochlorite.

4. The method according to any one of claims 1 to 3 , wherein the surface opening ratio of the porous membrane is from 25 to 60%.

5. The method according to any one of claims 1 to 3 , wherein the relationship between the tensile elongation at break E0 of the porous membrane before the cleaning step and the tensile elongation at break E1 of the porous membrane after the cleaning step is E1/E0×100≥98%.

6. The method according to any one of claims 1 to 3 , wherein the relationship between the tensile elongation at break E0 of the porous membrane before the cleaning step and the tensile elongation at break EX of the porous membrane after repeating the cleaning step X times (X is an integer of 2 to 10) is EX/E0×100≥97%.

7. The method according to any one of claims 1 to 3 , wherein the relationship between the flux L0 of the porous membrane before the filtration step and the flux L1 of the porous membrane after the cleaning step is L1/L0×100≥90%.

8. The method according to any one of claims 1 to 3 , wherein the relationship between the flux L0 of the porous membrane before the filtration step and the flux LX of the porous membrane after repeating the cleaning step X times (X is an integer of 2 to 10) is LX/L0×100≥90%.

9. The method according to any one of claims 1 to 3 , wherein the porous membrane is a hollow-fiber membrane.

10. The method according to any one of claims 1 to 3 , wherein the resin constituting the porous membrane is a thermoplastic resin.

11. The method according to claim 10 , wherein the thermoplastic resin is a fluororesin.

12. The method according to claim 11 , wherein the fluororesin is selected from the group consisting of a vinylidene fluoride resin (PVDF), a chlorotrifluoroethylene resin, a tetrafluoroethylene resin, an ethylene-tetrafluoroethylene copolymer (ETFE), an ethylene-monochlorotrifluoroethylene copolymer (ECTFE), a hexafluoropropylene resin, and a mixture of these resins.

13. The method according to any one of claims 1 to 3 , wherein the cleaning step includes a cleaning solution step of performing cleaning with the cleaning solution and a rinsing step of performing rinsing with rinse water for removing the remaining cleaning solution component.

14. The method according to claim 13 , wherein the amount of rinse water used in the rinsing step is 100 L/m 2 or less per unit area of the porous membrane.

15. The method according to claim 13 , wherein the chlorine concentration in the filtrate at the completion of the rinsing step is 0.1 ppm or less and the pH of the filtered liquid is 8.6 or less.