CN118846825A - A method and device for modifying a high gas transport membrane for bubble-free ventilation of a fermenter - Google Patents

Abstract

The present invention provides a novel fermentation bubble-free ventilation device and a preparation method thereof. The method uses a poly-4-methyl-1-pentene (PMP) hollow fiber membrane and uses a fluorinated polymer to modify it to prepare a bubble-free ventilation component. Air or oxygen is allowed to flow in the lumen of a bundle of hollow fiber membranes, and water or a biological reaction liquid flows outside the tube. Under the impetus of the oxygen partial pressure difference on both sides of the membrane, the oxygen in the lumen diffuses through the membrane wall or the micropores on the membrane wall into the liquid outside the tube to complete the bubble-free membrane oxygen supply process. Since the diameter of the membrane micropores is only 0.01-0.1 μm, there are no bubbles visible to the naked eye in the liquid, so it is called bubble-free oxygen supply. Compared with traditional bubbling oxygen supply, bubble-free oxygen supply has the following characteristics: (1) oxygen transfer efficiency is as high as 80% to 100%; (2) no foam is generated; (3) low requirements for the sterility of the air supply; (4) low power consumption.

Description

A method and device for modifying a high gas transport membrane for bubble-free ventilation of a fermenter

Technical Field

The invention relates to the preparation and device design of a ventilation membrane for a fermentation tank, and in particular to a method and a device for modifying a high gas transmission membrane for bubble-free ventilation of a fermentation tank.

Background Art

Fermentation tank refers to the device used for microbial fermentation in industry. Its main body is generally a main cylinder made of stainless steel plate, and its volume ranges from 1 to several hundred square meters. The structure of the fermentation tank used for anaerobic fermentation (such as the production of alcohol and solvents) can be relatively simple, but the fermentation tank used for aerobic fermentation (such as the production of antibiotics, amino acids, organic acids, vitamins, etc.) needs to continuously introduce a large amount of sterile air into the tank, and in order to consider the utilization rate of the introduced air, the structure of the fermentation tank is relatively complex. Commonly used aeration fermentation tanks include mechanical stirring fermentation tanks, bubbling fermentation tanks and airlift fermentation tanks, and there are ventilation pipes at the bottom to introduce air or oxygen required for bacterial growth.

At present, the main method of oxygen supply for biological fermentation reactions is bubbling ventilation, in which bubbles diffuse into the liquid phase during stirring. The disadvantages of this oxygen supply method are: (1) a large amount of foam will be produced, which will not only cause "liquid escape" but also easily cause bacterial contamination; (2) the oxygen transfer efficiency is low. In bubbling oxygen transfer, the oxygen transfer efficiency is controlled by the membrane resistance on the bubble interface. In biological reactions, the viscosity of the mash adheres to the bubble surface and increases the liquid membrane resistance, making the oxygen transfer efficiency even lower than that in the pure water phase, generally only 8% to 15%.

Summary of the invention

The purpose of the present invention is to provide a novel fermentation bubble-free ventilation device and a preparation method thereof. The method uses poly-4-methyl-1-pentene (PMP) hollow fiber membrane and uses fluorine-containing polymer to modify and prepare a bubble-free ventilation component. Air or oxygen is allowed to flow in the lumen of a bundle of hollow fiber membranes, and water or biological reaction liquid flows outside the tube. Under the promotion of the oxygen partial pressure difference on both sides of the membrane, the oxygen in the lumen diffuses into the liquid outside the tube through the membrane wall or the micropores on the membrane wall to complete the bubble-free membrane oxygen supply process. Since the diameter of the membrane micropores is only 0.01-0.1μm, there are no bubbles visible to the naked eye in the liquid, so it is called bubble-free oxygen supply. Compared with traditional bubbling oxygen supply, bubble-free oxygen supply has the following characteristics: (1) oxygen transfer efficiency is as high as 80% to 100%; (2) no foam is generated; (3) low requirements for the sterility of the gas supply; (4) low power consumption.

A surface-modified PMP hollow fiber membrane comprises a PMP porous base membrane in a hollow fiber configuration and a fluorine-containing polymer modification layer coated on the surface of the base membrane.

The thickness of the fluorine-containing polymer modification layer is 10-800 nm; the coating material includes but is not limited to HyflonAD, PFPE, fluorine rubber and other fluorine-containing polymers.

The PMP porous base membrane of hollow fiber configuration has a fiber inner diameter of 0.18-0.2 mm, a wall thickness of about 0.05-0.15 mm, a membrane wall micropore diameter of 0.1-0.5 nm, and a porosity of 45% to 65%.

The method for preparing the surface-modified PMP hollow fiber membrane comprises the following steps:

The PMP hollow fiber membrane is immersed in a 0.2-0.5 wt% fluorine-containing polymer solution for 1-40 minutes, and the hollow fiber membrane is taken out and placed in an oven at 30-60° C. for 12-24 hours.

The hollow fiber membrane bubble-free aerator device comprises the above-mentioned surface-modified PMP hollow fiber membrane.

Beneficial Effects

Poly-4-methyl-1-pentene (PMP) is a thermoplastic polyolefin with good mechanical and thermal stability. The PMP hollow fiber membrane prepared by thermally induced phase separation has an ultra-thin dense outer layer and a porous inner layer structure. The PMP material itself also has excellent air permeability, which is 12 times higher than that of polypropylene (PP). Therefore, PMP is an excellent breathable membrane material that can be used in liquid phases, especially in applications that require oxygen enrichment. PMP hollow fiber membranes can be used to make bubble-free ventilation membrane components.

The surface is coated with fluorine-containing polymers such as fluorine rubber to increase the hydrophobicity of the hollow fiber membrane, reduce the liquid or fermentation liquid entering the hollow fiber membrane pores, and improve the service life of the membrane and the gas transmission efficiency. At the same time, because it has extremely low surface energy and excellent anti-biological contamination performance, it reduces the low gas transmission efficiency caused by microbial adhesion and blockage during the fermentation process. It effectively provides a set of membrane material modification solutions and device manufacturing with high ventilation efficiency and bubble-free ventilation.

The beneficial effects of the present invention are: (1) compared with the traditional bubbling ventilation device with an efficiency of only 8% to 15%, the oxygen transfer efficiency of the bubble-free ventilation device can be increased to 80% to 100%; (2) no foam is generated, reducing the use of defoaming agents and avoiding the risk of contamination caused by foam overflow; (3) the requirements for the sterility of the air supply are low, because the diameter of the micropores in the dense layer on the surface of the hollow fiber membrane reaches the angstrom level, and bacteria of this size cannot pass through, so oxygen can be supplied directly without sterilization; (4) the power consumption is low, and there is no need to provide power through large-scale air supply equipment, thereby reducing energy consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a surface electron micrograph of Hyflon AD60/PMP composite membranes of different concentrations in Example 1.

FIG. 2 is an electron micrograph of the surface and cross section of the Hyflon AD60/PMP composite membrane at different coating times in Example 2.

FIG. 3 is an electron micrograph of the surface and cross section of the Hyflon AD60/PMP composite membrane at different coating temperatures in Example 3.

FIG. 4 shows (a) oxygen exchange rate and (b) pressure drop of the modified membrane in Example 4 at different gas-liquid ratios.

FIG. 5 shows (a) oxygen exchange rate and (b) pressure drop of the modified membrane in Example 4 at different liquid flow rates.

FIG. 6 is a microbial adhesion experiment in Example 5.

FIG. 7 is a diagram of the traditional bubbling aeration fermentation in Example 6.

FIG. 8 is a diagram of the bubble-free aerated fermentation in Example 6.

DETAILED DESCRIPTION

Example 1

The PMP hollow fiber membrane used in this embodiment is used as the base membrane. Taking Hyflon AD60 as an example, the monomer is dissolved in HFP with concentrations of 0.1wt%, 0.2wt%, 0.5wt% and 1wt%, respectively. The Hyflon AD60 coating liquid with appropriate viscosity is coated on the surface of the PMP membrane by immersion in a sedimentation tank for 10 minutes. The coating temperature is 60°C. The hollow fiber membrane is taken out and placed in an oven at 45°C for 12 hours.

Example 2

The PMP hollow fiber membrane used in this embodiment is used as the base membrane. Taking Hyflon AD60 as an example, the monomer is dissolved in HFP with a concentration of 0.5wt%. The Hyflon AD60 coating liquid with a suitable viscosity is coated on the surface of the PMP membrane by immersion in a sedimentation tank for 1mim, 5min, 10min, 20min, 30min. The coating temperature is 60°C. The hollow fiber membrane is taken out and placed in an oven at 45°C for 12h.

Example 3

The PMP hollow fiber membrane used in this embodiment is used as the base membrane. Taking Hyflon AD60 as an example, the monomer is dissolved in HFP with a concentration of 0.5wt%. The Hyflon AD60 coating liquid with a suitable viscosity is coated on the surface of the PMP membrane for 10 minutes by immersion in a sedimentation tank. The coating temperatures are 40°C, 60°C and 80°C. The hollow fiber membrane is taken out and placed in an oven at 45°C for 12 hours.

Example 4

The gas transmission performance of the above-mentioned Example 1 (concentration is 0.5wt%) was measured, and the homemade PMP membrane filament (the base membrane of Example 1 was not modified) and the modified membrane filament were used for comparison, and polyurethane glue was used for sealing to prepare two different types of oxygenator components. Physiological saline was used as the simulated liquid of blood, oxygen passed through the inside of the membrane filament, and the simulated liquid was circulated outside. The oxygen exchange rate and pressure drop performance during the measurement process were compared. Under the conditions of 300ml/min, V/Q=5/1, the oxygen exchange rate and pressure drop performance of the modified membrane and the homemade membrane were compared. The results showed that the oxygen exchange rate of the modified membrane (50ml/(min·m ² )) was higher than that of the homemade membrane (40ml/(min·m ² )), and the pressure drop of the modified membrane (30mmHg) was smaller than that of the homemade membrane (21mmHg). This shows that the modified membrane has a higher oxygen permeability than the homemade membrane under the same membrane area, and the surface stability of the modified membrane is better. The pore size of the membrane filament surface will affect the ability of the membrane surface to pass oxygen. The uneven pore size increases the possibility of oxygen entering the liquid through bubbles, thereby increasing the disturbance of liquid flow and increasing the flow resistance.

Embodiment 5:

The antimicrobial adhesion performance of the above Example 1 was measured. As shown in FIG6 , the membrane material of Example 1 has less microbial contamination than the original membrane, reduces pore blockage caused by microbial adhesion, and can ensure higher gas transmission performance.

Embodiment 6:

The effect of the aeration device prepared by the fiber membrane in the above-mentioned Example 1 on the performance of fermentation was measured. The bubble-free aeration device was fixed on the stirring shaft of the fermenter, and 200mL of the secondary seed liquid was inoculated into a 5L fermenter at a 10% inoculation amount with the fermentation medium (defoamer was added dropwise) for anaerobic fermentation. The fermentation temperature was 37°C and the stirring rate was 150rpm. 30% NaOH was supplemented to maintain the pH at 6.8. Under anaerobic conditions, _CO2 gas was introduced into the fermenter at a flow rate of 0.2L/min. The initial sugar concentration was 50g/L. After the glucose was exhausted in about 24h, 200ml of glucose mother solution (500g/L) was added to the fermentation medium again. The product yield was increased from 77.8% to 81.5%.

Claims (8)

1. A surface-modified PMP hollow fiber membrane, characterized in that it comprises a PMP porous base membrane in a hollow fiber configuration, and a fluorine-containing polymer modification layer coated on the surface of the base membrane. 2. The surface-modified PMP hollow fiber membrane according to claim 1 is characterized in that the thickness of the fluorine-containing polymer modification layer is 10-800 nm; the coating material includes but is not limited to HyflonAD, PFPE, fluorine rubber and other fluorine-containing polymers. 3. The surface-modified PMP hollow fiber membrane according to claim 1 is characterized in that the PMP porous base membrane with a hollow fiber configuration has a fiber inner diameter of 0.18-0.2 mm, a wall thickness of about 0.05-0.15 mm, a membrane wall micropore diameter of 0.1-0.5 nm, and a porosity of 45% to 65%. 4. The method for preparing the surface-modified PMP hollow fiber membrane according to claim 1, characterized in that it comprises the following steps: The PMP hollow fiber membrane is immersed in the fluorine-containing polymer solution, and the hollow fiber membrane is taken out and treated in an oven. 5. The preparation method according to claim 4, characterized in that the concentration of the fluorine-containing polymer solution is 0.2-0.5 wt%. 6. The preparation method according to claim 4, characterized in that the treatment condition in the oven is: stable at 30-60°C for 12-24h. 7. The preparation method according to claim 4, characterized in that the time for which the hollow fiber membrane is immersed in the fluorine-containing polymer solution is 1-40 minutes. 8. A hollow fiber membrane bubble-free aerator device comprising the surface-modified PMP hollow fiber membrane according to claim 1.