| Based on abundant resources, low cost, good comprehensive properties of water glass and polyvinyl alcohol as raw materials,this project was designed to develop a super advanced method for preparing ultrafiltration membrane. The pore size of the water glass and polyvinyl alcohol composite membrane prepared by the method can reach the level of ultrafiltration, suitable for separation and concentration of proteins or other macromolecules that are larger than the amount of molecular cut off, in particular, it can be used for water treatment. According to the test results,different water glass / PVA ratios and different modes of operation can produce the ultrafiltration membrane with different water flux and molecular cut off,the pure water flux of the prepared water glass polyvinyl alcohol composite membrane was 83.91-89.89 L/(m2·h), the molecular cut off was about 45000 Da,its mechanical strength and other characteristics are excellent. This is an important breakthrough in the preparation of ultra filtration membrane based on the basic water glass. The main results are summarized as follows:(1)The effect of the three factors including the ratio of the dilution ratio of the water glass, the concentration of the polyvinyl alcohol, the proportion of the water glass / polyvinyl alcohol on the membrane formation of water glass polyvinyl alcohol composite membrane was analyzed. The experimental results show that the combination of the ratio of water glass dilution being 1:8, polyvinyl alcohol concentration being 5%(w/w), and the proportion of water glass / polyvinyl alcohol being 1:1 produces the best ultrafiltration membrane among all combinations of them investigated.By determing the pure water flux and egg white protein retention rate of the composite membrane prepared by different solution after treatment, the results showed that the films become harder and thicker after ethanol treatment while the pure water flux is almost negligible. After the treatment of citric acid solution, the water flux of the membrane rose from 99.56 L/(m2·h) to 145.61 L/(m2·h) compared with pure water treatment,but egg white protein retention was reduced by half. The pure water flux of the membrane decreased slightly after treatment with sulfuric acid solution and Lglutamic acid solution,the rejection rate of proteins increased significantly. Especially, the egg white protein rejection rate of the membrane treated with sulfuric acid solution was increased. So, soaking the membrane for 24 h with 2 mol/L sulfuric acid solution resulted in the most reasonable water flux and egg white protein retention among all treatments investigated.A good composite membrane was made by using water glass dilution ratio of 1:8 and PVA concentration of 5%(w/w), water glass / PVA ratio of 1:1, and soaking the membrane in 2 mol/L H2SO4 solutions for 24 h. Its water flux was 86.90±2.99 L/(m2·h), and its egg white protein retention rate was 87.84±1.04%.(2) The retention properties, porosity, mechanical properties and surface morphology, porosity, mechanical properties and surface morphology of the water glass- PVA composite membrane made by using different concentration(w/w: 5.4%, 5.1% and 4.8%) of water glass were analyzed. Results showed that as the water glass mass fraction decreases, the pure water flux of the composite membrane decreases while egg white protein, BSA rejection retention rate, and pepsin retention rate all increased. When the water glass concentration decreases, the porosity of the membrane was increased, the maximum pull force was decreased, and the tensile strength was increased. The tensile length and elongation of the composite membrane made by using the water glass concentration 5.4%(w/w) were significantly better than that made by using the water glass concentration 5.4%(w/w) and 4.8%(w/w).When the water glass concentration is 5.1%(w/w), the water flux of the composite membrane was slightly decreased, but the rejection rate of BSA changed from 53.23% to 94.53%. The maximum tensile strength, tensile length, elongation and elongation of the composite membrane were increased after treatment with sulfuric acid, showed that the mechanical strength of the membrane after sulfuric acid treatment is better, which is more conducive to the use of the membrane.The membrane made by using the concentration of water glass was 5.1%(w/w), soaked in 2 mol/L H2SO4 solution for 24 h, has the pure water flux of 86.90±2.99 L/(m2·h), the egg white protein retention rate of 87.84±1.04%, and the molecular cut off of about above 45000 Da. It can also be verified by the pepsin interception rate of 81.21±3.01% and the BSA retention rate of 94.53%. Its porosity was 28.39%, its maximum tensile strength was 1.93 MPa, its tensile strength was 2.13 N, its tensile length was 156.5 mm, and its elongation was 314.6%.(3) In the adaptability test of the ultrafiltration membrane to concentrate or purify soya proteins, single factor experiments on the effect of filtration pressure, pH value of the extract, and filtration time on the flux of the composite membrane were carried out. The optimization experiment of the extraction conditions studied the filtration pressure, the pH value and the filtration time. It was found that the optimal extraction and filtration combination of the experimental conditions was as the following: the filter pressure of-0.1 MPa, the extract pH value of 10 and the filtration time of 20 min. The average flux of the membrane under this condition was 78.63 L/(m2·h). The NSI of the prepared soya protein concentrate was 86.45±0.26% while its oil absorption rate was 3.32 ±0.09 g/g, and its water holding rate was 5.67 ± 0.12 g/g. When the contaminated membrane was cleaned by using 0.05 mol/L NaOH solution, 90.16% of its water flux recovery rate was achieved. It is therefore concluded that the water glass-polyvinyl alcohol composite film produced in this study can be applied to the concentration of soybean protein. |
PDF Full Text Request