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Ultrasonic solve the membrane surface contamination

To solve the pollution problem of the membrane surface, at home and abroad have done a large number of experiments, whether to strengthen reflux, frequent washing, or other measures are not ideal. In the membrane separation process, the introduction of ultrasound, the use of Ultrasonic cavitation effects and role of "super stirred to weaken the membrane surface of the gel layer and other contamination, and by the evaluation apparatus, black liquor, ion-exchange membrane electrolysis The, Recovery introduction of ultrasonic eliminate membrane fouling were tested. The experiments show that ultrasonic waves can effectively prevent the formation of gel film surface, the elimination of membrane fouling, and reduces the energy consumption of the electrolysis process, to improve the membrane separation process. The experimental principle membrane surface contamination membrane separation technology of the biggest problems in the course of membrane fouling gel layer and polarization layer can be divided into two categories, according to the film type and isolate different membrane surface contamination layer. When using an ultrafiltration membrane separation of the organic solution, in the pressure differential is driven by water, ions and small molecules through the pores of the membrane reach the other side of the membrane, to entrap macromolecules in the membrane surface, resulting in an organic membrane surface The enrichment of the material.

The reverse of the macromolecules concentration slower diffusion and concentration diffusion direction opposite to the direction of flow of the liquid through the membrane, and slows down the diffusion, resulting in a membrane surface of the gel layer was generated, and the gel layer will continue to be thickened, a serious impediment to further separation. When using ion exchange membrane separating plasma state substance, due to the membrane only allows a class of charged ions through the shut-off while the other with ions of opposite charge, resulting in the deletion of a class of charged ions in the membrane surface and the opposite charged ions massive accumulation of the formation of the polarization caused by uneven distribution of ion concentration, when the operating current is large, the formation of precipitation, scaling and other serious membrane fouling. Membrane electrolysis process black liquor alkali recovery, two membrane fouling occur simultaneously, and very serious, the black liquor by high concentrations of organic molecules resulting in the generation of the gel layer on the membrane surface, and high concentrations of inorganic ions causes the membrane surface formation of polarization precipitation. Ultrasonic cavitation ultrasonic cavitation "role and ultrasonic cleaning action has very special properties, that is," "as an ultrasonic eliminate membrane fouling mechanism of action and practice City clever lack Tian remain held wear. When the ultrasonic passed encounter solid interface in the liquid, the sound waves are compressed at the collision point immediately after the rebound. The sound waves bounce caused the collision point formed a tiny "vacuum bubble". "Vacuum bubble" instant collapse of the local atmospheric pressure of hundreds and thousands of degrees of heat. This is the ultrasonic energy to carry an instantaneous release, called ultrasound cavitation phenomenon. Since the ultrasonic cavitation phenomenon is concentrated in the solid-liquid interface, and thus produce a strong shock on the point of its circumference, the gel layer and the precipitate deposited on the film surface to produce a strong peeling while being peeled off attachments ultrasonic driven by rapid diffusion, so that the concentration of the membrane surface and the bulk solution concentration tends to be consistent. In this study, alkali recovery process of papermaking black liquid membrane membrane fouling ultrasound to eliminate experiments.

Experimental methods and content of the test water study, Gansu, China, a paper mill soda wheat straw black liquor effective alkali content. Potassium dichromate method of the test method, a diluted inoculation method gravimetric method gravimetric method atomic absorption spectrophotometry. The experimental setup used plexiglass preparation, Shanghai Chemical Plant of phase cation exchange membrane, membrane and electrode size, overcast, the anode compartments each with a capacity ultrasonic oscillation frequency, power, experimental apparatus and the principle shown in Figure shown . Although the membrane alkali recovery a lot of people have done the corresponding experimental network, due to the characteristics of the black liquor, resulting in membrane surface of the gel layer is very serious, the film resistance increased by several times within a voltage to a The sharp increase in power consumption. Recovered in the electrolytic cell the cathode chamber, the current efficiency can reach above is preferable. The membrane electrolysis system power consumption, not only vary depending on the current flowing through the system and also vary depending on the experimental operation of the system operating voltage is approximately in the initial cleaning of the membrane surface when energized, and after about very serious membrane fouling, membrane The operating voltage reaches a recycling t base power consumption will reach above. Experiments show that serious film surface pollution has become a major obstacle to membrane electrolysis treatment of black liquor. Test conditions and experimental data in the experimental apparatus, the the ultrasonic oscillator occurrence probe deep black liquor, the probe from the membrane surface.

In the same working conditions, compared to non-ultrasonic oscillations the film surface pollution in the continuous ultrasonic oscillation and intermittent ultrasonic oscillation ways under specific experimental data, and, as shown. DC rectifier power cation exchange membrane ink electrode black liquor the loaded schematic diagram of the dilute solution of Figure experiment called Bu no ultrasonic a the Bu continuous ultrasound oscillation parked intermittent ultrasonic oscillation time juvenile stream under the conditions of operation of the the voltage curve table Tak flow conditions The voltage comparator is still the type of experiment the initial and the ultrasonic oscillation printed surface without a continuous Ultrasonic vibration, oscillation plus intermittent ultrasonic oscillation exhibition swing Note the test conditions for the flow rate of black liquor. Resistant, fixed operating current. The effective area of ​​the membrane and the electrode expansion, film and plate spacing, ultrasound each oscillation, the oscillation intermittent water purification technology water purification technology table current Tak pressure conditions change type of comparative experiments initial surface without ultrasonic vibration continuous ultrasound oscillation intermittent ultrasonic vibration.

Initial surface Note the test conditions for the black liquor flow rate, operating voltage, the effective area of ​​the membrane electrode gas film and plate spacing, ultrasonic cycle oscillation and the rest of the time for the intermittent time. The ultrasonic oscillation door Bu continuous ultrasonic vibration, Fen intermittent ultrasonic oscillation time the effect of pollution on the Elimination of film basically the same due to the intermittent role ultrasonic energy savings, thus better economic indicators. On the experimental papermaking black liquor under the conditions of the experiment, to each interval, the ultrasonic oscillation is preferable. In actual operation, according to the power and area of ​​the ultrasonic oscillator, through experiments detailed technical and economic comparison be established intervals. The experiment has not been found the ultrasonic vibration damage to the film. Subject to conditions, changes in the ultrasonic frequency and power are unable to carry out experiments in continuous high-intensity ultrasound under the action of the membrane surface will hurt, further research needs to be done. Conclusion, the use of ultrasonic oscillation to eliminate the membrane fouling is very effective The ultrasonic cavitation role play stripping and accelerate the diffusion of contaminants on the membrane surface. Intermittent ultrasound each ultrasound mode of action, the effect of membrane cleaning and continuous role in roughly equal, but an ultrasound can save energy consumption. Membrane fouling in membrane electrolysis chemical recovery using ultrasound to eliminate soda black liquor can guarantee stable operating voltage and current of the electrolysis process, and allows the power consumption of the recycling tons of alkali


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