With the rapid development of China's economy, environmental pollution has attracted more and more attention. Polydimethyldiallylammonium chloride, as a strong cationic polyelectrolyte, is used as a flocculant in water treatment. So it is very important to study the synthesis of polydimethyl diallyl ammonium chloride and the flocculation efficiency of water treatment.
Polydimethyldiallylammonium chloride is obtained by monomer dimethyldiallylammonium chloride and free radical polymerization. In the preparation of the monomer dimethyldiallylammonium chloride, a one-step process in an aqueous solution or a two-step process using an organic solvent and an excess of an alkali can be selected. The one-step process is simpler and more suitable for industrial use. The two-step process is more complex and suitable for laboratory synthesis. However, the two-step process produces less monomer impurities .
If the two-step synthesis of the monomer after three stages of temperature rise reaction, can be obtained through homopolymerization of polydimethyl diallyl ammonium chloride, the author of polydimethyl diallyl ammonium chloride water treatment Flocculation efficiency.
Select the main reagents: dimethylamine, sodium chloride, industrial grade kaolin, hydrochloric acid, ammonium hydroxide, allylamine, acetone, thyme phenolphthalein.
Prior to the experiment, the experimental equipment is prepared and debugged, and then the preparation of dimethyl diallyl ammonium chloride. First, dimethylamine was added to a three-necked flask equipped with a reflux condenser, which was subjected to electromagnetic stirring at 5 ° C, and thymolphthalein was used as an indicator. Then, allyl chloride and sodium hydroxide, which were purified by water washing, were alternately added dropwise over two hours under the condition that the color of the indicator was not changed. Finally, after about 1.5 h, allow sufficient reaction, and then use the separatory funnel for liquid separation, adding an equal volume of allyl chloride and two times the volume of acetone in the upper layer of sodium hydroxide drying for about two hours Oil phase, the temperature is adjusted to 45 ° C, two hours after the acetone will be found in the precipitation of white crystals, another two hours in acetone in the form of white crystalline monomer.
Dimethyldiallylammonium chloride was prepared after dimethyldiallylammonium chloride was prepared. First, a quantity of dimethyldiallylammonium chloride was added to a four-neck flask equipped with a refluxing condenser and a corresponding amount of ammonium sulfate initiator was added. Then, deionized water was first dissolved in the calculated amount of disodium ethylenediaminetetraacetate and added to a four-necked flask. Finally, under the protection of nitrogen, the ambient environment is lower than 40 ℃, through three stages of temperature preparation of polydimethyl diallyl ammonium chloride.
In the coagulation laboratory, first remove the 1000 ml of water samples, stir the water with a stirrer after adding 3mg of polydimethyl diallyl ammonium chloride, adjust the speed of the blender, stir roughly two minutes , And then adjust the speed of slow mixer, stirring roughly five minutes later, will be added polydimethyl diallyl ammonium chloride water sample standing for ten minutes, remove the liquid surface 2cm away from the clear liquid used for water quality testing. 2.4532 g of kaolin was weighed out, put in a 1000 ml beaker, and the speed of the stirrer was adjusted to 200 rpm and stirred for 10 minutes to obtain a uniform suspension having a transmittance of 5.6%. The water sample For the homemade water samples with kaolin.
The addition of 3 mg / L polydimethyldiallylammonium chloride in 1000 ml of water and adjusting the pH with sodium hydroxide solution resulted in: first, when the pH was below 6, the flocculation was poor . Second, when the PH value is equal to 7, the flocculation effect is very good. Third, when the PH value in the middle of 6 to 9, the flocculation effect is better.
The temperature of the simulated water sample with PH = 7 was controlled at 50 ° C and then 3 mg / L of polydimethyldiallylammonium chloride was added. After standing for different times, the following results were obtained: First, the simulated water sample was allowed to stand The longer the flocculation effect is, the higher the transmittance is. Second, the transmittance did not increase significantly after standing for 10 minutes in the simulated water sample.
In the simulated pH of 7 is different from the amount of polydimethyl diallyl ammonium chloride, will be: First, the flocculant dose increased to 4mg / L, the transmittance began to decline, the flocculation effect began Constantly deteriorating. Second, the flocculant dosage is 3mg / L, the flocculation effect is better.
The simulating water samples were placed in different temperatures, and the following results were obtained: First, the higher the temperature, the more the simulated water sample (pH = 3) The greater the transmittance, the better the flocculation effect. Second, when the temperature is 50 ℃, the flocculation effect is the best. Third, when the temperature exceeds 50 ° C, the transparency starts to drastically decrease.
In the preparation of the monomeric dimethyldiallylammonium chloride, a one-step process in an aqueous solution or a two-step process using an organic solvent and an excess of base may be selected. Dimethyl diallyl ammonium chloride monomer was prepared by the two-step method. When the monomer was synthesized by tertiary amine, the acetone solvent was added twice and the white monomer was precipitated in acetone. Add 3mg / L of polydimethyl diallyl ammonium chloride, to ensure that the coagulation temperature is 50 ℃, PH is equal to 7, standing l0 minutes, so that the state of dimethyl diallyl ammonium chloride has the best Of the transmittance, better flocculation effect.