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Recovery and purification of tetrahydrofuran

- Aug 23, 2018 -

Tetrahydrofuran, also known as 1,4-ethylene oxide, tetramethyl oxide (THF), is a commonly used organic solvent with strong toxicity, poisoning by inhalation of steam or skin contact, and the explosive limit of tetrahydrofuran in air. It is 2.3 to 11.8, and it also produces peroxide like ether, which is extremely explosive. Tetrahydrofuran is generally used to dissolve organic matter and react therein without itself participating in the reaction. After the reaction, the product is separated, and the remaining tetrahydrofuran cannot be reused because it contains impurities. If it is directly discarded, it causes a large economic loss and pollutes the environment. At present, the recovery and purification of tetrahydrofuran, because the main impurities are the water brought in during the feeding and the oxide formed by the oxygen in the air, the purification is more difficult, and the pure tetrahydrofuran is directly recovered from the industrial waste tetrahydrofuran.

1. experimental requirements

It reaches the industrial grade tetrahydrofuran standard, the water content is <0.5%, no peroxide, and can be stored for a period of time. The tetrahydrofuran waste liquid used in this experiment is from Shujiang Xingming Chemical Factory, and its water content is about 5%. The main impurities are water and peroxide, and the trace amount of raw materials or products contain no hindrance to reuse, but it is beneficial to waste recycling. Therefore, it is not necessary to consider the removal problem. In addition, since tetrahydrofuran is difficult to store, its preservation method should also be tested.

2. water, peroxide determination and removal method

2. 1 determination

The determination of trace moisture can be carried out by gas chromatography and Karl Fischer method. This experiment uses the Karl fischer method.

Determination of peroxide:

Qualitative: oscillate with 10% freshly prepared potassium iodide solution plus 10 ml of tetrahydrofuran. The peroxide is yellowish brown.

Quantification: 6 ml of acetic acid 4 ml of chloroform 1 g of potassium iodide was added to 50 ml of tetrahydrofuran, and placed in the dark for 5 minutes with 0. The 1N sodium thiosulfate solution was titrated to colorless, the peroxide percentage was: NXVX0.7 / G where N, V are the equivalent concentration and volume (ml) of sodium thiosulfate, respectively, and G is the weight of tetrahydrofuran (g ).

2.2 removal method

A, water removal: anhydrous calcium oxide, molecular sieve, calcium hydride

B, removal of peroxide: sodium hydroxide, sodium borohydride, calcium hydride, copper chloride solution, ferrous sulfate solution

After testing, sodium hydroxide can only mask the effect of measuring peroxide, and can not really remove peroxide, so it is not used; while copper chloride solution, ferrous sulfate solution is dehydrated due to the other focus of this experiment, adding this solution will increase Large water content, not suitable.

3. experimental scheme and results

Option 1: Dehydration after removal of peroxide

Qualitative determination of peroxides, determination of peroxides, addition of hydrides, distillation, distillation, distillation, removal, preservation

Found: Take tetrahydrofuran waste liquid and add 1% sodium borohydride for 15 minutes, determine the peroxide, completely remove, and then distill by water bath, the test results only accounted for 47. 15%, while the remaining liquid accounted for 52.85, the recovery rate is too low, unreasonable.

Option 2: Dehydrate before removing peroxide

Azeotropic dehydration plus calcium oxide dehydration, reduction of oxides with calcium hydride and further dehydration, distillation, preservation

Since tetrahydrofuran forms an azeotropic mixture with water at one atmosphere, the boiling point is 63.4 ° C and the water content is 5%. Therefore, when the water content is more than 5%, azeotropic dehydration can be performed first. Since the measured tetrahydrofuran used in this experiment has a measured water content of 4.9%, it does not require azeotropic dehydration.

(1) Calcium oxide + calcium hydride. Calculate the amount of calcium oxide: Take 200 ml of tetrahydrofuran and weigh about 200 X0. 888 = 177. 6 g, of which 177.6 X 4.9% = 8.88 g of water, reacted with calcium oxide to consume 8 of calcium oxide. 88 X 56/18 = 27. 6 plus, if the water content is 1%, add calcium oxide 27.6 X 4/5 = 22. 1 g.

The test was carried out by taking 200 ml of tetrahydrofuran. The results are shown in Table 1. <In the case of calcium hydride or a peroxide-removing agent, if less than 2.5 g, the peroxide cannot be completely removed, 3 g or more for safety. It can be seen from Table 1 that when the calcium oxide reaches 40 grams, the additional effect is not large, but the amount of tetrahydrofuran produced is reduced: on the other hand, as the calcium oxide decreases, the calcium hydride increases, when the calcium oxide is less than 20 grams. At the same time, the effect of calcium hydride increase gradually decreases, and the price of calcium hydride is about six times higher than that of calcium oxide, so the combination of the two should have an optimum value as found by the interlaced test results. :

Method A: 200 ml of tetrahydrofuran + 24 g of calcium oxide + 3 g of calcium hydride, the best effect, the water content is 0.1500, no peroxide, the amount of tetrahydrofuran obtained is 180 ml.

(2) The best combination of molecular sieve + sodium borohydride test is:

Method B: 200 ml of tetrahydrofuran, 50 g of molecular sieve, 2 g of sodium borohydride, the obtained tetrahydrofuran had the same water content as above, and the amount of tetrahydrofuran was 188 ml.

(3) The best combination of molecular sieve + calcium hydride test is:

Method C: 200 ml of tetrahydrofuran + 30 g of molecular sieve + 3 g of calcium hydride obtained a tetrahydrofuran having a water content as above, and the amount of tetrahydrofuran was 190 ml.

Preservation: In the test, adding 0.001 g of hydrogen to 100 ml of tetrahydrofuran can prevent the formation of peroxide in two months: while adding 0.0001 g of pyrogallic acid can prevent the formation of peroxide within two years but the container must be Fill it with a seal or fill it with nitrogen and store in a cool place.

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