Chapter 94: Chloroform extraction

　　 Under heating, the chloroform in the Erlenmeyer flask boils, and its vapor becomes liquid again after passing through the condenser and drips back into the extraction tube.
　　 Hot chloroform solution was gathered in the extraction tube, the sample was dissolved in chloroform, and the color of the solution quickly changed from colorless and transparent to blue.
　　 After collecting one tube, the solution in the extraction tube is transferred to the lower Erlenmeyer flask through the siphon effect.
repeatedly.
　　 Looking at the Soxhlet extraction device, Xu Qiu suddenly realized a problem:
　　 Conventional Soxhlet extraction, the upper end of the condenser tube is not sealed.
　　Because methanol, acetone, n-hexane, which are less toxic solvents, are used.
　　 And now, the chloroform solvent is used, which is more toxic. It is better to put a balloon on it.
　　 However, this is a simulation laboratory, so it doesn't matter.
　　The speed of extraction is very fast. After less than one hour, the color of the solution in the extraction tube becomes colorless and transparent.
　　 Xu Qiu stopped heating, and after the solution in the Erlenmeyer flask had cooled, it was transferred to a 500ml eggplant-shaped flask.
　　 This is actually a chloroform solution of a polymer with a very low concentration. The solvent needs to be evaporated to dryness by rotary evaporation to obtain a solid product.
　　……
　　 Rotary steaming operation, Xu Qiu used it in the course of "Organic Chemistry Experiment" before. The operation and principle are not difficult.
　　 And he also copied the senior sister's skills, the level 4 proficiency of 20%, barely enough.
　　Rotary steaming utilizes the principle of lowering the boiling point of solvents under low pressure, which can remove solvents with a boiling point greater than 100°C at room temperature or heating at 30-70°C.
　　 is somewhat similar to a vacuum oven.
　　Of course, for low boiling point solvents like chloroform, it can be removed without heating or even a low vacuum.
　　 Xu Qiu started to build a rotary steaming device.
　　The main body is a rotary steamer, and the center position is a four-neck bottle.
　　 is connected to a two-way valve on the left, and there is a long plastic tube on it, which is inserted to the far right to control the air pressure in the closed system;
　　 Below is an ordinary round-bottomed flask, which is used to receive the solvent that is evaporated by spinning;
　　 is connected to a very large serpentine condenser;
　　 The serpentine condenser is connected to a circulating cooling device, and the water pump is connected to the top through a hose.
　　 Xu Qiu was very impressed with the serpentine condenser.
　　 During the experimental class, a classmate overturned the rotary steaming device and fell to the ground.
　　 are all glass instruments, which break directly when they hit the ground.
　　 A set of glass instruments, the most expensive is this serpentine condenser, which costs nearly 1,000 yuan.
　　 Later, the school didn't make the classmate compensate, but he got a C- at the end of the course.
　　 The right side of the four-neck bottle is connected to the explosion-proof bottle and the eggplant bottle through a rotatable shaft.
　　Explosion-proof bottle is used to prevent sucking back, and it needs to be stuffed with cotton.
The eggplant-shaped bottle is the place where the sample solution is filled. After turning on the rotation, it can rotate along the axis. This is also the origin of the name of the rotary steaming instrument.
There is also a water bath heating device under the eggplant-shaped bottle, which can heat the solution in the eggplant-shaped bottle.
　　 After setting up the rotary steaming equipment, Xu Qiu first activated the circulating cooling device, which is similar in principle to the circulating water system of the Handan Laboratory.
　　It's just that the coolant circulating inside is a mixture of ethylene glycol and water.
　　This is because in the rotary steaming process, a large amount of hot solvent vapor is required to be cooled in a short time.
　　 Therefore, it is difficult to meet the requirements with conventional circulating water, and the freezing point of the mixed liquid of ethylene glycol and water can reach -20 to 40 degrees Celsius.
　　……
　　 The temperature of the cooling device reaches minus 20 degrees Celsius.
　　 Xu Qiu started the water pump, and you can see from the barometer that the vacuum in the system is slowly decreasing.
　　 starts to rotate, the eggplant bottle starts to rotate.
　　 It didn't take long for the vacuum to drop very low, and the chloroform solvent in the bottle began to boil violently.
　　He was busy adjusting the valve, putting some air in, increasing the vacuum inside the system, and keeping the solution in a slightly boiling state.
A large amount of condensed chloroform also appeared on the serpentine condenser, which flows along the inner wall of the glass instrument into the wetted bottle below.
　　The solution in the eggplant-shaped bottle gradually decreases, and no bumping occurs.
　　 Xu Qiu controls the valve to adjust the vacuum to the lowest level until all the solvent evaporates.
　　The polymer is attached to the bottle wall in the form of a film, because the product quality is too small to get them out directly.
　　Thinking for a moment, he has a plan.
　　 He again added fifteen milliliters of chloroform solution to the eggplant-shaped bottle and shook the bottle with his wrist to dissolve the solid film on the bottle wall.
　　 Subsequently, Xu Qiu used rotary steaming to treat the other three samples.
　　 This time, instead of letting the solvent evaporate completely, he left about fifteen milliliters of chloroform, which saved the step of dissolving again.
　　 Next, he dripped each of the four groups of solutions into the methanol solvent to precipitate the solid polymer, and finally filtered, dried in a vacuum, and weighed.
　　The output of the previous product was about 60 mg in the first batch, and about 120 mg in the second batch.
After 　　 was extracted, the first batch was left with 50 mg, while the second batch was only left with less than 70 mg.
　　 It can be seen that there are very many insolubles in the second batch of products.
　　Comprehensively, the yields of the two batches are almost the same, both are less than 50%.
　　 Of course, the focus is not on yield, but on solubility.
　　 15 ml of chloroform can dissolve 70 mg of polymer, so its minimum solubility in chloroform can reach 4 mg per ml.
　　With this solubility, the coating film is more than enough for devices.
　　 Xu Qiu prepared eight sets of solutions according to the daytime formula, except that the receptor was changed to PC[70]BM, other conditions remained the same.
　　 2 times acceleration, half an hour later.
　　 Xu Qiu picked up the prepared solutions, checked them one by one, and found that they all dissolved well.
　　 He tried the spin-coating feel with a glass plate again. Without filtering~EbookFREE.me~, the film obtained was very uniform and no solid particles remained.
　　 finally solved the trouble of a solution degree, Xu Qiu was very happy.
　　 glanced at the time, it was almost twelve o'clock in the middle of the night, unknowingly, he continued to experiment for more than four hours.
　　 He was about to leave the simulation laboratory when he suddenly saw the reaction device in the fume hood.
　　 Those were the three reactions he had made when he was practicing before. Because they have been accelerating twice, the actual reaction time is about 12 hours.
　　 He lifted the aluminum foil covering the reaction flask and wanted to see how the polymerization reaction was going on inside.
　　 The solid product has been precipitated in the reaction bottle, forming a circle around the inner wall of the bottle.
　　 Xu Qiu analyzes this:
　　 12 hours of reaction time may be enough to obtain relatively high molecular weight products.
　　 The insoluble matter in the second batch of products may be caused by too long reaction time.
　　 seems to have found another direction for improvement.
　　……
　　 On Saturday, Xu Qiu tried to make devices in the simulation laboratory.
　　 did not adjust too many parameters, just a preliminary attempt, the results are as follows:
　　 His two systems, 1# sample has the highest efficiency of 5.02%, and 2# sample has the highest efficiency of 5.91%.
　　 school sister’s two systems, 3# sample has the highest efficiency of 6.47% and 4# sample has the highest efficiency of 7.38%.
　　 There is a possibility of further improvement in the efficiency of both of them, but 10%, there is still no possibility of a breakthrough.
　　 However, Xu Qiu's current efficiency has reached the threshold of irrigation in the second district.
　　 There are two roads, one is to irrigate in the second district, and the other is to continue to optimize performance and strive to make a big article.
　　 Which way to choose?