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In the heated state, the chloroform in the Erlenmeyer flask boils, and its vapor becomes liquid again after passing through the condenser tube, and drops back into the extraction tube.

The hot chloroform solution gathered in the extraction tube, the sample was dissolved in chloroform, and the color of the solution changed from colorless and transparent to blue soon.

After one tube is collected, the solution in the extraction tube is transferred to the lower Erlenmeyer flask by 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.

This is because less toxic solvents such as methanol, acetone, and n-hexane are used.

However, chloroform solvent is used now, which is highly toxic, so it is better to put a balloon on it.

However, this is a simulation laboratory, so it doesn't matter.

The extraction speed is very fast, and after less than an hour, the color of the solution in the extraction tube tends to be colorless and transparent.

Xu Qiu stopped heating, and after the solution in the Erlenmeyer flask cooled, it was transferred to a 500 ml eggplant-shaped bottle.

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.

...

Xu Qiu used the rotary steaming operation before in the "Organic Chemistry Experiment" course. The operation and principle are not difficult.

And he also copied the senior sister's skills, the fourth-order 20% proficiency is barely enough.

Rotary evaporation utilizes the principle that the boiling point of solvents decreases under low pressure, and can remove solvents with boiling points greater than 100 degrees at room temperature or under heating at 30-70 degrees.

Kind of like a vacuum oven.

Of course, for low-boiling solvents like chloroform, it can be removed without heating, or even with a low vacuum.

Xu Qiu began to build the rotary steaming device.

The main body is a rotary evaporator, and the center is a four-necked bottle.

A two-way valve is connected to 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;

The following is an ordinary round bottom flask, used to receive the solvent from the rotary evaporation;

A very large serpentine condenser is attached to it;

The serpentine condenser is externally connected to a circulating cooling device, and the upper part is connected to a water pump through a hose.

Xu Qiu was very impressed with the serpentine condenser.

When I was in the experimental class before, a classmate knocked down the rotary steamer and fell to the ground.

They are all glass instruments, and they shatter immediately when they hit the ground.

For a complete set of glass instruments, the most expensive is the serpentine condenser, which costs nearly 1,000 yuan.

Later, the school did not ask the classmate to compensate, but he got a C- at the end of the course.

The right side of the four-neck bottle connects the explosion-proof bottle and the eggplant-shaped bottle through a rotatable shaft.

The explosion-proof bottle is used to prevent sucking back, and a ball of cotton needs to be stuffed inside.

The eggplant-shaped bottle is the place where the sample solution is placed. After the rotation is turned on, it can rotate along the axis, which is also the origin of the name of the instrument.

There is also a water bath heating device below 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 in Handan Laboratory.

It's just that the coolant that circulates inside it is a mixture of glycol and water.

This is because during the rotary evaporation 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 minus twenty to forty degrees Celsius.

...

Wait until the temperature of the cooling device reaches minus 20 degrees Celsius.

Xu Qiu started the water pump, and the vacuum in the system could be seen from the barometer to drop slowly.

Start the rotation, and the eggplant-shaped bottle starts to turn.

Not long after, the vacuum dropped very low, and the chloroform solvent in the bottle began to boil violently.

He hurriedly adjusted the valve, put in some air, increased the vacuum inside the system, and kept the solution in a slightly boiling state.

A large amount of condensed chloroform also appeared on the serpentine condenser, flowing along the inner wall of the glass instrument and flowing into the liquid contact bottle below.

The solution in the eggplant-shaped bottle gradually decreased, and the phenomenon of bumping no longer occurred.

Xu Qiu controlled the valve and adjusted the vacuum to the lowest level until all the solvent evaporated to dryness.

The polymers are attached to the bottle walls in the form of a film, and it is not very easy to get them out directly because the product mass is too small.

After thinking for a moment, he came up with a plan.

He added fifteen milliliters of chloroform solution to the eggplant-shaped bottle again, shaking the bottle with his wrist to dissolve the solid film on the side of the bottle.

Subsequently, Xu Qiu treated the other three samples with rotary steaming.

This time, he did not let the solvent evaporate completely, but left about fifteen milliliters of chloroform, which saved the step of dissolving again.

Next, he dropped each of the four groups of solutions into methanol solvent to precipitate solid polymers, and finally filtered them, dried them in vacuum, and weighed them.

For the previous product, the first batch yield was about 60 mg, and the second batch was about 120 mg.

After the extraction, 50mg remained from the first batch, while less than 70mg remained from the second batch.

It can be seen that there are a lot of insolubles in the second batch of products.

Taken together, the yields of the two batches of products are almost the same, less than 50%.

Of course, the point is not yield, but solubility.

15 milliliters of chloroform can dissolve 70 milligrams of polymer, so its minimum solubility in chloroform can reach 4 milligrams per milliliter.

With this solubility, the coating film is more than enough to make devices.

Xu Qiu prepared eight groups of solutions according to the daytime formula, except that the receptor was changed to PC[70]BM, and other conditions were not changed.

2x speedup, half an hour later.

Xu Qiu picked up the prepared solutions and checked them one by one, and found that they were all dissolved well.

He tried the feel of spin-coating with a glass slide again. Without filtration, the obtained film was very uniform and no solid particles remained.

Xu Qiu was very happy to finally solve the trouble of a solution.

Looking at the time, it was almost twelve o'clock in the middle of the night. Before he knew it, he continued to conduct experiments 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 threw when he was practicing before, because they had been accelerated by 2 times, so the actual reaction time was about 12 hours.

He lifted the aluminum foil covering the reaction bottle to see how the polymerization reaction inside was going.

A solid product has precipitated in the reaction bottle, forming a circle around the inner wall of the bottle.

Xu Qiu analyzed this:

The reaction time of 12 hours may be enough to obtain relatively high molecular weight products.

The insoluble matter in the previous second batch of products may be caused by too long reaction time.

It seems that there is another direction that can be improved.

...

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:

In his two systems, the highest efficiency of 1# sample is 5.02%, and the highest efficiency of 2# sample is 5.91%.

For the two systems of Senior Sister, the highest efficiency of 3# sample is 6.47%, and the highest efficiency of 4# sample is 7.38%.

The efficiency of both of them may be further improved, but at 10%, there is no possibility of a breakthrough yet.

However, Xu Qiu's current efficiency has reached the threshold of irrigation in the second district.

There are two ways, one is to irrigate in the second area, and the other is to continue to optimize performance and strive to make a big article out.

Which way should I choose?

Thanks to Lan Shiyu for the 500 point reward and new1981 for the 100 point reward.