Chapter 127 - Acid and Alkali (Part 3)

Safety in production was Ji Situi’s biggest headache. An accident at a chemical plant was not like one at an ordinary enterprise: it wasn’t just about worker casualties; the equipment would also be damaged, and the terrible consequences of a chemical leak were difficult to predict. The casual attitude of these former peasants towards dangerous goods was really unbearable for him—he had conducted several safety production education sessions and had severely reprimanded a few guys who did not wear protective clothing according to regulations.

A few unlucky guys stood with their heads bowed as he berated them for a full half hour. Given the climate of Lin’gao, operating by the furnace in full protective gear was indeed a form of torture. The fiberglass trouser covers, rubber aprons, long-sleeved gloves, and high-top boots were all non-breathable. Even if they weren’t operating by the furnace, they would be drenched in sweat after a few minutes.

“Do you want to become like him?!” Ji Situi took out a medical atlas—he had gotten it from the Grand Library. The photos inside were all of patients with chemical burns.

But the effect of the photos was too terrifying and had the opposite effect. Several native workers came to beg him, saying they didn’t want to do this work anymore. This made Ji Situi so angry that he was at a loss for words.

After a round of appeasement, promises, and hints that if they didn’t work, they would be sent to the labor reform team to taste the legendary whip of Fu Youdi, the morale in the sulfuric acid workshop was finally stabilized, and production returned to normal. Only then did Ji Situi find time to rush to the caustic soda workshop. Outside the workshop, large and small water tanks and a large amount of salt had already been piled up. Bingfeng was leading people to install the equipment.

“We have salt, tap water, and water tanks. While the project is not yet finished, let’s first prepare the saturated brine,” said Bai Yu, who had volunteered to bring students to help. Although he was a teacher, he was also a chemistry enthusiast.

“This salt won’t do,” Xu Yingjie shook his head. “It’s crude salt! There are too many impurities.”

The principle of producing caustic soda by electrolysis of salt is very simple. Saturated brine is directly electrolyzed to decompose into sodium hydroxide—also known as caustic soda—and at the same time, chlorine and hydrogen gas are also produced. However, the salt sent from the Yanchang Village was unrefined crude salt, which contained not only sodium salts but also various impurities such as potassium salts, magnesium salts, and sulfates. These impurities would affect the decomposition efficiency during production and damage the precious electrodes.

Therefore, before electrolysis, the crude salt must first be treated and refined to remove impurities, so that it becomes a pure saturated sodium chloride solution before it can be put into production. In the modern era, with a highly developed industrial system, the caustic soda industry could purchase refined sodium chloride products. Here, everything had to be done by oneself. The more backward and primitive the industry, the more self-supporting things were needed.

Ji Situi first analyzed the salt sent over. The quality of the salt from Yanchang Village was very high, and the content of sulfate, which had the greatest impact on electrolysis, was extremely low. This was good news for him: the industrial method of removing sulfate was to use barium chloride—he didn’t have this, and barium chloride was a highly toxic chemical. Even if he could synthesize it, he didn’t want to. As for the content of calcium and magnesium salts, it was not high either, making it a very ideal industrial salt.

He asked people to pour baskets of crude salt into the settling tank and add water until it was saturated. Then, Bai Yu, who was in charge of refining the electrolyte, took the soda ash and caustic soda he had received and added them in proportion according to the tested composition of the brine, so that the calcium and magnesium salts in it would react with them to form calcium chloride and magnesium hydroxide, which would then precipitate out. The clear liquid on top was the saturated sodium chloride solution for electrolysis. Because caustic soda and soda ash had been added, it had to be neutralized with a small amount of dilute hydrochloric acid.

The electrolysis of salt in production is a continuous process, and saturated sodium chloride solution must be continuously replenished into the electrolytic cell. Therefore, the refining of brine is carried out continuously throughout the electrolysis process.

The intermittent refining method of producing one tank at a time is simple to operate and requires simple equipment, but the labor intensity is too high and consumes too much manpower. Generally, a continuous refining method is used in industry. Although Ji Situi was using a native method, he still decided to make the production as automated as possible.

Ji Situi, based on his own conditions—having a tap water supply—decided to use continuous operation during the salt dissolving stage in formal production. Water would flow in from the bottom of a dedicated salt dissolving tank, pass through the salt layer in the tank, and overflow from the upper outlet of the tank. Salt would be added intermittently by manpower to maintain a certain salt layer. The dissolved brine would be saturated brine, which would be introduced from the salt dissolving tank to the settling tank for neutralization.

In order to reduce the labor intensity, the brine tanks were arranged in a stepped manner, one higher than the other, so that the brine could be transported using the principle of potential difference and siphon. From low to high, they were the salt dissolving tank, the settling tank, and the neutralization tank. Finally, the saturated sodium chloride solution flowing out of the neutralization tank was sent to the heating tank.

This system was simpler than the one used in industry and did not require any mechanical assistance. A small amount of manpower was sufficient.

“You even have to add caustic soda to make caustic soda!” said Bai Yu, who was in charge of treating the brine with his students.

Xu Yingjie said, “These are two different things. You are making refined brine, which has nothing to do with the production of caustic soda.”

Bai Yu said, “Fortunately, we brought a lot of chemical products. Otherwise, without them as a ‘primer,’ wouldn’t we be unable to start production?”

“That’s not necessarily the case,” Ji Situi said while paying attention to the reaction in the tank. “It would just be very damaging to the electrodes. It’s not impossible to refine sodium chloride physically. But it requires a large investment and has to start with directly modifying the salt production equipment in Yanchang Village.”

“The salt production equipment in Yanchang Village has already been modified a lot, hasn’t it?”

“The modification project carried out by Engineer Wang was mainly aimed at increasing production. He used windmills to lift the brine and sun-dry it, shortening the concentration time of the brine,” Ji Situi had been to Yanchang Village several times because of his business.

“Speaking of refining, it’s definitely not possible without a boiler,” Ji Situi continued. “The Planning Committee originally said that they would set up a refined salt factory in Bopu. Once our caustic soda workshop is put into production, this project will have to be launched.”

“A high tide of construction in the chemical industry!” Xu Yingjie said with emotion.

“It’s about time for the chemical industry. Think about it: pesticides, fertilizers, explosives, and medicine. With these four magic weapons, won’t we dominate the world!” Bai Yu was full of enthusiasm.

“We’re still far from that. Don’t try to bite off more than you can chew,” Ji Situi said. “There are still many supporting facilities and equipment needed in the chemical industry. The practical problems in production have to be solved slowly. Take the first batch of sulfuric acid produced by the sulfuric acid plant, for example. The impurity content is very high, which is very dangerous in some chemical production processes. But improving the purity requires meeting many conditions.”

He used an analogy, “This is like a jigsaw puzzle. After making the three acids and two alkalis, we have only just found the four corners of the puzzle and seen hope. But it will still take a long time to actually piece together the complete picture.”

Xu Yingjie commented, “This is like someone trying to make nitroglycerin from glycerin produced by the saponification method. The theory is correct, but in practice, it will be fatal.”

The entire process of brine reaction and precipitation would last for 24 hours. Ji Situi then led people to the lime kiln himself. Quicklime had already been prepared here. According to the data in the process manual, he calculated how much chlorine gas would be produced in 72 hours of continuous production and how much slaked lime would be needed to absorb it. He weighed a sufficient amount of quicklime and then slowly sprayed water on it to let it slake slowly. After the slaking was complete, he had the workers sift the slaked lime and then pack it in baskets and transport it to the caustic soda workshop.

Ji Situi had Xu Yingjie measure the water content of the slaked lime, which was about 3%. This ratio was a bit too high, so he had people pile the slaked lime in the shed for a few days. There was still some quicklime in the slaked lime, so the water would continue to slake the lime. In this way, the water content would drop to a suitable level below 1% after a few days.

After everything was ready, a large amount of white precipitate had already settled in the brine refining tank the next day. The clear liquid on top was extracted and tested, and the results showed that it already met the requirements for electrolysis. Bai Yu used the siphon principle to draw the clarified saturated sodium chloride solution into the heating tank. Ji Situi set up a fire under the heating tank to heat the brine to 70°C. The heating was to remove the carbon dioxide in it.

The white precipitate in the settling tank was collected. Its main components were calcium chloride and magnesium hydroxide. Both were useful chemicals and could not be easily discarded. In particular, calcium chloride could be used by the pharmaceutical factory to make calcium chloride injections and tablets to treat various diseases caused by low calcium. In industry, it could be used as a common desiccant, an antifreeze for the construction industry, a refrigerant for refrigeration equipment, and for deinking waste paper… Finally, it could also be used to make tofu.

Ji Situi separated them by taking advantage of their different solubility in water—calcium chloride is very soluble, while magnesium hydroxide is insoluble in water. By adding water, the calcium chloride would dissolve and could be poured out for separate treatment. The insoluble part was magnesium hydroxide. Although magnesium hydroxide was not as versatile, as an alkaline salt, it could replace caustic soda and lime as a neutralizer for acidic wastewater; it could be used as an oil additive for anti-corrosion and desulfurization; it could be used for insulation materials and as a building flame retardant. It was also an excellent desulfurizer, which was exactly what Ji Situi’s sulfuric acid workshop’s flue needed to effectively purify the polluted gas during the acid production process.

The heated sodium chloride solution was drawn into the electrolytic cell and filled. Ji Situi pulled the switch, and the entire electrolysis process began automatically. He wore a set of anti-electric labor protection clothing and anti-electric rubber-soled shoes. He used a test pencil to measure the surroundings of the electrolytic cell and the workshop floor—there was no leakage.

The electrolyte began to flow out of the outlet. The color was clear, and no terrible black liquid flowed out. He waited silently for five minutes to calculate whether the flow rate of the electrolyte was normal. Finally, he measured the temperature and voltage in the cell—everything was normal. Whether the temperature and voltage were normal determined the electrolysis efficiency in the cell.

“Is the liquid coming out now the caustic soda solution?” Bai Yu asked.