A technology related to the national economy and people's livelihood
——The invention and application of chemical fertilizers in the first half of the 20th century. As the saying goes: "A single crop depends entirely on fertilizer." However, in Before the 20th century, the sources of nitrogen fertilizer needed for crops were very limited.
At the beginning of the 19th century, a large sodium nitrate mine was discovered in the desert area of ??Chile, and it was quickly mined. By the middle of the 19th century, the nitrogen fertilizer used in the world mainly came from This deposit in Chile. However, since the production of natural saltpeter is extremely limited, the mine in Chile can only be mined for a few decades, so it was very rare in the world at that time. In addition to scarcity, the long distance from America to Europe is an important disadvantage.
In the late 19th century, with the gradual rise of the coking industry in European countries, people also discovered that using ammonia, a by-product of coking, as raw material, ammonium sulfate could be made and used as nitrogen fertilizer. In this way, cheap Coking by-products are increasingly becoming another source of nitrogen fertilizer. However, it is still far from meeting the needs. The nitrogen fertilizer used in agriculture at that time mainly came from organic by-products, such as: human and animal manure, peanut cakes, bean cakes, smelly fish, rotten shrimps and animal scraps, etc. In addition, a very small amount of nitrogen comes from nitrogen oxides formed by thunderstorm discharges.
With the development of agricultural production and the continuous increase of the earth's population, the amount of natural nitrogen compounds has become increasingly unable to meet the needs of crop growth. Countries around the world are increasingly demanding the establishment of large-scale production plants for nitrogen compounds. industry.
In 1898, the British physicist Crooks was the first to realize the importance of chemical fertilizers to mankind. He gave a speech at the British Science Association held in Bristol. After listing a large number of facts People were warned: "Due to the increase in population, the land has become narrower. If this continues, the era of food shortage will come. The solution is to find new nitrogen fertilizers."
(1) To the air Need nitrogen fertilizer
Where to find new nitrogen fertilizer? Scientists naturally thought of air. Scientists already know that nitrogen accounts for a considerable part of the air around the earth, about 79%, and it can be said to be inexhaustible. However, although there is a large amount of free nitrogen in the air, the chemical properties of nitrogen are very inactive, and it is still very difficult to directly utilize it. Scientists have discovered that under normal temperatures in nature, free nitrogen can only be directly utilized by a type of bacteria that grows on leguminous plants, called rhizobia. Rhizobium has a wonderful ability, that is, it has the function of fixing nitrogen. It can convert nitrogen in the air into the nitrogen fertilizer it needs at room temperature. Therefore, getting nitrogen fertilizer from the air has become the goal pursued by scientists.
Crooks' warning first attracted Germany's attention, because Germany had very few colonies and had to be self-sufficient in food. Like scientists from other European countries, German chemists also want to directly combine nitrogen in the air with hydrogen to synthesize ammonia and turn it into ammonium sulfate as a fertilizer. However, this is not as simple as combining oxygen and hydrogen to form water vapor. Many chemists think it is difficult to do, and even the famous chemist Liebig thought it was impossible.
However, Liebig’s conclusion is indeed a bit too far. After mankind entered the 20th century, scientists gradually turned all this into reality. They have developed several types of air nitrogen extractors that extract nitrogen from the air as compounds. Fixed method. Although not very practical, it lays the foundation for future development.
In early 1900, Professor Ostwald of the University of Leipzig announced after many years of research on catalysts that ammonia had been successfully synthesized. He used iron wire as a catalyst to decompose ammonia into nitrogen and hydrogen, and in turn synthesized ammonia from 6% of the volume of nitrogen and hydrogen. This is indeed possible, and using catalysts may allow for previously impossible combinations of nitrogen and hydrogen. To this end, he requested assistance of 1 million marks from the German Baden Aniline Soda Ash Company (BASF Chemical Company).
However, there are still many scientists who are skeptical. Among the many doubters, one person raised questions after careful consideration. He is Bosch, a young engineer who has just worked for BASF for one year. He was only 26 years old at the time.
After Bosch learned about Ostwald's successful method of synthesizing ammonia, he re-conducted the experiment of this great scientist. As a result, he found that the so-called synthetic ammonia was not synthesized at all, but was actually caused by When the ammonia decomposition experiment was carried out using iron wire, he thought again and again, wondering whether he should point out the error of this great scientist. Finally, he mustered up the courage to publish his research results and officially pointed out Ostwald's error.
For many famous scientists, Bosch was indeed a nobody. Some people accused him: "What do people who are new to the job know?"
However, some scientists later repeated Experiments were conducted, and the results proved that Bosch was correct. They began to look at Bosch with admiration, and Bosch became famous. From then on, he became interested in the method of fixing nitrogen in the air.
In 1902, scientists Frank and Kahler heated calcium carbide to more than 1000°C in an electric furnace to combine it with nitrogen in the air to produce lime nitrogen. However, this did not mean that artificial nitrogen was achieved. The dream of synthesizing nitrogen fertilizer is because to make calcium carbide, quicklime and coke must be put into a high-temperature electric furnace above 2300°C. This consumes a lot of electricity and is not practical. Therefore, there is no fundamental solution to the problem of chemical fertilizers needed in agriculture.
In 1903, Birkeland and Ed developed another method of fixing nitrogen. They used the method of releasing electric sparks in the air to combine the nitrogen in the air with oxygen to generate nitric acid. Calcium nitrate is then produced, but the same problem is: this method still requires a lot of electricity.
After Ostwald announced his experimental results, Bosch and others pointed out his mistakes, and finally, he himself realized his mistakes. He bent down and continued to conduct in-depth research on catalysts.
The University of Leipzig where Ostwald was located had built a large laboratory as early as January 1897, so he had the indispensable conditions for in-depth research. He worked with researchers on catalyst research. Once, they discovered that using only one ten millionth of a gram of colloidal platinum catalyst could increase the decomposition rate of hydrogen oxide by a million times. He firmly believes that catalysts must play an important role in industrial production. For a long time, what kind of catalyst is most effective for what kind of chemical reaction? What kind of catalyst structure accelerates or delays the chemical reaction? People don't understand these issues, and they all explore them based on experience. Ostwald conducted theoretical research, and he defined a catalyst as follows:
“A substance that can change the reaction rate before the final product of a chemical reaction occurs.”
He also vividly compared the catalyst to "mechanical lubricating oil". It does not give mechanical energy, but can reduce friction.
Osterwalder opened up the way for the industrial use of catalysts, one of the symbols of modern chemical technology, and paved the way for synthetic fertilizers. Without his catalyst theory, others would not have it in the future. Synthetic fertilizers.
(2) Harper contributed a lot
Up the Rhine River from Port Louis, where BASF is located, there is a place called Karlsruhe, where there is a famous The university is called Karlsruhe Institute of Technology. Fritz Haber, a professor of chemistry at the college, was also deeply affected by Crooks' warning at this time and began to devote himself to the research of ammonia synthesis.
In early 1902, in order to study the theory of ammonia synthesis, Harper went to the United States for a scientific investigation. He made a special trip to visit a factory in Niagara that produced fixed nitrogen that simulated natural thunderstorm discharges. Through the visit, he developed a strong interest in the research of fixing nitrogen into nitrogen oxides and ammonia. After returning to Germany, he dived into the laboratory and began this epoch-making research work.
In 1904, two chemical entrepreneurs in Vienna, the Margulis brothers, realized the great significance of this work, came to the Karlsruhe Institute of Engineering and formally signed an agreement with Haber. A contract to study the synthesis of ammonia from nitrogen and hydrogen elements. From then on, Haber and his students and assistants devoted all their efforts to experimental research on ammonia synthesis.
Harper studied the synthesis theory of ammonia, starting from the equilibrium conditions of reversible reactions. Harper believes that the knowledge of catalysts alone is not enough, and a new understanding of chemical reactions is needed - chemical equilibrium theory. The core of this theory is: the raw materials generally do not all become product substances, and at the same time, the generated substances will also A reverse reaction occurs.
Under certain reaction conditions, that is, concentration, temperature, and pressure, this forward and reverse reaction is balanced.
Harber realized that if the reaction conditions were adjusted according to this idea, ammonia synthesis, which was previously considered impossible, might be possible. Harper first thought that perhaps high temperatures would carry out this reaction. He began to conduct experiments according to his ideas, but the results were unexpected. When the temperature increased to 1000°C, the ammonia production was only 0.012% of the raw material volume, which was not as good as the production at low temperature. However, when the reaction temperature is lowered, the reaction becomes very slow. Harper believed that in order to speed up chemical reactions, appropriate catalysts were needed.
For more than a year from April 1904 to July 1905, although Harper and the others persisted in doing various boring experiments in the laboratory day and night, almost every experiment failed. The results were disappointing. As a result, the Margulis brothers canceled their financial support for the project when they saw that there was no profit. As a result, Harper fell into an extremely embarrassing situation.
At the same time, Professor Walter Hermann Nernst, who was studying chemical equilibrium theory at the University of Berlin, had also invested in research on the theory of ammonia synthesis. He personally built an autoclave to carry out high-temperature and high-pressure ammonia synthesis. experiment. After experiments, he found that there was something wrong with Haber's experimental results. The number was too large. In fact, it was only 0.0032%, which was an order of magnitude smaller. This proved that Haber's experimental results were not feasible.
In order to industrialize his research, Walter Hermann Nernst asked a well-known chemical company to manufacture equipment. Although the pressure was not too high, this company It was still difficult to produce equipment that could withstand such high temperature and pressure, so he made a huge mistake and gave up the idea of ??industrialization and immersed himself in laboratory research.
Although Haber was wrong in his calculations, in the debate with Nernst, he figured out that in order to further increase production, it was necessary to apply high pressure, Lower the temperature and use a catalyst.
Nernst was discouraged, but Haber was not. He started a new experiment where Walter Hermann Nernst left off. At this time, he was not only familiar with the theory of this experiment, but also had the foundation for success.
Under the guidance of chemical equilibrium theory, Haber and others began to conduct experiments bit by bit and patiently. They experimented with what percentage of pressure and temperature the yield could reach. They also made great efforts to find the best catalyst. They once embedded a reaction vessel that could withstand hundreds of atmospheres of pressure into a gun shell, and used platinum, tungsten, uranium and other rare metals provided by the gas lamp company of the Aouel Society. Find new catalysts.
It was under such a predicament that Harper continued to experiment at the risk of high temperature and pressure. At the critical moment when Harper's experimental research had repeatedly failed and was at a loss, the Proceedings of the French Academy of Sciences reported that French chemists used high temperature and high pressure to synthesize ammonia, which caused an explosion in the reactor. After learning about it, Harper was deeply inspired. He decisively changed the experimental conditions, especially increased the reaction pressure and improved the process. Finally, exciting progress was made, and the production of synthetic ammonia was significantly increased.
In 1907, Harper and others selected osmium or uranium as a catalyst and successfully obtained 8.25% ammonia under unusual high-pressure conditions of about 550°C and 150 to 250 atmospheres, which was the first For the first time, 0.1 kilogram of synthetic ammonia was successfully produced, making it possible for synthetic ammonia to move beyond the laboratory stage. This is undoubtedly a breakthrough with practical value. At this time, Nernst used platinum powder or fine iron powder and manganese as catalyst at 50 atmospheric pressure and 685°C, but only achieved a yield of 0.96% ammonia. Haber's experiment was almost eight times better than Nernst's experiment.
This victory greatly encouraged Harper and his assistants. They had a hunch that the experimental research on ammonia synthesis had entered the practical stage, so they stepped up their research on the high-temperature and high-pressure ammonia synthesis process. After arduous experimental research, they obtained a series of first-hand experimental data, greatly accelerated the pace of experimental research, and continued to make exciting new progress.
Haber's scientific research results greatly shocked the European chemical industry. People in the chemical industry purchased his patent for ammonia synthesis. The discerning German Baden Aniline Soda Ash Company was the first to arrive and paid Haber $2,500. Booking fee and promised to purchase all his future research results.
However, many engineers in the company expressed uneasiness about the red heat of the steel reactor vessel, and were even more surprised by the high pressure, so they had doubts about its industrialization. They thought of the news about the reactor explosion in France and said worriedly: "The autoclave that exploded yesterday only has 7 atmospheres of pressure." The implication is that Haber's high-pressure experimental conditions may also cause an explosion.
In 1909, Harper proposed a new concept of "circulation". The so-called "circulation" is to return the nitrogen and hydrogen that have not undergone chemical reactions to the reactor, and to separate the reacted ammonia through condensation. In this way, the process is repeated to increase the yield of synthetic ammonia and make the process practical. The introduction of this concept can be said to be a decisive breakthrough in the process of ammonia synthesis moving towards industrialization. The German government attached great importance to it and immediately accepted and adopted this new idea.
On July 2 of that year, Harper built a small model of an ammonia synthesis device in the laboratory. This was the world's first model of an ammonia synthesis device. Bosch, together with his subordinate Mittach, came to receive Haber's experimental technology and equipment as a representative of the Baden Aniline Soda Ash Company. Harper demonstrated his ammonia synthesis device on the spot, which magically synthesized ammonia at a rate of 0.08 kilograms per hour. Bosch saw the liquid ammonia dripping with his own eyes. The experts who came to watch agreed that it would not be long before it would become a device capable of producing several tons per day, thus clearly foreseeing its industrialization prospects.
The Baden Aniline Soda Ash Company immediately bought Haber’s patent for ammonia synthesis and received all its research results. The two parties also signed an agreement. The main point is: No matter how the production process is improved, the ammonia synthesis How does the selling price fall? For every ton of ammonia sold by the Baden Aniline Soda Ash Company, Haber shares 10 marks, and its income never changes.
In 1919, the Swedish Academy of Sciences considered that the synthetic ammonia invented by Haber had played a huge role in the economy. After careful consideration, it officially decided to award Haber the highest honor and award in science in the world in 1918— —Nobel Prize in Chemistry in recognition of his outstanding contributions to the research of ammonia synthesis. Since then, he has become one of the world's famous chemists.