According to H. W. Nernst theory, the electrode potential of gas is determined by the effective concentration of gas on the electrode. Hubble realized that the electrode potential is determined by the ratio of gas activity of anode and cathode. In the paper on electrochemical reduction of nitrobenzene published in 1898, Hubble first put forward the viewpoint that the electrode potential determines the reducing ability, and thought that the higher the electrode potential, the stronger the reducing ability of the reducing agent. Early researchers usually used a relatively constant current density to gradually increase the cathode potential. According to Haber, this is equivalent to using a series of chemical reductants with gradually increasing reducibility and generating a series of main reduction products at the same time. Hubble plans to change the current during electrolysis and keep the potential of the polarized cathode unchanged at the turning point of the current density-electrode potential curve, so that the released hydrogen can be used to reduce the depolarizer. In order to gradually separate the main reduction products from the low cathode potential, Hubble used platinum (sometimes nickel) with low hydrogen overpotential as the electrode. He believes that electrodes with high hydrogen overpotential, such as zinc, will produce a strong reduction reaction. He adopted Lejin's suggestion, using an auxiliary electrode to measure and control the potential of the cathode, and connecting the auxiliary electrode and the cathode with a thin-walled capillary glass tube, thus eliminating the potential drop through the electrolyte.
He used platinum as cathode to electrolyze the alkaline solution of nitrobenzene at low potential. Unexpectedly, the main product is azobenzene oxide. Through a series of studies on the reduction reactions of nitrobenzene, nitrosobenzene and benzene, Harper proved that the electrochemical reduction reaction and the common chemical reduction reaction follow the same steps: RNO2 (nitrobenzene) →RNO (nitrosobenzene) →RNHOH (benzene) →RNH2 (aniline), and other products come from side reactions. Azobenzene oxide appears as the main reduction product, which is due to the dehydration reaction of nitrobenzene and benzene in alkaline solution:
RNO+ RNHOH=RNONR+H2O
Hubble proved that nitrosobenzene and benzoxazine exist in common chemical reactions and electrochemical reactions. Nitrobenzene is a stronger depolarizer than nitrobenzene, so it can only exist in extremely dilute solution. Nitrobenzene and benzodiazepines can be detected by azo dye fixation. He also successfully prepared a large number of benzoxazines by electrochemical reduction of nitrobenzene, which was carried out in weak alkaline buffer solution. Nitrobenzene can be immediately reduced to benzoxazine at an appropriate high potential, so as to avoid the formation of azobenzene, but the potential should not be too high to avoid further reduction. He also discussed the formation of azobenzene, which is also the electrochemical reduction product of nitrobenzene. Azobenzene oxide only produces diphenyl hydrazine under strong reduction. Haber pointed out that nitrobenzene rapidly generates azobenzene in alkaline solution according to the following reaction:
2r NO2+3 rnhnhr = RNONR+3 rnnr+3H2O…………
Hubble believes that the main product of nitrobenzene electrolysis in alkaline solution of low hydrogen overpotential cathode is azobenzene oxide; Electrolyzing nitrobenzene with a cathode with high hydrogen overpotential has a stronger reduction effect, resulting in diphenylhydrazine and finally aniline.
Hubble also studied the electrolytic reduction of nitrobenzene in acidic solution, and found that the reaction (1) became very slow. In strong acid solution, benzene is quickly converted into p-aminophenol, and diphenyl hydrazine is converted into benzidine. The main products are p-aminophenol, benzidine and aniline, and their proportions are determined by acid concentration.
Hubble's success has attracted worldwide attention and has become a great driving force for his research in the field of electrolytic reduction and oxidation. 1898, Harper was promoted to associate professor at the age of 30 after entering Karlsruhe University of Technology for four years. In the same year, his first book, Fundamentals of Industrial Electrochemistry, was published, which further enhanced his reputation. He established a recognized school of electrochemistry. This is his most creative period, but continuous overwork has damaged his health. He is so absorbed in his work that he forgets himself. In his early research career, he just sought a short relaxation among his small group of like-minded friends. Most of his contacts are teachers, writers and artists. Harper likes talking with them, but even on this occasion, he doesn't want to rest his mind. 1902, Hubble was sent by the German Bunsen Society as a representative to attend the annual meeting of the American Electrochemical Society, from which we can see Hubble's fame. His outstanding talent and rigorous attitude left a deep impression on his American counterparts. His long report at the meeting was well received by European and American chemists. The report was published in the German Journal of Electrochemistry 1903, and is considered as an outstanding document with permanent value in the history of electrochemical industry. 1904, Hubble began to study the equilibrium of ammonia. At that time, he was a scientific adviser to the Vienna margulies brothers, who was interested in new industrial nitrogen fixation methods. Through the mixed gas of nitrogen and hydrogen, ammonia can be continuously synthesized under the action of catalyst. However, the maximum yield is always limited by the ammonia balance. Hubble decided to study the problem first. Chemists have done experiments on the reduction and regeneration of calcium nitride and manganese nitride, but because of the high temperature, these metals can not be used as catalysts. 1884, Ramsey and Yang tried the thermal synthesis of ammonia. They found that at 800℃, using iron as a catalyst, ammonia would never be completely decomposed. So, they tried to use its reverse reaction to synthesize ammonia, but they couldn't get ammonia at all. It is generally believed that nitrogen is extremely inert and can only be hydrogenated at high temperature. In fact, ammonia is completely decomposed at high temperature.
His first exploration experiment was to synthesize ammonia with iron as catalyst at 1020℃. Although Hubble fully knew that high pressure was beneficial to ammonia synthesis, he chose atmospheric pressure because the required equipment was simple. To Hubble's surprise, the experiment was very smooth, and the ammonia balance was achieved for the first time. However, the concentration of ammonia is very low, ranging from 0.005% to 0.012%, so it is difficult to choose a data that is closest to the truth. At that time, he was more inclined to the upper limit, but later research showed that the lower limit was close to the real value, and the high yield might be the special function of the new ironmaking catalyst. The original purpose of determining the equilibrium state of ammonia was achieved. He used this passage to describe his experimental results: "When the reaction tube is heated above the dark red heat, only a small amount of ammonia is produced under normal pressure without catalyst. Even if the pressure is greatly increased, the equilibrium position is still not ideal. Under normal pressure, if the catalyst is used, the temperature should not be higher than 300℃. "It seems that there is little hope for direct synthetic ammonia as the basis of industrial nitrogen fixation. Harper dropped the question and ended his cooperation with the Maguri brothers. 1906, when Nernst inspected the experimental data of gas equilibrium, he found that in the case of ammonia, Hubble's data was quite different from the calculated value of thermodynamic theorem. Therefore, Nernst re-measured the equilibrium data of ammonia at high pressure (50 atmospheres). The purpose of using high pressure is to increase the concentration of ammonia, thus reducing the experimental error. Nernst synthesized ammonia under pressure for the first time. He got much less ammonia than Hubble's data, which was close to the theoretical value. For example, at 1000℃, the theoretical values are 0.0045%, Nernst 0.0032% and Hubble 0.0 12%. 1in the autumn of 906, Nernst talked about this situation in his letter to Hubble. Therefore, Hubble and Le Seger used the original method to re-measure the equilibrium data of ammonia at one atmospheric pressure. The experiment was done in detail, and the results were in good agreement with the previous values. For example, at 1000℃, the new value is 0.0048%, which is close to the lower limit of the original determination of 0.005%. At the same time, it is proved that Hubble's initial approximate true value of 0.0 12% is indeed too high, as Nernst insisted. The difference between Hubble and Nernst's experimental data has been greatly reduced, but it has not been completely eliminated. Nernst reported his stress experiment at the meeting of 1907 German Benson Society. During the discussion, Hubble announced the withdrawal of the original valuation of 0.0 12% and announced the new value. Hubble's value is still about 50% higher than Nernst's. Nernst refused to admit the accuracy of Hubble's new measurement, thinking that the concentration of ammonia in the equilibrium mixture system was very low at one atmospheric pressure, and suggested that Hubble conduct research at high pressure to eliminate the source of error. Nernst thinks his data is credible, which is consistent with the thermodynamic theorem.
Hubble firmly believes in the accuracy of his data, regards Nernst's point of view as a great shame and feels that his honor has been damaged. Hubble and Luo Segur immediately re-measured the ammonia balance accurately. The experiment was carried out at 30 atmospheres. Their equipment is simple, but it can perfectly meet the experimental purpose. Through the thermal decomposition of ammonia, a mixture of nitrogen and hydrogen is obtained, which passes through a thick-walled quartz tube with an iron or manganese catalyst. Then, the equilibrium mixture was quickly taken out for cooling analysis. The Hubble free energy equation derived from the new data shows that the output of ammonia can be high enough to meet industrial use, but the conditions are harsh and difficult to achieve. For example, at 600℃ and 200 atmospheres, the conversion of ammonia reaches 8%. But at that time, the maximum pressure that the compressor could reach was 200 atmospheres, which was not used in large-scale chemical operation. The activity of the best catalysts (iron, manganese and nickel) was greatly reduced at 700℃. Therefore, if the obstacles of catalyst and high pressure are overcome, it will undoubtedly open up a bright road for industrial synthetic ammonia, and the problem of nitrogen fixation will be solved. Hubble accepted the challenge because he had the help of his close ideal partner, Luo Seger. High-pressure technology was quickly popularized and used in Karlsruhe laboratory, and was improved by Luo seguer. Rossegur is famous for his originality and first-class experimental skills. The research work started at 1908. They designed and manufactured a converter, which was installed in a steel high-voltage bomb and could work normally at 200 atmospheres. Everything is ready, just looking for a more active catalyst. After a long period of exploration, it is found that osmium has high catalytic activity below 550℃, but osmium is too rare. It was later proved that uranium had the same high catalytic activity. Fundamentally, the problem has been solved. Using new equipment and uranium as catalyst, the concentration of ammonia is already very high at 550℃ and 150 ~ 200 atmospheric pressure. Under the working pressure, after moderate cooling, the ammonia is liquefied and separated, and the mixed gas is recovered through the closed system of converter, compressor and circulating pump, while a proper amount of fresh mixed gas is continuously input, and finally a heat exchanger is installed. This device is simply a small factory, producing hundreds of milliliters of liquid ammonia per hour, with extremely low energy consumption. The prospect of industrialized synthetic ammonia seems bright. However, laboratory methods can rarely be directly used in industrial production, and experimental devices must be improved.
Synthetic ammonia is Hubble's greatest achievement in his life, but it didn't get the favor of industry immediately. What he got was indifference and doubt. Although BASF has a strong interest in nitrogen fixation and thinks that Hubble's research on electro-oxidation of nitrogen is very important, he has doubts about the prospect of Hubble's synthetic ammonia. Under the strong recommendation of Hubble's friend and colleague and BASF's consultant Karenger, BASF's technical leaders began to pay attention to Hubble's work. 1one day in July, 909, Dr. C. Bosh, an engineer from BASF, and Dr. A. Mittasch, a chemist, came to Karlsruhe to watch the demonstration experiment of synthetic ammonia. Tammy saw the flowing liquid ammonia with her own eyes and fully believed in the value of Harper's method. After returning to ludwigshafen, they immediately set about putting Hubble's achievements into large-scale industrial experiments. Three years later, a synthetic ammonia plant was officially put into operation. The honor of large-scale industrialization of synthetic ammonia has always belonged to Bosch. Although Karlsruhe laboratory has taken the most important step for the industrialized production of ammonia, there are still many thorny problems to realize industrialization. Under the leadership of Bosch, the successful solution of these problems is undoubtedly the most outstanding achievement in the field of chemical engineering. Hubble won the Nobel Prize in Chemistry in 19 19, and Bosch and Bergius won the same honor in 193 1 year. Harper said modestly in his acceptance speech: "People haven't fully realized that Karlsruhe Laboratory has not actually made any contribution to the industrialization of synthetic ammonia." While acknowledging the outstanding achievements made by Bosch and Burgess for the development of high-pressure method in industry, Harper and Luo Seger, pioneers of high-pressure method, should not be forgotten. As early as 1907, Hubble's laboratory was a famous high-voltage research center. After Belguise put forward the idea of high-pressure coal hydrogenation, he went to Karlsruhe for the first batch of experiments in 1908.
Before the 20th century 10, the research and industrial application of nitrogen oxidation under the action of electric arc developed rapidly. Hubble's laboratory has always been an important research center in this field. After the thermal balance of nitric oxide was measured by Nernst 1904, the pure thermal theory of arc nitrogen fixation was generally accepted, but it soon caused many doubts. Hubble found in an experiment that high yield is not consistent with pure heat theory, and electrical factors play a role to some extent. Hubble took great interest in this subject. During the period of 1906 ~ 19 10, he made a thorough and detailed study on nitrogen fixation under low temperature arc. Due to the electrical activity of the reactants, at the same temperature, the content of nitric oxide in the electric equilibrium state exceeds that in the thermal equilibrium state. After the electric field is removed, the excess nitric oxide will decompose until the thermal balance is completely established. Because the speed of this process decreases rapidly with the decrease of temperature, there is almost no decomposition at a sufficiently low arc temperature, and under such conditions, the output of nitric oxide reaches the maximum. When the final thermal balance is reached, high temperature arc will inevitably lead to low yield. Hubble completely confirmed this theory. The establishment of electric balance has also been proved. Let the air slowly pass through a 6 cm AC arc and burn in a long, narrow and cold quartz tube under the pressure of 100 mm Hg. The yield of nitric oxide thus obtained is much higher than that of arc at 2000℃. The higher the arc temperature, the more oxides are produced and the more important the decomposition is. Generally speaking, Hubble's work has great theoretical and technical value. Hubble's interest in flame and combustion is closely related to his early research on fuel technology. Thermodynamics of industrial gas reaction published by 1905 involves the study of gas reaction in flame. The initial experiment was to study the water vapor balance by using the homogeneous gas phase of hydrocarbon flame. Smither Wells invented the flame separator and analyzed the main combustion products of the inner cone of the flame. Twenty years ago, Le Chatelier first calculated the dissociation constant of carbon dioxide, and calculated the flame temperature according to the composition of flame gas. In 1865, De Ville obtained the temperature of the flame in carbon monoxide through a cold tube. Hubble uses a new type of Devili tube with high cooling efficiency to obtain the gas in the flame cone area. He proved that when the gas mixture passes through an inner cone with a temperature not lower than 1250℃, the equilibrium is actually established instantaneously. According to the relationship between equilibrium constant and temperature, Hubble deduced an improved and widely applicable free energy equation. In this way, the gas at any point of the flame can be extracted and analyzed, and the temperature at that point can be obtained. Using this chemical flame thermometer, Hubble measured the temperatures of hydrocarbon flame, carbon monoxide flame, hydrogen flame and acetylene flame, respectively, and they were in good agreement with the data obtained by other researchers in different ways later. Hubble also studied the oxidation of nitrogen in flames. As we all know, nitrogen oxides will be produced when gas explodes, but few people pay attention to this process in the flame. Hubble found that in the carbon monoxide flame, nitrogen fixation hardly occurs at one atmospheric pressure, but at 10 atmospheric pressure, the output of nitrogen oxides greatly increases. Under similar conditions, the production of nitric oxide in hydrogen flame is only half of that in carbon monoxide flame. Hubble studied the characteristics of the inner flame cone. It is estimated that the wall thickness of the inner cone is only 0.1mm. Hubble proved that it is the coldest part of the flame, not the hottest part as previously thought. At the same time, this region has extremely fast reaction speed, strong chemiluminescence and high ionization degree. Hubble believes that there is a close internal relationship between the three.
1906, Harper was promoted to be a professor at Karlsruhe University of Technology. 19 1 1 was invited as the first director of the newly-built Institute of Physical Chemistry and Electrochemistry of Emperor William in Dahom, a suburb of Berlin. This research institute was formally established on 19 12. At Kaiser's inauguration ceremony, Hubble showed off his invented gas flute, which can detect the presence of dangerous gas methane in coal mines. It is durable and effective, but it has not been put into use. Hubble's initial work in Dahomey was to improve the research on synthetic ammonia, determine the ammonia equilibrium and related thermodynamic data as accurately as possible, and obtain the final free energy equation. At the same time, Hubble began to pay attention to the application of Planck's quantum theory in chemistry, and was the first person to realize the important significance of Planck's theory in chemistry. This became the basis of many of his works in Dahome. Hubble pays special attention to the application of new physical knowledge in chemistry. His frequent discussions with his good friend M. Born are of great help to his academic thoughts. Bonn has just put forward the ion lattice theory: the lattice energy of ions is determined by the distance and force between ions, and the reaction heat of solid reaction is equal to the algebraic sum of its component lattice energy. Bonn believes that lattice energy removes an electron from a gaseous atom, resulting in the sum of the energy of gaseous ions and the energy of ions forming crystals. Hubble clearly explained this energy relationship, so it is called Bonn-Hubble cycle, that is, lattice energy U is the algebraic sum of generation heat Q, dissociation energy D, sublimation heat S, anion ionization energy I and cation ionization energy E. Hubble also boldly applied Bonn theory to HCl gas, and obtained the reaction heat of H++Cl-=HCl, which is much smaller than the calculated value in the cycle. In order to explain this deviation, in 19 19, he put forward the viewpoint of ion deformation, which later produced fruitful results in Yang Si.