Study on the Ferric Molybdate Formaldehyde Catalyst With High Activity
LI Gao-lin 1, DENG Shao-liang2 , ZHOU Zhen-hua 1, WANG Bo1 ,QIAO Chuan 2，QU Jun-ying 2, ZHOU Huan-wen
（1. Xinjiang Markor Chemical Co., Ltd., Xinjiang Korla 841000, China;2. Dalian Reak Science Technology Co., Ltd., Liaoning Dalian 110021, China）
Abstract: The ferric molybdate with high activity was prepared by grinding mixed solid molybdate and ferric salt. It was characterized
by X-ray diffraction and scanning electron microscope,and its activity and selectivity were tested by experiments. The results showed
that the crystal of prepared ferric molybdate catalyst was complete, and the particle distribution was uniform; its activity and selectivity
Key words: molybdate; ferric salt ; grinding; activity; selectivity
Formaldehyde is an important chemical raw material, and my country's formaldehyde production capacity in 2018 About 39 million tons, with more than 600 sets of production devices. Due to safety, environmental insurance, unit consumption, energy consumption, formaldehyde quality and other factors, Yin Fasheng The production process is gradually being replaced by the iron-molybdenum method. The iron molybdenum method is based on high Based on high-energy iron-molybdenum catalysts, domestic catalysts have been difficult for a long time. To meet the technical requirements of the process, key indicators such as catalyst activity, Stability, mechanical strength, etc. are not small differences with international advanced catalysts Distance [1-3]. Therefore, the development of high-performance iron-molybdenum catalysts to achieve catalytic The localization of chemical agents is of great importance to the healthy development of my country's formaldehyde industry. realistic meaning. Iron molybdenum method formaldehyde process below the lower explosive limit of methanol-air The operation is carried out using highly active and highly selective iron molybdenum oxide catalysts. Under the reaction conditions of 240~400 ℃, the yield of formaldehyde can reach 91%~94%. Main reaction: CH3OH + 1/2O2 → HCHO + H2O Side reactions: CH3OH + O2 → CO + 2H2O CH3OH + O2 → HCOOH + H2O 2CH3OH → CH3OCH3 + H2O Ferromolybdenum was first proposed by Adkins and Peterson in 1931 Mixed oxides can be used as catalysts for the selective oxidation of methanol to formaldehyde. In 1965, the Swedish PERSTORP company used iron molybdenum formaldehyde catalyst for the first time. The chemical agent realizes the industrial production of methanol oxidation to formaldehyde. Continuous improvement of molybdenum method formaldehyde process and continuous improvement of catalyst performance Gao, after the 1980s, newly built formaldehyde plants in foreign countries mainly The iron-molybdenum method is the main method. The catalysts currently used in industrial applications include Johnson Matthey FORMOX and Klein's FAMAX catalyst, two catalysts The reaction performance is similar, and the chemical composition of the catalyst is basically the same (MoO3: 80%, Fe2O3: 20%). The first domestic iron-molybdenum method formaldehyde plant was put into operation in 1996 Introducing the Swedish PERSTORP process (now Johnson Matthey Harvest) After 2000, due to downstream processes such as BDO, the high concentration of The demand for formaldehyde continues to increase, and the iron-molybdenum method formaldehyde plant increases rapidly. In recent years, due to environmental protection, safety and other factors, the newly built formaldehyde equipment The iron-molybdenum method is basically used for the construction. By the end of 2018, the completed There are more than 80 sets of iron-molybdenum method formaldehyde plants, and all catalysts need to be imported. close Over the years, many domestic scientific research institutes have developed iron molybdenum formaldehyde catalysts research, but most of them stay in the laboratory research stage and go into industry There are not many tests and applications. In this study, the method of grinding molybdate and iron salt by solid mixing Preparation of iron-molybdenum method for formaldehyde synthesis catalyst by X-ray diffraction, scanning The crystallinity and particle size distribution of the catalyst were studied by surface electron microscopy, and the The performance of the agent was evaluated in the laboratory. 1 Experimental part 1.1 Experimental materials Ammonium molybdate, ferric nitrate, nitric acid, deionized water. 1.2 Preparation of Fe-Mo catalysts The molybdenum-iron mixed material was prepared by solid-phase mixing. 63.4 g of ammonium heptamolybdate, 56.8 g of ferric nitrate and an appropriate amount of nitric acid were added. into the ball mill, and use different diameter grinding balls to grind. The most important thing is that the ferric nitrate and ammonium molybdate are fully reacted and evenly ground, and the grinding time is 4~12 h. Take out the material, wash it with 5 times the amount of water repeatedly to remove ammonium nitrate, The filter cake was air-dried at room temperature to a water content of less than 20%, and then Dry at 100 °C until the water content is less than 5%, and then calcined at 500 °C for 5 h, pressed into tablets, and finally pulverized to 40-80 Items to use. 1.3 Scanning Electron Microscope (SEM) Analysis was performed using a Hitachi S4800 SEM, the main observations Microscopic particle structure of catalysts
1.4 X-ray diffractometer (XRD)Using an X-ray diffractometer (XRD-7000) from Shimadzu, Japan,Investigation of the crystallinity of iron molybdate and the dispersion of molybdenum oxide in the catalyststate.1.5 Catalyst performance evaluation testThe catalyst was evaluated by a laboratory test evaluation device.The filling volume of 40-80 mesh catalyst is 3 mL, which is suitable for the catalyst respectively.The O2 concentration, reaction temperature, reaction space velocity and methanol concentration used were investigated, and the optimal reaction conditions for the catalyst were obtained.The catalyst evaluation process is shown in Figure 1: Mixed gas and methanolAfter mixing in a certain proportion, it is preheated to the reaction temperature in a preheater.The methanol-containing mixed gas reaching the reaction temperature enters the reactor and catalyzesThe oxidation reaction occurs when the agent contacts, and most of the methanol is oxidized to formaldehyde, which is reversed.The reacted mixed gas is absorbed by water, resulting in a concentration of about 37%The formaldehyde solution after absorption, the exhaust gas after absorption was analyzed by chromatography to confirmTo determine the concentration of by-products, the absorbed formaldehyde solution was analyzed by titrationFormaldehyde and formic acid concentrations.
Catalyst Evaluation Device:
2 Results and discussion2.1 Preparation of catalystsFigure 2 is the SEM image of the iron-molybdenum catalyst.
It can be seen from this that the co-grinding method of ammonium molybdate and ferric nitrate is used.The microscopic particle size distribution of the catalyst prepared by the method is uniform, and the particle-to-particleThe boundary between the two is obvious, and the particle size distribution is around 100 nm, which is different from the traditional method.Catalyst prepared by co-precipitation method of ammonium molybdate solution and ferric nitrate solutionThe particle size distribution is basically the same.Figure 3 shows the XRD analysis results of the catalyst, from which it can be seen that the catalystThe chemical agent has a complete crystalline state of iron molybdate, which has a smallerMolybdenum oxide crystalline peak, indicating excess oxidation during catalyst synthesisMolybdenum is evenly dispersed into the iron molybdate crystals, so that during useIt can well supplement the loss of molybdenum oxide in iron molybdate, so as to ensureThe catalyst has high activity during long-term use.
2.2 Evaluation of catalystsIn the process of industrial use, the formaldehyde catalyst mainly adjusts the reactionThe space velocity of the device, the oxygen content of the reactor inlet, the reactor inlet AThe alcohol content and the temperature of the reactor can adjust the production situation of industrial formaldehydesituation, therefore, during laboratory studies, it was determined that theAfter the preparation conditions, the reaction of the catalyst under different process conditions is mainly affected.The response performance was investigated.In the laboratory, the reactions were investigated under different process conditions.Space velocity, oxygen content, methanol content and reaction temperatureEffects of aldehyde catalysts on the oxidation of methanol to formaldehyde performance.
Reaction performance of catalysts at different space velocities :
Through the investigation of the reaction space velocity, it is found that the catalyst is in the space velocityIt is used under the conditions of 6 000~12 000 h-1, and has a suitable formaldehyde yield, which can meet the needs of catalyst application.
Reaction performance of catalysts under different oxygen content :
Through the investigation of the O2 content at the inlet of the reactor, it was found that the catalystUsed under the condition of O2 content of 6v%~12v%, it has suitableThe formaldehyde yield can meet the needs of catalyst application.
Reaction performance of catalysts with different methanol contents :
Through the investigation of the CH3OH content at the reactor inlet, it was found that the catalystThe chemical agent is used under the condition that the CH3OH content is 8 v%~10v%,It has suitable formaldehyde yield and can meet the needs of catalyst application.Through the investigation of different temperatures of the reactor, it was found that the catalyst was inIt can be used under the condition of 250~380 ℃, with suitable formaldehyde yield,Can meet the needs of catalyst applications.Through the above research and investigation, the iron molybdenum method formaldehyde catalyst was determined.The best use conditions are: airspeed 6 000~12 000 h-1, mixed gasOxygen content 6 v%~12 v%, methanol content 8 v%~10 v%, useThe temperature is 250~380 ℃, and it can play a catalytic role under this condition.optimum performance of the agent.
3 Conclusion (1) The catalyst was confirmed by scanning SEM and XRD analysis.The agent has better crystallinity of iron molybdate, more uniform particle size distribution andThe uniformly dispersed molybdenum oxide structure ensures that the catalyst has a highUse performance. (2) Through the investigation of different reaction conditions, the catalyticThe best conditions for the use of the catalyst, from the evaluation results of the catalyst, the catalystThe performance of the agent can meet the needs of current industrial applications.