At present, the market price of adipic acid has dropped by 12,000 yuan (ton price, the same below) compared to the highest price in more than ten years, which highlights the competitiveness of the adiponitrile production plant that has been suspended for many years.
At the same time, this process has exceeded the patent protection period.
Under the circumstance that no breakthrough has been made in the butadiene technology route, it is time to re-integrate and develop the process for the production of adiponitrile by the adipic acid ammoniation method .
Ammonia reaction is mainly liquid phase
The reaction of adipic acid and ammonia first produces ammonium adipate, which is dehydrated and converted to amide, and the amide is continuously dehydrated to form adiponitrile.
Before adiponitrile is formed, ammonium adipate and amine adipate reach a certain degree of equilibrium.
The reaction needs to neutralize two molecules of ammonia and remove four molecules of water.
The overall reaction is an endothermic reaction.
The whole reaction can be divided into neutralization reaction and dehydration reaction according to the reaction process.
The dehydration reaction generally requires the addition of catalysts such as liquid phosphoric acid and its derivatives.
The production process of adipic acid ammoniation is mainly divided into gas phase method and liquid phase method.
The gas phase method and the liquid phase method use different catalysts.
The gas phase method usually uses silica gel and supported solid catalysts, while the liquid phase method mainly uses phosphoric acid and its esters.
In the gas phase method, adipic acid is heated and gasified first, and then reacted with ammonia gas.
The reaction temperature reaches 300℃~350℃.
The catalyst uses boron phosphate.
Due to the high reaction temperature, the adipic acid is partially gasified at the same time.
Decomposition, the selectivity is 80%.
Therefore, fluidized bed reactors and rapid gasification are generally used to improve selectivity.
The liquid phase method is to melt adipic acid under the condition of 200℃~300℃, react with ammonia gas in the presence of a catalyst, and then dehydration, deweight, chemical treatment and vacuum distillation to obtain higher purity The yield of adiponitrile is 90%~94%.
Because the reaction temperature of the liquid phase method is lower than that of the gas phase method, there are fewer by-products generated during the reaction, and the damage to the catalyst is relatively reduced.
There is no need to activate the catalyst as often as the gas phase method, so the adipic acid is aminated The liquid phase method is the main method.
Overcapacity prices cut in half
The production process of adiponitrile produced by adipic acid amination method was successfully developed by the French Rhone Planck in the late 1960s.
PetroChina Liaoyang Petrochemical introduced a full set of nylon production technology from France in the 1970s, and the adiponitrile production process adopted the adipic acid ammoniation method.
In 2002, due to the high raw material cost of adipic acid, Liaoyang Petrochemical's adiponitrile plant was shut down.
At that time, the domestic production capacity of adipic acid was only about 150,000 tons.
From 2012 to 2018, the annual production capacity of adipic acid in my country continued to grow, from 1.
273 million tons in 2012 to 2.
56 million tons in 2018, and the annual output increased from 76.
10,000 tons increased to 1.
5 million tons in 2018, and the market demand in 2018 is about 1 million tons.
In recent years, the operating rate of adipic acid has not been high, basically maintained at about 50%, and the overcapacity is obvious.
At the same time, the market price of adipic acid has gradually declined from the highest level of 21,000 yuan in April 2011, reaching the highest price of 13,000~13,500 yuan in the past six years at the beginning of 2018, and then fell to 8,600~8,700 yuan in late March this year.
At the beginning of the month, it fell to 8200-8300 yuan, a drop of 12,000 yuan from the highest point in 2011.
Optimized design for technology elimination
The raw materials account for more than 80% of the production cost of adiponitrile, which plays a decisive role in the economics of the adipic acid amination process.
With the changes in market supply and demand, the adipic acid ammoniation route with higher raw material costs has regained market competitiveness.
After years of production optimization, Liaoyang Petrochemical’s adiponitrile plant has accumulated long-term stable operation technology and operating experience.
It can integrate and optimize the company’s original mature production process and subsequent process improvements, and develop a more mature production process package.
The main raw materials of the adipic acid ammoniation process are adipic acid and ammonia.
Among them, adipic acid is also another important raw material for the production of nylon 66.
After the successful restart of the adipic acid ammoniation process, adipic acid can be used as a raw material Realize the production of nylon 66.
Restarting the research and development of the adipic acid ammoniation process requires elimination, optimization and redesign.
The liquid phase method of adipic acid amination is a typical gas-liquid phase reaction.
As one of the key equipment of the adiponitrile production unit, the nitrification reactor is mainly a bubbling tubular reactor, and the reactants enter the bubbling section first.
Neutralization reaction, and then enter the high temperature tube section for dehydration reaction to generate adiponitrile.
The reaction of adipic acid amination is complicated, the temperature of the pipe section is high, and the side reactions are many, which leads to a lot of impurities in the product and the quality of the product is reduced, and the coking and corrosion of the reactor are serious.
It can be explored to improve the design by connecting a bubbling pre-reactor in series in front of the reactor, increasing the volume of the neutralization section and the reaction time of adipic acid through the bubbling tower of the pre-reactor in series, and setting a sieve in the pre-reactor to disperse the bubbles.
, Increase the neutralization reaction gas-liquid contact phase boundary area and reaction time to enhance gas-liquid mass transfer, reduce backmixing, reduce the concentration of adipic acid entering the reactor tube section, and ultimately reduce the coking of the main reactor tube section effect.
At the same time, select high-chromium-nickel alloy materials with high corrosion resistance to make the reactor, and strictly control the process parameters of the device.
The concentration of phosphoric acid catalyst in adipic acid should be maintained at 0.
22% to achieve continuous production.
The liquid acid catalyst can be dissolved in the reaction solution to achieve a better catalytic effect.
However, this type of catalyst is difficult to separate from the product.
As the reaction progresses, the catalyst is easily lost, and it is necessary to constantly replenish the catalyst during production.
In addition, coking and corrosion in the dehydration section of the reactor are largely due to the use of liquid phosphoric acid catalysts in the adipic acid amination process.
The dehydration temperature is around 280°C, and high temperature easily causes various side reactions to occur, which greatly increases the coke produced and affects the long-term operation of the device.
The process of adipic acid amination reaction can explore the use of solid phosphoric acid catalyst.
The solid phosphoric acid catalyst is composed of many phosphorus-containing silicon compounds, and its catalytic activity depends on the composition distribution and the content of each component.
In order to obtain the best catalytic effect, its preparation conditions need to be optimized.
At present, the solid acid catalyst under development also needs to build an industrial side-line device to test the catalytic activity, preliminary stability and service life, and provide data for the industrial scale production and application of the catalyst.
(Keyword: Restart of nitrile process)