Dehydrogenation of butane is carried out in a fluidized or moving bed of chromium and aluminum catalyst. The process is carried out at a temperature in the range from 550 to 575 degrees. Among the features of the reaction, we note the continuity of the technological chain.
Technology Features
Butane dehydrogenation is mainly carried out in contact adiabatic reactors. The reaction is carried out in the presence of water vapor, which significantly lowers the partial pressure of the interacting gaseous substances. Compensation in surface reaction apparatuses for the endothermic thermal effect is carried out by supplying heat through the surface with flue gases.
Simplified version
Dehydrogenation of butane in the simplest way involves the impregnation of aluminum oxide with a solution of chromic anhydride or potassium chromate.
The resulting catalyst contributes to the fast and high-quality process. This chemical process accelerator is affordable in a price range.
Production scheme
Butane dehydrogenation is a reaction in which no significant catalyst consumption is expected. Productsdehydrogenation of the starting material are taken to the extractive distillation unit, where the required olefinic fraction is isolated. Dehydrogenation of butane to butadiene in a tubular reactor with an external heating option allows for a good product yield.
The specificity of the reaction is in its relative safety, as well as in the minimal use of complex automatic systems and devices. Among the advantages of this technology, one can mention the simplicity of designs, as well as the low consumption of an inexpensive catalyst.
Process Features
Dehydrogenation of butane is a reversible process, and an increase in the volume of the mixture is observed. According to the Le Chatelier principle, in order to shift the chemical equilibrium in this process towards obtaining interaction products, it is necessary to lower the pressure in the reaction mixture.
Optimum is atmospheric pressure at temperatures up to 575 degrees, when using a mixed chromium-aluminum catalyst. As the accelerator of the chemical process is deposited on the surface of carbon-containing substances, which are formed during side reactions of the deep destruction of the original hydrocarbon, its activity decreases. To restore its original activity, the catalyst is regenerated by blowing it with air, which is mixed with flue gases.
Flow Conditions
During the dehydrogenation of butane, unsaturated butene is formed in cylindrical reactors. The reactor has special gas distribution grids, installedcyclones that capture catalyst dust carried away by the gas stream.
Dehydrogenation of butane to butenes is the basis for the modernization of industrial processes for the production of unsaturated hydrocarbons. In addition to this interaction, a similar technology is used to obtain other options for paraffins. Dehydrogenation of n-butane has become the basis for the production of isobutane, n-butylene, ethylbenzene.
There are some differences between technological processes, for example, when dehydrogenating all hydrocarbons of a number of paraffins, similar catalysts are used. The analogy between the production of ethylbenzene and olefins is not only in the use of one process accelerator, but also in the use of similar equipment.
Catalyst usage time
What characterizes the dehydrogenation of butane? The formula of the catalyst used for this process is chromium oxide (3). It is precipitated on amphoteric alumina. To increase the stability and selectivity of the process accelerator, it will be imitated with potassium oxide. With proper use, the average duration of a full-fledged operation of the catalyst is a year.
As it is used, a gradual deposition of solid compounds on the mixture of oxides is observed. They must be burned out in a timely manner using special chemical processes.
Catalyst poisoning occurs with water vapor. It is on this mixture of catalysts that the dehydrogenation of butane occurs. The reaction equation is considered at school in the course of organicchemistry.
In the case of an increase in temperature, an acceleration of the chemical process is observed. But at the same time, the selectivity of the process also decreases, and a layer of coke is deposited on the catalyst. In addition, the following task is often offered in high school: write an equation for the reaction of dehydrogenation of butane, combustion of ethane. These processes do not involve any particular difficulties.
Write the equation for the dehydrogenation reaction, and you will understand that this reaction proceeds in two mutually opposite directions. For one liter of the volume of the reaction accelerator, there are approximately 1000 liters of butane in gaseous form per hour, this is how the dehydrogenation of butane occurs. The reaction of combining unsaturated butene with hydrogen is the reverse process of the dehydrogenation of normal butane. The yield of butylene in the direct reaction is on average 50 percent. About 90 kilograms of butylene are formed from 100 kilograms of the starting alkane after dehydrogenation if the process is carried out at atmospheric pressure and a temperature of about 60 degrees.
Raw materials for production
Let's take a closer look at the dehydrogenation of butane. The process equation is based on the use of feedstock (mixture of gases) generated during oil refining. At the initial stage, the butane fraction is thoroughly purified from pentenes and isobutenes, which interfere with the normal course of the dehydrogenation reaction.
How does butane dehydrogenate? The equation for this process involves several steps. After purification, dehydrogenation of the purifiedbutenes to butadiene 1, 3. The concentrate containing four carbon atoms, which was obtained in the case of catalytic dehydrogenation of n-butane, contains butene-1, n-butane, and butenes-2.
It is quite problematic to carry out the ideal separation of the mixture. By using extractive and fractional distillation with a solvent, such a separation can be carried out, and the efficiency of this separation can be improved.
When carrying out fractional distillation on apparatuses with a large separating capacity, it becomes possible to fully separate normal butane from butene-1, as well as butene-2.
From an economic point of view, the process of dehydrogenation of butane to unsaturated hydrocarbons is considered an inexpensive production. This technology makes it possible to obtain motor gasoline, as well as a huge variety of chemical products.
In general, this process is carried out only in areas where the unsaturated alkene is needed, and butane has a low cost. Due to the reduction in cost and improvement of the procedure for dehydrogenation of butane, the scope of use of diolefins and monolefins has significantly expanded.
The procedure of butane dehydrogenation is carried out in one or two stages, there is a return of unreacted feedstock to the reactor. For the first time in the Soviet Union, butane dehydrogenation was carried out in a catalyst bed.
Chemical properties of butane
In addition to the polymerization process, butane has a combustion reaction. Ethane, propane, othersThere are enough representatives of saturated hydrocarbons in natural gas, so it is the raw material for all transformations, including combustion.
In butane, carbon atoms are in the sp3-hybrid state, so all bonds are single, simple. This structure (tetrahedral shape) determines the chemical properties of butane.
It is not capable of entering into addition reactions, it is characterized only by the processes of isomerization, substitution, dehydrogenation.
Substitution with diatomic halogen molecules is carried out according to a radical mechanism, and rather severe conditions (ultraviolet irradiation) are necessary for the implementation of this chemical interaction. Of all the properties of butane, its combustion, accompanied by the release of a sufficient amount of heat, is of practical importance. In addition, the process of dehydrogenation of saturated hydrocarbon is of particular interest for production.
Dehydrogenation specifics
Butane dehydrogenation procedure is carried out in a tubular reactor with external heating on a fixed catalyst. In this case, the yield of butylene increases, production automation is simplified.
Among the main advantages of this process is the minimum catalyst consumption. Among the shortcomings, a significant consumption of alloyed steels, high capital investments are noted. In addition, the catalytic dehydration of butane involves the use of a significant number of units, since they have low productivity.
Production has low productivity, soas part of the reactors is focused on dehydrogenation, and the second part is based on regeneration. In addition, the large number of employees in production is also considered a disadvantage of this technological chain. It must be remembered that the reaction is endothermic, so the process proceeds at an elevated temperature, in the presence of an inert substance.
But in such a situation there is a risk of accidents. This is possible if the seals in the equipment are broken. The air that enters the reactor, when mixed with hydrocarbons, forms an explosive mixture. In order to prevent such a situation, the chemical equilibrium is shifted to the right by introducing water vapor into the reaction mixture.
One-step process variant
For example, in the course of organic chemistry, the following task is offered: write an equation for the reaction of butane dehydrogenation. In order to cope with such a task, it is enough to recall the basic chemical properties of hydrocarbons of the class of saturated hydrocarbons. Let's analyze the features of obtaining butadiene by a one-stage process of butane dehydrogenation.
The butane dehydrogenation battery includes several separate reactors, their number depends on the operation cycle, as well as on the volume of sections. Basically, five to eight reactors are included in the battery.
The process of dehydrogenation and regeneration is 5-9 minutes, the steam blowing stage takes 5 to 20 minutes.
Due to the fact that dehydrogenationbutane is carried out in a continuously moving layer, the process is stable. This improves the operational performance of production, increases the productivity of the reactor.
The process of one-stage dehydrogenation of n-butane is carried out at low pressure (up to 0.72 MPa), at a temperature higher than that used for production carried out on an aluminum-chromium catalyst.
Since the technology involves the use of a regenerative type reactor, the use of steam is excluded. In addition to butadiene, butenes are formed in the mixture, they are reintroduced into the reaction mixture.
One stage is calculated through the ratio of butanes in the contact gas to their number in the reactor charge.
Among the advantages of this method of butane dehydrogenation, we note a simplified technological scheme of production, a decrease in the consumption of raw materials, as well as a reduction in the cost of electrical energy for the process.
The negative parameters of this technology are represented by short periods of contact of the reacting components. Sophisticated automation is required to correct this problem. Even with such problems, single-stage butane dehydrogenation is a more favorable process than two-stage production.
When dehydrogenating butane in one stage, the feedstock is heated to a temperature of 620 degrees. The mixture is sent to the reactor, it is in direct contact with the catalyst.
To create rarefaction in reactors,vacuum compressors are used. The contact gas leaves the reactor for cooling, then it is sent to separation. After the dehydrogenation cycle is completed, the raw material is transferred to the next reactors, and from those where the chemical process has already passed, hydrocarbon vapors are removed by blowing. The products are evacuated and the reactors are reused for butane dehydrogenation.
Conclusion
The main dehydrogenation reaction of normal butane is the catalytic production of a mixture of hydrogen and butenes. In addition to the main process, there may be many side processes that significantly complicate the technological chain. The product obtained as a result of dehydrogenation is considered a valuable chemical raw material. It is the demand for production that is the main reason for the search for new technological chains for the conversion of hydrocarbons of the limiting series into alkenes.