How to separate butane and butene
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I am working on a project that uses liquefied petroleum gas as a raw material, of which 65% is butylene and 35% is butane. However, for the processing unit, only butylene participates in the reaction; in that case, it is necessary to separate butylene from butane. I would like to ask everyone: what methods can be used to separate butylene from butane? Thank you!
As a supplementary note: Butane is mainly n-butane, while butenes are mainly 1-butene and 2-butene
Process principle: Butene concentration. Since the relative volatility of n-butane and n-butene in the C4 feedstock is low, and n-butane’s volatility lies between 1-butene and isobutylene-2, conventional distillation methods require a large number of theoretical plates; moreover, it is not possible to obtain n-butene along with 1-butene, cis-2-butene, and isobutylene-2 from a single column, which hinders the efficient utilization of n-butene. Boiling points and relative volatilities of various components in C4 feedstock
Component: Isobutane, Isobutylene, 1-Butene, 1,3-Butadiene, n-Butane, 2-Methylbutene, 2-Butene
Boiling point (°C): -11.73, -6.90, -6.26, -4.41, -0.50, 0.88, 3.74
Relative volatility: 1.13, 1.005, 1.000, 0.975, 0.863, 0.830, 0.800
The principle behind the concentration of butenes is extraction distillation: a mixed solvent of methylethyl ketone and nitrogen-formylmorpholine is added to the mixed C4 feedstock, and this solvent is used to alter the relative volatilities of butane and butenes. Through continuous distillation, the low-boiling-point alkanes (mainly butane) are first separated out, and then, via further continuous distillation, the olefins (mainly butenes) are separated from the solvent, thereby yielding relatively pure n-butene. Both are common solvents; they feature good solvating capacity for all the components of C4, along with low viscosity, low boiling point, and low toxicity, allowing them to be used as solvents for C4 separation. Since methyl ethyl ketone has a very low boiling point (~80°C), the temperatures at the bottoms of the extractive distillation column and the stripping column are low. Its good solvating capacity for tetrahydrocarbons combined with its low viscosity results in good liquid flow within the extractive distillation column, leading to efficient mass transfer and high productivity; there is no issue of dual-phase formation inside the column. However, its polarity is relatively weak, so it contributes little to the relative volatility of alkanes and alkenes. When the solvent/tetrahydrocarbon ratio is 10, the relative volatility of n-butane to 1-butene is around 1.2. Therefore, when using methyl ethyl ketone as the sole solvent for the extractive distillation separation of tetrahydrocarbon alkanes from alkenes, the column must be quite tall. The nitrogen-formylmorpholine solvent is characterized by high polarity, which has a significant impact on the relative volatility of alkanes and alkenes; however, it has poor solvating power for the C4 components, high viscosity, and a high boiling point. When the solvent/cetane ratio is 10, the relative volatility of n-butane to 1-butene is around 1.55; therefore, when using it as a solvent in extractive distillation to separate butane and butene mixtures, only a small number of theoretical plates are required. A mixture of methyl ethyl ketone and a polar solvent is used as the solvent, and extractive distillation is employed to separate butane from butenes. The advantage of this approach lies in it combining the strengths of both methyl ethyl ketone and the polar solvent, thereby complementing each other’s weaknesses. It retains the advantages of methyl ethyl ketone, such as its good solvating capacity for C4 compounds and low boiling point, while also benefiting from the ability of the polar solvent to increase the relative volatility of alkanes and alkenes. This improves mass transfer within the column, enhances separation efficiency, reduces the number of theoretical plates, lowers the solvent ratio, and decreases the temperature at the bottom of the column. The nitrogen-formylmorpholine mixed solvent, used together with alkane and alkene, is the best solvent for separating butane from butylene due to its significant contribution to the relative volatility of these compounds and its low toxicity. The use of a nitrogen-formylmorpholine-methylethyl mixed solvent effectively altered the relative volatility of n-butane and n-butylene. The volatility of butane is **increased to enable separation. After concentration, the butene content will exceed 96 wt%. Due to the low relative volatility of n-butane and n-butylene in the C4 fraction, and the fact that n-butane’s volatility lies between 1-butene and isobutylene-2, conventional distillation methods require a large number of theoretical plates; moreover, it is not possible to obtain n-butylene (1-butene, cis-butylene-2, trans-butylene-2) from a single column, which hinders the efficient utilization of n-butylene. The use of an N-formylmorpholine-methylethyl mixed solvent effectively altered the relative volatility of n-butane and n-butylene. This post was last edited by fushan on 2007-11-29 16:32]
Component: Isobutane, Isobutylene, 1-Butene, 1,3-Butadiene, n-Butane, 2-Methylbutene, 2-Butene
Boiling point (°C): -11.73, -6.90, -6.26, -4.41, -0.50, 0.88, 3.74
Relative volatility: 1.13, 1.005, 1.000, 0.975, 0.863, 0.830, 0.800
The principle behind the concentration of butenes is extraction distillation: a mixed solvent of methylethyl ketone and nitrogen-formylmorpholine is added to the mixed C4 feedstock, and this solvent is used to alter the relative volatilities of butane and butenes. Through continuous distillation, the low-boiling-point alkanes (mainly butane) are first separated out, and then, via further continuous distillation, the olefins (mainly butenes) are separated from the solvent, thereby yielding relatively pure n-butene. Both are common solvents; they feature good solvating capacity for all the components of C4, along with low viscosity, low boiling point, and low toxicity, allowing them to be used as solvents for C4 separation. Since methyl ethyl ketone has a very low boiling point (~80°C), the temperatures at the bottoms of the extractive distillation column and the stripping column are low. Its good solvating capacity for tetrahydrocarbons combined with its low viscosity results in good liquid flow within the extractive distillation column, leading to efficient mass transfer and high productivity; there is no issue of dual-phase formation inside the column. However, its polarity is relatively weak, so it contributes little to the relative volatility of alkanes and alkenes. When the solvent/tetrahydrocarbon ratio is 10, the relative volatility of n-butane to 1-butene is around 1.2. Therefore, when using methyl ethyl ketone as the sole solvent for the extractive distillation separation of tetrahydrocarbon alkanes from alkenes, the column must be quite tall. The nitrogen-formylmorpholine solvent is characterized by high polarity, which has a significant impact on the relative volatility of alkanes and alkenes; however, it has poor solvating power for the C4 components, high viscosity, and a high boiling point. When the solvent/cetane ratio is 10, the relative volatility of n-butane to 1-butene is around 1.55; therefore, when using it as a solvent in extractive distillation to separate butane and butene mixtures, only a small number of theoretical plates are required. A mixture of methyl ethyl ketone and a polar solvent is used as the solvent, and extractive distillation is employed to separate butane from butenes. The advantage of this approach lies in it combining the strengths of both methyl ethyl ketone and the polar solvent, thereby complementing each other’s weaknesses. It retains the advantages of methyl ethyl ketone, such as its good solvating capacity for C4 compounds and low boiling point, while also benefiting from the ability of the polar solvent to increase the relative volatility of alkanes and alkenes. This improves mass transfer within the column, enhances separation efficiency, reduces the number of theoretical plates, lowers the solvent ratio, and decreases the temperature at the bottom of the column. The nitrogen-formylmorpholine mixed solvent, used together with alkane and alkene, is the best solvent for separating butane from butylene due to its significant contribution to the relative volatility of these compounds and its low toxicity. The use of a nitrogen-formylmorpholine-methylethyl mixed solvent effectively altered the relative volatility of n-butane and n-butylene. The volatility of butane is **increased to enable separation. After concentration, the butene content will exceed 96 wt%. Due to the low relative volatility of n-butane and n-butylene in the C4 fraction, and the fact that n-butane’s volatility lies between 1-butene and isobutylene-2, conventional distillation methods require a large number of theoretical plates; moreover, it is not possible to obtain n-butylene (1-butene, cis-butylene-2, trans-butylene-2) from a single column, which hinders the efficient utilization of n-butylene. The use of an N-formylmorpholine-methylethyl mixed solvent effectively altered the relative volatility of n-butane and n-butylene. This post was last edited by fushan on 2007-11-29 16:32]
Addition: What the original poster said is still not clear enough. If the concentration of butene involved in the reaction is not highly specified, then the reaction itself indirectly separates butene from butane; of course, due to the limitations imposed by the butene conversion rate, butane will still contain some butene. Separation is only necessary when pure butene is required as the reactant.
Since the C4 feed mainly consists of n-butane and butylene, it is difficult to achieve separation using conventional distillation; the only option is extractive distillation. The extractants that can be used are: (1) MEK+NFM, (2) NOR+NFM, (3) acetonitrile, (4) DMF. The acetonitrile extraction method has the lowest energy consumption, but it generates a large amount of wastewater. The DMF method requires compression and has high operating costs; NOR+NFM necessitates consideration of anti-freezing measures. The most suitable option is still the MEK+NFM extractant. However, if your factory does not have strict environmental emission controls, it is recommended to use acetonitrile for extraction, as it results in the lowest operating costs. As for the low yield of butene obtained through MEK+NFM extraction, there are various reasons for this. Currently, in China, the use of these extractants results in a butene yield of over 98%, with this yield remaining stable at 98% over time, which is quite satisfactory. NFM production method: The raw materials, morpholine and formate, are fed into the reactor either continuously or indirectly; under continuous stirring, the reaction temperature is maintained between -20°C and 60°C℃ ； Place in a aging vessel for aging for 10–35 hours ； The aged reaction mixture is subjected to distillation in an alcohol removal tower to remove the alcohols produced as a result of the reaction; the liquid remaining in the bottom of this tower is then sent to a light-component removal tower, where it is processed under low vacuum to eliminate any remaining alcohols, esters, morpholine, and other light components ； During the light-end removal process, stripping gas is introduced for stripping; once the content of the light components reaches the required level, the liquid from the bottom of the light-end removal tower is sent to the product tower ； The product tower evaporates the product N-formylmorpholine under high vacuum. High-purity N-formylmorpholine was obtained at a high morpholine conversion rate using a purification method that combines reactive aging with vacuum distillation and stripping distillation. This post was last edited by 1681818 on 2008-3-22 21:50]
What is mentioned on the 3rd floor seems to be the butylene concentration process using German technology. This technology is based on industrial-scale experiments conducted in Germany; the first industrial-scale installation of this kind was built in China, and it constitutes a classified technology. This concentration unit is the key unit for producing both methanol and ethanol.
If it is 90% isobutane and olefins, can it be extracted using catalysts such as (1) MEK+NFM, (2) NOR+NFM, (3) acetonitrile, or (4) DMF? Thank you! This post was last edited by 372930 on 2009-4-10 14:22.]