KR102049312B1

KR102049312B1 - Method for providing a purified crude gaseous c4 fraction as an input stream for an extractive distillation using a selective solvent

Info

Publication number: KR102049312B1
Application number: KR1020147021970A
Authority: KR
Inventors: 베른드 하이다; 란돌프 휴고
Original assignee: 바스프 에스이
Priority date: 2012-01-11
Filing date: 2013-01-10
Publication date: 2019-11-28
Also published as: EP2802637A1; JP6067748B2; EP2802637B1; JP2015508409A; WO2013104692A1; KR20140120329A; CN104053752A; CN104053752B

Abstract

The present invention is a C ₃ hydrocarbon, C ₄ oligomer, C ₄ Use of optional solvent to obtain crude 1,3-butadiene on the basis of liquid crude C ₄ -fraction (1) as feed stream containing polymer and C ₅ ₊ hydrocarbons together butane, butene and 1,3-butadiene The crude gaseous C ₄ fraction (2) is provided as input stream for extractive distillation. The process comprises 1) purified crude gas phase C _4. C ₄ oligomer, C ₄ to be below the respective residual content previously specified for the fraction Separating the polymer and the C ₅ ₊ hydrocarbons, and 2) has a step of evaporation of the liquid crude C ₄ fraction in an evaporator tank (VK). The invention is characterized in that the evaporation tank (VK) is associated with a stripping column (K) having one or more separation stages and the liquid C ₄ fraction (1) is fed to the top of the stripping column. The stripping column exchanges gas and liquid directly with the evaporator tank (VK) at the bottom of the column and withdraws the crude crude gaseous C ₄ fraction (2) at the top of the stripping column. The stripping column K is operated without a condenser in the column head.

Description

METHODS FOR PROVIDING A PURIFIED CRUDE GASEOUS C4 FRACTION AS AN INPUT STREAM FOR AN EXTRACTIVE DISTILLATION USING A SELECTIVE SOLVENT}

The present invention relates to a process for providing a gas phase purified crude C ₄ cut as a use stream for extractive distillation using a selective solvent.

The term "C ₄ fraction" refers to a mixture of hydrocarbons having predominantly four carbon atoms per molecule. The C ₄ fraction is for example ethylene and / or propylene by thermal cracking in petroleum fractions, such as liquefied petroleum gas, light gasoline or gaseous oils, typically in steam crackers, in particular naphtha crackers or fluid catalyzed cracking crackers. Obtained in the preparation of. In addition, the C ₄ fraction is obtained in catalytic dehydrogenation of n-butane and / or n-butene. The C ₄ fraction generally comprises butane, butene, 1,3-butadiene, small amounts of C ₃ -and C ₄ -acetylene, 1,2-butadiene and C ₅ ₊ hydrocarbons.

Separation of the C ₄ fraction is a complex distillation problem because the relative volatility of the components has a small difference. Therefore, the separation is carried out by distillation, called extractive distillation, i.e. the addition of an optional solvent (also referred to as an extractant), which has a higher boiling point than the mixture to be separated and the relative volatility of the components to be separated. Increase the difference.

Many methods are known for separating the C ₄ fractions by extractive distillation using selective solvents. These, under suitable thermodynamic conditions, generally at low temperatures, often in the range of 20 to 80 ° C. and mild pressures, often at standard pressures to 6 bar, the C ₄ fraction to be separated flows countercurrently to the liquid selective solvent in vapor form, As a result, the components from the C ₄ fraction with higher affinity are loaded into the selective solvent, while the components with lower affinity for the selective solvent remain in the vapor phase and have the common feature of being taken off as a top stream. Subsequently, in one or more further process steps, the components in the optional solvent are removed from the loaded solvent stream by means of fractional distillation at higher temperatures and / or lower pressures as compared to suitable thermodynamic conditions, ie the first process step.

Crude C ₄ fraction is a problem in the extractive distillation, and more specifically, contain impurities causing a solvent droplet formation and the equipment fouling, and thus to ensure reliable operation in the extractive distillation, and these in particular crude C ₄ fraction to the extractive distillation It must be removed before it is supplied.

Impurities which cause this problem are in particular components having a higher boiling point than 1,3-butadiene, among which C ₅ ₊ hydrocarbons (hydrocarbons, isoprene, C ₄ oligomers and C ₄ polymers predominantly having at least 5 carbon atoms per molecule) Ie oligomers and optionally polymers of butadiene with the formula (C ₄ H ₆ ) _n in which n is 2 or more). The ratio of C ₅ ₊ hydrocarbons in the C ₄ fraction in particular columns is dependent on the operating conditions of degradation based on the total weight of the crude C ₄ fraction, 1000 ppmw or less, or even more than 5000 ppmw, a particular case, not more than 1% by weight . C ₄ oligomers and C ₄ The polymer is formed in particular as a result of storage and transportation; The proportion thus depends predominantly on the storage and transport conditions, in particular on the temperature, duration and degree of deactivation of the environment in which the storage and / or transport takes place.

In addition, C ₃ hydrocarbons in extractive distillation, ie hydrocarbons with three carbon atoms per molecule, can also cause problems. It is especially methylacetylene, which has similar affinity to the typical solvents typically used, for example 1,3-butadiene. Therefore, the proportion of C ₃ hydrocarbons in the feed stream for extractive distillation should be limited to less than 50 ppmw based on the total weight of the feed stream.

This problem in the prepurification of the feed stream for the extractive distillation of the crude C ₄ fraction is currently solved in several ways: In one known mode of operation, in a distillation column connected upstream of the extractive distillation, the C ₃ hydrocarbons are It is removed through the column and the remaining components are withdrawn through the column. The bottoms stream is subsequently fed to an evaporator vessel, ie a device having a single plate, for the removal of high boiling point components having a higher boiling point than 1,3-butadiene. In the evaporator vessel, the high boiling point component in the residual liquid component, which has a higher boiling point compared to 1,3-butadiene, is 5% by weight, in particular 1% by weight, or even based on the total weight of the crude C ₄ fraction fed to the evaporator vessel. To not exceed 0.1% by weight, the crude C ₄ stream depleted of the C ₃ component is substantially completely evaporated under flow control. The liquid stream remaining in the evaporator vessel is discharged as a purge stream. However, a disadvantage here is that the purge stream also releases a high proportion of valuable C ₄ hydrocarbons along with the high boiling point materials.

In this regard, it is an object of the present invention to remove secondary components of crude C ₄ fractions that interfere with extractive distillation in a technically simple manner at low capital and energy costs, resulting in a service life of the extractive distillation column. It provides a way to increase life.

This object is achieved through the process of providing a crude, gaseous purified C ₄ fraction as a use stream for extractive distillation using a selective solvent,

Butane, butene and 1,3-butadiene as well as C ₃ hydrocarbons, C ₄ oligomers, C ₄ Proceeds from the liquid crude C ₄ fraction as a feed stream comprising polymer and C ₅ ₊ hydrocarbons,

The purified gaseous crude C ₄ fraction is

Less than two thirds of the C ₅ ₊ hydrocarbons present in the feed stream and

Less than 5% by weight of the C ₄ oligomers and C ₄ polymers present in the feed stream

Including;

1) a process step of removing C ₄ oligomers, C ₄ polymers and C ₅ ₊ hydrocarbons in each case to the residual content specified above for the gas phase purified crude C ₄ fraction, and

2) Process step of evaporating the liquid crude C ₄ fractions from the evaporator vessel

Including,

here

The evaporator vessel is assigned to a stripping column having one or more plates, a liquid C ₄ fraction is fed to the top of the stripping column, and at the bottom of the stripping column direct exchange of gas and liquid with the evaporator vessel takes place and the gas phase from the stripping column The purified crude C ₄ fraction is withdrawn from its upper region and the stripping column is run without a condenser on the top of the column.

By associating the stripping column with the evaporator vessel, we increase the removal of high boiling point material in the evaporator vessel while reducing the C ₄ hydrocarbons lost through the purge stream from the evaporator vessel in a technically simple and not very energy intensive manner. I found it possible.

In this context, more particularly in the construction of new plants, it is possible to position the stripping column above the evaporator vessel, ie to integrate the evaporator vessel and the stripping column into a single device.

In another embodiment it is also possible to associate the evaporator vessel with the stripping column, in particular in an existing plant, ie to provide the evaporator vessel and the stripping column as separate devices.

Evaporator vessels are simple devices known in the process art. This generally includes a vessel capable of separating the gas phase from the liquid phase and a heat exchanger arranged inside or outside the vessel.

According to the invention, the stripping column is assigned to an evaporator vessel.

Since the stripping column and the evaporator vessel are only provided for the depletion of the high boiling point material, it is possible to operate the stripping column in a simple manner, without the condenser on the top of the column.

A typical crude C ₄ fraction from a naphtha cracker has the following weight percent composition.

The crude C ₄ fraction from the naphtha cracker thus predominantly comprises butane, butene and 1,3-butadiene. In addition, small amounts of other hydrocarbons are present. C ₄ -acetylene is often present in proportions of up to 5% by weight or up to 2% by weight.

In extractive distillation as defined above, useful optional solvents are generally substances or mixtures having a higher boiling point than the mixture to be separated and having a higher affinity with conjugated double bonds and triple bonds than with simple double bonds and single bonds, preferably Is a dipole, more preferably a dipole aprotic solvent. For device reasons, less corrosive or noncorrosive materials are preferred.

Suitable solvents suitable for the process according to the invention include, for example, butyrolactone, nitriles, for example acetonitrile, propionitrile, methoxypropionitrile, ketones, for example acetone, furfural, N-alkyl-substituted lower Aliphatic acid amides such as dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, N-formylmorpholine, N-alkyl-substituted cyclic acid amides (lactams), for example N-alkylpyrroli Money, especially N-methylpyrrolidone. Generally, N-alkyl-substituted lower aliphatic acid amides or N-alkyl-substituted cyclic acid amides are used. In particular dimethylformamide, acetonitrile, furfural and in particular N-methylpyrrolidone are advantageous.

However, mixtures of the above solvents, for example mixtures of N-methylpyrrolidone with acetonitrile, such solvents and cosolvents, for example water and / or tert-butyl ethers, for example methyl tert-butyl ether, It is also possible to use mixtures with ethyl tert-butyl ether, propyl tert-butyl ether, n- or isobutyl tert-butyl ether.

Particularly suitable are N-methylpyrrolidone, preferably N-methylpyrrolidone, which is an aqueous solution, especially N-methylpyrrolidone, which is an aqueous solution with 8 to 10% by weight of water, more preferably 8.3% by weight of water. Do.

To avoid problems with extractive distillation, the use stream to be fed with the optional solvent comprises less than 50 ppmw of C ₃ hydrocarbons, based on the total weight of the purified gaseous crude C ₄ fraction, present in the feed stream. ₅ ₊ is less than two-thirds of the C ₄ hydrocarbons and oligomers, and a gas phase purification the crude C ₄ fraction containing less than 5% by weight of the polymer present in the C ₄ feed stream.

The inventors have found that by associating an evaporator vessel with a stripping column, it is possible to improve the removal of high boilers in a simple manner.

In addition, it is possible in the process according to the invention to remove high boiling point components compared to 1,3-butadiene from the C ₄ fraction with much less loss of the valuable product C ₄ hydrocarbons.

Preferably, in the distillation column connected upstream of the evaporator vessel, the C ₃ hydrocarbons in the gas phase purification the crude C ₄ fraction, based on the total weight of the gaseous purification the crude C ₄ fraction, preferably to less than 10 ppmw, or more Preferably less than 4 ppmw.

Further preferably, the C ₅ ₊ hydrocarbons in the gaseous purified crude C ₄ fraction are depleted to less than half of the C ₅ ₊ hydrocarbons present in the feed stream.

The stripping column is preferably operated at tower pressure of 3 to 7 bar absolute, further preferably at tower pressure of 4.5 to 5.5 bar absolute.

The stripping column has in particular 1 to 15 theoretical singulars.

The invention is illustrated in detail by the figures and examples below.
Especially in drawings
1 and a schematic diagram of an evaporator vessel with a stripping column on top.
A schematic diagram of the evaporator vessel with which the stripping column is associated is shown in FIG. 2.
The schematic diagram of FIG. 1 shows the evaporator vessel VK in which the stripping column K is connected to the top of the evaporator vessel in such a way that the evaporator vessel VK and the stripping column K form a single device. At the bottom of the evaporator vessel (VK) is a reboiler.
The stripping column K is fed to the top thereof with a liquid crude C ₄ fraction as stream 1, and the purified crude C ₄ fraction, stream 2, is taken off onto the tower of stripping column K.
FIG. 2 is a schematic of a further preferred embodiment in which the evaporator vessel (VK) and the stripping column (K) are configured as separate devices and a direct gas and liquid exchange with the stripping column (K) is provided at the top of the evaporator vessel (VK). Diagram is shown.
The reboiler S is provided in the evaporator container VK.
The stripping column K is fed to the top thereof with a liquid C ₄ fraction as stream 1 and the gaseous purified crude C ₄ fraction, stream 2, is taken off as a tower stream.

Starting material was in each case 200 ppm propane, 400 ppm propene, 300 ppm propadiene, 400 ppm propene, 2.0% n-butane, 6.0% iso, based on the total weight of the feed stream Butane, 19.0% n-butene, 28.3% isobutene, 5.5% trans-2-butene, 4.4% cis-2-butene, 39.0% 1,3-butadiene, 0.2% 1,2-butadiene , As a feed stream for a 100 kt / year plant comprising 1200 ppm 1-butyne, 4500 ppm vinylacetylene and 1000 ppm isopentane, 3-methyl-1-butene and 2-methyl-2-butene Crude C ₄ fractions. C ₄ oligomers and C ₄ polymers may be present in the% range depending on storage and transport conditions. The C ₃ hydrocarbons were removed through the column and the remaining components were withdrawn through the column bottoms and then the bottoms stream was fed to an evaporator vessel, i.e. a device with a single plate, for the removal of high boiling components having a higher boiling point than 1,3-butadiene. For comparison with a plant with a distillation column, the crude C ₄ fraction was prepurified so that it could be used as a feed stream for extractive distillation. In the evaporator vessel, the crude C ₄ stream depleted of the C ₃ component evaporated substantially completely, with a high boiling point in the residual liquid component having a higher boiling point compared to 1,3-butadiene to minimize the loss of the C ₄ component in the liquid residue. The discharge was under flow control such that the point C ₅ component did not exceed 5% by weight based on the total weight of the crude C ₄ fractions fed to the evaporator vessel. The proportion of oligomers and polymers present in the liquid residue was much larger because of the low vapor pressure. The liquid stream remaining in the evaporator vessel was discharged as a purge stream.

According to an embodiment of the invention, the same crude C ₄ fractions were fed to the evaporator vessel (VK) as a feed stream, at the top of the evaporator vessel (VK) was placed a stripping column (K) of five theoretical stages, and liquid C _Four fractions (1) were fed to the top of the stripping column (K) and the gaseous purified crude C ₄ fractions (2) were withdrawn from the top of the stripping column (K), and the stripping column (K) was condenser on top of the column. It was operated without. The plant is shown schematically in FIG. 1.

According to the prior art, less than 5% of the C ₅ components present in the C ₄ fraction are removed via the residual stream (= purge stream), whereas in the process according to the invention, 3 of the C ₅ ₊ hydrocarbons present in the feed stream More than one-minute and more than 95% by weight of the C ₄ oligomers and polymers present in the feed stream exited the residual stream through the bottoms.

According to the prior art, the residue flow rate (from the evaporator vessel) was 160 kg / h with a 1,3-butadiene ratio of 38.6% by weight.

In comparison, in the process according to the invention the residue flow rate (bottom flow rate) from the distillation column was likewise 160 kg / h, but with only 23% by weight of 1,3-butadiene. 1,3-butadiene yield in preliminary distillation (1,3-butadiene in purified C ₄ fractions based on 1,3-butadiene in crude C ₄ fractions) is superior to 99.49% in the Examples of the present invention. 99.29%, depending on the technology. This means that higher yields of valuable 1,3-butadiene products are achieved in the process according to the invention.

As a further advantage, in the process according to the invention the purified crude C ₄ fraction has been removed in higher purity compared to the prior art methods. In a 32 t / h crude C ₄ feed with a total 3000% ppmw of C ₅ components (there may be additional proportions of C ₆ components and oligomers and polymers not considered here), 94.16 kg / h The C ₅ component was sent to extractive distillation according to the prior art. In contrast, for the present invention, only 55.1 kg / h of the C ₅ component was sent to the extractive distillation. Since the C ₅ component from the preliminary distillation was fed to the extractive distillation at lower levels, the loss of 1,3-butadiene in the extractive distillation or subsequent purified distillation was also correspondingly reduced. Based on the pure product (pure 1,3-butadiene) from the total extractive distillation, including pre-distillation, the yield of 1,3-butadiene according to the prior art (calculated as 100% 1,3-butadiene) was 96.47% , For the present invention was 96.66%.

In the large scale plant specified above of 1000 kt / a, the loss of valuable 1,3-butadiene product was therefore approximately 192 t / 1 year greater in the method according to the prior art than in the method according to the invention.

Thanks to the fact that the solvent forms a closed cycle, the solvent was kept clean by the preliminary removal of the problematic components and impurities, which minimized the regeneration complexity. At the same time, the fouling of the extractive distillation plant (dirty of the layers of the columns) and splash formation were minimized. As a result, less antifoam was required at a correspondingly lower cost. Reduced fouling reduced the cost of cleaning during shutdown. All shutdowns represent about two weeks of outages; Additional cleaning costs are required. This results in a cost in the 7-digit range.

Claims

Feeding liquid crude C ₄ fraction (1) comprising butane, butene and 1,3-butadiene as well as C ₃ hydrocarbons, C ₄ oligomers, C ₄ polymers and C ₅₊ hydrocarbons into an evaporator vessel (VK) and an evaporator Evaporating the liquid crude C ₄ fractions in a vessel (VK),
here
The evaporator vessel (VK) is assigned to a stripping column (K) having one or more plates, the liquid C ₄ fraction (1) is fed to the top of the stripping column (K), and at the bottom of the stripping column (K) the evaporator vessel ( Direct exchange of gas and liquid with VK) takes place, gaseous purified crude C ₄ fraction (2) from stripping column (K) is withdrawn from its upper region, and stripping column (K) without condenser on top of column Operating, the purge stream containing C ₄ oligomer, C ₄ polymer and C ₅₊ hydrocarbon is removed from the evaporator vessel (VK) to obtain the gaseous crude C ₄ fraction.
Less than two thirds of the C ₅₊ hydrocarbons present in the feed stream and
Less than 5% by weight of the C ₄ oligomers and C ₄ polymers present in the feed stream
To include,
Process for providing a gas phase purified crude C ₄ fraction (2) as a use stream for extractive distillation using an optional solvent to obtain crude 1,3-butadiene.

The process according to claim 1, wherein the stripping column (K) is located on top of the evaporator vessel.

The process according to claim 1, wherein the stripping column (K) is associated as a separate device to the evaporator vessel (VK).

The total of gaseous purified crude C ₄ fractions of the distillation column of claim 1, wherein the C ₃ hydrocarbons in the gaseous purified crude C ₄ fractions are connected upstream of the evaporator vessel (VK). Depleted to less than 10 ppmw by weight.

5. The method of claim 4, where the C ₃ hydrocarbons in the gas phase purification the crude C ₄ fraction, based on the total weight of the gaseous purification the crude C ₄ fraction, depleted to less than 4 ppmw.

The process according to claim 1, wherein the C ₅₊ hydrocarbons in the gaseous purified crude C ₄ fraction are depleted to less than half of the C ₅₊ hydrocarbons present in the feed stream.

The process according to any one of claims 1 to 3, wherein the stripping column (K) is operated at tower pressure of 3 to 7 bar absolute.

The process according to claim 7, wherein the stripping column (K) is operated at tower pressure of 4.5 to 5.5 bar absolute.

The process according to any one of claims 1 to 3, wherein the stripping column (K) has 1 to 15 theoretical singulars.