TW201329042A - Process for providing a vaporous purified crude C4 cut as a use stream for an extractive distillation with a selective solvent - Google Patents

Abstract

What is proposed is a process for providing a vaporous purified crude C4 cut as a use stream for an extractive distillation with a selective solvent, comprising the process steps of (1) removing the C3 hydrocarbons, (2) removing the C4 oligomers and polymers and the C5+ hydrocarbons, in each case down to the residual contents specified above for the vaporous purified crude C4 cut, and (3) vaporizing the liquid crude C4 cut, wherein all method steps (1), (2) and (3) are performed in a single distillation column, to which the liquid crude C4 cut is supplied in the upper third thereof to form a rectifying section and a stripping section, and from which a top stream comprising the C3 hydrocarbons, a bottom stream comprising the C4 oligomers and polymers and the C5+ hydrocarbons, and, from the stripping section, the vaporous purified crude C4 cut as a side stream are drawn off.

Description

Providing a vaporized purified C 4 fraction for extractive distillation using a selective solvent as a method of using a stream

The present invention relates to an extractive distillation using a selective solvent to provide the purified C ₄ fraction of a vaporous stream of the method.

The term "C ₄ fraction" means a mixture of hydrocarbons having predominantly 4 carbon atoms per molecule. For example, in the preparation of ethylene and/or propylene by thermal cracking, typically a petroleum fraction such as liquefied petroleum gas, light gasoline or gas oil is in a steam cracker (especially a naphtha cracker or an FCC cracker (fluid) In catalytic cracking)), a C ₄ fraction is obtained. In addition, a C ₄ fraction is obtained in the catalytic dehydrogenation of n-butane and/or n-butene. The C ₄ fraction generally comprises butane, butene, 1,3-butadiene, a small amount of C ₃ - and C ₄ -alkynes, 1,2-butadiene and C ₅₊ hydrocarbons.

The separation of the C ₄ fraction has a problem of complicated distillation due to the small difference in relative volatility of the components. Therefore, the separation is carried out by so-called extractive distillation, that is, the addition of a selective solvent (also referred to as an extractant) having a higher boiling point than the mixture to be separated and which can increase the component to be separated. Relative volatility differences.

Many methods are known based extractive distillation using a selective solvent by separating the C ₄ fraction. They have the following common features: in general, at low temperatures (often in the range of 20 to 80 ° C) and at moderate pressures (often at standard pressures up to 6 bar), suitable thermodynamic conditions are employed to allow the form of vapor to be separated. _{The 4} fraction is countercurrent to the liquid selective solvent, resulting in the selective solvent loading the component having a higher affinity in the C ₄ fraction, while the component having a lower affinity for the selective solvent remains in the gas phase and The top stream is drawn out. Next, by distillation, under suitable thermodynamic conditions (ie, higher temperature and/or lower pressure than the first process step), one or more further process steps are performed to release the supported solvent stream in the selective solvent. These components.

The C ₄ fraction contains impurities which will cause problems associated with extractive distillation (more specifically, solvent foam formation and equipment fouling), and therefore, specifically, before the C ₄ fraction is supplied to the extractive distillation, it must be They are removed to ensure reliable operation of the extractive distillation.

In particular, the impurities causing the above problems are components having a higher boiling point than 1,3-butadiene, and among them, it is worth mentioning that C ₅₊ hydrocarbons (mainly hydrocarbons having 5 or more carbon atoms per molecule, Isoprene, C ₄ oligomers and polymers (i.e., oligomers of butadiene having the formula (C ₄ H ₆ ) _n and optionally polymers, wherein n is greater than or equal to 2)). The proportion of C ₅₊ hydrocarbons in the C ₄ fraction depends, in particular, on the operating conditions of the thermal cracking and up to 1000 ppm (by weight) or even up to 5000 ppm by weight, based on the total weight of the C ₄ fraction. , up to 1% by weight in certain cases. The formation of C ₄ oligomers and polymers is due in particular to storage and transport; therefore the ratio depends primarily on storage and delivery conditions, in particular the degree of inerting of the temperature, duration, storage and/or transport atmosphere.

In addition, extractive distillation of C ₃ hydrocarbons (i.e., hydrocarbons having three carbon atoms per molecule) can also cause problems; especially methyl acetylene, which has similar affinity to commonly used selective solvents such as 1,3-butadiene. . The proportion of C ₃ hydrocarbons in the feed stream of the extractive distillation should therefore be limited to up to the feed stream 50 ppm (by weight) of the total weight.

The above-mentioned problems of pre-purification of the feed stream of the extractive distillation of the C ₄ fraction have heretofore been solved in different ways: in a known mode of operation, in the upstream of the distillation column connection of the extractive distillation, the C ₃ hydrocarbon is removed via the top And other components are extracted through the bottom. To remove the high boiling component compared to 1,3-butadiene, the underflow is then supplied to the vaporizer vessel, i.e., to a device having a single tray. In the vaporizer vessel, the crude C ₄ stream which consumes the C ₃ component is substantially completely vaporized under the control of the flow rate, so that the high boiling component of the residual liquid component is not more than that of the 1,3-butadiene. containers C supplied to the vaporizer ₄₅ wt% of the total weight of the fraction, in particular 1% by weight, or even 0.1 wt.%. The liquid flow remaining in the vaporizer vessel is discharged as a flushing stream. However, the drawback is that, together with the flushing stream is also high boilers, with a high proportion of the emission value was C ₄ hydrocarbons.

In this regard, one of the objects of the present invention provides a method for removing the secondary component of the extractive distillation cracking in the C ₄ fraction at a low cost and energy consumption in a simple technical manner, thereby extending the service life of the extractive distillation column. .

It reached the target by the following method: providing a purified vapor of the C ₄ fraction used as stream ₄ from the beginning as a fraction of the liquid feed stream C extractive distillation using a selective solvent of the containing butane, butene and 1,3-butadiene and C ₃ hydrocarbons, C ₄ oligomers and polymers, and C ₅₊ hydrocarbons, the vaporized purified C ₄ fraction comprises: - less than the purified C ₄ fraction of the vapor state 50 ppm by weight of C ₃ hydrocarbons, less than 2/3 of C ₅₊ hydrocarbons present in the feed stream, and less than 5% by weight of C ₄ oligomers and present in the The polymer in the feed stream.

The method comprises the following process steps: 1) removing the C ₃ hydrocarbons, 2) ₄ C to remove oligomers and polymers, and C ₅₊ hydrocarbons, in each case, reduced to purified C of the vaporous distillate ₄ above for a specified residual content, and 3) vaporizing the liquid C ₄ fraction, wherein: all process steps 1), 2) and 3) are carried out in a single distillation column, and the liquid C ₄ fraction is supplied to the upper three Dividing one part to form a rectifying section and a stripping section, and extracting a top stream containing C ₃ hydrocarbons, a C ₄ -containing oligomer and a polymer and a bottom stream of C ₅₊ hydrocarbons therefrom, and extracting steam from the stripping section Purification of the C ₄ fraction side stream.

A typical C ₄ fraction from a petroleum brain cracker has the following composition in weight percent:

The C ₄ fraction from the petroleum brain cracker thus mainly includes butane, butene and 1,3-butadiene. In addition, a small amount of other hydrocarbons are present. C ₄ -alkynes are often up to 5% by weight or up to 2% by weight.

With regard to the previously defined extractive distillation, useful selective solvents are generally those having a higher boiling point than the mixture to be separated and having a greater affinity for the conjugated double bond and the triple bond ratio for the simple double bond and the single bond. Good bipolar and better bipolar aprotic solvents. For reasons of equipment, it is preferably a weakly corrosive or non-corrosive substance.

Suitable optional solvents for use in the process of the invention are, for example, butyrolactone, nitrile (such as acetonitrile, propionitrile, methoxypropionitrile), ketones (such as acetone), furfural, N-alkyl substituted low carbon a number of aliphatic acid amines (such as dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide), N-methylmorphomorpholine, N-alkyl Substituted cyclic decylamine (indoleamine) (such as N-alkylpyrrolidone, especially N-methylpyrrolidone). In general, a N-alkyl substituted lower number aliphatic acid decylamine or an N-alkyl substituted guanidinium amide is used. Particularly advantageous are dimethylformamide, acetonitrile, furfural and, more preferably, N-methylpyrrolidone.

However, it is also possible to use mixtures of such solvents with each other (for example, N-methylpyrrolidone and acetonitrile), such solvents and cosolvents (such as water and/or a third butyl ether such as methyl tert-butyl) A mixture of ether, ethyl tert-butyl ether, propyl tert-butyl ether or n- or isobutyl tert-butyl ether.

Particularly suitable is N-methylpyrrolidone, which is preferably in the form of an aqueous solution, especially having 8 to 10% by weight of water, more preferably 8.3% by weight of water.

In order to avoid the problem of extractive distillation, the use stream to be supplied is 50 ppm (by weight) of C ₃ hydrocarbons containing less than the total weight of the purified C ₄ fraction of the vapor state, less than two-thirds of the presence in the feed stream. of less than ₄ and C ₅₊ hydrocarbon fraction of 5% by weight in the presence of purified C ₄ vaporous of oligomers and polymers of C feed stream.

It has been found the following process steps may be performed in a simple distillation column and rectifying section having a stripping section of the: 1) removing the C ₃ hydrocarbons, and 2) removal of oligomers and polymers C ₄ and C ₅₊ hydrocarbons, at in each case, reduced to a residual content above for purified C of the vaporous fraction designated _4, and 3) vaporizing the liquid C ₄ fraction. Since this column, out through the top component C _3, C ₄ out through the bottom of oligomers and polymers, and C ₅ hydrocarbons, and purified withdrawn from the stripping section of the C ₄ fraction of a vaporous side stream.

Compared to the known method, all the process steps required for the treatment of the C ₄ fraction supply to the extractive distillation of the single distillation column can be carried out in a relatively simple manner in a single distillation column by the method according to the invention, and Correspondingly, capital and energy costs are saved.

Further, the method of the present invention can be removed in the C ₄ fraction parts of 1,3-butadiene as compared to high-boiling, and the product of value of C ₄ hydrocarbons greatly reduced loss. The bottom stream of the distillation column can be concentrated substantially without restriction by discharging a liquid flushing stream from the vaporizer vessel. For practical reasons, especially based on thermal integration reasons, the underflow concentration is often limited such that it still contains about 50% by weight of the C ₄ component, which means that the bottom temperature of the distillation column should not be too high, before recycling to extractive distillation, The waste heat of the process stream (eg, waste heat from a selective solvent) can be used more efficiently for heating.

Preferably the vaporous purified C ₄ fraction of C ₃ hydrocarbons are depleted to less than purified vapor of C ₄ 10 ppm (by weight) of the total weight of the fraction, or less than 4 ppm (by weight).

More preferably, the vapor of purified C ₄ fraction depleted in C ₅₊ hydrocarbon feed stream to a half or less of C ₅₊ hydrocarbons.

The distillation column is preferably operated at a top pressure of 4 to 10 bar (absolute), more preferably at a top pressure of 6 to 7 bar (absolute).

The distillation column is preferably a tray column.

The tray column has in particular 30 to 100 actual trays or more preferably 50 to 70 actual trays.

The invention will be specifically described below with reference to the drawings and the operation examples.

The only figure (Fig. 1) shows a distillation column K, in which the liquid C ₄ fraction is supplied to the upper third of the feed stream 1, and the top stream 2 containing C ₃ hydrocarbons is withdrawn therefrom. The bottom stream 3 of the high boiling component of butadiene and the vapor side of the stripping section of the distillation column K draw the stream 4 and supply the latter to the extractive distillation.

The starting material is a liquid C ₄ fraction feed stream of 100 kt/a plant comprising 200 ppm propane, 400 ppm propylene, 300 ppm propadiene, 400 ppm propyne, 2.0% n-butane, 6.0% different Butane, 19.0% n-butene, 28.3% isobutylene, 5.5% trans-2-butene, 4.4% cis-2-butene, 39.0% 1,3-butadiene, 0.2% 1,2-butadiene 1200 ppm 1-butyne, 4500 ppm vinyl acetylene and 1000 ppm of isopentane, 3-methyl-1-butene and 2-methyl-2-butene, in each case, The total weight of the stream. The C ₄ oligomers and polymers can be present in the % range depending on storage and delivery conditions. For use as a feed stream for extractive distillation, the above C ₄ fraction is prepurified for comparison in a plant having a distillation column in which C ₃ hydrocarbons are removed overhead and other components are passed through the bottom The lower stream is then fed to a vaporizer vessel (i.e., a device having a veneer) to remove the higher boiling component of the 1,3-butadiene. In the vaporizer vessel, the crude C ₄ stream which consumes the C ₃ component is substantially completely evaporated and discharged under the control of the flow rate, so that the residual liquid component has a higher boiling point than the 1,3-butadiene C. _5% by weight of not more than 5 parts by group C supplied to the vaporizer ₄ containers of the total weight of the fraction, thus minimizing liquid residue in loss of C ₄ components. The proportion of oligomers and polymers present in the liquid residue is much greater due to lower vapor pressure. The liquid flow remaining in the vaporizer vessel is discharged as a flushing stream.

According to an embodiment of the present invention, the C ₄ fraction is supplied as a feed stream to a single distillation column, from which a hydrocarbon-containing overhead stream, a C ₄ oligomer-containing polymer and a C _{5 +} hydrocarbon bottom stream, and a purified C are withdrawn. Steam side stream of ₄ fractions.

In both cases (comparative examples and examples of the invention), the purified C ₄ fraction meets the specifications defined in the technical solution for the C ₃ component, which means that in each case, it contains less than the purification of the vapor C. 50 ppm by weight of C ₃ hydrocarbons based on the total weight of the ₄ fractions. According to the prior art, C ₄ fraction in the presence of less than 5% of the C ₅ components in the residue stream (= flushing stream) is removed, however, in the process of the present invention, the C ₅₊ hydrocarbon feed stream in the presence of 95 and a third or more by weight of the feed stream in the presence of C ₄ oligomers and polymers in the residue stream is discharged through the bottom% or more.

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

In contrast, the residue flow rate (bottom flow rate) from the distillation column in the process of the present invention was 183 kg/h, and 1,3-butadiene was 20% by weight. According to the prior art, the initial distillation of the yield of 1,3-butadiene (C ₄ fraction to the count of the purified 1,3-butadiene in the C ₄ fraction 1,3-butadiene) was 99.29%, by contrast, is 99.49% in the present example.

As a further advantage, in the method of the present invention, prior art methods to remove more purification C ₄ fraction of higher purity. Feeding a total of 3000 ppm (by weight) of C ₅ components (additionally other proportions of C ₆ components and oligomers and polymers, which are not considered here) at 32 t/h the C _4, to 96 kg / h of C ₅ components to be delivered according to the prior art extractive distillation. In the case of the present invention, only 41 kg/h of the C ₅ component was delivered to the extractive distillation. Due to the relatively small amount of C ₅ from the initial distillation the components supplied to the extractive distillation, hence reducing loss of subsequent purification distillation or extractive distillation of the 1,3-butadiene. Based on the pure product from the overall extractive distillation including preliminary distillation, the yield of 1,3-butadiene (in 100%) was 96.47% according to the prior art, and in the case of the present invention, 96.69%.

In a large equipment designated above 100 kt/a, the loss of the valuable 1,3-butadiene product is increased by about 218 t/a according to the method of the prior art.

By the fact that the solvent forms a closed loop, the problem components and impurities are removed in advance, leaving the solution transparent, which minimizes regeneration complexity. At the same time, the scale of the extractive distillation apparatus (scale in the column) and the formation of the foam are minimized. Therefore, a small amount of antifoaming agent is required, and the cost is accordingly reduced. In the case of downtime, the reduced fouling reduces cleaning costs. Each stoppage means a production interruption of about 2 weeks; the cleaning cost increases. This leads to 7 digits The cost of the number.

1‧‧‧feed stream

2‧‧‧ top flow

3‧‧‧ Underflow

4‧‧‧ side draw

K‧‧·Distillation Tower

Figure 1 shows a distillation column K in which a liquid C ₄ fraction is supplied to the upper third of the feed stream 1 from which the top stream 2 containing C ₃ hydrocarbons is withdrawn, and the 1,3-butadiene is contained. The bottom stream 3 of the high boiling component and the vapor side of the stripping section of the distillation column K draw the stream 4 and supply the latter to the extractive distillation.

1‧‧‧feed stream

2‧‧‧ top flow

3‧‧‧ Underflow

4‧‧‧ side draw

K‧‧·Distillation Tower

Claims (9)

A method for providing a vaporized purified C ₄ fraction by extractive distillation using a selective solvent as a use stream, starting from a feed stream of a liquid C ₄ fraction, the feed stream comprising not only butane, butene and 1,3-butadiene and hydrocarbons comprising C _3, C ₄ oligomers and polymers, and C ₅₊ hydrocarbons, purification of the vaporous fraction comprising C _4: purification of less than C ₄ fraction of the vaporous 50 ppm by weight of C ₃ hydrocarbons, less than 2/3 of the C ₅₊ hydrocarbons present in the feed stream and less than 5% by weight of the C ₄ oligos present in the feed stream oligomer and a polymer, the method comprising the following process steps: 1) removing the C ₃ hydrocarbons, 2) removal of oligomers and polymers C ₄ and C ₅₊ hydrocarbons, in each case, for which the above reduced vapor Purifying the residual content of the C ₄ fraction, and 3) vaporizing the liquid C ₄ fraction, wherein: all process steps 1), 2) and 3) are carried out in a single distillation column, and the liquid C _{4 is} distilled. Supplying to the upper third of the portion to form a rectifying section and a stripping section, and extracting a top stream containing C ₃ hydrocarbons, a C ₄ -containing oligomer and polymer, and an underflow of C ₅₊ hydrocarbons therefrom, and The stripping section extracts the purity of the vapor state C ₄ fraction stream side. The method of claim 1, wherein the C ₃ hydrocarbons in the purified C ₄ fraction of the vapor state are consumed below 10 ppm by weight of the total weight of the purified C ₄ fraction of the vapor state. The method of claim 2, wherein the C ₃ hydrocarbons in the purified C ₄ fraction of the vapor state are consumed below 4 ppm by weight of the total weight of the purified C ₄ fraction of the vapor state. The method of any one of claims 1 to 3, wherein the C ₅₊ hydrocarbons in the purified C ₄ fraction of the vapor state are depleted to less than one-half of the C ₅₊ hydrocarbons present in the feed stream . The method of any one of claims 1 to 3, wherein the distillation column is operated at a top pressure of 4 to 10 bar (absolute). The method of claim 5, wherein the distillation column is operated at a top pressure of 6 to 7 bar (absolute). The method of any one of claims 1 to 3, wherein the distillation column is a tray column. The method of claim 7, wherein the tray has 30 to 100 actual trays. The method of claim 8, wherein the distillation column has from 50 to 70 actual trays.