Utilize the method for extracting rectifying aromatics separation from hydrocarbon mixture
The present invention is a method of utilizing aromatic hydrocarbons in the selective solvent extracting rectifying separating hydrocarbons mixture.
Aromatics separation mainly contains two class methods from reformed oil or cracking hydrogenated gasoline, and a class is liquid-liquid extraction process, and a class is an extraction fractional distillation.Compare with liquid-liquid extraction process, extraction fractional distillation have flow process and simple to operate, facility investment is low, low power consumption and other advantages, be particularly suitable for from the high hydrocarbon mixture of aromaticity content, reclaiming aromatic hydrocarbons.
Existing extraction fractional distillation generally adopts the separation process scheme of raw material prefractionation-extracting rectifying-solvent recuperation, certainly also comprises the parts such as regeneration of the distillation of non-aromatics or washing, solvent.The solvent of selecting for use in the extracting rectifying process mainly contains N-Methyl pyrrolidone (NMP), N-formyl morpholine (NFM) or tetramethylene sulfone.In general, relatively poor to the selectivity of aromatic hydrocarbons and naphthenic hydrocarbon because N-Methyl pyrrolidone is too strong to the hydro carbons dissolving power, yield is on the low side when being used to reclaim single benzene or dimethylbenzene etc., and reason makes its application be subjected to bigger restriction.Relative N-Methyl pyrrolidone, the N-formyl morpholine has selectivity preferably, is the technology of solvent with the N-formyl morpholine therefore, has obtained industrial application in extracting rectifying benzene.EP708072A
1Disclosing a kind of is solvent with NFM, reclaims C simultaneously with extraction fractional distillation
6~C
7The method of benzene, toluene in the fraction, this method are divided into raw material rich benzene and are the richest in two kinds of intermediate products of benzene by distillation type stabilization procedures earlier, and then the different sites that these two kinds of intermediate products feed extractive distillation column is respectively handled.This method is difficult to handle C in a system owing to be subjected to the restriction of NFM to naphthenic hydrocarbon and arenes selectivity
6~C
8Fraction obtains highly purified benzene, toluene and dimethylbenzene simultaneously, and the required extractive distillation column stage number of this method is more, is about 70, and the yield of benzene and toluene is on the low side, does not all reach more than the 99 heavy %.Meet and hydrolysis easily take place behind the water and generate formic acid and morpholine owing to the solvent N-formyl morpholine selected for use in this technology again, in case in the system because certain a variety of causes when having water to exist, hydrolysate can cause corrosion to equipment.Even under water-free situation, the operational condition during owing to solvent recuperation is harsh, and the temperature at the bottom of the recovery tower is higher, and the N-formyl morpholine also is easy to generate coking, decomposition.
CN1091413A also discloses a kind of method with seperation of hydrocarbon mixture as function of extractive distillation, this method mainly is to select a kind of solvent with highly selective, can be under used concentration and temperature with feed liquid in hydrocarbon polymer form and mix the gap, control extractive distillation condition, make that considerable part forms two liquid phases in the whole height of extraction distillation column, mass transfer is not only carried out between two liquid phases, also between liquid phase and vapour phase, carry out.The solvent that this method is selected for use mainly is N-formyl morpholine and tetramethylene sulfone; as being solvent with the N-formyl morpholine; this method is applicable to from boiling point separates alkene and paraffinic hydrocarbons for-12~50 ℃ the hydrocarbon mixture that contains alkene and paraffinic hydrocarbons, as separating butane and butylene from the c4 fraction of pyrolysis gasoline.If is solvent, can from pyrolysis gasoline and catalytic reformate, separate obtaining benzene with the tetramethylene sulfone.Obviously, control the extracting rectifying process and between two liquid phases, carry out, bring difficulty can for operation and control.
USP5,310,480 disclose a kind of comparatively simple method with extraction fractional distillation aromatics separation and non-aromatics, this method is not established prefractionation, only the aromatic hydrocarbons in the raw material is separated with non-aromatics with an extractive distillation column that contains reboiler, adopt cyclonic separator with aromatic hydrocarbons and separated from solvent afterwards again, solvent and water behind the aromatics separation all recycle.Though the operation of this method is simple, its extracting rectifying operation is to carry out under than the condition of (7~11) at high solvent, so energy consumption is higher, and this method only is applicable to aromatics separation and non-aromatics from the low raw material of naphthene content.The extraction distillation solvent of selecting for use in this method has glycols and tetramethylene sulfone class.
The purpose of this invention is to provide a kind of selective solvent extracting rectifying that utilizes, the method for aromatics separation more effectively from hydrocarbon mixture is with the separable mixture that obtains high-purity benzene or benzene, toluene and dimethylbenzene of this method.
This area the professional all know, in extracting rectifying, the selection of extraction solvent plays decisive action to the energy consumption of purity, yield and the process of recovery product.Different solvents has different selectivity, and same choice of Solvent reduces along with the rising of extraction temperature, and therefore, extracting rectifying should be chosen lower service temperature as far as possible when guaranteeing certain mass-transfer efficiency.But temperature is too low, and the top of extractive distillation column easily forms two liquid phases and is unfavorable for operation control; Otherwise,, can not bring into play choice of Solvent well again if service temperature is selected too highly.
We find, after from the raw material that is rich in aromatic hydrocarbons, isolating the benzene fraction with common rectifying tower, it is fed extractive distillation column, as long as this moment is the operational condition of control extracting rectifying, can make its operation reach the critical state that dissolves each other, the so-called critical state of dissolving each other is meant such state: operation keeps a liquid phase, will reach two liquid phases, but not reach the state of two liquid phases.Operate under the critical state that dissolves each other, it is little to extract used solvent ratio, effectively the energy consumption of economizer.
Specifically, method of the present invention comprises the steps: that (1) is that 60~98 hydrocarbon mixtures that weigh % are told the benzene fraction by prefractionation from aromaticity content, (2) the benzene fraction is fed the middle part of extractive distillation column, solvent is fed by cat head, and the working pressure of control extractive distillation column is 0.10~0.30MPa, it is 80~130 ℃ that solvent is gone into the tower temperature, (3) rich solvent that is rich in benzene that the extracting rectifying tower bottom is discharged feeds the solvent recovery tower that water stripping is arranged, the cat head fraction obtains the purified petroleum benzin product after condensation, the lean solvent of discharging at the bottom of the tower is introduced the recycle of extracting rectifying top of tower again.
Aforesaid method is applicable to from the raw material that is rich in aromatic hydrocarbons and separates purified petroleum benzin, but the present invention also is applicable to from the raw material that is rich in aromatic hydrocarbons and separates BTX aromatics, promptly isolate benzene,toluene,xylene (BTX), its concrete operations step comprises: (1) is that 60~98 hydrocarbon mixtures that weigh % are told the benzene fraction by prefractionation from aromaticity content, and control
The methylcyclohexane that contains in the system benzene fraction is not more than 40 heavy % of this material total amount in the raw material, and (2) feed the bottom of extractive distillation column with the benzene fraction, tell the benzene fraction after remaining benzene after cut feed
The top of extractive distillation column, solvent is fed by cat head, and the working pressure of control extractive distillation column
Be 0.10~0.30MPa, it is 80~130 ℃ that solvent is gone into the tower temperature, and the rich solvent that is rich in aromatic hydrocarbons that (3) discharge the extracting rectifying tower bottom feeds the solvent recuperation that water stripping is arranged
Tower, the cat head fraction obtains BTX aromatics after condensation, and the lean solvent of discharging at the bottom of the tower is introduced collection again
Get the recycle of rectifying tower top.
Method of the present invention promptly is suitable for Separation of Benzene from the raw material that is rich in aromatic hydrocarbons, also is applicable to separate other aromatic hydrocarbons from hydrocarbon mixture, as the mixture of BTX.For the process of Separation of Benzene, the benzene fraction that (1) step prefractionation obtains is admitted to extractive distillation column, and remaining benzene after cut is discharged from, and can be used as gasoline blending component.For the process of separating BTX aromatics, bottom and top that benzene fraction and benzene after cut are introduced extractive distillation column respectively, can bring into play the effect that extracting rectifying removes the heavy non-aromatics to greatest extent like this, in same extractive distillation column, finish separating of aromatic hydrocarbons and non-aromatics, and then in solvent recovery step, remove extraction solvent and obtain BTX aromatics.BTX aromatics can obtain highly purified benzene,toluene,xylene with the conventional further rectifying of method.
Described extraction distillation solvent is selected from general formula
The sulfone class, R in the formula
1, R
2, R
3, R
4Be selected from hydrogen, C respectively
1~C
10Alkyl, C
7~C
12Aralkyl, C
1~C
8Alkoxyl group.Comparatively preferred solvent is tetramethylene sulfone, 2-methyl sulfolane or 2, and 4-dimethylsulfolane, highly preferred solvent are tetramethylene sulfone.
The weight ratio of solvent and rectifying material in the described extracting rectifying step, promptly solvent ratio is 3.0~6.0, and hydrocarbon content is 0.2~1.0 heavy % in the extraction distillation solvent, and water-content is 0.2~0.6 heavy %.
In described step (3) the solvent recuperation process, the weight ratio of water stripping and circulating solvent is 0.003~0.02 in the recovery tower, is preferably 0.005~0.015.
Equipment used was followed successively by separation column, extractive distillation column and recovery tower during said process respectively went on foot, wherein extractive distillation column and recovery tower are selected from packing tower or tray column, perhaps epimere is the combined column of tray column for the packing tower hypomere, and the preferred epimere of recovery tower is the combined column of packing tower.Obtain purified petroleum benzin if separate during operation, then controlling extracting rectifying cat head temperature is 65~110 ℃, column bottom temperature is 125~165 ℃, it is 80~110 ℃ that solvent is gone into the tower temperature, obtain BTX aromatics if separate, then controlling extracting rectifying cat head temperature is 70~120 ℃, and column bottom temperature is 130~175 ℃, and it is 90~130 ℃ that solvent is gone into the tower temperature.
Method of the present invention can be carried out with general extracting rectifying equipment and device, for C
9Aromatic hydrocarbons can select for use a pre-rectifying tower to implement the inventive method, for C less than the raw material of 0.5 heavy %
9The raw material that aromaticity content is high can select for use two separation column series connection carrying out prefractionations to implement the inventive method.
Fig. 1 is the schematic flow sheet with the inventive method Separation of Benzene.
Fig. 2 is the schematic flow sheet with the inventive method aromatics separation mixture from hydrocarbon mixture.
Raw material enters preliminary fractionator 2 by pipeline 1 among Fig. 1, the benzene fraction is discharged by cat head and is entered drainer 19, non-condensable gas is discharged by pipeline 4, the benzene fraction part of condensation passes back into tower 2 through pipeline 5, rest part enters the middle part of extractive distillation column 8 through pipeline 6, and the benzene after cut of preliminary fractionator 2 bottoms is discharged by pipeline 7.In the extracting rectifying process, solvent enters extractive distillation column 8 by cat head, and through extracting rectifying, non-aromatics is discharged by overhead line 9, and this material also needs to reclaim trace solvent through a simple distillation plant, does not draw among the figure.The rich solvent that is rich in benzene of discharging at the bottom of the tower enters solvent recovery tower 12 middle parts through pipeline 11, water vapor enters recovery tower 12 bottoms by pipeline 16, in the presence of water vapor, the reduce pressure stripping distillation of this tower 12, overhead product enters drainer 20 through pipeline 13, a high-purity benzene part that obtains after oily water separation passes back into the recovery cat head through pipeline 14, and a part is discharged through pipeline 18 and promptly obtained purified petroleum benzin.The water that obtains after the oily water separation is recycled into recovery tower 12 through pipeline 16 after passing through interchanger 21 heat exchange by pipeline 15 again, and the lean solvent of discharging at the bottom of the recovery tower enters extractive distillation column 8 top recycles after passing through interchanger 21 and 22 heat exchange by pipeline 17.
In the above-mentioned tripping device, the number of theoretical plate of extractive distillation column 8 is 20~30, the theoretical plate number of recovery tower 12 is 5~15, the working pressure of recovery tower 12 is 0.035~0.05MPa, column bottom temperature is 150~185 ℃, tower top temperature is 45~65 ℃, and the weight ratio of water stripping and solvent (water stripping ratio) is 0.003~0.02, is preferably 0.005~0.015.
Fig. 2 is the schematic flow sheet with the inventive method aromatics separation mixture from hydrocarbon raw material, its operation is basic identical with the method for separating purified petroleum benzin, different is top that benzene after cut that preliminary fractionator 2 tells introduces extractive distillation columns 8 by pipeline 7, the bottom that the benzene fraction is introduced extractive distillation column 8 by pipeline 6, what discharged at recovery tower 12 tops is BTX aromatics, wherein a part passes back into recovery tower 12 tops through pipeline 14, a part is discharged through pipeline 18, the BTX aromatics of discharging can obtain highly purified aromatic hydrocarbon product with the further rectifying of the method for routine, as benzene, toluene, dimethylbenzene.
The present invention is than general extracting rectifying process, owing to select the good sulfone kind solvent of selectivity for use and by prefractionation, from hydrocarbon feed, tell the benzene fraction, especially during the aromatics separation mixture, raw material is divided into the benzene fraction and two strands of materials of benzene after cut enter extractive distillation column by prefractionation, the operational condition that control is suitable, the extracting rectifying process is operated under the critical state that dissolves each other, solvent ratio when therefore the inventive method can reduce the extractive distillation column operation, further reduce plant energy consumption, and obtain highly purified aromatic hydrocarbons mixture.
Below by example in detail the present invention, but the present invention is not limited to this.
Example 1
This example reclaims the situation of benzene for the flow process of pressing accompanying drawing 1, raw material is obtained the benzene fraction through prefractionation, extracting rectifying is carried out at the middle part that the benzene fraction is fed extractive distillation column again, raw materials used is the cracking hydrogenated gasoline, raw material and the benzene fractional composition after prefractionation see Table 1, the extracting rectifying operational condition sees Table 2, and solvent is a tetramethylene sulfone, and extracting rectifying the results are shown in Table 3.
Example 2
This example is the situation of pressing the flow process recovery benzene,toluene,xylene of accompanying drawing 2, and raw material of selecting for use and extraction solvent are with example 1.Earlier raw material is obtained benzene fraction and benzene after cut through prefractionation, extracting rectifying is carried out on bottom and the top that benzene fraction and benzene after cut is fed extractive distillation column respectively again, benzene fraction that obtains after prefractionation and benzene after cut composition see Table 1, the extracting rectifying operational condition sees Table 2, and extracting rectifying the results are shown in Table 3.
Table 2
Project | Example 1 | Example 2 |
Extractive distillation column number of theoretical plate solvent advances column plate benzene fraction and goes into column plate benzene after cut and go into the column plate solvent ratio (to raw material, weight) tower top pressure, the MPa solvent is gone into the tower temperature, ℃ solvent comprises water amount, heavy % raw material is gone into the tower temperature, ℃ benzene fraction benzene after cut tower top temperature, ℃ column bottom temperature, ℃ | 25 3 16 - 4.5 0.22 105 0.45 80 - 105 148 | 25 3 16 10 4.5 0.20 110 0.27 80 50 113 153 |
Recovery tower number of theoretical plate feed plate tower top pressure, the MPa water stripping is than (to solvent, weight) tower top temperature, ℃ column bottom temperature, ℃ | 10 5 0.05 0.008 55 177 | 10 5 0.04 0.01 66 177 |
Table 3
Project | Example 1 | Example 2 |
Non-aromatics content in the aromatic hydrocarbons, ppm | 425 | 542 |
Aromatics yield, heavy % benzene toluene dimethylbenzene | 99.92 - - | 99.95 99.97 98.85 |
Aromaticity content in the non-aromatics, heavy % benzene toluene dimethylbenzene | 0.45 - - | 0.25 0.52 0.62 |
Extractive distillation column thermal load cat head, * 10
9At the bottom of Jiao Er/ton aromatic hydrocarbons tower, * 10
9Jiao Er/ton aromatic hydrocarbons
| 0.09 0.61 | 0.09 0.60 |
The recovery tower thermal load
* | | |
Cat head, * 10
9Jiao Er/ton aromatic hydrocarbons
| 0.89 | 0.90 |
At the bottom of the tower, * 10
9Jiao Er/ton aromatic hydrocarbons
| 0.84 | 0.81 |
*The only heat exchange of lean solvent and water stripping at the bottom of the consideration recovery Tata