Background technology
Poly-basic aromatic carboxylic acid is the important source material of producing polyester (PET) fiber and resin, main at present employing alkylaromatic hydrocarbon air oxidation process is produced, this method is dissolved in the raw material alkylaromatic hydrocarbon in the acetate solvate that contains catalyst acetic acid cobalt, manganese acetate, hydrogen bromide (or tetrabromoethane), bubbling air or oxygen rich air are carried out oxidation, generate the solid product aromatic carboxylic acid.Typical temperature of reaction is 120~225 ℃, pressure 0.1~2MPa, the residence time 40~120min, reaction heat shifts out by solvent evaporation, in the Returning reactor, the slurry of generation obtains high purity aromatic carboxylic acid product through follow-up separation and refining step again behind the vapor condensation.
Oxidation reactor is the core apparatus that high purity aromatic carboxylic acid (for example pure terephthalic acid) is produced, and the oxidation reactor that uses has two types of stirring tank and bubble towers at present.Rectifying tower separation solvent acetic acid and water are set above oxidation reactor can directly utilize reaction heat to carry out rectifying separation, favourable energy-conservation.Therefore, some patents have proposed measure that reactor and rectifying tower are combined.For example, patent JP14098/1979 proposes a rectifying tower is set above reactor, and this rectifying tower is not made up of with the throngh flowing type tray of downtake polylith.But complicated component in the reaction end gas except the water that solvent acetic acid and reaction generate, also contains solid particulate and liquid foam, a large amount of non-condensable gases and a spot of alkylaromatic hydrocarbon and other organic constituent.Therefore, the design requirements of this solvent distillation section is containing under the situation of non-condensable gases separating acetic acid and water efficiently, and entrained solid and liquid foam in the absorption reaction tail gas effectively, and other organic constituent also will prevent the solid accumulation simultaneously and stop up.Though can not avoid deposition of solids and blocking problem with the dual-flow tray of downtake and adopt, its cost is that plate efficiency is low, plate only imitates 13~23%, and turndown ratio is low.In order to overcome this defective, the disclosed reactor of patent ZL94103145.4 adopts structured packing to carry out the rectifying separation of tail gas on top, simultaneously the multi-layer solid absorption tray is set below packing tower and results in blockage, the phegma even distribution device is set above packing tower to avoid the liquid distribution inequality to avoid solid to enter packing layer.Though these measures can improve separation efficiency, its structure more complicated.Simultaneously, because structured packing need be a material with the corrosion resistant metal of costliness, consumption is very big, and material and cost of processing are all very high, have increased the cost of oxidation reactor greatly.
On the other hand, its conversion zone of the oxidation reactor that has segregation section and the segregation section size of using at present is all different.The reactor reaction section diameter that has is big, and the segregation section diameter is little, and purpose is in order to obtain the high gas speed of segregation section, to reach the design requirements of segregation section.But diameter sharply dwindles in the junction of conversion zone and segregation section, and in a single day the liquid level of conversion zone arrives and be easy to form liquid level behind the contraction section and advance by leaps and bounds during operation, causes the segregation section liquid flooding and stops.The reactor that has is provided with an expanding reach separate solid particles and liquid foam on top, but but be difficult to prove effective for this scheme of alkylaromatic hydrocarbon oxidising process, because this process gas treatment capacity and solvent evaporation amount are very big, empty tower gas velocity high (can reach 0.4~1.0 meter per second) adopts expanding reach to be difficult to effective separate solid particles and minimizing liquid foam entrainment.
Summary of the invention
The object of the invention is to provide a kind of simple in structure, oxidation unit that performance is produced aromatic carboxylic acid efficiently, to overcome the defective of above-mentioned all kinds of reactors.
Technical solution of the present invention: be that gas fallaway section above reactor adopts the efficient tray column have downtake to replace existing packing tower or the column plate that do not have a downtake carries out rectifying separation, adopting up and down uniformly simultaneously, bubbling column reactor replaces the existing all kinds of conversion zone oxidation reactor different with the segregation section diameter.
The oxidation unit of producing aromatic carboxylic acid comprises an even straight-cylindrical bubble tower, be followed successively by gas fallaway section in the tower from top to bottom, free space segment and three phase reaction section, gas fallaway section accounts for 10~30% of bubble tower total height, three phase reaction section accounts for 60~85% of bubble tower total height, free space segment accounts for 5~15% of bubble tower total height, gas fallaway section is made up of 5~20 layers of supporting liquid column plate that has downtake, lower horizontal at three phase reaction section is equipped with gas distributor, gas distributor links to each other with the bubble tower inlet mouth, 1/4~1/2 place that is positioned at the three phase reaction section height above gas distributor is provided with material feeding tube, be provided with discharge nozzle at the bottom of the tower, cat head is provided with offgas duct, tail gas condenser and phlegma return line, the inlet of tail gas condenser links to each other with offgas duct, the pneumatic outlet of condenser links to each other with follow-up tail gas treating unit, and the liquid exit of tail gas condenser links to each other with follow-up dehydration tower with the phlegma return line respectively.
The gas fallaway section of setting of the present invention is positioned at bubble tower cylindrical shell top, is made up of the supporting liquid column plate of sandwich tape downtake, no phegma uniform device and gas uniform device, and it highly accounts for 10~30% of bubble tower height overall.
The supporting liquid column plate ratio of band downtake does not have significant advantage with the throngh flowing type tray of downtake, be exactly that being arranged so that on the column plate of downtake overflow weir can keep the certain liquid level height all the time, avoided that to cross the low gas-to-liquid contact that causes bad owing to liquid level on the column plate, or problem such as the too high formation liquid flooding of liquid level, thereby have higher plate efficiency and security.In addition, the column plate of band downtake also has bigger operating restraint and stability than turbogrid tray.The quantity of downtake is decided on phegma flow and tower diameter on the column plate, is generally sieve plate with 1 or 2 downtake, with the fixedly perforate floating valve tray of 1 or 2 downtake or blister-type column plate, float valve type column plate, inclined hole shape column plate.Wherein preferred wide aperture sieve plate and fixing perforate valve tray.
During work, add continuously in the three phase reaction section of bubble tower oxidation unit from feed-pipe behind raw material alkylaromatic hydrocarbon, solvent comprises water acetic acid, the catalyst cobalt-manganese-bromine uniform mixing, air or oxygen rich gas inlet mouth at the bottom of the tower enters gas distributor, bubbling is by the liquid bed after gas distributor disperses, carry out oxidizing reaction with the liquid phase reaction thing, generate product aromatic carboxylic acid solid.Reaction paste by tower at the bottom of discharge nozzle discharge continuously, be input to follow-up separation and refining step and further handle.Reaction heat shifts out by solvent acetic acid and evaporation of water gas.Because gas flow is big, carrying part liquid foam and solid particulate in the tail gas secretly, when gas passes through the gas fallaway section on tower top, to pass multilayer and hold the liquid tower tray, the gas that the phlegma of trim the top of column and Ta Nei rise carries out counter current contact step by step at gas fallaway section, most acetic acid is separated with water, entrained solid particle in the tail gas, liquid foam and organic composition enter liquid phase by gas phase, and be back in the reactor downwards with liquid with acetic acid, the tail gas that leaves gas fallaway section shifts out reactor through offgas duct and enters overhead condenser, solvent in the tail gas is by in the reflux tower of condenser condenses rear section, and part is delivered to follow-up dehydration tower dehydration in addition.
Device reaction section of the present invention does not have stirring rake and other moving parts, the gas fallaway section tray structure is simple, no gas-liquid even distribution device, the bubble liquid level that can stably keep certain height on column plate, increase gas liquid contacting efficiency and plate and imitate, overcome the problem of previous patent.Device of the present invention is applicable to the reaction conditions of various alkylaromatic hydrocarbon liquid phase catalytic oxidations, for example, the aromatic carboxylic acid product can be terephthalic acid, m-phthalic acid, phthalic acid, Tetra hydro Phthalic anhydride, naphthalic acid, benzenetricarboxylic acid, biphenyl carboxylic acids and phenylformic acid, 120~225 ℃ of temperature of reaction, pressure 0.1~2.0MPa, catalyzer total concn (Co+Mn+Br) 1000~3000ppm, charging solvent ratio (acetic acid: alkylaromatic hydrocarbon, kg/kg) 3~10: 1, water content 3~18% in the tower, reactor residence time 40~120min.
Embodiment
With reference to Fig. 1, the oxidation unit of producing aromatic carboxylic acid comprises an even straight-cylindrical bubble tower, be followed successively by gas fallaway section 3 in the tower from top to bottom, free space segment 10 and three phase reaction section 1, gas fallaway section 3 accounts for 10~30% of bubble tower total height, three phase reaction section 1 accounts for 60~85% of bubble tower total height, free space segment accounts for 5~15% of bubble tower total height, gas fallaway section 3 is made up of 5~20 layers of supporting liquid column plate 9 that has downtake, lower horizontal at three phase reaction section 1 is equipped with gas distributor 2, gas distributor 2 links to each other with the bubble tower inlet mouth, 1/4~1/2 place that is positioned at the three phase reaction section height above gas distributor 2 is provided with material feeding tube 5, be provided with discharge nozzle 6 at the bottom of the tower, cat head is provided with offgas duct 7, tail gas condenser 4 and phlegma return line 8, the inlet of tail gas condenser 4 links to each other with offgas duct 7, and the pneumatic outlet of condenser 4 links to each other with follow-up tail gas treating unit, and the liquid exit of tail gas condenser 4 links to each other with follow-up dehydration tower with phlegma return line 8 respectively.
Shown in Figure 2 is supporting liquid column plate with single downtake, is applicable to the less and lower situation of liquid flow rate of tower diameter, and chord downcomer 11 of 9 need of every block of column plate is positioned at the column plate avris.Shown in Figure 3 is the supporting liquid column plate of the two downtakes of band, be applicable to the big and liquid flow rate condition with higher of tower diameter, every block of column plate 9 is with a central downtake 12 and two limit downtakes 11, shown in legend, central downtake 12 is long and narrow rectangle, and limit downtake 11 is arc.
Usually, make the downtake total area on the supporting liquid column plate account for 1~20% of tower cross-sectional area, preferred 4~15%, the downtake height of weir plate is 30~100mm.The shape of downtake can be arc, rectangle and circle, is preferably chord downcomer and square downcomer.Adopt chord downcomer when downtake is arranged on the column plate avris, adopts square downcomer when downtake is arranged on column plate central authorities, the downtake of adjacent tray is staggered, and makes the liquid cross-flow by all areas of column plate.
The overflow weir of downtake has on the retaining plate liquid layer and makes the effect uniformly of liquid stream.Height of weir plate should not be low excessively, liquid holdup is few on the too low then plate, also unsuitable too high, too high then veneer pressure drop increase causes the downtake liquid flooding, suitable height of weir plate is 10~150mm, be preferably 30~100mm, its objective is the liquid level kept on the column plate tray spacing 40~60% between.The choose reasonable that the weir is long can guarantee the uniform distribution that liquid flows, and downtake weir, limit length is preferably 0.5~0.8 beta footpath, and the central downtake weir is about and equals tower diameter.The spacing of downtake bottom and column plate is determined that by liquid flow rate and downtake liquid level preferred spacing is 20~80mm.
Tray spacing size on the supporting liquid column plate has determined the height of equipment, and distance between plates too greatly makes tower height increase, and cost of equipment increases, if distance between plates is too little, liquid flooding in the time of can causing operation and serious entrainment reduce plate efficiency; The too high meeting of percentage of open area on the column plate causes the column plate leakage, and too low then aperture gas speed is too high, carries secretly seriously, all will influence plate efficiency.Usually, making tray spacing is 300~800mm, and the percentage of open area on the column plate is 5~20%, and the preferred 5~25mm in aperture, the bubble liquid level on the column plate are 40~60% of distance between plates.Fixedly the gas flow opening direction of perforate float valve is vertical with the liquid flow path direction, and gas-liquid discharges to both sides, makes liquid stream pass through column plate without barrier.
Separated from the gas section diameter of three phase reaction section of the present invention is identical, and the liquid level of conversion zone and diameter ratio are 3~7.
Following examples system is at the process of p-Xylol liquid-phase oxidation system terephthalic acid, and the method that is adopted also is applicable to other aromatic carboxylic acid production process.
Embodiment 1:
Conversion zone adopts bubble tower, and gas fallaway section adopts multilayer wide aperture sieve plate, and which floor column plate that is positioned at the segregation section bottom is because the gas-liquid flow is bigger, and its distance between plates and percentage of open area are respectively 500mm and 15% more greatly; Which floor the column plate gas-liquid flow that is positioned at segregation section top is less, so distance between plates and percentage of open area reduce, and is respectively 450mm and 11%.Reaction conditions is listed in table 1, and the structure of reactor parameter is listed in table 2, and conversion zone liquid phase output-index is listed in table 3, and the gas fallaway section output-index is listed in table 4.
Table 1 oxidation reaction condition
The PX treatment capacity (ton/hour) | Reaction pressure Mpa (absolute pressure) | Temperature of reaction ℃ | Catalyst concn ppm | Residence time min | Empty tower gas velocity m/s | Solid content % |
??Co | ??Mn | ??Br |
?25.7 | ??1.18 | ????188 | ??450 | ??450 | ??900 | ????73 | ??0.58 | ????26 |
Table 2 structure of reactor parameter
Diameter (mm) | Conversion zone height (m) | Segregation section height (m) | Freeboard height (m) | Stage number | The downtake number | Cofferdam height (mm) | Tube sheet spacing mm | Hole diameter of sieve (perforated) plate mm | Percentage of open area | Distance between plates Mm |
??4800 | ??20.0 | ??6.0 | ??4.0 | ??12 | ??1~2 | ??50 | ??45 | ??10 | ?0.11~ ?0.15 | ??450~ ??500 |
Discharging parameter at the bottom of table 3 reactor column
PX transformation efficiency (%) | TA yield (%) | Liquid phase P T concentration ppm | Liquid phase 4-CBA concentration (ppm) | Liquid phase water concentration wt% | Solid phase 4-CBA concentration (ppm) | TA crystal particle diameter μ m |
????99.8 | ????95.0 | ????9850.9 | 2555.7 | ????9.4 | ??5227.1 | ????80.1 |
Table 4 gas fallaway section output result
The phlegma reflux temperature (℃) | Overhead condensation liquid is formed wt% | Gas phase behind the overhead condensation is formed wt% |
Acetic acid | Water | ????PX | Acetic acid | Water | Non-condensable gas | ??PX | Solid particulate |
??100 | ??25.5 | ????74.5 | ????0.012 | ??0.79 | ????5.2 | ??93.6 | ??0.036 | Do not have |
Symbol PX represents p-Xylol in the table, and TA represents terephthalic acid, and 4-CBA represents intermediate product to carboxyl benzaldehyde.
Present embodiment is stressed that emphatically, gas fallaway section adopts after the wide aperture sieve-tray tower of band downtake, make that level stability is in about 50% (220~250mm) of distance between plates on the column plate, column plate does not stop up simultaneously, do not contain solid particulate in the cat head tail gas, gas phase entrained solid TA and PX are reclaimed by phegma.The height of overhead condensation liquid acetic acid content is a leading indicator weighing the gas fallaway section rectification effect, after gas fallaway section of the present invention adopts 12 wide aperture sieve plates, overhead condensation liquid acetic acid content is reduced to 25.5% of condensator outlet by about 70% in the conversion zone rising steam, the theoretical plate number suitable with this separating effect is 6, actual sieve plate number has adopted 12, and therefore full tower separation efficiency is 50%.Bubbling column reactor that the present invention provides is described except the requirement that can satisfy reaction, the high capacity tray that is adopted also can reach than higher separation efficiency.
Comparative Examples 1: for the efficient of more dissimilar column plates, in the industrial experiment device, adopt the multilayer dual-flow tray of no downtake to constitute gas fallaway section, conversion zone still is a bubble tower, the index that the adjustment reaction conditions provides its reaction result and table 3 is approaching, the effect of emphasis comparison gas segregation section.Oxidation reaction condition is listed in table 5, and the structure of reactor parameter is listed in table 6, and segregation section output the results are shown in table 7.
Table 5 oxidation reaction condition
The PX treatment capacity (ton/hour) | Reaction pressure Mpa (absolute pressure) | Temperature of reaction ℃ | Catalyst concn ppm | Residence time min | Empty tower gas velocity m/s | Solid content % |
??Co | ??Mn | ??Br |
??6.3 | ?1.12 | ??186 | ??630 | ??394 | ??984 | ????60 | ??0.31 | ??21.9 |
Table 6 structure of reactor parameter
Type of reactor | Gas fallaway section diameter mm | Gas fallaway section height m | Stage number | The downtake number | Hole diameter of sieve (perforated) plate mm | Percentage of open area | Distance between plates mm |
Bubble tower | ??2350 | ????8.1 | ??17 | Do not have | ???3.18~6.35 | ??0.2265 | ??400~ ??500 |
Table 7 gas fallaway section output result
The phlegma reflux temperature (℃) | Overhead condensation liquid is formed wt% | Gas phase behind the overhead condensation is formed wt% |
Acetic acid | Water | ??PX | Acetic acid | Water | Non-condensable gas | Solid particulate |
??97.8 | ??41 | ????59 | ??0.012 | ??3.2 | ??4.8 | ??92.0 | Do not have |
After adopting the dual-flow tray of above-mentioned no downtake, the overhead condensation liquid acetic acid content of in situ measurement is 41%, with the corresponding theoretical plate number of this separating effect be 3.8, number of actual plates is 17, therefore full tower separation efficiency only is 22.4%.Through in situ measurement, liquid level has only 70~90mm on the column plate, and liquid holdup is low excessively on the plate, has caused gas-to-liquid contact insufficient thus, and plate is imitated on the low side.
Comparative Examples 2: the dual-flow tray and the reactor of employing and Comparative Examples 1 same type experimentize in bigger reaction unit and measure plate efficiency to investigate scale effect.Reaction conditions is listed in table 8, and the structure of reactor parameter is listed in table 9, and gas fallaway section output the results are shown in table 10.
Table 8 oxidation reaction condition
The PX treatment capacity (ton/hour) | Reaction pressure Mpa (absolute pressure) | Temperature of reaction ℃ | Catalyst concn ppm | Residence time min | Empty tower gas velocity m/s | Solid content % |
??Co | ??Mn | ??Br |
???25.2 | ?1.12 | ??186 | ??670 | ??304 | ??974 | ??60 | ???0.39 | ???22.5 |
Table 9 structure of reactor parameter
Type of reactor | Gas fallaway section diameter mm | Gas fallaway section height m | Stage number | The downtake number | Hole diameter of sieve (perforated) plate mm | Percentage of open area | Distance between plates mm |
Bubble tower | ??4000 | ??8.2 | ??15 | Do not have | ?3.18~6.35 | ???0.2265 | ????500 |
Table 10 gas fallaway section output result
The phlegma reflux temperature (℃) | Overhead condensation liquid is formed wt% | Gas phase behind the overhead condensation is formed wt% |
Acetic acid | Water | Acetic acid | Water | Non-condensable gas | Solid particulate |
????98.8 | ????58 | ????42 | ????5.1 | ????3.6 | ????91.3 | Do not have |
The overhead condensation liquid acetate concentration of measuring in the table 10 shows that up to 58% dual-flow tray is poorer through amplifying the back separating effect, and the rectification effect of its gas fallaway section only is equivalent to 2 theoretical plate numbers, and the actual plate number is 15, and therefore full column efficiency only is 13.3%.The cold mould research in laboratory confirms that the reason that causes inefficiency is the problem of the uniform aspect of phegma.Because the turbogrid tray liquid holdup is few, after tower diameter increases, original phegma uniform device can't accomplish that cloth liquid is even on whole column plate cross section, the liquid that causes a large amount of backflows is from the regional area percolation of column plate and descend, cause the liquid short circuit, therefore make gas-to-liquid contact seriously bad, it is lower to compare the segregation section plate efficiency of ratio 2 with Comparative Examples 1.
Application of the present invention is not limited to the given scope of the foregoing description, and the tower tray of any band downtake and the unitized construction of bubbling column reactor all belong to Application Areas of the present invention.