RO122809B1 - Process and installation for recovering propene from exhaust gases - Google Patents

Abstract

The invention relates to a process for recovering propene from exhaust gases of butyraldehyde oxo-synthesis installations, and to an installation for applying the process. According to the invention, the process consists in the absorption of the C3 fraction (propene, propane) from the exhaust gases resulting after butyraldehyde oxo-synthesis, in a raw mixture of butyraldehydes, at a temperature ranging between 0...30A C, at a pressure of 10...25 bars, followed by the partial desorption of the traces of easily absorbed components, at a pressure of 10...25 bars, then being followed by the total desorption of the absorbed C3 fraction, at a pressure of 17...25 bars and a temperature of 180...210A C and, in the end, the propene-propane mixture rectification at a pressure of 16...20 bars and a temperature of 30...70A C. According to the invention, the installation has an absorption column K1, a partial desorption column K2, a total desorption column K3 and a depropanizing column K4, as main components.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process and an installation for recovering propene from waste gases resulting from oxy-synthesis plants in which butyraldehyde is manufactured.

It is known that butyraldehyde isomers are manufactured exclusively today by low pressure oxosynthesis (15 ... 50 barg), from propene and synthesis gas with equimolar carbon monoxide ratio, according to reactions 1 and 2 in the following scheme:

+ co + h ₂

(1) propene synthesis gas n-butyraldehyde

H ₃ C ^ proper

4- CO + H ₂ synthesis gas

(2) i-butlraldehyde

H ₃ C ^^ + ^H 2 - * - h ₃ c ' ^x ^ ch ₃ (3) propene hydrogen propane

in the case of C ₄ aldehydes, oxosinteză process is carried out in homogeneous catalysis (triphenylphosphine rhodium catalysts modified with organic bisphosphites or higher) or heterogeneous (rhodium catalysts modified with the sodium salt of meta-trisulphonated triphenylphosphine).

Currently, the oxosynthesis plants in operation have either a single reactor to which a gas phase is recirculated containing the reactants, or two reactors in series between which the liquid reaction phase is recirculated. For economic reasons, the raw materials fed into the reactors are of technical purity. Thus, the synthesis gas contains varying amounts of methane, nitrogen and carbon dioxide, and propane is most often impurified with propane. An appreciable amount of propane is formed in the oxosynthesis reactor by hydrogenation of propane. These impurities are inert to the chemical process. Regardless of the performance of the catalyst and the configuration of the installation, in order to maintain a constant concentration of the inert compounds accumulated in the system, it is necessary to continuously eliminate an unreacted gas flow, hereinafter called waste gas. In the composition of waste gases, non-converted reactants (propene, carbon monoxide and hydrogen) and inert substances (propane, methane, nitrogen, carbon dioxide, etc.) are found in various proportions. Often, these gases have an energy destination (fuel for steam boilers), but over time several technical solutions for higher recovery have been proposed. [Bahrmann, H., Bach, Η., Οχο Synthesis, Ullmann's Encyclopedia of Industrial Chemistry, 7 ^th Edition, 2004, Billing, E., Bryant, DR, Oxoprocess, Kirk-Othmer Encyclopedia of Chemical Techologz, 4 ^{, h} Edition, 2001]

The procedure is known from the patent DE 3102281 A1, which consists of the use of a combination of oxosynthesis installations, the first high pressure, the second, low pressure.

Thus, the waste gases resulting from the high pressure oxy-synthesis plant are sent to the reactor supply of a low pressure oxy-synthesis plant. The main disadvantage of this process derives from the fact that in the residual gases of the high pressure oxosynthesis plant there are impurities, which considerably shorten the life of the catalysts.

RO 122809 Β1 of rhodium used in low pressure oxosynthesis. Thus, an advanced purification of 1 waste gases is required, much purification made more difficult by the presence of aldehydes in these gases. The specific pitfalls of rhodium catalysts, present in the waste gases of the 3 high pressure oxosynthesis plant, are mainly due to the poor purification of the raw materials supplied in these installations. 5

Alternatively, in US Pat. No. 4,533,755, the residual gas of a low-pressure oxy-synthesis plant is compressed and used as a raw material for a high-pressure oxy-synthesis plant. Since cobalt catalysts are much less susceptible to poisoning than rhodium-based ones, the disadvantage of catalyst poisoning 9 disappears in this case, but the need to use a compressor for high pressure appears, in order to compress the waste gases from the oxy-synthesis plant under pressure. 11 reduced. Other disadvantages, common to the procedures detailed in the mentioned patents, concern the complexity and implicitly the reliability of the proposed reaction systems and the need to use 13 high pressure oxy-synthesis plants, recognized as having low energy efficiency. 15 in US patent 4210426, it is shown that there have been attempts to convert waste gas together with isobutyraldehyde (secondary reaction product with low economic value 17) into synthesis gas, olefins and hydrogen, but as a result of the continuous increase in the price of propene. , its conversion into synthetic gas is not advantageous. 19

There is still known a process for recovering propene from waste gases, for the purpose of reuse in oxosynthesis, by fractionation, but it is difficult to apply due to the low temperatures required for complete liquefaction of the gas mixture. Simulation calculations show that, depending on the composition of the waste gases, liquefaction temperatures up to 23 -70 ° C may result. Investments in a compressor-holder cooling system and its high operating costs are unjustified, while liquefied gases require an advanced removal of water and carbon dioxide to prevent frost in the recovery system. 27

Another known procedure for recovering propane is the absorption of the fraction

C ₃ (propane and propylene) from the waste gases, in a solvent suitable for the absorption of olefins, such as diethylpropionamide, methanol, acetonitrile, furfurol, dimethoxyetraethylene glycol, etc.

Most of the solvents presented may be poisonous or catalytic inhibitors of 31 oxosynthesis, which is why advanced purifications of the recovered propene must be performed before being reintroduced into the reaction system. The solvents indicated in the recovery by absorbing 33 are oxoalcoolii C _4, C ₄ aldehydes, in particular iso-butyraldehyde [US 4210426] and the catalyst solution oxosinteză complex [US 5001274]. These substances are commonly found in the oxosynthesis reactor; therefore the traces of solvent left in the recovered propene should no longer be removed. 37 in US patent 4210426 there is presented an installation where the contact of the waste gases with the isobutyraldehyde is carried out in a column, in order to absorb the propane and propane. 39 Some of the non-absorbed gases containing carbon monoxide and hydrogen are recycled to the oxy-synthesis reactor, the remainder sent to combustion. Propane and propene are desorbed together 41 from the mixture with the aldehyde which is recycled to the absorption phase. Propane is finally separated from the mixture with propane in a common fractionation column. The second variant developed in the same patent is distinguished from the first by the fact that the gases not absorbed in the absorption phase are completely eliminated from the system, and from the desorption column only 45 propene is separated at the top, the propane-aldehyde mixture being further processed. in a separate column. The isobutyraldehyde used has the advantage of a higher thermal stability compared to n-butyride- 47 aldehyde and an absorption capacity for the C ₃ fraction greater than butanols, but more

RO 122809 Β1 lower than that of n-butyraldehyde. At low propensity concentrations in waste gases, a higher absorption pressure is required, which involves installing additional compressors for waste gases. Also, experimentally, it was found that the depreciation of the mixture of normal and isobutyraldehyde, by exposure at temperatures of 200 ° C for one hour, is negligible. Thus, it is not justified to separate the isomers and use as the C ₃ fraction absorber only the isobutyraldehyde.

Another major disadvantage, not obvious by the inventor, is the presence of methane in the waste gases. The solubility of methane in C ₄ aldehydes, under absorption conditions (pressure 15 ... 35 bar, temperature 15 ... 50 ° C), is not negligible. The desorption of the C ₃ fraction from the mixture with the aldehyde also implies the inevitable desorption of the absorbed methane, which considerably hinders the rectification phase of the C ₃ fraction. Thus, for a methane concentration in the waste gases of 10 ... 20%, the rectification of the propane-propylene mixture is possible only if low temperatures are maintained in the column condenser, which leads to the increase of the operating costs. In addition, it is impossible to remove the entire amount of methane from the oxy-synthesis system, which leads to its accumulation.

The technical problem solved by the invention consists in the advanced recovery of propene from waste gases from oxy-synthesis plants.

The process for recovering propane from waste gases from oxy-synthesis plants in which butyraldehyde is manufactured, according to the invention, is that, in a first step, the raw waste gas mixture, having a composition of 0 ... 30% H ₂ , 0 ... 10% CO, 0 ... 5% CO _{Z (} 0 ... 15% N ₂₎ 0 ... 25% CH ₄ , 10 ... 50% C ₃ H _B , 10 ... 60% C ₃ H ₈ , 0 ... 5% n-butane, 0 ... 2% i-butane, discharged from the oxy-synthesis plant at a temperature of 20 ... 60 ° C and a pressure of 15. .22 bar, is contacted countercurrently with a crude mixture of normal and isobutyraldehyde, at a pressure of 10 ... 25 bar, preferably 15 ... 22 bar and at a temperature of O ... 3 O ° C, followed by partial desorption of traces of light components absorbed at a pressure of 10 ... 25 bar, preferably 15 ... 22 bar and at a temperature of 8O ... 13O ° C at the base of the column of partial desorption and a temperature of O ... 2O ”C at the peak, followed by the total desorption of the C ₃ fraction from the mixture with the aldehyde hide, at the pressure of 17 ... 25 bar, preferably between 14 and 20 bar and the temperature of 180 ... 210 ° C, and finally the rectification of the C ₃ fraction in a depropanization column, at a pressure of 16. ..20 bar, preferably between 18 and 20 bar, and a temperature of 30 ... 70 ° C, preferably between 40 and 60 ° C, the recovered propylene being vaporized and introduced into the feed of the oxosynthesis reactor.

The installation for applying the propane recovery process according to the invention consists in the fact that the crude mixture of butyraldehyde, used for absorption, is sent to the top of an absorption column (K1), equipped with trays or other industrial filling, and at the base of the column The absorption gases are supplied counter-current by the residual gases from the oxosynthesis installations, the non-absorbed gases leave the absorption column at the peak, and the aldehyde loaded with C ₃ fraction and traces of light components is sent to a partial desorption column (K2), provided with a booster (1) and a partial condenser (2), from which the desorbed gases are eliminated at the top of the column, and the charged aldehyde with the C ₃ fraction accumulated in the base is fed into a total desorption column (K3), equipped with a a booster (3) and a total condenser (4), where the top product of the column (K3), containing propane and propane, is condensate and collected in a reflux vessel (5), after which a part is sent as reflux back to the column, and the rest feeds a depropanization column (K4), where the mixture of propane and propane is known to be rectified, propane recovered it is vaporized and sent to the feed of an oxytosynthesis reactor, and the aldehyde in the column base (K3), poor in the C ₃ fraction, is sent to the stabilization phase of the oxyosynthesis facility.

RO 122809 Β1

The process and installation of propane recovery according to the invention have 1 advantages:

- the absorbent used is even the crude product of the oxosynthesis reaction (the mixture of 3 isomeric aldehydes) which is fully recovered;

- because the working pressure in the machinery of the recovery plant is between 5 15 and 22 bar, it is not necessary to install additional compressors for the compression of the waste gases, these being available in the oxosynthesis installations in the usual way 7, at pressures in the mentioned range ;

- by introducing a partial desorption column, the process and installation 9 presented are useful for the recovery of propane from the waste gases resulting from any type of oxosynthesis installation, regardless of the content of inert (methane, nitrogen, propane, etc.); 11

- By low pressure vaporization, the liquid propane separated in the decomposition phase can be used to cool the condenser of the partial desorption column K2 and 13 of the absorber required at the absorption column K1, which leads to minimizing the operating costs; 15

- for the boiler attached to the K2 column, cheap heating agents, such as the cooling water of the chemical reactors, hot condensate, etc. can be used; 17

- due to the high operating pressure, the capacitors of columns K3 and K4 do not require special cooling agents, the water recirculated from the cooling towers being appropriate in this case.

The following are two examples of embodiment of the invention, in connection with the figure 21, which represents the flow diagram of the propane recovery plant from waste gases.

Example 1. A flow rate of 700 kg / h residual gases with 1500 kg 23 aldehyde is contacted in the K1 absorption column with 15 theoretical plates, operated at a pressure of 17.6 bar. The absorption aldehyde, containing 90% n-butyraldehyde and 10% i-butyraldehyde, is fed with a temperature of 20 ° C at the tip of the absorption column. The residual gases, fed with a temperature of 50'C in countercurrent, at the base of the absorption column, have 27 the following volumetric composition: 20% H ₂ , 4.5% CO, 0.5% CO ₂ , 4% N ₂ , 8, 1% CH ₄ ; 25% C ₃ H ₆ ; 36.1% C ₃ H ₈ ; 1.6% n-butane and 0.2% i-butane. The corresponding propane flow rate in 29 waste gases is 230 kg / h. Aldehyde accumulated on the basis of column K1, containing 96.2% of the propene existing in the waste gases, is sent to the partial desorption column 31 K2, from which at the top are traces of light absorbed gases (methane, hydrogen, monoxide and carbon dioxide). ). in conditions of maintaining a temperature of 8 ° C in 33 column capacitor and 116 ° C in boiler and at 18 bar pressure, at a reflux ratio of 1.3: 1, the loss of propene in the desorbed gases in column K2 is approx. 1.8%. 35

The aldehyde charged with fraction C ₃ , purified by the traces of light gases, is fed from the base of column K2 in the desorption column K3 operated at the pressure of 18 bar. For a temperature of 198 ° C in the base, 48 ° C in the condenser and a relay ratio of 3: 1, a desorption degree of the C ₃ fraction of 99.1% is obtained. The C ₃ fraction is further rectified in column 39 K4, equipped with 140 theoretical plates, of which 210 kg / h is distilled with 98% propene. The K4 depropanization column operates under a pressure of 18.5 bar, 56 ° C at the base and 41 46.5 "C at the top and a reflux ratio of 22: 1. The overall yield of propene recovery under the conditions of this example is 91.6%. 43

Example 2. In the absorption column K1 provided with 12 theoretical plates, a flow of 300 kg / h residual gas with 650 kg aldehyde is contacted at the pressure of 17 bar. 45

Absorption aldehyde, containing 90% n-butyraldehyde and 10% i-butyraldehyde, is fed at 15'C at the tip of the absorption column. The waste gases, supplied with a temperature of 40 ° C in counter current, at the base of the absorption column, have the following

RO 122809 Β1 volumetric composition: 15% H ₂ , 3.5% CO, 0.5% CO ₂ , 4.2% N ₂ , 15% CH ₄ ; 15% C ₃ H ₆ ; 45% C ₃ H _a ; 1.6% n-butane and 0.2% i-butane. The corresponding propane flow rate in the waste gases is 58.2 kg / h. The aldehyde accumulated on the basis of column K1, containing 98.7% of the propene existing in the waste gases, is sent to the partial desorption column K2, where at the top the traces of the light absorbed gases (methane, hydrogen, monoxide and carbon dioxide) are removed. under the conditions of maintaining a temperature of 6 ° C in the column condenser and 114'C in the boiler at 18 bar pressure, at a reflux ratio of 1: 1, the loss of propene in the desorbed gases in column K2 is about 2.4% . The aldehyde charged with fraction C ₃ , purified by the traces of light gases, is fed from the base of column K2 in the desorption column K3 operated at a pressure of 17 bar. For a temperature of 195.5'C in the blazer, 48'C in the condenser and a reflux ratio of 3.45: 1, a desorption degree of the C ₃ fraction of 99.2% is obtained. Fraction C ₃ is further rectified in column K4, equipped with 160 theoretical plates, of which 210 kg / h is distilled with 98% propene. The K4 depropanization column operates under a pressure of 18.5 bar, 56 ° C at the base, 46.5C at the top and a reflux ratio of 31: 1. The overall yield of propene recovery under the conditions of this example is 93.5%.

Claims (2)

1. Process for recovering propene from waste gases from oxy-synthesis plants, characterized in that, in a first step, the raw mixture of waste gases, having composition 0 ... 30% H ₂ , 0 ... 10 % CO, 0 ... 5% CO ₂ , 0 ... 15% N ₂ , 0 ... 25% CH ₄ , 10 ... 50% C ₃ H ₆ , 10 ... 60% C ₃ H ₈ , 0 ... 5% n-butanal, 0 ... 2% i-butanal, evacuated from the oxosynthesis plant at a temperature of 20 ... 60 ° C and a pressure of 15 ... 22 bar, if it contacts in countercurrent with a crude mixture of normal and iso-butyraldehyde, at a pressure of 10 ... 25 bar, preferably 15 ... 22 bar and at a temperature of O ... 3O ° C, followed by the partial desorption. of traces of light components absorbed at a pressure of 10 ... 25 bar, preferably 15 .. .22 bar and at a temperature of 8O ... 13O ° C at the base of the partial desorption column and a temperature of O ... 2O ° C at the top, followed by the total desorption of the C ₃ fraction in the mixture with aldehydes, at a pressure of 17 ... 25 bar, preferably between 14 and 20 bar and the temperature of 180 .. .210 ° C, and finally the rectification of the C ₃ fraction in a depropanization column, at a pressure of 16 ... 20 bar, preferably between 18 and 20 bar, and a temperature of 30 ... 70 '0, preferably between 40 and 60 ° C, the recovered propylene being vaporized and introduced into the feed of the oxosynthesis reactor. 2. Plant for applying the propane recovery process from the waste gases from the oxosynthesis plants, defined in claim 1, characterized in that the crude mixture of butyraldehyde used for absorption is sent to the top of an absorption column (K1), equipped with plates or other industrial filling, and at the base of the absorption column, the residual gases from the oxosynthesis installations are fed countercurrently, the unabsorbed gases leave the absorption column at the top, and the aldehyde loaded with C ₃ fraction and traces of light components is sent to a column. of partial desorption (K2), provided with a cooler (1) and a partial condenser (2), where the desorbed gases are eliminated at the top of the column, and the charged aldehyde with the C ₃ fraction accumulated in the base is fed into a column of total desorption (K3), equipped with a booster (3) and a total condenser (4), where it produces the top column column (K3), containing propane and propane, is condensed and collected in a reflux vessel (5), after which a part is sent as reflux back into the column, and the rest feeds a depropanization column (K4) , where the mixture of propane and propane is known to be rectified, the recovered propane is vaporized and sent to the feed of an oxosynthesis reactor, and the aldehyde in the column base (K3), poor in fraction C ₃ , is sent to the stabilization phase of the plant. oxosinteză.