CA1093566A - Maleic anhydride production with recycle treatment - Google Patents
Maleic anhydride production with recycle treatmentInfo
- Publication number
- CA1093566A CA1093566A CA267,822A CA267822A CA1093566A CA 1093566 A CA1093566 A CA 1093566A CA 267822 A CA267822 A CA 267822A CA 1093566 A CA1093566 A CA 1093566A
- Authority
- CA
- Canada
- Prior art keywords
- maleic anhydride
- reactor
- effluent
- acids
- butane
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
- C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
- C07C51/215—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of saturated hydrocarbyl groups
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
- C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
- C07C51/25—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring
- C07C51/252—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring of propene, butenes, acrolein or methacrolein
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Furan Compounds (AREA)
- Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
MALEIC ANHYDRIDE PRODUCTION
WITH RECYCLE TREATMENT
A process for producing maleic anhydride from a C4 hydrocarbon selected from n-butane and n-butene feed which comprises: (a) feeding the C4 hydrocarbon and air to a reactor;
(b) contacting the C4 hydrocarbon and air in the reactor with a catalyst comprising vanadium and phosphorus oxides at reaction conditions including a temperature between 550 and 1000°F so as to obtain a reactor effluent containing maleic anhydride, unreacted butane, nitrogen, oxygen, and acrylic, acetic or maleic acid or mixtures of the foregoing acids; (c) removing maleic anhydride from the reactor effluent to obtain maleic anhydride-lean effluent; (d) removing said acids from at least a portion of the maleic anhydride-1ean effluent to obtain a purified recycle stream containing less than 100 ppm of the acids; and (e) recycling the purified stream to the reactor. Preferably the acids are removed in step (d) by water and/or caustic scrubbing the maleic anhydride-lean effluent.
MALEIC ANHYDRIDE PRODUCTION
WITH RECYCLE TREATMENT
A process for producing maleic anhydride from a C4 hydrocarbon selected from n-butane and n-butene feed which comprises: (a) feeding the C4 hydrocarbon and air to a reactor;
(b) contacting the C4 hydrocarbon and air in the reactor with a catalyst comprising vanadium and phosphorus oxides at reaction conditions including a temperature between 550 and 1000°F so as to obtain a reactor effluent containing maleic anhydride, unreacted butane, nitrogen, oxygen, and acrylic, acetic or maleic acid or mixtures of the foregoing acids; (c) removing maleic anhydride from the reactor effluent to obtain maleic anhydride-lean effluent; (d) removing said acids from at least a portion of the maleic anhydride-1ean effluent to obtain a purified recycle stream containing less than 100 ppm of the acids; and (e) recycling the purified stream to the reactor. Preferably the acids are removed in step (d) by water and/or caustic scrubbing the maleic anhydride-lean effluent.
Description
3S~6 BACKGROUND OF THE INVENTION
The present invention relates to the oxidation of a butane feed to maleic anhydride.
Oxidation of hydrocarbons to maleic anhydride is well known.
Feeds which have been disclosed include benzene, butene, and n-butane. A
series of patents to Kerr, including United States Patents 3,156,705, '706, '707, 3,238,254, 3,255,211, '212, '213, 3,288,721, 3,351,565 and 3,385,796, -discloses vanadium-phosphorus oxide catalysts for oxidation of butene to maleic anhydride.
Friedrichsen et al United States Patent 3,478,o63 discloses oxida-tion of olefinically unsaturated hydrocarbons with a catalyst containing vanadium and phosphorus oxides and wherein the amount of phosphorus oxide is at least equal to twice that of the-vanadium oxide and wherein the catalyst contains at least one other oxide of chromium, iron, cobalt or nickel, and the catalyst is preferably on a carrier. The patent discloses a-t Col. 4 that the catalyst may have a surface area from 1 to 100 m /g.
Bergman United States Patent 3,293,268 discloses a vanadium-phos-phorus oxide eatalyst for oxidation of butane to maleic anhydride. Surface area is not diselosed ~or the eatalyst in the Bergman reference. Also, as 20 in the Friedrichsen et al reference, the Bergman catalyst is prepared by an aqueous solution method.
Schneider United States Patent 3,864,280 discloses a vanadium-phosphorus mixed oxide catalyst having an intrinsic surface area of 7 to 50 m /g. The Schneider catalyst can be prepared using an organic medium as opposed to an aqueous medium.
The use of recycle of unreacted constituents to a reactor is, of eourse, well known and frequently is employed in various processes.
Bissot et al, in "Oxidation of Butane to ~aleic Anhydride", IEC Vol. 2, No. 1, ~arch 1963, pp. 57-60, disclose 30 that, in a process for conversion of butane to ma]eic anhydride , ~3566 unreacted butane may be recycled to the reactor. However, Bissot et al prefer to use sequential reaction~ with maleic anhydride separation between the reactors, and with unreacted butane from the first reactor being fed to the second reactor, etc.
United States Patent 3,904,652 discloses the oxidation of n-butane to maleic anhydride using enriched oxygen and with a recycle stream of reactor effluent which lowers the oxygen concentration in the total feed to the reactor. It is known that explosive mixtures of butane and oxygen exist and that some oxygen concentrations can cause an oxygen-butane-nitro-gen mixture to go into the explosive range; see, for example, Bureau of Mines Bulletin 503 (1952), Figure 35, page 62, and Bureau of Mines Bulletin 627 ~1965~, Figure 21, page 23. In United States Patent 3,904,652, the reactor feed mixture is kept below explosive (flammable) limits by the addition of an inert gas, e.g., nitrogen, to the enriched oxygen fresh feed.
Butane conversion levels in United States Patent 3,904,652 are 30 to 70% per pass. The uncoverted butane passes out of the oxidizer reac-tor as part of the reactor effluent. The effluent is processed to remove maleic anhydride. The maleic anhydride is removed from the efflwent in part by cooling to condense out liquid maleic anhydride. Completion of maleic anhydride removal from the effluent is carried out by scrubbing the vapor/ !, gaseoas material left from the condensation step. The scrubbing is done by contacting the effluent with a recirculated aqueous maleic acid solution to which is added an undisclosed amount of fresh water. The maleic anhydride-free gaseous effluent is then divided into two parts, a recycle stream which is recycled back to the reactor, and a purge stream which is removed from the system.
,~ :
~D35~6 SU~RY OF THE IN~ENTION
.
According to the present invention, a process is provided for producing maleic anhydride from a C4 hydrocarbon selected from n-butane and n-butene feed which comprises: (a) feeding the C4 hydrocarbon and air -to a reactor; (b) contacting the C4 hydrocarbon and air in the reactor with a catalyst comprising vanadium and phosphorus oxides at reaction conditions including a temperature between 550 and 1000 F so as to ob-tain a reactor ef-fluent containing maleic anhydride, unreacted butane, nitrogen, oxygen, and acrylic, acetic, or maleic acid or mixtures of the foregoing acids; (c) re-moving maleic anhydride from the reactor effluent to obtain maleic anhyd-ride-lean effluent; (d) removing said acids from at least a portion of the maleic anhydride-lean effluent to obtain a purified recycle stream contain-ing less than 100 ppm of the acids; and (e) recycling the purified stream to the reactor.
Among other factors, the present invention is based on our finding that surprisingly improved n-butane feed conversion and also selectivity of ;
the conversion to maleic anhydride are achieved in a recycle operation if acids are removed from the recycle down to a low level below at least 100 ppm. ~e have found, for in~tance, that when a s-tream is taken directly from the effluent of the oxidation reactor and is recycled back to the reactor (or to a similar test reactor), the conversion and selectivity are deleter-iously affected. One might have assumed that since the effluent, of course, comes from the oxidation reactor itself, simply putting a portion of this effluent back to the reactor would not have any substantial and prompt effect 7 but we have found to the contrary.
Preferably the acids are removed in step ~d) of the above process by water or aqueous caustic solution scrubbing the maleic anhydride-lean effluent. The water scrubbing can be carried out, for instance, using an :' :~9356~ii absorption column wherein the maleic anhydride~lean effluen-t is contacted countercurrently with water to thereby absorb and remove acids from the maleic anhydride-lean effluent prior to recycling the maleic anhydride-lean effluent to the reactor. The water, and/or aqueous basic solution such as sodium or potassium hydroxide, carbonate, or bicarbonate must be used in an amount and purity (or base concentration) sufficient to remove the acids in sufficient amount so that the maleic anhydride-lean effluent which is recycled to the reactor contains no more than 100 ppm of the acids.
Preferably the scrubbed e-ffluent is treated with suf~icient water or other means for removing light acids so that the acid content is reduced to less than 10 ppm, and still more preferably less than 7 ppm. The use of a water scrubbing system which already contains substantial amounts of acids, such as in the case of a recirculated maleic acid aqueous solution, is thus not desirable as such a solution is ineffective or of substantially reduced ef-fectiveness to remove light acids down to a very low level in the resultant scrubbed maleic anhydride-lean effluent.
In addition to the removal of acids from the reactor recycle `~
stream, usually and preferably other partially oxidized by-products, such as formaldehyde, are removed so that the recycle stream contains no more than 100, preferably no more than 10, and still more preferably no more than 7, ppm partially oxidized by-products such as the light acids and formaldehyde.
Unless otherwise indicated, the parts per million acids or other partially oxidized by-products in the purified effluent are by weight. The terminology "partially oxidized" is used in contrast to carbon oxides which result from completely oxidizing the C4 hydrocarbon feed.
In the process of the present invention, rather than ~ `
:
356~
tbe use of a condensation-a~ueous malelc anhydride recovery s~st~m, it is preferred to recover the maleic anhydrlde from the reactor effluent to obtain the malelc anh~vdrlde-lean effluent solely by countercurrently con-tact~ng the reactor effluent with an organic absorb~nt. The maleic anhydride is then recovered frcn the organlc absorkent by conventional absorb~nt strlpping methods. Suitable organic absorbents Lnclude benzophenones such as the polymethyIben~ophencnes, e.g~, di-, tri- and tetramethylben20phenone, as disclosed in Canad~an Patent No. 1,057,766 entitled "A~hydride Separation Process".
Preferred operating condit~ons for the oxidation reactor are as follows:
~ore Most Prefer~ed Preferred Preferred Temperature, F 650-950 700-850 700-800 Pressure, psig 10-1000 20-50 25-40 Space rate, VHS ~ 1000-10,000 2000-50003500-4500 Feed n-butane content, com-bined resh ~ recycle feed. v~1.% 1-5 1.5-4 2-3.5 % effl~ent recycled dixect~y 20-95 65-90 80 ~remain~er of effluent n-butane recycled after separation frcn other effluent gases) 1 Total volume of gas at 70F and 1 abm. per hour per cublc foot of catalyst ;~
volume Preferred catalysts fo~ use in the present ~nve~tion are high-activity, high-surface-area vanadium-phosph~us oxide catalys~s, preferably h2vLng an intr~nsic surace area between about 7 an~ 50 m2/q~
PaLticularly preferred catalysts for use in the process o~ th2 present mvent on are those dasclosed in Schneider United States Patent 3,864,280, specifically crystall~ne phosphorus-vanadi~m ~Lxed oxide catal~sts containing pentavalent phospho~us, vanadium and ox~gen, said vanadium having -~
an average valence ln the range from about ~3.9 to ~4.6, saàd c~xade having a phosphorus-to-~anadlum atom~c ratio m the ~ange rom about 0.9-1.8 to l,and 6~
an intrm sic surface area in the range from about 7 to 50 m2/g.
As defmed m the '280 patent, the term "intrinsic surface area"
is used here m to mean the surface area of the mixed vanad~um-phosphorus oxide mat rial itself, i.e., per se, in the absence of a support or carrier.
The catalysts of Un~ted States Patent 3,864,280 are particularly suLted ~Qr use in the process of the present invention.
Preferred oparating con~itions fQr removal of the acids ~rom the maleic anhydride lean reactor effluent ~y use of water scrubbing are as follows:
More Preferred Preferred Water feed rate to maleic anh~dride-lean effl~ent feed rate, g/std. ft31 to 100 1 to 25 Counte~current contacting stages, theoretical stages 1 to 25 1 to 10 F~esh water feed temp~LatULe/ F 50 to 120 50 to 80 Qperating pxessure, psig 0 to 1000 5 to 40 The drawing is a schemat w process flcw diagram ill~trating a preerred embcdlment o the present invention.
Example 1 Feed butane in line la, made up f~c~t 97 lbs/hr o fresh-feed butane m llne 1 and 36 lbs/h~ of recycled butane in line 16 is mlxed with abcut 1426 Ibs/h~ o fresh maka-up air int~cduced via line 2, and about 5995 lbs/hr of recycled off-gas, and the mLxture is introduced into ox-idizer reactor 4 through l me 3~a). The oxidizer reactor consists of conventional heat exchanger-type design with catal~st pack0d in tubes surrounded by a heat-transfer liquid ~a "salt bath"). The reaction mixture ~s , .. .
~35g-~
.
oxidlzed in the presence of a catalyst effectiv~ for accelerating the reaction of n-butane with air to form maleic anhydride. Preferred catalysts ccmprise mixed ox~des of vanadium and phosphorus, especially those described in the previousl~ cited United States Patent 3,864,280, and prefe~red reaction temperatures are in the range 700-800F.
Follcwlng oxidation, the gaseous effluent flows through line 5 into absorber 6. ~bout 104 ~bs/hr of maleic anhyd~ide is absorbed ~n the organic sol~ent flcwing into ~ho abso~ber ~an line 7. T.he gaseous stream, 7450 Lb5/
hr, leaves the absorber throu~h line 9 at a temperature of about 160F ~nd is glven a wate~ ~ash in vessel 10. The solvent-maleic an-hydride strean leaves the absorber thxough l me 8 fcr maleic anhydride ~tripping in stripper 17 cmd then through line 18 for further purlfication of the crude product in vess~l 19. The desi-red m~leic anh~d~ide pro~uct leaves vessel 19 through line 20.
The rema ming 7450 lbs/hr oE t~he maleic anhydride-lean stream 9 ls washed in countercurrent wat~r scrubber 10 using fresh water introduced through line 11 to ~move the unabsor~ed ac.ids. In a typical single-stage scrutber, ab~lt 21,900 lbs/hx of fresh water rem~es about 3-4 lbs~hr of ligllt acids ~acetic, ao~yllc, n~leic and ~races of butyric and the like~ and unak~orbed maleic anhydrlde through lLne 12. The ~ater rcquiremen~s may be reduced b~ use o a m~lt~-stage sc~ubber. The acid content of the 7331 Lbs/hr stre~m 13 is belcw about 10 p~m, speo.ifically about 6 pFm, in this mode of operation.
Washed of-gas leaVing the water wash at a temperatu~e of about 100 to 120F is spl~t into st~eams 3 and 14. About 5995 lbs/hr of this washed off-gas is compressed and recycled back to the oxidizer th~ough llne 3 and the rema ming 1336 lbs/hr of off-gas is passed through line 14 for butane reco~ery in abso~be~ 15.
Butane Ln line 14 is absorbed in the absorber by a cyclic operation us~ng mL~tiple beds filled w.ith absorbents such as activatecl carbon. The denuded off-gas, 1300 lbs/hr, m~lnly contain mg ox~gen, nitrogen and oxides of carbon, is v~nt0d out .... g_ 35~
.
and -the butane adsorbed on the adsorben-t is recovered by suitable desorption such as steaming at about 250 F followed by condensation and phase separa-tion. The recovered butane, 36 lbs./hr., is then recycled back through line 16 to the reactor.
To reduce the amount of aqueous scrubbing solution and/or to ob-tain more nearly complete removal of the acids from the recycle portion of the reactor effluent, a solution of sodium or potassium hydroxide, carbon-ate, or bicarbonate in water is advantageously used in place of simply water.
Example 2 The process was carried out as in Example 1, with single-stage scrubbing of the maleic anhydride-lean off gas to remove light acids from the recycle to the reactor.
The effects of acid contaminants in a reactor feed were tested in a separate test reactor (as we did not want to vary conditions in our main reactor) using the same type catalyst that was used in the main reactor. The reactant feed to this test reactor consisted of a slipstream from either stream No. 5 or 13 of Figure 1. When the test reactor feed is obtained from stream 13, the test reactor was exposed to a washed off gas consisting of butane, oxygen, nitrogen and carbon oxides with only minute traces of light acids (about 6 ppm). The rate da-ta obtained for the first run (see Run No.
1 in Table I below) was used for further comparison.
Subsequent test runs consisted of alternately switching the test reactor feed to-slipstreams from streams 5 and 13 and evaluating the test reactor performance for each such run.
The performance of the test reactor under these conditions is ~;
shown in Table I. It is to be noted that the presence of acid contaminants ~ -in the feed immediately dropped the catalyst activity and selectivi-ty for maleic anhydride production. See Run No. 2 in Table I. Also, this deleter-ious effect was found irreversible with removal of the feed contaminants in " ' ~1~93S66 the subsequent test run. See Run No. 3 in Table I. The performance of the eatalyst continues to degrade as it is further treated with an acid-con~
taminated stream. See Run No. ~, second exposure to stream No. 5.
A rather surprising finding of these experiments is that the pres-ence of acid contaminants in the feed inereases the light aeid produetion rate in the su~sequent test runs. In a reeyele operation with less effee-tive removal of acid contaminants from the reeyeled effluent stream, this deleterious effeet asssures a eontinued, aeeelerated degradation of the eat-alyst performanee. Thus, it is espeeially advantageous to remove the light aeids in accordance with the process of the present invention. Further ex-periments with a synthetic feed containing butane with either acetic or acr~lic acid in -the absence of maleic anhydride confirm the deleterious effeet observed using stream 5.
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The present invention relates to the oxidation of a butane feed to maleic anhydride.
Oxidation of hydrocarbons to maleic anhydride is well known.
Feeds which have been disclosed include benzene, butene, and n-butane. A
series of patents to Kerr, including United States Patents 3,156,705, '706, '707, 3,238,254, 3,255,211, '212, '213, 3,288,721, 3,351,565 and 3,385,796, -discloses vanadium-phosphorus oxide catalysts for oxidation of butene to maleic anhydride.
Friedrichsen et al United States Patent 3,478,o63 discloses oxida-tion of olefinically unsaturated hydrocarbons with a catalyst containing vanadium and phosphorus oxides and wherein the amount of phosphorus oxide is at least equal to twice that of the-vanadium oxide and wherein the catalyst contains at least one other oxide of chromium, iron, cobalt or nickel, and the catalyst is preferably on a carrier. The patent discloses a-t Col. 4 that the catalyst may have a surface area from 1 to 100 m /g.
Bergman United States Patent 3,293,268 discloses a vanadium-phos-phorus oxide eatalyst for oxidation of butane to maleic anhydride. Surface area is not diselosed ~or the eatalyst in the Bergman reference. Also, as 20 in the Friedrichsen et al reference, the Bergman catalyst is prepared by an aqueous solution method.
Schneider United States Patent 3,864,280 discloses a vanadium-phosphorus mixed oxide catalyst having an intrinsic surface area of 7 to 50 m /g. The Schneider catalyst can be prepared using an organic medium as opposed to an aqueous medium.
The use of recycle of unreacted constituents to a reactor is, of eourse, well known and frequently is employed in various processes.
Bissot et al, in "Oxidation of Butane to ~aleic Anhydride", IEC Vol. 2, No. 1, ~arch 1963, pp. 57-60, disclose 30 that, in a process for conversion of butane to ma]eic anhydride , ~3566 unreacted butane may be recycled to the reactor. However, Bissot et al prefer to use sequential reaction~ with maleic anhydride separation between the reactors, and with unreacted butane from the first reactor being fed to the second reactor, etc.
United States Patent 3,904,652 discloses the oxidation of n-butane to maleic anhydride using enriched oxygen and with a recycle stream of reactor effluent which lowers the oxygen concentration in the total feed to the reactor. It is known that explosive mixtures of butane and oxygen exist and that some oxygen concentrations can cause an oxygen-butane-nitro-gen mixture to go into the explosive range; see, for example, Bureau of Mines Bulletin 503 (1952), Figure 35, page 62, and Bureau of Mines Bulletin 627 ~1965~, Figure 21, page 23. In United States Patent 3,904,652, the reactor feed mixture is kept below explosive (flammable) limits by the addition of an inert gas, e.g., nitrogen, to the enriched oxygen fresh feed.
Butane conversion levels in United States Patent 3,904,652 are 30 to 70% per pass. The uncoverted butane passes out of the oxidizer reac-tor as part of the reactor effluent. The effluent is processed to remove maleic anhydride. The maleic anhydride is removed from the efflwent in part by cooling to condense out liquid maleic anhydride. Completion of maleic anhydride removal from the effluent is carried out by scrubbing the vapor/ !, gaseoas material left from the condensation step. The scrubbing is done by contacting the effluent with a recirculated aqueous maleic acid solution to which is added an undisclosed amount of fresh water. The maleic anhydride-free gaseous effluent is then divided into two parts, a recycle stream which is recycled back to the reactor, and a purge stream which is removed from the system.
,~ :
~D35~6 SU~RY OF THE IN~ENTION
.
According to the present invention, a process is provided for producing maleic anhydride from a C4 hydrocarbon selected from n-butane and n-butene feed which comprises: (a) feeding the C4 hydrocarbon and air -to a reactor; (b) contacting the C4 hydrocarbon and air in the reactor with a catalyst comprising vanadium and phosphorus oxides at reaction conditions including a temperature between 550 and 1000 F so as to ob-tain a reactor ef-fluent containing maleic anhydride, unreacted butane, nitrogen, oxygen, and acrylic, acetic, or maleic acid or mixtures of the foregoing acids; (c) re-moving maleic anhydride from the reactor effluent to obtain maleic anhyd-ride-lean effluent; (d) removing said acids from at least a portion of the maleic anhydride-lean effluent to obtain a purified recycle stream contain-ing less than 100 ppm of the acids; and (e) recycling the purified stream to the reactor.
Among other factors, the present invention is based on our finding that surprisingly improved n-butane feed conversion and also selectivity of ;
the conversion to maleic anhydride are achieved in a recycle operation if acids are removed from the recycle down to a low level below at least 100 ppm. ~e have found, for in~tance, that when a s-tream is taken directly from the effluent of the oxidation reactor and is recycled back to the reactor (or to a similar test reactor), the conversion and selectivity are deleter-iously affected. One might have assumed that since the effluent, of course, comes from the oxidation reactor itself, simply putting a portion of this effluent back to the reactor would not have any substantial and prompt effect 7 but we have found to the contrary.
Preferably the acids are removed in step ~d) of the above process by water or aqueous caustic solution scrubbing the maleic anhydride-lean effluent. The water scrubbing can be carried out, for instance, using an :' :~9356~ii absorption column wherein the maleic anhydride~lean effluen-t is contacted countercurrently with water to thereby absorb and remove acids from the maleic anhydride-lean effluent prior to recycling the maleic anhydride-lean effluent to the reactor. The water, and/or aqueous basic solution such as sodium or potassium hydroxide, carbonate, or bicarbonate must be used in an amount and purity (or base concentration) sufficient to remove the acids in sufficient amount so that the maleic anhydride-lean effluent which is recycled to the reactor contains no more than 100 ppm of the acids.
Preferably the scrubbed e-ffluent is treated with suf~icient water or other means for removing light acids so that the acid content is reduced to less than 10 ppm, and still more preferably less than 7 ppm. The use of a water scrubbing system which already contains substantial amounts of acids, such as in the case of a recirculated maleic acid aqueous solution, is thus not desirable as such a solution is ineffective or of substantially reduced ef-fectiveness to remove light acids down to a very low level in the resultant scrubbed maleic anhydride-lean effluent.
In addition to the removal of acids from the reactor recycle `~
stream, usually and preferably other partially oxidized by-products, such as formaldehyde, are removed so that the recycle stream contains no more than 100, preferably no more than 10, and still more preferably no more than 7, ppm partially oxidized by-products such as the light acids and formaldehyde.
Unless otherwise indicated, the parts per million acids or other partially oxidized by-products in the purified effluent are by weight. The terminology "partially oxidized" is used in contrast to carbon oxides which result from completely oxidizing the C4 hydrocarbon feed.
In the process of the present invention, rather than ~ `
:
356~
tbe use of a condensation-a~ueous malelc anhydride recovery s~st~m, it is preferred to recover the maleic anhydrlde from the reactor effluent to obtain the malelc anh~vdrlde-lean effluent solely by countercurrently con-tact~ng the reactor effluent with an organic absorb~nt. The maleic anhydride is then recovered frcn the organlc absorkent by conventional absorb~nt strlpping methods. Suitable organic absorbents Lnclude benzophenones such as the polymethyIben~ophencnes, e.g~, di-, tri- and tetramethylben20phenone, as disclosed in Canad~an Patent No. 1,057,766 entitled "A~hydride Separation Process".
Preferred operating condit~ons for the oxidation reactor are as follows:
~ore Most Prefer~ed Preferred Preferred Temperature, F 650-950 700-850 700-800 Pressure, psig 10-1000 20-50 25-40 Space rate, VHS ~ 1000-10,000 2000-50003500-4500 Feed n-butane content, com-bined resh ~ recycle feed. v~1.% 1-5 1.5-4 2-3.5 % effl~ent recycled dixect~y 20-95 65-90 80 ~remain~er of effluent n-butane recycled after separation frcn other effluent gases) 1 Total volume of gas at 70F and 1 abm. per hour per cublc foot of catalyst ;~
volume Preferred catalysts fo~ use in the present ~nve~tion are high-activity, high-surface-area vanadium-phosph~us oxide catalys~s, preferably h2vLng an intr~nsic surace area between about 7 an~ 50 m2/q~
PaLticularly preferred catalysts for use in the process o~ th2 present mvent on are those dasclosed in Schneider United States Patent 3,864,280, specifically crystall~ne phosphorus-vanadi~m ~Lxed oxide catal~sts containing pentavalent phospho~us, vanadium and ox~gen, said vanadium having -~
an average valence ln the range from about ~3.9 to ~4.6, saàd c~xade having a phosphorus-to-~anadlum atom~c ratio m the ~ange rom about 0.9-1.8 to l,and 6~
an intrm sic surface area in the range from about 7 to 50 m2/g.
As defmed m the '280 patent, the term "intrinsic surface area"
is used here m to mean the surface area of the mixed vanad~um-phosphorus oxide mat rial itself, i.e., per se, in the absence of a support or carrier.
The catalysts of Un~ted States Patent 3,864,280 are particularly suLted ~Qr use in the process of the present invention.
Preferred oparating con~itions fQr removal of the acids ~rom the maleic anhydride lean reactor effluent ~y use of water scrubbing are as follows:
More Preferred Preferred Water feed rate to maleic anh~dride-lean effl~ent feed rate, g/std. ft31 to 100 1 to 25 Counte~current contacting stages, theoretical stages 1 to 25 1 to 10 F~esh water feed temp~LatULe/ F 50 to 120 50 to 80 Qperating pxessure, psig 0 to 1000 5 to 40 The drawing is a schemat w process flcw diagram ill~trating a preerred embcdlment o the present invention.
Example 1 Feed butane in line la, made up f~c~t 97 lbs/hr o fresh-feed butane m llne 1 and 36 lbs/h~ of recycled butane in line 16 is mlxed with abcut 1426 Ibs/h~ o fresh maka-up air int~cduced via line 2, and about 5995 lbs/hr of recycled off-gas, and the mLxture is introduced into ox-idizer reactor 4 through l me 3~a). The oxidizer reactor consists of conventional heat exchanger-type design with catal~st pack0d in tubes surrounded by a heat-transfer liquid ~a "salt bath"). The reaction mixture ~s , .. .
~35g-~
.
oxidlzed in the presence of a catalyst effectiv~ for accelerating the reaction of n-butane with air to form maleic anhydride. Preferred catalysts ccmprise mixed ox~des of vanadium and phosphorus, especially those described in the previousl~ cited United States Patent 3,864,280, and prefe~red reaction temperatures are in the range 700-800F.
Follcwlng oxidation, the gaseous effluent flows through line 5 into absorber 6. ~bout 104 ~bs/hr of maleic anhyd~ide is absorbed ~n the organic sol~ent flcwing into ~ho abso~ber ~an line 7. T.he gaseous stream, 7450 Lb5/
hr, leaves the absorber throu~h line 9 at a temperature of about 160F ~nd is glven a wate~ ~ash in vessel 10. The solvent-maleic an-hydride strean leaves the absorber thxough l me 8 fcr maleic anhydride ~tripping in stripper 17 cmd then through line 18 for further purlfication of the crude product in vess~l 19. The desi-red m~leic anh~d~ide pro~uct leaves vessel 19 through line 20.
The rema ming 7450 lbs/hr oE t~he maleic anhydride-lean stream 9 ls washed in countercurrent wat~r scrubber 10 using fresh water introduced through line 11 to ~move the unabsor~ed ac.ids. In a typical single-stage scrutber, ab~lt 21,900 lbs/hx of fresh water rem~es about 3-4 lbs~hr of ligllt acids ~acetic, ao~yllc, n~leic and ~races of butyric and the like~ and unak~orbed maleic anhydrlde through lLne 12. The ~ater rcquiremen~s may be reduced b~ use o a m~lt~-stage sc~ubber. The acid content of the 7331 Lbs/hr stre~m 13 is belcw about 10 p~m, speo.ifically about 6 pFm, in this mode of operation.
Washed of-gas leaVing the water wash at a temperatu~e of about 100 to 120F is spl~t into st~eams 3 and 14. About 5995 lbs/hr of this washed off-gas is compressed and recycled back to the oxidizer th~ough llne 3 and the rema ming 1336 lbs/hr of off-gas is passed through line 14 for butane reco~ery in abso~be~ 15.
Butane Ln line 14 is absorbed in the absorber by a cyclic operation us~ng mL~tiple beds filled w.ith absorbents such as activatecl carbon. The denuded off-gas, 1300 lbs/hr, m~lnly contain mg ox~gen, nitrogen and oxides of carbon, is v~nt0d out .... g_ 35~
.
and -the butane adsorbed on the adsorben-t is recovered by suitable desorption such as steaming at about 250 F followed by condensation and phase separa-tion. The recovered butane, 36 lbs./hr., is then recycled back through line 16 to the reactor.
To reduce the amount of aqueous scrubbing solution and/or to ob-tain more nearly complete removal of the acids from the recycle portion of the reactor effluent, a solution of sodium or potassium hydroxide, carbon-ate, or bicarbonate in water is advantageously used in place of simply water.
Example 2 The process was carried out as in Example 1, with single-stage scrubbing of the maleic anhydride-lean off gas to remove light acids from the recycle to the reactor.
The effects of acid contaminants in a reactor feed were tested in a separate test reactor (as we did not want to vary conditions in our main reactor) using the same type catalyst that was used in the main reactor. The reactant feed to this test reactor consisted of a slipstream from either stream No. 5 or 13 of Figure 1. When the test reactor feed is obtained from stream 13, the test reactor was exposed to a washed off gas consisting of butane, oxygen, nitrogen and carbon oxides with only minute traces of light acids (about 6 ppm). The rate da-ta obtained for the first run (see Run No.
1 in Table I below) was used for further comparison.
Subsequent test runs consisted of alternately switching the test reactor feed to-slipstreams from streams 5 and 13 and evaluating the test reactor performance for each such run.
The performance of the test reactor under these conditions is ~;
shown in Table I. It is to be noted that the presence of acid contaminants ~ -in the feed immediately dropped the catalyst activity and selectivi-ty for maleic anhydride production. See Run No. 2 in Table I. Also, this deleter-ious effect was found irreversible with removal of the feed contaminants in " ' ~1~93S66 the subsequent test run. See Run No. 3 in Table I. The performance of the eatalyst continues to degrade as it is further treated with an acid-con~
taminated stream. See Run No. ~, second exposure to stream No. 5.
A rather surprising finding of these experiments is that the pres-ence of acid contaminants in the feed inereases the light aeid produetion rate in the su~sequent test runs. In a reeyele operation with less effee-tive removal of acid contaminants from the reeyeled effluent stream, this deleterious effeet asssures a eontinued, aeeelerated degradation of the eat-alyst performanee. Thus, it is espeeially advantageous to remove the light aeids in accordance with the process of the present invention. Further ex-periments with a synthetic feed containing butane with either acetic or acr~lic acid in -the absence of maleic anhydride confirm the deleterious effeet observed using stream 5.
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Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing maleic anhydride from a C4 hydrocarbon selected from n-butane and n-butene feed which comprises:
(a) feeding the C4 hydrocarbon and air to a reactor;
(b) contacting the C4 hydrocarbon and air in the reactor with a catalyst comprising vanadium and phosphorus oxides at reaction conditions including a temperature between 550 and 1000°F so as to obtain a reactor ef-fluent containing maleic anhydride, unreacted C4 hydrocarbon, nitrogen, oxygen, and acrylic, acetic or maleic acid or mixtures of the foregoing acids;
(c) removing maleic anhydride from the reactor effluent to ob-tain maleic anhydride-lean effluent, (d) removing said acids from at least a portion of the maleic anhydride-lean effluent to obtain a purified recycle stream containing less than 100 ppm of the acids; and (e) recycling the purified stream to the reactor.
(a) feeding the C4 hydrocarbon and air to a reactor;
(b) contacting the C4 hydrocarbon and air in the reactor with a catalyst comprising vanadium and phosphorus oxides at reaction conditions including a temperature between 550 and 1000°F so as to obtain a reactor ef-fluent containing maleic anhydride, unreacted C4 hydrocarbon, nitrogen, oxygen, and acrylic, acetic or maleic acid or mixtures of the foregoing acids;
(c) removing maleic anhydride from the reactor effluent to ob-tain maleic anhydride-lean effluent, (d) removing said acids from at least a portion of the maleic anhydride-lean effluent to obtain a purified recycle stream containing less than 100 ppm of the acids; and (e) recycling the purified stream to the reactor.
2. A process in accordance with Claim 1 wherein the C4 hydrocarbon feed is n-butane.
3. A process in accordance with Claim 2 wherein the acids are re-moved in step (d) by water scrubbing the maleic anhydride-lean effluent.
4. A process in accordance with Claim 3 wherein the maleic anhydride is removed from the reactor effluent to obtain the maleic anhydride-lean ef-fluent solely by countercurrent contacting of the reactor effluent with an organic absorbent to thereby absorb the maleic anhydride into the organic absorbent.
5. A process in accordance with Claim 3 wherein the acids are re-moved from the maleic anhydride-lean effluent to obtain a purified recycle stream containing less than 7 ppm acids.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US64558475A | 1975-12-31 | 1975-12-31 | |
| US645,584 | 1975-12-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1093566A true CA1093566A (en) | 1981-01-13 |
Family
ID=24589605
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA267,822A Expired CA1093566A (en) | 1975-12-31 | 1976-12-14 | Maleic anhydride production with recycle treatment |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS6055513B2 (en) |
| BE (1) | BE849980A (en) |
| CA (1) | CA1093566A (en) |
| DE (1) | DE2658191C2 (en) |
| FR (1) | FR2337132A1 (en) |
| GB (1) | GB1516430A (en) |
| IT (1) | IT1067952B (en) |
| NL (1) | NL187747C (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3277533D1 (en) * | 1982-07-20 | 1987-12-03 | Amoco Corp | Process for production of maleic anhydride |
| JPS62286824A (en) * | 1986-06-06 | 1987-12-12 | Diesel Kiki Co Ltd | Blowing device for car room |
| US6194587B1 (en) * | 1999-08-19 | 2001-02-27 | Scientific Design Company, Inc. | Production of maleic anhydride |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3741993A (en) * | 1970-02-03 | 1973-06-26 | Tenneco Chem | Maleic anhydride process |
| US3864280A (en) * | 1972-06-19 | 1975-02-04 | Chevron Res | Catalyst for a n-butane oxidation to maleic anhydride |
| JPS5144141B2 (en) * | 1972-07-29 | 1976-11-26 | ||
| US3904652A (en) * | 1972-11-16 | 1975-09-09 | Standard Oil Co Indiana | Recycle process for oxidation of n-butane to maleic anhydride |
| GB1528451A (en) * | 1974-10-03 | 1978-10-11 | Atomic Energy Authority Uk | Manufacture of bags |
-
1976
- 1976-12-14 CA CA267,822A patent/CA1093566A/en not_active Expired
- 1976-12-22 JP JP51153548A patent/JPS6055513B2/en not_active Expired
- 1976-12-22 DE DE19762658191 patent/DE2658191C2/en not_active Expired
- 1976-12-23 FR FR7638912A patent/FR2337132A1/en active Granted
- 1976-12-23 NL NL7614362A patent/NL187747C/en not_active IP Right Cessation
- 1976-12-29 BE BE173739A patent/BE849980A/en not_active IP Right Cessation
- 1976-12-30 IT IT3098976A patent/IT1067952B/en active
- 1976-12-31 GB GB5445576A patent/GB1516430A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2658191A1 (en) | 1977-07-14 |
| BE849980A (en) | 1977-04-15 |
| DE2658191C2 (en) | 1985-01-31 |
| IT1067952B (en) | 1985-03-21 |
| FR2337132A1 (en) | 1977-07-29 |
| NL187747B (en) | 1991-08-01 |
| NL7614362A (en) | 1977-07-04 |
| NL187747C (en) | 1992-01-02 |
| FR2337132B1 (en) | 1980-08-08 |
| JPS6055513B2 (en) | 1985-12-05 |
| GB1516430A (en) | 1978-07-05 |
| JPS5283324A (en) | 1977-07-12 |
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