CA2128648A1 - Process for the continuous preparation of high-molecular-weight carboxylic acids - Google Patents
Process for the continuous preparation of high-molecular-weight carboxylic acidsInfo
- Publication number
- CA2128648A1 CA2128648A1 CA002128648A CA2128648A CA2128648A1 CA 2128648 A1 CA2128648 A1 CA 2128648A1 CA 002128648 A CA002128648 A CA 002128648A CA 2128648 A CA2128648 A CA 2128648A CA 2128648 A1 CA2128648 A1 CA 2128648A1
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- reaction
- reactor
- chromic
- olefin
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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
- C07C51/305—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with sulfur or sulfur-containing compounds
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
Abstract
Abstract Process for the continuous preparation of relatively high-molecular-weight carboxylic acids The oxidation of olefins having from 16 to 70 carbon atoms by means of chromic/sulfuric acid in a single-stage or multistage process in at least one reactor having a narrow residence time spectrum enables the preparation of carboxylic acid mixtures. These can be processed with monoalcohols or polyols such as glycol, glycerol, trimethylolpropane, pentaerythritol or sorbitol to give esters and partial esters or mixtures of such esters.
Reaction with basic oxides or metal hydroxides can be used to prepare the corresponding soaps of the carboxylic acids by direct reaction or by trans-precipitation.
Reaction with amines or aminoalcohols gives the amides, amidoesters and aminoesters. These products have a pale colour, good thermal stability and a wide range of applications.
Reaction with basic oxides or metal hydroxides can be used to prepare the corresponding soaps of the carboxylic acids by direct reaction or by trans-precipitation.
Reaction with amines or aminoalcohols gives the amides, amidoesters and aminoesters. These products have a pale colour, good thermal stability and a wide range of applications.
Description
~ 2128~48 HOECHST AKTIENGESELLSCHAFT XOE 93/F 212 Dr.DA/sch Description , ' Proces~ for the continuou~ preparation of relatively high-molecular-weight carboxylic acid~
The invention relate~ to a process for preparing relatively high-molecular-weight carboxylic acid~ by oxidation of ethylenically unsatura~ed compounds with chromic acid.
There are numerous syntheses known for preparin~ relat-ively high-molecular-weight, linear aliphatic carboxylic acids. However, only a few proce~es are u~ed indust-rially.
Thu~, the demand for relatively high-molecular-weight fatty or wax acid~ is met almo~t exclusively by natural products.
'::
The oxidation of para$fin~ to carboxylic acids has been implemented industrially. However, this proce~s has the dlsadvantage that the attack of the oxidant cannot be controlled and a wide range of carboxylic acid~ and other oxygen-containing compounds i~ formed.
These disadvantages can be avoided if the raw materials used are long-chain olefin~ and the oxidant used i~, for example, chromic acid in sulfurlc acld solution. There are single-stage or multi-stage processes known for the oxidatlon of olefin~ (cf. DE 2 165 858, DE 2 262 130, DE 23 10 425). Theae processes have, besides the incom-plete conversion, the high oxidAnt consumption and the poor separation, the $urther di~advantage that the olefin is only insuf f icientiy disper~ed in the oxidant. In addition, there is the formation of a viscous, chromium-containing organic phase which interfere~ with a con-trolled reaction course.
21286~8 It is known that the disadvantage~ of a batchwise mode of operation can be compensated for in a continuous mode of operation. Thus, for example, the oxidative bleaching of natural waxe~ iB, for the purpo~e of better handling of the viscous reaction mixture, carried out with exploit-ation of gaseous oxidation products in a reac~or having the characteristic of a narrow residence time ~pectrum (cf. DE 28 55 263).
It has been found that the oxidation of olefin~ is possible in a modified proce~s procedure.
The invention accordingly provides a proce~ for the continuous preparation of relatively high-molecular-we~ght, linear aliphatic carboxylic acids by oxidation of olefins having from 16 to 70 carbon atoms with approxim-ately 1 molar, ba~ed on CrO3, chromic/sulfuric acid at atemperature of from 90 to 200C and a pres~ure of from 100 mbar to 20 bar, which compri6es carrying out the reaction in cocurrent mode in at least one reactor having a narrow residence time spectrum, the mixing of the reactants being carried out by the steam formed as a result of the heat of reaction and the reaction gae and also the additional blowing-in of air.
The process of the invention is carried out in con-tlnuously operated reactor~ having the characteristic of a narrow re~idence time spectrum, for example in tube reactors, cascades of stirred reactor~ or cascaded bubble column reactor~ having mesh tray~, with preference being given to u~ing the caecaded bubble column reactors. In these reactors, the mixing of the reactants by the steam formed as a result of the exothermic reaction, by the liberation of gaseous reaction products, by the blowing-in of air/steam and by the arrangement and shape of the meeh trays i8 particularly effective, without the incor-poration o~ moving mechanical part# being reguired for thi~ purpo~e. A further advantage of the ~ubble-column cascade reactors i~ that low-molecular-weight and ~team-212864~
volatile oxidation products are carried out of thereactor by the steam formed. Without this stripping proce~s, these products would either remain in the used chromic/sul~uric acid and interfere with the regeneration thereof, or they remain in the oxidate and interfere with the further uae o$ this oxidate.
The apparatus u~ed for the process of the invention i~
shown in the figures, Figure 1 ~howing an apparatus for a ~ingle-~tage mode of operation, Figure 2 showing an apparatu~ for a two-~tage mode of operation and Figure 3 ~howing an apparatu~ for a three-~tage ~ode of operation.
In the figures 111 = Reactor for the first ~tage ~ ;
112 = Feedline for olefin 113 = Feedline for chromic/~ulfuric acid 114 = Feedline for air 115 . Pipe 116 = Feedline for ~eparating agent 211 . Reactor for the 2nd etage 212 . Feedllne for olsflr./carboxylic acid mixture 213 = Feedline for fre~h chromic/~ulfuric acid 214 . Feedline for air 215 . Pipe 216 . Separation ve~sel 217 ~ Outflow line 311 a Reactor for th~ 3rd ~tage 312 . Feedline for olefin~carboxylic acid mixture 313 - Feedline for fresh chromic/sulfuric acid 314 . Feedline for air 315 . Pipe 316 = Separation vessel 317 . Outflow line 411 = Degaesing vessel 412 = Separat~on ve~sel for final product , 2l286~8 413 = Dechromer 414 = Condensate ~eparator 415 = Pipe 416 = Pipe 417 - Outflow line 418 = Waste gas line 419 = Wa0te ga6 line 420 = Waste ga~ line 421 = Outflow line 422 = Discharge line for final product 423 = Condensate outflow line The reactor~ (111), (211) and (311) are divided into individual reaction chambers by a plurality of sieve tray~. The distance of the trays from one another i~ $rom 1 to 5 times, preferably from 1 to 3 time~, the column diameter.
In the figura, the sieve tray~ are only indicated.
In accordance with Figure 1, the reactor (111) is pro-vided at the bottom with feedline~ for olefin (112), chromic/sulfuric acid (113) and air (114). From the top of the reactor (111), a pipe (115) leads into the top third of the dega~eing vo~el (411). From the bottom of the degassing vessel (411), a pipe leads into a point halfway up the separation ve~sel (412), the upper part of which is connected by a pipe (416) to the lower part of the dechromer (413). A waste gas line (419) from the top of the degassing veasel (411) and a waste gaa line (418) from the top of the separation veseel (412) lead to a conden~ate separator (414). Furthermore, an outflow line (417) leads from the bottom o4 the ~eparation vessel (412) to a chromic acid preparation facility (not shown).
An outflow line (421) coming from the bottom of the dechromer (413) enters this outflow line (417). The dechromer (413) is here ~hown as an adsorption column. It is discharged from the top ~ia the line (422). The conden~ate separator (414) is provided with a waste gas line (420) at the top and with an outflow line (423) at - ,5~2~_~86 ~ .
the bottom.
The apparatu~ for the two-stage proceE~s i~ identical with the apparatus for the ~ingle-~tage proces~, but with the additional apparatua component~ of items (211) to (216).
In Figure 2, the reactor (111) i8 provided at the bottom with feedlines for olefin (112), chromic/~ulfuric ac:id (113~ and air (114). From the top of the reactor (111), a pipe (115) leads into the ~eparation ve~eel (216) from the upper third o which a pipe (212) leads to the b~ttom of the reactor (211). At the ~ame time, a feedline (214) for air and a feedline (213) for fre~h chromic/~ul$uric acid are connected to the pipe (212) in the Yicinity of the bottom of the reactor (211). From the top of the reactor (211), a pipe (215) leads into the top third of the degassing ve~el (411). From the bottom of ~ the dega~sing ve~el (411), a pipe lead~ to a poin~c halfwAy up the separation ves~el (412), the upper part of which i5 connected via a pipe (416) to the lower part of the dechromer (413). A waste ga~ line (419~ from the top of ~:
the degassing veseel (411) and a waste ga~ line (418) from the top of the separation ve~el (412) lead to a condensate separator (414). Furthermore, an outflow line : .
(417) leads from the bottom of he separation ve~el (412) to a chromic acid preparation facility (not ~hown).
An outflow line (421) coming from the bottom oî the dechromer (413) and an outflow llno (217) from the bottom of the ~eparatlon vessel (216) enter this outflow line :: :
(417). ~ :
The apparatus for a three-~t~ge mode of operation in accordance with Figure 3, comprise~ a further group of apparatus components of item~ (311) to (316~. In Figure 3, the reactor (111) i~ provided at the bottom with feedlines for olefin (112), chromic/sul~uric acid (113) and air (114). From the top of the reactor (111), a pipe (115) leads into the separation vessel (216), from the uppor third of which a pipe (212) lead0i to the }~ottom of the reactor (211). At 'che same time, a feedline (214) for ~ 21286~8 air and a feedline (213) for fre~h chromic/sulfuric acid are connected to the pipe (212) in the proximity of the bottom of the reactor (211). From the top of the reactor (211), a pipe (215) leads into the ~eparation ve~el (316), from the upper third of which a pipe (312) leads to the bottom of the reactor (311). At the same time, a feedline (314) for air and a feadlina (313) for fresh chromic/sulfuric acid are connected to the pipe (312) in the vicinity of the bottom of the reactor (311). From the top of the reactor (3113, a pipe (315) lead~ into the upper third of the dega~sing vessel (411). The bottom of the separation vessel (316) i8 connected via an outfl~w line (317) with the outflow line (~17). From the bottom of the degas~ing vessel (411), a pipe lead~ to a point halfway up the ~eparation ve~sel (412), the upper part of which i~ conr~ected via a pipe (416) with the lower part of the dechromer (413). A waste ga~ line (419) from the top of the degassing vessel (411) and a waete gas line (418) from the top o$ the ~eparation ve~sel (412) lead to a conden~ate separator (414). Furthermore, an outflow line (~17) leads from the botto~ of the separation vessel (412) to a chromic acid preparation facility (not ~hown).
An outflow line (421) coming from the bottom of the dechromer (413) and an outflow line (217) cc~ming from the bottom of the eeparation ~ressel (216) enter thi~ outflow line (417).
All reactors, ves~els and pipes are provided with tem-perature control facilities.
~ ~'' ' ", For carrying out the proce~s of the invention, use of o~e, two or three stages can be chosen. For this purpo~e, the various reactor ~tages can be combined with one another~ In addition, a ~ingle reactor or a plurality of reactors can be used for each stage.
In the single-stage mode of operation in accordance with Figure 1, the olefin, together with a part of the chromic/sulfuric acid (feedline (113)) and air (feedline 21286~8 (114)), i~ introduced, via the feedline (112), into the first reactor (111). The mixture flows, with intensive mixing, through the reactor (111). The product i~ then conducted into a dega~sing Btage comprising the dega~ing ve~sel (411) and the 3eparation ve~el (412). Here the volatile component~ are 6eparated off via the top, and in a condensate separator (414) the conden~able con~tituents are removed from the waste gas s~rea~. The wa~te gas is conducted away via the outflow line (420) and the conden-sate i conducted away via the outflow line (423). After ~eparation of the oxidate and oxidant in the ~eparation vessel (412), the oxidate ie further freed, in the dech-romer (413), of colloidal or chemically bound chromium compound~. This purification can be carried out in the form of a ~crubbing stage, an adsorption ~tage or a 3eparation by means of a centrifuge. The oxidate iB drawn off via the line (422). The used chromic/~ul~uric acid iB
conducted via line6 (417) and (421) to regeneration.
In the two-~tage mode of operation in accordance with Figure 2, the reaGtion mixture is fed from reactor (111) into a separation ve~sel (216). There the oxidate separa-tes from the chromic/eulfuric acid which flows through the line (217) to regeneration, and i8 metered into the reactor (211) with fre~h chromic/sulfuric acid and air via the line (212). From this reactor~ the rsaction mixture again flows into the above-described work-up ~tages.
The three-stage mode of operation in accordance with Figure 3 proceed~ in the same way, an additional reactor (311) and a ~eparation vessel (316) being incorporated between the reactor (211) and the degasaing ves~el (411).
The reaction mixture is thu~ ~eparated after each fitage and either worked up to give the final product or metered into the next stage together with ~resh chromic/~ulfuric acid and air.
~ - . . :- ,: .. ,.; ~ , : -21286~8 In the process o$ the invention, olefins having an internal double bond and a total of from 16 to 70, preferably from 20 to 50, carbon atoms are u~ed. Example~
of ~uch olefins are tho~e of the formula Rl-CH=CH-R2, in which R1 and R2 are a hydrogen atom or a C1-C68-, prefer-ably C1-C48-alkyl group and Rl and Rl together have from 14 to 68, preferably from 18 to 48, carbon atom~, or of the formula R3-C(R9)=CH2, in which R3 and R4 are a C1-C6a-, preferably C~-C~-alkyl group and R3 and R~ together have from ~4 to 68, preferably from 18 to 48, carbon atom~.
Example~ of euch olefin~ are hexadec-1-ene, octadec-l-ene, Eico~-1-ene, doco~-1-ene, tetracos-l-ene, triacont-l-ene, 2-ethyltriacont-1-ene and aloo l-olefin mixture~ which predominantly compri~e C22- to Cs~-olefins.
The oxidant used is a aolution o~ CrO3 and Cr2~SO~)3, if desired even of alkali metal dichromate, in aqueo~s ~ulfuric acid. Approximately 1-molar solutions, baaed on the CrO3 content, are used. In general, the chromic/
sulfuric acid u~ed compri~es from 500 to 600 g of E2SO4 and from 95 to 110 g of CrO3 per dm3.
The amount of chromic/sulfuric acid required for the oxidatlon of the olefin to the de~ired degree of conver-sion can, in the multi~tage proce~, be fed together with the olefin melt into the reactor of the f$rst reaction stage. ~owever, the process procedure of metering in the chromic/sulfuric acid in portions ha~ proven more ~uit-able. In this method, the u~ed oxidant is separated off in a ~eparation vessel and transferred out prior to the addition of the fresh chromic/~ul$uric acid.
The ratio of amounts of olefin to oxidant here depends on the molecular weight of the olefinic components and their reactivity. In the oxidation of an olefin mixture com-prising vinylolefin, vinylideneolefin and olefin having internal double bonds and the iodine number (IN) of 45, such as is, for example, commercially available a~
~Chevron C30,-olefin, a total amount of from 120 to 150 %
, ~ 21286~8 by weight, corre~ponding to from 165 to 200 mol%, o~ CrO
based on the olefin u~ed, i8 required to obtain a mixture of long-chain aliphatic carboxylic acid~ having an acid number (AN) of from 105 to 125. In a two-stage reaction, about 90~ of the olefin used can here be converted. A
carboxylic acid mixture having an AN of 105 i~ obtained.
About 60% by weight of the oxidant i~ here added in the first stage and in the second atage.
A three-~tage reactio~ u~ing 60% by weight of oxidant in the first stage, 50% by weight in the ~econd ~tage and 30% in the third stage leads, at an olefin conversion of ~ 95%, to a carboxylic acid mixture having an acid number AN of from 120 to 125.
The mixing requ~red for the process to be ~uccessful automatically result~ from the type of reactor and from the action of the steam formed and the volatile reaction gases. In addition, air is blown into the first reactor of each stage.
The reaction i5 carried out at a temperature of from about 90C to 200C, preferably in the range from 110C
to 125C, and at a pree~ure of from 100 mbar to 20 bar, ¦ preferably from 1 bar to 5 bar. The residence time~ in the individual reactor ~tages are from 60 minutes to 180 minutes. The res$dence time depends on the phase ratio and on the de~ired conver~ion of olefin or oxidant.
Carboxylic acid mixture~ prepared by the process of the invention can be further proce~ed with monoalcohol~ or polyols such as glycol, glycerol, trimethylolpro~ane, pentaerythritol or sorbitol to give esters and partial esters or mixtures of such esters. Reaction with basic oxides or metal hydroxide~ can be used to prepare the corresponding soaps of the carboxylic acids by direct reaction or by trans-precipitation. Reaction with amines or aminoalcehols gives the amides, amidoestera and amino-esters.
.*
~ 21286~8 . :
These productQ have a pale colour, good thermal ~tability and a wide range of applicationQ.
The esterQ and/or ~oapQ can thu~ be u~ed a~ pa~te waxe~, emulsion waxe~, release agent~ or a~ lubricants.
The following example~ illustrate the invention.
:
The experiment~ were carried out using a laboratory apparatu~ having a reactor capacity of about 6 dm3 per reaction stage.
Example 1 Single-stage oxidation u~ing a variable proportion of ox~dant.
An olefin mixture comprising vinylolefin, vinylidene olefin and olefin having internal double bonds and an iodine number (IN) of 4g (Chevron C30~-olefin) was melted and placed in a heated re~ervoir. The temperature of the melt was ad~u~ted to from 95 to 100C by ~team heating.
The olefin wa~ con~eyed into the fir~t reactor via a ~team-heated line and a heated pump.
The chromic acid was convayed from a temperature-controlled re~ervolr into the roactor via an acid-resis-tant pump. 100 dm3/h of aix at a pres~ure of 0.5 bar were lntroduced i~to the reactor. The three component~ were mixed in a multl-fluld nozzle ak the bottom o~ the reactor and lnjected lnto the fir~t reactor chamber. The reaction mixture was conveyed through the reactor cham-ber~ and after pa~eing through the individual reactor ~tage~ wa~ conveyed via the dega~ing ~tep into the separation ves~el. There the used oxldant was separated o$f. At thi~ point, the separation could be improved by addition of a eeparating agent (amount from 0.1 to 0.5%
by weight, ba~ed on olefin u~ed).
~ ~ ; " ; ~ ?`
., 21286~8 Conversion of olefin and oxidant are here dependent on the amount conveyed through and thu~ on the residence time in the reactor.
The oxidate thu~ obtained was further freed of re~idual chromium compou~ds by centrifugation.
Table 1: Continuou~ oxidation of ~-olefin Experiments using constant metering of olefin/chromic acid Experiment Wax Chromic CrO3 _ ~rO3 cm3/h Am3i/dh Feed % Con~umption _ .
_ _ _ _ _ Feed = Amount fed in, % by weight based on olefin Con~umption = Con~umption in % by weight, based on olefin Example 2 Single-~tage proces~ with ~ariable metered amounts at constant proportion of oxidant The olefin was melted and placed in a heated re~ervoir, The temperature o$ the melt wa~ adjueted to fxom 95 to 100C by steam h0ating. The olefin wae conveyed into the 2l286~8 ~:
first reactor via a ~team-heated line and a heated pump.
The chromic acid was conveyed from a temperature-con-trolled reservoir into the reactor via an acid-resi~tan~
pump. 100 dm3/h of air at a preR~ure of 0.5 bar were introduced into the rea~tor.
The three co~ponent~ were mixed in a multi-fluid nozzle at the bottom of the reactor a~d injected into the fir~t reactor chamber. While filling the reactors, an increased conveying rate could be used. The amount of olefin and chromic acid conveyed wa~ then reduced to ~et an optimum uRe of oxidant.
The reaction mixture was conveyed through the reactor chambere and after passing through the individual reactor stages was conducted via the degas~ing ~tep into the separation vessel. There the u~d oxidant was oeparated off. At this point the ~eparation could be improved by addition of a separating age~t (amount from 0.1 to 0.5 %
by weight, ba~ed on olefin u~ed).
The oxidate thus obtained wa~ furt~er freed of residual chromium by centrifugation.
. "
Table 2: Continuou~ oxidation of ~-olefin Experiments using variable ~etering of olefin/
chromic acid ¦ Experiment WaxChromic Acid CrO3 ANCrO3 l 100 Feed % Consumption ¦ :
cm3/h cm3/h 96 l . I I , .
l 6s-so- 39-30-24 60 57 56 1 13 65 - 4039 - 24 6Q 65 59 I . .
l __ l _ _ ~ - _ l : , Feed = Amount fed in, % by weight ba~ed on olefin -- 2l2~)6~8 Consumption = Consumption in % by weight, ba~ed on olefin Example 3 Two-stage proces~ with con~tant proportion of oxidant and variable met~ring The ole$in wa malted and placed in a heated re~ervoir, The temperature of the melt was adjusted to from 95 to 100C by ~team heating. The olefin was conveyed into the firat reactor via a ateam-heated line and a heated pump.
The chromic acid was conveyed from a temperature-con-trolled re~ervoir into the reactor via an acid-re~iatant pump. 100 dm3/h of air at a pre~ure of 0.5 bar were introduced into the reactor.
The three component~ were mixed in a multi-fluid nozzle at the bottom of the reactor and injoated into the first reactor cha~ber. The reaction mixture was conveyed through the reaction chamber~ and, after flowiny through the first reaction ~tage, was pas~ed into the ~eparation veaael, the uaed oxidant wa~ aeparated off and the pre-oxidized olefin wa~ conv~yed together with freah chromicacid and air into the second reaction ~tage. After paaaing through all reaction chambera, the product waa degaaaed, the used oxidant was aeparated off and re~idual chromium compound~ were ~eparated off from the ox~date in a centr~fuge.
, .
Table 3: Continuou~ oxidation of a-olefin Experiments u~ing variable metering of olefin/ .-.
chromic acid, 2nd stage ¦ Experiment Wax Chromic CrO3 - CrO3 10 cm3/hAcid Feed t Consumption 100 cm3/h _ .
510 (1 - 5)60 - 50 36 - 30 60 109 54 , .
8 (6) 65 - 45 36 - 25 SS 101 55 9 (7) 60 - 40 36 - 24 60 lOB 60 _ 12 (11) 65 - 40 39 - 24 60 108 59 14 (13) 65 - 40 39 - 24 60 110 58 1018 (17) 60 - 40 36 - 24 60 109 58 .
Feed = Amount fed in, % by weight ba~ed on olefin Con~u~ption = Consumption in % by weight, ba~ed on :~:
olefin The values ln () indicate the experi~ent number of the 15 first stage ~
': '';
Example 4 Three-stage process with constant proportion of oxidant and variable amounts metered in ::
'~;
The procedure wa~ as in Example 3. After the ~econd reaction stage, the oxidate and freah chromia acid were introduced into the third reaction stage and worked up as described above. Use of 50~ by weight of CrO3 gave an oxidate having an AN of 125. .~;
.
: '.
,'' ,'~
'
The invention relate~ to a process for preparing relatively high-molecular-weight carboxylic acid~ by oxidation of ethylenically unsatura~ed compounds with chromic acid.
There are numerous syntheses known for preparin~ relat-ively high-molecular-weight, linear aliphatic carboxylic acids. However, only a few proce~es are u~ed indust-rially.
Thu~, the demand for relatively high-molecular-weight fatty or wax acid~ is met almo~t exclusively by natural products.
'::
The oxidation of para$fin~ to carboxylic acids has been implemented industrially. However, this proce~s has the dlsadvantage that the attack of the oxidant cannot be controlled and a wide range of carboxylic acid~ and other oxygen-containing compounds i~ formed.
These disadvantages can be avoided if the raw materials used are long-chain olefin~ and the oxidant used i~, for example, chromic acid in sulfurlc acld solution. There are single-stage or multi-stage processes known for the oxidatlon of olefin~ (cf. DE 2 165 858, DE 2 262 130, DE 23 10 425). Theae processes have, besides the incom-plete conversion, the high oxidAnt consumption and the poor separation, the $urther di~advantage that the olefin is only insuf f icientiy disper~ed in the oxidant. In addition, there is the formation of a viscous, chromium-containing organic phase which interfere~ with a con-trolled reaction course.
21286~8 It is known that the disadvantage~ of a batchwise mode of operation can be compensated for in a continuous mode of operation. Thus, for example, the oxidative bleaching of natural waxe~ iB, for the purpo~e of better handling of the viscous reaction mixture, carried out with exploit-ation of gaseous oxidation products in a reac~or having the characteristic of a narrow residence time ~pectrum (cf. DE 28 55 263).
It has been found that the oxidation of olefin~ is possible in a modified proce~s procedure.
The invention accordingly provides a proce~ for the continuous preparation of relatively high-molecular-we~ght, linear aliphatic carboxylic acids by oxidation of olefins having from 16 to 70 carbon atoms with approxim-ately 1 molar, ba~ed on CrO3, chromic/sulfuric acid at atemperature of from 90 to 200C and a pres~ure of from 100 mbar to 20 bar, which compri6es carrying out the reaction in cocurrent mode in at least one reactor having a narrow residence time spectrum, the mixing of the reactants being carried out by the steam formed as a result of the heat of reaction and the reaction gae and also the additional blowing-in of air.
The process of the invention is carried out in con-tlnuously operated reactor~ having the characteristic of a narrow re~idence time spectrum, for example in tube reactors, cascades of stirred reactor~ or cascaded bubble column reactor~ having mesh tray~, with preference being given to u~ing the caecaded bubble column reactors. In these reactors, the mixing of the reactants by the steam formed as a result of the exothermic reaction, by the liberation of gaseous reaction products, by the blowing-in of air/steam and by the arrangement and shape of the meeh trays i8 particularly effective, without the incor-poration o~ moving mechanical part# being reguired for thi~ purpo~e. A further advantage of the ~ubble-column cascade reactors i~ that low-molecular-weight and ~team-212864~
volatile oxidation products are carried out of thereactor by the steam formed. Without this stripping proce~s, these products would either remain in the used chromic/sul~uric acid and interfere with the regeneration thereof, or they remain in the oxidate and interfere with the further uae o$ this oxidate.
The apparatus u~ed for the process of the invention i~
shown in the figures, Figure 1 ~howing an apparatus for a ~ingle-~tage mode of operation, Figure 2 showing an apparatu~ for a two-~tage mode of operation and Figure 3 ~howing an apparatu~ for a three-~tage ~ode of operation.
In the figures 111 = Reactor for the first ~tage ~ ;
112 = Feedline for olefin 113 = Feedline for chromic/~ulfuric acid 114 = Feedline for air 115 . Pipe 116 = Feedline for ~eparating agent 211 . Reactor for the 2nd etage 212 . Feedllne for olsflr./carboxylic acid mixture 213 = Feedline for fre~h chromic/~ulfuric acid 214 . Feedline for air 215 . Pipe 216 . Separation ve~sel 217 ~ Outflow line 311 a Reactor for th~ 3rd ~tage 312 . Feedline for olefin~carboxylic acid mixture 313 - Feedline for fresh chromic/sulfuric acid 314 . Feedline for air 315 . Pipe 316 = Separation vessel 317 . Outflow line 411 = Degaesing vessel 412 = Separat~on ve~sel for final product , 2l286~8 413 = Dechromer 414 = Condensate ~eparator 415 = Pipe 416 = Pipe 417 - Outflow line 418 = Waste gas line 419 = Wa0te ga6 line 420 = Waste ga~ line 421 = Outflow line 422 = Discharge line for final product 423 = Condensate outflow line The reactor~ (111), (211) and (311) are divided into individual reaction chambers by a plurality of sieve tray~. The distance of the trays from one another i~ $rom 1 to 5 times, preferably from 1 to 3 time~, the column diameter.
In the figura, the sieve tray~ are only indicated.
In accordance with Figure 1, the reactor (111) is pro-vided at the bottom with feedline~ for olefin (112), chromic/sulfuric acid (113) and air (114). From the top of the reactor (111), a pipe (115) leads into the top third of the dega~eing vo~el (411). From the bottom of the degassing vessel (411), a pipe leads into a point halfway up the separation ve~sel (412), the upper part of which is connected by a pipe (416) to the lower part of the dechromer (413). A waste gas line (419) from the top of the degassing veasel (411) and a waste gaa line (418) from the top of the separation veseel (412) lead to a conden~ate separator (414). Furthermore, an outflow line (417) leads from the bottom o4 the ~eparation vessel (412) to a chromic acid preparation facility (not shown).
An outflow line (421) coming from the bottom of the dechromer (413) enters this outflow line (417). The dechromer (413) is here ~hown as an adsorption column. It is discharged from the top ~ia the line (422). The conden~ate separator (414) is provided with a waste gas line (420) at the top and with an outflow line (423) at - ,5~2~_~86 ~ .
the bottom.
The apparatu~ for the two-stage proceE~s i~ identical with the apparatus for the ~ingle-~tage proces~, but with the additional apparatua component~ of items (211) to (216).
In Figure 2, the reactor (111) i8 provided at the bottom with feedlines for olefin (112), chromic/~ulfuric ac:id (113~ and air (114). From the top of the reactor (111), a pipe (115) leads into the ~eparation ve~eel (216) from the upper third o which a pipe (212) leads to the b~ttom of the reactor (211). At the ~ame time, a feedline (214) for air and a feedline (213) for fre~h chromic/~ul$uric acid are connected to the pipe (212) in the Yicinity of the bottom of the reactor (211). From the top of the reactor (211), a pipe (215) leads into the top third of the degassing ve~el (411). From the bottom of ~ the dega~sing ve~el (411), a pipe lead~ to a poin~c halfwAy up the separation ves~el (412), the upper part of which i5 connected via a pipe (416) to the lower part of the dechromer (413). A waste ga~ line (419~ from the top of ~:
the degassing veseel (411) and a waste ga~ line (418) from the top of the separation ve~el (412) lead to a condensate separator (414). Furthermore, an outflow line : .
(417) leads from the bottom of he separation ve~el (412) to a chromic acid preparation facility (not ~hown).
An outflow line (421) coming from the bottom oî the dechromer (413) and an outflow llno (217) from the bottom of the ~eparatlon vessel (216) enter this outflow line :: :
(417). ~ :
The apparatus for a three-~t~ge mode of operation in accordance with Figure 3, comprise~ a further group of apparatus components of item~ (311) to (316~. In Figure 3, the reactor (111) i~ provided at the bottom with feedlines for olefin (112), chromic/sul~uric acid (113) and air (114). From the top of the reactor (111), a pipe (115) leads into the separation vessel (216), from the uppor third of which a pipe (212) lead0i to the }~ottom of the reactor (211). At 'che same time, a feedline (214) for ~ 21286~8 air and a feedline (213) for fre~h chromic/sulfuric acid are connected to the pipe (212) in the proximity of the bottom of the reactor (211). From the top of the reactor (211), a pipe (215) leads into the ~eparation ve~el (316), from the upper third of which a pipe (312) leads to the bottom of the reactor (311). At the same time, a feedline (314) for air and a feadlina (313) for fresh chromic/sulfuric acid are connected to the pipe (312) in the vicinity of the bottom of the reactor (311). From the top of the reactor (3113, a pipe (315) lead~ into the upper third of the dega~sing vessel (411). The bottom of the separation vessel (316) i8 connected via an outfl~w line (317) with the outflow line (~17). From the bottom of the degas~ing vessel (411), a pipe lead~ to a point halfway up the ~eparation ve~sel (412), the upper part of which i~ conr~ected via a pipe (416) with the lower part of the dechromer (413). A waste ga~ line (419) from the top of the degassing vessel (411) and a waete gas line (418) from the top o$ the ~eparation ve~sel (412) lead to a conden~ate separator (414). Furthermore, an outflow line (~17) leads from the botto~ of the separation vessel (412) to a chromic acid preparation facility (not ~hown).
An outflow line (421) coming from the bottom of the dechromer (413) and an outflow line (217) cc~ming from the bottom of the eeparation ~ressel (216) enter thi~ outflow line (417).
All reactors, ves~els and pipes are provided with tem-perature control facilities.
~ ~'' ' ", For carrying out the proce~s of the invention, use of o~e, two or three stages can be chosen. For this purpo~e, the various reactor ~tages can be combined with one another~ In addition, a ~ingle reactor or a plurality of reactors can be used for each stage.
In the single-stage mode of operation in accordance with Figure 1, the olefin, together with a part of the chromic/sulfuric acid (feedline (113)) and air (feedline 21286~8 (114)), i~ introduced, via the feedline (112), into the first reactor (111). The mixture flows, with intensive mixing, through the reactor (111). The product i~ then conducted into a dega~sing Btage comprising the dega~ing ve~sel (411) and the 3eparation ve~el (412). Here the volatile component~ are 6eparated off via the top, and in a condensate separator (414) the conden~able con~tituents are removed from the waste gas s~rea~. The wa~te gas is conducted away via the outflow line (420) and the conden-sate i conducted away via the outflow line (423). After ~eparation of the oxidate and oxidant in the ~eparation vessel (412), the oxidate ie further freed, in the dech-romer (413), of colloidal or chemically bound chromium compound~. This purification can be carried out in the form of a ~crubbing stage, an adsorption ~tage or a 3eparation by means of a centrifuge. The oxidate iB drawn off via the line (422). The used chromic/~ul~uric acid iB
conducted via line6 (417) and (421) to regeneration.
In the two-~tage mode of operation in accordance with Figure 2, the reaGtion mixture is fed from reactor (111) into a separation ve~sel (216). There the oxidate separa-tes from the chromic/eulfuric acid which flows through the line (217) to regeneration, and i8 metered into the reactor (211) with fre~h chromic/sulfuric acid and air via the line (212). From this reactor~ the rsaction mixture again flows into the above-described work-up ~tages.
The three-stage mode of operation in accordance with Figure 3 proceed~ in the same way, an additional reactor (311) and a ~eparation vessel (316) being incorporated between the reactor (211) and the degasaing ves~el (411).
The reaction mixture is thu~ ~eparated after each fitage and either worked up to give the final product or metered into the next stage together with ~resh chromic/~ulfuric acid and air.
~ - . . :- ,: .. ,.; ~ , : -21286~8 In the process o$ the invention, olefins having an internal double bond and a total of from 16 to 70, preferably from 20 to 50, carbon atoms are u~ed. Example~
of ~uch olefins are tho~e of the formula Rl-CH=CH-R2, in which R1 and R2 are a hydrogen atom or a C1-C68-, prefer-ably C1-C48-alkyl group and Rl and Rl together have from 14 to 68, preferably from 18 to 48, carbon atom~, or of the formula R3-C(R9)=CH2, in which R3 and R4 are a C1-C6a-, preferably C~-C~-alkyl group and R3 and R~ together have from ~4 to 68, preferably from 18 to 48, carbon atom~.
Example~ of euch olefin~ are hexadec-1-ene, octadec-l-ene, Eico~-1-ene, doco~-1-ene, tetracos-l-ene, triacont-l-ene, 2-ethyltriacont-1-ene and aloo l-olefin mixture~ which predominantly compri~e C22- to Cs~-olefins.
The oxidant used is a aolution o~ CrO3 and Cr2~SO~)3, if desired even of alkali metal dichromate, in aqueo~s ~ulfuric acid. Approximately 1-molar solutions, baaed on the CrO3 content, are used. In general, the chromic/
sulfuric acid u~ed compri~es from 500 to 600 g of E2SO4 and from 95 to 110 g of CrO3 per dm3.
The amount of chromic/sulfuric acid required for the oxidatlon of the olefin to the de~ired degree of conver-sion can, in the multi~tage proce~, be fed together with the olefin melt into the reactor of the f$rst reaction stage. ~owever, the process procedure of metering in the chromic/sulfuric acid in portions ha~ proven more ~uit-able. In this method, the u~ed oxidant is separated off in a ~eparation vessel and transferred out prior to the addition of the fresh chromic/~ul$uric acid.
The ratio of amounts of olefin to oxidant here depends on the molecular weight of the olefinic components and their reactivity. In the oxidation of an olefin mixture com-prising vinylolefin, vinylideneolefin and olefin having internal double bonds and the iodine number (IN) of 45, such as is, for example, commercially available a~
~Chevron C30,-olefin, a total amount of from 120 to 150 %
, ~ 21286~8 by weight, corre~ponding to from 165 to 200 mol%, o~ CrO
based on the olefin u~ed, i8 required to obtain a mixture of long-chain aliphatic carboxylic acid~ having an acid number (AN) of from 105 to 125. In a two-stage reaction, about 90~ of the olefin used can here be converted. A
carboxylic acid mixture having an AN of 105 i~ obtained.
About 60% by weight of the oxidant i~ here added in the first stage and in the second atage.
A three-~tage reactio~ u~ing 60% by weight of oxidant in the first stage, 50% by weight in the ~econd ~tage and 30% in the third stage leads, at an olefin conversion of ~ 95%, to a carboxylic acid mixture having an acid number AN of from 120 to 125.
The mixing requ~red for the process to be ~uccessful automatically result~ from the type of reactor and from the action of the steam formed and the volatile reaction gases. In addition, air is blown into the first reactor of each stage.
The reaction i5 carried out at a temperature of from about 90C to 200C, preferably in the range from 110C
to 125C, and at a pree~ure of from 100 mbar to 20 bar, ¦ preferably from 1 bar to 5 bar. The residence time~ in the individual reactor ~tages are from 60 minutes to 180 minutes. The res$dence time depends on the phase ratio and on the de~ired conver~ion of olefin or oxidant.
Carboxylic acid mixture~ prepared by the process of the invention can be further proce~ed with monoalcohol~ or polyols such as glycol, glycerol, trimethylolpro~ane, pentaerythritol or sorbitol to give esters and partial esters or mixtures of such esters. Reaction with basic oxides or metal hydroxide~ can be used to prepare the corresponding soaps of the carboxylic acids by direct reaction or by trans-precipitation. Reaction with amines or aminoalcehols gives the amides, amidoestera and amino-esters.
.*
~ 21286~8 . :
These productQ have a pale colour, good thermal ~tability and a wide range of applicationQ.
The esterQ and/or ~oapQ can thu~ be u~ed a~ pa~te waxe~, emulsion waxe~, release agent~ or a~ lubricants.
The following example~ illustrate the invention.
:
The experiment~ were carried out using a laboratory apparatu~ having a reactor capacity of about 6 dm3 per reaction stage.
Example 1 Single-stage oxidation u~ing a variable proportion of ox~dant.
An olefin mixture comprising vinylolefin, vinylidene olefin and olefin having internal double bonds and an iodine number (IN) of 4g (Chevron C30~-olefin) was melted and placed in a heated re~ervoir. The temperature of the melt was ad~u~ted to from 95 to 100C by ~team heating.
The olefin wa~ con~eyed into the fir~t reactor via a ~team-heated line and a heated pump.
The chromic acid was convayed from a temperature-controlled re~ervolr into the roactor via an acid-resis-tant pump. 100 dm3/h of aix at a pres~ure of 0.5 bar were lntroduced i~to the reactor. The three component~ were mixed in a multl-fluld nozzle ak the bottom o~ the reactor and lnjected lnto the fir~t reactor chamber. The reaction mixture was conveyed through the reactor cham-ber~ and after pa~eing through the individual reactor ~tage~ wa~ conveyed via the dega~ing ~tep into the separation ves~el. There the used oxldant was separated o$f. At thi~ point, the separation could be improved by addition of a eeparating agent (amount from 0.1 to 0.5%
by weight, ba~ed on olefin u~ed).
~ ~ ; " ; ~ ?`
., 21286~8 Conversion of olefin and oxidant are here dependent on the amount conveyed through and thu~ on the residence time in the reactor.
The oxidate thu~ obtained was further freed of re~idual chromium compou~ds by centrifugation.
Table 1: Continuou~ oxidation of ~-olefin Experiments using constant metering of olefin/chromic acid Experiment Wax Chromic CrO3 _ ~rO3 cm3/h Am3i/dh Feed % Con~umption _ .
_ _ _ _ _ Feed = Amount fed in, % by weight based on olefin Con~umption = Con~umption in % by weight, based on olefin Example 2 Single-~tage proces~ with ~ariable metered amounts at constant proportion of oxidant The olefin was melted and placed in a heated re~ervoir, The temperature o$ the melt wa~ adjueted to fxom 95 to 100C by steam h0ating. The olefin wae conveyed into the 2l286~8 ~:
first reactor via a ~team-heated line and a heated pump.
The chromic acid was conveyed from a temperature-con-trolled reservoir into the reactor via an acid-resi~tan~
pump. 100 dm3/h of air at a preR~ure of 0.5 bar were introduced into the rea~tor.
The three co~ponent~ were mixed in a multi-fluid nozzle at the bottom of the reactor a~d injected into the fir~t reactor chamber. While filling the reactors, an increased conveying rate could be used. The amount of olefin and chromic acid conveyed wa~ then reduced to ~et an optimum uRe of oxidant.
The reaction mixture was conveyed through the reactor chambere and after passing through the individual reactor stages was conducted via the degas~ing ~tep into the separation vessel. There the u~d oxidant was oeparated off. At this point the ~eparation could be improved by addition of a separating age~t (amount from 0.1 to 0.5 %
by weight, ba~ed on olefin u~ed).
The oxidate thus obtained wa~ furt~er freed of residual chromium by centrifugation.
. "
Table 2: Continuou~ oxidation of ~-olefin Experiments using variable ~etering of olefin/
chromic acid ¦ Experiment WaxChromic Acid CrO3 ANCrO3 l 100 Feed % Consumption ¦ :
cm3/h cm3/h 96 l . I I , .
l 6s-so- 39-30-24 60 57 56 1 13 65 - 4039 - 24 6Q 65 59 I . .
l __ l _ _ ~ - _ l : , Feed = Amount fed in, % by weight ba~ed on olefin -- 2l2~)6~8 Consumption = Consumption in % by weight, ba~ed on olefin Example 3 Two-stage proces~ with con~tant proportion of oxidant and variable met~ring The ole$in wa malted and placed in a heated re~ervoir, The temperature of the melt was adjusted to from 95 to 100C by ~team heating. The olefin was conveyed into the firat reactor via a ateam-heated line and a heated pump.
The chromic acid was conveyed from a temperature-con-trolled re~ervoir into the reactor via an acid-re~iatant pump. 100 dm3/h of air at a pre~ure of 0.5 bar were introduced into the reactor.
The three component~ were mixed in a multi-fluid nozzle at the bottom of the reactor and injoated into the first reactor cha~ber. The reaction mixture was conveyed through the reaction chamber~ and, after flowiny through the first reaction ~tage, was pas~ed into the ~eparation veaael, the uaed oxidant wa~ aeparated off and the pre-oxidized olefin wa~ conv~yed together with freah chromicacid and air into the second reaction ~tage. After paaaing through all reaction chambera, the product waa degaaaed, the used oxidant was aeparated off and re~idual chromium compound~ were ~eparated off from the ox~date in a centr~fuge.
, .
Table 3: Continuou~ oxidation of a-olefin Experiments u~ing variable metering of olefin/ .-.
chromic acid, 2nd stage ¦ Experiment Wax Chromic CrO3 - CrO3 10 cm3/hAcid Feed t Consumption 100 cm3/h _ .
510 (1 - 5)60 - 50 36 - 30 60 109 54 , .
8 (6) 65 - 45 36 - 25 SS 101 55 9 (7) 60 - 40 36 - 24 60 lOB 60 _ 12 (11) 65 - 40 39 - 24 60 108 59 14 (13) 65 - 40 39 - 24 60 110 58 1018 (17) 60 - 40 36 - 24 60 109 58 .
Feed = Amount fed in, % by weight ba~ed on olefin Con~u~ption = Consumption in % by weight, ba~ed on :~:
olefin The values ln () indicate the experi~ent number of the 15 first stage ~
': '';
Example 4 Three-stage process with constant proportion of oxidant and variable amounts metered in ::
'~;
The procedure wa~ as in Example 3. After the ~econd reaction stage, the oxidate and freah chromia acid were introduced into the third reaction stage and worked up as described above. Use of 50~ by weight of CrO3 gave an oxidate having an AN of 125. .~;
.
: '.
,'' ,'~
'
Claims (4)
1. A process for the continuous preparation of relatively high-molecular-weight, linear aliphatic carboxylic acids by oxidation of olefins having from 16 to 70 carbon atoms with approximately 1 molar, based on CrO3, chromic/sulfuric acid at a temperature of from 90 to 200°C and a pressure of from 100 mbar to 20 bar, which comprises carrying out the reaction in cocurrent mode in at least one reactor having a narrow residence time spectrum, the mixing of the reactants being carried out by the steam formed as a result of the heat of reaction and the reaction gas and also the additional blowing-in of air.
2. The process as claimed in claim 1, wherein the reaction is carried out in a cascaded bubble column reactor.
3. The process as claimed in claim 1, wherein the reaction is carried out in a plurality of stages, used chromic/sulfuric acid being separated off after each stage and the amount of chromic/sulfuric acid required for the oxidation being continuously metered in in portions at the beginning of each stage.
3. The process as claimed in claim 1, wherein C20-C50-olefins having internal double bonds or having vinylidene double bonds or having vinyl double bonds or mixtures of these compounds are used.
3. The process as claimed in claim 1, wherein C20-C50-olefins having internal double bonds or having vinylidene double bonds or having vinyl double bonds or mixtures of these compounds are used.
4. The process as claimed in claim 1, wherein the separation of the organic phase and the inorganic phase in the separation vessel is accelerated by the addition of surface-active compounds.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4324719.9 | 1993-07-23 | ||
| DE4324719 | 1993-07-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2128648A1 true CA2128648A1 (en) | 1995-01-24 |
Family
ID=6493511
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002128648A Abandoned CA2128648A1 (en) | 1993-07-23 | 1994-07-22 | Process for the continuous preparation of high-molecular-weight carboxylic acids |
Country Status (11)
| Country | Link |
|---|---|
| EP (1) | EP0635475B1 (en) |
| JP (1) | JPH0753444A (en) |
| AT (1) | ATE153647T1 (en) |
| AU (1) | AU673440B2 (en) |
| BR (1) | BR9402918A (en) |
| CA (1) | CA2128648A1 (en) |
| DE (1) | DE59402888D1 (en) |
| DK (1) | DK0635475T3 (en) |
| ES (1) | ES2105434T3 (en) |
| HK (1) | HK1006709A1 (en) |
| TW (1) | TW277064B (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2165858C3 (en) * | 1971-12-31 | 1974-11-28 | Farbwerke Hoechst Ag, Vormals Meister Lucius & Bruening, 6000 Frankfurt | Process for the production of higher molecular weight, aliphatic monocarboxylic acids |
| DE2855263C2 (en) * | 1978-12-21 | 1983-11-24 | Hoechst Ag, 6230 Frankfurt | Process for the continuous oxidative bleaching of raw montan wax |
-
1994
- 1994-06-03 TW TW083105085A patent/TW277064B/zh active
- 1994-07-18 EP EP94111132A patent/EP0635475B1/en not_active Expired - Lifetime
- 1994-07-18 ES ES94111132T patent/ES2105434T3/en not_active Expired - Lifetime
- 1994-07-18 AT AT94111132T patent/ATE153647T1/en not_active IP Right Cessation
- 1994-07-18 DK DK94111132.0T patent/DK0635475T3/en active
- 1994-07-18 DE DE59402888T patent/DE59402888D1/en not_active Expired - Fee Related
- 1994-07-21 AU AU68603/94A patent/AU673440B2/en not_active Ceased
- 1994-07-22 JP JP6171237A patent/JPH0753444A/en active Pending
- 1994-07-22 BR BR9402918A patent/BR9402918A/en not_active Application Discontinuation
- 1994-07-22 CA CA002128648A patent/CA2128648A1/en not_active Abandoned
-
1998
- 1998-06-23 HK HK98106078A patent/HK1006709A1/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| AU6860394A (en) | 1995-02-02 |
| HK1006709A1 (en) | 1999-03-12 |
| ATE153647T1 (en) | 1997-06-15 |
| DK0635475T3 (en) | 1997-12-15 |
| AU673440B2 (en) | 1996-11-07 |
| DE59402888D1 (en) | 1997-07-03 |
| EP0635475B1 (en) | 1997-05-28 |
| BR9402918A (en) | 1995-04-11 |
| JPH0753444A (en) | 1995-02-28 |
| TW277064B (en) | 1996-06-01 |
| EP0635475A1 (en) | 1995-01-25 |
| ES2105434T3 (en) | 1997-10-16 |
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