CA1088564A - Hydrogen fluoride removal from glycolic acid - Google Patents
Hydrogen fluoride removal from glycolic acidInfo
- Publication number
- CA1088564A CA1088564A CA297,670A CA297670A CA1088564A CA 1088564 A CA1088564 A CA 1088564A CA 297670 A CA297670 A CA 297670A CA 1088564 A CA1088564 A CA 1088564A
- Authority
- CA
- Canada
- Prior art keywords
- hydrogen fluoride
- glycolic acid
- purification
- carried out
- hydrogen
- 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
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/42—Separation; Purification; Stabilisation; Use of additives
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/42—Separation; Purification; Stabilisation; Use of additives
- C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
- C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Crystallography & Structural Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
HYDROGEN FLUORIDE REMOVAL
FROM GLYCOLIC ACID
The concentration of hydrogen fluoride in crude glycolic acid made by the hydrogen fluoride-catalyzed reaction of formaldehyde and carbon monoxide can be reduced to less than about 1% by weight by heating the crude glycolic acid to a temperature above about 130°C during the purification step, and distilling or stripping with inert gas to remove the hydrogen fluoride.
HYDROGEN FLUORIDE REMOVAL
FROM GLYCOLIC ACID
The concentration of hydrogen fluoride in crude glycolic acid made by the hydrogen fluoride-catalyzed reaction of formaldehyde and carbon monoxide can be reduced to less than about 1% by weight by heating the crude glycolic acid to a temperature above about 130°C during the purification step, and distilling or stripping with inert gas to remove the hydrogen fluoride.
Description
~ . ~
10~564 ~3ACKGROUND OF THE INVENT~OE!
10~564 ~3ACKGROUND OF THE INVENT~OE!
2 This invention concerns an improved process for
3 removing hydrogen fluoride from glycolic acid.
4 Recently hydrogen fluoride has been found to be a surprisingly effecti~e catalyst for glycolic acid production.
6 Por instance, U.S. Patent 3,911,003, granted October 7, 1975, 7 describes a process for preparing glycolic acid by contacting B formaldehyde, carbon monoxide and water in the presence of a 9 hydrogen fluoride catalyst. For economy of process and for subsequent processing of the crude product, it is necessary to 11 separate the hydrogen fluoride catalyst from the crude glycolic 12 acid product. It is usually necessary to reduce the hydroge~
13 fluoride content of the product to a few parts per million, or 14 even to less than one part per oillion, before the product can be used. It would be espected that, as hydrogen fluoride is quite 16 ~olatile, it would reatily be removed by distillation or ~y ~;
17 stripping with i~ert gas at moderate temperatures. For eYa-Fle, 18 U.S. Patent 2,534,017 sho~s that hydrogen fluoride can readily be 19 reuo~ed from aromatic aldehydes by vacuum distillation at 55C to ~5C; and U.S. Patent 3,962,343 ~hows rapid re~oval of hydrogen 21 fluoride in a similar system by stripping with a hydrocar~on 22 diluent or b~ decomposing in a film-evaporator at B0C to 110C.
23 It has been found, in agreement with this, that most of the 24 h~drogen fluoride can be remo~ed from the crude glycolic acid-2S hydrogen fluoride prcduct formed by the process of U.S. Patent 26 3,S11,003 by distilling or stripping vith gas at te~peratures at 27 or below 110C. However, when the concentration of hydrogen 28 fluoride in crude glycolic acid has been reduced to about 4~ by 29 veight, i.e., about 40,000 pp~, further strippinq with an inert gas or distillation at these temperatures does not significantly 31 reduce the hrdroqen fluoride concentration.
lOl~S~;4 1 Accordingly, in order to obtain a glycolic wid prcduct 2 ha~ing less than a~out 4~, by weight, of hydrogen fluoride, an 3 iuproved process is desira~le.
4 SUM~ARY OF THE INVENTIO~
S It has been found that the concentration of hydrogen 6 fluoride in crude glycolic acid may be reduced to less than about 7 0.1~ by ~eight by heating the crude glycolic acid to a tempera-8 ture of at least about 140C during the purification step.
9 B~IEF ~ SCRIPTION OP THE D~AT~ING
The Pigure compares tbe purification o crude glycolic 11 acid by hydrogen fluor~de stripping at a continuous temperature 12 of about 110C to strlpping at an increased temperature of a~out 13 140C. Both runs were carried out at atmospheric pressure using 14 nitrogen as an inert gas. As described in EYample 1, stripping at 93C for over 8 hours did not reduce the hydrogen fluorid~
16 concentration below about 4%. In contrast, stripping at 110C
17 for about 6 hours follo~ed by only 1 hour of stripping at an 13 increased temperature of about 140C reduced the hydrogen 19 fluoride concentrat~on to less than 2 ppm. Thus, ~hile both temperatures Yere satisfactory for removing the bulk of tbe 21 hydroqen fluoride, to obtain a useful product, for example one 22 containing less than about 5 ppm of hydrogen fluoride, purifi-23 c~tion had to be carried out at a temperature in excess of about 24 130C, preferably 140~C.
DETA~L~_DE~Ç~E~IaN OF THE INVENTIO~
26 This invention provides an improved process for 27 purifying a crude glycolic reaction product. The term "crud~
28 glycolic acid" refers to the reaction product of the hydrogen-29 fluoride~catalyzed reaction of formaldehgde and carbon moDo~ide to form glycolic acid. This reaction is described in U.S. PateDt 31 3,911,003. The crude product generallg contains in e~cess of 40 32 by weight hydrogen fluoride.
- 3 _ 1(~88564 1 ~hile the purification of crude glycolic acid can be 2 carried out in a variety of ~ays, the central feature of the 3 invention i5 based on the discovery that, in order to reduce the 4 hydrogen fluoride concentration to less than about ~, the final stages of the reooval of hydrogen fluoride must be carried out at 6 a temperature in excess of about 130C, preferably in excess of 7 140C. Lo~er te~peratures can be used during tho initial stages 8 to reduce the hydrogen fluoride content to about 4~, but the 9 fiDal reduction to less than about 4~ requires a temperature in excess of about 130C. Thus, the process comprises heating crude 11 gl~colic acid contaiDiDg hydrogen fluoride to a te~perature abo~e 12 about 90C until the concentration of hydrogen fluoride i8 about 13 4% by weight, and subseguently heating the crude product to a 14 tenperature in excess of about 130C. If desired, the entire purification process can be conducted at temFeratures above lS 130C. In this vay, the quantity of HF remaining in the product ~7 can be easil~ reduced to a value less than 100 ppm, preferably ~ less than 10 ppm.
19 The physical removal of hydrogen fluoride can be done by any kno~n method. One method is to distill off the hydrogen 21 fluoride at reduced pressure in a still or an evaporator.
22 Another method of removing hydrogen fluoride is to pass an inert 23 gas through tbe crude product, thereby stripping out the hydrogen 24 fluoride.
Inert gas stripping and distillation are ~ell-kno~D
26 methods of refining crude organic products. In general, inert 27 gas stripping is carried out by passing an inert gas throuqh a 2~ liquid mixture at a given temperature and pressure ~hich are 29 kno~n to effect transfer of a volatile liguid component i~to the inert gas. In this ~ay, a refined product ha~ing ~ reduced 31 ccncentration of the transferred liquid is obtained. A thorough ~08~564 1 discussion of gas-stripping principles is contained in Perry ~6 2 Che~ical Engineers~ Handbook 4th, Chapter 14.
3 The i~ability to re~ove hydrogen fluoride by contiDuous 4 purification at temperatures of about 110C is apparently du6 to solvent differences at these temperatures. ~he vapor pressure of 6 pure hydrogen fluoride is only twice as high at about 150C as at 7 a~out 100C; so, if the solvent ~ere unchanged, hydrogen fluoride 8 removal ~ould be only t~ice as fast at 150C as at 100C. at the 9 lo~er temperature, the solvent is mainly glycolic acid. The 4~
eight hydrogen fluoride retained in the solution correspond to 11 about 1 ~ol of hydrogen fluoride for every 6 ~ols of glycolic 12 acid. A ætrong acid such as hydrogen fluoride ~ould be expected 13 to be sol~ated by 4-8 ~ols of a hydroYylic solvent. Thuæ, it is -14 believed that the surprising increase in reduction of hydrog~n fluoride content ~hich can be obtained by purification at a 16 te~perature $n e~ceæs of about 140C is due to the tendency of 17 glycolic acid to for~ polyglycolideæ. Apparently the coD~ersion 18 o~ glycolic acid to polyglycolide at about 140C not only 19 aocreages tbe content of free hydroxyl and carboxyl group , but also forss solvent ~olecules vhich are too bulky to perJit --21 sol~ating protons ~ith a large number of hydroxyl groups. Th~s 22 change in sol~ent properties thefi results in a greatly ~ncreased 23 volatility for hydrogen fluoride. As a result, continuouæ
24 stripping or distillation at about 110C will not re-ove the last 4% of the hydrogen fluoride, ~hile an increase ~n te~perature to 26 about 130C, preferably about 140C, causes an alaost logarith-ic 27 reduction ~ith ti~e. This suggests that the ~ydrogen fluoride ~2-8 vapor pressure at teoperatures abov~ about 140C ~8 essentially 29 proportional to the hydrogen fluoride concentration in the ;~ 30 sclution.
-10885~4 1 In a preferred e~bodiment of the invention, purifica-2 tio~ of crude qlycolic acid is carried out by inert gas striFping 3 u~ing synthesis gas or carbon monoxide-depleted synthesis gas as 4 the inert gas. As thoroughly described in U.S. Patent 3,911,033,- -crude glycolic acid is prepared by the reaction of formaldehyde 6 and car~on monoxide in the presence of a hydrogen fluor~de 7 catalyst. A preferred source of carbon monoxide in that process 8 is synthesis gas co~prising carbon monoxide and hydrogen. This 9 synthesis gas can al~o act as a source of inert gas for the purification step. Alternatively, the carbon monoxide-depleted 11 synthesis gas which is recovered after the reaction of carbon 12 ~onoxide with formaldehyde to form glycolic acid can be used as a 13 source of inert gas for the Furification step.
14 The following example further illustrates practice of the present invention.
16 EXA~PLE
17 In the following example, crude glycolic acid contain-1a lng about 40% by ~eight hydrogen fluoride ~as sub~ected to 19 nitrogen stripping for about 2 hours at 23C to 93C and then for about ~ hours at 93C to prepare a product containing 4.3% ~eight 21 hydrogen fluoride. Stripping for 5 additional hours at 112C
22 re~oved only a minor amount of the hydrogen fluoride fron this 23 mixture. However, after stripping the ~iYture for 1.5 additional 24 hours at 143C, the hydrogen fluoride content of the product decreased to about 2 pp~. Purther gas stripping at 143C reduced 26 the h~drogen 1uoride content of the product to 0~1-0.2 pp~ cf 27 hydrogen fluoride. These results are plotted in the Pigure. ~he 28 Figure is a plot of the percent hydrogen fluoride re~aining in 29 the reaction ~ixture after nitrogen stripping for a given Du-ber of hours at either 112C or 143C. The plot is OD a log scal~e in 31 order to cover the entire concentration range of 1 ppn to 5~
..
1 ~50,000 pp~ s seen fro~ the Figure, the influence of 2 te~perature on crude glycolic acid pur fication is extre-ely 3 significant.
~ .
',':
r ~ 7 ~
6 Por instance, U.S. Patent 3,911,003, granted October 7, 1975, 7 describes a process for preparing glycolic acid by contacting B formaldehyde, carbon monoxide and water in the presence of a 9 hydrogen fluoride catalyst. For economy of process and for subsequent processing of the crude product, it is necessary to 11 separate the hydrogen fluoride catalyst from the crude glycolic 12 acid product. It is usually necessary to reduce the hydroge~
13 fluoride content of the product to a few parts per million, or 14 even to less than one part per oillion, before the product can be used. It would be espected that, as hydrogen fluoride is quite 16 ~olatile, it would reatily be removed by distillation or ~y ~;
17 stripping with i~ert gas at moderate temperatures. For eYa-Fle, 18 U.S. Patent 2,534,017 sho~s that hydrogen fluoride can readily be 19 reuo~ed from aromatic aldehydes by vacuum distillation at 55C to ~5C; and U.S. Patent 3,962,343 ~hows rapid re~oval of hydrogen 21 fluoride in a similar system by stripping with a hydrocar~on 22 diluent or b~ decomposing in a film-evaporator at B0C to 110C.
23 It has been found, in agreement with this, that most of the 24 h~drogen fluoride can be remo~ed from the crude glycolic acid-2S hydrogen fluoride prcduct formed by the process of U.S. Patent 26 3,S11,003 by distilling or stripping vith gas at te~peratures at 27 or below 110C. However, when the concentration of hydrogen 28 fluoride in crude glycolic acid has been reduced to about 4~ by 29 veight, i.e., about 40,000 pp~, further strippinq with an inert gas or distillation at these temperatures does not significantly 31 reduce the hrdroqen fluoride concentration.
lOl~S~;4 1 Accordingly, in order to obtain a glycolic wid prcduct 2 ha~ing less than a~out 4~, by weight, of hydrogen fluoride, an 3 iuproved process is desira~le.
4 SUM~ARY OF THE INVENTIO~
S It has been found that the concentration of hydrogen 6 fluoride in crude glycolic acid may be reduced to less than about 7 0.1~ by ~eight by heating the crude glycolic acid to a tempera-8 ture of at least about 140C during the purification step.
9 B~IEF ~ SCRIPTION OP THE D~AT~ING
The Pigure compares tbe purification o crude glycolic 11 acid by hydrogen fluor~de stripping at a continuous temperature 12 of about 110C to strlpping at an increased temperature of a~out 13 140C. Both runs were carried out at atmospheric pressure using 14 nitrogen as an inert gas. As described in EYample 1, stripping at 93C for over 8 hours did not reduce the hydrogen fluorid~
16 concentration below about 4%. In contrast, stripping at 110C
17 for about 6 hours follo~ed by only 1 hour of stripping at an 13 increased temperature of about 140C reduced the hydrogen 19 fluoride concentrat~on to less than 2 ppm. Thus, ~hile both temperatures Yere satisfactory for removing the bulk of tbe 21 hydroqen fluoride, to obtain a useful product, for example one 22 containing less than about 5 ppm of hydrogen fluoride, purifi-23 c~tion had to be carried out at a temperature in excess of about 24 130C, preferably 140~C.
DETA~L~_DE~Ç~E~IaN OF THE INVENTIO~
26 This invention provides an improved process for 27 purifying a crude glycolic reaction product. The term "crud~
28 glycolic acid" refers to the reaction product of the hydrogen-29 fluoride~catalyzed reaction of formaldehgde and carbon moDo~ide to form glycolic acid. This reaction is described in U.S. PateDt 31 3,911,003. The crude product generallg contains in e~cess of 40 32 by weight hydrogen fluoride.
- 3 _ 1(~88564 1 ~hile the purification of crude glycolic acid can be 2 carried out in a variety of ~ays, the central feature of the 3 invention i5 based on the discovery that, in order to reduce the 4 hydrogen fluoride concentration to less than about ~, the final stages of the reooval of hydrogen fluoride must be carried out at 6 a temperature in excess of about 130C, preferably in excess of 7 140C. Lo~er te~peratures can be used during tho initial stages 8 to reduce the hydrogen fluoride content to about 4~, but the 9 fiDal reduction to less than about 4~ requires a temperature in excess of about 130C. Thus, the process comprises heating crude 11 gl~colic acid contaiDiDg hydrogen fluoride to a te~perature abo~e 12 about 90C until the concentration of hydrogen fluoride i8 about 13 4% by weight, and subseguently heating the crude product to a 14 tenperature in excess of about 130C. If desired, the entire purification process can be conducted at temFeratures above lS 130C. In this vay, the quantity of HF remaining in the product ~7 can be easil~ reduced to a value less than 100 ppm, preferably ~ less than 10 ppm.
19 The physical removal of hydrogen fluoride can be done by any kno~n method. One method is to distill off the hydrogen 21 fluoride at reduced pressure in a still or an evaporator.
22 Another method of removing hydrogen fluoride is to pass an inert 23 gas through tbe crude product, thereby stripping out the hydrogen 24 fluoride.
Inert gas stripping and distillation are ~ell-kno~D
26 methods of refining crude organic products. In general, inert 27 gas stripping is carried out by passing an inert gas throuqh a 2~ liquid mixture at a given temperature and pressure ~hich are 29 kno~n to effect transfer of a volatile liguid component i~to the inert gas. In this ~ay, a refined product ha~ing ~ reduced 31 ccncentration of the transferred liquid is obtained. A thorough ~08~564 1 discussion of gas-stripping principles is contained in Perry ~6 2 Che~ical Engineers~ Handbook 4th, Chapter 14.
3 The i~ability to re~ove hydrogen fluoride by contiDuous 4 purification at temperatures of about 110C is apparently du6 to solvent differences at these temperatures. ~he vapor pressure of 6 pure hydrogen fluoride is only twice as high at about 150C as at 7 a~out 100C; so, if the solvent ~ere unchanged, hydrogen fluoride 8 removal ~ould be only t~ice as fast at 150C as at 100C. at the 9 lo~er temperature, the solvent is mainly glycolic acid. The 4~
eight hydrogen fluoride retained in the solution correspond to 11 about 1 ~ol of hydrogen fluoride for every 6 ~ols of glycolic 12 acid. A ætrong acid such as hydrogen fluoride ~ould be expected 13 to be sol~ated by 4-8 ~ols of a hydroYylic solvent. Thuæ, it is -14 believed that the surprising increase in reduction of hydrog~n fluoride content ~hich can be obtained by purification at a 16 te~perature $n e~ceæs of about 140C is due to the tendency of 17 glycolic acid to for~ polyglycolideæ. Apparently the coD~ersion 18 o~ glycolic acid to polyglycolide at about 140C not only 19 aocreages tbe content of free hydroxyl and carboxyl group , but also forss solvent ~olecules vhich are too bulky to perJit --21 sol~ating protons ~ith a large number of hydroxyl groups. Th~s 22 change in sol~ent properties thefi results in a greatly ~ncreased 23 volatility for hydrogen fluoride. As a result, continuouæ
24 stripping or distillation at about 110C will not re-ove the last 4% of the hydrogen fluoride, ~hile an increase ~n te~perature to 26 about 130C, preferably about 140C, causes an alaost logarith-ic 27 reduction ~ith ti~e. This suggests that the ~ydrogen fluoride ~2-8 vapor pressure at teoperatures abov~ about 140C ~8 essentially 29 proportional to the hydrogen fluoride concentration in the ;~ 30 sclution.
-10885~4 1 In a preferred e~bodiment of the invention, purifica-2 tio~ of crude qlycolic acid is carried out by inert gas striFping 3 u~ing synthesis gas or carbon monoxide-depleted synthesis gas as 4 the inert gas. As thoroughly described in U.S. Patent 3,911,033,- -crude glycolic acid is prepared by the reaction of formaldehyde 6 and car~on monoxide in the presence of a hydrogen fluor~de 7 catalyst. A preferred source of carbon monoxide in that process 8 is synthesis gas co~prising carbon monoxide and hydrogen. This 9 synthesis gas can al~o act as a source of inert gas for the purification step. Alternatively, the carbon monoxide-depleted 11 synthesis gas which is recovered after the reaction of carbon 12 ~onoxide with formaldehyde to form glycolic acid can be used as a 13 source of inert gas for the Furification step.
14 The following example further illustrates practice of the present invention.
16 EXA~PLE
17 In the following example, crude glycolic acid contain-1a lng about 40% by ~eight hydrogen fluoride ~as sub~ected to 19 nitrogen stripping for about 2 hours at 23C to 93C and then for about ~ hours at 93C to prepare a product containing 4.3% ~eight 21 hydrogen fluoride. Stripping for 5 additional hours at 112C
22 re~oved only a minor amount of the hydrogen fluoride fron this 23 mixture. However, after stripping the ~iYture for 1.5 additional 24 hours at 143C, the hydrogen fluoride content of the product decreased to about 2 pp~. Purther gas stripping at 143C reduced 26 the h~drogen 1uoride content of the product to 0~1-0.2 pp~ cf 27 hydrogen fluoride. These results are plotted in the Pigure. ~he 28 Figure is a plot of the percent hydrogen fluoride re~aining in 29 the reaction ~ixture after nitrogen stripping for a given Du-ber of hours at either 112C or 143C. The plot is OD a log scal~e in 31 order to cover the entire concentration range of 1 ppn to 5~
..
1 ~50,000 pp~ s seen fro~ the Figure, the influence of 2 te~perature on crude glycolic acid pur fication is extre-ely 3 significant.
~ .
',':
r ~ 7 ~
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a process for purifying crude glycolic acid containing hydrogen fluoride by inert gas stripping or distillation, the improvement which comprises heating said crude glycolic acid at a temperature in excess of about 130°C.
2. A process according to Claim 1 wherein purification is carried out by gas stripping.
3. A process according to Claim 1 wherein the purification is carried out at a temperature of about 100°C for a period of time sufficient to obtain a product having about 4% by weight hydrogen fluoride and subsequent purification is carried out at a temperature of about 130°C to 160°C.
4. A process according to Claim 1 wherein the purification is carried out at about 130°C for a time sufficient to reduce the hydrogen fluoride content to less than about 100 parts per million.
5. A process according to Claim 1 wherein the purification is carried out by inert gas stripping using a mixture of carbon monoxide and hydrogen as the inert gas.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US79022177A | 1977-04-25 | 1977-04-25 | |
| US790,221 | 1977-04-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088564A true CA1088564A (en) | 1980-10-28 |
Family
ID=25150005
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA297,670A Expired CA1088564A (en) | 1977-04-25 | 1978-02-24 | Hydrogen fluoride removal from glycolic acid |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS53132522A (en) |
| BE (1) | BE864566A (en) |
| CA (1) | CA1088564A (en) |
| DE (1) | DE2817563A1 (en) |
| FR (1) | FR2388786A1 (en) |
| GB (1) | GB1583294A (en) |
| IT (1) | IT1094716B (en) |
| NL (1) | NL7804407A (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4016208A (en) * | 1974-06-19 | 1977-04-05 | Chevron Research Company | Acid production |
| US3911003A (en) * | 1974-06-19 | 1975-10-07 | Chevron Res | Process for the production of glycolic acid and oxydiacetic acid |
-
1978
- 1978-02-24 CA CA297,670A patent/CA1088564A/en not_active Expired
- 1978-03-03 BE BE185677A patent/BE864566A/en not_active IP Right Cessation
- 1978-04-07 GB GB13829/78A patent/GB1583294A/en not_active Expired
- 1978-04-17 FR FR7811208A patent/FR2388786A1/en active Granted
- 1978-04-20 IT IT22507/78A patent/IT1094716B/en active
- 1978-04-21 DE DE19782817563 patent/DE2817563A1/en active Granted
- 1978-04-24 JP JP4860778A patent/JPS53132522A/en active Granted
- 1978-04-25 NL NL7804407A patent/NL7804407A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| FR2388786A1 (en) | 1978-11-24 |
| IT7822507A0 (en) | 1978-04-20 |
| DE2817563C2 (en) | 1987-08-06 |
| GB1583294A (en) | 1981-01-21 |
| DE2817563A1 (en) | 1978-10-26 |
| BE864566A (en) | 1978-07-03 |
| JPS53132522A (en) | 1978-11-18 |
| FR2388786B1 (en) | 1982-12-03 |
| NL7804407A (en) | 1978-10-27 |
| IT1094716B (en) | 1985-08-02 |
| JPS6213336B2 (en) | 1987-03-25 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |