EP0043525B1 - Corrosion inhibitors for alkanolamine gas treating systems - Google Patents

Corrosion inhibitors for alkanolamine gas treating systems Download PDF

Info

Publication number
EP0043525B1
EP0043525B1 EP81104985A EP81104985A EP0043525B1 EP 0043525 B1 EP0043525 B1 EP 0043525B1 EP 81104985 A EP81104985 A EP 81104985A EP 81104985 A EP81104985 A EP 81104985A EP 0043525 B1 EP0043525 B1 EP 0043525B1
Authority
EP
European Patent Office
Prior art keywords
vanadium
compound
corrosion
acid
composition
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
Application number
EP81104985A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0043525A1 (en
Inventor
John Groome Mccullough
Kenneth James Barr
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Union Carbide Corp
Original Assignee
Union Carbide Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Union Carbide Corp filed Critical Union Carbide Corp
Priority to AT81104985T priority Critical patent/ATE10293T1/de
Publication of EP0043525A1 publication Critical patent/EP0043525A1/en
Application granted granted Critical
Publication of EP0043525B1 publication Critical patent/EP0043525B1/en
Expired legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
    • C23F11/06—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in markedly alkaline liquids

Definitions

  • This invention relates to novel corrosion inhibitors for alkanolamine gas treating systems.
  • Gases such as natural gas, flue gas, and synthesis gas have been purified by the utilization of aqueous alkanolamine solutions for the absorption of acid gases such as CO 2 , H 2 S, and COS contained in the gas stream.
  • acid gases such as CO 2 , H 2 S, and COS contained in the gas stream.
  • a 5 percent to 30 percent by weight alkanolamine solution e.g., a monoethanolamine solution
  • the process is a continuous and cyclic one which can be reversed at higher temperatures by desorbing the acid gases from the alkanolamine solution.
  • the US-A-3808140 claims a corrosion inhibited composition consisting essentially of an aqueous alkanolamine solution employed in acid gas removal service and an inhibiting amount of a combination of a V(V)-compound and an antimony compound. It further discloses that the choice of vanadium compound is not critical since it is the vanadium-containing anion, particularly vanadium in the plus 4 or 5 valence state which provides the corresion-inhibiting property in combination with antimony ions.
  • the US-A-3896044 and 3959170 disclose the use as inhibitors in aqueous alkanolamine solutions used in acid gas removal of, inter alia, nitroaromatic acids and their salts and antimony compounds, stannous salts, organocompounds and V(IV)- or V(V)-compounds, but the US-A-3896044 claims a corrosion inhibitor selected from the class of nitro-substituted aromatic acids and nitro-substituted acid salts and the US-A3808140 claims a corrosion inhibitor in form of a stannous salt or mixtures thereof in an amount of 0.01 to 2 weight per cent based on the weight of the alkanolamine solution.
  • a corrosion inhibitor comprising synergistic combinations of particular vanadium compounds wherein the vanadium therein is in the plus four or plus five valence state and an organic compound selected from the group consisting of nitro-substituted aromatic acids, nitro-substituted acid salts, 1,4-naphthoquinone, and mixtures thereof.
  • the organic compound is preferably selected from the group consisting of p-nitrobenzoic acid, m-nitrobenzoic acid, 3,5-dinitrobenzoic acid, p-nitrophenol, m-nitrophenol, m-nitrobenzenesulfonic acid, 1,4-naphthoquinone and mixtures thereof.
  • the inhibiting amounts of the vanadium compound and organic compound employed may each be less than the amount of vanadium compound or organic compound that when employed alone provides protection, although other beneficial results are believed to occur when the combination of these compounds is employed in higher concentrations.
  • the corrosion inhibitors described herein are especially useful in aqueous monoethanolamine scrubbers employed for removing hydrogen sulfide and carbon dioxide in natural gas treating systems.
  • vanadium compounds in this invention is not critical since it is the vanadium therein in the plus 4 or 5 valence state, preferably plus 5, which provides this unusual corrosion inhibiting property in combination with the organic compounds.
  • vanadium compounds in this invention can employ V 2 0 5 , NaV0 3 , Na 3 V0 4 , KV0 3 , NH 4 V0 3 , VOCI 3 , VOS0 4 , VO 2 , VOCI 2 , the like and mixtures thereof.
  • the organic compounds employed as corrosion inhibitors in combination with the aforementioned vanadium compounds are selected from the group consisting of nitro-substituted aromatic acids, nitro-substituted acid salts, and 1,4-naphthoquinone, and preferably selected from the group consisting of p-nitrobenzoic acid, m-nitrobenzoic acid, 3,5-dinitrobenzoic acid, p-nitrophenyl, m-nitrophenol, m-nitrobenzenesulfonic acid, 1,4-naphthoquinone, and mixtures thereof.
  • the effect of concentration of inhibitor is generally monotonic, i.e., the inhibitor fails to provide protection from corrosion below a minimum concentration, while above this concentration it always provides protection.
  • This critical concentration is referred to as the minimum effective concentration (hereinafter the m.e.c.) for the inhibitor.
  • the m.e.c. for an individual inhibitor may be determined simply by testing the inhibitor at various concentrations to determine the minimum concentration required to provide protection. It has been found that the combination of the vanadium compounds and the organic compounds of this invention at concentrations below these minimum effective concentrations provides protection surprisingly superior to each one alone at the same concentration. Further, it is believed that when the vanadium compound(s) and organic compound(s) are employed in combination in an amount above their individual minimum effective concentrations that other advantageous results are obtained.
  • the concentrations of the vanadium compounds and organic compounds may vary from 0.01 mM to 50 mM.
  • the synergistic combinations of the particular vanadium compound and the organic compound are generally added in an amount to provide a concentration of from 0.01 mM to 1 mM for the vanadium compound and in an amount to provide a concentration of from 0.1 mM to 10 mM for the organic compound, and preferably in an inhibiting amount to provide a concentration for both the vanadium compound(s) and organic compound(s) less than each of their respective minimum effective concentrations.
  • Alkanolamine systems which are benefited by the inclusion of the instant combined corrosion inhibitor are those mono- and polyalkanolamines having 2 to 4 carbon atoms per hydroxyalkyl group.
  • Typical alkanolamines are monoethanolamine, diethanolamine, and monoisopropanolamine.
  • the corrosion inhibitors of the instant invention were tested in monoethanolamine-water-carbon dioxide-hydrogen sulfide solutions because, while aqueous monoethanolamine solutions are not corrosive towards ferrous metals, when saturated with carbon dioxide and/or hydrogen sulfide they become quite corrosive to mild steel. It is thought that electro-chemical corrosion is involved with the anodic reaction expected to produce products such as ferrous hydroxide, ferrous carbonate, ferrous sulfide, or certain complexes.
  • the ability of a given corrosion inhibitor to provide protection was determined by measuring the relative corrosion rate for the alkanolamine solution containing the inhibitor and by measuring the steel's potential at the end of the test to determine whether the steel was active or passive.
  • the relative corrosion rate for a particular alkanolamine solution is the corrosion rate of the alkanolamine solution with the inhibitor divided by the corrosion rate of the alkanolamine solution without the inhibitor.
  • the corrosion rate in each case is calculated by determining the weight loss of a metal sample after conducting the test for a given period of time.
  • a relative corrosion rate greater than 0.5 ⁇ 0.1 is considered to indicate that the inhibitor failed to provide protection.
  • the potential of the steel was measured at the end of each test.
  • a potential more positive than about -500 mV at 20°C is considered to indicate that the steel is passive and that the inhibitor has provided protection.
  • Heat transfer corrosion tests were conducted as follows: A circular coupon of cold-rolled mild steel 89 mm in diameter and 0.8 mm thick was cleaned and weighed. The coupon was then clamped to a borosilicate glass corrosion cell so as to form the bottom surface of the cell. The corrosion cell was charged with 30 percent by weight monoethanolamine solution saturated with carbon dioxide. Any residual air was purged from the cell with carbon dioxide. The steel coupon was made active by electrochemically reducing its air-formed passive film. Alternatively, if it is desired to have a passive steel coupon, this electrochemical reduction is omitted. A sample of 30 percent by weight monoethanolamine solution saturated with hydrogen sulfide is introduced anaerobically into the corrosion cell.
  • the volume of this sample is about 25 percent of the volume of the monoethanolamine-carbon dioxide employed initially to charge the corrosion cell.
  • the monoethanolamine saturated with hydrogen sulfide is prepared from carefully purified hydrogen sulfide to assure that sulfur, which might otherwise be an adventitious inhibitor, is not present).
  • active steel is prepared under 30 percent monoethanolamine saturated with a mixture of about 20 percent by weight hydrogen sulfide and about 80 percent by weight carbon dioxide with the careful exclusion of oxygen, which might oxidize hydrogen sulfide to sulfur.
  • the purging gas is now changed from carbon dioxide to a gas containing about 20 percent by volume hydrogen sulfide and about 80 percent by volume carbon dioxide.
  • the corrosion cell is now ready to test the inhibition of cold active steel, and if this is desired test, the inhibitor is injected anaerobically and the cell is heated through the test coupon to reflux temperature.
  • the inhibition of hot active steel may be tested by heating the corrosion cell to reflux prior to introduction of the inhibitor being tested.
  • the mixed hydrogen sulfide and carbon dioxide purge gas is replaced by carbon dioxide and the cell is permitted to cool.
  • the potential of the steel test coupon is then remeasured. The steel coupon is cleaned and corrosion rate is then calculated.
  • the corrosion inhibitors of this invention are tested. Examples 1-24 were all conducted on hot active steel under hydrogen sulfide and carbon dioxide for twenty-four hours per the previously described procedure. In each example, the vanadium was added before adding the other inhibitor.
  • the corrosion rate of uninhibited monoethanolamine-water-carbon dioxide-hydrogen sulfide solutions was initially determined by carrying out tests on twenty-nine steel coupons without adding a corrosion inhibitor. Each test coupon showed a weight loss that corresponded to a corrosion rate of 228.6 ⁇ 35 f lm/a in the one-day test and a corrosion rate of 104.1i25 am/a in the eight-day tests. These corrosion rates were employed to calculate the relative corrosion rates of all the examples in Tables I and II. These corrosion rates show that the efforts to exclude adventitious inhibitors from the tests were successful.
  • the vanadium compound used in Examples 1-47 was either V 2 0, or NaV0 3 .
  • Table I shows the results obtained by employing the combined corrosion inhibitors of the invention at concentrations where each inhibitor alone fails to provide protection but when employed together the combination provides protection.
  • Examples 1-7 show the superior protection provided by the combined inhibitor.
  • Examples 1-3 show vanadium (V) has an m.e.c. between 0.2 and 0.3 mM when used alone on hot active steel.
  • Examples 4-6 show that the m.e.c. for p-nitrobenzoic acid is between 10 and 20 mM on hot active steel.
  • Example 7 shows the superior protection that the combination of 0.1 mM vanadium (V) and 1.0 mM p-nitrobenzoic acid provides for hot active steel.
  • Table II shows the protection realized with the vanadium (V)-p-nitrobenzoic acid combination. In addition, Table II shows that at concentrations in excess of those employed for the combined inhibitors that the individual additives failed to provide protection.
  • Table II show that the combination of vanadium (V) and p-nitrobenzoic acid provides protection when the vanadium (V) is at a concentration of from 0.02 mM to 0.25 mM and when the p-nitrobenzoic acid is at a concentration of from 0.6 mM to 8.0 mM. When employed at these concentrations, the combination of vanadium (V) and p-nitrobenzoic acid provides protection even though the m.e.c. for each additive is not employed.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Preventing Corrosion Or Incrustation Of Metals (AREA)
  • Gas Separation By Absorption (AREA)
  • Preparation Of Compounds By Using Micro-Organisms (AREA)
EP81104985A 1980-06-30 1981-06-26 Corrosion inhibitors for alkanolamine gas treating systems Expired EP0043525B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT81104985T ATE10293T1 (de) 1980-06-30 1981-06-26 Korrosionsinhibitoren fuer anlagen zur behandlung von gasen mit alkanolaminen.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US16397580A 1980-06-30 1980-06-30
US163975 1980-06-30

Publications (2)

Publication Number Publication Date
EP0043525A1 EP0043525A1 (en) 1982-01-13
EP0043525B1 true EP0043525B1 (en) 1984-11-14

Family

ID=22592441

Family Applications (1)

Application Number Title Priority Date Filing Date
EP81104985A Expired EP0043525B1 (en) 1980-06-30 1981-06-26 Corrosion inhibitors for alkanolamine gas treating systems

Country Status (20)

Country Link
EP (1) EP0043525B1 (en:Method)
JP (1) JPS604272B2 (en:Method)
AR (1) AR228276A1 (en:Method)
AT (1) ATE10293T1 (en:Method)
AU (1) AU542053B2 (en:Method)
BR (1) BR8104104A (en:Method)
CA (1) CA1158852A (en:Method)
CS (1) CS242870B2 (en:Method)
DE (1) DE3167178D1 (en:Method)
ES (1) ES503481A0 (en:Method)
GR (1) GR75712B (en:Method)
HU (1) HU185932B (en:Method)
IN (1) IN154625B (en:Method)
MX (1) MX161784A (en:Method)
NO (1) NO163537C (en:Method)
NZ (1) NZ197575A (en:Method)
PH (1) PH16622A (en:Method)
PL (2) PL130311B1 (en:Method)
RO (1) RO81354B (en:Method)
ZA (1) ZA814278B (en:Method)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10137404B2 (en) 2012-08-30 2018-11-27 IFP Energies Nouvelles Method of absorbing acid compounds contained in a gaseous effluent using an amine-based aqueous solution

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS60180877U (ja) * 1984-05-14 1985-11-30 新潟ビ−．エス．アンド．ビ−．セイフテイ．システムズ株式会社 溶接形破裂板の保持構造
JPS6254696U (en:Method) * 1985-09-24 1987-04-04
JPH02119192U (en:Method) * 1989-03-13 1990-09-26
JPH02122691U (en:Method) * 1989-03-15 1990-10-08
AR010696A1 (es) * 1996-12-12 2000-06-28 Sasol Tech Pty Ltd Un metodo para la eliminacion del dioxido de carbono de un gas de proceso

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3808140A (en) * 1970-07-13 1974-04-30 B Mago Antimony-vanadium corrosion inhibitors for alkanolamine gas treating system
US3896044A (en) * 1971-11-22 1975-07-22 Union Carbide Corp Nitro-substituted aromatic acid corrosion inhibitors for alkanolamine gas treating system

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3959170A (en) * 1971-11-22 1976-05-25 Union Carbide Corporation Corrosion inhibitors for alkanolamine gas treating system
US3951844A (en) * 1974-04-29 1976-04-20 Union Carbide Corporation Corrosion inhibition of aqueous potassium carbonate gas treating systems

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3808140A (en) * 1970-07-13 1974-04-30 B Mago Antimony-vanadium corrosion inhibitors for alkanolamine gas treating system
US3896044A (en) * 1971-11-22 1975-07-22 Union Carbide Corp Nitro-substituted aromatic acid corrosion inhibitors for alkanolamine gas treating system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10137404B2 (en) 2012-08-30 2018-11-27 IFP Energies Nouvelles Method of absorbing acid compounds contained in a gaseous effluent using an amine-based aqueous solution

Also Published As

Publication number Publication date
GR75712B (en:Method) 1984-08-02
PH16622A (en) 1983-11-28
CA1158852A (en) 1983-12-20
DE3167178D1 (en) 1984-12-20
CS494581A2 (en) 1984-06-18
MX161784A (es) 1990-12-27
PL130311B1 (en) 1984-07-31
AR228276A1 (es) 1983-02-15
PL127863B1 (en) 1983-12-31
RO81354B (ro) 1983-02-28
EP0043525A1 (en) 1982-01-13
RO81354A (ro) 1983-02-15
AU542053B2 (en) 1985-02-07
ATE10293T1 (de) 1984-11-15
ZA814278B (en) 1982-07-28
ES8300875A1 (es) 1982-11-16
JPS604272B2 (ja) 1985-02-02
NO812157L (no) 1982-01-04
NO163537B (no) 1990-03-05
ES503481A0 (es) 1982-11-16
NO163537C (no) 1990-06-13
CS242870B2 (en) 1986-05-15
IN154625B (en:Method) 1984-11-24
PL231927A1 (en:Method) 1982-03-15
JPS5739178A (en) 1982-03-04
BR8104104A (pt) 1982-03-16
HU185932B (en) 1985-04-28
AU7240181A (en) 1982-01-07
NZ197575A (en) 1984-10-19

Similar Documents

Publication Publication Date Title
US4143119A (en) Method and composition for inhibiting the corrosion of ferrous metals
US4100100A (en) Cobalt-containing inhibitor for sour gas conditioning solutions
US4102804A (en) Inhibitor for gas conditioning solutions
US3959170A (en) Corrosion inhibitors for alkanolamine gas treating system
US4372873A (en) Vanadium-amine corrosion inhibitor system for sour gas conditioning solutions
JPS5942073B2 (ja) 防食用組成物
US4446119A (en) Method and compositions for reducing corrosion in the removal of acidic gases from gaseous mixtures
US4431563A (en) Inhibitors for acid gas conditioning solutions
EP0043525B1 (en) Corrosion inhibitors for alkanolamine gas treating systems
US4595723A (en) Corrosion inhibitors for alkanolamines
US4502979A (en) Corrosion inhibitors for alkanolamine gas treating systems
US6036888A (en) Corrosion inhibitor for alkanolamine units
CA1220774A (en) Process for preventing corrosion in alkaline systems
US4959177A (en) Reducing stress corrosion cracking in treating gases with alkanol amines
US4116629A (en) Corrosion inhibition of stainless steel exposed to hot carbonates
US4405584A (en) Process for removing acidic gases
US4452764A (en) Bismuth inhibitors for acid gas conditioning solutions
US4499003A (en) Antimony-molybdenum salt corrosion inhibitor composition
US4944917A (en) Use of thiosulfate salt for corrosion inhibition in acid gas scrubbing processes
JPS5837392B2 (ja) コウテツ ノ ボウシヨクホウ
US5885487A (en) Corrosion inhibitor for alkanolamine units
US5472638A (en) Corrosion inhibitor
US4590036A (en) Process for corrosion inhibition utilizing an antimony-molybdenum salt corrosion inhibitor composition
US4857283A (en) Use of sulfur dioxide for corrosion inhibition in acid gas scrubbing processes
GB1589932A (en) Corrosion inhibiting compositions for use in gas scrubbing solutions

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

AK Designated contracting states

Designated state(s): AT BE DE FR GB IT LU NL SE

RAP1 Party data changed (applicant data changed or rights of an application transferred)

Owner name: UNION CARBIDE CORPORATION

17P Request for examination filed

Effective date: 19820709

ITF It: translation for a ep patent filed
GRAA (expected) grant

Free format text: ORIGINAL CODE: 0009210

AK Designated contracting states

Designated state(s): AT BE DE FR GB IT LU NL SE

REF Corresponds to:

Ref document number: 10293

Country of ref document: AT

Date of ref document: 19841115

Kind code of ref document: T

REF Corresponds to:

Ref document number: 3167178

Country of ref document: DE

Date of ref document: 19841220

ET Fr: translation filed
PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: LU

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 19850630

PLBE No opposition filed within time limit

Free format text: ORIGINAL CODE: 0009261

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: NO OPPOSITION FILED WITHIN TIME LIMIT

26N No opposition filed
PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: AT

Payment date: 19860422

Year of fee payment: 6

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: AT

Effective date: 19890626

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: SE

Payment date: 19900615

Year of fee payment: 10

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: BE

Payment date: 19900709

Year of fee payment: 10

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: GB

Payment date: 19910614

Year of fee payment: 11

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: FR

Payment date: 19910619

Year of fee payment: 11

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: SE

Effective date: 19910627

ITTA It: last paid annual fee
PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: BE

Effective date: 19910630

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: NL

Payment date: 19910630

Year of fee payment: 11

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: DE

Payment date: 19910723

Year of fee payment: 11

BERE Be: lapsed

Owner name: UNION CARBIDE CORP.

Effective date: 19910630

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: GB

Effective date: 19920626

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: NL

Effective date: 19930101

NLV4 Nl: lapsed or anulled due to non-payment of the annual fee
GBPC Gb: european patent ceased through non-payment of renewal fee

Effective date: 19920626

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: FR

Effective date: 19930226

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: DE

Effective date: 19930302

REG Reference to a national code

Ref country code: FR

Ref legal event code: ST

EUG Se: european patent has lapsed

Ref document number: 81104985.7

Effective date: 19920109