CA1188650A - Solvent stripping process - Google Patents
Solvent stripping processInfo
- Publication number
- CA1188650A CA1188650A CA000428092A CA428092A CA1188650A CA 1188650 A CA1188650 A CA 1188650A CA 000428092 A CA000428092 A CA 000428092A CA 428092 A CA428092 A CA 428092A CA 1188650 A CA1188650 A CA 1188650A
- Authority
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- Canada
- Prior art keywords
- solvent
- stripping
- steam
- water
- stripping operation
- 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.)
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- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Especially in solvent extraction processes, solvents are removed by stripping with steam the amounts of solvent remaining in the extract and in the raffinate,respectively,in an extract stripp-ing column and raffinate stripping column, where-upon the condensates of the solvent-containing overhead vapours are transferred to a separator where the condensates separate into two phases, the aqueous phase is withdrawn from the separator and the amounts of solvent remaining in the aqueous phase are stripped with steam in a water stripping column and the condensate of the overhead vapours is introduced into the same separator, whereby the water from which solvent has been removed is accumulated at the bottom of the water stripping column, is withdrawn therefrom and transferred to a vessel where it is re-evaporated by indirect heat exchange with hot process streams withdrawn from the solvent recovery section and is returned in the form of steam to the respective stripping column as stripping steam.
Especially in solvent extraction processes, solvents are removed by stripping with steam the amounts of solvent remaining in the extract and in the raffinate,respectively,in an extract stripp-ing column and raffinate stripping column, where-upon the condensates of the solvent-containing overhead vapours are transferred to a separator where the condensates separate into two phases, the aqueous phase is withdrawn from the separator and the amounts of solvent remaining in the aqueous phase are stripped with steam in a water stripping column and the condensate of the overhead vapours is introduced into the same separator, whereby the water from which solvent has been removed is accumulated at the bottom of the water stripping column, is withdrawn therefrom and transferred to a vessel where it is re-evaporated by indirect heat exchange with hot process streams withdrawn from the solvent recovery section and is returned in the form of steam to the respective stripping column as stripping steam.
Description
6g~
A SOLVENT STRIPPIN _PROCESS
The present invention relates to a process for stripping solvents, and particularly to a special steam recycling during steam stripping operations in solvent recovery plants.
In mineral oil technology as well as in gene-ral chemical technology solvent extraction processes are used for separating blends of materials by means of the differing solubility of their components in solvents and, respectively, in solvent mixtures.
The main proportion of the solvent contained in the extract and also the small solvent quantities present in the refined product have to be recovered, and this is usually done in a multi-stage evaporation plant.
From the solvent recovery of, say, a mineral oil extraction plant there result , for instance, in addition to a solvent stream a raffinate stream and 20 also an extract stream from which solvent has been :
removed to a large extent. However, these streams still contain small amounts of solvent. These residual amounts are separated in stripping columns in which _ 1 _ the solvent components are stripped by means of steam. ~s the specification for the products require a removal to only a few ppm of solvent, the stripping steam must be free of solvent.
5 Steam, which contains the solvent components, is removed from the top of the stripping columns and condensed in a condenser, and in a downstream separator the condensate is separated into a solvent phase and an aqueous phase. Both the 10 solvent phase and the aqueous phase contain small amounts of oil. In accordance with the physical :
properties of the respective solvent the aqueous phase also still contains some residual solvent.
Therefore, the aqueous phase is fed into a column 15 in which these residual solvent quantities are also stripped by means of steam , and the solvent free water is withdrawn at the bottom of the column and is discharged from the plant.
~ecause of the possible contamination of these 20 volumes of water with oil they flow to the waste water treatment plant. In some countries due to government regulations which are based on the creator principle, high waste water charges arelevied on the waste waters. Furthermore, the waste water treatment 25 causes additional costs. It is therefore desirable in connection with the raffination of mineral oils -to minimize the amounts of waste wa.er or, where possible, to even elimina-te the dlscharge of waste water.
One way of eliminating -the production o:E consiclerable volumes of waste wa-ter in the stripping secti.on oE a solven-t rc~covc:ry pl.ant :is the replacc-~ment o:E -the str:ipplng steam by rc!c~c.l..c.~d st:r:i.pp:i.ncJ cJases. I-~owever, when strlpplng qases are ~Is,ecl the amount of power requlred :Eor the compression oE the gases constitutes a drawback.
It was -therefore the object of the presen-t lnventlon to provide a process for the stripping of solvents by means of steam, whlch ellminates as far as posslble the dlscharge of waste water into the waste water system.
The present invention provides ln one aspect especial]y for solvent extraction plants a process for stripping residual solvents by means of s-team ln an extract and a raffinate strlpp-ing column, transferring the condensates of the solvent-containing overhead vapours into a separatox, wi-thdrawing the aqueous phase from the separator, and stripplng the solvent quantltles remainlng ln said aqueous phase by means of steam in a water stripping column and introduclng the condensate of the overhead vapours into the same separator, sald process being characterlzed in that the water, from which solvent has been removed, is accumulated at the bottom of the water stripplng column, is withdrawn therefrom and transferred into a vessel where it is re-evaporated by lndirect heat exchange with hot process streams withdrawn from the solvent recovery section and is returned in form of steam into -the respective stripping columns, while extraneous steam is supplied as stripping steam to the respective stripping columns only during start-up and extraneous thermal energy is supplied only when the amounts of heat originating from -the process streams and required for re-evapora-tion of the water are insufficient.
According to another aspect of the present invention there is provided a process for separating solvent from a charge mix-ture con-taining a hydrocarbon oil and a solvent wh:lch comprises steam st:rlpping said charcJe m:ixture in a solvent str:i.pp:i.nc,l operat.i.on thereby formi.ng strippe~d bot-toms containing hyclrocarbon oi.:l. and solvent stripping operation overhead con-tainlng steam ancl solvent;
withdrawing stripped bottoms containing hydrocarbon oil from said solvent stripping operatlon;
condensing said solvent stripping operation overhead containing s-team and solvent -thereby forming a solvent stripp-ing operation overhead condensate;
collecting said solvent stripping opera-tion overhead condensate in a collection vessel containing an upper aqueous phase and a lower solvent phase;
withdrawing said lower solvent phase;
steam stripping said upper aqueous phase in a water stripping operation thereby forming a water stripping operation overhead containing water and solvent and wa-ter stripping operation bottoms containing water;
condensing said water stripping operation overhead thereby forming a water stripping operation overhead con-densate;
passing said water stripping operation overhead condensate to said collection vessel;
passing said water stripping operation bottoms to a reboiler;
heating said water stripping operation bo-ttoms in said reboiler by indirect heat exchange against a hot stream, thereby forming steam; and passing said steam as the steam stripping medium to said solven-t s-tripping operation and said water stripping operat.ion.
Suitable solvents -to be recovered accordinc3 to the E):l^ecsent l.nvention are ~:hose being partly or completely soluble .in wal:c!r, wh:Lch can be steam stripped, e.cJ. methyl ethyl ketone, .Eu:r:Eural, methylene chloride and dichloroe-thane.
In the process according to the invention practically no eontamina-ted waste water is produced although stripping steam is used Eor the solvent recovery. Only a small quantity of water (e.g. up to 5 vol.-%, and 10 vol.-% at the most) has -to be drained in intervals, similar to the "blowciown"
-4a-from steam boilers,in order to avoid concentration of undesirable components.
The watcr required for the stripping steam ls recycled, and at the same time heat that has so 5 far not been utilized and is contained in the process streams obtained in the solvent recovery (e.g. hot solvent) is utilized for the production of stripping steam.
An embodiment of the process according to the 10 present invention will be described with reference to a mineral oil extraction plant and its flow dia-gram shown in the accompanying drawing.
The oil fraction - either raffinate or extract-which still contains residual solvent is introduced 15 into the stripping column 2 through line 1. During the start-up phase line 3 delivers externally supplied s~ripping steam to the column 2. In the bottom of column 2 the oil stripped of solvent accumulates and is withdrawn through line 4 and pump 5 to the storage 20 tank- The vapour withdrawn from the top of the column
A SOLVENT STRIPPIN _PROCESS
The present invention relates to a process for stripping solvents, and particularly to a special steam recycling during steam stripping operations in solvent recovery plants.
In mineral oil technology as well as in gene-ral chemical technology solvent extraction processes are used for separating blends of materials by means of the differing solubility of their components in solvents and, respectively, in solvent mixtures.
The main proportion of the solvent contained in the extract and also the small solvent quantities present in the refined product have to be recovered, and this is usually done in a multi-stage evaporation plant.
From the solvent recovery of, say, a mineral oil extraction plant there result , for instance, in addition to a solvent stream a raffinate stream and 20 also an extract stream from which solvent has been :
removed to a large extent. However, these streams still contain small amounts of solvent. These residual amounts are separated in stripping columns in which _ 1 _ the solvent components are stripped by means of steam. ~s the specification for the products require a removal to only a few ppm of solvent, the stripping steam must be free of solvent.
5 Steam, which contains the solvent components, is removed from the top of the stripping columns and condensed in a condenser, and in a downstream separator the condensate is separated into a solvent phase and an aqueous phase. Both the 10 solvent phase and the aqueous phase contain small amounts of oil. In accordance with the physical :
properties of the respective solvent the aqueous phase also still contains some residual solvent.
Therefore, the aqueous phase is fed into a column 15 in which these residual solvent quantities are also stripped by means of steam , and the solvent free water is withdrawn at the bottom of the column and is discharged from the plant.
~ecause of the possible contamination of these 20 volumes of water with oil they flow to the waste water treatment plant. In some countries due to government regulations which are based on the creator principle, high waste water charges arelevied on the waste waters. Furthermore, the waste water treatment 25 causes additional costs. It is therefore desirable in connection with the raffination of mineral oils -to minimize the amounts of waste wa.er or, where possible, to even elimina-te the dlscharge of waste water.
One way of eliminating -the production o:E consiclerable volumes of waste wa-ter in the stripping secti.on oE a solven-t rc~covc:ry pl.ant :is the replacc-~ment o:E -the str:ipplng steam by rc!c~c.l..c.~d st:r:i.pp:i.ncJ cJases. I-~owever, when strlpplng qases are ~Is,ecl the amount of power requlred :Eor the compression oE the gases constitutes a drawback.
It was -therefore the object of the presen-t lnventlon to provide a process for the stripping of solvents by means of steam, whlch ellminates as far as posslble the dlscharge of waste water into the waste water system.
The present invention provides ln one aspect especial]y for solvent extraction plants a process for stripping residual solvents by means of s-team ln an extract and a raffinate strlpp-ing column, transferring the condensates of the solvent-containing overhead vapours into a separatox, wi-thdrawing the aqueous phase from the separator, and stripplng the solvent quantltles remainlng ln said aqueous phase by means of steam in a water stripping column and introduclng the condensate of the overhead vapours into the same separator, sald process being characterlzed in that the water, from which solvent has been removed, is accumulated at the bottom of the water stripplng column, is withdrawn therefrom and transferred into a vessel where it is re-evaporated by lndirect heat exchange with hot process streams withdrawn from the solvent recovery section and is returned in form of steam into -the respective stripping columns, while extraneous steam is supplied as stripping steam to the respective stripping columns only during start-up and extraneous thermal energy is supplied only when the amounts of heat originating from -the process streams and required for re-evapora-tion of the water are insufficient.
According to another aspect of the present invention there is provided a process for separating solvent from a charge mix-ture con-taining a hydrocarbon oil and a solvent wh:lch comprises steam st:rlpping said charcJe m:ixture in a solvent str:i.pp:i.nc,l operat.i.on thereby formi.ng strippe~d bot-toms containing hyclrocarbon oi.:l. and solvent stripping operation overhead con-tainlng steam ancl solvent;
withdrawing stripped bottoms containing hydrocarbon oil from said solvent stripping operatlon;
condensing said solvent stripping operation overhead containing s-team and solvent -thereby forming a solvent stripp-ing operation overhead condensate;
collecting said solvent stripping opera-tion overhead condensate in a collection vessel containing an upper aqueous phase and a lower solvent phase;
withdrawing said lower solvent phase;
steam stripping said upper aqueous phase in a water stripping operation thereby forming a water stripping operation overhead containing water and solvent and wa-ter stripping operation bottoms containing water;
condensing said water stripping operation overhead thereby forming a water stripping operation overhead con-densate;
passing said water stripping operation overhead condensate to said collection vessel;
passing said water stripping operation bottoms to a reboiler;
heating said water stripping operation bo-ttoms in said reboiler by indirect heat exchange against a hot stream, thereby forming steam; and passing said steam as the steam stripping medium to said solven-t s-tripping operation and said water stripping operat.ion.
Suitable solvents -to be recovered accordinc3 to the E):l^ecsent l.nvention are ~:hose being partly or completely soluble .in wal:c!r, wh:Lch can be steam stripped, e.cJ. methyl ethyl ketone, .Eu:r:Eural, methylene chloride and dichloroe-thane.
In the process according to the invention practically no eontamina-ted waste water is produced although stripping steam is used Eor the solvent recovery. Only a small quantity of water (e.g. up to 5 vol.-%, and 10 vol.-% at the most) has -to be drained in intervals, similar to the "blowciown"
-4a-from steam boilers,in order to avoid concentration of undesirable components.
The watcr required for the stripping steam ls recycled, and at the same time heat that has so 5 far not been utilized and is contained in the process streams obtained in the solvent recovery (e.g. hot solvent) is utilized for the production of stripping steam.
An embodiment of the process according to the 10 present invention will be described with reference to a mineral oil extraction plant and its flow dia-gram shown in the accompanying drawing.
The oil fraction - either raffinate or extract-which still contains residual solvent is introduced 15 into the stripping column 2 through line 1. During the start-up phase line 3 delivers externally supplied s~ripping steam to the column 2. In the bottom of column 2 the oil stripped of solvent accumulates and is withdrawn through line 4 and pump 5 to the storage 20 tank- The vapour withdrawn from the top of the column
2 comprises the supplied stripping steam, the residual solvent quantities stripped from the oil and possibly traces of oil; it is transferred through line 6 to the condenser 7. The liquid phase produced in the con-25 denser 7 is supplied through line 8 to the separator 9 6S~
where it is separated into the aqueous phase anda solvent-containing phase which may be returned to the extraction zone. The aqueous phase is delivered from the separator 9 through line 10 (the pumps re-5 quired for transport are not shown in the drawing)to the column 11, to whlch in the start-up phase extraneous stripping steam is supplied through line 12 to remove the residual amounts of solvent con-tained in the aquoues phase from the top of column 11 10 through line 13.
After condensation in the condenser 14 the aqueous, residual solvent-containing condensate is also introduced into the separator 9. The solvent-free water, which may, however, still contain small 15 amounts of oil, accumulates at the bottom of the column 11. This water is not discharged in the usual manner to the waste water system but flows through line 15 to vessel 16. The interior of this vessel 16 is provided with a heating coil 17 through which hot (ca. 140C) 20 product from the solvent recovery section is passed.
This hot product, e.g. solvent, which is with-drawn from the solvent recovery process, has to be cooled,anyway, prior to its re-use in the extraction stage. Cooling is normally performed by air or water coolers in which the heat is lost without being uti-lized because the commonly used processes do not provide for full utilization thereof.
In accordance with the present invention, the 5 heat of these hot solvent streams is used to evaporate the volume of water accumulating in vessel 16 at an absolute pressure of 1.5 bar and a temperature of 110C. In most cases the amount of heat liberated during cooling of the solvent from 140C to 120C
10 will be sufficient for the generation of steam. If desired, additional heating with steam may be per-formed by means of coil 18. The steam from vessel 16 flows through line 19 and valve 20 into the stripping column 2, which operates at an absolute pressure of 15 0.3 bar. The amount of steam supplied through line 19 increases during the start-up period, and the amount of steam supplied through line 3 is decreased accordingly. Further volumes of steam from the vessel 16 are supplied through line 21 to column 11. ~essel 20 16 and column 11 operate at the same absolute pressure of 1.5 bar. In the case of column 11, too, the amount of steam supplied through line 1~ is decreased in accordance with the increasi-ng-amount of steam pro-duced in vessel 16.
6~
At the end of the start-up phase both the steam line 3 and the steam line 12 are closed, for then a steam/water cycle has been achieved which normally does not require any additional extraneous 5 steam.
No waste water to be purified in waste water treatment plants will be produced.
For purposes of simplification the flow diagram shows only one stripping column for stripping the 10 residual solvent contained in the oil, wherein the solvent-containing steam is removed overhead and after condensation is passed to the separator.
In commercial processes it is, however, common practice to supply the condensates from the extract 15 and from the raffinate stripper to the same separator and to treat the aqueous phase obtained from the con-densate of both stripping columns in one water stripp-ing column.
The volumne of steam produced in vessel 16 is of 20 such amount that the steam is sufficient not only for operating the water stripping column but a;lso for ope-rating the extract stripper as well as the raffinate stripper.
For instance, in the solvent recovery plant of a mineral oil extracti.on system operated with furfural the following quantities are obtained per day:
360 tons of extract 840 tons of raffinate.
At the specified daily capacity the extract stripper according to the prior art consumes 18 tons of steam, 10 the raffinate stripper consumes 35 tons of steam, the water stripper consumes 32 tons of steam .
In accordance with the invention it is thus possible to save 85 tons of steam per day, and the production of 85 m3 of waste water per day is elimi-15nated.
where it is separated into the aqueous phase anda solvent-containing phase which may be returned to the extraction zone. The aqueous phase is delivered from the separator 9 through line 10 (the pumps re-5 quired for transport are not shown in the drawing)to the column 11, to whlch in the start-up phase extraneous stripping steam is supplied through line 12 to remove the residual amounts of solvent con-tained in the aquoues phase from the top of column 11 10 through line 13.
After condensation in the condenser 14 the aqueous, residual solvent-containing condensate is also introduced into the separator 9. The solvent-free water, which may, however, still contain small 15 amounts of oil, accumulates at the bottom of the column 11. This water is not discharged in the usual manner to the waste water system but flows through line 15 to vessel 16. The interior of this vessel 16 is provided with a heating coil 17 through which hot (ca. 140C) 20 product from the solvent recovery section is passed.
This hot product, e.g. solvent, which is with-drawn from the solvent recovery process, has to be cooled,anyway, prior to its re-use in the extraction stage. Cooling is normally performed by air or water coolers in which the heat is lost without being uti-lized because the commonly used processes do not provide for full utilization thereof.
In accordance with the present invention, the 5 heat of these hot solvent streams is used to evaporate the volume of water accumulating in vessel 16 at an absolute pressure of 1.5 bar and a temperature of 110C. In most cases the amount of heat liberated during cooling of the solvent from 140C to 120C
10 will be sufficient for the generation of steam. If desired, additional heating with steam may be per-formed by means of coil 18. The steam from vessel 16 flows through line 19 and valve 20 into the stripping column 2, which operates at an absolute pressure of 15 0.3 bar. The amount of steam supplied through line 19 increases during the start-up period, and the amount of steam supplied through line 3 is decreased accordingly. Further volumes of steam from the vessel 16 are supplied through line 21 to column 11. ~essel 20 16 and column 11 operate at the same absolute pressure of 1.5 bar. In the case of column 11, too, the amount of steam supplied through line 1~ is decreased in accordance with the increasi-ng-amount of steam pro-duced in vessel 16.
6~
At the end of the start-up phase both the steam line 3 and the steam line 12 are closed, for then a steam/water cycle has been achieved which normally does not require any additional extraneous 5 steam.
No waste water to be purified in waste water treatment plants will be produced.
For purposes of simplification the flow diagram shows only one stripping column for stripping the 10 residual solvent contained in the oil, wherein the solvent-containing steam is removed overhead and after condensation is passed to the separator.
In commercial processes it is, however, common practice to supply the condensates from the extract 15 and from the raffinate stripper to the same separator and to treat the aqueous phase obtained from the con-densate of both stripping columns in one water stripp-ing column.
The volumne of steam produced in vessel 16 is of 20 such amount that the steam is sufficient not only for operating the water stripping column but a;lso for ope-rating the extract stripper as well as the raffinate stripper.
For instance, in the solvent recovery plant of a mineral oil extracti.on system operated with furfural the following quantities are obtained per day:
360 tons of extract 840 tons of raffinate.
At the specified daily capacity the extract stripper according to the prior art consumes 18 tons of steam, 10 the raffinate stripper consumes 35 tons of steam, the water stripper consumes 32 tons of steam .
In accordance with the invention it is thus possible to save 85 tons of steam per day, and the production of 85 m3 of waste water per day is elimi-15nated.
Claims (8)
- THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
l. A process beneficial to the environment for recovering water soluble solvents suitable for steam stripping by stripping such solvents with steam in a stripping column, especially in solvent extraction processes for removal of solvent remaining in the extract and in the raffinate in an extract stripping column and a raffinate stripping column, respectively, transferring the condensates of the solvent-containing overhead vapours into a separator where the condensates separate into two phases, withdrawing the aqueous phase from the separator, stripping the amounts of solvent remaining in said aqueous phase in a water stripping column, introducing the condensate of the overhead vapours of said water stripping column into said separator, accumulating the water from which solvent has been removed at the bottom of said water stripping column, withdrawing it therefrom and transferring it into a vessel where it is again evaporated by indirect heat exchange with hot process streams withdrawn from the solvent recovery section and returning it in the form of steam into the respective stripping columns as stripping steam, while extraneous steam is supplied as stripping steam to the respective stripping columns only during start-up, and extraneous thermal energy is supplied only when the amounts of heat derived from the process streams and required for re-evaporation of the water are insufficient. - 2. A process for separating solvent from a charge mixture containing a hydrocarbon oil and a solvent which comprises steam stripping said charge mixture in a solvent stripping operation thereby forming stripped bottoms containing hydrocarbon oil and solvent stripping operation overhead containing steam and solvent;
withdrawing stripped bottoms containing hydrocarbon oil from said solvent stripping operation;
condensing said solvent stripping operation overhead containing steam and solvent thereby forming a solvent stripping operation overhead condensate;
collecting said solvent stripping operation overhead condensate in a collection vessel containing an upper aqueous phase and a lower solvent phase;
withdrawing said lower solvent phase;
steam stripping said upper aqueous phase in a water stripping operation thereby forming a water stripping operation overhead containing water and solvent and water stripping operation bottoms containing water;
condensing said water stripping operation overhead thereby forming a water stripping operation overhead condensate;
passing said water stripping operation overhead condensate to said collection vessel;
passing said water stripping operation bottoms to a reboiler;
heating said water stripping operation bottoms in said reboiler by indirect heat exchange against a hot stream, thereby forming steam; and passing said steam as the steam stripping medium to said solvent stripping operation and said water stripping operation. - 3. A process as claimed in claim 2 wherein said hot stream in said indirect heat exchange is a hot process stream from solvent extraction.
- 4. A process as claimed in claim 2 wherein said hydrocarbon oil is a lubricating oil stock.
- 5. A process as claimed in claim 2 wherein said solvent is furfural.
- 6. A process as claimed in claim 2 wherein said solvent is furfural at a temperature of about 140°C.
- 7. A process as claimed in claim 2 wherein the heat supply to said reboiler includes indirect heat exchange against a hot process stream from solvent extraction and supplemental steam in an amount sufficient to effect reboiling.
- 8. A process as claimed in claim 2 wherein additional steam from an outside source is admitted to said solvent stripping operation and said water stripping operation during start-up.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000428092A CA1188650A (en) | 1983-05-13 | 1983-05-13 | Solvent stripping process |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000428092A CA1188650A (en) | 1983-05-13 | 1983-05-13 | Solvent stripping process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1188650A true CA1188650A (en) | 1985-06-11 |
Family
ID=4125229
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000428092A Expired CA1188650A (en) | 1983-05-13 | 1983-05-13 | Solvent stripping process |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1188650A (en) |
-
1983
- 1983-05-13 CA CA000428092A patent/CA1188650A/en not_active Expired
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