Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M175/00—Working-up used lubricants to recover useful products ; Cleaning
  • C10M175/0016—Working-up used lubricants to recover useful products ; Cleaning with the use of chemical agents

Definitions

• Used high viscosity index lubricants as employed for automobile lubrication, present a tremendous problem to the environment.
• Such lubricants commonly contain relatively large amounts of various detergents and extreme pressure additives in the form of polyvalent metal soaps as well as lead compounds, oxidized carbonaceous materials, water, etc. Due to their relatively high content of various additives, used lubricating oils cannot be burned simply Without seriously polluting the air. Thus, literally millions of gallons of used lubricants are discarded annually because there is no economical way to recycle them.
• the quantity of lubricating oil which can be recovered economically by reclaiming procedures has decreased.
• the yield of lubricating oil which can be obtained by reclaiming is in the order of 50% or less of the recoverable organic material. Due to the severity of treatment, a substantial quantity of the recoverable organic material in the oil is lost. This makes the reclaiming procedure less economical and also results in the production of an increased quantity of sludge and byproducts whose disposal causes contamination of the environment.
• the used lubricating oil is first treated with caustic at an elevated temperature such as 400 F. to 600 F. to drive off water and to break soaps in the oil as well as to neutralize the oil. Also, in the course of heating, the light ends are flashed off and are generally burned. After the heating procedure, the oil is then cooled to about 100 F. or less and a small quantity of concentrated sulfuric acid is added. After settling, the bottoms are drawn 01f which contain an acid sludge comprising sul- States Patent 0 3,835,035 Patented Sept. 10, 1974 ice furic acid and dissolved sulfonates and oxygenated hydrocarbons.
• the sludge which may constitute about 5 to 20% by weight of the used oil being treated, is disposed of by being placed in a closed container to prevent the escape of acid fumes. The sludge is then dumped. Due to the noxious properties of acid sludge, it is presently very diflicult to find a land-fill which will accept material of this type. For example, in the Los Angeles area, acid sludge is hauled to San Diego where there is a landfill having a high lime content which will accept acid sludge.
• the top oil is then generally heated and finely divided clay is added at a temperature of about 350 F.
• the mixture of clay and top oil is then taken to a temperature of about 600 F. in a heater and after being held at this temperature for suificient time is cooled to about 350 F. or less and passed through a filter press.
• Another procedure which has been used for treatment of used lubricating oils involves treatment of the oil with lime and finely divided clay.
• a still further procedure involves treatment of the oil with a mixture of caustic and sodium silicate. All of the above noted procedures give a yield of purified oil of 50% or less based on the weight of the used oil being treated together with the production of 5% to 20% of light ends or tops which are burned. Additionally, all of the above procedures produce substantial quantities of sludge which cannot be recycled and must be dumped.
• the present process for the purification of used lubricating oils is economicalproviding a yield of about to about or more of the recoverable organic material in the used oiland also produces a very small amount of residue composed of polyvalent metal compounds in admixture with oxidized hydrocarbons and all of the myriad materials which are found in the sludge from used lubricating oils.
• the process provides a means for substantially reducing environmental pollution resulting from the dumping of waste oil.
• the process provides a new source of high viscosity index oils which are presently in short supply and are urgently needed in industrialized countries for automotive lubrication.
• used lubricating oils which may be collected from various sources, such as independent service stations throughout a large area, are first admixed with a predominantly hydrocarbon liquid diluent which preferably has a boiling range within the temperature region of about F. to about 550 F.
• the liquid diluent may be either aromatic or aliphatic and is mutually soluble with the used hydrocarbon lubri cating oil undergoing treatment.
• the function of the liquid diluent in the process, as envisioned, is to lowerthe viscosity of the used lubricating oil and to change the. characteristics of the used lubricating oil dispersion to.
• Impurities which may be present in the liquid diluent, which may be recycled light ends from the purified lubricating oil may include, for example, small quantities of sulfur-containing compounds, such as mercaptans, and oxygenated hydrocarbons such as aldehydes or ketones.
• the impurities which may be present in the liquid diluent will vary depending on the makeup of the used lubricating oil which is the source of the recycled light ends. Thus, the above listing of impurities is not intended to be all inclusive.
• the predominantly hydrocarbon liquid diluent has a boiling range within the temperature region of about 100 F. to about 500 F. althOugh lower boiling hydrocarbon liquids, such as liquid propane, may also be employed.
• the purified lubricating oil produced in accord with the process may be subjected to distillation. In the course of the distillation, the light or naphtha ends may be recycled to the process to serve as the predominantly hydrocarbon liquid diluent for the used lubricating oils being treated.
• the process will be self-sustaining with sufficient naphtha light ends being supplied through distillation of the purified oil or organic phase to satisfy the need for liquid diluent in diluting the as received used lubricating oil.
• the quantity of the liquid diluent which is employed in diluting the as received used lubricating oil may be varied in accord with the process.
• a particularly practical range of liquid diluent with respect to used oil ranges from about 1:1 to about 1:2 by volume, although other dilutions may be used, if desired, such as 2:1 or even 4:1 depending, for example, on the solids content and viscosity of the used drain oil undergoing treatment and the efficacy of the diluent liquid in furthering contact by the extraction solvent.
• the diluted lubricating oil is then contacted with a mixture of Water, a water miscible alcohol, and a small quantity of an acid.
• the acid functions to displace polyvalent metal ions from the various metallic soaps which are present in the diluted lubricating oil undergoing treatment.
• the soaps are converted to lower molecular weight acids. With the decrease in molecular weight, the solubility of the resulting acids in the diluted lubricating oil is decreased while their solubility in the water-alcohol phase is increased.
• the water miscible alcohols which may be used in this step of the process are methanol, ethanol, isopropyl alcohol, n-propyl alcohol, sec-butyl alcohol, and tert.-butyl alcohol.
• the higher alcohols such as amyl alcohol and also alcohols having a lower water solubility such as nbutyl alcohol, have such a low solubility in water that they are generally ineffective in the present process.
• the water miscible alcohols which are suitable in the process including polyhydric alcohols, generally have a solubility of about 20% or more by volume in water.
• the material undergoing treatment i.e., used lubricating oil
• the specific operating conditions employed may be varied to suit the particular batch of lubricating oil which is being treated. For example, if the batch of lubricating oil undergoing treatment has a relatively high water content, this factor may be taken into consideration in determining the ratio of alcohol to water in treating the lubricating oil after it has been diluted with a predominantly hydrocarbon liquid diluent as described.
• the lubricating oil may, for example, be collected in a relatively large holding tank. When the holding tank is full, representative samples may then be taken and analyzed with a view to determining the optimum process conditions for treating the used oil in that tank.
• the behavior of the samples may be determined in considering how much of the predominantly hydrocarbon liquid diluent available for processing to mix with the used lubricating oil on a volume-to-volume relationship to obtain the optimum basis for handling and centrifugation.
• samples of the used lubrieating oil in the holding tank may be treated on a small scale according to the present process to determine the conditions which provide the greatest reduction in the ash content of the oil being treated and the greatest yield of purified oil.
• a particularly suitable quantity of the water miscible alcohol-water mixture is about one volume of the mixture for each volume of the diluted used lubricating oil for onestage extraction of the diluted lubricating oil.
• the diluted lubricating oil may be subjected to multiple-stage extraction with a water miscible alcohol-water mixture, as described, and also the quantity of the alcohol-Water mixture may be varied, for example, from about one-half volume of alcohol-water mixture to two volumes of the diluted lubricating oil to higher volume ratios in excess of 1:1.
• the volume of the water miscible alcohol- Water mixture is kept as low as possible since this simpli: fies the subsequent processing steps in terms of equipment size, cost, etc.
• Various water soluble acids may be employed in the alcohol-water mix-ture used in treating the diluted lubricating oil.
• hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid have all been employed and found suitable.
• the decomposition of the polyvalent metal soaps generally bivalent metal soaps
• the removal of the organic acids from the organic layer to the alcohol-Water layer reduces the efficacy of the non-ionic dispersants remaining in the oil to maintain the micellular configuration necessary to kee the solids and sludge in dispersed form in the diluted oil.
• the displaced metal ions may form salts with the anionic portion of the treating acid.
• the treating acid is preferably one which does not contain a bulky anionic group, e.g., a sulfonic acid group. which would enhance the solubility in the Oil phase of salts formed with the displaced polyvalent metal ions and, thereby, inhibit migration of such salts into the alcohol.
• Agitation is generally employed during the treatment of the diluted lubricating oil with the alcohol-water mixture containing an acid.
• the agitation may be provided by mixing within a large vessel through use of a mixing impeller, in a continuous, metered in-line mixing device such as a gear pump or homogenizer, or by using any other mixing procedure.
• the agitation of the diluted lubricating oil and alcoholwater mixture is generally carried out until an emulsion forms which indicates that the diluted oil has been thoroughly contacted with the alcohol-water mixture.
• the emulsion is generally unstable and is broken during the subsequent centrifuging step. If the emulsion is not broken during centrifuging, this is undesirable since the process yield is reduced by trapping of recoverable oil in the emulsion phase. It is preferred that the formation of a stable emulsion which is not broken by centrifuging be kept to a minimum. This may be accomplished by taking representative samples of the used oil being treated and then varying the process parameters on a small scale to determine the optimum yield conditions. By determining the optimum processing conditions for a particular used oil, the formulation of a stable emulsion may be minimized to provide the maximum yield of recoverable organic material in the oil.
• the resulting mixture is then fed to a centrifuge for separation of the sludge from the lubricating oil and also separation of the alcohol-water mixture from the organic mixture of liquid diluent and lubricating oil.
• Industrial centrifuges are well known and any of the various types of centrifuges may be used in the present process.
• the resultant mixture is simply fed into the centrifuge with the sludge depositing out on the walls of the centrifuge While the alcohol-water mixture is taken off through one outlet and the organic mixture of liquid diluent and lubricating oil is removed through another outlet.
• the sludge formed on the interior of the centrifuge may be removed by ejection, backwashing or by spraying the interior of the centrifuge bowl with a jet of water.
• the alcohol-water stream which is taken from the centrifuge contains organic acids.
• the mixture of water miscible alcohol and water may be recycled directly to the process for use in treatment of used lubricating oil diluted with a predominantly hydrocarbon liquid, as described.
• the alcohol-water stream may also first be subjected to a clean-up operation before return to the process. Any conventional procedure may be used for cleaning the alcohol-water stream to remove organic acids such as extraction of the organic acids, ion exchange, distillation or neutralization followed by distillation of the alcohol followed by addition of fresh make up water to the alcohol, etc.
• the mixture of purified lubricating oil and predominantly hydrocarbon liquid diluent may be used as a low ash fuel or the mixture may be separated through conventional distillation.
• the naphtha fraction from the distillation may, as described previously, be recycled for use in the process in diluting the used lubricating oil.
• the purified lubricating oil fraction from the distillation may be used as the base stock in compounding new lubricating oils.
• a convenient and accurate way of measuring the ef fectiveness of the present process in terms of the purity of the lubricating oil obtained is to compare the ash content of the as-is used lubricating oil with the ash content of the purified lubricating oil product obtained from the process.
• the present process may provide a reduction in the ash content of the oil of to For example, an ash content of about 2% in the as received used oil was reduced to about 0.2% in the purified oil.
• there is a reduction in the additive content of the oil which simplifies further processing of the purified oil using conventional refinery procedures.
• the residue from the process which consists of the various materials that are present in the sludge of a used lubricating oil may constitute about 3% by weight of the as received used lubricating oil.
• the residue is only a very small fraction of the weight of the used lubricating oil.
• the residue from the process has a high metallic content, predominantly lead, and, thus, represents a potentially valuable source of metals.
• the process residuce from all the used oil would be quite sizable in terms of total weight of metals, even though the residue represents only a small percentage by weight of the used lubricating oil being treated.
• the residue may be processed, where economically feasible, to recover its metal fractions.
• a used lubricating oil is purified by mixing the used lubricating oil with a mutually soluble predominantly hydrocarbon liquid diluent which preferably has a boiling range within the temperature region of about F.
• the alcohol-water mixture contains a small amount of an ammonium or alkali metal base while in the present process the alcohol-water mixture contains a small amount of an acid.
• various water soluble ammonium and alkali metal bases may be employed in the alcohol-water mixture used in treating the diluted lubricating oil.
• ammonium carbonate, sodium carbonate, potassium carbonate, lithium carbonate, and sodium hydroxide have all been employed and found suitable.
• sodium carbonate and sodium phosphate are preferred.
• the carbonate and phosphate anions are particularly effective in reducing. the solubility of the polyvalent metal cations which are displaced from the metallic soaps in the diluted lubricating oil by the monovalent ammonium and alkali metal ions, and in reducing the efficacy of the non-ionic dispersants remaining in the oil to maintain the micellular cofiguration necessary to keep the solids and sludge in dispersed form in the diluted oil.
• closely related anions such as the bicarbonate ion, were found to be less effective in the process than the carbonate ion.
• the purified oil obtained from the process will have a higher ash content than that obtained by using a lesser quantity of the ammonium or alkali metal base.
• the quantity of the ammonium or alkali metal base is sufiicient to displace the polyvalent metal ions from the soaps within the oil but that the base not be present in any great excess of that amount.
• the ash content of the oil is reduced by as much as about 80 to 90%.
• the content of monovalent cations, e.g., sodium, in the thus purified oil is generally high due to the presence of the base in the alcohol-water mixture used in the process.
• a purified oil or oil phase resulting from treatment according to our prior process is then subjected to a second stage treatment using the conditions of the present process, there is a further marked reduction in the ash content by as much as another 80 to 90%.
• the first stage treatment according to our prior process may reduce the ash content to about 0.2%.
• the thus purified oil is then subjected to a second stage treatment according to the present process, its ash content may be further reduced to about 0.02%.
• centrifuging was a modification of' ASTM method D179662.
• cone shaped tubes (described in the ASTM method) were first filled with the resultant mixture formed from the diluted drain oil and the mixture of alcohol with water.
• the cone shaped tubes and their contents were then whirled in a Precision Oil Centrifuge (Catalog No. 67343) to produce a relative centrifugal force of 800 at the tips of the tubes;
• the contents of the tubes had separated into several layers.
• a layer of sludge which had been removed from the drain oil by the process of the invention.
• Above the lower sludge layer was a water miscible alcoholwater layer and above this layer was an organic layer containing a purified organic phase of the predominantly hydrocarbon liquid diluent with the purified drain oil. This upper layer is termed the organic layer.
• an emulsion or dispersion formed which was not completely broken by the centrifuging and which appeared within the organic or the alcohol-water phase or as a layer at the interface between the organic layer and the alcohol-water layer.
• the yield of recoverable organic material in volume percent of the drain oil was determined by measuring the volume of the purified organic layer and subtracting the volume of the hydrocarbon liquid diluent from this volume. The remaining volume, which is the volume of the recovered organic material from the drain oil, was then divided by the original volume of the drain oil to determine the percent yield of recoverable organic material. In some instances, as indicated in the tables, the yield of recoverable organic material from the drain oil was observed to be in excess of In these instances, a dispersion or emulsion was observed and there had obviously been a transfer of material into the organic layer which produced the high reading.
• a sample was removed from the organic phase using a 100 ml. syringe fitted with an 8-inch needle.
• the sample from the organic phase was then analyzed to determine its solids content and the ash content of the solids.
• the ash content of the purified drain oil was then converted to an ash content based on the weight of the original drain oil by multiplying the ash content of the solids by the percent solids in the original oil. This, then, permitted a direct evaluation of the process in terms of the percentage reduction which was obtained in the ash content.
• a ten gram sample was weighed into a soft, crimped aluminum dish having a diameter of 2% inches, a depth of inches and a fingergrip handle.
• the dish was placed on a Corning Pyroceram GOO-watt hotplate with a temperature dial set to produce a surface temperature of approximately 450 F. and preheated to the operating temperature. Heating at about 450 F. was maintained for one hour, after which the dish was removed, cooled to ambient temperature, and reweighed. The percent of solids was then determined by dividing the final weight of the residue by the weight of the sample and multiplying by 100.
• the ash content of the drain oil or the purified organic layer was determined by ASTM method D482-63.
• the analytical problems which are associated with the presence of phosphorus and lead compounds were disregarded since the results were used on a comparative basis. In other words, any error produced by the presence of phosphorus or lead would have a similar effect in the ash analysis of the used drain oil as in the ash determination for the purified organic liquid. Thus, the errors, if any, would not affect the validity of the comparison of the ash content of the used drain oil with that of the purified organic liquid.
• the method for determining ash consists of weighing a sample of the material to be ashed into a 30 ml. porcelain crucible. The material in the crucible is then ignited and allowed to burn until only ash and carbon remain. The carbonaceous residue is then reduced to an ash by heating in a muffle furnace at 775 C., followed by cooling and weighing.
• the ash content primarily indicates the metals content of the sample expressed in terms of the inorganic salts of the metals which are predominantly phosphates, oxides, silicates, sulfates, etc.
• the solids content and the ash content of the used drain oil were determined as a percentage of the weight of the drain oil sample.
• the ash content of the purified organic layer was also determined as a percentage based on the solids content of the sample from the purified organic layer. Conveniently, the weight of solids of the purified organic layer was determined and these solids were then burned to determinne the ash content of the solids.
• the ash content of the purified organic layer expressed as a percent of the solids in the sample, is then converted to weight percent ash based on the drain oil by multiplying by the percent of solids in the used oil.
• the basis for the conversion of the ash in the purified organic layer to percent ash based on the used drain oil is based on the fact that the ash is contained in the solids and the total solids content of both the drain oil and the purified organic layer is relatively constant and is only slightly affected by the present process.
• the liquid hydrocarbon diluent in the sample from the purified organic layer is driven off.
• the solids which remain are those obtained from the used drain oil being treated.
• the heating at about 450 F. drives olf the light fractions as well as any water present in the drain oil.
• the solids which remain are largely hydrocarbons which have a boiling point in excess of 450 F., and these solids are almost entirely recovered by the present process.
• the weight of the solids which are removed is very small in comparison to the total weight of solids composed mainly of hydrocarbons whose boiling point is in excess of 450 F.
• the assumption that the solids content from the drain oil remains fixed throughout the process is reasonably valid and any errors resulting from this approximation are within an error of about of the observed values, i.e., 10.05 times the observed values.
• Examples 1-3 are each concerned with a drain oil having an ash content of 1.44% by weight.
• the ash content was reduced to 0.84%, based on the weight of original drain oil, while in Example 2 the ash content was reduced to 0.36%.
• the striking effect of adding an acid to the alcohol-water mixture is illustrated by the results of Example 2 in which all of the process conditions were otherwise the same as in Example 1.
• Example 1 illustrates the effect of dilution in which 50 mls. of drain oil were admixed with 50 mls. of naphtha diluent and then centrifuged directly without being contacted by the alcoholwater mixture.
• Example 2 where the diluted drain oil was thoroughly admixed with 50 mls. of a 50% by volume 10 mixture of isopropyl alcohol and water which contained a small quantity of an acid.
• Table II illustrates the effect of dilution, i.e., variations in the amount of hydrocarbon diluent with respect to the amount of drain oil, without a following treatment with an alcohol-water mixture.
• dilution i.e., variations in the amount of hydrocarbon diluent with respect to the amount of drain oil
• Table II illustrates the effect of dilution, i.e., variations in the amount of hydrocarbon diluent with respect to the amount of drain oil, without a following treatment with an alcohol-water mixture.
• Table IV sets forth the results obtained in Examples 13l5 in which the alcohol present in the alcohol-water mixture was varied. As illustrated, all of the various alcohols tested were found to be effective and, in addition to iro-propanol, ethanol, n-propanol and tert-butanol were found to be particularly effective.
• Table VI illustrates the results obtained from Examples 2224 in which the hydrocarbon diluent was varied. These examples demonstrate that a wide variety of hydrocarbon diluents may be employed in the process in obtaining a marked reduction in the ash content of the treated oil.
• the use of kerosene as a diluent demonstrates that rela tively high molecular weight solvents are suitable while the use of xylene demonstrates that an aromatic diluent may likewise be employed.
• Example 30 illustrates the results of a two-stage purifi cation procedure in which the first stage (Example 30) is carried out according to the process of our previous US: Application 336,733.
• 25 mls. of a used drain oil having an ash content of 1.73 weight percent was admixed with 25 mls. of a naphtha diluent and the mixture was then contacted with 50 mls.
• Example 31 The organic layer provided by the procedure of. ample 30 (a 50:50 volume mixture 'of recovered drain oil and naphtha diluent) was then employed as the start ing material for a second stage treatment.
• the second stage treatment was the process of the present invention in which 50 mls. of the purified organic layer from the first stage was used as the starting mate rial.
• the'use of the present process as the second stage to a first stage treatment according to the process of our application 336,733 reduced the ash content of the purified oil from 0.30% to 0.49% by weight based on the weight of the original used oil. This is a drastic reduction which is much greater than the reduction obtained when boththe first and second stages are conducted according to the process of application 336,733 or when both stages are conducted using the conditions of the present process.
• Example 32 the alcohol was eliminated in a second stage treatment which are otherwise carried out using the conditions of the present process. As indicated, the elimination of the water miscible alcohol in Example. 32 greatly reduced the effectiveness of the second stage treatment. While some further reduction of the ash content of the oil was achieved, the reduction was not nearly as great as that obtained in Example 31.
• Table IX illustrates the characteristics of the hydrocarbon diluents referred to in the'various Examples. As indicated by Table TX and the Examples, a variety of diluents may be employed in the present process, ranging from aliphatics to aromatic and including a dehydrated overhead from a used drain oil.
• Example 30 the metals analysis set forth in Table X was conducted on the used drain oil which was treated in Example 30 having an ash content of 1.73 percent by weight.
• a first stage treatment using the conditions of Example 30, i.e., the process of our prior application 336,733 the metals content of the purified oil was determined.
• organic material obtained according to Example 30 50-50 volume mixture of purified drain oil and naphtha diluent
• Example 31 the present process
• the metals content of the purified oil after both the first and second stage treatments is corrected to the weight of the original used oil (as is condition) in the same manner as described previously.
• the data demonstrate that the present process is very ,eliective as a second-stage treatment to a purified oil after a first-stage treatment according to the process of our prior application 336,733 as exemplified by Example 30.
• the sodium content of the oil after the first-stage treatment since the base present in the alcohol-water mixture contained sodium.
• the sodium content was reduced to nil.
• Phosphorus which is not a metal, is indicated in Table X since it does affect the weight of the ash. Since more than half of the weight of the ash in the oil after the second-stage treatment is represented by phosphorus, the actual metals content of the oil at this point is about 0.02 percent. The tremendous reductions in metals content of the oil, which parallel closely the reduction in ash content of the treated oil, clearly demonstrate the worth of 14 our process in recovering valuable metals, as Well as in recovering valuable high viscosity index oils.
• the presence of metals in a used lubricating oil makes the oil very difiicult to treat by conventional refinery processes.
• the resulting oil may then be treated further using conventional refinery processing, such as distillation, hydrotreating, etc.
• the present process provides a solution to the long-standing problem of recycling used lubricating oils.
• the use of the process will make a substantial contribution to environmental quality by providing a reduction in pollution of the air or water from the burning or disposal of used lubricating oils.
• the present process represents a substantial contribution to the conservation of natural resources since it enables the reuse of relatively scarce high viscosity index oils which are needed for automotive lubrication.
• a method of purifying a used lubricating oil comprising:
• centrifuging to remove sludge and metal compounds from the oil and to separate the diluted oil phase from the alcohol-water phase.
• a method of purifying a used lubricating oil comprising:
• a multistage method of purifying a used lubricating oil comprising:
• centrifuging to remove sludge and metal compounds from the oil and to separate a second diluted oil phase from the alcohol-water phase.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Organic Chemistry (AREA)
• Lubricants (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

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• 1973
  • 1973-07-30 US US00383706A patent/US3835035A/en not_active Expired - Lifetime
• 1974
  • 1974-07-23 CA CA205,496A patent/CA1036091A/fr not_active Expired
  • 1974-07-25 GB GB3296974A patent/GB1445498A/en not_active Expired
  • 1974-07-27 DE DE2436309A patent/DE2436309C3/de not_active Expired
  • 1974-07-29 FR FR7426270A patent/FR2239520B1/fr not_active Expired
  • 1974-07-30 JP JP8741674A patent/JPS5422449B2/ja not_active Expired

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