US2851355A - Process for the preparation of semi-cellulose - Google Patents

Process for the preparation of semi-cellulose Download PDF

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Publication number
US2851355A
US2851355A US256593A US25659351A US2851355A US 2851355 A US2851355 A US 2851355A US 256593 A US256593 A US 256593A US 25659351 A US25659351 A US 25659351A US 2851355 A US2851355 A US 2851355A
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cellulose
cooking
acid
semi
chemical
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Battenberg Ernst
Haas Heinz
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Zellsloff Fabrik Waldhof AG
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Zellsloff Fabrik Waldhof AG
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/04—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides
    • D21C3/06—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides sulfur dioxide; sulfurous acid; bisulfites sulfites

Definitions

  • the invention relates to a process for the preparation of semi-chemical cellulose pulp by the treatment of cellulose containing raw materials with an acidified bisulfite cooking solution at a pH of about 3.5-6, containing from l.43.0% of S at cooking temperatures between 115 and 140 C., to effect thereby a mild decomposition of the cellulose starting material, which only slightly attacks the cellulose and hemi-cellulose and which removes to a great extent the lignin binding the cellulose fibers in the middle lamellae of the starting cellulose material to produce cellulose fiber bundles which adhere so solidly that they require additional mechanical defibrillation to provide separate individual fibers in the product.
  • cellulose containing plant prod-- sets may be employed which are obtained from any convenient source such as deciduous or foliaceous trees, coniferous trees, soft woods, hard woods, annual plants, and plant wastes such as bagassee, palm oil fibers and alfalfa fibers.
  • the hard WOOdS may be hardwoods such as: Aspen (Populus tremuloides and delt0z'des)Large-toothed aspen (Populus grandidemata)-Beech (Fagus grandiyolis Antropuncea and .s'ylvatl'ca) Red alder (Alnus rubrflfisycamore (Platanus occidenlnlis)'fupelo gum (Nyssa aquatica)- Black gum (Nyssa sylvatica) Red gum (Liquidamber styraciflua) Red maple (Acer rubrum) White maple (Acer saccharinum) Buckeye (Aesculus glabra)-Cucumber magnolia (Magnolia acumirmta)-Yellow poplar (Liriodendron tulipifera)- American elm (Ulmus americana)--Easswood (Tilia americana
  • Stem-plants such as: Hemp stem (Cannabis saziva), manila stem (Musa textilis), jute stem (Corchorus capsularz's) paper mulberry (Broussonetia papyrz'yera), Agave (Agave rigida), sisal, flax straw (Linum usitatissimum), cane (arlmdo donax and Plzragmites), Ghinda Calotropis procera), cotton stems (Gossypium), sugar cane bagasse, bamboo (Bambusa arwzdinacea) are useful.
  • Plant wastes of special plants as: palm oil (Elaeis guineensis) fibers, and other fibers having same physicochemical composition, Cecropia may be used.
  • Wood Waste such as saw mill waste, ply-wood waste,
  • the semi-chemical pulp in the process of the application is obtained in yields of approximately 70-80% relative to the cellulose content of the starting material as contrasted with the yields of approximately 45% realized in the normal pulping process.
  • the alkaline semi-chemical decomposition processes consist in using the cooking liquors which are conventional for the sulfite or soda processes, in some cases with addition of accumulated waste liquors, which may be of lesser concentration, and conducting the cooking in such manner at temperatures of l60-170 C. and at a pH above 7 that the obtained semi-chemical fiber bundles are capable of mechanical defibrillation.
  • the alkaline decomposition process for the preparation of semi-chemical cellulose pulp is required to conduct the cooking of the lignin containing cellulose starting material to a point where the fibers are easily separated.
  • Such cooking under the alkaline conditions present in the cooking liquor and at the temperature employed causes a far greater loss of hemi-cellulose in the semi-chemical pulp product and at the same time provides lower yields as increasing amounts of lignin are removed. This results in poorer strength characteristics in the product.
  • the neutral sulfite process is carried out with concentrations of 3-5%, all the sulfurous acid being bound to alkali so that generally an excess of alkali is present, this process being therefore carried out at pH- values above 7.0 and at temperatures of 160-170".
  • the cellulose decomposition In the neutral sulfate process of alkali sulfate semichemical cellulose pulp decomposition the cellulose decomposition is greater, but there is a smaller dissolvingout of hemi-celluloses and extracted substances, and more lignin than obtained in the alkaline process.
  • the cellulose decomposition as compared to the other processes, is lower, the fraction of dissolved-out hemi-celluloses and extracted substances is higher, and the lignin solution is smaller.
  • the neutral sulfite process which is more expensive than the process of the invention because of its greater consumption of chemicals, has nevertheless been widely adopted in the United States because it was not heretofore possible according to known acid bisulfite processes to obtain semi-chemical cellulose pulp with sufficient strength properties, as compared to those from the neutral sulfite process.
  • This neutral sulfite process represents a compromise between the high yield of the acid bisulfite process and the good strength properties of the alkaline process.
  • Table 1 indicates that the acid semi-chemical pulps have the lowest lignin contents and at the same time the highest semi-cellulose contents.
  • Table 11 summarizes the operating conditions of the alkali semi-chemical pulp process, the neutral sulfite process, the acid sulfite process of the prior art and of the process of the invention.
  • the values indicated in Table 11 below encompass deciduous woods and coniferous woods of the most valuable type, the individual data corresponding to the particular wood being used.
  • the yield in the normal bisulfite process usually amounts to about -50% and for all semi-chemical cellulose pulp decomposition processes to about 70-85%. These yields are not determined by the process itself, but are dependent upon particular selected conditions.
  • deciduous wood e. g. aspen wood
  • Table III the manufacturing costs, callnto semi-chemical cellulose pulp according to the known culated from the costs of the chemicals and the total proprocess under alkaline, neutral and acld conditions, and 50 duction costs such as steam, water, labor, including colthen according to the process of the application, in each case to a 75% wood yield, there obtain the aforementioned total ingredients in the amounts as set forth in Table I.
  • the cellulose and lateral costs of unbleached semi-chemical cellulose pulp prepared according to the known process are compared with the corresponding costs for semi-chemical cellulose pulp prepared according to the process of the present invention, and that for deciduous woods (beech).
  • the values relate to one ton of absolutely dry (atro) semichemical cellulose pulp, at a 75% yield.
  • An object of the invention is the decomposition of cellulose containing starting materials with a bisulfite cooking liquor containing from about 1.4-3% of S at a pH of from 3.5-6 and a reaction temperature of about 115- 140 C. to obtain thereby a removal of the lignin from the cellulose fibers in the middle lamellae of the starting material and to provide a product which can be readily mechanically defibn'llated.
  • a further object of the invention is the preparation of semi-chemical cellulose pulp by the treatment of cellulose containing raw material with a bisulfite solution containing 1.4-3% S0 in the bisulfite liquor, at a pH of 3.5-6, and a reaction temperature of about 1l5-140 C., Where- 111 the cooking liquor is buttered by polyphosphates, metaphosphates, hexainetaphosphates, imidoacetic acid, nitrilotriacetic acid, etc. together with a base such as sodium hydroxide, sodium carbonate, potassium hydroxide, calcium hydroxide, magnesium oxide, aluminum hydroxide, ammonia and alkaline organic amines.
  • a base such as sodium hydroxide, sodium carbonate, potassium hydroxide, calcium hydroxide, magnesium oxide, aluminum hydroxide, ammonia and alkaline organic amines.
  • the semi-chemical cellulose pulp decomposition takes place in aqueous solution of S0 and of a base, such as bases derived from calcium, magnesium, sodium, ammonia, aluminum, etc., under reaction conditions which may broadly be considered as between those of the known acid bisulfite process and the neutral sulfite process.
  • a base such as bases derived from calcium, magnesium, sodium, ammonia, aluminum, etc.
  • reaction conditions which may broadly be considered as between those of the known acid bisulfite process and the neutral sulfite process.
  • This requires that the pH-value of the cooking acid, as compared with the pH-values of the acid process, be higher and that the SO -content as well as the reaction temperatures be lower, relative to the neutral sulfite process.
  • the new reaction conditions are explained in greater detail in the following.
  • the increase in pH-value of an alkali-, e. g. calcium bisulfite-cooking acid means that the quantity of free S0 is greatly reduced and the possibility of a hydrolytic decomposition of the cellulose decreased.
  • the reaction conditions prevailing in the neutral sulfite process are thus more nearly approached. With the individual cations, this is possible only to a certain extent, since a certain amount of free S0 has to be present if the bisulfite is to remain in solution.
  • the increase in pH-value can take place after buffering e. g. with NaOH, KOI-I, NH amines, etc.
  • the butfering agent has to be added in the presence of a com plex builder.
  • Complex builders are e. g. polyphosphates, such 'a Calgon (a water-softening agent consisting essentially of sodium hexametaphosphate), tripolyphosphates, sodium polyphosphate, sodium pyrophosphate, acid sodium pyrophosphate, etc., nitrilotriacetic acid or imidodiacetic acid.
  • the process employs a smaller quantity of S0 relative to the normal bisulfite decomposition.
  • About 45% of the lignin present is sulfonated and removed as lignin sulfonic acid or its salts in the process of the invention.
  • the reaction temperature exerts an essential influence on the hydrolysis of the hemi-celluloses and of the cellulose present.
  • a temperature increase is prejudicial to the fiber strength properties because of an increase in the hydrolysis.
  • Temperatures can be adopted for various degrees of acidity, below which temperatures, no appreciable impairment of fiber strength takes place.
  • the ratio of wood to liquor is, according to the invention, about 1 :4-5.
  • the time of impregnation i. e. of the first part of the cooking, amounts to about 3-7 hours, at temperatures which, compared to the end temperatures of the cooking proper, are about 20-30 C. lower than the end temperatures.
  • the cooking proper lasts 3-5 hours, the temperature being preferably raised in one stage.
  • the product is Well bleachable by the usual bleaching processes employing a total quantity of about 10-14% chlorine, the achieved degree of whiteness being between and units on the GE scale.
  • the bleachability is essentially better than that obtained according to the sulfite process, for which the bleaching degree is at most 85% on GE scale.
  • the yield in cellulose product rich in bleached semichemical cellulose pulp is 60-65%, relative to the wood, which yield also is greater than the yield of cellulose according to the neutral sulfite process.
  • the strength properties and bleachability of the semichemical cellulose pulp are considerably improved compared With the corresponding cellulose of the usual processes.
  • Semi-chemical cellulose pulps which are cooked to obtain yields of 75-80% have the best strength values, while with higher yields, i. e., with increasing lignin content, an increasing brittleness and a decrease in strength properties, especially in folding number, becomes perceptible.
  • the strength properties of the semi-chemical cellulose pulp prepared according to the process of the present invention are equal to those obtained from the material decomposed according to the neutral-sulfite process; a particular advantage relative to this process of the invention is the lower consumption of chemicals and thus the lower manufacturing costs.
  • a further improvement of the properties of the material is realized by bleaching, the strength properties being enhanced due to the removal of the lignin.
  • any suitable acid e. g. bisulfite liquor
  • the acid should be diluted and gassed-up to such extent that by addition of the calculated amount of dilute buffer solu tion, e. g. caustic soda solution, the particular SO -concentration desired is obtained.
  • the requisite caustic soda or the like for raising the pH value can not be calculated stoichiometrically but must be determined in each instance.
  • the character of the complex builder is of essential infiuence on the amount of buffer solution which has to be added. It appears that the addition of a certain amount of caustic soda solution for buffering reaches a maximum pH value in the presence of the complex builder and that, upon further additions, a drop in pH takes place which is accompanied by a strong clouding of the solution.
  • the cooking liquid is heated up to the temperature of 105-120", depending upon the starting material, necessary for the sulfonation.
  • the per se known impregnation, and formation of the lignin sulfonic acid takes place at these temperatures within about 3-7 hours, depending upon the starting material.
  • An increase in temperature of 10-20", above the foregoing temperature causes a hydrolytic splitting of the lignin sulfonic acid of the lignin sulfonic acid-cellulose compounds to take place in 3-5 hours, so
  • the semi-chemical cellulose pulp shreds obtained by the decomposition can be defibrillated into individual fibers in a known manner with the usual defibrillating devices, such as disk mills or the like, to obtain the resultant fibers which are of light color, somewhat like that of unbleached conventional sulfite cellulose.
  • the waste liquors can be recovered and used for the production of yeast.
  • the strength properties depend on the pH as shown by the following two examples for which two beech semi-chemical pulps were employed and having the same cellulose yield:
  • a cooking acid with a pH of 4.3 having a total SO -content of 1.57%, 46% of the S0 being bound to CaO, and 27% being buffered by NH
  • the pH value of 4.3 is realized by the addition of 50 mg./ liter of Calgon, Na P O a water softening agent containing sodium hexametaphosphate as the main constituent.
  • the cooking temperature is raised to C. in 1 hour, maintained at this temperature for 6 hours, heated 1 hour at 1l5 C. and 3 additional hours at C. After raising the temperature to 125 for 4 hours, as is necessary for the decomposition of the lignosulfonic acid, the cooking is ended.
  • the obtained semi-chemical cellulose pulp shreds are defibrillated in known manner in a disk mill.
  • the yields amount to 82% relative to the starting wood.
  • the degree of whiteness in percent GE was measured with an American General Electric Brightness Tester, which is described in TAPPI T217 m-48.
  • the degree of grinding fineness was determined with a Schopper-Riegler (SR) degree of fineness tester.
  • Copper viscosity was determined according to the Kiing-Modified Method of the Technical Association of the Pulp and Paper Industry, Sieber book, page 514 et seq.;
  • Alpha cellulose was determined according to TAPPI In a jacketed cellulose digester, a cooking acid which contains 1.6% total SO and 0.6% CaO is added to beechwood chips. The pH value is adjusted to 4.6 by buifering with 0.5 NaOH in the presence of 50 mg./liter of nitrilotriacetic acid N(CH CO H) After impregnation for 6 hours at 105", final cooking is carried out in 4 hours at 128 C. The SO -content of the cooking liquid is about 0.5% at the end of the cooking.
  • the Waste liquor contains 11% reducing substance.
  • the semi-chemical cellulose pulp obtained in a yield of 76%, determined according to standard methods, has the following strength properties:
  • the strength properties of the product which is prepared with a cooking acid of the same sO -concentration but without buffering according to the invention, are essentially lower.
  • the maximum tear length at 85 S. R. is only 6.5 km., the fold numbers run about 350 and the breaking pressure is 3.5 kg./cm.
  • Pine wood chips are covered in a cooker with a cooking liquid which contains 2.2% total S 0.56% CaO and 0.5% NaOH.
  • the pH value is adjusted to 4.2 by the addition of caustic soda solution in the presence of a tripolyphosphate of the formula, H P O
  • the initial temperature is maintained constant for 4 hours below 105.
  • decomposition of the lignin sulfonic acid is achieved by a 6-hour cooking at 135.
  • the SO -content of the cooking acid drops, during the cooking, to 0.4%.
  • the pH value is 3.4.
  • a 77% yield is obtained of a light-colored pine semi-chemical cellulose pulp, which is easily defibered, and which has a degree of decomposition (according to Sieber) of 97 and a Cu-viscosity of 250 cp.
  • the strength properties determined according to standard methods are the following:
  • the bleachability of the semi-chemical cellulose pulp is good. A yield of 59% relative to the wood is obtained. There are a degree of whiteness of 86%, a maximum tear length of 9000 m. and a folding number of 6000 in the product.
  • EXAMPLE 4 A ten-fold quantity of cooking acid, which contains 1.3% S0 0.64% CaO, 0.3% NaOH and 0.005% of a sodium polyphosphate of the formula, Na P O is added to an unsorted mixture of comminuted Wheat straw in a cooker provided with a circulating pump. After a precooking period of 3 hours and a cooking period of 7 hours at 123, a readily defibered product is obtained in a yield of- 81%. Of the added S0 12% can be recovered by degasification following the cooking.
  • EXAMPLE 5 In a jacketed cellulose cooker provided with a recycler, beechwood chips are treated with a magnesium bisulfite acid. The amount of S0 used is 88 kg. per ton of absolutely dry Wood. The pH value of the cooking acid, employed in the proportion of 5 cubic meters per ton of Wood, was raised to a pH of 6.2 by the addition of dilute caustic soda solution in the presence of 50 mg. per liter of sodium h'exametaphosphate of the formula (NaPO After an impregnation stage at C., the cooking takes place for a period of 4 hours at 152 C. maximum temperature. There is produced a semi-chemical cellulose pulp in a yield of 72%, which semi-chemical cellulose pulp can be defibered in normal manner in a disk mill.
  • the thus obtained cellulose is distinguished by an especially high pliability for beechwood as is shown by the very high folding number of 2000 at a degree of grinding of 83 Schopper-Riegler.
  • the tear length, at this degree of grinding, is 8000 meters.
  • the semi-chemical cellulose pulp can be bleached in a four-stage bleach with a total of 12.5% chlorine, relative to the material, to a whiteness degree of 83% GE.
  • EXAMPLE 6 Beechwood chips are treated in a cooker with a sodium bisulfite cooking acid having an SO -content of 1.6%. The quantity of cooking acid is adjusted that 4-5 cubic meters of acid per ton of wood is used. The NaOH- bound amount of S0 is of such magnitude that a pH value of 5.8 prevails. After a precooking and impregnating period of 8 hours and a following cooking period of 8 hours at a 73% yield of easily defibrillated prodnot is obtained.
  • the bleachability of the semi-chemical cellulose pulp is good.
  • any of the polyphosphates mentioned may be used interchangeably in appropriate equivalent quantities with the pyrophosphates, imidoacetic acid and nitrilotriacetic acid without any change in the process conducted and product obtained.
  • imidoacetic acid, nitrilotriacetic acid and pyrophosphates may be used interchangeably with each other and with the polyphosphates, without change in L the process conducted and product obtained.
  • Process for the preparation of semi-chemical cellulose which comprises treating cellulose-containing raw materials obtained from foliaceous trees, coniferous trees and annual plants with buffered bisulfite cooking solutions consisting of aqueous sulfur dioxide containing about 1.4-3.0% sulfur dioxide and a base selected from the group consisting of the hydroxides of calcium, magnesium, sodium, and ammonium, in an amount, depending upon the base and cellulose raw material employed, to provide an initial pH value of 3.5-6, cooking with said solution in the presence of a buffer selected from the group consisting of alkali metal hexametaphosphates, tripolyphosphates, polyphosphates and pyrophosphates at a 12 reaction temperature of 115-140" C., to repress the excessive hydrolytic decomposition of the cellulose and to remove a substantial amount of the lignin'binding the cellulose fibers in the middle lamallae, and thereafter mechanically subdividing the product into individual fibers.
  • buffered bisulfite cooking solutions consisting of

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US256593A 1951-02-28 1951-11-15 Process for the preparation of semi-cellulose Expired - Lifetime US2851355A (en)

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BE (1) BE504423A (en, 2012)
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FR (1) FR1062445A (en, 2012)
GB (1) GB736300A (en, 2012)
NL (1) NL90306C (en, 2012)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3046184A (en) * 1958-12-31 1962-07-24 Kimberly Clark Co Manufacture of cellulosic products
US3088861A (en) * 1960-08-03 1963-05-07 Weyerhaeuser Co Method of manufacturing chemical pulp from lignocellulose material
US3448003A (en) * 1966-01-03 1969-06-03 Dow Chemical Co On-stream cleaning of wood chip digesters using chelating agents
US3769152A (en) * 1970-05-13 1973-10-30 Mo Och Domsjoe Ab Digestion of wood with oxygen in the presence of alkali
US8747709B2 (en) * 2012-05-03 2014-06-10 Empire Technology Development Llc Phosphonate-substituted lignin as a flame retardant
WO2016145276A1 (en) * 2015-03-11 2016-09-15 Andritz Inc. Processes and systems for the pulping of lignocellulosic materials

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2906659A (en) * 1953-07-13 1959-09-29 Abitibi Power & Paper Co High yields bisulphite pulping process
US3013931A (en) * 1957-02-01 1961-12-19 Hawaiian Dev Company Ltd Printing paper and process of making the same
US3069310A (en) * 1960-10-14 1962-12-18 Hammermill Paper Co Semichemical pulping process for soft woods

Citations (9)

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Publication number Priority date Publication date Assignee Title
BE496841A (en, 2012) * 1949-07-12
US1244525A (en) * 1917-08-02 1917-10-30 Tsuneya Marusawa Process of manufacturing paper-pulp.
US1566118A (en) * 1925-03-21 1925-12-15 Citizens Of The United States Method for the prevention of corrosion in steel digesters
US1792510A (en) * 1925-07-01 1931-02-17 Brown Co Kraft-simulating pulp and process of producing same
US1859848A (en) * 1926-09-03 1932-05-24 Arthur M Hyde Production of fibrous pulp from vegetable material
GB384455A (en) * 1931-01-09 1932-12-08 Patentaktiebolaget Grondal Ram An improved process of producing sulphite cellulose
US1891337A (en) * 1930-01-09 1932-12-20 Du Pont Process of producing cellulose
US2019598A (en) * 1932-03-04 1935-11-05 Dreyfus Henry Production of cellulosic materials or cellulose
US2564028A (en) * 1946-01-17 1951-08-14 Rayonier Inc Wood pulp digestion

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1244525A (en) * 1917-08-02 1917-10-30 Tsuneya Marusawa Process of manufacturing paper-pulp.
US1566118A (en) * 1925-03-21 1925-12-15 Citizens Of The United States Method for the prevention of corrosion in steel digesters
US1792510A (en) * 1925-07-01 1931-02-17 Brown Co Kraft-simulating pulp and process of producing same
US1859848A (en) * 1926-09-03 1932-05-24 Arthur M Hyde Production of fibrous pulp from vegetable material
US1891337A (en) * 1930-01-09 1932-12-20 Du Pont Process of producing cellulose
GB384455A (en) * 1931-01-09 1932-12-08 Patentaktiebolaget Grondal Ram An improved process of producing sulphite cellulose
US2019598A (en) * 1932-03-04 1935-11-05 Dreyfus Henry Production of cellulosic materials or cellulose
US2564028A (en) * 1946-01-17 1951-08-14 Rayonier Inc Wood pulp digestion
BE496841A (en, 2012) * 1949-07-12

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3046184A (en) * 1958-12-31 1962-07-24 Kimberly Clark Co Manufacture of cellulosic products
US3088861A (en) * 1960-08-03 1963-05-07 Weyerhaeuser Co Method of manufacturing chemical pulp from lignocellulose material
US3448003A (en) * 1966-01-03 1969-06-03 Dow Chemical Co On-stream cleaning of wood chip digesters using chelating agents
US3769152A (en) * 1970-05-13 1973-10-30 Mo Och Domsjoe Ab Digestion of wood with oxygen in the presence of alkali
US8747709B2 (en) * 2012-05-03 2014-06-10 Empire Technology Development Llc Phosphonate-substituted lignin as a flame retardant
US8852468B2 (en) 2012-05-03 2014-10-07 Empire Technology Development Llc Phosphonate-substituted lignin as a flame retardant
US20140378671A1 (en) * 2012-05-03 2014-12-25 Empire Technology Development Llc Phosphonate-substituted lignin as a flame retardant
US9410088B2 (en) * 2012-05-03 2016-08-09 Empire Technology Development Llc Phosphonate-substituted lignin as a flame retardant
WO2016145276A1 (en) * 2015-03-11 2016-09-15 Andritz Inc. Processes and systems for the pulping of lignocellulosic materials
CN107429484A (zh) * 2015-03-11 2017-12-01 安德里兹有限公司 用于木质纤维素材料的制浆的方法和系统
US10724174B2 (en) 2015-03-11 2020-07-28 Andritz Inc. Processes and systems for the pulping of lignocellulosic materials
US11352746B2 (en) 2015-03-11 2022-06-07 Andritz Inc. Processes and systems for the pulping of lignocellulosic materials

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BE504423A (en, 2012)
FR1062445A (fr) 1954-04-23
NL90306C (en, 2012)
CH300957A (de) 1954-08-31
GB736300A (en) 1955-09-07

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