[1]8-1,0 7 S R CR-OSS REFERE@llCF. SEARCH, RNti FIP8303 XR 344819827 United States Patent @f,"'Y'ffice P a t e n t e d D e c . 2 , 1 9 6 9 3,481,827 PROCESS FOR BLEACHING WOOD PULP WITH FLUORINE, HYDROFLUORIC ACID, AND OXYGEN DIFLUORIDE Arthur M. Brooks Baltimore, Md., assignor to W R Grace & Co., iqew York, N.Y., a corporatio@ oi Connecticut No Drawing. Continuation-in-pait of application Ser. No. 582,177, Aug. 25, 1966. This application Aug. 2, 1968, Ser. No. 749,620 Int. Cl. D21e 9112 10 U.S. Cl. 162-63 5 claims ABSTRACT OF THE DISCLOSURE 15 A method of bleaching wood pulp with fluorine, hydrofluoric acid, or oxygen difluoride. The pulp is contacted with from 0.5 to 9% by weig4t of pulp of one of the above compounds for a period of from I to 4 hours and at a temperature of from 60-160' F. Subsequent to the bleaching process the bleach liquor is treated with a cal- 20 pium compound, such as, lime to precipitate the fluorides in the liquor. CROSS REFERENCE TO RELATED 25 APPLICATION This application is a continuation-in-part of U.S. Ser. No. 582,177, filed Aug. 25, 1966. BACKGROUND OF THE INVENTION This invention relates to processes of bleachin.- flbrous materials. In one aspect, the invention relates to p@ocesses o f bleaching wood pulp and natural fibers, such as ire used i n the pr I ocesses for making p@per, and the like. In a 3 5 f urther aspect the invention ref@tes to a process for the c ombined bleachiiig and . removal of siliceous compounds f rom the nodes of grasses such as bagasse and the like. I n another aspeci, the invention relates to a bleachiing 4 0 p rocess. in which pollution cauied by waste liquors and Wash waters can be more readil@ removed by sub equ-.nt tr eatments. I n a further aspect, my invent.ion relates to a combined b leaching and pollution treatin@;g process which siubstan4 5 ti ally reduces or eliminates pollution caused by waste li quors and wash waters. THE PRIOR ART The prior art processes of bleaching wood pulp and 5 0 o ther cellulosic fibers to high whiteness and brightness u sing chemical bleaching agents such as chlorine or hypoc hlorite are frequ6ntly accompanied by deleterious fiber d egradation or deterioration during the bleaching. Curr ent bleaching technology, particularly applied to the 5 5 b leaching of chemical wood pulp for paper, uses chlorine, c austic soda, calci,um and'sodium hypochlorites, chlorine d ioxide, sodium 6nd hydrogen peroxides. With groundwood pulp, reducing agents, such as zinc or sodium hydros ulphite may be used, with or without the use of hydro6 0 g en peroxide. In the usual conventional processes, several c hemicals are used in series or stages, with residues from t he reaction usually b-@ing washed out between the stage@. I n spite of the Iarge amount of work that has been done i n this field, and the large number of multi-stage bleaching 6 5 p rocesses that have been developed, there is still no comp letely satisfactory, answer to the problem of bleachiiig wi'hout some fiber d6gradation. F urther, the wash waters, particularly from the bl6achi ng of wood pulps, present a disposal and pollution prob7 0 l em since they usually contain unexhausted bleaching 2 chemicals as well as the materials removed from the pulp by the bleaching process. The prior art has discovered that chlorine dioxide used in one or more stages has:the property of bleaching without substantial degradation, but chlorine dioxide is quite costly and requires special handling due to its explosive tendency. Thus, chlorine dioxide does not represent a completely satisfactory solution. The use of hydrofluoric;icid to remove adventitious and adhering sand from cotton linters is known to the art as described in U.S. Patent 1',911,030. However, the use of fluorine or fluorine compotinds to effect combined bleaching and removal of siliceous compounds which are internally formed within or as-a part of the nodes of grasses such as bagasse is to my knowledge heretofore unknown. Thus, it would be very 4@sirable to provide a bleaching process which would alleviate both the fiber degradation and pollution problems of the prior art. OBJECTIVES AND SUMMARY OF THE INVENTION Objects It is therefore an objedt of my invention to provide improved bleaching processes and also to provide bleaching processes which facilitate pollution control. It is a further object of my invention to provide improved bieaching processes which cause substantially less fiber degradation. It is a stiII further obj6ct of my invention to provide It is another object of my invention to provide bleaching processes using fluorine 6r a fluorine-generating compound as a bleaching agent for fibers. It is also an object of m@ invention to provide a process for the combined bleachin'g and removal of siliceous compounds from the nodes of,.'grasses such as bagasse, wheat straw, esparto grass and th6 like. It is still another obje'pt of my invention to provide bleaching processes wher6in the wash waters 6nd waste liquors from the bleaching process can be handled in a manner to eliminate or n@arkedly reduce the p6llution of water courses to which tli6y are usually run, or the pollution of the general enviroriihent. Another object of my ir@Vention is to provide combined fiber bleacbing and polltition removal processes. Additional objects will be apparent, and in part obvious, from the following description and appendant claims. Summary In summary, I have discovered that these and oiher objects can be obtained by the use of fluorine and/or the reaction product of fluorine compounds, as a bleaching agept. I have also discovered that a very substantial increase in brightness can be secured in bleaching fibrous maerials, such as for example, wood pulp, by treating it with fluorine compounds or gaseous fluorine and further that this bleaching is accomplished with very little fiber degradation. While my invention is particularly advantageous for the bleaching of wood pulp, it is also well suited for the bleaching of natural fibers in general. However, m@ bleaching process sh6uld be distinguished from processes such as are used to remove stains from fabrics. According to my bleaching process the actual whiteness and brightness of the fiber in its nalural state is increased prior to its manufacture into paper or fabric. By brightness is meant the index of light reflected from a light s6urce having a wave length of about 457 angstroms measured by the General Electric Brightness tester. The bleaching process according to my invention can '30 bleaching processes whicfi yield fibers having increased Field of the invention brightness.
[2]3@481,827 3 b e carried out using conventional mechanical procedures a nd equipment such as is for example used for bleaching w ith chlorine or chlorine compounds, but using at least o ne gaseous fluorine or fluorin6 compound bleaching step. I n summary, the process controlling bleaching polluti(>-.1 5 a ccording to my invention coinprises treating the waste li quors and wash waters from my bleaching pro.-ess with a reactive calcium compound, conveniently lime. The fluo rine constituent will be partially or completely, depe@idin g upon interfering substances, precipitated as an insol1 0 u ble calcium compound. This precipitate can then be rem oved by conventional liquid-solid separation processes; s uch as for example settling, c@ntrifuging, filterin 6 the g r @l io @--or by a combination of such separating processes. D ESCRIPTION OF THE I PREFERRED 1 5 E MBODIMENTS C onsidering now my invention in greater detail, my in vention can be conveniently described with reference to a conventionai bieaching seque'nce. 2 0 A conventional bleaching sequence, for example, uses a s eries of stages which for coyenience are designated by c ertain letters. For example, C is used to designate c hlorination, E for extracting using caustic soda, H for s odium or calcium hypochlorite, D for chlorine dioxide 2- 5 a nd P for hydrogen peroxide, Thus, for example, a bleachin g sequence for a sulphite ptilp might be designated as C EH; C for chlorination, E f6r caLlStiC soda extraction, la nd H for hypochlorite. A bleaching cycle for sulphate p ulp might be designated as CEHED; i.e. chlorination, 3 0 e xtraction, hypochlorite, extraction and chlorine dioxide. A nother cycle mig4t,be six stage as CEHEHD; i@e. chlori nation, extraction,,hypochlorite, extraction, - hypochlorite a nd chlorine dioxide. Another cycle might be CEDED. It is apparent that many other combinations may be tised a ccording to the properties desired in the bleached pulp a nd the starting material used in the process. T he C stage is used mostly for purification of the pulp b y chlorinating th6 non-cellulosic materials present s@ch A s lignin. The E stage is used to solubilize and wash out 4 0 c hlorinated substances. The H stage is used to bleach @nd w hiten the pulp and the D stage is added to further whiti3n th e pulp without substantially decreasing its strength. The P stage is sometimes used at..the end to reduce losk of b rightness of the pulp,upon aging. 4 5 In each stage it is importa'nt to control the concentrati on or "consistency" of the pulp in stispension 'm water (c alled consistency by the industry), the percentage of the ch emical used based upon tkO amount of fiber present, th e temperature, the contact time, sometimes known as 6 @0 " dwell" time, and the pH. In the first stage of my process, I can use a fluorine gas previously dissolved in water or passed directly into ,the pulp suspension. Alternatively gaseous fluorine can be generated in the presence 'of the pulp. Another suit @able source of fluorine is commercial anhydrous hydrogen fluoride; this can be added directly to the pulp suspension .alone or in combination with gaseous fluorine or sodium fluoride. Further, any fluorine compound which will act, or can be suitably, activated,to act, as a fluorinating or 6. 0 oxidizing agent can be used in the practice of my in@ention. The effects of the fluori.ne or its compounds upon the pulp are completed before the pulp is exposed to human contact. The fluorine bleaching treatment of fiiy invention can be carried outby contacting the pulp with 6@ fluorine or a suitable fluorin6 compound in an amo;unt equal to 0.5 to 9 percent by wcight based on the weight 6f the pulp at a temperature of,about 90 to 160' F. fbr a period of I to 4 hours. Suitable bleaching agents which can be used in any process include fluorine, - hydroflu6rine 70 acid and oxygen difluoride. , I prefer to designate my fluorine stage as F so that it clan be written for example in a bleaching sequence as IEH meaning: fluorine, extraction and - hypochlorite. Other examples where. a fluorine stage can be used in 75 4 place cf a chlorine stage, according to my invention, include systems designated FEHED, PEHEHD, FEDED, FED and th-- like. Particulraly useful forms of fluorine compounds are the oxy compounds, such as for example, oxygen difluoride (OF2)- Oxygen difluoride canconveniently be prepared in a continuous @rocess by bubbling fluorine into a 2% by weight sollition of sodium hydrox . The effluent from this process is an oxvgen difluoride gas that can be passed directly into th-!,. pulp at any stage of my bleaching process. This is particularly useful in a final superbleaching stage such as,is usually carried out by the use of chl6rire d4 xide. Ev where chlorine d' xide is used 10 en 10 in: @ star@ other th the final stage, oxygen difluo ide an r c@n be used to replace ii in that stage. Oxygen difluoride articularly suitable source 6f fluorine for the purpose is a p of my invention since it decomposes into the components oxygen and fluorine at the temperatures of operation used in the rormal bleaching system. Hereafter, I shall for convenience, designate the use of oxygen difluoride as the 0 stage. The amounts of fluorine compounds to be added in my novel process will closely parallel the amounts of chlorine compounds which would be used in a chlorine system. Thus, if fluorine is add6d, it is used in the amount of 4 to 901o, usually about 7% by weight based on the pulp in the first stage, and the gaseous fluorine, added as such or generated in the pulp. Typ:cally, a 3 % piilp consistency is used. The bleaching reaction can, for example, be, carried out at the temperature of about @ 80 to 90' F. with a retention time of about I to 4 hours, usually about 1112, hours. The extraction stage with caustic soda can be carried out with a solution of 1/2 to 3 "lo by weight caustic soda, preferably about 21/2% caustic soda at a pulp consistency of preferably about 12% and a temperature of about 120' F. to 180' F. for a period of preferably about 1 hour and an alkaline pH. in the dioxide stage of the process, the reaction @would be carried out preferably ably with about O@5% of the fluorine compound at prefer about 12% by weight consistency, at a temperature about 160' F. for a period of about I hour. In normal op-@ration, the pulp would be washed between stages. If the pulp were to be treated with a peroxide, it would be a final treatment of the bleached pulp using about 1% Ily without subsequent washing. More broadly this usua embodiment of my invention comprises the steps of' fluorination of the pulp with flliorine or a suitable fldorine compoun'd; washing and@extracting the pulp with a sodium hydroxide sblution; treating the pulp with oxygen difluoride; and then washing and recovering the bleached product. A more specific form of this general embodiment the fluorination is carried out using a gaseous hydrogen fluoride at a fluorine concentrati6n of 2 to 9% and the oxygen difluoride treatment is carried out with .5 to 15% of the compound (i.e. oxygen difluoride) and a pulp consistency of 3 to 12%. Considerable variation can be practiced in the amount of chemicals, consistency of the pulp, temperature, dwell time and the number and sequence of steps; and can be arranged to obtain the desired results as to pulp quality, brightness, opacity, strength, viscosity, permanganate number and the like, within, of course, the limits of the original pulp and the effectiveness of the cbemical emDloyed. Optimum operating conditions can be obtained by @outine experimentation. Groundwood pulps are bleached according, to the prior art process, in a single stage using about 1% sodium or zinc hydrosulphite at 2 to 5% consistency for about 1 to 2 hours, a temperature of about 110 to 150' F. and a pH of about 4.5 to 6 for the zinc and a pH of about 6-7 for the sodium salt. The single stage can be supplemented by a subsequent stage of 1% sodium or hydrogen peroxide (stabilized with sodium silicate and magnesium sulphate) at 10 to 15% consistency and an alkaline pH for about 3 to 4 hours at 100' F. In accordance with my
