US2687352A - Process of refining hardwood pulp - Google Patents

Description

Aug. 24, 1954 B. G. Hoos 2,687,352

PROCESS OF REFINING HARDWOOD PULP Filed Feb. 21, 1946 s Sheets-Sheet 1 INVENTOR.

r //-vS 1 Qw ION Stock-Densz'i'y.

2.0 5.0 L CAUSTIC SODA EOLUTION T U L Q s A D O 5 m m U A P L m W m FER CENT I NITM 0 000000 MM8W65 32| I Aug. 24, 1954 B. G. Hoos 2,587,352

PROCESS OF REFINING HARDWOOD PULP Filed Feb. 21, 1946 3 Sheets-Sheet 2 PER CENT INITIAL CAUSTIC SODA SOLUTION PER CENT INITIAL STOCK DENSITY Ill] u. I00 I 0 90 u fi an m g? 70 065%S1ockflensli'y. mo 2 a 60 +10% 2 150 0/57; In 5 x252 3 CL 40 5 o 5!] Lu g 20 l0 4 D 0 0 .l 0.2 0.3 0.4 INVENTOR.

F'ER' CENT ETHEH-SOLUBLE CONTENT OF F'ULF.

Aug. 24, 1954 B. G. HOOS 7,

PROCESS OF REFINING HARDWOOD PULP Filed Feb. 21, 1946 3 Sheets-Sheet 3 CAUSTIC ABSORBENCY INSTABILHY FACTOR OF PULP aw m f n 0 .05 .10 J5 .20 .25 .50 .55 PER CE NT ETHER-E OLUBLE CONTENTQF PUL INVEN TOR.

BY aw M 1:

@W WZQM Patented Aug. 24, 1954 UNITED srArs erENT OFFICE PROCESS OF REFINING HARDWOOD PULP Benjamin G. Hoos, Berlin, N. H., assignor, by mesne assignments, to Brown Company, Portland, Maine, a, corporation of Maine Application February 21, 1946, Serial No. 649,297

6 Claims. 1

This invention relates to the productionfrom hardwoods, such as white birch, yellow birch, maple, beech and the like, of a cellulose pulp product useful in the production of cellulose derivatives, particularly cellulose ether, and is concerned specifically with the production for such use of refined alpha pulp from sulfite or sulfate stock constituted of the above type of hardwoods.

Quality of cellulose derivatives is directly alfected by the characteristics of the source of cellulose from which the derivatives are produced. Softwood pulps, such as refined spruce sulfite pulp, may be readily produced which have the necessary characteristics for high grade cellulose derivative production and for the production of cellulose ethers, but, prior to this invention there has been no known hardwood pulp which could be satisfactorily substituted in these uses for the softwood pulps, despite the lower cost advantage which would result from such substitution. Hardwood pulps have been wholly unacceptable in continuous cellulose ether processes.

Softwood pulps of the above type are acceptable for these uses because of their low ethersoluble resin content. However no known process of refining or otherwise treating pulp has been capable of producing the necessary low resin content in the case of hardwood stock as distinguished from softwood stock.

Reduction of resin content in hardwood pulprefinement is dealt with in Richter Patent No. 2,228,127. This patent proposed as a remedy for excessive lignin and/or resin content subjecting preliberated hardwood pulp to a multi-stage sequence which included an initial hypochlorite treatment to prevent excessive development of resistance in the resins of the pulp. -In such manner the patentee was successful by. a multi-stage prebleach-chlorinationhot caustic soda-soap digestionalkaline bleach sequence in realizing ether-soluble constituentsor resin content of only about 01 to 0.2%, as shown in Example 1 of that patent.

My experience has shown that, while pulp with these ether-soluble contents has valuable uses, its ether-soluble content is still too high for manufacture of high quality cellulose derivatives. In addition, such pulps are not adapted for use in continuous cellulose ether processes because they have too slow absorption rate for the caustic solutions therein used. No modification in the Richter multi-stage process has produced a hardwood pulp possessing absorbency rates for caustics sufficiently high, after a usual storage period, to permit its acceptance as a reliable source material in such continuous processes.

In fact, prior to this invention, such. qualities as unacceptably high resin content and poor absorption of caustic solutions have left hardwood pulp products, as a class, unadapted as materials for high quality cellulose derivative production or for any cellulose derivative production which involves caustic treatment of the pulp as in the production of cellulose ethers.

The primary object of this invention is to produce a hardwood pulp, particularly of mixed hardwoods, which has, along with other acceptable qualities, including an alpha cellulose content exceeding 92.5%, a caustic solution rate of absorption which renders the pulp useful in commercial cellulose derivative processes involving caustic solution treatment and which absorption rate is relatively independent of time so that storage intervals do not affect the desired absorbency quality to a point beyond a practically useful limit, thus lending the pulp to use as an improved source for cellulose other production. Hardwood pulps of this invention also have exceedingly low ether-soluble contents never before attained in the pul industry, and which lend the pulp to widespread use in general cellulose derivative production, as a lower cost substitute for softwood pulp, even when a high rate of caustic absorption is not an essential quality. It has been established that caustic absorption of the pulp is directly related to ether-soluble content so that by precise control of ether-soluble content, desired caustic'absorbency rates are simultaneously secured. More broadly, then, an object of this invention is the production of a hardwood pulp which is substantially free of ether-soluble resin content.

The invention has for a further object the provision of a process for yielding hardwood pulp of the above characteristics.

For the purposes of this application, certain terms are herein used with the following meaningsz Caustic absorbency connotes the time interval in seconds between the deposit and complete absorption of a drop of 35% NaOH solution at 25 C. from a 5 diameter glass rod, rounded on the end, on and by a simulated dryer sheet of about 300 basis (weight in pounds of 480 sheets, 24 inches by 36 inches) prepared by pressing 5 inch diameter wet sheets under a one ton weight and then drying on a drum heated by steam at 20 pounds gauge steam pressure, the sheets being turned every two minutes.

Initial caustic absorbency is caustic absorbency before storage of the sheets.

Ultimate caustic absorbency is caustic absorbency after the simulated dryer sheets have been submitted to an arbitrary accelerated aging by heating for 16 hours at 100 C.

Caustic absorbency instability factor is the ratio of ultimate to initial caustic absorbency.

In accordance with this invention, hard-wood pulp products are formed having ether-soluble contents less than 0.10%, ultimate caustic absorbency values less than about 40 seconds, which represents a practical maximum absorbency value acceptable for commercial cellulose ether production, initial caustic absorbency values preferably less than seconds, and caustic absorbency instability factors not greater than about 2.8.

It has been found that these desirable characteristics may be attained in hardwood pulp products by establishing in a three-stage refining sequence involving prebleach-hot caustic soda soap digestion-alka1ine bleach, novel relations of stock density and caustic solution concentration in the digestion step.

An example of preferred procedure is as follows:

Wood chips made from mixed hardwoods such produce 10% stock density and a 2.2% NaOH and 0.33% soap concentration, both based on the weight of the liquor. The pulp was then digested at 205 to 210 F. for 5 hours. The pulp was then washed, thickened to 12% stock density and treated from 3 to 4 hours at 110 F. with 0.7% chlorine equivalent as sodium hypochlorite plus 0.25% NaOH, based on the weight of the pulp, at 10% stock density. The pulp was then washed, treated with a dilute S02 solution to neutralize residual chlorine and then washed again. The washed pulp was then formed into simulated dryer sheets.

For purposes of comparison, a control was established wherein the only variant was the use of l%.% NaOH solution which is about the customary concentration, instead of 2.2% NaOH solution.

The simulated dryer sheets had the following characteristics The ultimate caustic absorbency of the control sample, 595 seconds, way over the maximum of =10 seconds, is so poor as to render this pulp wholly unacceptable for use in commercial cellulose ether production involving continuous saturation of the pulp sheet with a caustic soda solution. On the contrary, the initial and ultimate caustic absorbency values of 15 and 34 seconds, respectively, of the higher caustic usage sample are within the range suitable for use in such production. Furthermore, the relatively high ether-soluble content of the control sample renders the pulp unsuitable for use in the production of any high quality cellulose derivatives.

As the above example illustrates, ultimate caustic absorbency is brought within the range of usefulness for cellulose ether production and ether-soluble content within the desired low range by utilization of excess caustic during as white birch, yellow birch; beech and maple 5C digestion at the 10% stock density of the ex- Were cooked in a sodium-base sulfite cooking acid amp e. containing 5% free S02 and 1% combined S02. Experiments indicate, however, that there is a The liberated fiber was washed, screened and fi e a ip. in the production of P 1 thickened. The unbleached fiber was then having the preferred characteristics of this intreated at 4% stock density for 30 minutes at vention, between initial stock density and initial F. with the equivalent of 1.4% chlorine, based caustic concentration in the digestion sequence. on pulp, as sodium hypochlorite. This pre- The efiect of variation of caustic per cent at bleached fiber was washed and thickened to 10% stock density upon ultimate caustic absorbabout 14% stock density. The thickened fiber ency is shown in the following table, the process was then mixed with suflicient 25% caustic soda 00 otherwise remaining as stated in the example solution, 10% soap solution, and hot water to given above:

Table II I 't'al Ultimt- Ca t' 53% Percent 3235 332? o tuc Caust ic Abso l l lfb lfl cy Solution Stock Solution Soluble g ggg gg figgg gg ia ggg 1. s3 10 as o. 27 25 595 23. s 1. e7 10 .33 0. ll 31 269 s. 1 1. 94 1o 33 0. 09 29 104 a. s

2.22 10 .33 0.09 15 a4 2.3 a. s3 10 a3 0. 04 7 11 1. 6 4. 44 1c .33 0. 04 7 10 1. 4 5.55 10 .33 0.06 5 7 1.4 6.66 10 .33 0.08 5 9 1.8

. Examples appearing below the horizontal line have ultimate caustic absorbency values within the desired low range, as contrasted to the higher unsatisfactory values of those appearing above the horizontal line.

The effect of variation in stock density at different percentages of NaOH are shown in the following table, the process again remaining otherwise the same, and the horizontal lines again segregating, in the case of each stock density,-

caustic per cent solution producing desirable and undesriable ultimate caustic absorbencies.

Table III Initial Ultimate ggggfifi Percent Percent Percent Percent Caustic Caustic ency Stock NaO H Soap ther Absorb- Absorb- Instw Solut1on Solution Soluble ency m ency 1n bflity Seconds Seconds Factor 6. 25 l. 67 33 0. 07 8. 9 25 2. 8 6. 25 1. 94 33 0. 03 6. 1 12. 75 2. l 6. 25 2. 22 33 0. 02 6. 1 12. 75 2. 1 6. 25 3. 33 .33 0.02 6.1 11 1.8 6. 25 4. 44 33 0. 03 5. 4 10. 25 1. 9 1G 1. 33 33 0. 18 10. 0 83 8. 3 16 1. 67 83 0. 18 10. 4 51 4. 9 16 l. 94 33 0. 11 10. 5 42 4. 0

Certain relations shown in the above tabulations are plotted in the graphs shown in the accompanying drawings, in which Fig. 1 shows curves of initial caustic soda concentration in per cent plotted against percentage ether-soluble content of the pulp, for 6.25, 10, 16 and 25% initial stock densities, respectively;

Fig. 2 shows curves of initial caustic soda concentration in per cent plotted against ultimate caustic absorbency values in seconds, for 6.25, 10, 16 and 25% initial stock densities, respectively;

Fig. 3 shows a curve of initial stock density plotted against per cent caustic solution defining the lower limit of ratios therebetween necessary for the production of the pulps of this invention;

Fig. 4 is a graphical representation of percentage ether-soluble content of the pulp plotted against ultimate caustic absorbency values in seconds, for 6.25, 10, 16 and 25% initial stock densities, respectively, and indicating in broken lines the approximate maximum values for ether-soluble content and/or ultimate caustic absorbency in pulps of this invention; and

Fig. 5 is a curve similar to that shown in Fig. 4 except that the ether-soluble content is plotted in Fig. 5 against caustic absorbency instability factor instead of against ultimate caustic absorbency as in Fig. 4 and again showing in broken lines the approximate maximum values for the production of pulps in accordance with this invention.

As indicated by the curve of Fig. 1, ether-soluble content drops exceedingly rapidly with increase in initial per cent caustic usage and after reaching a certain critical initial caustic usage for each stock density producing ether-soluble contents less than-0.10%,ether-soluble content values are 0.10% ether-soluble content abscissa of Fig. 1. The curve AB of Fig. 3 thus represents the lower limit of initial stock density to per cent caustic solution ratio permissible for the production of preferred pulps of this invention, a plotted ratio, when falling in the area above the curve AB of Fig. 3, producing such a pulp and when falling in the area on or below the curve AB, not producing such a pulp.

In Fig. 4, values shown in Figs. 1 and 2 are plotted to show per cent ether-soluble content against ultimate caustic absorbency in seconds. Pulps of this invention have ratios which, when plotted on the graph of Fig. 4, fall to the left of the vertical broken line or under the horizontal broken line or both. A similar segregation of satisfactory and unsatisfactory pulps is represented in Fig. 5 wherein the ether-soluble content is plotted against caustic absorbency instability factor in lieu of ultimate caustic absorbency in seconds. Pulps of this invention have values falling to the left of the vertical dot and dash line or under the horizontal dot and dash line or both. I As shown by the curve AB of Fig. 3, for initial stock density values greater than about 14% it is essential, to produce preferred pulps of this invention, to utilize caustic solutions in excess of 2% and progressively increasing. Below about 14% initial stock density, as indicated by the curve AB, the caustic solution per cent may go below 2% and still produce satisfactory low ethersoluble content pulps.. In fact, the minimum caustic solution percentage for values of initial stock density less than about 14% are related to the amount of excess caustic present over that necessary to refine the pulp. The efiect of caustic excess for values of initial stock density of 6.25

and 10% initial stock densities are illustrated in the following tabulation:

Table IV Initial Caustic Residue Percent Percent Caustic Residue Percent Ether- Stock Percent of Percent of of Caustic Soluble Solution Solution Input Content 10 1. 67 0. 65 39 0.14 10 l. 33 O. 30 22. 6 0. 27 6. 25 2. 22 1. 54 69. 4 0. (32 6.25 1. 94 l. 25 64. 5 0. 03 6. 25 1. 67 1.01 60. 5 0. 07

As shown by the above table, at initial stock densities of 10 and 6.25%, respectively, ethersoluble contents less than 0.10% are produced only in those cases (appearing above the horizontal lines in Table IV) where the per cent caustic residue based on initial caustic input is exceedingly high as compared with the residues encountered in normal refining processes, which are always maintained as low as possible and rarely, if ever, exceed 10%. For practical purposes of this invention the residue in the case of initial stock densities less than about 14% must exceed 25% of the initial caustic input and running in some cases at the lower densities, as shown by the above table, upwards of 60% where ether-soluble contents materially below 0.05% are desired.

In practice, the waste liquors derived from digestion of pulps of this invention, when relatively concentrated both in caustic and the more expensive soap may be recycled by being fortified with additional soap and caustic without any detrimental result on the product. Despite continued recycling use, no loss in the efficiency of the process has been found.

With regard to soap usage, the concentration should be in excess of about 0.11% and preierably the concentration is 0.20% or greater. Soap concentrations of 0.33% have been found to be particularly suitable. The effect of variation in soap concentration at 10% stock density is shown by the following table:

Table V i nitial "iglltimrte Gaugtic Percent Percent Percent austm ans Absor Absorb- Absorb- Insta- Soap NaOH Stock ency in ency in bility seconds seconds seconds 11 2. 22 I 10 36 450 12. 0. 33 2. 22 i l0 l4. 8 34 2. 3 0. 56 2. 22 13. 5 22 l. 6 0. 33 l. 33 10 25 595 23. S 0. 56 l. 33 10 27. 5 393 14. 3

The resin or ether-soluble content of the pulp given herein is determined by the standard method for ether extraction known as T204-m of the Technical Association of the Pulp and Paper Industry.

I claim:

1. The process of refining preliberated hardwood pulp to ether-soluble contents less than 0.10% in a multistage chemical refining process, including a hot caustic-soap stage, comprising subjecting the hardwood pulp, in the hot causticsoap stage, to hot caustic :soda refining liquor having @a soap concentration between about 0.11% and 0.56% based on the solution, and regulating the initial stock consistency in said stage between about 6.25% and about 25% and the concentration of caustic soda in the refining liquor in said stage between about 1.54% and 6.66% based on the solution, so that in a graph plotting the per cent initial stock consistency against the per cent initial caustic soda based on the solution, the per cent of caustic soda based on the solution lies above a straight line extending through the plots for about 1.54% caustic soda concentration at 6.25% stock consistency and 2.7% caustic soda concentration at 25% stock consistency.

2. A process of refining preliberated hardwood pulp to ether-soluble contents less than 0.10% as claimed in claim 1, wherein the initial stock consistency is between about 14% and about 25% based on the solution.

3. A process of refining preliberated hardwood pulp to ether-soluble contents less than 0.10% as claimed in claim 1, wherein the said soap concentration is about 0.33%.

4. A process of refining preliberated hardwood pulp to ether-soluble contents less than 0.10% as claimed in claim 1, wherein the concentration of caustic soda in the refining liquor in said stage is between about 1.54% and 4.44% based on the solution.

5. The process of refining preliberated hardwood pulp to ether-soluble contents less than 0.10% in a multistage chemical refining process, including a hot caustic-soda stage, comprising subjecting the hardwood pulp, in the hot causticsoap stage, to hot caustic soda refining liquor having a soap concentration between about 0.11% and 0.56% based on the solution, and regulating the initial stock consistency in said stage between about 6.25% and about 25% and the concentration of caustic soda in the refining liquor in said stage between about 1.54% and 4.44% based on the solution, so that in a graph plotting the per cent initial stock consistency against the per cent initial caustic soda based on the solution, the per cent of caustic soda based on the solution lies above a straight line extending through the plots for about 1.54% caustic soda concentration at 6.25% stock consistency and 2.7% caustic soda concentration at 25% stock consistency, the hardwood pulp being subjectcd to said refining liquor at a temperature of about 205-210 F. for a period of about five hours.

6. A process or" refining preliberated hardwood pulp to ether-soluble contents less than 0.10% in a multistage chemical refining process, including a hot caustic-soap stage, comprising subjecting the hardwood pulp, in the hot caustic-soap stage, to hot caustic soda refining liquor having a soap concentration between about 0.11% and 0.56% and an initial caustic soda concentration between 2.22% and 6.66%, both based on the solution, at a stock consistency of about 10% and temperature of about 205-210 F. for a period of about five hours.

References Cited in the file of this patent UNITED STATES PATENTS liumber Name Date 1,806,309 Richter May 19, 1931 1,833,976 Richter Dec. 1, 1931 1,847,311 Schur Mar. 1, 1932 1,945,202 Richter Jan. 30, 1934 {Other references on following page) 10 UNITED STATES PATENTS OTHER REFERENCES Number Name Date Industrial and Engineering Chemistry, vol. 23,

1,947,106 Plumstead Feb. 13, 1934 N0. 2, pages 138 and. 139. 1,949,549 Richter Mar. 6, 1934 Bulletin U. S. D. A. No. 80, Aug. 31, 1914, pages 1,991,499 Drewsen Feb. 19, 1935 5 1s, 19 and 22. 2,030,383 Luth et a1 Feb. 11, 1936 Refining of Pulp by Rys and Bonisch, Paper 2,041,958 Richter Mar. 26, 1936 Trade Journal, May 11, 1939, pages 31 to 40. 2,118,039 Dreyfus May 24, 1938 The Hot Alkaline Purification of Cellulose I by 2,159,675 Richter May 23, 1939 Meller Paper Trade Journal, Sept. 27, 1945, pages 2,228,127 Richter Jan. 7, 1941 133 to 145.

0 Gray Aug. 15, 1950 Cellulose and Cellulose Derivatives by Ott,

published by Interscience Publishing, New York

Claims (1)

1. THE PROCESS OF REFINING PRELIBERATED HARDWOOD PULP TO ETHER-SOLUBLE CONTENTS LESS THAN 0.10% IN A MULTISTAGE CHEMICAL REFINING PROCESS, INCLUDING A HOT CAUSTIC-SOAP STAGE, COMPRISING SUBJECTING THE HARDWOOD PULP, IN THE HOT CAUSTICSOAP STAGE, TO HOT CAUSTIC SODA REFINING LIQUOR HAVING A SOAP CONCENTRATION BETWEEN ABOUT 0.11% AND 0.56% BASED ON THE SOLUTION, AND REGULATING THE INITIAL STOCK CONSISTENCY IN SAID STAGE BETWEEN ABOUT 6.25% AND ABOUT 25% AND THE CONCENTRATION OF CAUSTIC SODA IN THE REFINING LIQUOR IN SAID STAGE BETWEEN ABOUT 1.54% AND 6.66% BASED ON THE SOLUTION, SO THAT IN A GRAPH PLOTTING THE PER CENT INITIAL STOCK CONSISTENCY AGAINST THE PER CENT INITIAL CAUSTIC SODA BASED ON THE SOLUTION, THE PER CENT OF CAUSTIC SODA BASED ON THE SOLUTION LIES ABOVE A STRAIGHT LINE EXTENDING THROUGH THE PLOTS FOR ABOUT 1.54% CAUSTIC SODA CONCENTRATION AT 6.25% STOCK CONSISTENCY AND 2.7% CAUSTIC SODA CONCENTRATION AT 25% STOCK CONSISTENCY.

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