830
I N D U S T R I A L A N D ENGINEERING CHEMISTRY Conclusion
From these results it is apparent that the secondary acetates can be safely used either in the base lacquer or thinner and inasmuch as the manufacturing process allows for any blend or combination of solvents desired, the authors be-
Vol. 22, No. 8
lieve that these esters will be of particular interest to the lacquer chemist. Literature Cited (1) Davidson and Reid, IND. END.CHEX.,20, 199 (1928). (2, Hofmann and Reid, 687 (192s). (3) Reid and Hofmann, Ibid., 20, 497 (1928).
Reaction Variables of the Alkaline Pulping Process' C. E. Curran and Mark W. Bray FOREST PRODUCTS LABORATORY, MADISON, WIS.
The effect of changes in the pulping variables on the delignification reaction in three alkaline pulping processes-soda, sulfate, and semi-chemical-is presented. The variables concerned are temperature, concentration of chemical, ratio of chemical to wood charged, and ratio of caustic to sulfide or of bicarbonate to sulfite. As far as the data presented are concerned, the temperature of digestion affects only the rate a t which the reaction proceeds. An increase in the concentration of the reacting chemicals increases the rate of reaction as well as affecting the physical properties of the resulting pulp. The lower concentrations result in higher yields of stronger pulps that are more easily bleached. An increase in the ratio of chemical to wood accelerates the pulping reaction and, where this increase is accompanied by a decrease in concentration, does not lower pulp
strength appreciably. Replacement of caustic soda by sodium sulfide, as in the sulfate process, for example, increases the reaction rate and results in less harm to the physical and chemical properties of the resulting pulp than the straight soda reaction, even though the alkalinities of the two pulping agents are identical. Sulfate pulps cooked to the same yield are generally stronger and more easily bleached than soda pulps. Somewhat similar observations have been made for semi-chemical pulps, in which sodium sulfite is replaced by sodium bicarbonate. Semi-commercial pulping tests, using the modified cooking conditions developed in this work, have resulted in strong kraft pulps from southern yellow pines t h a t can be bleached to a good white color without material loss in strength properties.
.............. HIS article deals with the results of changing independently certain variables that affect the delignification reaction in the alkaline pulping process. Information on the effects of temperature, concentration of the cooking chemicals, ratio of chemical to wood, and replacement of certain reagents by others of more or less alkaline characteristics is presented; this information concerns the rate of delignification and the physical and chemical properties of the resulting pulps. For clarity some information that has already been published is included with the results that have not heretofore been reported. Three pulping processes are considered-namely, the soda process in which the active pulping agent is caustic soda; the sulfate or kraft process, in which a combination of caustic soda and sodium sulfide is used; and the semichemical process in which sodium sulfite and sodium bicarbonate are employed. The first two of these processes are strongly alkaline, whereas in the third the reagents are essentially neutral, although they tend slightly toward the alkaline side. The research now under way a t the Forest Products Laboratory, together with research previously reported and a compilation of information now in process, has the objective of a fuller delineation of the pulping reaction in general. From the work done thus far i t appears that the essential pulping reaction is the same chemically in all cases, but that its velocity and the quality of the resulting product may be varied considerably by modification of the variables mentioned in the preceding paragraph, as well as by change in the species of wood used. The effect of the species of wood used for pulp is of sig-
T
1 Received April 18, 1930. Presented before the Division of Cellulose Chemistry a t the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 t o 11, 1930.
nificance in the efforts to develop more efficient utilization of our forest crop, particularly the utilization of fast-growing or little-used species. Knowledge of these reaction variables may permit the commercial introduction of new and heretofore unused species for pulp and may increase the number of products for which species now limited in use will prove suitable. A case in point is the southern yellow pine group, which up to the present time has been largely restricted in pulp use to kraft and the wrapping grades of paper. Earlier developments in this investigation have shown that a slight modification of the present pulping and bleaching reaction permits the use of these species for strong white papers and hence opens up a new field of exploitation for the fastgrowing pines. Material, Apparatus, and Procedure The wood used for the experimental digestions consisted of sawdust, which was prepared and analyzed as previously described (1, S), while for the pulping trials of larger scale standard pulp chips were employed. The species pulped will be described under the discussions of each series of experiments. For the small-scale pulping reactions the steel autoclave of 350 cc. capacity and the electrically heated thermostatically controlled oil bath for heating purposes that have been previously described ( 1 ) were used, while the digestions of larger scale were conducted in autoclaves ( 5 ) of 3.7 gallons capacity. The experimental procedure (1) and the methods ( 2 ) used for analysis and testing of the fibrous residues (pulps) have been given in detail in previous publications from this laboratory.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
August, 1930 Series I-Effect
of Digestion Temperature
The work showing the temperature relationship was a t first conducted with the simplest alkaline reagent, sodium hydroxide. This course was also followed for the study of some of the other pulping variables, such as concentration and chemical ratio. Later a similar observation was made of the effects produced when a part of the sodium hydroxide is replaced by sodium sulfide; this work was done in order to determine whether or not deviations from the general
831
pulp having similar chemical properties is obtained a t the higher temperature in half the cooking time. Comparing the data previously published (1) for the soda process with that given in Figure 3 for the neutralsulfite (semi-chemical) process, in which black gum (Nyssa sylvatica) was digested with a neutral solution of sodium sulfite and sodium bicarbonate, the same conclusions may be drawn with respect to the effect of temperature on the rate of the pulping reaction. This same relationship has been observed by other investigators (4) for the acid-sulfite process on spruce wood. A comparison of the effect of temperature in the three pulping processes just mentioned is given in Table I. The data for this table were selected from digestions that had been continued until a given yield had been reached. Although it is somewhat beside the point, attention may here be called to the relatively greater efficiency of the acid-sulfite process, in comparison with the soda and the neutral-sulfite processes, in lignin removal when the reaction has been continued to equal yields of cellulose. A logarithmic relationship between yield and duration of the reaction for four different digestion temperatures was illustrated in the paper dealing with the chemistry of the alkaline pulping process (1). This relationship, together with the logarithmic relationship between apparent monomolecular velocity constants and duration of the reaction, for the temperatures studied, holds not only for alkaline reagents but also for neutral pulping agents as well. Figure 4 shows the logarithmic relationship between yield and duration of pulping for black gum pulped with a solution
Figure 1-Relation of Wood Substance Dissolved to t h e Chemical Consumed i n Pulping White Spruce by the Soda Process Total chemical added. 20 per cent: total concentration, 20 grams per liter
I n the first series of tests 25gram samples of alcoholbenzene extracted spruce sawdust were digested, as previously described ( I ) , with 20 per cent by weight of sodium hydroxide at a concentration of 20 grams per liher. It was found, as shown in Figure 1, that the weight of' wood substance dissolved is a linear function of the weight of alkali consumed. This relahionship, holding for the four temperatures employed-namely, 140°, 160°, 170", and 180" C.may be expressed mathematically, thus affording a means of calculating, for a given set of pulping conditions, the consumption of chemical for any desired yield. Upon plotting the yield of pulp against the percentage of lignin remaining in the fibrous residue (Figure 2), a similar relationship was found to exist after the yield had dropped below 85 per cent. Above this value the easily soluble materials appear to be removed with but little alkali consumption. I n previous work (1) it has been shown that the velocity of the reaction in the soda digestion is a little more than doubled for each 10" C. rise in temperature; that is, with an equivalent consumption of chemical an approximately equal yield of
Digestion number Duration, hou5s Temperature, C. Yield, per cent Lignin, per cent Cellulose, per cent Chemical consumed, per cent
i
I-
ALKALINE COOKING LIQUOR
Spruce with caustic soda 405 4 160 66.9 17.2 49.8 13.4
409 2 170 65.6 15.8 49.6 13.6
413 1 180 64.8 15.5 48.4 13.3
LIGNIN @€R C€NT OF WOOD CHARGED)
Figure 2-Relation of Yield to Lignin Content of White Spruce Pulps Produced by the Soda Process Total chemical added, 20 per cent; total concentration, 20 grams per liter
of sodium sulfite made neutral with sodium bicarbonate (S), while Figure 5 presents the logarithmic relationship for the monomolecular velocity constants and the duration of the pulping reaction. Thus it is obvious that, when time of digestion is the only variable, only two experiments are required to predict the yield of pulp for any given time of
NEUTRAL COOKING LIQVOR
Black gum with NaZS03 and NaHCOa 233 4 150 77.4 19.1 51.3 10.9
245 2 160 75.7 18.5 51.1 11.0
240 1 170 75.3 19.0
49.8 10.7
ACIDCOOKINO LIQUOR
Spruce with acid-sulfite cooking liquor (soda base) 47 20.0 120 51.5 1.6 48.3
..
37 10 5 130 49.2 1.4 46.8
..
39 5.25 140 49.4 1.3 47.6
..
40 2.75 150 48.1 1.0 46.4
..
INDUSTRIAL A N D ENGINEERING CHEMISTRY
832
75.28
2839
70.07 .I179
65.30
0.1065 Il. 62 49.50
170'C. 44.80 2.116
Vol. 22, No. 8
3.680
4.48Z
19.72
52.20
I
I
0
I
I
2
I
I
3
4
T I M E OF DIGESTION
Figure 3-Relation
of Temperature t o Other Pulping Variables, for Black G u m , in t h e Semi-Chemical Process
digestion. The prediction may be made by either graphical or mathematical methods. Since, as shown in Figure 5, the monomolecular velocity constants decrease with increase in time of digestion, the reaction appears to be, not monomolecular, but rather one of a higher order. It has been found, upon plotting the reciprocal of the concentration of residual chemical a t any given period of digestion against the time of pulping, a series of straight lines that pass through a given point is obtained. The lines differ from one another only in slope, which is a function of the digestion temperature. Furthermore, a similar set of lines is obtained when the reciprocal of the lignin concentration is plotted against the time of digestion. These relationships indicate that the reaction proceeds as though i t were of the second order. Further discussion and mathematical calculations regarding the order of the alkaline pulping reaction will appear in another paper.
to be changed in order to maintain the specifled conditions, were kept constant. The volumes of liquor for the several concentrations just mentioned were 250, 125, and 62.5 cc., respectively; that is, the volume of each successive concentration of cooking liquor was exactly half of that used in the next lower concentration. The effect of concentration on the velocity of the alkaline pulping reaction has heretofore been largely disregarded. The data of Table I1 show that increasing the concentration from 30 grams per liter to 60 grams per liter, accompanied by the necessary decrease in volume of water in the experimental digester so as to maintain the chemical ratio constant, practically doubled the rate of delignification reaction. This same doubling of the reaction rate was also obtained when the concentration was increased from 60 to 90 grams per liter, with a corresponding decrease in volume from 125 to 62.5 cc. per digester charge.
Series 2-Effect
Table 11-Effect of Changing S o d i u m Hydroxide Concentration in Cooking Liquor on Rate of Pulping Reaction for Loblolly Pine (All percentages are based on the weight oven-dry of the wood charged, except the two that as noted are based on the dry weight of the residue.) D I G E S T I O X 5 DIGESTION 8 DIGESTION 11 Duration, hours 8 4 2 Total concentration, NaOH in grams per liter 30 60 90 Yield, per cent 39.0 38.7 39.6 Lignin, per cent 2.4 2.2 3.2 37.1 Cellulose per cent 37.3 36.9 Cellulose: per cent (based on weight of residue) 95.5 95.3 93.8 Chemical consumed, NaOH in 21.0 22.0 22.0 per cent Chlorine required for cellulose isolation, per cent (based on weight of residue) 10.0 10.5 12.0
of Concentration of Chemicals in Cooking
Liquor
I n this series 25-gram samples of unextracted loblolly pine (Pinus tuedu) sawdust, having the following chemical characteristics, were used as the raw material for charging the autoclave:
,
(UOU4$'
Per cent Solubility in hot water.. . . . . . . . . . . . . . . . . . . . 3 . 3 Solubility in 1 per cent N a O H . . . . . . . . . . . . . . 14.7 Solubility in ether.. ....................... 1.3 30.2 Lignin ................................... 60.4 Cellulose. ................................ 44.7 Alpha-cellulose ........................... 12.1 Total pentosans.. .........................
The sawdust was digested in a 350-cc. autoclave for various periods a t a temperature of 170" C. with 30 per cent of its weight oven-dry of sodium hydroxide. Concentrations of 30, 60, and 90 grams per liter of chemical, expressed as sodium hydroxide, were used. All other conditions of digestion, except the volume of cooking liquor, which had
Although Table I1 presents the results for one series of experiments only, similar results with change in concentration were observed in other series made under the same conditions but for different digestion periods. The data show that the pulps cooked to the same yield a t the lower concentrations were purer from the standpoint of lignin removal and cellulose
IA$7DUXTRIALAAVDENGINEERING CHEXISTRY
August, 1930
833
40 than for digestion 38, thus indicating a lighter and more brightly bleached pulp for the product of the more dilute liquor.
content. I n addition these pulps required sornewhat less chlorine for the isolation of the cellulose than those pulped a t the higher concentrations. APPLICATroN To SULFATE PnocEstiThe showing the effect of concentration upon the nature of the soda pulping reactions, gained from the laboratory-scale experiments, was applied to pulping trials of larger scale. Similar results were then obtained even for the sulfate pulping process. Six pounds (5.3 pounds oven-dry weight) of loblolly pine chips of standard size were digested with sulfate cooking liquor in a 3.7-gallon capacity experi" mental digester. I n this series of experiments, the results of which are given in Table 111, all condi9 tions of cooking, with the exception of concen- Q&I tration of chemical and the necessary change 5 in volume of liquor that accompanies B change in concentration, were maintained c o n s t a n t . T h e & digesters were heated indirectly so as to eliminate the variable of steam condensation. The digestion G 50 conditions for the two trials recorded in Table I11 were as follows :
Series 3-Effect
of Replacing Caustic Soda with Sodium Sulfide
Comparisons demonstrating the effects of the several pulping variables of the alkaline pulping reaction are made in this article from data obtained for both the soda and the sulfate processes. Hence i t may be of interest, at this point,
2
'
I
Maximum digestion temperature. . . . . . . . . . . . Period of temperature increase.. . . . . . . . . . . . . Duration a t maximum temperature.. . . . . . . . . Ratio of sodium hydroxide to sodium sulfide in cooking liquor.. ...................... Total chemical of the weight oven-drv of the wood charged. ..........................
I
I 2
40!
170' C. 11/z hours 21/2 hours 3 to 1 30 per cent
COOKING LIQUOR
0
b
per 100 lbs."
! IOFE :~ ;;
1
I
I
I
I 8
7
I
I
l
l
9 1 0
1 1
IVESCOLORREADINGS
No.
%
Parts
46 60 33 53
20
STRENGTH DEVELOPMENT OF UNBLEACHED PULPS b
Gals.
%
Min.
Lbs.
120
30.0
37.3
40 80 120 160
43.6 44.9 48.0 49.7
Bursting strength factor
Elmeqdorf tearing test
Points/ Ib./ream 0.67 0.71 0.47 0.48
Grams/ lb./ream 2.4 1.9 1.6 1.3
Double folds
BLEACH USED (35% C1)
Red
87
Green
77
Blue
70
Based on the weight of the wood when oven-dry. Conditions of test for hand sheets: relative humidity, 65 per cent; temperature, 72' F. of R e p l a c i n g S o d i u m Hydroxide w i t h S o d i u m Sulfide, W h i l e M a i n t a i n i n g Alkalinity, C o n s t a n t on t h e R a t e of P u l p i n g of Loblolly P i n e
I
COOKINO CHEMICAL'
TION
NaOH
Series 2
Na:&
NaOH
Grams/liler
Series 1
I
I
COOKINGCONDITIONS CONCENTRA'CIOX
60 51.2
17:2
!?.2
l7:2
Per cent
1 ~~
4
I
6
I
I
to show the effect of replacing sodium hydroxide with sodium sulfide on the rate of delignification and the chemical properties of pulps so obtained. Two series of experiments were conducted, with the use of the loblolly pine sawdust previously mentioned. I n the first series only caustic soda was employed, for periods of 2 and 4 hours, respectively, a t 170" C. I n the second series a mixture of 3 parts of caustic soda and 1 part of sodium sulfide was used and the digestion periods were 1 and 2 hours; other conditions were the same as in the first series. The alkalinity of the caustic soda-
Time in Ream w t . pebble 24 X 36-500 mill sheets
Grams/liter
T a b l e IV-Effect
8 217
I
of C o n c e n t r a t i o n of C h e m i c a l s on t h e R a t e of S u l f a t e P u l p i n g R e a c t i o n w i t h Loblolly P i n e C h i p s
T a b l e 111-Effect
38
I
4 5 TIME OF DicEsrioN [HOURS)
I
F i g u r e 4-Effect on Yield in R e l a t i o n to T i m e of Digestion, C a u s e d b y V a r y i n g T e m p e r a t d e in E x p e r i m e n t a l P u l p i n g of B l a c k Gum Total chemical added, 25 per cent; ratio of sodium sulfite to sodium bicarbonate (calcd. as sodium carbonate), 4 t o 1
The values given in Table I11 indicate that decreasing the concentration of chemical in the cooking liquor decreased the rate of the pulping reaction; that is, higher yields of pulps are obtained for a given period of digestion when the wood is digested with the more dilute cooking liquor. Decreasing the concentration not only produces higher yields of stronger pulps, but the pulps obtained have somewhat easier bleaching qualities. I n comparing the Ives color reading for the two pulps, both of which were bleached in one stage with a given amount of bleaching powder solution, the figures show higher values for digestion
DIGESTION
I
3
NazS
Per cent
Total Pt.7 cent
25.65
8:55
30 34.2
30 25.65
8:55
30 34.2
CHEMICAL PROPERTIES
I
TOTAL
'I?IME OB DIGESTION "IELD
k:l: Cc.
1
1
500 500
Lignin
Hours
Per cenl
Per cent
2
44.5 43.2
4.9 3.0
35.7 39.4
2.2 1.2
1
~~
All values except cellulose and chlorine consumed are based on the oven-dry weight of the wood charged.
I I
CELLULOSE Base~cpn ~~~~d on
. Chlorinea
consumed in isolation of cellulose
charred
pulpa
Per cenl
Per cent
40.1 40.5
90.1 93.8
14.7 9.9
36.9 38.6
96.3 97.9
10.5
.-Per cent
8.0
INDUSTRIAL AND ENGINEERIIVG CHEMISTRY
834
sodium sulfide solution was adjusted to equivalence with that of the caustic solution used in the soda pulping experiments of this series. Assuming that sodium sulfide hydrolyzes with water in stoichiometric proportions according to the equation: Na2S
+ HzO = NaOH + NaHS
then every part of sodium sulfide taken will be equivalent to 0.513 part of sodium hydroxide. Thus, for a ratio of caustic to sulfide of 3 to 1, which is 25.65 per cent sodium I
I
I
1
1
1
I
E
4
I
6
l
l
8
TIME OF DIG€ST/DN (HOURS)
Figure 5-Effect of Temperature on Velocity of Pulping Reaction i n Experimental Pulping of Black G u m Total chemical added, 25 per cent: total concentration, 50 grams per liter; ratio of sodium sulfite to sodium bicarbonate (calcd. as sodium carbonate), 4 to 1.
hydroxide and 8.55 per cent sodium sulfide in terms of the weight of oven-dry wood, the potential alkalinity of the (0.513 X 8.55) = 30.03 sodium mixture will be 25.65 hydroxide. The total chemical in the cooking liquor, however, will be 34.2 per cent of the weight oven-dry of the wood charged. For a 25-gram sample (oven-dry basis) of loblolly pine wood 125 cc. of the cooking liquor were added for both the soda and the sulfate pulping trials; thus the concentrations of chemical in the cooking liquor for the two pulping processes were 60 and 68.4 grams per liter, respectively. The data given in the two series of Table IV show a remarkable increase in the velocity of the pulping reaction when a part of the sodium hydroxide is replaced with sodium
+
sulfide, even though the total available alkali, expressed a8 sodium hydroxide, is maintained the same for the two methods of pulping. The soda digestion 7 required 2 hours to reach a yield of 44.5 per cent, while the sulfate digestion 216 reached even a lower yield (43.2 per cent) in half the cooking time. Of course the total chemical content of the sulfate cooking liquor exceeded that of the soda liquor by 4.2 per cent, because of the sodium bisulfide content of the hydrolyzed sodium sulfide added. This increase in reaction velocity, however, can hardly be attributed solely to the increased concentration of sodium ions in the cooking liquor, as will be illustrated later (Table V), where the effect of chemical ratio will be discussed in greater detail. The increase, both in reaction velocity and in efficiency of d e lignification, should rather be attributed to some specific effect of the sulfides present in the strongly alkaline cooking liquor. The reaction velocity decreases when sodium sulfide and sodium bisulfide only are used as the pulping agents, but increases again when caustic soda is added to these chemicals. I n addition to the increased reaction velocity, the data in both the series of Table IV show that, for equal yields, the sulfate process produces a purer product as regards cellulose and lignin content than that produced by the soda process. Less chlorine is necessary to isolate cellulose of a given degree of purity from a sulfate pulp than from pulps produced by the soda process. Although no definite correlation between the chlorine consumption and the bleach requirements has yet been made, it is nevertheless a fairly safe assumption that these two factors go hand in hand. I n other words, in comparing pulps of a given yield, those obtained by the sulfate process have easier bleaching properties than those obtained by the soda process, provided that they are pulped under similar conditions. Series 4-Effect of Changing Ratio of Chemical t o Wood While Maintaining Volume of Liquor Constant
The conditions of digestion employed in obtaining the data for this series of experiments were similar to those described under the discussion of the effect of temperature (Series 1). I n addit'ion, however, is the fact that when increasing the ratio of chemical to wood charged it is necessary to increase a t the same time either the concentration or the volume of the solution. Since the digestions were all made with a constant volume of cooking liquor, changes in concentration were necessitated, thus introducing an additional variable. Hence Table V is arranged as nearly as possible in groups of similar yields.
of Changing Ratio of Chemical to Wood While Maintaining t h e Volume of Liquor Constant. o n Rate of Pulping Spruce Wobd w i t h S o d i u m Hydroxide
Table V-Effect
BASEDO N WEIGHT
BASEDON WEIGHT OF OVEX-DRY WOOD COOKING CHEMICAL
I
1-
Series I
427 Series 2 411 439 Series 3
i I I
Concn. In terms of of NaOH wood charged
Total duration
1
I
~
Grams/Ziter
Per cent
Series 4
.
432 416 440
I
Hours
Max. temp.
c.
Chemical consumed
Total yield oven-dry Pulp
Per cent
30
180 180 170
15.8 16 5 16.2
56.3 56.2 56.3
20 40
40
170 160
17.0 17.2'
52.5 53.7
180 160 170
17.3 17.7 18.0
50.8
180 180 160
18.7 18.9 19.4
45.7 46.4 46.6
2
I 4
40
I 20 30 40
I 8
40
I
OF
OVEN-DRY RESIDUE
Lignin in pulp
Cellulose in pulp
Chlorine consumed in isolation of cellulose
Per cent
Per cent
Per cent
I
Per cent
20 30 30
20 443
Vol. 22, No. 8
I 1 I
1
I
17.4 17.1 16.9
82.9 84.0 83.6
26.8 22.7 22.9
15.1 13.9
86.3 85.5
21.2 19.4
13.1 13.8 11.1
87.6 87.8 90.4
21.7 17.1 14.8
10.6 7.3 7.3
90.9 94.4 94.7
15.3 11.3 9.8
August, 1930 Upon increasing the ratio of chemical to wood the efficiency of the delignification reaction is increased even more t h a n the velocity of the reaction, in spite of the fact that the concentration of chemical in the cooking liquors was somewhat greater for the digestions made a t the higher chemical ratios. At first glance this finding seems contradictory to the conclusions drawn f r o m t h e d a t a s h o w i n g the effect of concentration in the production of easier bleaching pulps set forth in Tables I1 and 111. I n the present series the solutions used were more dilute than those in the series prev i o u s l y mentioned, and this fact accounts for the results. Table V shows that, for a given yield, pulps of higher purity Tvith lower chlorine requirements (for cellulose isol a t i o n ) are obtained as the ratio of chemical to wood in the cooking liquor is increased. On the assumption that pulps of higher purity have easier bleaching qualities, it may be concluded t h a t the higher chemical ratios are more suitable for the production of pulps of higher cellulose and lower lignin content and thus of lower chlorine requirements. H o w e v e r , t h e u s e of high chemical ratios, accompanied as it is by an increase in rea c t i o n v e l o c i t y , appears to have a deleterious effect upon the pulp strength unless the reaction is under control at all times. It is therefore necessary to introduce some factor that will tend to reduce the reaction velocity and at the same time give pulps of higher strength values without materially decreasing the bleachability of the resulting pulps Decreasing the concentration of chemical in the cooking liquor causes a tendency in the desired direction An example of the practical value of the results reported in this article is afforded by certain semi-commercial pulping experiments, recorded in Table VI, wherein conditions for the sulfate or kraft process were selected to yield a comparatively strong and at the same t i m e a n easy-bleaching pulp f r o m loblolly p i n e (Pinus taeda). The total chemical
INDUSTRIAL. YD ENGINEERING CHEMISTRY N N
w cn
835
N
DICESTICX
E
I
I e 0
Wt. moist
0
a
?
Wt. oven-dry
3
c7
NaOH
m
6
:
Y
-I
Na2S
c 3
3
L7
't.
-2
c
Total
8
8
z
C
0 pi
0
P
a
c: N 67
P a
Ratio combined t o total alkali
a u 0:
c
yof an oil may change greatly during refinement with sulfuric acid while the volatility remains almost constant. Variations in field temperatures of 55’ F. have been known to cause fluctuations in viscosity from 75 to 250 seconds Saybolt, giving marked differences in penetration and spreading. Kerosenes pass readily through the tracheal system (breathing tubes) of an insect ( 2 ) ,while oils of a viscosity of 100 penetrate very slowly but also are, with difficulty, dislodged. A somewhat similar action takes place when oils penetrate tlie leaf structure. Kerosenes enter readily but are soon lost through volatilization and the ease with which
837
they are translocated in the tracheids or water tubes. Viscous oils enter the leaf more slowly, but portions of them remain for weeks or months. The presence of a considerable quantity of the heavier oils in leaves leads to functional disturbances, especially the production of starch. This difference in the behavior of oils has led to the general use of viscosities of 50 to 75 seconds Saybolt at 100” F. for almost all purposes, including that of the apple, while viscosities of 95 to 110 are reserved for use on the most resistant insects. OsIDATIoN-The refined petroleum oil, as used on foliage, is composed largely of saturated hydrocarbons. These are not active chemically but, when exposed in thin fdms to the action of oxygen and sunlight, undergo a slight change with a corresponding increase in acidity. Oxidation is measured by the Sligh method (3) modified to the extent that the degree of acidity, rather than the measurement of sludge, is taken as the criterion. Further confirmation is needed to correlate the rate of oxidation and plant injury. It can be said, however, that oils of the greatest stability, according to this test, are among those proving the safest in field trials. UNSULFONATABLE RESIDUE (Sulfonation Tests)-There are two large classes or groups of compounds found in petroleum oil: (1) the saturated hydrocarbons, naphthenes, and paraffins, which are largely inert; and (2) chemically active hydrocarbons of the aromatic series and the olefins (cracked oils). The second group, being more active chemically, would be considered, and has been found to be most active as an insecticide but too dangerous to the plant for general use. Hence it becomes necessary to rely principally on the group of chemically inert fractions and to separate the two classes very sharply (1). A modified method of separating these two classes of oils is now in general use under the name “unsulfonatable residue.” This test, in combination with viscosity, volatility, and oxidation value,. has become the basis for the sale of practically all refined oils for plant spraying. It was at one time considered necessary to use oils of 98 to 100 per cent unsulfonatable value, but this has been slightly modified, especially with the general use of less viscous, volatile oils. It should be noted that the unsaturates, aromatics and olefins, are the more active insecticides, and if a small percentage of these can be retained and yet not endanger the plant a more efficient spray results. I n some instances it has also been found, as mentioned under “Oxidation,” that oils of 98 to 100 per cent unsulfonatable are less stable than those receiving a lower degree of refining with sulfuric acid. Present Uses of Petroleum Oil Sprays
It has been seen that certain petroleum fractions have been experimented with as insecticides for sixty years, but with little growth in the practice or any degree of permanency being attained. Then, with the establishment of the use of light refined petroleum oils, consisting principally of saturated hydrocarbons, an enormous and an increasing consumption occurs, this growth being due to an increase in efficiency of control rather than to the general displacement of other types of insecticides. The exception to this has been the reduction in fumigation of citrus groves with liquid hydrocyanic acid gas. The substitution of oil sprays for fumigation in southern California has amounted to one-third, or more, of the total volume of control work. Substitution, for specific needs, has also occurred of oil sprays for lime-sulfur solutions, largely in the interest of increased efficiency. The prolonged use of any one chemical
838
INDUSTRIAL A N D ENGINEERING CHEMISTRY
or compound on the same orchard or type of organism is almost certain to lead to difficulties or lowered efficiency which may be avoided by an alternating spray program. The use of oil in combination with lead arsenate and frequently including nicotine as a control for codling moth in the apple districts is a distinct advance in raising the standard of the fruit and without an increase in the arsenical residue on the fruit. The latter use of oil seems to be a very satisfactory contribution and one which can be extended to much wider fields. The value of petroleum oil in orchard spraying is dependent not alone on the insecticidal action of the oil itself, but also on physical characteristics that enhance its action in spray applications and make possible its use as a carrier for other and more active chemicals. These physical characters are high power of penetration, low surface tension, and solvent powers. Petroleum oils of the lower viscosities and certain oil emulsions penetrate readily into the insect body through the breathing tubes, thus intensifying their own toxic action and offering means of acting as carriers of other chemicals. The low surface tension of oil emulsions favors their spread over leaf surfaces and insect bodies, thus facilitating coverage. The solvent power of petroleum for wax, commonly present on leaf surfaces and the bodies of insects, also facilitates coverage. Oils are being used as carriers for other materialsfor example, the active principles of Pyrethrum and nicotine, the latter use being commonly with some of the pinetar oils which have a decided affinity for the alkaloid nicotine. Oil Emulsions for the Orchard
The paste or “mayonnaise” type of emulsion is that most favored on the Pacific Coast. Such emulsions are dipped out of the barrel rather than allowed to run out. The emulsifier itself varies greatly, but should not react with hard water to the extent that the emulsion is broken, nor should there be chemical reactions with other insecticides. The amount of emulsifier should be kept a t a low point (2) as it is possible to reduce insecticidal value by the use of an excess. The common practice of manufacturers is to use the minimum amount of emuldifier consistent with the formation of an emulsion that will not break down in storage and varying temperatures. Undue stress has a t times been attached to the respective merits of stable versus “quickbreaking” emulsions, but if the above plan is followed there is rarely any deterioration in insecticidal value from the amounts now commonly used. It should be noted, however, that the quick-breaking type of emulsion was devised for the highly refined and necessarily expensive oil, so that its contact with the insect might be increased. The principle should not be applied, or only with caution, to oils of a moderate degree of refinement even when used on dormant trees. Oil concentrations in the commercial emulsion range from 60 to 90 per cent or more. The diluted emulsion, as applied in the orchard, ranges from 0.75 to 5.0 per cent concentration of oil, Foliage applications range from 0.75 to 2.0 per cent oil. Fungicidal Oils
A recent interesting development is the use of oils containing organic sulfur in the cyclic series. This compound of sulfur and oil has a high fungicidal value almost entirely lacking in the refined white oils forming the basis for our present foliage type of oil sprays. The disadvantage of spray applications, lacking fungicidal value is evident when it is considered that the pests present in our orchards, both
Vol. 22, No. 8
in the dormant and growing season, nearly always include injurious fungi as well as insects. to Fungus Spores ( B o i r y t i s sp.) of Petroleum Oil w i t h and without Combined Sulfur
Table I-Toxicity
CONCN. OF OIL
No. 1
PETROLEUM OIL USED
ORGANIC AS APGERSULFURPLIED TO MINATION IN OIL SPORES EMULSIFIEROF SPORES. Per cent Per cent Per cent 2.5 0.01 Pervadol 15.1 6.5 0.01 Pervadol 13.3 2.5 0.01 Fish-oil soap 15.8 6.5 0.01 12.5 Fish-oil soap 6.5 0.01 Triethanolamine and oleic acid 7.5
2 3 4 5
Oil containing sulfur Oil containing sulfur Oil containing sulfur Oil containing sulfur Oil containing sulfur
6
Oil containing sulfur plus kerosene
2.5
0.01
7
Oil containing sulfur
2.5
0.01
8 9
Oil uartiallv refined Highly refi6ed oil, viscosity 60 seconds Highly refined oil, viscosity 95 seconds Check in distilled water
8.1
0.01
Triethanolamine and oleic acid 10.3 Triethanolamine and oleic acid 1 0 . 4 Fish-oil soap 8.7
...
0.1
Calcium casein
46.5
0.1
Calcium casein
49.2
.... . ....
78.0
10
11
...
..
The peach orchard may have San Josd scale and a t least two fungus diseases, all of which are controllable at the same time. The apple may have codling moth and scale, as well as mildew, scab, or canker. Oil-sprayed orange groves in California a t times develop a soft rot which takes a large proportion of the crop. The use of sprays having the dual value of an insecticide and a fungicide is insurance against the development of disease, or may obviate the necessity and expense of two separate spray applications. Experiments with these oil-sulfur compounds during the past two years have shown them to possess both insecticidal and fungicidal value, and by selection certain ones can be found usable both on the growing and dormant stage of the plant. Laboratory studies on the toxicity of such compounds are given in Table I. The fungus used is one of the vegetable molds, Botrytis. The spores from the culture are suspended in the emulsion diluted as indicated. It should be noted that the refined oils are used a t ten times the concentration as that of the oil-sulfur compounds. The tests are made in a closed cell of saturated humidity and room temperature. The pH value of the solution in which the spores are suspended is held a t 4.5 to 5 . Counts of germinated spores are made under the microscope at the end of 24 hours’ exposure. Check cultures are handled in the same way, the spores being suspended in distilled water adjusted to the same pH value. Field trials on pear scab, peach blight, and curl leaf confirm the laboratory findings of fungicidal value, while the refined, white petroleum oil shows practically no value for such control work. Future Needs of Oils for Use on Plants
It will be noted that the present expansion and permanency in the consumption of oil sprays is directly associated with the establishment of exact laboratory specifications for insecticidal values and plant tolerance. It seems reasonable to believe, then, that the use of oils on plants will be made to serve the horticulturists’ needs even more widely and the consumption still further expanded as our knowledge of the subject increases. Little is known of volatility, penetration, and oxidation rates and their relation to this subject. Laboratory standards for these subjects and many further data on the physiological reactions of oils on plants are needed. The blending of oils to attain desired specifications is a. subject about which almost nothing is known. It is usually considered desirable to blend only oils rather closely related as to viscosity and volatility, but where the boundaries may be is only conjecture and the direction in which safety or’
August, 1930
INDUSTRIAL AND ENGINEERI-VG CHEMISTRY
danger lies is unknown. The cooperation of oil chemist, entomologist, and plant physiologist is needed in the study of these complex problems with the strong assurance that continued progress in research will open equally large or larger fields than have now been developed.
839
Literature Cited Gray and de IND. ENG.CxEM., 181 1 7 j (lg26). (2) On& de, Knight, and Chamberlain, H i l s a r d i a (Calif. Agr. Expt. S t n I . 2, 351 (1927). ( 3 ) Sligh, Proc. Am. Soc. Testing M u f e r i a l s , 24, Pt. 11, 1 (1924).
Heat Transfer in the Low-Temperature Carbonization of Coal' V. C. Allison 36 W. BLACKWELL Sr., DOVER, N. J.
In the carbonization of coal, part of the entering EMI-COKE is much results obtained. For the heat raises the coal charge to a suitable reaction temmore easily penetrated sake of simplicity and to perature and the remainder promotes the carbonizaby heat than coal and avoid complicating the probtion, chemical and physical reactions requiring a the transformation of coal to lem to an undue degree, the definite time to proceed to completion. Heat can semi-c o k e therefore overFourier theorem and the use penetrate coal layers less than 0.52 inch thick more comes one of the greatest diffiof Bessel's functions will be rapidly than the carbonization reactions can proceed. culties in the thermal procdisregarded. Therefore, in carbonizing stationary coal layers the essing of coal. The transIt is customary to conthroughput in pounds per square foot of heated surformation occurs at 390" C. sider that the time, M , reface per hour decreases when the coal layer thickness (735" F.) f o r o n e of t h e quired for carbonization is reis less than 0.52 inch. best known American coking lated to the thickness, R, of Heat enters the coal charge largely by radiation, coals, Pittsburgh seam, and the coal layer which must be but the heat inflow is rhythmically interrupted by the the continued addition of penetrated by the heat and a periodic formation of the plastic layer which, before heat above this point, serves term, K , which is a constant it changes to semi-coke through the completion of the to cure or mature the semia t a n y fixed temperature, carbonizing reactions requiring time, is relatively coke into coke. through a formula of the type impervious to heat penetration either by radiation or This early stage of the carM = KR2 conduction. Restriction of the plastic layer formation bonizing of coal, concerned to one performance will speed up carbonization. with the change of the coal There are certain fundamento semi-coke. has come to be tal objections to a formula generally known as low-temperature carbonization. Low- of this type when applied to the carbonization of coal, and temperature carbonization may be considered as a method one of these objections is that as R is made infinitely small of producing a smokeless solid fuel together with gaseous zero carbonization time is approached and as the carbonizaand tarry by-products, or as a preliminary stage on the ther- tion of coal involves chemical reactions possessing a finite mal process involved in the changing of coal into metallurgical time of reaction zero carbonization time is not to be expected, coke or into gas. Lowtemperature carbonization, as such even with a coal layer of very small thickness. This formula a preliminary stage, is already more or less differentiated does become applicable, however, when a small constant in gas manufacture; but it is customarily submerged or is introduced as disregarded entirely, as a separate stage, in the manufacture M = K ( R + C)z of metallurgical coke. The appearance of coal is deceptive even to those long This formula was developed to fit the experimental results accustomed to its complexity, for close inspection of the seemingly uniform, black material reveals a mixture highly obtained in a series of nine tests where Pittsburgh seam complex both chemically and physically. This complexity coal was carbonized in vertical, cylindrical metal retorts renders very difficult the examination of coal on a small, varying in radius from 1.03 to 6.28 inches and a t retort refined scale. Larger scale apparatus, using sufficient temperatures varying from 590" C. (llOOo F.) to 780" C. coal to overcome the characteristic heterogeneity of the coal, (1440' F.). Low-temperature carbonization was judged butdnot so large as to prevent easy manipulation, is indicated. complete when the center of the middle of the charge attained a temperature of 390" C. (735" F.), for this is the only Development of Formula definite "break-point" on the time-temperature curve Thermodynamics offers an almost ideal method of attacking above the 100" C. (212' F.) water-evaporation flat section reactions which proceed reversibly and under equilibrium and is immediately followed by increased heat penetrability conditions. The carbonization of coal, however, is not of the charge, as is shown by the increased steepness of the generally carried out under equilibrium conditions and the time-temperature curve. Kinety-five per cent of the total carbonization is also an irreversible reaction. Thermo- loss of weight, obtainable under low-temperature carbonizadynamics also gives only the tendency for a reaction to pro- tion conditions, has occurred when this 390" C. (735" F.) ceed in a given direction and has little to say about the point is reached with this particular coal. By means of this formula the carbonizing time, M , in velocity of the reaction. The problem in hand is intimately bound up with reaction velocity, and an attempt will be made minutes, can be calculated for the nine tests mentioned to attack the problem from a purely empirical viewpoint above with the following errors: and then develop a tentative theory from the empirical Average error = *4.7%
S
1
Received February 12, 1930.
Maximum error = *13.4%
