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in temperature control which showed t h a t in order t o obtain the maximum yield of wood alcohol i t was very necessary t o control the distillation just before the t a r began t o be formed. FOREST PRODUCTS LABORATORY MADISON,WISCONSIN ~~
THE INFLUENCE OF MOISTURE ON THE YIELD OF PRODUCTS IN THE DESTRUCTIVE DISTILLATION OF HARDWOOD By R. C. PALMER AND H. CLOUKEY Received October 17, 1917
OBJECT O F WORK
I n the destructive distillation of hardwood i t has been considered for a long time the best practice t o season t h e wood for a t least 1 2 months before using it. The reason for this practice lies chiefly in the increase in operating expenses, due t o an excessive dilution of the crude liquor. It is also the opinion of some operators t h a t besides increasing the volume of liquor, green wood gives lower yields of products than dry, especially of acid. Other operators do not hold this view. I n discussing the importance of using seasoned wood Klar’ says “the yields of acetate of lime are inversely proportional t o the water content of the wood carbonized-while the yield of alcohol is increased if changed a t all.” There exists then no agreement among operators as t o the influence of a n excess of moisture on the yields. Many plants are now using wood with a higher moisture content than formerly because of changes in economic conditions of wood supply. I n making commercial experiments and demonstrations in controlling the distillation in order t o secyre the maximum yield of products, i t became apparent t h a t former experiments in controlling dry wood should be extended t o determine the influence of moisture under controlled conditions. I n view of these conditions and the possible influence of moisture in temperature control, the experiments described in this paper were made. The tests also included a study of the effect of moisture under conditions comparable with uncontrolled as well as controlled plant conditions. EXPERIMENTAL PROCEDURE
DISTILLATION-AS i t was thought t h a t different species might be affected differently, the three standard distillation species, beech, yellow birch and hard maple, were studied separately. The material was ordinary cord wood from a commercial plant containing wood seasoned for about 18 months and wood seasoned from 4 t o 6 months. The tests were all made in a laboratory retort2 holding about 5 0 Ibs. of wood. I n all previous work in the same retort i t was the usual practice t o start the distillation from a cold retort. By this method any excess moisture present was always distilled over before i t could play any part in the destructive distillation reaction and no effect of moisture could be noted. I n these tests the empty retort was first heated t o 1
“Technologie der Holzverkohfung,” 1910 edition, p. 77. . and THISJOURNAL, 7 (1915), 663.
* Forest Service Bulletin 129,
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what would correspond t o the end temperature of a commercial distillation, a t which time a specially constructed basket containing the wood was quickly introduced into the retort. I n this way the’distillations were comparable t o continuous daily plant practice. Destructive distillation had always commenced in parts of t h e charge, while the water in another part continued t o distil over. Uncontrolled and controlled distillations were made for both green and seasoned wood of the three species. I n former laboratory tests, in which the importance of control features was established, t h e procedure was based on the temperature-percentage distillate relation. I n continuous plant practice i t is not possible t o determine the proportion of the total distillate at any stage of t h e distillation, so i t was thought important t o determine if the time-temperature relation would not serve as well. There seems t o be no doubt but t h a t it can, as the curves drawn for these relations were found in these tests t o be quite parallel. I n uncontrolled distillation the maximum fire was kept under the retort until the tar-point was well established and t h e fire was then checked so t h a t t h e distillation was completed largely by means of the exothermic reaction. I n the controlled runs, as soon as the first indications of t a r were noted in the distillate, the fire was checked and the firing so regulated t h a t after t h a t point the rate of rise in temperature was appreciably lower t h a n in t h e uncontrolled runs. ANALYSES-The yields of settled tar and charcoal were determined by actual measurement. The yields of acetic and formic acids, dissolved t a r and wood alcohol were determined by analysis of t h e clear pyroligneous acid. For acid and dissolved tar determinations IOO cc. of pyroligneous acid were distilled until no further distillate came over and the temperature, measured in the residue, reached 1 4 0 O C. The residual t a r was then washed with 50 cc. of water and the distillate added t o the first, the distillation being stopped when the temperature in the residue reached 150’ C. The residue was dissolved tar. A 2 5 cc. portion of the distillate was titrated with normal NaOH t o give total acid, calculated as acetic. Another 2 j cc. portion was diluted with loo cc. water and placed on the steam bath with an excess of mercuric oxide and allowed t o remain for about 2 hours, or until it was evident t h a t there was no further reduction of the oxide. The flask was shaken occasionally. The whole was then distilled from phosphoric acid. Titration of the distillate with N / r o NaOH gave acetic acid. The difference between t h e total acid and acetic acid determinations was taken as the formic acid, t h e formic being oxidized by t h e mercuric oxide. Phenolphthalein was the indicator in both titrations. Wood alcohol was determined by distilling from a 500 cc. sample of t h e pyroligneous acid. The distillate was made alkaline with strong NaOH and 6 j per cent distilled from it. After again being sure t h a t t h e distillate was alkaline a third distillation of 60 per cent was made. About 2 cc. of &SO4 were added to
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this distillate and a fourth distillation of 60 per cent made. The final distillate was weighed and the specific gravity determined a t 15.5' C. in a standardized pycnometer. The amount of alcohol was then determined b y consulting the tables of Dittmar and Fawsett.' No analyses were made of the settled t a r so t h e yields of acid are proportionately lower t h a n in plant practice, where t h e t a r is washed for recovery of soluble producxs dissolved in it. RESULTS
The results of distilling t h e wet and dry wood under controlled and uncontrolled conditions are given separately for t h e different species in Table I. The results for the mean of equal weights of beech, birch a n d maple are also given in the table. The data represent in every case the mean yield from a t least t w o runs. I n Table I1 the same d a t a are figured on a relative TABLE I-THE YIELD OF
Condition Dry-Notcontrolled Dry-Controlled Wet-Notcontrolled Wet-Controlled
... ....... ... .......
Moisture 24.90 22.25 31.80 32.27
... ....... ... .......
Dry-Notcontrolled 20.82 21.10 Dry-Controlled Wet-Notcontrolled 30.17 Wet-Controlled 26.78 (a) The yields are all given
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ACETIC AND FORMIC Acms-The acetic and formic acid results are very important from a commercial viewpoint. T h e effects of moisture and' control are different for different species. The beech with higher moisture gave decidedly more total acid whether controlled or not, but when not controlled the increase in acid was largely formic acid, while when controlled the increase was nearly all acetic acid. When the drier beech was controlled the acid yields were appreciably decreased instead of increased. I n order t o obtain the maximum yields of acetic acid from beech the experiments show quite conclusively t h a t the wood should not be seasoned too long and the distillation should be controlled as carefully as possible. Birch shows somewhat the same tendency as beech t o give higher yields of acetic acid from the wetter wood but the differences are not nearly so great. The
BEECH,BIRCHAND MAPLEWITH DIFFERENTAMOUNTSO F MOISTUREAND UNDER CONDITIONS OF CONTROL(U) BEECH MAPLEDisForDisChar- Settled solved Total Total Acetic mic Wood Mois- Char- Settled solved Total Total coal Tar Tar Tar Acid Acid Acid Alcohol ture coal Tar Tar Tar Acid 21.32 38.66 5.80 6.98 12.78 5.43 39.45 5.21 4.91 10.15 5.52 4.62 0.69 1.74 22.80 42.35 5 . 1 6 4.77 10.13 5.49 9.82 5 . 0 4 4.12 0.73 1.78 42.00 4 . 9 3 4.89 32.80 39.20 6.12 5.05 11.17 5.37 38.72 5 . 4 5 5.03 10.48 6.23 4 . 9 8 1.03 1.80 27.03 38.92 4.87 4 . 9 1 9 . 7 8 5.59 39.85 5 . 0 1 5.64 10.65 6.25 5 . 6 3 0.54 1.91 MEAN,Equal Portions Beech, Birch BIRCH 22.31 38.98 5.66 5.84 11.50 5.32 38.88 5.96 5.64 11.60 5 . 0 2 4.28 0.59 1.62 22.05 42.20 5.04 4.83 9.87 5.32 9.66 5.42 4.83 0.48 1.73 42.30 5 . 0 4 4.62 31.59 39.39 5 . 8 3 4.78 10.61 5.74 40.25 5 . 9 3 4.26 10.19 5.62 4.97 0.52 1.58 28.69 40.36 5 . 1 3 5.28 10.41 5.78 42.30 5 . 5 2 5.28 10.80 5.52 4.92 0.44 1.41 in per cent weight of t h e oven-dry wood distilled. PRODUCTS FROM
DIFFERENT For- Wood Acetic mic AlcoAcid Acid hol 4.92 0 . 3 8 1.77 4.61 0 . 6 8 1.92 4.54 0.66 1.88 5.17 0 . 3 3 1.83 and Maple 4.54 0.55 1.71 4.52 0 . 6 3 1.81 4.83 0.74 1.75 5.24 0.44 1 . 7 2
TABLE 11-THE RELATIVEYIELD OF PRODUCTS FROM BEECH BIRCHAND MAPLEWITH DIFFERENTMOISTURE CONTENTS A N D UNDERDIFPERENT BEECH-
-
~ O N T R O LCONDITIONS(U)
DisForMois- Char- Settled solved Total Total Acetic mic Wood Condition ture coal Tar Tar Tar Acid Acid Acid Alcohol Dry-Notcontrolled 74.8 94.0 95.7 87.1 95.4 8 8 . 4 82.1 67.0 91.1 Dry-Controlled 69.0 100.0 9 0 . 5 86.7 92.2 80.7 73.2 70.9 93.2 Wet-Notcontrolled 9 8 . 3 92.2 100.0 8 9 . 2 98.5 99.6 88.5 100.0 94.2 Wet-Coutrolled 100.0 94.9 9 2 . 0 100.0 100.0 100.0 100.0 52.4 100.0 BIRCH Dry-Notcontrolled 69.0 92.0 100.0 100.0 100.0 89.3 86.1 100.0 93.7 Dry-Controlled ...... . 69.9 100.0 84.6 81.9 83.3 9 6 . 5 97.2 81.4 100.0 Wet-Notcontrolled 100.0 95.2 99.5 75.5 87.9 100.0 100.0 88.2 91.3 Wet-Controlled 88.8 100.0 92.6 93.6 93.2 9 8 . 2 99.0 74.6 81.6 (a) The yield from t h e condition giving t h e highest result is taken as 100 per cent,
......
...... . . . . ...... ..........
...... .. .
...... ..........
basis, taking the highest yield of each product as IOO per cent. Moisture and control do not affect the t a r and charcoal yields in the same way for t h e three species. Without control the wood containing more water gives more t a r for beech but less t a r for birch and maple, and when the distillations were controlled t h e wetter wood gave more t a r for beech and birch b u t less for maple. Control itself gave less t a r for all species in t h e case of dry wood b u t more for beech a n d birch and less for maple in the case of t h e wood with a larger per cent of water. The charcoal yields are always increased by control but the effect of more water is different for the different species. For higher moisture beech gave lower yields of charcoal. Birch gave higher or the same charcoal yields and maple gave more when not controlled but less when controlled. T h e relative difference, due t o different conditions, are shown more clearly in Table 11. Trans. Roy. SOC.Edin., 33 (quoted in Smithsonian Physical Tables).
MAPLEDisForMois- Char- Settled solved Total Total Acetic mic ture coal T a r Tar Tar Acid Acid Acid 65.0 91.3 9 4 . 8 100.0 100.0 97.2 95.2 54.6 69.5 100.0 84.3 88.4 78.3 98.2 89.2 100.0 100.0 92.8 100.0 72.4 87.4 96.9 87.8 97.1 82.4 91.9 79.6 70.3 76.5 100.0 100.0 48.5 MEAN.Eaual Parts Beech. Birch and MaDle 70.7 9 2 . 4 9 i . l 100.0 100.0 92.1 86.7 - 7 4 . 4 69.7 100.0 86.5 82.7 85.9 92.1 86.3 85.1 100.0 93.3 100.0 82.0 9 2 . 3 9 9 . 3 92.2 100.0 9 0 . 8 95.7 88.0 90.4 90.5 100.0 100.0 59.4
-
Wood Alcohol 92.2 100.0 97.7 95.4
94.5 100.0 96.7 95.0
effect on formic acid is not especially marked. The control of dry birch gave good increases in acetic acid, in fact almost as much as the control of the wood with higher moisture content. The d a t a do not show t h a t there is much preference between controlled and uncontrolled distillations, if wet wood is being distilled. Considering all factors, however, the results would indicate t h a t , as far as acetic acid is concerned, there is no advantage in seasoning birch too long. I n the case of maple also the wood with higher moisture is t o be preferred for best acetic acid yields, provided the distillation is controlled, the results being almost as striking as with beech. If dry wood is distilled the uncontrolled distillations give t h e highest yields of acetic acid. Considering the three species the best yields of acetic acid are evidently obtained from carefully controlled distillations of wood t h a t has seasoned only about 6 months. These conditions gave nearly 1 5 per cent more acetic acid t h a n either controlled or uncontrolled 18 months old wood.
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It is of interest in this connection t o give the results of a commercial temperature-control test lasting about three weeks. The plant was of about 5 0 cords per day capacity, distilling wood composed of about threequarters maple and one-quarter birch. Approximately 1100cords were distilled during the test. The wood had not been seasoned for more t h a n 8 months and could be considered very comparable with the wet wood used in the laboratory tests described in this paper. The yield of acetate of lime in the commercial test was increased about 1 2 per cent over former uncontrolled practice. As the plant had been using wood of the same quality prior t o the test, t h e results of these experiments in the laboratory, comparing wet uncontrolled with wet controlled runs for birch and maple, indicate t h a t the increase in acetate was due largely t o t h e maple. The increases obtained in the plant and in these tests check surprisingly well. W O O D ALCOHOL-The influence of moisture on the wood alcohol is almost as pronounced as on the acids. The beech, with the higher moisture, gave decidedly the highest yield of wood alcohol when controlled and even the uncontrolled wet beech gave a little more alcohol than either the controlled or uncontrolled dry beech. The alcohol results, therefore, also indicate t h a t beekh should not be seasoned too long and t h a t the distillation should be carefully controlled. I n the case of maple, both uncontrolled and controlled wet wood gave higher yields of alcohol t h a n the dry uncontrolled runs, showing t h a t moisture also Eavors the alcohol in this species. However, decidedly the highest yield was obtained from t h e dry controlled distillation, verifying former experiments. Considering both alcohol and acetate, the d a t a would indicate t h a t for best results from maple the wood should be only moderately seasoned and the distillation carefully controlled. The alcohol results for birch showed t h a t without doubt this species should be well seasoned for the highest yields, as the wetter wood gave much smaller amounts of alcohol. The dry controlled birch gave the highest yield. Since the acetate yield for the dry controlled birch was so nearly the same as from the wood with higher moisture, although slightly lower, it would seem, considering both products, t h a t birch should be well seasoned and the distillation carefully controlled for the best returns. Birch, then, seems t o be different from beech and maple as regards the influence of moisture on the more valuable products, such as alcohol, acetic acid and charcoal. SUMMARY
I-Semi-commercial laboratory destructive distillations were made with beech, birch and maple. One lot was seasoned for about 18 months and another lot about 6 months. The results showed t h a t moisture had a decidedly favorable influence on the yields of acetic acid when the distillations were controlled after the exothermic reaction had begun. The data indicate t h a t beech and maple should be distilled only after moderate seasoning in order t o secure the highest yields of acetic acid, provided the distillations are carefully controlled. The yields of acetic acid from
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birch which had been well seasoned were so nearly the same as from the wood which had been seasoned only about 6 months t h a t there is no preference for this species, provided the distillations are controlled. 11-If the recovery of formic acid should become important in the distillation of hardwoods, the experiments showed t h a t t h e highest yields were obtained from rapid (uncontrolled) distillations of wet wood, this being particularly true of beech. 111-A commercial temperature-control test using wood seasoned for only about 8 months gave practically the same increases in acetate as obtained in the laboratory tests. IV-Former experiments showing the value of temperature control in increasing the yield of wood alcohol have been verified in these tests. Additional data on the influence of moisture shows t h a t a n excess tends t o give still higher yields of alcohol in t h e case of beech and the same tendency is shown t o a lesser degree for maple. With birch, however, t h e drier wood is preferred for the highest alcohol yields and although moisture favors t h e alcohol t o a slight extent with maple as compared t o uncontrolled dry distillation, the controlled d r y maple runs gave decidedly the highest yields of alcohol for t h a t species. V-An excess of moisture in general gives lower t a r and charcoal yields, but beech is the exception for t a r and birch for charcoal. FOREST PRODUCTS LABORATORY MADISON,WISCONSIN
THE EFFECT OF CATALYZERS ON THE YIELD OF PRODUCTS 1N THE DESTRUCTIVE DISTILLATION OF HARDWOODS By R. C. PALMER^ Received October 17, 1917
PURPOSE O F W O R K
The purpose of the work was t o study the influence of various reagents or catalyzers on the formation of wood alcohol, acetic acid, etc. ( I ) during the primary reaction occurring in the destructive distillation of wood and ( 2 ) during any secondary reactions t h a t take place between t h e original products. S C O P E OF W O R K
The experiments conducted so far have been preliminary and include a study of the effect of hydrolyzing acid catalyzers in an attempt t o induce t h e maximum splitting off of acetyl or formyl groups from the cellulose or ligno-cellulose and the hydrolysis of these groups t o acetic and formic acids or the decomposition of intermediate products, such as carbohydrates, into these products. Any influence on the formation of other products was, of course, noted. Phosphoric acid was selected as a catalyzer in these preliminary tests as being the most adaptable. I t could be readily injected into the wood in solution and was non-volatile, being transformed into the metaphosphoric acid a t the maximum temperature of the destructive distillation of wood. Maple and beech reduced t o chips about I in. by 1 Acknowledgment is made to Mr. H. Cloukey for making a number of the analyses.
