U . S. Department of Commerce Research Paper RP2086 National Bureau of Standards Volume 44, April 1950
Part of the Journal of Research of the National Bureau of Standards
Heats of Combustion and Formation of Cellulose and Nitrocellulose (Cellulose Nitrate) By Ralph S. Jessup and Edward 1. Prosen
This paper gives t he results of bomb calorimetric measurements of heats of co mbustion at 30° C of one sample of cellul ose and four samples of nitrocellulose from cotton linters, and of one sample of cel lulose and four samples of nitrocellulose from wo od pulp. The results have been combined with values for the heats of formation of carbon d ioxide a nd water to obtain values of heats of formation of the celluloses a nd nitr oc e lllllo ~es . Empirical equations are given ex pressin g heat of combustion and heat of formation of the nitrocel luloses as fun ctions of nitrogen content.
1. Introduction in stead of the stale of lhe real gases at atmos ph eric pressure. The work described in this papcr was don e at II. Materials th e request of th e N alional Defense R esearch Committee, and the res ults were ori gin a ll y re The materials whose heat of combuslioll .h ave ported in their Armor and Ordnance Report No. been determined were miLcle avail abl e to th e A- 285 (OSRD No. 3932). National Bureau of Stand ards through arrange The data presen ted in tlli s paper differ from ments made by til(' National Defense R esearch Comm iL tee with th e Offi ce of the Chief of Ord those given in the above report in the follow in g nancc, IiVa l' D epartmell t. respects: (J ) the resul ts are now expressed in The lots oJ eellulose from colton lin ters and terms of the absolu te joule in stead of tb e in te1" wooel pulp wcre obLiLin ed from the Hercules national joule as the fundamental energy unit; Powder Co., Radford Ordnance Works, Radford, (2) the resul ts have been r educed to the basis Va. For the nitrocellulose, the manufacture!', that all gases in volved in the r eac tions disc ussed mft tel'ial nitriLted , iL nd th e ni t rogen contents were are in the thermodynamic state of uni t fu gacity as follows:
Lot ;\0. Source of cellulose ?\ itrogcll )j"anufacturcr ------Percent A 4801 SL ______Cotton lin ters ______13. 42 A 4803S7 ______do ______12.62 R er cLl les Powder Co., Hadforcl Ord EPA 1963 RRSL ______Wood pulp ______13. 36 j nance \Y ork s, Hadford Va. EPA 1964 HRS7 ______do ______12.53 403-74- 2______Cotton lin ters ______12. 14 416-50 ______clo ______II. 49 403- 74- L ______.. \1iT ood p ul p __ 12. 12 }H"'"'''' P",d" Co.,Pa d;", N. J. 416-49 ______do ____ _ I I. 7-+
The analyses for nitrogen wel'e made by the heats of combustion oJ the actual plant samples Hercul es Powder Co. The samples of cellulose were desired, no atlempt was miLde to purify the and nitrocellulose were regular plant amples. samples further. B ecause of the urgent need for the datiL, and as the
Heats of Combustion of Nitrocellulose 38l III. Preparation and Weighing of Samples 0.380 liter. Two types of experiments were made. In one of these a measured quantity of energy The following procedure of preparation and was supplied to the calorimetric system, and the weighing of the samples was followed. A batch resulting rise in temperature was observed. In of cellulose or nitrocellulose sufficiently large to the other type of experiment a weighed sample of serve for all the experiments on that sample was cellulose, or nitrocellulose, was burned in the placed in a desiccator, which was evacuated until bomb, the resulting rise in temperature was ob the material seemed dry and fluffy. Then por served, and the mass of carbon dioxide formed was tions about 10 percent larger than the amount determined. The first type of experiment gives needed for an experiment, about 2 g, were roughly the energy equivalent (effective heat capacity) weighed out and placed in separate beakers. of the calorimetric system, and when the energy These portions were then wetted with distilled equivalent is known, the temperature rise in the water and were compressed into tight pellets in a second type of experiment is a measure of the pellet press. The pellets then contained approx heat produced by combustion [4, 5]. For each imately 20 to 30 percent of water. These pellets experiment the mass of the dry sample of material were placed in separate weighing bottles having burned, the mass of carbon dioxide formed in ground-glass necks and evacuated in a desiccator combustion in the bomb, and the mass of carbon for about 3 to 8 hr. The bottles were then dioxide formed in subsequent oxidation of gaseous placed in an oven, kept at 100° C for 1 hr, cooled products of incomplete combustion were deter in a desiccator, stoppered with their ground-glass mined. The mass of carbon dioxide formed by stoppers, and weighed against a tare (an empty oxidation of the products of combustion was weighing bo ttle of the same size). They were usually 0.01 or 0.02 percent of the mass formed again placed in the oven at 100° C for intervals of in combustion in the bomb. Correction for in 7f hr until constant weight (within about 0.1 mg) complete combustion was made on the assumption was obtained. This was usually reached within that the only product of the incomplete combustion about 2 hI' in the oven at 100° C. About 10 was carbon monoxide. The details of the methods percent of water, an amount that was found to used have been described elsewhere [3, 6] . produce the best conditions for burning the samples in the bomb, was added to the pellets, and the In connection with the correction for the heat pellets were transferred from the weighing bottles of formation of nitric acid in the bomb, the ques to the platinum crucible in which they were to be tion arose as to whether some nitrous acid might also be formed, especially when the nitrocelluloses bumed. The weighing bottles, together ~~h any particles of sample left in them, were put m the were burned in the bomb. To answer this ques oven at 100° C for 1 hr and reweighed against the tion tests for nitrous acid were made by W. S. tare. From these weighings the weight of dry Clabaugh 2 o'n the washings from the bomb after sample was obtained. each of four combustions, two of benzoic acid All weights were corrected to the vacuum basis and two of nitrocellulose. The air initially in using the factor 1.00080, obtained by assuming a the bomb was flushed out with oxygen before value of 1.25 g/ml for the density of dry cellulose burning the two samples of nitrocellulose and and nitrocellulose. before burning one of the samples of benzoic acid but was not flushed out in the case of the second IV. Apparatus and Method for Measure sample of benzoic acid. The amount of nitric ments of Heats of Combustion acid formed in the second combustion of benzoic acid was, therefore, several times that formed in Measurements of heats of combustion were made the first. The amount of nitrous acid found did by burning weighed samples of the material in not exceed 0.5 percent of the total acid formed oxygen in a constant-volume bomb that was part in any of these experiments. The error int.:'o of a calorimetric system described elsewhere duced into the results of heat of combustlOn [1, 2, 3).1 The bomb was made of a corrosion measurements by assuming all the acid to be resistant alloy (illium) and had a capacity of nitric acid is entirely negligible.
1 Figures in brackets indicate the literature references at the end of this paper. 2 Chemistry Division of the National Bureau of Standards.
388 JoW'nal of Research V. Calibration of Calorimeter VI. Calorimetric Experiments on Cellulose and Nitrocellulose The energy equivalent of the calorimeter for the temperature interval 28.5° to 30° C was 1. Measurements of Heat of W etting determined by burning NBS Standard Sample Since th e samples were wet when ignited in the 39f of benzoic acid in the bomb, usin g th e value bomb, the observed heat produced by combustion 26433.8 absolute joules per gram mass (weight in of each sample was lower than thaL for the dry vacuum), recently obtained in this laboratory sample by an amount equal to the heat of weLLing [3 , 9, 10], for the heat of combustion of this of the dry sample with the amount of water added material under the conditions of the standard to it. In order to obtain data for correeLing the bomb process at 25° C. Appropriate corrections observed heats of combusLion for this effect, were made to take account of differences between measurements were made of the heats of wetting the actual and standard bomb processes. The of the various materials. results of these calibration experiments are as The method used was similar to that described follows: Series I , five experiments, energy equiva by Katz [7]. Samples of 2 to 5 g of each cellulose lent 13862 .6 ± 2.1 (standard deviation of mean) and nitrocellulose were placed in weighed glass joules per deg C; Series II, six experiments, cnergy tubes of about 12-mm inside diameter, one end equivalent ]3833.9 ± 1.2 (sdm) joules per deg C. of which was drawn down to a fine capillary and These values of energy equivalen t are for th e scaled. The samples were then dried in vacuum calorimeter containing the same mass of water (residual pressure less than 10- 4 mm of mercury) as in th e experiments on th e nitrocelluloses, and until no water could be detected with the McLeod with the bomb contalning 1 g of water and oxygen gage after the vacuum pump had been shut off for under a pressure of 30 atm at 30° C. In the several hours. Dry air was then admitted Lo the mcasuxemen ts on the nitroeelluloses th e values vacuum space, and the tubes were removed, corked used for the energy equivalent differed from th e immediately, and weighed. mean values given above by two small correc To determine the heat of complete wetting, a tions, one for the h eat capacity of the charge of tube containing dry material was immersed in the nitrocellulose and one for the heat capacity of water of a calorimeter with the sealed end down the oxygen in the bomb in excess of that required and the open end projecting 2 or 3 cm above the to fill it to 30 atm at 30° C. top of the calorimeter jacket. The top of the The mean value of the en ergy equivalent ob sample of material in the tube was 6 cm or more tained in Series I was used in calculating the below the surface of the water in the calorimeter. results of m easurements on the samples of nitro The temperature of the water in the calorimeter cellulose made from cotton linters and con taining was slightly lower than that of the jacket, so that 11.49 percent and 12.]4 percent of nitrogen . there was no heat transfer by evaporation of water After the measurem ents on these samples were from the calorimeter and condensation on the completed, the insulation of the firing elec trode jacket. After sufficien t time had elapsed for the in the bomb failed, and the n ecessary repairs attainment of a steady state, a series of readings involved some change in the heat capacity of the of calorimeter temperature and corresponding time bomb. The calorimeter was therefore reeali was made. The fine capillary at the bottom of bra ted with the repaired bomb. The calibration the glass tube was then broken by pressing it experiments of the second series were made under against the bottom of the ca,lorimeter vessel, per the same conditions as those of the first, except mitting water to rise in the tube and wet the mate that the calorimeter contained a smaller amount rial contained therein. R eadings of time and of water in the second series. The mean value temperature were continued for about 10 min of energy equivalent obtained in Series II was after the rate of temperature change had become used in calculating the results of all m easurements constant. Similar measurements were made on of heat of combustion, except those on the two samples to which small kliown amounts of water samples of nitrocellulose just m entioned. had been added after drying and weighing.
Heats of Combustion of Nitrocellulose 389 The results of the measurements of heat. of of the gaseous reactan ts and products is in its wetting of the completely dry materials are given th ermodynamic standard state of unit fugacity in table 1, together with values calculated for th e at 30° O. The correction for heat of wetting nitrocelluloses from the empirical equation: was made on the basis of the observed value for heat of wetting of th e dry material, alld the data (2 = 93.20- 67lj, (0.115;;;'.1;;;' 0.135) , represented by th e dash ed curve of figure l. In column 4 of table 2 are given values of the where Q is heat of wetting in joules per gram , and ratio of carbon di oxide formed in combustion in .1 is the mass fraction of nitrogen in the sample. the bomb and in oxidation of products of incom plete com bus lion to tb a t calculated from the TARLE l. 17alues fu r heats of wetting oJ samples of dry cellulose and nitrocellulose masses of dry sa,m pIes, based on the assumption that they were pure cellulose or nitrocellulose Heat of wciting Observed represented by the form ula C6Hl 0- X0 5( 0 2) X' Iff 1\itrogen 1-----;----1 minus Source of cellulose co ntent calcu is the m ass fraction of nitrogen in the sample and o bserved ~:~~;r lated m the mass of sample bllrned, then the calculated ------m ass of carbon dioxide was taken as (l.62859 Percent jfg jig j i g CoLton lintcrs ______0. 00 47.7 - 5.23177f)m. The values of atomic weights used Do ______. 00 45. 9 \,"ood pulp ______. 00 59.3 ill this and other calcul ations connected with this Do ______. 00 58.6 report are 0 = 16 .000 ,0= 12 .01 0, H = l.0080, and Cotton linter3 ______It. 49 16.5 16. 1 + 0. 4 Do ______II. 49 16.6 16. 1 + . .) N = 14.008. Do ______12. 14 11. 7 It. 7 0 Do ______12. 62 8.5 8. 5 . 0 3. Further results derivable from experimental Do ______13. 42 3.8 3. 2 +.fl data Wood pulp ______11. 74 14 . 9 14. 4 +.5 Do ______J I. 74 13. i 14. 4 -. i It will be seell from table 2 that the averago Do ______12.12 J I. 2 II. 9 -. 7 Do ______12.53 8. i 9. 1 - .4 values of the r atio (carbon dioxide formed: carbon Do ______13.36 3. ,I 3. 6 -.2 dioxide calculated) are less than unity by amounts ranging from 0.4 to 0.9 percent, indicating that The resul ts of mel:l.SLlremen ts on samplrs co n the samples probably con tained at least the cor taining small amounts of water are shown graph responding amounts of impurity. If it is assumed 1, ically in fi gu re where the abscissa is the mass of 1.0 water pel' gram of dry material, and th e ordinate () - 6 - / f.- is the diffrrence between the heats of wetting of .r;: f-- the dry and wet materials expressed as a fraction 0 .8 ,0 i / of the heat of wetting of the dry material. The I I / solid curve in figure 1 represents data calculated w 0 .6 oz from Katz's [7] equation for cellulose. The w I dashed curve is drawn through the poin ts repre '"w t 0.4 I senting the experimental d ata obtained in this o I investigation. I 0.2 2 . Results of Measurements of Heats of Combustion o o 0.1 0.2 0 .3 0.4 0.5 0 .6 0.7 The results of the measurements of heats of g WATER / g DRY MATERIAL combustion at 30° 0 ar c summarized in table 2. FIG URE 1. R esults oJ measurements of heat of wetting for The observed values of - t:.. UB , the heat of com samples containing small amounts of water. bustion under the condit ions of the bomb process, Abscissa. grams of water PCI' gram of dry materi al. Ordinate, difIercnce were corrected for heat of wetting, and reduced, be tween hea ts of wetting of dry and wot materials expressed as a fraction of in accordance with the procedure outlin ed by the heat of wetting of the dry materi al. Solid curve, Kat z's data on cellulosc . Dotted curve d rawn to represent data obtained in present work. 6 , Cellu ""'IVashburn [8], to th e corresponding values of lose from cotton linters; 0 , nitrocellulose from wood pulp , 11.74 perce nt - t:.. U~, the decrease in internal energy ac nitroge n; D , nitroce llulose from wood pulp, 12. L2 percent nitrogen; (), nitro cellulose fr om cotton linters, 1l.49 percent nitroge n; .., nitrocellulose from companyIng the combustion reaction when each co tton li nters, 12 .14 percent nitroge n.
390 Journal of Research T AB L E: 2. Experimental data on the heats oj combustion'
Heat of com bustion based on Heat of co mbustion based.on Number the mass of sa mple burned Of carbon dIOx id e ~it l' ogc n H~~iid~ f [~~.I;l~~g dt~ }~ll~I~~~ SS Source of cellulose content Of ex peri ca r bon diox ide ______ments ca lculat d - ;,.u. - LiU ~ - ClUB - ~u ~ ------Percent jig jig jig co, jig CO, Cotton linters ...... 0.00 C. 99576 ± 0. 00020- 17320.9 17352. 6 ± 2.3- 10680. 8 10700. 4 ± 2. Ut\ Wood pulp ...... 00 b. 99590 ± O. 00076 17343. I bI7:385. 9. ± 18. 9 1069:3.8 10720. :1 ±
Cotton linters ...... 11. 49 '. 99577 ± 0.0001 3 10667.9 ' 10667.6 ±3. 1 104 28.7 10428.8 ± 2. 4 Do ...... 12.14 . 994 12 ± O. 00025 10 277. 3 10272.7 ± 2. 6 1.0406. I 10401. 4 ± 2.'1 Do ...... 12. 62 b.99489 ± 0.00014 10013.6 10005. :3 ± 3. 1 10393. 0 b10385.5 ± :3.:J Do ...... 13.42 .99407 ± 0. 00019 9538.8 9526. 6 ± 1. 9 10:357. I 103·13.9 ± 2.3
Wooel pulp ...... I l. 74 . 99338 ± O. 00059 10506.3 10504. I ± i.6 10421;.4 10·124 .2 ± 2. 2 Do ...... 12. 12 .99238 ± 0.000 19 10279. 2 10273.9 ± 2. 8 1041 5. 5 10'110.0 ± 2.2 Do ------12.53 .99162 ± 0.000 15 10029. 2 10021. 9 ± 2.6 1039·1. 0 10386.5 ± 1.9 Do ...... , .... 13.36 .99079 ±0.00023 9540. I 9527.7 ± 2. 2 10357.9 10:IH . 6 ± 2. I
IL '1'ho values (ollowing the ± sign in this table arc the standard deviations of the m CEL l1. b 1(ean of three experim ents. c M:ean of two cxpcrilllCJlts. that all tli e impurity in the "amples \\·as il1<'l't tion at 30° C as a function of tho cOL'l'ected n itrogen m atel'i al t hat did not enter into the combusti on conten t. The fo llowing eq uat ions, whicb were reaction in ti ll y way, then the values gj\·en in derived by the m ethod of least squares, represent table 2 based on th e mass of carbon dioxide formed the heats of combustion pel' gram of ni troce llulose should be the heats of combusti on of pure cellulose within about 0.03 percent. For nitrocellulose and pure nitrocellulose. Under this assumption. from cot ton linters: ho\\·ev('r , the vallles of t il e nitroge n contents must be adj Li sted, clu e to the fact th at the n i trog-e n co n M-I ~ = - 4 1 69 .; ~2 + l4069.1' caljg (0.11 5 ~j' ~ 0.13 5). tent of a nitrocellulose containing jnert impurjt~' (1) is higher than th at reported for the impul" (, sample. For nitrocellulose from wood pulp : If w(' let R be th(' ratio (c arbon dioxide formed : car Ml~ = - -1186.3 6+ 1420Ql' cal/g (0.115 ~} ' ~ 0.1 35), bon dioxid e calculated) (sec table 2), } br the mass fr action of n itroge n as rr ported (sec table 2), (2) and i gr am be the amollnt of impurity P('L' (I -i) where}' is the correc ted frac tion of nitl'ogen in the gram of C6H 10-X0 5( N02)X , then it can be shown nitrocellulose. that
1-i=R + 3.2125}(1 - R) . T ABLE 3. Derived data Jor cellulose and nitrocellulose
I The con eded value,./', of the m ass fraction of Corrected -tl ]f ~ - Cllf, Source of ce llu lose nitrogen -Clu ~ at 30° C nitrogen in the nitrocellulose is content at 30° C at 30° C ------callu catlg cat lg }, =_L .. nitrocel- nilrocel- nitrocel- I -'/, Percent .i/uCO, tutose lulo8e lulo8e CoLton linters ______0.00 10700. 4 ±2. 9 - 41 65.0 41 65. 0 1421. 0 Wood pulp .. . 00 10720.3 ± 4. 'I 4172. 8 41 72. 8 1413.2 The derived values for the heats of combustion ------and formation of cellulose and nitrocellulose, to Cotton lill ters ...... I L 52 10428. 8 ± 2.
Heats of Combustion of Nitrocellulose 391 20 (; tion from the heat of combustion tlH'L given by (; (; eq 3. The dotted lines represent eq 1 and 2. 10 - 0 Although there were significant differences • 0 • 0 . ", "-'" 0 • if) - - --- between the heats of combustion of cellulose from w --- a: 'V cotton linters and from wood pulp, 0.18 percent, g -10
3 It is of interest to compare tbe data on cellulose and nitrocellulose witb tlHj=-5896.88+ 26178j' caljg (0.115 ~j' ~ 0.135). similar data on etbanol and ethyl nitrate. Tbe differences between tbe beats (4) of formation of cellulose and nitrocellulose range from 24.4 to 25.0 kcal per nitrate group. Tbe co rresponding difference between the heats of formation of liquid ethanol and liquid ethyl nitrate (referen ce [19], tables 23-29 The data on the nitro cell uloses are plotted in and 2.1-45 (1948» is 22. 1 kcal. Combination o[ the latter value witb figure 2. The abcissa is the nitrogen content of an accurate value for tbe heat of [ormation of cellulose would, tbere[ore, • bave yielded values [or the heats o[ formation of d initrocellulose and trini· the nitrocellulose, while the ordinate is the devia- trocellulose in error by about 5 and 7.5 kcal per monomer unit. res pectively.
TABLE 4. H eats of combustion and formation of cellulose, dinitrocellulose, and trinitroc ellulose
Material Source of ccll ulose - 6 (J ~ at 30° C - M'I~ at30° C -t>Jf7 at 30 0 C I kcal/monomer I kcal/monomer kcal/monomer callg unit callg unit cal/g unit {cotton linters ______675. 3 Cellulose __ . ______4165. 0 4165.0 675.3 1421. 0 230.4 Wood pulp ______. 4172.8 676.6 4172.8 676. 6 1413.2 229.2 2614.4 659.2 2606.0 657.1 715.3 180.4 Dinitroeellulose. _. ______rill"'mW"Wood pulp_. _ _._.....__ . __.__. 2616.9 659.8 2608.6 657.7 712.8 179.7 Cotton linters. ______2190. 2 650.8 2179.5 647.6 523.9 155.7 Trinitrocellulose ____ . ___ Wood pulp_. ____ . ____ 2188.7 650.4 2178.1 647.2 525.4 156. 1
392 Journal of Research l
Where sufficient data were given, the reported [4] F. D. Rossini, Chem. Rev. 18, 233 (1936). values of heat of combustion or heat of explosion [5] F. D. Rossini and W. E. Deming, J . Wasil. Acad. Sci. 29, 416 (1939). were corrected to the basis of the energy units [6] R. S. J essup, J . R esearch NBS 21, 475 (1938) RP1l40. used in the present work, and for the ·Washburn [7] J . R . Katz, Proc. R oy. Soc. Amsterdam 13 II, 958 (1911). eff ect [8], and, where necessary, werc reduced to a [8] E. W. Washburn, BS J . R esearch 10, 525 (1933) constant pressure basis. The resulting values were RP546. then combined with values for heats of formation [9] R . S. Jessup, J. R esearch NBS 36, 421 (1946) RPI71l. [10] NBS Circula r C475, p. 22 (1949). [19] of the products of the combustion 01' explosion [11] San'au and Vieill e, Com pt. rend . 93, 269 (J 88 1) . reaction to obtain the values of - t::,I-1~ . The [12] H . Kast, Spreng- und ;t;i.ind stoffe p. 71 (1921). Data various values were not reduced to a common taken from reference [15]. temperature, because no data on the heat capaci [13] Muraour, Data taken from reference [1 5]. ties of nitroeclluloses have been found. The [14] M. Prettre, Mem. P oudres 24, 223 (1931) . K differences between the results of different observ [15] Tomioka, J . Cellulose In t., T okyo 8, 88 (1932). [16] A. Schmidt and F . Becker, Z. ges. Schiess-u. Spreng- ers are so large that the reduction of the results stoffw. 28, 280 (1933). to a common temperature would not improve the [17] P . R. Milus, Ind. E ng. Chem. 29, 492 (1937). agreem ent to a significant extent. [18] J . Taylor and C. R. L . H all , J . Phys. Che m. 51, 593 (1937) . VIII. References [19] Selected values of chemical thermodynamic properties, National Bureau of Standa rds, ·Washington, D . C., [1] H . C. Dick inson, Bul. BS 11, 189 (19L4) S230. Series I, Vol ume I , T ables 8- 1 (1947) and 23- 2 [2] R . S. Je ssup and C. B. Green, J . Research NBS 13, (1948). 496 (1934) RP721 . [3] R . S. Jessup, J . Research NBS 29, 247 (1942) RP1499. W ASHINGTON, D ecember 14, 1949.
Heats of Combustion of Nitrocellulose 393