Chlorine Determination in Coal W. A. SELVIG AND F. H. GIBSON,Pittsburgh Experiment Station, U. S. Bureau of Mines, Pittsburgh, Pa.
T
HE determination of chlorine in coal has received but little attention from coal chemists. I n connection with their investigation of formulas for calculation of the amount of mineral matter in coal, Parr and Wheeler (2) determined chlorine in a number of Illinois coals by digesting pulverized coal with water and titrating with standard silver nitrate solution (Mohr’s method). From 0.0 to 0.56 per cent of chlorine was found in the coals tested. Dunningham (1) mentions the probability of relatively large amounts of chlorine causing corrosion in boiler furnaces and economizers. For a number of British coals he shows analyses of chlorine ranging from a trace up to 1.00 per cent chlorine as determined by the Carius method. I n the ceramic industry high-chlorine coals are considered undesirable for the firing of unglazed clay products because of the glazing action of volatile alkali chlorides. The tests described in this paper show that extraction of pulverized coal with water may give results much too low for chlorine. A simple method is proposed whereby the organic coal substance is destroyed by ignition in an oxygenbomb calorimeter and chlorine is determined in the bomb washings. Volhard’s volumetric method for determinatian of chlorine, used in the tests described herein, includes any bromine or iodine that may be present in the coal. There appear to be no published data concerning the amount of bromine occurring in various coals. Wilke-Dorfurt and Romersperger (3) determined the iodine content of twelve European coals and found from 0.85 to 11.17 mg. of iodine per kg. of coal. The largest amount found would correspond to only 0.001 per cent of the coal.
EXPERIMENTAL DATA Twelve bituminous coals from Illinois, Indiana, West Virginia, Pennsylvania, Ohio, and Oklahoma were selected. The samples were pulverized to pass a 60-mesh sieve. For the water-extraction method 4-gram samples were used, except for the Oklahoma coal where 1-gram samples were taken on account of its high chlorine content. For the bomb-washing method, which is described later, the coal was burned in increments of 1 gram, except in the case of
the high-chlorine Oklahoma coal where 0.5-gram samples were used. In the water-extraction method, 4 grams of 60-mesh coal were wetted by shaking with 75 cc. of water in a stoppered Erlenmeyer flask, after which 5 cc. of nitric acid (1 to 5) were added. A short-stem funnel was inserted into the top of the flask and the contents boiled gently for one-half hour, then filtered and washed thoroughly. The filtrate was evaporated t o a volume of approximately 100 cc. Volhard’s method, described in the procedure for the bomb-washing method, was used for the determination of chlorine, and was found to be more suitable than Mohr’s method, in which the water extraction is titrated for chlorine with silver nitrate. Some coals, especially if weathered, contain a sufficient quantity of iron sulfate to interfere with the end point in Mohr’s method. Table I shows that the bomb-washing method gives consistently higher results for chlorine than does the waterextraction method, which is apparently not reliable, as it is likely t o give much too low results. It is of interest to note that the differences between the two methods for the coal tested from Illinois, Indiana, and Ohio are relatively small, whereas large differences are shown for the coals tested from Oklahoma , West Virginia, and Pennsylvania. Tests were made to determine whether finer grinding of the samples would give higher results in the water-extraction method, as well as to determine the effect of longer digestion and of better wetting of the coal particles by lowering the surface tension of the water by means of alcohol. The water-alcohol mixture used contained 25 per cent ethyl alcohol. Table I1 gives the results of these additional tests, and shows (1) that fine grinding of the coal increased the amount of chlorine extracted, (2) that prolonged digestion increased the chlorine extracted, and (3) that more chlorine was extracted by means of the water-alcohol mixture than by water alone. I n the tests in which the water-alcohol mixture was used the digestion flasks were provided with water-cooled condensers. A comparison of the results obtained with chlorine determined by means of the bombwashing method shows that in all cases the chlorine values by the extraction methods are too low. Additional tests were made to determine the chlorine remaining in the residue from the water-extraction method.
IN COALAS DETERMIXED BY WATER-EXTRACTION AND BOMB-WASHING TABLEI. CHLORINE METHODS
State
SOURCIE OF COAL County
Bed
Illinois
Marshall
No. 7
Illinois
Will
No. 2
Illinois
Marshall
No. 7
Illinois
Jack 8on
No. 6
Indiana
Knox
No. 4
West Virginia
Preston
Bakerstown
West Virginia
Ohio
Pittsburgh
West Virginia
Boone
Alma
Pennsylvania
Jefferson
Lower Freeport
Pennsylvania
Indiana
Upper Freeport
Ohio
Jackson
Sharon
Oklahoma
Okmulgee
Henryetta
VOLHARD WATER-EXTRACTION BOMB-WABHING METHOD METHOD LABORATORYIndividual Individual NUMBER determinations Average determinations Averaae % % % ._ % 0.106 o.los A45464 0.106 0.110 0.105 0.109 0.009 0.007 A62979 0.007 0.006 0.007 0.008 0.027 0.028 A46318 0.028 0.028 0.028 0.028 0.010 0.013 A48816 0.010 0,010 0.011 0.012 A67483 0.068 0.061 0.068 0.058 0.062 0.062 A28926 0.022 0.184 0.022 0.022 0.180 0.182 A32387 0.028 0.072 0.028 0.028 0.073 0.074 A74397 0.038 0.247 0.038 0.037 0.242 0.245 A34491 0.020 0.140 0,020 0.020 0.135 0.138 A72831 0.023 0.176 0.022 0.178 0.021 0.180 A66308 0.009 0.012 0.009 0.008 0.012 0.012 A68380 0.209 , 0.459 0.209 0.460 0.208 0.461
189
BOMB-WASHING METHOD TO COMPARED WATEEEXTRACTION METHOD
% $0.003
+O.OOl 0.000 +0.002 4-0.004 +0.160 4-0.045 +0.207
+O. 118 4-0.166 +0.003 $0.261
ANALYTICAL EDITION
190
Vol. 5 , No 3
AND USE OF WATER-ALCOHOL MIXTUREON TABLE11. EFFECTOF FINENESSOF SAMPLE, TIMEOF DIQESTION, DETERMINATION OF CHLORINE BY VOLHARD WATER-DIGESTION METHOD
CHLORINE EXTRACTED
c_
LABORATORY NUMBER
TIMEOF
WATER-EXTRACTION
FINENESS OF SAMPLE, MESH
DIQESTION
A74397
Hours 0.6
60
A74397
0.5
200
A74397
0.5
325
A74397
4
325
A72831
0.5
60
A72831
0.5
200
A72831
0.5
326
A72831
4
325
Individual determinations
Average
%
%
0.038 0.037 0,044 0.044 0.077 0.078 0.128 0.125 0.023 0.021 0.029 0.031 0.046 0.044 0.073 0.075
Samples of 60-mesh coal were extracted for one-half hour a t boiling temperature by the water-extraction method and chlorine was determined in the filtrate by Volhard's method. The residues were then burned in an oxygen bomb and chlorine determined in the bomb washings. The sum of the chlorine extracted by water and the chlorine in the residues should comprise the total chlorine of the coal and agree with the chlorine as determined in the original coal by the bombwashing method. Table I11 gives the results of these tests and shows that relatively large amounts of the chlorine of some coals cannot be dissolved by extraction with water. The sum of the chlorine as determined by water extraction and that remaining in the residue agree satisfactorily with the total chlorine as determined in the original coal by the bomb-washing method, which method is recommended for the determination of chlorine in coal. IN RESIDUES FROM VOLHARD TABLE111. CHLORINE WATER-EXTRACTION METHOD c -BOMB-WASHINQ
METHOD--
CHLORINE SUM OF IN WATERORIQIEXTRACT- NAL COAL. ABLE AS DECHLORINE TERMINED BY PLUS CHLORINE BOMBWABEINQ IN REBIDUE METHOD ~
VOLHARDWATER- RESIDUIJS FROM EXTRACTION WATER-EXTRACTION M~THOD METHOD Individual LABORA-Individual TORY
determina- Average
NUMBER tions
%
%
A45464
0.105 0.104
A52979
0.008
0.105
A46318 A48816 A57483 A28926 A32387 A74397 A34491 A72831 A66308 A68380
0.007 0.026 0.025 0.012 0.011 0.058 0,056 0.023 0.020 0.030 0.028 0.034 0.035 0.016 0.017 0.024 0.022 0.008 0.008 0.210 0.207
0.008 0.026 0.012 0.057 0.022 0.029 0.036 0.017 0.023 0.008 0.209
determina- Avertions age
% 0,009 0.007 0.002 0,002 0.007 0.008 0.003 0.002 0.002 0.004 0.169 0.164 0.046 0.043 0.215 0.219 0.116 0.119 0.161 0.156 0.001 0.001 0.257 0.255
0.038 0.044 0.078 0.127 0.022 0.030 0.045 0.074
WATER-ALCOHOL MIXTURE
'
Individual determinations
Average
%
%
%
0.047
0,245
0,060
...
0.049 0.044 0.059 0.060 0.095 0.094 0.143 0.146 0.033 0.034 0.043 0.044 0.062 0.059 0.087 0.091
-
BOMB-WASHINQ METHOD
0.096
...
0.145
...
0.034
0,178
... ...
0,044 0.061 0.089
across the terminals of the bomb t o ignite the coal. Fill the bomb with oxygen to a pressure of about 30 atmospheres and submerge in water in the calorimeter bucket. Fire the charge electrically and allow the bomb t o stand in the calorimeter water for not less than 5 minutes after firing. Remove the bomb from the calorimeter water and open the valve carefully to allow the gases to escape a t an approximately even rate so the pressure is reduced to atmospheric in not less than 1 minute. The bomb should be provided with a device for controlling the valve so as to permit a slow and uniform release of the gases. Wash all parts of the interior of the bomb, including the tra with a fine jet of distilled water. It is essential to wash &rough the valve opening also, as considerable spray may collect in this opening. Collect the washings in a beaker, filter, and wash the filter paper with hot distilled water. Evaporate the washings to about 100 cc..and add 5 cc. of dilute nitric acid (1 to 5). Add standard silver nitrate solution to about 2 cc. in excess and warm, with frequent stirring, until the silver chloride precipitate coagulates. Allow to cool in the dark, filter, and wash with distilled water containing 1 per cent by volume of nitric acid. Add 5 cc. of nitric acid (1 t o 1) and 4 cc. of ferric ammonium sulfate as an indicator, and titrate the excess silver nitrate with standard ammonium thiocyanate solution until a faint ink persists after vigorous stirring. All the nitric acid used in t i e method should first be boiled until colorless to remove lower oxides of nitrogen. Make a blank determination covering the entire procedure as described. The blank determinations were found to be low, averaging about 0.1 cc. of the standard silver nitrate solution.
For some coals the chlorine is so low that it is advisable to burn more than 1 gram of coal. I n such cases the coal is burned in increments of 1 gram. One blank determination multiplied by the number of burnings of coal will suffice for the blank correction in such cases. The amount of coal to be burned in order to give satisfactory results is as follows.
%
%
%
0.008
0.113
0.109
0.002
0.010
0.008
0,008
0.034
0.028
0.003
0.015
0.012
0.003
0.060
0.062
0.167
0.189
0.182
0.045
0.074
0.073
0.217
0.252
0.245
0.118
0.135
0.138
SOLUTIONS USED
0.159
0.182
0.178
0.001
0.009
0.012
0.266
0.465
0.460
1. 4.79 grams of silver nitrate, water to make 1 liter. 2. 2.2 grams of ammonium thiocyanate, water to make 1 liter. 3. 16.48 grams of pure fused sodium chloride, water to make 1 liter. Dilute 100 cc. of this stock solution to 1 liter, then 1 cc. is equivalent to 0.001 gram of chlorine. 4. Cold saturated solution of ferric ammonium sulfate. Add 5 cc. of nitric acid (1 to 1) per 100 cc. of solution. The
BOMB-WASHING METHODFOR CHLORINEDETERMINATION
A Parr oxygen bomb of illium metal was used for the chlorine determinations. Other types of oxygen bombs are equally satisfactory if they have inner surfaces which are not attacked by the products of combustion. Place about 0.5 cc. of distilled water in the bottom of the bomb to saturate with moisture the oxy en used for combustion. Put a 1-gram sample of coal (60-mes%) in a platinum tray, the bottom of which is covered with fused alumina (alundum). Connect a short length of iron wire of about No. 34 B. & S. gage
CHLORINE % Over 0 . 4 0.4-0.1 0.1-0.06 Under 0.05
Qrams
0.5 1 2 4
nitric acid used should be boiled until colorless.
To standardize the ammonium thiocyanate in terms of silver nitrate take 100 cc. of water, add 5 cc. of recently boiled nitric acid (1 to 1) and 4 cc. of ferric ammonium sulfate indicator. Add a measured amount of silver nitrate solution (4 to 6 cc.) and titrate with ammonium thiocyanate. To standardize the silver nitrate in terms of chlorine add 5 to 8 cc. of the standard sodium chloride solution to 100 cc. of water containing 5 cc. of recently boiled nitric acid
.
May 15, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
(1 to 5 ) . Add an excess of about 2 cc. of the silver nitrate solution, and determine the excess of silver nitrate according to the procedure described for the bomb-washing Calculate the strength of the silver nitrate solution in terms of chlorine. ACKNOWLEDGMENT This investigation of the bomb method was made at the suggestion of A. c. Fieldner, chief engineer, Experiment Stations Division, U. S. Bureau of Mines.
191
LITERATURE CITED (1) Dunningham, A. C., J . Inst. Fuel, 5, 303 (1932). (2) Parr, S. W., a n d Wheeler, W. F., Univ. Ill. E n g . E x p t . Sta., Bull. 37, 1909. (3) Wilke-Dorfurt, E., and Romersperger, H., 2. anorg. allgem. Chern., 186, 159 (1930). RECEIVEDJanuary 10, 1933. Presented before the Division of Gas and Fuel Chemistry a t the 85th Meeting of the American Chemical Society, Washington, D. C., March 26 t o 31, 1933. Published by permission of the Director, U.S. Bureau of Mines.
__.-
Determination of Plasticizers in Organic Cellulosic Plastics J. D. RYANAND G. B. WATKINS,Libbey-Owens-Ford Glass Co., Toledo, Ohio
I
N RECENT years where greater stability and lower
flammability of plastic compositions have been sought, organic esters and ethers of cellulose have replaced cellulose nitrate to a considerable extent. Frequently, practical workers in the field of plastics are confronted with the analysis of these newer cellulosic compositions and the methods employed have been largely those which have proved timeworthy in the realm of cellulose nitrate plastics. Many of the methods (2) used in the analysis of pyroxylin (cellulose nitrate) plastic are basically founded upon the recognition that the major component is unstable a t elevated temperatures. By taking advantage of the greater temperature stability of the organic derivatives of cellulose, it has been found possible greatly to expedite and simplify the analysis of such plastics. OF PLASTICIZER CONTENT OF TABLEI. DETERMINATION CELLULOSE DERIVATIVE PLASTICS
PLASTIC ANALYZED"
Present
%
PLASTICIZER CONTENT Found Difference
%
%
41.2 40.6 0.6 Cellulose acetate, Type A 41.2 40.5 0.7 Cellulose acetate Type B 41.2 41.0 0.2 Cellulose acetate' Type C 28.6 28.3 0.3 Cellulose acetate' Type D 47.4 46.9 0.5 Cellulose acetate: Type E 33.3 32.7 0.6 Ethyl cellulose Type A 33.3 32.9 0.4 Ethyl cellulose' Type B 13.0 12.8 0 .2 Benzyl cellulose, Type A 11.1 11.0 0.1 Benzyl cellulose, Type B a In order to prove that the method possesses wide applicatiqn, the $astic samples analyzed were made from dlfferent p!asticizera and different inds of cellulose derivative. The cellulose derivatwes varied in chemipal properties (acetyl, content, ethoxy content, etc.), or physical properties (melting point, vlscoslty, etc.).
Of primary significance to the plastic chemist is the determination of the character of the cellulose derivative and the amount as well as chemical nature of the plasticizer used. As in the case of lacquers ( I ) , these determinations are usually conducted by dissolving the plastic in a suitable low boiling point solvent and subsequently precipitating the cellulose derivative by addition of a low boiling point nonsolvent for the cellulose derivative which is a solvent for the plasticizer. The precipitated cellulose derivative is filtered, washed, and dried. The filtrate is concentrated by distillation to remove the low boiling point solvents, leaving a still residue which constitutes the plasticizer. I n general, this method is satisfactory for the separation of the cellulose derivative, although it is frequently necessary to employ great dilutions or repeat the precipitation to obtain the cellulose derivative in the pure state.
However, for the rapid determination and identification of plasticizers, the precipitation method as outlined becomes extremely burdensome. Frequently, plastic compositions contain a mixture of plasticizers and the use of large samples greatly aids the separation of the mixture into its components. To separate large amounts of the plasticizer from the plastic by the precipitation method requires large volumes of costly solvents and the operations are time-consuming. I n order to circumvent these difficulties, the following method of separation was devised.
PROCEDURE Five hundred grams of plastic material cut into small strips are placed in a 2-liter distilling flask equipped with a thermometer and the flask immersed in an oil bath almost to the side arm; or if preferred, the neck of the distilling flask may be wrapped with asbestos cord. A receiving flask of 500 cc. capacity is attached to the side arm of the flask and kept cool by immersion in a freezing mixture or by other suitable means. A vacuum of 0.1 mm. of mercury is applied to the system and the oil bath rapidly heated. The analysis of a number of plastic compositions made from cellulose acetate, ethyl cellulose, benzyl cellulose, and plasticizers of different types led to the adoption of an oil bath temperature of 250" to 260" C. This temperature, while resulting in a slight charring, did not produce any appreciable amount of volatile decomposition products of the cellulosic material, yet it was found sufficiently high to effect distillation of the high boiling plasticizers in common usage. Lower temperatures, while satisfactory if the plasticizer is not characterized by too high a boiling point, unnecessarily prolong the time of separation. Higher temperatures produce volatile decomposition products of the cellulosic material, which, however, are usually easily removable by the customary methods of purification. Using an oil bath temperature of 250" to 260" C., a complete separation may be carried out in a few hours. When separation is completed, which is indicated by the fact that distillate no longer collects in the receiving flask, the contents are redistilled in the usual way or by the method of Hickman and Sanford (3).
DISCUSSION Samples of ethyl cellulose, benzyl cellulose, and cellulose acetate plastics were analyzed by the above procedure. The results obtained are outlined in Table I. I n all cases, the
