Removal of Nitroglycerol and Nitroglycol from a Nitration Plant Effluent by Means of Solvent Extraction Odd B. Michelsen’ lnstitutt for Atomenergi, Postboks 40, 2007 Kjeller, Norway
Sverre 0stern Dyno lndustrier A I S , Research and Development Department, Explosives Division, Nedre Slottsgt. 2, Oslo 1, Norway
Washwater containing blasting oil from washing out residual nitric acid from the reaction mixture in a nitration plant is extracted with dinitrotoluene, another common component of high explosives, in a mixer-settler apparatus. T h e dinitrotoluene used for this purpose can then enter directly into the ordinary manufacturing schemes. This report describes some of the experimental work done to develop a suitable process and the full-scale equipment built for continuous treatment of the washwater from the plant. In the explosives industry nitration of polyalcohols like ethylene glycol and glycerol is a common process. One step in this process is the washing out of residual nitric acid from the formed nitro compounds by means of a solution of alkali, usually sodium carbonate, thus converting most of the carbonate to nitrate. However, during this operation, the solution becomes saturated with the product of the nitration reaction, Le., the explosive liquid known as blasting oil, in addition to droplets of the oil being suspended in it. Up to quite recently the spent wash solution has been regarded as just another effluent and in most cases has been released to the nearest convenient recipient, whether this be a municipal sewage system or a nearby river or the sea. For reasons well known, this is no longer a popular course of action. At Dyno Industrier A/S, at their facilities a t Ski, Norway, the problem became acute when new legislation governing environmental discharge came into force. The idea came up that perhaps the blasting oil could be removed from the wash solution by means of a n extraction procedure, and, perhaps, the extracting agent could be another constituent of high explosives, viz., dinitrotoluene, thereby avoiding the introduction of chemical compounds foreign to the normal processing scheme. Since Dyno Industrier themselves possessed no specialized knowledge on extraction technology, they came to the Institutt for Atomenergi (IFA) a t Kjeller, where research and development work pertaining to extraction has been conducted for a number of years. The basic experiments necessary to establish the feasibility of an extraction process along the lines indicated were then undertaken by IFA and carried out in their laboratories. Subsequent equipment and pilot plant studies were performed on site in the so-called wash house at Dyno Industrier, Ski. The final full-scale equipment with instrumentation was planned and built and set in operation using the expertise of both parties. Besides Norway ( I ) , the process has been granted patents in a number of countries, including the US.( 2 ) .
treated in the sedimentation tank. I t contains, in addition to NG, about 10%sodium nitrate and 1.5%sodium bicarbonate. T h e p H is normally around 8. The density ranges from 1.08 to 1.11g/mL. The commercial dinitrotoluene (dinol) used is a complex mixture of isomeric dinitrotoluenes. It also contains considerable amounts of nitroxylenes plus, to a minor degree, impurities such as phenolic compounds. T h e density a t room temperature varies markedly, depending upon composition, but may for guidance be set a t 1.35 g/mL, while the melting point usually is between 30 and 35 “C. The fact that the extractant is not only a solid a t room temperature, but is also “heavier” than the aqueous phase, makes a somewhat extraordinary situation in an extraction context. It means for one thing that the organic liquid will constitute the lower phase in the extraction system, but a more important implication which follows is that the extraction cannot be run a t room temperature. Separatory Funnel Experiments. The initial experiments were conducted with authentic samples of wash solution which were shaken out with dinol a t various volume ratios. The temperature was kept at 45 “C. These experiments established t h a t distribution ratios in all cases were of such a magnitude t h a t efficient extraction was feasible. The distribution ratio, D , is then defined as the ratio between the concentration of NG in the organic and the aqueous phase after equilibrium, i.e.
Experimental Basic Process Facts. The blasting oil in the present case is a mixture (NG) of nitroglycol and nitroglycerol with a density of about 1.48 g/mL. I t dissolves inthe wash solution to the extent of about 5 g/L. In addition, there is always some NG suspended in the wash solution when it leaves the production line. Most of this is removed by sedimentation in a special tank before it is passed on. In this report the feed solution used for extractions is always the liquid that has been 0013-936X/79/0913-0735$01 .OO/O @ 1979 American Chemical Society
Small Scale Continuous Extraction. Actually, these experiments were done both with mixer-settlers and pulsed columns as extraction apparatus, but although they did not show much difference in performance, the mixer-settler was preferred because of its simple design, flexibility, and easy manner of control. Another factor that determined the choice was the limited head room available in the wash house where the final equipment was to be set up. The following description will be confined to the mixer-settler apparatus alone. The separatory funnel experiments had given, apart from distribution ratios, two other important pieces of information. First, the aqueous phase after equilibrium contained dissolved and dispersed dinol typically ranging from 500 to 1000 mg/L. (The solubility itself was found to be ca. 250 mg/L.) Second, in order to get smooth and rapid phase separation an oil-inwater type emulsion had to be provided during mixing. As long as the main objective of the process was to get rid of the NG from the wash- (waste-) water, the presence of dinol would be of no concern. However, since the water contains considerable amounts of nitrate, the release of which to “natural” recipients was known to be under public scrutiny, it was found desirable to try a simple but obvious method for removing the dinol in order to be prepared for expected legal restrictions also on the release of the nitrate water. If the spent washwater would have to be worked up to produce nitrate in a commercially acceptable form, the dinol could not be allowed to contaminate the product. Therefore, a second extraction step was introduced whereby the dinol is extracted with toluene. Volume 13, Number 6, June 1979
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A r o m a t i c solvent reser voir
Dinol reservoir on w a t e r b a t h
Wash w a t e r reservoir -Magnetic
Flow meter
Flow meter
a
s
L
HT
M
s
m
n?
0
/
M
Flow m e t e r
Heat e x c h a n g e r
,a
Ruffinate 1
0
__e
I
17
HT
s
S M
0
a
0
1
-u-r
Extract
Mi x I ng
c ornp ar tme n t
5
Settling
N
M
0
r
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stirrer
a
0
I
2
o
Orgamc phase
a
Aqueous
HT
HT
1
Extract I c o n t g NG
Heating t a p e
N
Figure 1. Schematic illustration of extraction process
Table 1. Results from Small-Scale Mixer-Settler Runs (Concentrations in mg/L)
a
sampling time, days after start-up
washwater NG (initial)
AG
dlnol
1 2 6 13 19
3800 4700
23 84
635 3070
n.d.
n.d.
n.d.
5600
27 22
580 415
n.d. =
n.d.
raffinate 1
22 000 26 300 n.d. 24 200 25 200
raffinate 2
P n.d.a 4 20 21 6
n.d. 1 10
9 7
not determined.
Toluene was chosen in this case because Dyno Industrier also makes dinitrotoluene (dinol), and the extract (toluene) from the secondary extraction can be used as a raw material for this production. This extraction does not require temperature control. T h e experimental setup is schematically illustrated in Figure 1. Here mixer-settlers I and I1 represent the two-stage dinol extraction process, and mixer-settlers I11 and IV constitute t h e extra extraction battery required to remove the dinol which the washwater carries from the first step. It should be mentioned that in addition to the heating devices indicated on t h e figures, a coil of stainless steel tubing was inserted in both mixer-settlers I and 11. Through these was circulated water from a thermostat. With these precautions, it was no problem to keep the extraction running at a fixed temperature and to avoid crystallization of the higher melting components of the dinol, even during longer breaks such as overnight. The mixer-settlers were operated with a flow ratio aqueouxorganic of 5:l in both the NG and t h e dinol extracting sections. Retention time in the mixers was approximately 5 min, while in the settlers it was about 6 min for t h e aqueous phase and 30 min for the organic one. The process was run 8 h a day for almost 3 weeks. Samples for analysis were drawn a t intervals to check the performance of the extraction procedure. The results are shown in Table I. For designation of samples the reader is referred to Figure 1.
Table I indicates that the first extraction step reduces the concentration of NG by a factor of approximately 200. I t is 736
extract 1 NG
Environmental Science & Technology
further reduced in the second step (the toluene section), but the real magnitude of the effect here is uncertain owing to a poor analytical accuracy a t this low level. The exceptionally high value for the dinol (and also the NG) concentration found in raffinate 1 , 2 days after the beginning of the experiment, is due to traces of emulsion still remaining dispersed in the aqueous phase, as a result of having inadvertently started that day's run with the stirrer (propeller) immersed in the organic phase. This produced, as it will, a water-in-oil type of emulsion which in this particular system is very stable. The emulsion gradually disappeared after interruption of the run and starting up again with the propeller properly positioned in the mixing chamber. Determination of NG and dinol was basically made according to methods devised by Pristera ( 3 )(IR spectroscopy), but adapted a t Dyno's analytical laboratory to suit their special needs.
Full Scale Installation Process and Equipment. For reasons to be mentioned later, the second extraction was omitted in the first full scale installation that was built. T h e nitration plant has a capacity corresponding to a maximum flow of 1500 L/h with respect to the wash solution. The equipment was designed with this figure in mind. A flow sheet of the extraction process is shown in Figure 2. Frorp a retention tank known as the labyrinth, the wash solution runs into tank 1 of the NG removal system. In this tank, which holds 2000 L, the temperature of the solution is maintained a t 45 "C. The liquid level is automatically
2
Wosh s o l u t i o n from labyrinth
0
>
To p r o d u c t i o n o f cxplos~vcs
NG/d/nol based
F = Flow meter RC:
Ratio c o n t r o l l e r
Figure 2. Flow sheet of full-scale process
controlled. In order to prevent settling of any remaining dispersed NG, the content of t h e tank is kept under continuous stirring. By means of an air-lift pump the solution is taken u p to a small overflow head tank (tank 2), whence it is transferred to the mixer-settler unit, passing underway through a flow meter (F). T h e dinol tank ( t a n k 3) is supplied from a large outside storage tank. T h e temperature of the dinol in these tanks and all connecting pipe lines carrying this substance is kept a t about 70 "C. The volume ratio of dinol to wash solution was set at 15 also for t h e full size installation because this allowed all the dinol used in the manufacture of dinol-based explosives to be channeled through the extraction process. Since the flow rate of wash solution is not constant, a ratio controlling device (RC) was placed between tank 3 and t h e mixer-settler unit. This controller is operated by signals received from t h e flow meter F. T h e mixer-settler unit contains two stages. I t is heated by a hot water pipe which runs through t h e various compartments just above the bottom. T h e temperature in the unit is thermostatically controlled and is normally kept a t about 50 "C. T o minimize explosion risks t h e impellers are rotated by air driven motors. The volumes of the mixer-settler compartments are 180 and 720 L, respectively, with effective measurements, given in the same order, of200 cm X 60 cm X 60 cm and 50 cm X 60 cm X 60 cm (length X width X height). Run a t full capacity this gives an approximate retention time of 6 min in the mixers for either phase, while in the settlers it will be about 72 min for t h e organic phase and about 14.5min for the aqueous one, supposing that the interface is set a t half available height in t h e latter. T h e organic phase (extract) from the extraction process is collected in an intermediate tank (tank 4), which is connected with t h e production facilities for NG/dinol based explosives through a pipe line. T h e aqueous phase (the raffinate) from t h e mixer-settler unit passes through a dinol trap, where
suspended dinol and sludge formed by impurities in t h e extraction components are given time to settle out. T h e t r a p is simply a vessel of effective measurements 200 cm X 60 cm X BO cm (length X width X height) which gives a volume of 720 L. The minimum retention time is thus about 30 min. In order t o avoid contamination from extraneous material either floating on the surface or settled on the bottom, the outlet port is placed halfway between the top and the bottom level. After leaving the dinol trap, the raffinate, now virtually free of NG, runs to a n intermediate tank (tank 5). When this tank is filled u p to a certain level, a signal is sent to a control unit in the control room, and pumping of the liquid into a 30-ms3outside storage tank is automatically started. T h e storage tank and the intermediate tanks 4 and 5 were made of ordinary steel. For all other parts of the equipment, stainless steel was used. The process is controlled from the same control room which also operates the nitration plant, and by t h e same single operator. A panel contains all start-up and shut-down switches, regulators and indicators needed for complete remote control. Safety. Normally the NG content of the extract will be -2%. Experiments performed a t Dyno Industrier show t h a t even a dinol extract containing 20% NG cannot be initiated with a T N T (trinitrotoluene) primer in a steel tube of diameter 12 m m a t 60 "C. T h e conclusion is therefore that dinol containing u p to 20% NG is as safe to handle as the dinol itself.
Disposal of Treated W a s h w a t e r The full size extraction assembly was started up in January 1977. Until now the product of'the extraction process, the nitrate-containing raffinate, has for a great deal been disposed of through internal applications in the manufacture of explosives. Other ways of taking care of the product have also been considered. One possibility is to use it for fertilizing purposes, another as a nutrient in the biological treatment of certain effluents. A variety of the latter possibility was actually Volume 13, Number 6, June 1979
737
tested. T h e company has developed a biological method for destroying harmful organic compounds contained in a particular waste solution. T h e active microorganisms involved are normally fed by addition of urea or ammonium nitrate. I t was found that these organisms thrived equally well on a diet of treated washwater containing some dinol. However, the output of nitrate from this source proved much too large to be absorbed by this process alone. I t has now been decided to work u p the dinol-extracted wash solution t o produce nitrate of commercial quality. This may be done by evaporation, preferably following recirculation of t h e wash solution (after adding more alkali), thereby increasing the nitrate concentration. Another way to go is ex-
traction of the nitrate according to a method developed in Finland ( 4 ) .In either case the toluene extraction step mentioned earlier will become a necessary part of the purification scheme. Literature Cited (1) a s t e r n . S., Norwegian Patent 134 885 (1976). ( 2 ) a s t e r n , S., U.S. Patent 4 047 989 (19771. ( 3 ) Pristera, F., A n a / . C h e n . , 25, 844 (1953). ( 4 ) Mattila, T. K.. Lehto. T. K.. I n d . !,'rig C'hem.,Process Des. Deu., 16,469 (1977).
Kccciicd f o r repieit, M a r c h 17, 1978. .4cc(,ptPd Januar?, 2. 1979
Biosynthesis and Release of Organoarsenic Compounds by Marine Algae Meinrat 0. Andreae" and David Klumpp2 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, Calif. 92093 T h e uptake of arsenate from seawater, the biosynthesis of organoarsenic compounds, and the release of arsenite, methyl arsonate, and dimethyl arsinate have been studied in pure cultures of marine phytoplankton species, most of them bacteria free. Complex uptake kinetics and a wide variation in t h e degree of arsenic incorporation from the environment were found. In addition to a substantial amount of arsenic strongly bound to structural parts of the cell, u p to 12 soluble organoarsenic compounds were formed by the algae. All species released substantial amounts of methyl arsonate and dimethyl arsinate into their environment. The production of arsenite was also common, and especially conspicuous with two species of coccolithophores. These findings explain a t least in part the common occurrence of these arsenic compounds in the aquatic environment. Recent studies on the speciation of arsenic in the aquatic environment showed the occurrence of arsenite and two methylated forms of arsenic, monomethyl arsonate and dimethyl arsinate, in both terrestrial and marine waters (I-3j. In t h e marine environment, a strong positive correlation between the concentration of these forms and photosynthetic activity was observed: the methylarsenicals were found only in the euphotic zone, and their concentrations show a strong positive correlation with COe-assimilation rates. This suggested t h a t planktonic algae might be the producers of these compounds. Lunde ( 4 ) and Irgolic et al. (5) had shown that algae were able to take up arsenic from their environment and synthesize various water- and lipid-soluble compounds, which, however, remain to be chemically identified. Lunde ( 4j did not find methyl arsonate and dimethyl arsinate in the cell extracts by thin-layer chromatography. Neither Lunde nor Irgolic indicated t h a t their cultures were bacteria-free. Methods Bacteria-free algal cultures were obtained from the culture collection of the Food Chain Research Group of the Institute Present address, Department of Oceanography, T h e Florida State University, Tallahassee, Fla. 32306. * Present address, DeDartment of Botanv and Biochemistrv. Westfield College (Univkrsity of London), "Kidderpore Avenue, London NW3 7ST, U.K. 738
Environmental Science & Technology
of Marine Resources, University of California, San Diego. They were grown on IMR seawater medium (6). For the arsenate uptake experiments, 10-mL samples containing a total of 2.5 X IO6 cells were transferred into flasks containing 50 mL of medium with varying phosphate and arsenate concentrations. T h e background arsenate concentration of the medium was 13 nM. Carrier-free i4As tracer (2.2 X lo6 cpmj in the form of arsenate was added to the flasks. After the incubation the cells were filtered on Whatman GF/C or 1.2-pm Millipore filters and washed with tracer-free seawater, and the activity was determined in a well-type y counter. For the studies on the biosynthesis of organoarsenic compounds, the cells were grown in batch cultures of 60 mL in IMR medium. Initial concentrations of phosphate and arsenate were 25 p M and 13 nM, respectively. The cells were harvested by filtering on Whatman GF/C filters, except for Gonyaulax (the only culture that was not bacteria-free),which was filtered on an 8-pm Millipore filter. T o avoid cell disruption, the pressure differential during filtering was kept below 0.15 atm. The cells were then homogenized in a Virtis blender with a mixture of water. methanol, and chloroform (1:2:4),the phases separated, and their activities determined by y counting. Paper chromatography of the methanollwater extracts and the deacylated lipids was performed on SVhatman No. 4 paper. T h e extracts were developed with butanollwater (1800:121) mixed with an equal volume of propionic a c i d h a t e r (800: 1020). For thin-layer chromatography, a solvent system conwas used. The sisting of chloroform/methanol/water/NH~OH arsenic compounds were detected by autoradiography. The concentration of arsenite, arsenate. and the methylated forms of arsenic in natural waters and growth media was determined by the method of Andreae ( 7 ) ,which allows their detection in the parts per trillion range with a precision between 2 and 5?& The procedure is based on volatilization of the compounds by reduction with sodium borohydride, gas chromatographic separation of the hydrides, and their detection by atomic absorption and electron capture for the inorganic and organic species, respectively. Results a n d Discussion T h e chemical similarity between phosphate and arsenate suggests that these ions would show competitive behavior with
0013-936X/79/0913-0738$01.00/0
@
1979 American Chemical Society
