INDUSTRIAL AND ESGINEERING CHEMISTRY
988
a boiler plant, and impossible to employ it as a fuel in gas engines. It is true that, by covering the boiler tubes with some acidresisting material of high heat conductivity (such as Carborundum), some of the thermal energy of this corrosive gas may be recovered, but this increases the cost of installation and fails to give the desired efficiency. Probably the chief criticism offered to the two-step process iS that greater losses of the final Product (p205)are involved where phosphorus is condensed, handled, and subsequently burned in a separate combustion chamber, than where it is burned directly in the vapor phase without handling and transferring. I n the opinion of the writer, the losses entailed in handling, transferring, and working up phosphorus residues are fully offset by the losses occurring in the one-step proc-
Vol. 24, No. 9
ess where enormous surfaces of hot reactive silicates are exposed to the action of PzOa. After careful consideration of all the factors involved, it appears that the fuel furnace two-step process offers the greatest promise of being the ultimate method adopted in the production of phosphoric acid for use in concentrated fertilizers, as well as for food and chemical purposes. LITERATURB CITED (1) Johnson, J. E., Jr., “Principles, Operation, and Products of Blast Furnace,” pp. 33-42, McGraw-Hill, 1918. (2) Klugh, B. G., Chem. Met. Eng., 36, 666-9 (1929). (3) G., Ibid.t 37p (lg30). (4) Klugh, B. G., IND. ENG.CHEM.,24, 371-4 (1932). (5) Kochs, A., Chem. Met. Eng,, 36, 741-2 (1929). ( 6 ) Royster and Turrentine, IND.ENQ.CHEM.,24, 223-8 (1932). R~~~~~~~M~~ 17, 1932.
Manufacture of Concentrated Pyrethrum Extract C. B. GNADINGER AND C. S. Corn, McLaughlin Gormley King Co., Minneapolis, Minn.
D
URIKG the past ten years Pyrethrum cinerariae- in the flowers. Manufacturers accordingly standardized folium has become one of the most important insec- their extracts on the basis of the weight of flowers used per ticides. It is particularly adapted for controlling gallon of spray, the only method of standardization then household insects and also for use on fruits and vegetables available. The work describing the isolation and identificabecause it is nonpoisonous to man, although to insects its tion of the active principles was published in 1924 (8). In active principles are among the most toxic compounds 1929 the development of a quantitative method for deterknown. The chief consumption of pyrethrum is in the mining the active principles (1) showed that the percentage manufacture of various kinds of extracts or liquid sprays. of the pyrethrins in different grades of flowers varied from These products are best classified, according to the purpose 0.4 to 1.2 per cent (3). Other investigations (4, 8) proved for which they are used, as household insecticides, horti- that the toxicity of pyrethrum depends entirely on the pyrethrin content. Hence in 1929 it became possible for cultural sprays, and cattle or live stock sprays. The household insecticides are extracts of pyrethrum in the first time to manufacture a pyrethrum insecticide having mineral oil. The best commercial extracts contain the a definite and constant pyrethrin content and toxicity. It has been mentioned that the horticultural extracts active principles from one pound of high-test flowers to the gallon. The oil is usually the kerosene fraction, sometimes are much more concentrated than the household sprays. highly refined to improve the odor. Generally the odor is The former contain from 8 to 100 pounds of flowers to the gallon, making it impossible to manufacture them by the further masked by a suitable perfume. The horticultural sprays are usually extracts of pyrethrum simple process of percolation or extraction employed for in alcohol or acetone. Occasionally oleoresin of pyrethrum making household sprays. Simple extraction is also unsatisfactory for making the emulsified with soft soap is cattle sprays, on account of used, but such a mixture is the high viscosity of the oils likely to deteriorate on standA process is described for manufacturing used in these products. ing, because the alkali deIt gradually became evident concentrated pyrethrum extracts. Ethylene dicomposes the p y r e t h r i n s or that a h i g h l y concentrated active principles. Oil extracts chloride is used for the ektraction. No measurstandardized product of uniof pyrethrum properly emulable loss of pyrethrins takes place in the process. form pyrethrin content and sified are sometimes used on The eject of heat on solutions of pyrethrins is toxicity, which could be used plants; these oil e x t r a c t s , discussed, as well as the effect of storage and for any of the three classes of however, are different from sprays, would find a ready sunlight on Concentrated and standard-strength the h o u s e h o l d insecticides. market. This was eventually As a rule, the horticultural pyrethrum extracts. proved to be the case by the sprays contain a much higher fact that approximately onep r o p o r t io n of p y r e t h r i n s third of all the pyrethrum imt.h.~ a -n t h e h o u s e h o l d i n secticides and are greatly diluted with water for use on ported into the United States in 1931 was p i t through the plant and process described below. plants. Live stock sprays are usually made with the heavier PURCHASING THE FLOWERS mineral oils and should contain about one pound of flowers Until 1929, Dalmatian closed flowers were considered the to the gallon. Various chemicals, reputed to be more or best obtainable. I n that year it was shown (5) that Japanese less repeilent to flies, are also added to these sprays. When the first pyrethrum household insecticides were flowers are superior to Dalmatian and that the pyrethrin placed on the market about 1919, nothing was known re- content increases as the flowers mature ( 2 , 9). The Japsgarding the nature and percentage of the active principles nese crop has been found to contain from 0.58 to 1.21 per cent
SI!ptcrnlJcr, 1Y32
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pyrethrins. It is obvious, therefore, that enormous savings can he effected in the manufacture of a standardized extract, if the flowers are bought. on the bask of the pyrethrin content. .Japanese dealers will not sell on a guaranteed pyrethrin content unless the purchaser accepts or rejects the lot before it is loaded on the st,eamer. This has made necessary the establishment of a laboratory by this company in Japan to analyze all the pyrethrum used in the process, which is I)ought on a guaranteed pyrethrin content of 0.90 per m r t or better. Recently it has been found t.li:Lt i,yrct,hriun flowers lose a considerable percentage of their pyrethrin content during storage (ii)Consequent.ly, . as the e n d o f t h e c r o p y e a r is reachcd, it beconies increasin@y difficult to find lots which will pass this guarantee. In 1931 about 30 per cent of tlie lots offered w r c rejected.
SELECTION or SOLVENT The pyrethrins are viscous liquids, solublein petroleum ether, ether, alcohol, a c e t o n e , ethylene dichloride, and most other organic solvents. When pyrethrum iiowers are extracted, the pyrethrins are dissolved t o g e t h e r with inert materials, the amount of which d e p e n d s o n the solvent used. Petroleum ether extracts less inert matter tliaii any other solvent, and ethyl alcohol extracts more; the foririci extracts about 4 per cent of the weight of the floivers, and the latter about 16 per cent. The petroleum ether extract will dissolve almost completely in kerosene to form a clear yellow solution exactly like t.hat produced when pyrethrum is extractcd directly with kerosene. The alcohol extract, Iioweyer, cannot be dissolved completely in kerosene, and the solution is dark green, making it unsuitable for a household spray. Acetone yields an extract which is only partly soluble in kerosene, and the kerosene solution is also dark green. Other solvents such as benzene are too toxic to the workmen in the plant. Some, such as carbon tetrachloride and most other chlorinated compounds, decompose with the formation of hydrochloric acid u;hen distilled in the presence of moisture, thus corroding the equipment. Still others, such as ether, petroleum ether, and naphtha, are highly explosive. Petroleiim ether and naphtha have the additional disadvant.age of wide boiling ranges, although certain petroleum fractions can now be obtained with a narrower distillation range than was formerly available. The lowboiling fractions of the petroleum solvents are difficult to recover during the pro1 , resulting in high solvoiit losses and increased costs. The solvent which conics nearest meeting all of the requirements is probably ethylene d chloride.' It readily dissolves the pyrethrins, extracting only 7 per cent of the weight of the Rowers; it yields an extract which dissolves in kerosene with a yellow color and is also soluble in alcohol, acetone, and nearly all other organic solvcnt,s. Its toxicity to the aorkmeii is about the same as that of gasoline ( 7 ) . I t is the most stnblc of all the clilwiiiated hydrocarbons when distilled in the presence of moistiirn. Its flash point is comparatively high (14' C . ) , and it docs 8
A piteut ia portdine covering tlie use vi elhyleiir iiicliliiiide
p'ocess.
ih
tlris
c I1 13 >1I
989
not support combustion readily. Its boiling point is constant (83.5- C.) and sufficiently low, under vacuum distillation, to prevent decomposition of the pyrethrins by overheating; a t the same time, it is high enough to permit easy and almost complete recovery of the solvent. Ethylene dichloride also has the advantage of being immiscible with water, permitting easy separation from the small amount of water which distils over in one step of the process. Finally, its cost is low EXTRACTIOX OF FLOWERS
The flowers are ground for e x t r a c t i o n in special mills a t a temperature below 40" C. to prevent decomposition of t h e p y r ethrins. The ideal g r i n d would be a uniform No. 30 powder, hut of rourse it is impossible to obtain this in practice. The ground flowers a l w a y s c o n t a i n some fine material which is very rich in pyret,hrins. The a m o u n t of t h i s fine mat~erial must he kept as low as possible to prevent clogging of the extractors. St the same time, t h r achenes or seeds, which contain most of the pyrethrins, EXTRACTORS must be cracked to permit complete extraction. The qound flowers we assayed immediately before they are charged into the extractors. The extractors consist of covered vertical tanks mounted on trrinnions as shown in Figure I. They are fitted with false bottoms so constructed that, the solvent passes through readily bot the ground flowers are held hack. Each extractor is charged with I500 pounds of ground flowers, and sufficient ethylene dicliloride is pumped in from a storage tank to fill the extractors. The solvent is then circulated through the flowers with a %inch rotary pump for 8 hours and is allowed to stand overnight. Thc next morning it is circul&d 2 hours and is then drawn oiT into a collecting t,aiik. A second portion of fresh ethylene dichloride is then pumped into tlie extractor and is circnlatcd in t,he same way as the first extraction. This process is repeated until five extractioiis have been made. The lajt three extracts, which are weak, are kept separate from the first two strong extractions, and are used for the first two extracts of the mccceding batch. That is, the first two extractions (for every charge after the first) are made with the wenk extracts from the preceding batch, while the last three extractions are made with fresh ethylene dichloride. In this way the amount of solvent which must be distilled is reduced by half. The exhausted flowers in the extractors are now dumped liy rotating the extrnctor on its trunnions and are conveyed to a rotary drier. The ethylene dichloride in the marc is distilled of? and conducted back to the storage tank, after separating the sinall amount of water which comcs from the llnwcrs. The exhausted flowers, frce from ethylene dicliloridc, can he burned as fuel. The ethylcne dichloride extrnwt containing tile pyrethrins in rim iiito a vacimm still and distilled a t a teinperature hclow 60' C. until all ethylcne dichloride is driven off and coiivryed hack to the ethylene dichloride storage tanks. The loss of solvent in the entire process is less than 3 per
Y90
I N D U S T H I A I,
AND
E N G 1 N E E R I N G C II E M I S T R Y
cent. The residue i n the still is i~ dark viscous oily liquid which becomes semi-solid on cooling. About 100 pounds of this oleoresin are obtained from the 1500-pound charge of flowers, the amount varying slightly witah different lots of flowers. This oleoresin contains pract.ically all the pyrethrins that. were present in the flowers. The pyrethrins are easily dissolved from the oleoresin by almost any organic solvent. 'The oleoresin is transferred to a mixing kettle nhere it is trentod with thc desired solvent. This may be
Vol. 21, h9
in the pure condition (11, they are appartxitly not injured by heat when dissolved in ethylene dichloride or mineral oil. Three thousend pounds of flowers Were extracted with 810 gallons of ethylene dichloride. A sample of the ethylene dichloride extract was reserved, and the remainder was distilled in vacuum in the regular way, yielding 191 pounds of oleoresiri. A portion of the oleoresin was dissolved in suffcieiit ethylene dichloride to make the concentration of the solution the sitme as before distillation; this was estaiilished by determining the solids in the two solutions and adjusting the volume of the oleoresin solution accordingly. The two ethylene dichloride solotions were then diluted with seven volumes of kerosene and tested on flies by the I'eetGrady method ( 6 ) . The results are shown in Table I.
,.IABLEI.
EFFECT OF DISTILLATIOZ. ON Toxrcirv ETHYLENE Dicrrr,o~msE~TE.LCT
KTRYLIINZ 1 ) i ~ s L " a I " i ; -
K s i i o r m ~E~X ~ K T Mmr;
CxTnAc-
Prnr-
TIYE
TENINS
Cmm/lOii
Mn./lOO
Tisrr
-
OF
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,**i:r,1932
CHEMISTRY
ISDUSTRIAL A N D ENGINEERING
were lost in bhe process. This extrmt was compared for toxicity with a kerosene extract, made by direct extraction of the flowers, d m containing 90 mg. of pyretlvins per 100 cc. The results of these two experiments, which were made several weeks apart, are given in Table 111.
YY1
stored in amber glass. Flint snd blue glass were unsatisfactory containers for pyrethrum extract. The walls of the blue glass bottles were much thinner than those of the flint glass bottles. This probably accounts for the greater loss of toxicity in the extract stored in blue glass,
TAB].=111. TOXICITY OW EXTRACTS M A D E FXOM CONCENTHATES COMPARED WITH DIRECTEXTIMCTSOF SAME FLOWERS PYnETZ,iliV
SAX.
DEacaiPriox U P
PI.#
SPR*Y
513s 5135
1xreot extiact Eatraot msdds iroin eoi3eentrste Diioot extract Extract made Irom concentrate
5145 5145
C o n r E I r or _.__ I
