May, 1930
INDUSTRIAL AND ENGINEERING' ('IIEi1IISTRY
of cooling, with the resultant fonriation of uiidesirahle quantitics of amylene and of dichlorides. The present system, consist.ing of pipe coolers and condensers with an open water spray, does not conserve the heat of the gases, but it does satisfy the special requirements of the process. The first equipment was of copper, but this was replaced by iron because of cost considerations. Sron stands up well BS long BS the g&3 is perfectly dry, but corrodes rapidly if slight amounts of nioisture are allowed to enter the system. Although a close check is kept on the chlorine entering the plant to prevent the entry of water from this source, and the pentanes are dehydrated with dry bydrochloric aeid in the mixing tank, traccs of nioisture do occasioually get into the lines. In order to decrease the failures due to the almost unavoidable slight corrosion, all replacenients in thc chlorinatioii process are now being made with Toiman iron, and cast-iron elbows and return bends are being replaced with Tnbe-Turns of Tonean iron welded into the lines.
413
Final Products
Vrorn the initial mixture of normal and iso-pentane there are produced two main products-a mixture of amyl alcohols of the approximate composition shown in Table 11, and a mixture of amyl acetates together with asmall amount of alcohols, corresponding to the composition shoun in Table 11s. I n addition the following intermediate or by-products are derived from the process: mixed amyl chlorides of the approximate composition shown in Table I, amylene dichlorides, amylenes, diainylene, and dianiyl ether. Any of the six amyl alcohols, normal amyl chloride, and normal x obt.ained by fractionation of the and iso-pentane may also l products or of the raw materials. The mixed amyl alcohols and the acetate-alcohol mixture are uscd as high-boiling constit,ucnts in lacquer solvents. Investigations are under u.ay at the present time leading toward tho establishment of industrial uses for the other products altd by-products.
The Calcination or Enrichment of Phosphate Rock' C. G . Memminger, W. €1. Waggaman, and W. T. Whitney CORONST I"O.PH.4TB
Cmd.*NY, PLANT
czl'u. F L I
HE modern tendelicy in all industrial processes is to Erim 60 per cent to ti8 per cent tricalciuiu phosphate; arid rnanuEacturo or turn out a more coilcentrated product. a large export trade grew up for high-grade phosphate rock This movement has gained considerable impetus in containing from 75 to 78 per cent of this compound. Although the hard-rock phosphate of Florida is on the the fertilizer industry within the past decade, owing to increased froight rates, more costly handling charges, and the x h d e of soniewliat higher grade, the pockety nature of these developrrient of improsed methods of producing phosphoric deposits caused farsighted operators to concentrate their efforts i n developing the more extensive and cheaply acid and synthetic ammonia. The deniand for high-grade phosphate rock has also iri- niiiied pebble deposits. This resulted io a falling off in the creased, as new outlets for phosphoric acid and phosphatc production of hard rock, hilt the demand for the higher products have been opened up and the farmer has become grades of phosphate still enabled t.he hard-rock producers to export substantial tonnages of their product and dispose educated to the use of more concentrated fertilizers. W-hile in the early dags of the phosphatc industry in Sout,li of an a.ppreciable qnnniity in this country for the manuficture of phosCarolina, phosphoric acid f o r phate rock averfood arid cheurical aging as low as 60 purposes. per cent tricalcium phosphate was reDevelopment of garded a s q u i t e Calcination satisfactory, t h e Process discovery of hardrock and pebbleSince an attracphosphate dcpostive premium is it.sin Florida, hot.11 paid for the higher of which wore OS g r a d e s of phosmuch higher grade phate rock, t h e and of greater exoperators in the tent than any prepebble field made viously exploited, every effort to caused production compete for this to fall off rapidlyirr m a r k e t . IZot South C a r o l i n a , only were higher aud now mining grade deposits o p e r a t i o n s have s o u g h t , but the ceased entirely in possibilities of enthat state. The riching pebble sta,ndard for dophosphate by suhmestic phosphate seqnent treatment rock was raised of t h e u ~ a s h e d product were I Received >lsri.li vigorously inves1 . 1030. Figure l~-General view "f Calcinsti"" Plant
T
444
Pikure 2
Flow Sheer of C a l c i n i n g Plnnf, Coronet Phosphate Company
tigated by this c o i i i j m ~ ~ayt its ltzborntory sitar Plant City, Fla.. Tlie results of these prcliriiiriary iwrestigatiuris made it appear that. calcinat.ion at. relatively high tempmatures offered a prolnising lrletliod not only of eliriciiiiig ~ i c 6 b l ephosphate, but of eliniioatiirg as B wliole or in part certa.in iiiipurities whieti were acid-consttiriiiig aiid inrparted ol~jectionahleproperties to pliosphoria acid produced thereirorrr . Accordingly experillietits were coiidiiefml at a piht plant a i d the commercial possibilit,ics tliiis established. Finally two full-sized calcining units were installed with a daily capacity of 600 tons, which have been operated more or lcas coritinuously for the past twelve years. A patent was issued in 1916 to C. G. Meiiiriiiriger (2) covering this process, hut tire details of the plant and the mode of operation haw been given no publicity up t o tlie prescnt time. This hasic patent is quite broad in its scope and covers the calciniiig of the phosphate rock at temperatores sulficienbly high to bring about the decomposition of carbonaies contained therein aiid to cause the free lime formed t o cornbine with silica, thus iriswing a permanent increase in the percentage of P,Oa present i n tho product. In 1923 a patent, was also issued to E. P. Stevensori (9) tin i~ similar process. This inventor claims that, while lie hcats the rock t o a temperature sufficiently high to decompose tlic calcium carbonate, t,he free lime docs not Sorni calcium silicate, hut combines wit.11 the triealciuin phosphntc to form more hnsic conipounds. Ttiis claim does riot appear warranted, n.s mure basic phospliatcs are formed as a r u l e at exceedingly high temperatures such as those obtained in a Ihsserner converter, while calciurri silicato is pruduccd ut much lower teisijnvatures.
constitution, ealciuin carbonate, iiuoriile cunipounds, and organic matter. Every one of those ca.n be decomposed or partially volatilized a t high temperatures when intimately associated a6 they are iii phosphate rock, even the silica present being slightly reduced in the presence of calcium fluoride by the forrnrttion of silicon t.etrafluoride. In a h a 1 practice, however, the main purpose is to eliniinabe all water of colistitution, burn out or char all organic mat,tcr, decompose dl or part of the calcium carbonate prcmit,, and coinbine t h free lime thus formed with silica so that it will riot take t i l ) carbon dioxide and he again converted into carbonate. Iiy Iieating the rock to 2000" F. in an oxidizing atmosphere, practically all OS tlie reactions sought are accomplished with the exception of the complete decornpositioii of tho fluorides, and the tricalcium phosphate eontcnt is raised from 4 to 5 per cent.
Object of Calcining Phosphate Rock
Although it is the general practice to dry phospliat,o Y O C ~ rotary kilns by mrms uf fuel oil ur coal, tlie ternperattire of tlie rock lear4ng t i m e kilns seldom averages above 300" 14'. In ot.lier words, tliis procedure is merely for the purpose o S cliiniiiating the bulk of the free rnoisture present in waslied pebble phosphate. The object sought in calciniiig pliospliate rock at high temperatures is to increase permaiicntly tlie percentage of P,O, by tlie decomposition and volatilization US certaiii substances present in the rock as impurities or diluents, thus saving freight arid liandling charges and economizing on tlie quantity of acid normally required t o effect the conversion of P_ A into . an available forin. Practically all phuspliate rock contains, in additioii bo pliosphatc of lime, appreciable quantities OS silica, water US iii
Figure 3
Brick-Lined Rotary Kiln8 (140 x sfeat) in W h i c h Pebble P h o s p h a t e 18 Enriched a n d Purified
The eoiiiniercial use of phosphate treated by this process has shown that in certain instances it i s not desirable to bring
the temperature OS the phosphate rock as high as 2000" F. for, while such a product contains a higher percentage of tricaleium phosphate than that heated to a lower temperature, the physical and chemical nature of the material has certaiii disadvantages which tend to offset the added concentration of the product. For instance, where highly calcined phos&ate, free from carbonates. is used in the manufacture of super&ospIiabe iiy the ordinary den process, the action be~
tween the acid and the rock dust is so slow that complete decomposit,ion of t,he p1iosptiat.e ia inisch delayed and the final product. is not so porous or so readily cured as that. made from phosphate rock containing carbonate of lime. The inbroduction of improved inet.hods of manufacturing superphosphate, however, wherein the heat of chemical reaction is riot dissipat,ed so rapidly as in the den process, may make this highly calcined phosphate more desirable for this purpasc than that which is i:aloined at, lower t,omperatiirrs.
this teirrl~ratnrc,but for certain purposes this type of calcined o h o a r h t e has advantams over that heated to t~hehigher after Ce1cinine. CIICINBD A I
1600* F. Uciure
AiiW
Per cent I'rr /e"* 0.83 0.11
Moisture
1.46 34.20 2.70
2.82
0.40 30.32
1.32
2.94
0.44 0.2s 8 ~ 9 3 7.28 48.1X1 40.12 0.27 Trace 0.86 1.02 1.72 1.33
io05 1 is __
I
llld
9K5i
ov3
u.11
s.43
n.4o 77.18 8.00 6.03 0.48 2.17
uuu
5.46 5.78 0.78
i Piaurc 4 - R o l e r y Coolers for Reduciiie Ibnzpersfure Phosphate after Calcination Proeeis
