Butadiene Storage a t the Rubber Reserve Copolymer Plant Operated hy the R . F. Goodrich Chemical Company a t Port Neches. Tex.
Commercial Chemical Development of Butadiene TRANSPORTATION AND HANDLING JA3lES H. BOYD,
250 Park Awe., iVew Y n r k 17, S. Y .
T
HIS paper is concerned T h e production of butadiene for synthetic rubber 1,a-butadiene will be r r f r r ~ r d only n-ith the problems manufacture is a n outstanding example of rapid comnierto as butadiene. I t s isomer, arising in the commercial cia1 development of a bulk chemical. Butadiene in 1940 1,2-butadiene, in itself is was a laboratory reagent handled in small cylinders, development of a chemical unimportant commercial1.v after its pot'eiitial utility was whereas in 1941 it w a s shipped in railway tank cars. The and has industrial significance urgency of impending war compressed into months the demonstrated experimentally only as a contaminant of I ,3period of years usually required for the transition from and a usable product' was butadiene. research laboratory to full scale commercial utilization. developed. These problems For practical purposes, in have received litt,le if any The solution of many butadiene transportation and hanthe United States in 1940, recognition in the literature dling problems stemmed from previous experience with butadiene was of interest only liquefied'petroleum gas b u t the different chemical propcrand, in general, receive scant, for synthetic rubbers made by not,ice when the new chemical ties of butadiene created new difficulties; its readj- arid copolymerization with aciyis in the laboratory and pilot safe control was important to the success or the governlonitrile, methyl methacryment rubber program. plant stages of its dereloplate, or styrene. Butadienc ment. The solution of these consumption wab negligible problems is essential to then but the extensive laboracommercial success; they vary in number and kind with differtory evaluation work already done plus the German commercial ent materials but their general character is me11 illustrated by experience had demonstrated the value of these copolymers. It those encountered in the commercial development of 1,3-butamas evidrnt that commercial quantities of butadiene would be diene in 1940 and 1941 when it emerged from the laboratory to required. In 1941 the manufacture of butadiene-acrylonitrile become a major chemical of commerce. For convenience here, rubbeis began on a commerrial wale in several private plants and
1703
1704 TABLE I.
INDUSTRIAL AND ENGINEERING CHEMISTRY PHYSICAT, P R O P E R T I E S O F c O M \ I E R C I A L 1 , 3 - R E T A D I E S E
( 1 , 2, 18, 21) iiccepted Values 24.06 164.05 0.6272 5.229 8 : 36 6 59.3 64 1 92 4
Earlier X-aluesU 0.622, 0.626, 0.628, 0.631, 0.834 which correspond t o s . 1 9 , 5.22, 5.24, 5.26, 5 . 2 9
54.7 37.0-65.9
T a k e n from business correspondence i n 1940 a n d 1941. T h e differences in values f o r specific gravities a n d f o r vapor preasure led t o t h e work which resulted in t h e accepted values shown. Q
Vol. 40, No. 9
circumstances, a popcom polyiner can form hut' this is of practical significance only in msnufact,uring operations (8). This polymerizat,ion is slow a t ordinary tempera of butadiene as polymer is negligible. Althouah matter of practical experience, it is conceivable that prolongcd storage of butadiene a t elevatcd temperatures mi;,ht lcad to sufficient exothermic butadiene polymerization i o auiocatdyzc the reaction to a runan-ay polymerization. This has never occurred in commercial practice and this hazard assumc only in experimental 17-ork involving the heating of butadiene a t elcvatcd temperatures. The properties of butadiene m-hich sigiificantly affected its commercial development are shown in Table 111. CO;\IMERCIA L DEVELOPMENT
the tank car movement of butadiene was necessary to suppcrrt, this operation. Knowledge and experience in the transportation aiid handling of butadiene &,ailleda t this stage proved invaluable later when the goveriimc.nt production .of bxtadicne and synthetic rubber beLan in 1942 ( l d j . PROPERTIES OF BU-TADIENE
Butadiene normally is a gajeoua, colorleas, malodorous hydroand is liquefied carbon with the carbon skeleton, C=C-C-C readily by the application of pressure. I t s unsaturation makes it high14 reactive chemically and its structure lends itself to the chain polymer formatioil necessary for elastomer synthesis. I t s chemical properties, at least in polymerization, were not known with complete certainty in 1940 because of purification difficulties and attendant' inability to procure pure butadiene in sufficient quantity t o permit its polymerization behavior to be determined fully. Until tank car shipment of butadiene was imminent, interest in this hydrocarbon had been centered on its chemical properties which affected polymerizatioii and the literature values on the physical properties of butadiene had been accepted without serious question. These literature values of physical properties, as reflected in business correspondence of the time and shown in Table I, n-ere discordant and obviously n-ere obtained using impure butadiene. The reactivity of butadiene with oxygen is of first importance in determining the procedures employed in its commercial utilization. The formation of butadiene peroxides from butadiene and atmospheric oxygen is not understood generally and attempts in two laboratories t,o synthesize them failed, though their formation in butadiene manufacture and/or storage has been reported. Butadiene peroxides are found as, or in, a yelloir- moderately viscous liquid of limited solubility in butadiene. This liquid occasionally is spontaneously flammable on exposure to air and frequently is subject to detonation by mechanical impact, as with a hammer blow. It catalyzes the polymerization of butadiene. Butadiene peroxides are destroyed on heating with strong aqueous caustic soda solution. The dangrrous charact,er of butadime peroxides was evident and this hazard was recognized and controlled so that from its early commercial use butadiene handling has not resulted in accidents from this source. An important precaution is to n-ithdraLT only liquid hut.adiene from ft container to preclude accumulation of peroxides. There appears to be a relation betn-een the method of purification of butadiene and its susceptibility to peroxidation. The ammoniacal cuprous acetate met'hod of purification seems to yield a puiified butadiene either more susceptible to peroxidation or with a hi;her peroxide content than thc butadiene purified by the furfural extractive distillation process. Possibly, because furfural has a stronger reducing action t,han butadiene, it protect,s the latter from oxidation whereas the converse is true in the ammoniacal cuprous acetate system. I n storage, butadiene polymerizes slowly to dimer and lesser amounts of a hetero higher polymer. The polymerization is exothermic and is catalyzed by peroxides as shown in the da.ta of Robep, Vlese, and Morrcll (1Y) in Table 11. Under unusual
In the suininer of 1940, the Bureau of Esplosives anticipatcd the cmiing deniand f:;r tank car transportation ol butadion(: and began accamulatirig the inforniation necessary for its propc:~ hazard classification. From consideration of itFi physical properties it is clear that butadiene is properly classed as a liquefied petroledin pas. However, the uusat,nation renders it chemically react,ive with oxygen: or oxidizing agents hence the need for the exclusion of o nhich are hazardous to avoid thc formation of butadiene per materials (6). From a practical viewpoint atmospheric o is the chief concern. Coinplete exclusion of atmospheric oxygeii at all times from all parts of the butadiene tanka;^, lines, and tank cars would have been difficult if not impossible. Thcreforc;, a small amount of a protective chemical or inhibitor of peroxido formation XTas added as a precautionary measure. The use of inhibitors has continued and the addition of at least 200 parts pt:r million of tert-butyl catechol t o the butadiene is regarded as good practice ( 1 5 ) . It offers ample protect.ion azainst the accidcntal or unavoidable admission of minor quantities of oxyp.en to thv occurs even n i t h careful operation. AIaj9r admisen must be purged from the system with inert gas. Experience during the war years in the transportation of butadiene has proved valid the preliminary con reau of Explosives that, with reasonable care, butadiene can be handled and transported with no more hazard than obtains in the handling of the other liquefied pet,roleum gases of commercesuch as propane, isohutane, and n-butane. This coiiclusion was reached after consultation with the technical and traffic dcpartmciits of the industrial organizations then affect,ed. For safcty purposes, butadiene was and is classified as a liquefied pctrolcum
TABLE 11. Teinperat,xe, 86 86 86 140 140 180
TABLE111.
POLYUERIZaTION OF
F.
13 1
BUTADIENE 70Polymerized
per
Hour 0.0007 0,0033 0.0356 0.0160 0.0300 0.15
P R O P E R T I E S O F LIQCIU BVT-4DIEXE A F F E C T I S G I T S C0MA1ERCIA4LDCJrEI,OPxfEST
Property
K a t e r solubility Gas nolubilitya Oxygen reactivity a n d peroxide formationa Polymerization
Active Os, P.P.M. 1 13 330 1
Operation Affected Filling density Filling denyity Invoice weights Selection of tan!< car3, 1o3ding temperatures, unloading temperatures Use of antifreeze E q u i p m e n t purging Loading, unloading, handling, a n d purging procedures; equipment design a n d use of inhibitor Storage
a These properties of sixnifioance f o r butadiene b u t not i n general f o r liquefied petroleum gas.
September 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
1705
Modern Insulated Pressure Tank Car for Shipment of Butadiene
gas (LPG); its shipment is governed by the relevant Interstate Commerce Commission (ICC) regulations ( 5 ) . When bulk transportation of butadiene became possible legally, shipment' was csscntially thc same as a liquefied petroleum gas except that the chemical character of butadiene required some differences of procedure in the loading and unloading of tank cars and customer education in these procedures was necc=ssary. Liquefied petroleum gases are t>ransport,edin pressure tank cars of approximately 10,000 gallons net capacity; these are built in accordance with ICC specifications 104A and 10L4 which govern the type of construction. The insulated 104il and 104A-W are suitable for transporting liquefied petroleum gas whose vapor pressure does not exceed 75 pounds per square inch gage a t 105" F. and the insulated 105A300 and 105A300W cars are suitable for liquefied petroleum gas with vapor pressure not in excess of 228 pounds per square inch gage a t 105°F. B temperature of 105 ' F. is safely above the maximum liquid temperature experienced on protracted exposure of the insulated shell to summer sunlight. With unlazged containers, such as cylinders, the vapor pressure of liquefied petroleum gas a t 130" F. governs from a regulatory viewpoint as this liquid temperature is above that attainable within the cylinder after several days' exposure to the southern summer sun. Butadiene at 105" F. has a vapor pressure of 49.4 pounds per square inch gage; accordingly, cars of ICC classes 1048 and 105A300, 400, and 500 are approved for butadiene shipment. All 104A and 105A cars are insulated, but if unlaCged, a 104A mould be unsuit,able for but,adiene whose vapor pressure a t 130" F. is 77.7 pounds per square inch gage which exceeds the permissible maximum of 75 pounds per square inch g:age for a 104A car. Thus the vapor pressure of butadiene limits the type of pressure tank car suitable for its transportation. Although uncertainty existed as to the vapor pressure of butadiene in 1940, this uncertainty did not affect the choice of cars for butadiene as liquefied petroleum gas experimce had shown the superiority of lagged or insulated tank cars which now are required for transportation service. The insulated cars are cheaper in first cost than the unlagged cars because of the thinner and lighter tank shell required for the lower working temperature (and vapor pressure). Also, the insulation cushions the tank shell on accidental impact, such as a train wreck. Insulation, of approved type, is in a 4-inch layer on the tank shell; this in turn has a 0.125-inch external steel cover on which is stenciled certain information concerning the tank car. The insulation
also keeps the liquid butadiene cool, preventing excessive pressure buildup in summer, and simultaneously minimizes polymerization which is favored by higher temperatures and by the presence of peroxides as shown. In making shipments of butadiene or liquefied petroleum gas in pressure tank cars (or any sealed pressure vessel), it is necessary when loading the car to make proper allowance for the thermal expansion of the liquid t o preclude liquid expansion t o fill the shell completely or go hydrostatic with resultant liquid leakage through the relief valves on further expansion. Such leakage is not only a loss of valuable hydrocarbon but is also a fire hazard. The necessity for such pressure relief is shown by the fact that if a container is filled completely with liquid C , hy$rocarbons at 50" F. and the liquid temperature rises t o 75 F. without pressure relief, the vessel would be subjected t o a pressure of roughly 1500 pounds per square inch (1). To avoid overloading tank cars the ICC regulations ( 5 ) prescribe "filling densit.y tables" which when used with the tank car outage determine the maximum permissible loading of liquefied petroleum gay The outage table for a tank car is the liquid height-volume calibration table for the partibular car. Outage tables are available from the maker or lessor of the car. The liquefied petroleum gas filling density of a tank car is the per cent of the water weight capacity permissible to load for shipment. The tank car shell must not be filled completely a t 105" F. even though the car is loaded a t some lower temperature. Thus the filling density of liquefied petroleum gas is related directly t o and corrects for thermal expansion. The theoretical filling density of liquefied petroleum gas at 105" F. is 100 times its specific gravity at 60" F. times the volume a t 60" F. occupied by unit volume a t 105" F. I n practice the permissible filling density is the theoretical value decreased by a safet;y fact,or. When the filling density tables for liquefied petroleum gas were first calculated it was found that thermal expansion of mixtures of the lower paraffins (the original liquefied petroleum gas) was a function of the specific gravity of the mixture and the tables were calculated on this basis for the specific gravity range 0.500 t o 0.623 at 60" F. Table I shows that in 1940 the specific gravity of butadiene a t 60" F. mas ascribed various values between 0.622 and 0.634; hence the then current filling density tables might or might not have been applicable depending on the value selected. T o clear up this difficulty it was necessary t,o determine anew the specific gravity a t 60" F. of butadiene; Dean and Legatski found it t o be 0.6273 ( 3 ) . Later, after consideration of all work, the National Bureau of Standards (1)adopted the value of 0.6272 given in Table I. The work of Dean and Legatski showed t h a t butadiene was beyond the established filling density-specific gravity range. The same workers then determined the thermal expansion of butadiene and these data were used in advance of publication for the extension of t,he filling density t)ables for the specific gravity range 0.623 t o 0.635 as now used (6, 1 7 ) . This new specific gravity determination also affected the calculation of invoice weights for customer billing.
Vol. 40, No: 9
INDUSTRIAL AND ENGINEERING CHEMISTRY
1706
From To Tank
50 32
Fnll
60 32 l'ull
70 32 Fill1
80 32 Fall
60 60 3i 24 1~1111 lCrnl>t>
C'oolinq Tinie. n a y s
31 li 3 lj 17 24 28 23 12 " 0 12' 16 20 9 12 1; 18 9 1 ..i i 10 13 15 8 ... a &timati,, of tiiiies t o c o o l to 32' 1'. w e r ~iiiaiie i n thi. s t t i d y of I C ? formation i n t a n k cas&: t o cool t o 3 7 O F.(butadiene v a p o ~prcsuiirc ' 3 pouiidr gage) in the s t u d y o f c a r unloading; and t o rxool t o 24' F. in t h e ytiidy of vaciiiini forination in e m p t y butadienc rars. 20 10 0 -- 10
To cietrrmine the butadicu>lading at tiiiic 0 1 filliiig it is IICCOJmeasure the temperature and voluine oi thc lnitadiene in the car. The liquid &iisit>- of butndienr is 1cnon.n. Thc ternperature is determiiied by wading the tank ciii' rhc:i~nometci~ after at least 10 iniriut tx' iinnit~rsioiiin kerosene or oilitxi liquid 1 ~ 1 1 . The voluinc~i&deterin bottom of tank car t hc~rinoinc~trr mined by gaging the dt:pth of liquid in thc car wing a Flip-tubc gage. This is a tube pi,ovidd ai the up pi^ end ivith a pressure valve that runs t'hrough a packing glr~ndto ptirmit raising or lowering of lube. Thr tube i s raised i.0 thr e or king Ir.vt~l:tnd the valve opened slightl?-. If liquid csoines out, the tube is raised slo\j-ly until liquid flow changes to gas; t.his prrniits deterrnination of the dept,li of t,he gah-liquid intc-i,faccbclow t hc i,efrrenrr plane; this is called the outage. By rrfercncc to t,lic: t,mlr cai' number, the shell capavily of its t u l i and t h e aipplirable out table are obtained; thrse x i t h the outage reading xnd cor1 volume for temperature enable calculation of thc net gallons of' product in car. The net gallons and liquid deiisily of the product det,erminc the *eight of lading for invoice purposes and rnsui't: t,hat the perniissible loading drrisity is not cxceoded. Tn act ual practice precautions must, be t,akcn also to ensure saftbtg of t,ht. operat,or and accuracy of readings (12,I?), The weight of the liquid contviit of a tank ear oC liqurfied petroleum gas mag he determind by track scale iveights ov by slip-tubc gaging. The practice- of the liquefied pc~1i~oh:uin gas indust,ry based on esperiericc is to use slip-tuhis gaging to determine the lading both for perinissihlc~filling: drnsit,y and for invoice weights because of thv following advani ages: sal'?- to
Gaging is more reproduciblr. It is independent of quality of nmiiit eriarice of t t a c k scales. Track scale invcstmcnt, a t ahippcr's plant or t h o alternative of routing car over track scalrs for weighing at point n c origin ~ of shipment is eliminated. Reliance on original tare \wight stenciled on insulat ion slid1 of car is not necessary. The tare of a car changes n-ith \vc,atl
nt~soi,ber. Less frequently cars art' loaded by pressuriiig the tank with butadicne vapor from a vaporizer or with vapor withdrawn from the tank car b y a compressor which discharges t o thc storn#c tank vapor spacc. TThcn compressor reprcssuring is u s c d care must he taken to avoid air lraliagc into the suction sidr o f the compressor with subsequent discharge into tlic storage .Sy5t('Ill.
Liquid butadieiie is unloaded h u m tank cam eithcr b)- coinuring of t,he tank car vapor space vith vapor v-ithdmwi from the storage tank or vc-ith vapor from a liquid hutu-. tiic,rw vaporizer. The la1ter method is preferable for new irisiallatiom as it miriiniizes the oxygen contamination of the butadiene Yystein. Liquid n-ithdrand is always preferable t o v drairal t o avoid peroxide accumulation in the pressure Butadicnc boils at 24' F. and wintcr tomperai~ures This are iiot uiicoriimon in the iior,thcastern l,7nited SIates. Nut adione, like all hydrocarbons, vi11 dissolve some \vat er n.hicIi 011 cooling prccipitates out and collects in tlic unloading sump of the tank car. I n winter it) can frecze there or, morc frcqwntly, es in the exposed unloading lines, plugging them and p1.cvrnting or liampering unloading. To prewnt this in the. coldest 2 gallons of antifi.cc~xrart: added on loadilig a ( ' L U art or \\-(%ather, ivnioval of as much XTl-ater from the cai. as is possiblc. The standard automobile antifreezes are satisfactory. It is dc,sirable a190 to load thc cars n-ith butadi high a5 80' F. for winter shipincnts consigned i and northern Ohio tlrst inations. This onables t) ai destination with cont.ents at a temperature above 37" J', so that, a vacuuni cannot be pulled on the tank car when unloading. 'rhc car is unloaded by removal of all liquid and pumping out the iwidual vapor down to a prmsure of 5 pounds gage suinnier and wiiiter, In thr \\.inter iriert gas, prrft:rably nitrogen, is blown inlo t h e
