R.
n.
BLOM
VALERIE KOLLONITSCH
C.
H.
KLINE
Only known use is in East Germany. Selectivity and resistance to poisoning are excellent; potential applications numerous
R HENIUM CATALYSTS n developing commercial-scale production of rhenium, Icome. US. producers have had difficulties to overThe element, one of the last in the periodic table several
to be isolated, is widespread throughout the earth’s crust, but in minute concentrations. Molybdenite ores have the highest content, but even the richest, such as those found in Norway, contain only about 35 p.p.m. In this county, such concentrations are considered too low for economic recovery, and therefore no rhenium is xtracted from naturally occurring sou~’ces. Rather, it is recovered from a by-product of another > r o d . e . , from molybdenite concentrates which are )btained as a by-product of copper refining. These molybdenites are roasted to obtain the main product, molybdic oxide; and during the process rhenium, volatized as the heptoxide, is scrubbed or leached from the flue gases and dust for conversion to ammonium perrhenate. The ammonium salt itself can he used, or it can be either converted to other compounds or reduced to powdered metallic rhenium which in turn can be compressed or sintered in hydrogen. Not all of these molybdenites, however, contain recoverable rhenium. Their content may range from 10 to 1000 p.p.m. with 100 p.p.m. considered as the minimum for economic recovery. Even the flue dust itself from which rhenium is recovered directly contains only 1500 to 3000 p . p . ~ . Nevertheless, estimates are that only about 3% ofthe rhenium potentially available from these by-product ores is recovered. The balance is vented to the atmosphere and irretrievably lost. 16
INDUSTRIAL AND ENGINEERING CHEMISTRY
Recently estimated gross figures regarding rhenium (both metallic and combined) in the United States show thispattern: Thovrand
Troy Or.
Recovrrable reserm-s Potential $roctical annual production Immediate annual targct of thc industry Resent production Resent consiun$tion
71,ooo 300-450 250 10 5
Domestic interest in rhenium and its salts is rapidly accelerating. The element is spread thin, but estimated reserves for the free world are 17 million troy ounces, of which 11 million are found in the United States. With this ample domestic supply, price of rhenium will probably remain stable, whereas that of platinum under foreign control has historically fluctuated. The total world reserves of platinum, estimated at 15 million troy ounces which is less than those of rhenium, are found largely in Africa (40%) with the balance in the Soviet Union and the rest of the world. Rhenium is cheaper than platinum. The present price in combined form is about $1.40 per gram compared with $2.60 for platinum metal. Another factor may be important: Rhenium producers hope to achieve a production volume which lags less behind that of platinum. For example, in 1960 total domestic use of platinum amounted to about 325,000 troy ounces, with
nd petroleum industries a the I abour ~ u ~ , u uounces. u Rhenium produKns LWF IV recover in the foreseeable future 250,000 ounces annually. Until World War 11, Germany supplied the world with rhenium and this may be why interest in foreign countries seems to be greater than here. Rhenium catalysts are being tested extensively in East German refineries, and a considerable bcdy of Russian literature is being published. Total production of rhenium and its salts in East Germany is not known; however, a partial figure of 3500 troy ounces has been reported. In 1942, when German imports were cut off,workers at the University of Tennessee found a source of rhenium in molybdenite roaster flue dusts from the Miami Copper Co.'s smelter in Miami,Ariz. Extraction methods were developed, and for several years, the University of Tennessee was the only domestic producer; however, Miami Copper's operations have closed down. In 1954, the Kennewtt Capper Carp. began recovery from the by-product molybdenite of its western low grade copper ores, and in 1955 its subsidiary, the Chase Brass and Copper Co., began to fabricate rhenium and its allays on a small scale. Recmtly, the Shattuck Chexni: cal Co. began producing rhenium chemicals and Chase Brass has gone into commercial production of the metal and fabricated products. Even with this expanded activity, rhenium and its salts still suffer h m two economic ilk: They are byproducts of by-products and information about properties and potential uses has not been widely disseminated.
RHENIUM CATALYSTS
Potentials
Selective hydrogenation
Hi$
Dehydrogenation
Extreme poison resistance
Dehydroisomerization of alkyl cyclopentones and dehydrocyclization of paraffins to aromatics
High activity
Vapor- and liquid-phase oxidation
Relative low cost
Selective dehydrochlorination
Ready availability from domestic mineral deposits
VOL 5 4
NO. 4 A P R I L 1 9 6 2
17
Rhenium catalysts not In d & a w n q : e v e n particularly for though +y show definiEe Certain hydrogenation re for reforming : re6neiy products. As the s, the chemical^ industry may find that it has, bacfically on its doorstep, '', a new class of catalygts that offerdi@kcteconomic and technological advantages. Rh.enium is intriguing, and with increased availability, i.i new usea will certainly be found. T?Emetal has a melting point which is second highestpf the metals and third highest of all elements. Density is fourth. potential of its salts, used now o d y in research qu&titii%: is pmmising. The full F p l o f their , d u l n e s s to the#\ chemicalindustry has not even begun to emerge.
"
'
PPKIPITATE RHI SULFIDE
PUKE AMMOP iRRHENATE CI
Hydrog.ndlon
Heptasulfide and Heptasclcnide. These compounds, unsupported, have unusual selectivity, great resistance to poisoning, and high activity at 50' to 250' C. and 60 to 400 a m . Also they are convenient to use because they can be stored in air of ordinary humidity without loss of activity. They are not affected by non-
R. H. Blom is Resiaht of S. W.Shathrck Chemical Go. Valerk Kollonitsch is a Technical Injmation Specialist with C. H . Kline 6" Go., Inc., comltants, and Charles H.Kline is Pwsiaht of that company, and a directw of Shuttuck Chemical. AUTHORS.
18
INDUSTRIAL AND ENGINEERING CNEMISTRY
'6xidiaing acids, and
