Technology
Speclrometrists aim for higher selectivity Combination of analytical methods can boost selectivity of spectrometry technique, cut time and effort spent on sample preparation
1981 ACS ANNUAL MEETING With all the recent advances in spectrometry, analytical chemists now routinely detect, identify, and measure substances at parts-per-billion and even parts-per-trillion levels. If conditions are just right, that is. But if the substance is but one of many compounds in a complex organic mixture—like coal liquids or biological fluids—and if many of the other compounds are similar to and .more abundant than the "target" compound, then the analysis is no longer routine. In such cases, it's often the sample, rather than the spectrometer, that is
the limiting factor. Getting the sample into a form that can take full advantage of the instrument's capabilities may be the hardest part of the analysis. Consequently, analysts are looking for ways to improve the selectivities of the spectrometric technique, to reduce the amount of time and effort that now must be spent on sample preparation. Evidence of progress in that direction was presented at a symposium on spectrometric characterization of complex samples. The symposium was organized by Earl L. Wehiy of the University of Tennessee and sponsored by the Division of Analytical Chemistry. Some of the most generally useful methods for analysis of trace organic compounds in mixtures combine the high separation efficiency of gas or liquid chromatography with the high sensitivity of mass spectrometry. For multicomponent analyses or for total characterization of a sample, these combinations are hard to beat. Still, GC/MS and LC/MS have their shortcomings. Chromatographic separation isn't always complete. Incomplete separation can lead to confusing interferences in the mass spectrometer. The mass spectrometer by itself can't distinguish among different ions having the same mass. According to mass spectrometrists
Low-temperature spectrometry method aids analysis of polyaromatic hydrocarbon mixtures Trigger pulse
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Dye laser
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V. A. Faasel, Ames Laboratory
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Helium refrigerator
Fred W. McLafferty of Cornell and R. Graham Cooks of Purdue, one way to get around these shortcomings— particularly when a mixture is being analyzed for a few specific components—is to substitute another mass spectrometer for the gas or liquid chromatograph. This technique is called tandem mass spectrometry or, for short, MS/MS. With MS/MS, McLafferty explains, initial ionization conditions are chosen to favor the selected components. A mixture of ions characteristic of these components is separated in the first mass spectrometer. To distinguish ions of the components of interest from other ions having the same mass, the separated ions are caused to collide with a gas. This decomposes them into fragment ions, which are measured in the second mass spectrometer. The components of interest can be identified by their unique fragmentation patterns. MS/MS is almost as sensitive as "normal" MS, McLafferty says. Although the collisionally activated decompositions occasion some ion losses, these are mostly offset by reductions in "noise" in the second analyzer. Also, he adds, MS/MS is much faster than GC/MS or LC/MS. Early MS/MS experiments were done on reverse-geometry sector mass spectrometers, which suffered from poor fragment ion resolution. Since then, a number of other instrumental configurations have been developed, including multiple sector, multiple quadrupole, and hybrid systems, the last employing both sector and quadrupole analyzers. Each type seems to be finding its niche. For low or medium molecular weight compounds, the multiple quadrupole systems offer higher resolution at lower cost. Tandem double-focusing instruments are the most expensive, but they afford high resolution even for compounds of high molecular weight. For example, McLafferty says, a tandem double-focusing MS/MS system recently built at Cornell will, when fitted with a new, stronger magnet, allow separations of m/e 50,000 ions of 2-keV energy, with unit resolution. Applications include structure determinations of complex organic molecules such as steroids
and penicillins, and trace quantita tion of tetrachlorodibenzodioxin in the presence of polychlorinated biphenyls, he notes. According to Cooks, MS/MS al ready has become an accepted alter native to GC/MS for mixture analy sis, with particular application in the fields of natural products, medicinal chemistry, and synthetic fuels. For example, one Purdue study of nutmeg used simple MS/MS spectra to iden tify several dozen components in the spice and also used alternative types of MS/MS spectra to obtain molecu lar weight profiles of compounds with common structural features. "Al though this spice has been studied by GC/MS, we managed to identify one new compound," Cooks says. The Purdue workers have built a new hybrid instrument that combines a magnetic sector analyzer with two quadrupole filters. The system pro vides moderate precursor ion resolu tion, high transmission, variable col lision energy, and unit mass resolu tion of fragment ions, Cooks says. The ability to vary the internal energy of the precursor ions adds another res olution element that is particularly useful in differentiating isomeric ions. Mass spectrometry certainly isn't the only tool for analyzing complex mixtures. In fact, says Larry T. Tay lor of Virginia Polytechnic Institute and State University, it's unlikely that any single method will unequiv ocally identify a compound when it's in a mixture of hundreds of un knowns. "On the other hand," Taylor adds, "given η specific monitoring methods, no two compounds should exhibit the same properties in every measurement." What's needed, then, is a "multidimensional approach." An an example, Taylor cites the analysis of coal-derived products, which he describes as a "chemical jungle." One multidimensional tech nique being developed at VPI in volves the preliminary LC separation of a coal liquid into "files," followed by on-line *H nuclear magnetic reso nance detection, and leading to an "LC^H NMR profile." Detection of aliphatics, aromatics, olefins, and hydroaromatics is readily achieved, with lower detection limits of 10 to 20 μ% for single components in the mo lecular weight range of 100 to 300. In addition, *9F NMR spectrometry shows promise for analyzing many of the oxygen-, nitrogen-, and sulfurcontaining compounds that may be found in coal liquids. Other coal liq uids studies at VPI involve two-di mensional chromatography with on line IR detection.
If combining two analytical tech niques is good, combining three techniques might be even better. That's the reasoning of Charles L. Wilkins and coworkers at the Uni versity of California, Riverside. To characterize complex organic mix tures, they're using gas chromatog raphy followed by simultaneous Fourier transform infrared spec trometry and mass spectrometry. FTIR and MS are often comple mentary, Wilkins points out. What's difficult with FTIR is often simple with MS, and vice versa. Thus, using both for a single GC should allow more complete and unambiguous analyses of mixtures. In the GC/FTIR-MS system, the GC effluent is split, with 1% going to the mass spectrometer and 99% to the less sensitive FTIR instrument. Each detector has its own data system that keeps track of what's going on. In addition, each data system searches its spectral library to find the five best matches for each sample component. Ideally, the two searches will produce a common match and the component will be identified. Things aren't always ideal, Wilkins
admits. For example, in an analysis of peppermint oil (which is fairly com plex), more than half the GC peaks, representing 84% of the sample, were unambiguously identified. But the remaining peaks, representing the low-concentration components, weren't. Thus, more work needs to be done; in particular, FTIR sensitivity must be increased. Nevertheless, Wilkins says, the results so far are "encouraging." When it comes to analysis of comlex mixtures of polynuclear aromatic ydrocarbons (PAH), LESS is more, according to Velmer A. Fassel of Iowa State University's Ames Laboratory. LESS, Fassel explains, stands for "laser excited Shpol'skii spectrome try." He notes that resolution of complex PAH mixtures is often dif ficult. And optical spectrometry at room temperature is of limited use fulness, because the spectra are usu ally broad and featureless, with much spectral overlap. However, Fassel says, if PAH mixtures are dissolved in n-alkane solvents and frozen to 77 Κ or below, they yield high-resolution spectra with sharp absorption band widths
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CIRCLE 58 ON READER SERVICE CARD 58 C&ENSept. 7. 1981
Technology (the Shpol'skii effect). This allows the selective excitation of individual PAH's in the mixture by means of sharp line tunable laser excitation, leading to distinctive fluorescence spectra for the PAH components. Fassel and his Ames associates are using LESS for, among other things, the direct quantitative determination of selected highly carcinogenic PAH's in shale, diesel and crude oils, and in coal liquefaction products. The analyses are performed without any prior separation of the PAH's. Fassel says that it's possible, through the use of deuterated analogs as internal references, to compensate for intermolecular luminescence quenching and enhancement effects and thus to obtain unambiguous quantitative determinations. A competitive (but in some re spects similar) low-temperature spectrometric technique is matrix isolation (MI) spectrometry. Ten nessee's Wehry is one of its propo nents. In MI, Wehry explains, the sample is vaporized, greatly diluted with a "matrix gas" (nitrogen, for example), and then deposited as a solid on a "cold finger" at 15 Κ in the sample chamber. That way, Wehry says, each solute molecule is isolated from other solute
molecules in the matrix, so that its spectrometric behavior isn't in fluenced by the other substances present in the sample. The cryogenic solvent gives the advantage of high spectral resolution. Like Fassel, Wehry is analyzing complex PAH mixtures by laserexcited fluorescence spectrometry. But instead of dissolving the PAH's in liquid solvent, he vaporizes the sample and the alkane solvent, using the latter as the matrix gas. The two chemists are at something of a stand off over which method is better. Fas sel asserts that LESS, with its frozen solutions, is simpler than MI and more adaptable to quantitative transfer. Wehry concedes the first point but denies the second. Wehry notes that MI isn't limited to fluorescence spectrometry; it also can be used with FTIR and probably with other types of spectrometry as well. Also, he says, some samples are so complex that they will need at least a degree of fractionation, no matter how selective the spectrometric technique. Since the MI sample is introduced as a vapor, the MI tech nique could be used to monitor GC effluents. Work is under way at Ten nessee and elsewhere to develop GC/MI systems. D
Hindered amines boost scrubber absorbency
1981 ACS ANNUAL MEETING A new class of improved absorbents for carbon dioxide scrubbers has been developed at Exxon Research & En gineering Co.'s corporate research laboratory, Linden, N.J. The ab sorbents are highly hindered amines, which are expected to sharply in crease the capacity of scrubbers al ready in service and/or corre spondingly diminish the capital and energy needs for new installations. The first public description of the amines was given to the Division of Industrial & Engineering Chemistry by Exxon senior research associate Guido Sartori. Main uses for the new hindered amine scrubbing systems likely will be in natural gas treatment plants that scrub out carbon dioxide prior to delivery of the natural gas to consumer pipelines, and in high-vol ume refinery streams. Most commercial processes for
scrubbing carbon dioxide from gas streams are based on selective ab sorption of carbon dioxide in solu tions of monoethanolamine, diethanolamine, and similar compounds. These absorbents are used either in aqueous solutions or as promoters in potassium carbonate solutions. They usually are limited in scrubbing ca pacity by the formation of stable carbamates with the amines. A prac tical limit is about 0.5 mole of carbon dioxide per mole of amine. More sterically hindered tertiary amines don't form carbamates so readily, and some have capacities approaching 1 mole of carbon dioxide per mole of amine. However, most of the contentional tertiary amines ex hibit an absorption rate too low to be of commercial interest. Exxon be lieves that the problems of low ca pacities and low rates are overcome simultaneously with its new class of hindered amines. According to Sartori and his asso ciate David W. Savage, a sterically hindered amine is defined as either a primary amine in which the amino group is attached to a tertiary carbon atom or a secondary amine in which
Exxon's Sartori, Savage work wHh equip ment used In hindered amine studhs
the amino group is attached to either a secondary or a tertiary carbon atom. Examples of hindered amines that have proved useful in the Exxon de velopment program are 2-amino-2methyl-1-propanol, 2-piperidineethanol, and 1,8-p-methanediamine. The very slight tendency of the hin dered amines to form carbamates, and thereby limit absorption capaci ty, is attributed to steric effects and the intrinsic basicity control afforded by the amines. More than 100 potentially useful amines have been identified, but not all of them are commercially avail able. Extensive tests of hindered amine scrubbing systems were con ducted by Exxon Research & Engi neering over a two-year period on natural gas streams from Libyan wells. The technology is available for license. The absorption chemistry of pri mary and secondary amines centers on three important reactions: carbamate formation C0 2 + 2R2NH ^ R2NCOO+ R2NHJ bicarbonate formation C0 2 + R2NH + H 2 0 ^ HCO3 + R2NH£ and carbamate reversion to bicar bonate R2NCOO- + H 2 0 — HCO3 + R2NH A key item in this chemistry is the stability of the carbamates in solu tion. Highly stable carbamates se
verely limit absorption capacity and are harder to regenerate for amine recycle. Similarly, absorption rates appear to depend to some extent on the stability of the carbamate, possi bly through the effects of competition for reacting species. The subject of carbamate stability has not been treated to any great extent in the lit erature, and Sartori and Savage con ducted an extensive investigation in the development of hindered amines. With the aid of carbon-13 nuclear magnetic resonance, they determined the appropriate stability constants for carbamates. The stability determi nations were based on the relative intensities of carbonyl peaks from carbamate and bicarbonate species in solution. Absorption rates were determined from single-sphere absorber tests. This new method gives the absorption rate of carbon dioxide as a function of carbon dioxide loading in the amino solution. Unpromoted carbonate so lutions have absorption rates about 30% faster than simple physical ab sorption. Addition of hindered amines increases the rate up to two orders of magnitude. Sartori and Savage suggest that the enhancement of absorption rates is probably now the highest possible with available chemistry. From the technical viewpoint, the
Typical hindered amines
HO—CH 2 — C — N H 2 CH3 2-Amino-2-methyl-1 -propanol
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biggest advantage of the new Exxon scrubber system is the ability to retrofit existing scrubbers and thereby roughly double capacity with little or no capital investment, in most cases. If capacity is not a problem, then the alternative benefit would be lower processing costs associated with a sharply reduced pumping require ment and regeneration capacity. D
Wet-process acid may be vanadium source
JMLl 1981 ACS ANNUAL MEETING Wet-process phosphoric acid made from Western U.S. phosphate rock is an "attractive" potential source of commercial quantities of vanadium, says P. David Bowerman, a research chemist at Kerr-McGee's technology division in Oklahoma City. Although the vanadium concentration is low, the tonnages of acid are such (about 500,000 tons of P 2 0 5 per year) that they could yield an estimated 4 mil lion lb of vanadium pentoxide (V2O5) annually. Vanadium finds use as an alloying agent in steels and other alloys. It also has chemical uses—for example, in the production of various industrial catalysts. Although it hasn't been classified as a "critical strategic ma terial" (as, for example, chromium and cobalt have), demand for vana dium has been growing and domestic reserves of high-grade ore are fast disappearing. In a presentation to the Division of Fertilizer & Soil Chemistry, Bowerman noted that Kerr-McGee is in terested in "exploiting unusual raw material situations," so it has been studying the possibility of supple menting its Idaho V2O5 production with vanadium from wet-process acid. Area acid producers also are inter ested, Bowerman says, because of the opportunity to make more money by selling vanadium as a by-product. Several processes for recovering V2O5 from wet-process acid had been devised over the years, Bowerman says, but none were commercially feasible under current conditions. So Kerr-McGee set out to develop its own process. After many tests, trin-octylphosphine oxide (TOPO) was found to be the best available exSept. 7, 1981 CAEN 59
Technology tractant. TOPO also is used in some processes for recovering uranium from wet-process acid. In the Kerr-McGee process, the acid is oxidized to raise the vanadium to the pentavalent state and then cooled to precipitate certain impurities. The oxidized, clarified wet-process acid is reheated and sent to an extraction circuit with five countercurrent stages, where it is mixed with TOPO in kerosine. After extraction, the solvent goes to a scrub circuit that removes about 80% of the coextracted phosphate and fluoride and then to a strip circuit,
where the vanadium/phosphorus/ fluorine-TOPO complex is removed from the solvent and sodium carbonate solution. The strip solution is further processed to yield vanadium pentoxide that, Bowerman says, meets existing consumer specifications. The process has been tested successfully in a pilot plant cooperatively operated by Kerr-McGee and J. R. Simplot Co. at the letter's Pocatello, Idaho, wet-process acid plant. In the pilot plant tests, about 85% of the available vanadium could be recovered, Bowerman says. D
Cost will limit use off in-situ combustion
1981 ACS ANNUAL MEETING In-situ combustion probably is most thought of these days as a process applied to coal utilization, but it also can be used as a secondary or tertiary method for enhancing oil recovery from old wells. It is, says J. J. George Stosur, acting director of the Department of Energy's oil division, one of the most imaginative and widely applicable methods of enhanced oil recovery currently being investigated. That it also is one of the most technologically difficult and expensive, however, will most likely limit its use. There have been recent significant improvements in the process and there are likely to be further important improvements in the next decade, Stosur told a symposium on heavy oils in the Geochemistry Divi-
sion. Nevertheless, the method will continue to be an expensive and a high-risk one. The basic concept behind the process is simple. A small fraction of the oil remaining in a reservoir after initial recovery—or after water flooding as a secondary recovery method—is burned in the reservoir. The energy derived from this combustion is used to help remove the remaining oil from the reservoir. The energy helps in two ways: by heating the residual oil so that it flows more easily, and by generating steam and other gases at the combustion site that help to push the oil out of a well. In-situ combustion is difficult to control in the field, however, and even more difficult to simulate in a computer, Stosur says. Serious corrosion problems, made worse by working at high temperatures, and the possibility of an explosion at the injection well if it is not completely free from oil are some of the causes of difficulty. Economic factors, too, seem to be stacked against the process. It is expensive, and most of the cost comes in
Burning a fraction of residual oil drives rest from reservoir Production well
Injection well Air
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C&EN Sept. 7, 1981
Oil bank
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Oil and water
the form of air compressors, special equipment, and other capital costs that must be met before any production begins. Thus, it is hardly surprising that of the more than 100 field trials that have been conducted since the early 1950's, only 17 are still in operation. Results from early projects were generally discouraging, Stosur says, although more recent test results have been more positive. Indeed, with all the negative aspects of the technique, why continue testing it at all? "Next to water flooding, in-situ combustion is perhaps the most widely applicable enhanced-recovery method," Stosur says, and "the process definitely can produce additional oil where water flooding cannot." All enhanced recovery methods use some sort of fluid to help drive the residual oil from the reservoir, and in-situ combustion has the major advantage of using what are probably the two cheapest and most readily available fluids possible: air and water. Thus, despite its difficulties, there is probably a place for the method in future enhanced oil recovery plans. D
Seawater uranium: appealing but costly
1981 ACS ANNUAL MEETING For a number of reasons the extraction of uranium from seawater has great appeal. The supply is very large; the environmental disruption, if any, would be very small; and the technology for doing the job is available. However, a report from Exxon Nuclear Co., Richland, Wash., indicates that, as attractive as seawater extraction of uranium may be, it isn't very profitable and won't become so for a long time. Exxon did the study on seawater extraction in cooperation with Oregon State University to determine the feasibility of the process as an alternative to the mining of ores. According to Exxon's Milton H. Campbell, who described the study to the Division of Industrial & Engineering Chemistry, the extraction of uranium was considered to provide the uranium both as a sole product and as a
coproduct. In neither case were the economics very attractive. The current consensus of the chemical community is that about 98% of the uranium in seawater oc curs in the dissolved state as nega tively charged uranyl carbonate complex ions. Less than 2% occurs as negatively charged uranyl hydroxide ions. Minor amounts of other forms may exist but their quantities are in significant. Uranium, Campbell says, behaves as a conservative component of seawater, meaning that the rates of for mation and consumption are very low compared to the total available sup ply. T h e average concentration of uranium in seawater is about 3.3 ppb and seems t o be associated with av erage salinity. T h e total amount available is estimated at about 4.5 billion tons. However, only the upper 100 meters of the oceans are consid ered accessible for uranium recovery and that lowers t h e potentially
available amount to about 160 million η tons. Even so, that amount is conίsidered a practically unlimited supplyy for the foreseeable future. û The Exxon study examined several types of extraction plants, includingg >floating platforms at sea and bargeîr mounted plants at sea, as well as river η treatment plants ashore. Open ocean ie seawater was determined to be the most favorable resource, if for noo 5other reason than that the flows re )f quired to yield the desired amount of $t uranium exceed the flow of the largest river in the U.S. il The final design for a conceptual it process utilized an extraction plant >r ashore with pumped seawater. For ιdesign purposes, a location in south east Puerto Rico was selected as a ir reference site.# T h e location near « Puerto Yubucoa and the Guayanes il River Valley has a narrow coastal shelf, which allows the Antilles Curr>f rent to bring in a constant supply of warm saline water with low clarifica-1-
tion requirements. The onshore Ιο cation of the plant has the requisite characteristics of low population density, low use intensity, and adequate freshwater supply, The process selected for uranium extraction was adsorption with hydrous titanium oxide as the adsorbent of choice. The four operational steps in the process include loading the titanium oxide by direct contact with the seawater, eluting the uranium from the adsorbent by contact with ammonium carbonate, steam strip ping the eluate to recover the ammo· nium carbonate, and preparing a solid uranium product from the extract. Of the possible contact devices available, a continuous fluidized bed was selected because of stability and simplicity. A minimum of 160 vertical turbine pumps were specifîed to meet peak flow requirements for a 550 ton-per-year reference plant producing U3O8. The annual labor cost for a force of 700 is estimated to be
Telephone link brings ACS fertilizer sessions to Muscle Shoals audience Fertilizer researchers at Tennessee Valley Authority's National Fertilizer Development Center in Muscle Shoals, Ala. (left), listen in on sessions of the Division of Fertilizer & Soil Chemistry that are taking place at the New York Sheraton Hotel, a thousand miles away. The Alabamans were linked to New York by a two-way telephone setup, with microphones and loudspeakers, that not only let them hear what was being said in New York but also let them ask questions of the speakers and make comments on the presentations. For many of the presentations, graphic materials had been delivered to Muscle Shoals in advance so that the Alabama group could see these materials along
with their colleagues at the New York meeting. Most of the Alabamans were em ployees of the National Fertilizer De velopment Center. Others came from the neighboring International Fertilizer Development Center and from com mercial fertilizer plants in the Muscle Shoals area. The telephone link was an experi ment, one of several avenues being explored in attempts to find inexpensive alternatives to attendance at national meetings. Dan Norman, past chairman of the Wilson Dam (Ala.) local section of ACS and one of the organizers of the experiment, says the out-of-pocket ex penses for this particular alternative
were less than $100. Most of this expense was to "patch" the hotel meeting site into the federal telephone system. The total "rear· costs were somewhat more—TVA furnished the telephone equipment and the long-distance telephone service—but were nonetheless modest. Norman estimates that the total cost was probably less than the cost of sending one person from Muscle Shoals to New York for the meeting. The consensus at both ends of the line was that the experiment was a success. Norman says the concept is worthy of expansion; he suggests that ACS consider offering such meeting telephone hookups (for a fee) to interested institutions and companies.
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Technology smaller soil particles. This suggested that a dry screening would concentrate radioactivity in the small-particle cut. However, the effect of dry screening was not large. Wet screening did successfully concentrate the radioactivity in the small-particle cut. The decontaminated soil exhibited radioactivity levels of less than the target level of 25 disintegrations per minute per g. Wet screening thus is considered the primary means of soil decontamination in the process. Secondary methods that further reduce the radioactivity level include attrition scrubbing with such agents as oxalic acid, desliming, flotation with surfactants, and particle separations based on density differences. Method cleans up Wet screening has decontaminated about 65% of the soil from the Rocky radioactive soil Flats spill. Attrition scrubbing of the remaining contaminated soil can further reduce the volume to 11% of the contaminated sample and calcination can yield an additional 26% volume reduction. Navratil suggests that employing the primary and sec1981 ACS ANNUAL MEETING ondary methods tested by Rockwell and others will reduce the original contaminated volume about 80%. Extensive tests over a long period of Further concentration may be possitime of soil contaminated by radio- ble with such tertiary processes as active plutonium and americium in acid leaching, magnetic separations, an accidental spill at a nuclear facility and vitrification. None of these are have resulted in a series of decon- considered economical at present. D tamination methods that now have been offered as a composite conceptual process for soil contamination. Chemicals from syngas The process is suitable for a similar a factor by year 2000 spill, but other radioactive species might require different processing. The conceptual process and its antecedents were described to the Division of Industrial & Engineering Chemistry by James D. Navratil, a scientist with Rockwell International. The accidental spill at the Rocky 1981 ACS ANNUAL MEETING Flats, Colo., nuclear defense plant of Rockwell International some 15 years The various scenarios for the coming ago inadvertently contaminated of the age of synfuels and syngasabout 150,000 sq ft of soil to depths of derived chemicals have begun to apup to almost 8 inches. The contami- proach a consensus. The most recent nation was almost entirely pluto- articulation of part of what is close to nium-239 with small amounts of am- the consensus was given by Mohamed ericium-241. These radioactive ma- Defrawi, manager of technical supterials were partly in the form of port for base chemicals R&D at Shell soluble compounds in mixtures of oil Oil Co., Houston, to the Division of and carbon tetrachloride and partly Industrial & Engineering Chemas very small particles of plutonium istry. dioxide suspended in the fluids. The The gist of Defrawi's remarks is fluids leaked into the surrounding that the potential impact of largesoil. scale commercial production of lowOther than small particles of plu- molecular-weight oxygenates from tonium dioxide, most of the radioac- synthesis gas on the existing industry tivity in the contaminated soil was for those chemicals could be strong contained in an adsorbed state on the before the end of the century. Largeabout $12.5 million, and the capital cost of the plant is estimated to be about $6.2 billion. That capital cost, as indicated by sensitivity studies, may be lowered to about $4.9 billion under some conditions. If such a plant were built in the next 15 years, the cost of extracting uranium is projected to be from $2100 to $2600 per lb of υ3Οβ, with govern ment support. A private venture without government support proba bly could not produce U3Ô8 for under $2700 per lb and the most probable cost would be about $3600 per lb. This prices uranium from seawater extraction out of competition at present without a federal subsidy. D
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scale production of light olefins from synthesis gas is not likely to have much of an impact until after the turn of the century. The reasons are simply that the demand for oxygenates will be small and the demand for olefins will be large. According to notes provided by Defrawi, whether the future becomes economically attractive for syngasderived chemicals depends on four factors: the rate at which the price of crude oil or natural gas increases relative to the price of coal; the value of synthesis gas in relation to other feedstocks; whether the chemical in question is a low-molecular-weight oxygenate or similar material that can use syngas effectively, or whether it is a pure hydrocarbon that rejects oxygen and/or forms water; and the degree to which catalysts and new processes can be developed to improve yields and make it possible to exploit them commercially. Much of the future success of syngas-derived chemicals depends on the demand of petrochemicals in general and on ethylene in particular. The expectation is that ethylene will reach market saturation in the late 1990's, and demand is expected to level off. However, because the absolute demand is so great, ethylene demand still will double between 1980 and 2000. The question is how to meet that demand. Is it to be done with conventional feedstocks or syngas? Nobody really knows, but Defrawi has his opinion—namely, that there will be a rapid decrease in the demand for heavy liquid feedstocks after 1995. Coal requirements possibly will reach 85,000 tons per day to take up the slack, something of a bitter pill for conventional technology. Another big "if is the importance of direct liquefaction with respect to indirect liquefaction. Most of the oxygenates can be produced with only about 10% of the feedstock requirements necessary for hydrocarbons such as ethylene. Under almost every scenario worked up so far, there appears to be no supply crunch for the oxygenates but possibly a very big one for hydrocarbons. The driving force, as usual, is economics and optimists believe that crude oil prices will continue to escalate and coal prices will level off. Pessimists have the opposite opinion. Defrawi suggests, but hedges his predictions, that coal-derived feedstocks will make themselves felt after 1995 with the oxygenates, and then hydrocarbons will come along more slowly in the next century. D
