TECHNOLOGY Ft. Worth Section of ACS, which provided matching funds for the ACS grant. The objective was not so much to teach, science principles, she says, but rather to expose the children to the beauty of chemistry and to "invoke a sense of wonder." As one part of the project, volun teers from the local section present ed chemical "magic shows" to ele mentary school classes. In addition, for the students in grades two and three, the demonstrator offered ex periments in "kitchen chemistry" for the students to take home and do with their parents. One experi ment, for example, dealt with paper chromatography of felt-tip pen ink. The Dallas-Ft. Worth Section sent certificates to children who did the experiments and returned their ex ercise sheets to the teacher—if the teacher in turn sent them on to the section. There were some problems with followup. Nevertheless, the program was considered a success. And, Hendrickson adds, "It's been our experience that requests and in volvement continue, once teachers know that ACS people are willing and able to contribute." James R. Grissom, a high school chemistry teacher in Santa Ana, Calif., didn't get a PACTS grant. Nevertheless, he's doing his bit. For the past few years, he has invited second- through fifth-grade classes in local schools to visit high school chemistry laboratory sessions. The young students actually car ry out experiments, guided by the older students, who have already done those particular experiments. Particularly successful have been ex periments involving the collection and properties of hydrogen and car bon dioxide. The students enjoy the spectacular reactions, and the topic of gases fits in well with the sci ence curriculum of the lower grades. "We usually get letters of appre ciation from the younger students," Grissom relates. "These are highly prized by my students. One that I received was especially gratifying to me. It was from a fifth-grade boy who wrote: Ί appreciate that you spent your time with us. When I grow up I want to be a scientist. Maybe if I get lucky I might be a teacher.' " Ward Worthy
New hydroformylation catalysts developed Los Angeles New hydroformylation catalysts de veloped by Union Carbide exhibit as much as 100 times the activity of previous catalysts. In addition to their intrinsic worth in industrial chemistry, the diorganophosphitemodified rhodium catalysts may per mit the utilization of raw materials previously considered too unreactive for commercial use. Speaking at a symposium on new developments in monohydric alco hols, sponsored by the Division of Industrial & Engineering Chemis try, David R. Bryant, research chem ist at Carbide's South Charleston (W.Va.) Technical Center, also not ed that the new class of phosphite ligands that are used to make the catalysts are "remarkably more sta ble" than conventional triorganophosphites. Rhodium catalysts that are modified with the new diorganophosphites accomplish hydro formylation with sharply increased rates and allow the hydroformyla tion of less active olefins such as 2-butene and 2-methylpropene un der mild conditions.
Hydroformylation refers to the production of aldehydes by the cat alytic addition of synthesis gas (car bon monoxide and hydrogen) to ole fins. Cobalt and rhodium usually catalyze this reaction. Alcohols may be made from the corresponding aldehydes by hydrogénation. The original industrial processes for hydroformylating olefins required pressures up to 6000 psi and temperatures up to 180 °C. There was also some difficulty in controlling the relative amounts of branched and normal isomers that were produced. The low-pressure oxo process, which was commercialized in 1975, decreased the pressures and temperatures required. However, some potential applications, such as using 2-butene and 2-methylpropene to make a- and β-branched alde hydes in large yield, were not real ized. According to Bryant, Carbide can now do this. The organophosphites are esters of phosphoric acid and are consid erably more reactive than the phosphines. Phosphites also require more careful handling but offer great po tential for the hydroformylation of internal olefins. Phosphite-modified rhodium cat alysts have naturally high hydro-
Carbide's diorganophosphites are made from diol -OPCI 2
^-o Diorganophosphite
October 10, 1988 C&EN
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Technology formylation activity but also exhib it some undesirable side reactions— specifically, formation of the adduct with an aldehyde, catalyzed hydrol ysis, hydrogenolysis of the phosphite ligand, and transesterification. There is also a possibility of autocatalytic decomposition of the phosphites. The particular attraction of the diorganophosphites is that upon hy drolysis they give both an organic diol and an organic mono-ol. Con ventional triorganophosphites give three mono-ols. Several synthesis routes to diorganophosphites exist.
The very high hydroformylation activity of the diorganophosphitemodified rhodium catalysts offers much scope for making aldehydes and alcohols. For example, 3-phenylpropyl alcohol and 2-phenylpropyl alcohol may be made by hydroformylation of styrene using the diorganophosphite-modified rhodium catalyst, followed by re duction of the aldehydes. Other hard-to-formylate olefins include vi nyl acetate, 2-methylpropene, and cyclohexene. Joseph Haggin
Ghemical sensors are boon to microanalysis
Los Angeles Miniaturization is a continuing trend in the field of analytical chem istry. Another trend is the growing use of sensors that depend on chem ical as well as physical phenomena. At a symposium on chemical sen sors and microinstrumentation, sponsored by the Division of Ana lytical Chemistry, it appeared that the trends were mutually reinforc ing. For example, surface acoustic wave (SAW) devices are finding increas ing use as chemical sensors in a variety of applications, according to David S. Ballantine Jr. of GeoCenters Inc. (Ft. Washington, Md.) and Hank Wohltjen of Microsensor Systems (Fairfax, Va.). A SAW de vice is a quartz plate with electrodes attached to its surface. When volt age is applied, an acoustic wave is generated at the surface of the plate; the frequency depends on the sur face mass of the crystal. Tradition ally, the SAW device has been used as a chemical vapor sensor, respond ing to changes in the mass or in the conductivity of a thin film on its surface, caused by reaction with the impinging vapors. Recent experiments indicate that the SAW also responds to changes in the elastic properties of surface films, Ballantine and Wohltjen say. Thus, SAW devices also can be used to characterize polymeric materials. 28
October 10, 1988 C&EN
Specifically, the two have used 158-MHz dual SAW devices to mea sure such properties as glass transi tion temperatures, melting temper atures, thermal expansion coeffi cients, and shear modulus values. The technique is extremely sensi tive, they say, permitting the analy sis of very small samples. And their small size should make them useful in in-situ applications—for exam ple, in monitoring a curing pro cess. At Sandia National Laboratories, meanwhile, Gregory C. Frye and coworkers have been using SAW
Surface acoustic wave devices are finding increasing use as chemical sensors in a variety of applications devices to measure molecular diffu sion coefficients and adsorption iso therms in a variety of thin films. For example, oscillation frequencies were monitored during the diffu sion of nitrous oxide and several alcohols into thin polymer films cast on SAW devices. The frequency changes translated into diffusivities between 10"9 and 10~13 sq cm per second. Diffusion is measured in real time, Frye points out, with results obtained in minutes to hours. Similar techniques were used to obtain nitrogen adsorption iso
therms at 77 Κ for several porous silicate films. Pore size distributions were also calculated from the ad sorption data. Films with less than 0.2 sq cm total surface area have been characterized, Frye says, noting that that represents an improvement of 104 over the minimum surface area measurable with conventional apparatus. In related studies at Sandia, An tonio J. Ricco and associates have been exploring the use of acoustic plate mode (APM) devices as sen sors in liquid-phase environments. APM waves are launched and de tected with interdigital-pattern elec trodes and piezoelectric quartz sub strates similar to those used for SAW devices. However, APM waves prop agate through the bulk of the sub strate, allowing sensing with either crystal face. The APM waves have negligible surface-normal displace ment components, and therefore aren't subject to the excessive atten uation that limits the use of SAW devices in liquids. Electrode reactions, electroless de position, and corrosion of thin met al films all have been measured with nanogram-per-square-centimeter mass resolution using APM devices, Ricco says. He adds that solution properties such as dielec tric coefficient, ionic conductivity, and viscosity also affect APM wave propagation characteristics, and thus also can be monitored. Several other symposium speak ers dealt with new electrochemical sensors of various types, including sensors capable of detecting anions. In one such presentation, Universi ty of Michigan chemist Mark E. Meyerhoff noted that highly selec tive polymeric membrane electrodes are now used routinely for direct measurement of various common cations. However, there are relative ly few such devices for measuring anions. To help remedy that situation, Meyerhoff and his research team have been working on new types of sensors. In the field of anion sensing, for example, they have de veloped a new solvent/polymeric membrane electrode said to have unique selectivity toward anionic salicylate. The electrode is made by incorporating 5,10,15,20-tetraphe-
nyl(porphyrinato)tin(IV) dichloride into a plasticized polyvinyl chloride membrane. Response to chloride ion is minimal, so the new electrode could prove useful for measuring salicylate ion levels in biological samples. The team has also prepared another membrane electrode, incorporating bis(diethyldithiocarbamato)mercury(II) into PVC, that is highly selective for sulfite ion.
Chemical microscopy might eventually measure secretions from single cells or follow corrosion processes in cracks At the University of Cincinnati, chemist Harry B. Mark Jr. and associates are taking a different approach to anion detection. They have made a series of conducting polymers that behave as charge sensors under a positive applied potential and show a peak-shaped current signal for ionic analytes in a flowing system. The kind of polymer, its morphology, the synthesis electrolyte, and the analyte electrolyte all seem to affect the signal, Mark says. For example, detection limits are in the microgram per liter range for NO2""/ NO3-, CICV, CI", and SCNT but about 100 times greater for other ions such as HCO3", BO33", and CN" in aqueous solution. Two of the conducting polymers under study, poly(3-methylthiophene) [PMeT] and the related
Acoustic plate mode device senses changes in liquids Teflon cell
Input transducer
Piezoelectric quartz substrate
Solution in contact with surface
Acoustic plate mode
Output transducer
copper(II) PMeT, have been particularly encouraging. PMeT has some degree of selectivity that can be manipulated by the synthesis procedure. In contrast, Cu(II) PMeT is more or less equally sensitive to all anions. Mark notes that both materials are very stable in air and in aqueous media and adds that they should be good detectors for ion chromatography. In chemical analysis of a sample, the values that are normally measured are average concentrations, says R. Mark Wightman of Indiana University. However, he points out, most samples actually aren't homogeneous. And it's often edifying to examine the inhomogeneities. To that end, Wightman and coworkers are using microelectrodes to probe spatially heterogeneous concentrations. One of the sensors the Indiana group has developed—a carbon fiber microelectrode—has been especially useful. Wightman notes that carbon fibers are highly conductive and commercially available in a variety of sizes. They're easily incorporated into sensors of various shapes. They can be coated with polymer films to provide additional selectivity. Coupled with a sensitive potentiostat, the electrodes can sense submicromolar concentrations with subsecond response time. And, with the use of a micromanipulator, an electrode can be "rastered" through a solution to measure the variations of concentration in space with a resolution of a few micrometers. One series of experiments has dealt with band broadening in liquid chromatography and flow injection analysis. Other studies have involved measuring dopamine concentration in the brains of rats, as a function of distance from secreting sites. In the future, Wightman says, smaller electrodes will afford even higher resolution. Automation will simplify the procedures. Eventually, Wightman expects that the technique will develop into a form of "dynamic chemical microscopy" that can measure secretions from single cells, follow corrosion processes in pits and cracks, and provide further insights into solution flow. Ward Worthy
Advances made in direct coal liquefaction
Los Angeles Technical and economic improvements in direct coal liquefaction have been made during the oil glut of recent years, but have gone almost unnoticed. The U.S. Department of Energy's goal to have coal liquids available for the manufacture of fuels and chemicals for $25 per barrel by 1995 is considered by some to be achievable. Probably the most unexpected result of the liquefaction R&D effort is the realization that coal is a highly modifiable raw material. The economic progress in direct liquefaction was outlined at a Division of Fuel Chemistry symposium on coal liquefaction by David Gray of Mitre Corp. Mitre has used a liquefaction cost model to evaluate the numerous modifications made since 1981. The objective of the model is to estimate the outputs from the various processing schemes and to project a selling price for products from a conceptual plant. The model considers commercial plant output, product quality, and the internal flows in the light of actual test data from pilot and demonstration plants. Postulated results also may be considered. There are also certain internal consistency parameters used in the model to keep the conceptual plant within realistic boundaries. Specifically, the model plant operates with no output of material having a boiling point above 850 °F. Bottoms rejected by the plant are gasified to generate needed hydrogen. If insufficient bottoms are produced to generate the hydrogen required, additional coal may be gasified. This additional coal is assumed to be gasified by the Texaco process. Oxygen for gasification is produced by steam-driven air separation equipment. A coal-fired steam plant with flue gas desulfurization is used to superheat the steam from in-plant heat recovery and to proOctober 10, 1988 CAEN
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Technology duce any additional superheated steam. Cost analyses were made with the aid of designs previously done for DOE by UOP/Scientific Design. These were considered the base case with a wide variety of two-stage configurations. The required selling price was computed as annual costs divided by annual output in barrels. Baseline economic assumptions include 25% equity, 15% discounted cash flow, 3% inflation, 34% tax rate, 8% interest on the debt, and a five-year construction period. Four different two-stage configurations were considered, each resulting in cost reductions and product quality improvements. The net result is that, in the projected conceptual plant, raw coal liquids can be produced for about $35 per bbl. This would be equivalent to crude oil at $30 per bbl. The cost difference reflects basic differences in characteristics of the products, such as hydrotreatability.
Gilbert V. McGurl, acting director of the liquid fuels division at DOE's Pittsburgh Energy Technology Center. McGurl suggests that the greatest opportunities for improvements lie in coal cleaning prior to liquefaction, preconditioning of the feed coal, better catalysts to suppress unwanted side reactions, improved hydrotreating, and better bottomsprocessing technology. A number of areas were singled out for special attention. It is now appreciated, for example, that coal can change drastically prior to entering the reactor. Even at temperatures as low as 200 °C, there may be carbon dioxide evolution, which McGurl attributes to internal crosslinking in the molecular structure of the coal. This reduces the inherent reactivity of the coal. Similarly, swelling of the coal between 200 and 500 °C is another evidence of crosslinking and, says McGurl, usually means that preheating before reaction has consid-
Probably the most unexpected result of the liquefaction R&D effort is the realization that coal is a highly modifiable raw material The Mitre model also indicates that, if all currently available improvements in processing were used in a single integrated plant, an additional 16% cost reduction would be realized. The assumption in all cases is that the feed coal is Illinois No. 6 coal. This would reduce the possible cost to about $29 per bbl or the crude equivalent of about $25 per bbl. Over the past 10 years or so, the projected selling price of raw coal liquids has been reduced from $49 per bbl to $36.60, or about 25%. Most of the reduction is due to improvements in product quality, primarily a 35% increase in the amount of available distillate. Further cost reductions are believed possible with continued design improvements. Some of the continued design improvements, present and future, were outlined at the symposium by 30
October 10, 1988 C&EN
erably reduced the action of the reactor. The bottom line is that coal is much more reactive than previously thought and the reactions more subtle than suspected. It all boils down to the need for a lot of very basic knowledge of coal chemistry to accomplish the reliable design of liquefiers and gasifiers. The emphasis placed on the production of distillates and more products from residuum conversion implicitly assumes that there are more similarities between raw coal liquids and crude oil than may actually exist. There are, in fact, substantial differences, although that doesn't automatically relegate coal to an inferior position as a raw material. One example is behavior toward hydrogénation. Petroleum is conventionally cracked and the smaller product molecules subsequently
hydrotreated. With coal, the hydrotreating must be done first or the large coal molecules won't crack. The implications for the process designer are obvious. Since hydrogénation, in either event, is catalytic, much depends also on the nature of the catalyst and its regenerability. Present catalysts are easily deactivated, usually because of carbonization and the effects of nitrogen in the coal. The mechanism of catalyst deactivation is not well understood. In the course of process development, it has become appreciated that coal is a more or less modifiable raw material. Physical and chemical modifications have been proposed. Two cases in point are beneficiation and cleaning. Obviously the elimination of ash would improve coal reactivity unless there are intrinsic catalysts in the ashforming fraction of the coal. Similarly, thermal or chemical beneficiation would make raw materials more uniform and /or easier to convert. One often cited advantage would be a reduction of the possibility for side reactions. Such a simple thing as size reduction may have a great effect on the behavior of coal in the converters, even if only because of the partial elimination of inorganic sulfur. Again, there is a lack of information on basic coal chemistry. Integration of preconversion, reaction, and postconversion steps in the liquefaction process remains of great practical importance. Effective optimization requires more basic data than are currently available. McGurl concludes that, of the several processes proposed thus far, the best is the catalytic two-stage process developed by Hydrocarbon Research Inc. He says it produces the highest yield of liquid product having the highest quality and does it at a lower cost than previous processes. Even so, significant improvements are necessary to achieve the DOE goal of $25-per-bbl oil by 1995. The most promising areas for development are preconversion chemistry, hydrogénation and cracking chemistry, coal preparation, and solids rejection. Joseph Haggirt
