REPORTS A N D COMMIZNTS
FACE LIFT FOR SILICA Chemically altering the surface of colloidal silica greatly alters some of its physical properties When one first thinks of silica, one of the most abundant minerals to be found on the face of the earth, it’s not long before silica gel comes to mind. Silica gel’s most widespread use is as a desiccant, a use which takes advantage of its marked hydrophilic nature to remove water vapor by adsorption. The availability of very fine particles of silica (silica “smoke” or “fumed” silica) in recent years has given science and industry a most fascinating material with which to work, one which finds myriad applications and one which is also hydrophilic in character, though otherwise unlike silica gel. Fumed silica is normally made by vapor-phase hydrolysis of silicon tetrachloride. The SiC14, made by chlorinating ferrosilicon (iron silicide) with gaseous chlorine and removing the iron chloride formed, is burned in a mixture of hydrogen and oxygen to yield very fine silica particles and hydrogen chloride. Although many grades of fumed silica are available, they all display certain
Hydrophilic (left) and hydrophobic (right) grades of fumed silica-particle size is the sane f o r both grades 6
characteristic properties: small particle size, typically 10 to 40 mp; large specific surface area, usually more than 150 m2/g; and high purity, better than 99.8% SiO2-the main trace impurities are the oxides of aluminum and titanium, and HC1. All grades also display hydrophilic tendencies; this is attributed to the presence of silanol groups on the particle surface :
smoke to ensure that moisture cannot interfere with the reaction. Though process details are not available, it is known that the reaction takes place in a fluidized bed at about 400°C. There the silica, carried in a nitrogen stream, reacts with a mixture of dimethyldichlorosilane [(CH3)2SiCl2] and steam. Degussa scientists think that the reaction produces a surface covering :
Chemists in Degussa, Inc., in New York City, have calculated for their Aerosil@ 200 grade of fumed silica that there are about 2000 such Si-OH groups on the surface of the average silica particle. Hydrophilic grades of fumed silica are widely used as fillers and thickening agents in the paint, plastics, and rubber industries. Hydrogen bonding between the silanol groups on adjacent silica particles causes a considerable increase in viscosity of a liquid when small amounts of the silica are added. Kumerous attempts have been made to react the surface silanol groups with organic compounds in order to reduce or remove the hydrophilic characteristics of regular grades of fumed silica. The Degussa Co. has recently developed a method of chemically changing the silica surface to impart hydrophobic characteristics to the resulting silica particles. This Degussa process uses newly formed silica
in which the siloxane (Si-0-Si) bridge is formed by hydrolysis. 70y0 of the available silanol groups are reacted. In any event, the resulting silica is strongly hydrophobic (see photo a t left) and contains over 1o/c carbon in the form of the substituted methyl groups. Other physical properties are much the same, however. Particle size is still in the range 10 to 40 mp, but specific surface is slightly reduced to about 120 m2/g. Purity is slightly less, of course, because of the presence of the carbon. Degussa has found numerous uses for this hydrophobic grade of fumed silica (called by them Aerosils R-972). These uses all take advantage of the hydrophobic nature of the silica: it is used to keep powders, such as fire extinguishing powders, free flowing; to improve water resistance of plastics and rubbers; and to improve the corrosion resistance of water-thinnable coatings and paints.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Since the inaccessibility of whatever silanol groups remain on the particle surface makes hydrogen bonding much more difficult, much higher loadings can be used to increase viscosity to any given extent should this be desired.
PUBLISH OR PERISH: A NEW DILEMMA Universities would like to see research institutes funded by industry publish more in the open literature Go to any chemical engineering conference these days and chances are that on the program there will be a panel discussion about university research. At any of these sessions, which are usually well attended and lengthy, the proceedings are fairly predictable. Industry representatives on the panel accuse universities of turning their backs on real problems and, instead, working on esoteric projects. Professors, when their turn comes, complain that they are given no guidance about what to work on-nor are they given any money by industry. After these opening pleasantries, the discussion is thrown open to the floor and quickly degenerates into a well-mannered free-for-all in which the participants take one side or the other or, but rarely, the middle ground. One subject that has emerged in this type of discussion-at the Heat Transfer Conference in Philadelphia in August and a t the Tripartite Chemical Engineering Conference in Montreal in September, for example-is the function of the specialized research company. Two such companies are well known in the chemical engineering world : Fractionation Research, Inc. (FRI), which performs large-scale distillation research, and Heat Transfer
Research, Inc. (HTRI), which specializes in research into process heat transfer. The reason for setting up these firms was simple. Engineers in a large petroleum company felt that the costs of performing research on a large scale were so burdensome, especially when the same work was duplicated in several companies, that it would be simpler and cheaper for the work to be done just once. The idea evolved that each of a number of companies should contribute a n amount, proportional to that company’s sales, into a common pool on which the newly established specialized research company would draw for research funds. The idea has, by all accounts (except those of the universities), been successful. A very large number of firms contribute to FRI and I-ITRI and there are remarkably few holdouts, even among the biggest chemical companies who might be thought to possess all the resources to do their own large-scale research. The snag is, from the university point of view a t least, that the specialized research companies have not exactly been peppering the open literature with the results of their labors. I n fact, the actual number of research papers coming out of this industry-sponsored work has been very small indeed. I n this year’s I&EC Annual Review of Distillation (this issue, p 29) for example, only one of the papers reviewed stems from a piece of F R I research. Of course, this is not to say that F R I sponsors are not getting their money’s worth. Sponsors receive regular progress reports and correlation reports and also have representation on technical and economic committees to ensure a say in what research is done and how their contributions are spent. The chemical
engineering professor’s criticism is that he cannot find out what these specialized outfits are doing so as to decide whether a project he or his students might undertake would be a redundant piece of work. If indeed, as rumor has it, the specialized companies are covering in depth the whole spread of the technical subject (distillation, say) then, in the absence of any evidence in the literature to support or refute the rumor, the professor is discouraged from making any forays into that area of research. According to this professorial argument, which is admittedly open to some debate, industry is effectively ensuring that useful research will not be done a t the universities, a state of affairs about which industry is already berating professors. The irony of the professor’s conclusion has its counterpart in the position that F R I and H T R I must find themselves in. If they make public the results of their research, what incentive will there be for their sponsors to continue to contribute funds when all they need to do to see the’results is to look a t a technical journal? At the same time, the research companies are aware that they need the very best personnel to do their research. These days, research workers whether in industry or in academic life want to publish papers in the open literature. Any pressure to prevent them from doing so must presumably result in disgruntlement or loss of valuable personnel. Fortunately for all concerned there is now a concerted movement, both within and without F R I , for instance, to encourage the publication of as much research as possible without hurting anyone proprietarily. And a t such time as these industry-sponsored researches do
VOL. 6 0
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REPORTS
start to appear regularly in the literature, we shall be looking to the universities to see what their next step will be. Whether university departments should (or for the matter really want to) engage in large-scale research is a subject for another of those panel discussions.
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CHEMICAL REFINERIES Traditionally fuel producers, oil rejineries could make petrochemicals their most important products The most important products of petroleum refineries have generally always been fuels of various volatilities for a variety of uses. The flexibility characteristic of the modern refinery has been necessary to adapt to surging needs in special conditions-for aviation spirit in wartime or for increased fuel oil output during cold winters, for example. This flexibility of operation and outlook has also led oil refiners to “integrate forward” into the manufacture of organic chemicals derivable from petroleum; this move has been especially marked since the second world war. A story in Euroeean Chemical News (October 4, 1968, p 30) suggests that in some respects the time is ripe for the “chemical refinery,” a complex that would refine crude oil to produce predominately petrochemical products. One of the factors that is tending to make this idea a practical possibility is that the growth in demand for organic intermediates-olefins, butadiene is much greater than that for traditional refinery products. I n addition, all the technology needed to make such a complex a reality is available. Steam cracking and hydrocracking have simplified operations for converting heavier fractions, such as fuel oils, into the light hydrocarbons needed for organic chemical synthesis.
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DECEMBER 1 9 6 8
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REPORTS WHY TAKE “SECONDS”
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I N D U S T R I A L AND ENGINEERIN
According to Chem Systems, ECN’s source for the story, a n integrated chemical refinery producing an absolute minimum of fuel products and concentrating on organic chemical production would cost less to run than a conventional oil refinery and might also give a return on investment running as high as 20 to 25%. The incentive for “straight” chemical companies to jump on the bandwagon by integrating backward into oil refining is obviously great. But, even though several large chemical companies have ventured into agreements with oil companies to obtain crude oil supplies, the oil companies themselves see the profit potential in chemical refineries from the successful results of their existing petrochemical sidelines. Since these oil producers control oil distribution, they are not very likely to fall into the trap of letting nonoilbased companies reap all the benefits chemical refineries have to offer.
ANNUAL REVIEWS 1968 is the 23rd consecutive year of appearance of I&EC Annual Reviews. Annual Review authors and the editors of I&EC are anxious to learn whether their approach to reviews, developed over the years, is still valid. To this end, some of you have recently received a questionnaire from us, asking certain specific questions about your need for and use of reviews. Whether or not you have personally received this questionnaire, we urge you to write us and state your views. We seek the answers to such questions as: How long should the reviews be? Should they be aimed a t experts or at the general technical audience? Should titles of papers be given in the bibliography? Please-let us have your thoughts. According to specialists in information transfer, effective reviews may be a major long-term approach to combatting technical obsolescence. C H EM1 ST R Y
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