Coatings may protect beaches against oil
Vapor reactors provide best ethylene yields Ethylene yields 60% 30% conversion conversion
304 stainless steel Incoloy 800 Vycor "Wall-less" reactor
84% 89 93.5 97.5
69% 79.5 89 93
a In ethane pyrolysis in smaU-diameter tube reactors. Source: Albright et al., Purdue Univer sity
long activity period, the researchers say. Low-carbon steel and nickel reac tor surfaces that were carbon-condi tioned after prolonged runs still main tained a residual amount of activity when compared to all other carbonconditioned reactor surfaces. The interaction of the reactor walls with propylene molecules is clearly dif ferent on different surfaces, Crynes says, suggesting that the reaction is at least partially heterogeneous. All reac tor surfaces treated with oxygen exhib ited initial catalytic activity, which was caused by the oxygen that was ad sorbed and/or reacted with the reactor walls to form oxides. The level of this activity was drastically affected by the nature of the surface and was related, to some extent, to oxygen treatment 'temperature. Hydrogen sulfide treat ments passivated all reactor surfaces, possibly by forming a protective metal sulfide film, and prevented any regain of wall activity with subsequent oxygen treatment of the walls. Several other symposium speakers mentioned the importance of surface reactions. For instance, a group from France's Institut National Polytech nique de Lorraine finds that the type of surface is important for the pyrolysis of neopentane (2,2-dimethylpropane), es pecially when trace amounts of oxy gen are present. Similar findings by two other French groups were obtained for the pyrolysis of various alkanes. And researchers at Akzo Chemie and Eindhoven University of Technology in the Netherlands report evidence of how an "active" wall enters in the reaction scheme for the thermal hydrocracking of poly aromatic compounds. Purdue's Albright indicates that the material of construction of tube reac tors also has an important effect when 1,2-dichloroethane is cracked to pro duce vinyl chloride. Yet, he says, this fact is not widely known. Albright notes that there is still a need to col lect much more data for the selection of the best materials of construction for different types of pyrolysis furnaces. Consideration should be given both to tube life in a furnace and also to mini mizing the surface reactions. These surface reactions, he says, are generally most undesired, since they result in loss of desired products and in the for mation of undesired by-products. Π 30
C&EN Dec. 8, 1975
A large slick of oil spilled in a marine accident is advancing toward a valu able resort beach. How can the beach be protected, damage minimized, and cleanup and restoration carried out easily, quickly, and inexpensively? At present, the answer is, they gen erally can't be. But someday, shoreline defenders may repulse the oil by spraying on the beach such armaments as plastic thin-film coatings, surfaceactive protective agents, microbial preparations, or natural polysaccha rides. Work on such unconventional oilfighting weapons is moving toward field testing, under a one-year contract funded by the American Petroleum In stitute and the Environmental Protec tion Agency. Now in final stages of ne gotiation, the contract calls for "real world" tests of several materials found "most promising" by three API-spon sored laboratory studies. The lab studies, for which final re ports recently were issued, were carried out for API by Tracor Inc., Shell De velopment Co., and Exxon Research & Engineering Co. The three firms took different but basically related ap proaches, notes Dr. Jack Gould of API's department of environmental af fairs. All involve surface treatment of shoreline materials with chemical agents to interpose a barrier to inti mate contact of oil with the materials, thus preventing adherence, staining, absorption, and contamination. The oil then can, hopefully, be readily re moved. The chemicals will be applied for protection before oil hits, rather than using them to clean up afterwards, em phasizes J. Stephen Dorrler, chief of the oil spills research section at EPA's Industrial Environmental Research Laboratory in Edison, N.J. There often is enough warning time for such appli cation to at least part^of endangered shorelines, he notes, including not only beaches and rocky coasts, but also piers, boats, and other waterfront property. Tracor's work focused on use of spray able thin-film shoreline coatings. 18 polymeric resin systems, selected from a literature review, were tested for suitable properties. Experiments on two of these film formers were con ducted using several crude oils and "simulated beaches" (synthetic seawater, wet sand, rocks, and wood in a child's wading pool mounted on a rock ing platform). The tests showed that protection against oil is provided by spraying with one or two coats of Bor den Inc.'s Polyco 694 (an aqueous sus pension of polyvinyl acetate, similar to Elmer's Glue, also made by Borden). The Polyco 694 film is cleaned easily by a salt water rinse and is not stained or penetrated by crude oil. Use of the material, which sells for 26 cents a lb
in carload lots, would be relatively in expensive (the thickness used would cost $1250 for a 10-foot-wide, mile-long strip). Shell's work concentrated on surfaceactive agents. Using a bench-scale apparatus, Shell scientists found that sodium borate and sodium silicate—in the form of borax and waterglass, re spectively—effectively protect rocky shorelines and aid in oil elution and cleanup from them. These surfactants do not perform well on simulated sandy shorelines, however. Conversely, a commercial oil spill control agent —Shell's Oil Herder—does an excellent job of protecting simulated sandy shore lines and is effective on rocky shore lines under wet or damp (normally ex isting) conditions, but is less effective than borate or silicate on dry rocky substrates. An approach using microbial prepa rations and natural plant products was undertaken by Exxon. Microorganisms in live, freeze-dried, and spray-dried forms, natural plant polysaccharides and proteins, and an extracellular polysaccharide were evaluated on sim ulated rocky coastlines and pebbly beaches. The most effective protective agent for dry rocks was a commercially avail able xanthan gum, Exxon's Biopolymer 9700—an extracellular polysaccharide of about 2 million molecular weight that is produced by the microorganism Xanthomonas campestris. Next in
Oil from tank barge that ran aground covers Delaware resort beach
order comes a natural plant polysaccharide, citrus pectin, followed by freeze-dried Micrococcus cerificans (Acinetobacter calcoacetius) and spray-dried M. cerificans. Exxon also studied protection and restoration from oil contamination of salt marsh grasses. Salt marshes, and the broad spectrum of plant and animal life in them, are vital to coastal ecosystems. Using a small marsh "microcosm" test area, Exxon scientists find that Biopolymer 9700 and citrus pectin prevent severe fouling of several species of salt marsh grass. However, neither material can restore grass already fouled. Dorrler points out that there are many questions still to be answered by the forthcoming API/EPA-sponsored project, which will involve both lab studies and field tests. For example, best application techniques and rates must be determined, and costs of use estimated. Toxicity, shelf life, and the most appropriate circumstances for use of each agent must be studied. Furthermore, the effective life and fate of each agent under attack by waves, sand erosion, weather, and biodegradation must be investigated. An agent must stay around long enough to protect against oil contact and to allow cleanup, but must itself be readily cleanable and removable thereafter. For instance, Dorrler cites thin-film polymeric beach coatings: "Esthetically, a plastic coat on the beach is not exactly the most pleasing prospect." In their report, in fact, Tracor scientists recommend reformulating the polymeric resin to include an additive that would promote its oxidative breakdown or ultraviolet photodegradation, or increase its emulsification and solubility in salt water. Another possibility, the EPA scientist adds, might be pulverization to merge the coating with beach sand. The field tests will involve controlled spilling of up to 10 bbl of oil onto as much as 100 yards of real shoreline and marsh, Dorrler says. The next step may be use on real spills. In the meantime, EPA is sponsoring preparation of practical field manuals for dealing step by step with specific oil spill situations. The manuals will cover estuaries, cold climate areas, river- and lakefronts, ocean areas, and marshes. However, Dorrler stresses, shoreline surface treatment agents "are not a panacea. They're only one tool that goes in the tool box. They can't apply to every site, every spill, and every condition." The basic strategy of dealing with marine oil spills (C&EN, April 9, 1973, page 12) is first of all to prevent them, then to contain the oil's spread and collect it before it gets to shore. Oil still will get ashore in some cases, nevertheless, and for them EPA and API hope that the new chemical agents will prove effective. Richard J. Seltzer, C&EN Washington
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