TECH NOLOGY
New Reactor Aids Fast-Reaction Studies Fast-mixing and -quenching reactor leads to process for high-pressure oxidation of butane 149TH
ACS
NATIONAL
MEETING
Petroleum C h e m i s t r y A new fast-mixing and -quenching reactor developed at Phillips Petroleum makes possible the study of very rapid chemical reactions. In potential commercial practice, the reactor offers a new way to make olefins by high-pressure air oxidation of butane. Using the new reactor, Dr. M. M. Johnson and C. E. Smith of Phillips Petroleum have obtained data on butane oxidation in a region of reaction conditions not explored previously. Short reaction times—approximately 10 millisec. at 150 p.s.i.a. and 1250° F.—make conventional methods of studying reactions using premixed materials impractical. In nearly all such situations where premixed reactants are used, much reaction would occur during preheating.
As a result, temperatures would be meaningless and reaction times uncertain. The reactor built by Dr. Johnson and Mr. Smith combines direct jet impingement for mixing with expansion through a deLaval nozzle for rapid quenching. An apposed jet system gives good mixing at reactor pressures up to at least 200 p.s.i.a., Dr. Johnson says. When the reacting gas is expanded through the nozzle to about atmospheric pressure, its temperature drops several hundred degrees in a fraction of a millisecond. Quench water also is added upstream of the nozzle to prevent the temperature of the reaction products from increasing in the subsonic zone following the nozzle. Both butane and air fed to the reactor are preheated. Usually air is heated to a higher temperature than the final mixture temperature and butane heated to a lower temperature.
Water injected upstream of the throat of the deLaval nozzle gives a condensed aqueous phase in the nozzle. The volume of water is enough to maintain an aqueous phase in the first of two cyclone separators located following the reactor. Both the aqueous and gaseous effluents from the first cyclone separator are sampled to monitor the amount of reaction. The gas stream then passes through a condenser and to another separator. This second separator removes an aqueous stream, containing small quantities of formaldehyde and formic acid, which could corrode the steel flare line. Three key parameters have most effect on conversion of butane, Dr. Johnson says. These are preheat temperature, reactor residence time, and butane/oxygen mole ratio. Pressure, another important parameter, depends on temperature and other variables and its effects were not studied.
TEST. C. E. Smith (left) and Dr. M. M. Johnson of Phillips Petroleum observe an experimental run of their equipment used to study fast reactions, including high-pressure oxidation of butane to make olefins
66
C&EN
APRIL
12,
1965
Enamel Durability Predictable Durability of acryfic enamel correlates with composition of three-component copolymer resins 149TH
ACS
NATIONAL
MEETING
Organic Coatings and Plastics Chemistry Compositions of three- to five-component copolymers that vail give maximum durability of acrylic enamels are predictable. Ν. Β. Graham of Canadian Industries, Ltd., Central Research Laboratory (McMasterville, Que.) told a symposium on Thermo setting Film Formers that the relation ship between copolymer composition in thermosetting acrylic resins and durability of enamel coatings has been systematized. The study shows that durability reaches a sharp peak at optimum composition for each co polymer. Dr. Graham, and co-workers F. R. Crowne and D. E. MacAlpine of CIL's Paint Research Laboratory in Tor onto, undertook the study to eliminate guesswork in determining the most durable copolymer compositions. Pre viously, Dr. Graham says, one multicomponent acrylic copolymer might yield a durable enamel, but a re lated copolymer of similar composition would give unexpectedly poor results. Weatherometer tests of panels
coated with various three-component copolymers of acrylamide with a va riety of monomers provided the basic data for the study. The copolymers were pigmented with rutile titanium dioxide or aluminum flakes. The weatherometer simulates accelerated sunlight and atmospheric moisture with an arc-light and water spray. Test panels were rated periodically for gloss retention by visually checking the reflection clarity of a clear-glass, electric light bulb's filament. This arbitrary but easy rating method was correlated with the usual method of measuring gloss using a Gardner gloss meter. Dr. Graham points out that gloss retention is a measure of a polymer-pigment system's resistance to degradation. Thus, he says, gloss re tention is presumably also a measure of the coating system's durability (assuming no checking or adhesive failure occur). The weatherometer exposures showed that acrylic enamels exhibit maximum gloss retention at definite compositions. Outdoor exposure tests in Florida, using aluminum flake-pigmented acrylic enamels, showed simi lar maxima. Agreement between weatherometer
ete
In a small reactor, which gives a short residence time of about 7 millisec, an increase in temperature with a fixed butane/oxygen ratio often reduces conversion of butane. In larger reactors, where residence times are 20 and 40 millisec, increasing temperatures (above 820° F.) increase conversion. A jump in conversion occurs at about 820° F., at which temperature the reaction becomes exothermic. Then nearly all oxygen is consumed and products are mostly hydrocarbons whose molecular weight is lower than butane, carbon monoxide, and water. At higher butane/oxygen mole ratios, the oxidation process becomes exothermic at lower temperatures, Dr. Johnson says. With shorter residence times (small reactor), higher b u t a n e / oxygen ratios also increase the fraction of butane and oxygen converted in the process. As might be expected with higher preheat temperatures, butane conversion increases with increased oxygen content of feed gases. For mixture preheat temperatures below about 1250° F., and with residence times short enough to keep butane cracking low, butane conversion percentage equals roughly 200 divided by the butane/oxygen mole ratio. Product. For butane/oxygen ratios of 2 to 5, yields of butène by high-pressure oxidative dehydrogenation are high at low conversions. Butène yields fall off rapidly with increased conversion. Generally, 1-olefins are favored over 2-olefins in this process. Propylene yields are highest when oxygen concentrations in the feed are low. For conversion of butane up to 50%, propylene yield increases; above this conversion it falls off, although slowly, up to 70% conversion. High yields of ethylene result with high conversions. Maximum ethylene yield, Dr. Johnson says, occurs at about 80% conversion. High conversion generally holds down undesired products—CO, C 0 2 , and water-soluble oxygenated hydrocarbons—in the product stream, Dr. Johnson says. However, high conversion increases yields of methane and ethane, offsetting some of the advantage that would be obtained from high conversion. At high conversions, the high pressure gives a product mix and yield similar to those of thermal cracking of butane. Olefin/paraffin ratios in the products also are similar.
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APRIL
12, 196 5 C & E N
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