STI BERNARD LEWIS and GUENTHER von ELBE CENTRAL EXPERIMENT STATION, U. S. BUREAU O F MINES, PITTSBURGH, P A .
INCE the war, interest in combustion processes has increased sharply; for this the impetus of jet-fiame and ramjet developments has no doubt been largely responsible. Apart from many technical contributions dealing with t,he conventional reciprocating engine, as well as the new-typc engines, with furnace design, etc., there has been a very considerable increase in fundamental scientific investigations related to combustion. The importance of this trend cannot be overstrcssed because sound technical developments in this difficult field require the support of basic understanding of the processes involved. This review covers the more important unclassified developments in fundamental research since the appearance of “Combustion, Flames and Explosions of Gases’’ (78) in 1938 and “Explosions- und Verbrennungsvorgange in Gasen” (60) in 1939, as c d as various technical developments that have taken place during and after the war. FUNDAMENTAL INVESTIGATIONS ON GASEOUS COMBUSTION A new approach to the problem of the theory of flame propagation in nonturbulent gases has been made by Tanford and Pease ( 1 1 7 , 118). Equilibrium c~ncentrat~ions o f hydroxyl radicals and of hydrogen and oxygen atoms in moist carbon monoxide flames have been calculated. Coinpa,rison with burning velocities measured by the Bunsen burner method reveals close correlation between observed burning velocities and such calculat,ed hydrogen atom concentrations. Only a slight correlation ekists with hydroxyl radical concent’rationa and none at, all with oxygen atom concentrations. An investigation is made of the relative importance of heat conduction and diffusion in establishing concentrations of hydrogen atoms near the fiame front. To do this, differential equations are set up for heat transfer and for material transport. These equations are solved for mixtures of oxygen with moist carbon monoxide and with hydrogen. It, is shown that the temperature falls rapidly as the distance from the flame front increases and that the thermal equilibrium concentration of hydrogen atoms falls even more rapidly. On the other hand, the nonequilibrium concentration of hydrogen atoms, which is caused by diffusion from the flame front info the unburned gas, falls only slightly with distance. It is thus conchided that diffusion plays a more important role than heat transfer. A notable contribution to the problem of the effect of turbulence on flame velocity has been made by Damkahler (38). Both the physicochemical and the hydrodynamic aspects of the problem are analyzed, and a number of new deductions are made. An approximate expression for the velocity of flame propagation in small scale turbulent flow has been obtained. The work has becn reviewed by Shelkin (loti),who also derives an expression for the velocity of flame propagation in large scale turbulent flow. Other Russian work on the theory of flame propagation in turbulent, and nonturbulent flow, as well as on ignition, is summarized in a paper by Zeldovich (144). Various investigators have studied the ignition of explosive gas mixtures by electric sparks. Boyle and Llewellyn (925) have examined the influence of discharge capacity, electrode shape and size, electrode material, temperature of the vapor-air mixture, and resistance in the discharge circuit on the ignitibility of a number of solvent vapor-air mixtures. They find t>hat
ignition occurs at a mininium energy xThen tiic capacit,y is lo\v ; when the electrodes are not points, a minimuni voltage is necessary for ignition independent, of the size of the capacitors, but with point elect,rodes the critical factor is the energy stored in the capacitor. These results appear to be in substantial agrceniont, with values on mixtures of methane, oxygen, and inert gases reported by Blanc, Guest, von Elbe, and Lewis (%O). The minimum ignition energies are found to be substantially independent of gap voltage. With increasing gap lengths, they attain a minimum a t critical distances which are €unctions of‘ mixture composition and pressure and which mark the farthest penetration of the flame-quenching effect of the electrode mat,erial. hbove these “quenching” distances the energies remain constant over s0r.e range which is governed by mixture composition and pressure. Data of such minimum energies and of quenching distances are given for mixt,ures a t room temperature and pressures ranging from 0.2 to 1 atmosphere. In a subsequent t,heoretical paper, Le\Tis and von Elbe (80) develop t.he concept of an absolute minimum of the ignition energy and a minimum spherical flame volume. By mcans of a simplified model of flame propagation, these quantities are correlated with the burning velocit,y, flame temperature, heat conductivity, den&, specific heat, and temperature of the unburned gas. From measured minimum ignition energies the diameters of thc niinimurn flame volumes are calculated and found to be in sat~isfactory agreement with flamo diameters estimated from quenching distances. The stability of burner flames a t laminar fiow has been irivestignted theoretically and experimentally by Lewis, von Elbe, and Mentser (79? ZB9). From considerations of the distributiori of gas velocity and burning velocity at’ the stream boundary, it f o h v s that flash back and blowoff occur a t critical values of the gas velocity gradient a t the stream boundary. Expeiirnents ~ i t h cylindrical streams of explosive gas mixtures and with strcanie flowing from annular channels showed, in confirmation of tho theory-, that the critical gradients are independent of tube diameter over a wide range of conditions. According to Bollinger and ITilharns (e3’),who performed experiments on flames of propanc and air, this result remains valid in thc range of turbulent flow. Garside, Forsytti and Townend have similarly recognized that flame stabilization results from the distribution of gas velocity and burning velocity a t the stream boundary (46). I n studies of limits of inflammability, Laffitte and Panneticr (74, 93’) have found a hitherto urilrnown influence of the condition of the wall. Interesting experiments on the radiation from the conibustiori zone of flames have been reported by Gaydon ( 4 7 ) . By maintaining a flame at very low pressures, a fiat and enlarged combustion zone is produced which is suitable for spectroscopic observations. Different spectra arc obtained at various depths of the zone. I n another paper (48),Gaydon reports the presence of free oxygen atoms in various flames. The oxygen atoms are detected by the addition of nitric oxide, with which they react under emission of a continuous spectrum in the yellow-green. Oxygen atoms are considered to be responsible for the formation of sulfur trioxide from sulfur dioxide reported by Dooley and Whittinyham (40). I n the field of reaction kinetics, von Elbe and Lewis ( I d ? , 1.28) ha.ve investigated the thermal reaction between hydrogen
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INDUSTRIAL AND ENGINEERING CHEMISTRY
and oxygen. A reaction mechanism has been developed which quantitatively describes the reaction rates and explosion limits of mixtures of hydrogen, oxygen, and inert gas in reaction vessels. Egerton and Minkoff (43) have shown that in the explosive combustion of hydrogen-oxygen mixtures a t low pressure, up t o 30 grams of hydrogen peroxide per 100 ml. of condensate can be obtained by cooling with liquid air. An experimental and theoretical study of the oxidation of methane has been made by Audibert (12). In the oxidation of higher hydrocarbons and other organic compounds, the phenomenon of “coo1 flames” remains a subject of special interest. Recent experimental observations are summarized by Townend (124). Walsh (152) has contributed to the chain theory of paraffin oxidation. The point of oxygen attack is thought to be almost exclusively at a tertiary CH bond if present, otherwise preferentially a t a secondary CH with some simultaneous attack a t a primary CH.
OTTO ENGINES In the a r t of knock rating, developments are continuing. Ab pointed out by Brooks (29), the octane number scale was fairly satisfactory until fuel ratings above iso-octane became available. Several means of extending this scale have gained limited acceptance, but experimental fuels have now exceeded the range of these systems. A CFR group working on the problem has proposed a “triptane number” scale and an interchangeable knock index. It is hoped that research now in progress will provide information on which adoption of this scale can be based. As a contribution to the development of standard procedures, Cook, Held, and Pritchard (56) have knock-tested a sensitive fuel and a relatively insensitive fuel in a large scale air-coded cylinder. The effects of fuel-air ratio, compression ratio, inletair temperature, spark advance, exhaust pressure, and cylinder temperature were observed, and the results tabulated and charted. In studies of the knock resistance of individual organic compounds, Branstetter and Meyer (26) found xylidine an unpromising material, whereas vinyl ethyl ether as a blending agent, according to ShostakovskiI and Papok (lor), raises the octane number more effectively than iso-octane or benzene. Roegener and Jctst (61, 62, 99) have made a notable contribution toward an ultimate scientific solution of the fuel rating problem. Knock is produced, not in an engine, but in an apparatus that permits very rapid and substantially adiabatic compression of a fuel-air mixture t o well defined levels of temperature and pressure. With paraffinic fuels, knock develops in two phases. In the first phase, the pressure of the fuel-air mixture rises a t an increasing rate for a while and then levels off. In the second phase, the pressure rises from the new level a t an increasing rate t o explosion. The two phases respond differently to experimental variables. Tetraethyllead is found to lengthen the second phase only. The first phase is substantially independent of the fuel-air ratio over a wide range; the second phase decreases as the ratio of fuel to air is increased. The first phase is undoubtedly a “coo1 flame” of the type described earlier by Townend and others. A reaction-kinetic discussion of the data on the basis of the thermal and branched-chain theory of explosions is given. Investigations of this type appear applicable to engine knock when it is considered that the combined length of the preknock phases determines whether or not knock will occur. The significance of the time concept in engine knock has also been discussed by Leary and Taylor (76) and suggestions are made concerning a more satisfactory comparison method for knock data. Several details of the engine knock process during and after the spontaneous ignition of fuel-air mixture in front of the spark-ignited flame have been made visible by Miller and others (7,89,100) by means of ingenious high speed photography. Comparisons of Russian aviation gasoline with the American reference fuel S have been published by KolomatskiI and Dery-
1591
abin (72), who suggest that gasolines be classified according to American practice. According to Spencer (110) preignition and knock in the Otto engine are separate and distinct phenomena, although they frequently occur in conjunction. The flame originated by preignition has the same characteristics as the flame caused by a spark plug, the only difference being the time and location of ignition. This is in accord with observations by Miller (89)on high speed motion pictures. A summary of the investigations undertaken by the Bureau of Aeronautics, U. S. Navy Department, of chemical means of increasing speed, rate of climb, and ceiling of airplanes for short periods has been published by Masi, Fiock, and Crosselfinger (88). These chemical means include the addition of oxygen or nitrous oxide. The question of oxygen boost has also been investigated by Spencer, Jones, and Pfender (111) and by Hawthorne (&), and nitrous oxide boost by Willich (240) and Tauschek, Corrington, and Huppert (120). The war witnessed a revival of interest in the use of water as a coolant and knock suppressor inside the engine cylinder. A review of this subject and new data regarding the use of water in engines of very high compression-ratio to promote increased part-load efficiencies with low-octane fuels have been given by Green and Shreevc (61). The subject of water injection is also treated by Wiegand and Meador (137),by Engelman and White (44),and by Wear, Held, and Slough (1.94). During the war, some work was done in Germany on the elimination of spark plugs in aircraft engines, wRich are considered to be the weakest part of the engine, especially for work at high altitudes. Ignition is produced by spraying into the combustion chamber a t the appropriate moment of the compression strokr a liquid which will ignite spontaneously a t the temperature of the cylinder, thus igniting the combustible charge. A report on this process, which is called the Ring process, has been prepared by Bender (17). Also available from German files is a report by Caroselli (31) on thermodynamic and aerodynamic processes taking place in the combustion chamber of an Otto or Diesel motor. The present state of investigations into the movement of gases in cylinders and the process of combustion are discussed as far as these processes are affected by the form of the chamber. Relationships between the location of valves and the form of the chamber, the arrangement of spark plugs and fuel nozzles, and the thermal stress of the chamber are dealt with on the basis of results of theoretical and practical investigations. The relationship between the compression ratio and the thermal efficiency is discussed by Bent (18). Kettering (66) reports on more efficient utilization of fuels provided by new high-compression automobile engines. An article by Taub (119) deals with the future development of automobile engines,
DIESEL ENGINES An experimental study of mixture formation and combustion during fuel injection has been made by Blume (21). Instead of an engine the author used a test bomb with quiescent air. A fuel jet was directed against obstacles of different shapes a n 4 at different temperatures. It was found that liquid contact of t$g fuel droplets with the wall is negligible and does not occur a t all a t wall temperatures over 550’ to 600’ C. From German files, a paper on the general thermodynamics of mixture formation at’ injection in Diesel motors by Holfelder (67) has become available. This paper deals with the intimate connection of mechanics and thermodynamics in the process of mixing air and fuel in combustion motors. The mechanical part of the process is considered as far as it affects the thermal side of mixing, the heat transition, evaporation, and chemical reaction up to the start of combustion. The different properties of Diesel fuels are examined in relation to the thermodynamics of the mixture. Another contribution to the theory of fuel sprays, dealing with the influence of spray
INDUSTRIAL AMI) ENGINEERING CHEMISTRY
E592
particle size arid dismibutiun in tht. combustion o f oil dropleta, has been made by Propert (96). A technique of measuring the ignition delay of Diesel fuels: using photoclcctrie cells, has been reported by Stallechner (lid), wbo conducted the tests in a test bomb. Studies of evaporation and ignition of fuel sprays in test bombs and engines have also been reported by Starlcman (114.). An exhaustive literature and patent search of ignition accelerators haw been made by Bogen a.nd Wilson (22). The survey demonstrates t h a t use of ignil-ion accelera,tors is a practical means of improving the cetane number of Diesel fuels. Recent developments in low temperature starting of both Diesel and Otto engines have been reported by Barrington, Davis, aiid Brook (15), Work carried out during the war has enabled reliable starting to be obtained down t o temperatures o f -40 O F. An enpine burning gaseous fuel or Diesel oil is described by Nash (91) The gas is injected in the same way as oil is injected, asmall amount of “pilot oil” being included to initiate combustion of the gas a t definite point in the cycle. Questions of safe operation of large Diesel engines a,re discussed by Wicker (136) in an article on causes and remedieq of ’ires in Diesel locomotives. Z i i reviewing economic possibilities offered by fuel geography bnd technology, Broeze (28) discusses the extent to which fuel restrictions are imposed by the combustion process itself. The discussion includes fundamental requirements of dark fuels in Diesel engines, in boilers, i n industrial furnaces, and i n gas turbines. h report in Eluilwu~ Age (10) discusses comparative prices and combustion by railways of Diesel fuel and coal from 1933 to 1946. A revised edition or standard practices for low and medium speed stationary Diesel engines has been published by the Diesel Engine Manufacturers’ Association (39) Probable futuro improvements of the Dicsel engine are discussed in Industql and Pouer (6). The use of Diesel engines in underground mining is discussed by I-Iarrington a,nd East (6.6) and by Borgw, Elliott, I-Io!tz, and Sclirenk. (19). ~
GAS TURBINES Reviews arid discussions of existing designs of gas turbine8 have been published by Gibh and Bowden (4.9) and by Yellott (141). The present status of the gas turbine engine as used for aircraft propulsion and its future development are treated by Xamaras (102). Articles dealing specifically with the problem of combustion in the gas turbine have been published by Shepherd (106) and by Lloyd (82). Shepherd’s article deals in detail with the combustion chamber which must conform to eight paramount requirements: complete efficiency of combustion; minimum pressure loss; reliability under mechanical stress and at high temperatures ; minimum volume and weight; absence of carbon deposits; Rtability of combustion under a11 conditions; ease of ignition; and evennesi3 of temperature distribution at discharge. hccordtng to the author, improvement is still needed in the second, third, and fourth items. I n Lloyd’s article, the minimum requirements of the combustion system are similarly defined as minimum space and weight, high combustion efficiency, minimum total pressure ioss in flow through the system, operation under a wide range o f ruel-air ratios and fuel flows, a substantially uniform outlet temperalure, and reliable starting. The essentials of the technique which has been evolved in tbe past 5 years are the use of fuel in the kerosene ramge, so avoiding the secondary disadvantages of lighter and heavier filels; liquid fuel injection by pressure jet, using special deviccs t o maintain atomization a t l.ow flows; fitabilization of flame in a primary zone to which only a part of the air is admilted and in which a flow reversal is created to make the flame self-piloting; subsequent mixing of secondary air by injection through ports in tho flame tube so arranged as to interleave ?;he hot aiid cold air sthams; and sheet-metal construction rcl-ying
Vel. 40, Ne. 9
on air eooling. ,.In account is given of expc!rimental technique an.d remarch. In another paper (81) Lioyd anaiyzea ‘chc essential proccsses of combustion in a gas turbine and adduces reasons for regarding the rnechaniam of flame sta,bilization as being controlled by the spontaneous ignition of liquid fuel parLiclcs in the hot gas stream. Combustion equipment in gas turbines, particularly in aircra.fi gas turbines, is discussed by Watson and Clarke (135). S o n ~ c a6caniftype combustion chambers are reviewed, with particular reference t o entry swirl, atomizers, torch ignition, fuels, and Bame tube temperature. For aircra€t, the space and weight of the combustion unit are a t a premium: and means of overcoming these special problems are described. Several authors have kreated the thermodynamics of gas turbine cycles. An exhaustive study has been made by Chambadal (3)of the following six cycles: the cycle without intermediate reheating and without recuperation of heat; the cycle without intermediate reheating but with recuperation of heat from the exhaust, gases; the cycle with intermediate reheating and without, recuperation of hea,t; the cycle with intermediate reheating and with recuperation of heat; combination of the gas-turbine cycle with a low pressure cycle; and combination o f the gas-turbine cycle with a high pressure cycle, It is shown that the highest efficiency is attained theoretically by application of a heat exchanger but that this is of practical valuc only in combination with intermediate reheating and exhaust-gas cooling. An efficiency of about 32% can thus be reached, which compares well with that of the best steam plants but is still inferior to that of Diesell engines. On the other hand, combination of the gas-. turbine cycle with a high pressure cycle gives an efficiency of 36 to 407& which is comparable with that of the Diesel. KleinSchmidt (68) show5 that gas-turbine cycles are available which have the cliaracteristics essential t o successful naval use-namely. small size per unit power output, full load efficiency, and near full-load efficiency over a, wide range of partial loads. A sumrmry of the various cycles used in gas turbines, including perCormance data, operating characteristics, and general construction detaifs, is given by R C J W ~and ~ J TS h o t s k i (101). Thermodynamic charts for use in gas turbine and jet-propulsion combustion analysis have been prepared by Hall (53) and by Pinkell and Turner (94). Kantrowits and Huber (63) consider the problem of heat capacity lag in turbine working fluids. Gases require a finite time-the relaxation time---to adjust the vibrational part of their internal energy t o a change in temperature. If changes in temperature occur in gas flow in times of the order of or shorter than the relaxation time, entropy increases occur. Partly to evaluate the importance of these heat capacity lags in turbines, the relaxation times of steam and nitrogen have been studied. Several reports deal with the development of coal-burning turbines (6, 9,98, 113, 142). JET PROPULSION The principles of jet propulsion for aircraft art? described by Keirn and Shoults (6“4)* The measurement of the efficiency of jet propulsion is discussed, and detailed calculations are given of the thrust and pressure cycle, including ram intake, pressure performance, combustion equations, a,nd turbine and nozzit. thermodynamic equa,tions. Typical thermal jet-propulsion cycles are illustrated by diagrams. An article in Plight (4) discusse.: the “athodyd” or ‘‘ram jet^" At high speeds of flight the dynamic pressure of air a t intake obviates the need for a compressor in the conventional jet engines. The turbine, which serves only to drive the compressor, is also not necessary. This leads to the conception o f B forward-facing duct in which air i s compressed in a divergent’ portion, and fuel is added and burned in the pressure rise region and ejected to produce expansion and jet reaction. Disadvantages of the athodyd are high fuel consumption (50 to l O O 7 , greater than gas turbine), nccessity of
September 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
providing launching power, and low climb performance. Unlike the rocket, i t loses power with height but gains i n efficiency with higher forward speeds. The evolution of the pulsating jet engine and its future prospects are described by Edelman (41). The burner requirements of the jet engine are described by Mock (90)as: easy and consistent starting; reliable firing a t all speeds, altitudes, and throttle positions; positive ignition under any rate of fuel flow without accumulation of liquid fuel; minimum carbon formation; and no tendency t o vapor-lock. The magnitude of the problem is shown by the fact that during acceleration the fuel-air ratio may be 0.026 and may fall t o 0.0034 during deceleration. Maintaining the flame is more difficult at higher air velocities and easier with higher fuel feeds. In simple burners, yellow flames seem more stable than blue ones, and attempts t o obtain more complete combustion by weakening the mixture often result in blowout. To achieve high liberation of energy with small combustion volume, a highly developed technique of air mixing is required. This involves introducing enough air slowly t o the initial combustion nucleus t o obtain high temperature while burning only a fraction of the fuel, then adding the air necessary for complete combustion gradually to avoid local cooling, and finally introducing enough air t o bring the flame temperature down t o safe limits. Irregular combustion or complete blowout may occur at high air speeds and rich mixtures. A scheme of rating burners is suggested. Childs, McCafferty, and Surine ($4) report tests on a n annular type burner under conditions simulating altitude operation of the turbojet engine. From German files a report by von Stein (130)has become available showing diagrams of the entropy, enthalpy, and composition of oil-oxygen combustion gases and their application to the rocket motor.
HIGH EXPLOSIVES Experiments on the combustion of explosives a t low pressures have been reported by Andreev (2). A paper by Belyaev (18) discusses the mechanism of the thermal ignition of explosives. Andreev and Kostin (3) report data on the inflammability of explosives. Interesting experiments by Bowden and eo-workeis (24) on the ignition of nitroglycerin showed t h a t nitroglyccrin is greatly sensitized t o impact detonation by tiny bubbles of air or other gases. Under impact these bubbles are adiabatically compressed and become sources of ignition. An equation of state for gases at the extremely high pressure of the detonation wave has been published by Caldirola (30) and critically reviewed by Rrinkley (,E’).
FUNDAMENTAL INVESTIGATIONSON THE BURNING OF CARBON The chemistry and physics of the burning of carbon continue t o attract the interest of investigators. From a study by Jones and Townend (59, 124), it appears t h a t the mechanism of the spontaneous oxidation of coal is probably the rapid accumulation of per-oxygen. This reaction takes place only in the presence of moisture. The carbon-oxygen-water complex begins t o break down at 70” to SOo C., opening the structure for further attack. A literature review of the action of oxygen on coal at moderate temperatures has been made by Ilramers (73). Letort and Martin (76) have studied kinetic facts pertaining to the mechanism of formation of surface oxides in the combustion of graphite. Audibert and Racz ( I S ) propose a theory of carbon oxidation above 1500’ C. The over-all reaction is represented by 3C f 202
NEW FUELS FOR TURBINES AND ROCKETS The use of hydrogen peroxide in German weapons is described by McKee (84). A concentration of 80 t o 85% of the chemical was used in conjunction with a catalyst and a fuel mixture of hydrazine hydrate and methyl alcohol. It has been applied for propelling V-1 and V-2 bombs and jet aircraft. . Torpedoes and submarines burned a mixture of hydrogen peroxide, Diesel oil, and a catalyst in a combustion chamber into wHich cooling water was sprayed to lower the temperature of the combustion gas. The steam generated was expanded in a turbine and passed into a condenser. Also available from German fLles is a treatise. translated by Zborowski, on the use of nitric acid as oxygen carrier in rocket propulsion (143). A summary of present knowledge oi fuels of this type, so-called 6Lpropergo1s,”has been prepared by Levi (77).
INTERNAL BALLISTICS Thermodynamic properties of the products of high pressure combustion have been compiled by Corner (36). Internal energy, heat content, specific heats, and equilibrium constants of the normal products of combustion are expanded as power series i n the density. Tables are presented based on the most recent intermolecular forces, and covering the range from 1600O to 4000” K. The tables give covolumes of propellants with a systematic error of less than 5%. Taylor, Hall, and Thomas (121) have developed a method for calculating the calorific values and gas volumes of nodern propellant powders. A method for the direct determination of burning rates of propellant powders has been developed by Crawford, Huggett, Daniels, and Wilfong (37). I n this method, strands of propellants i n a n inert atmosphere are ignited at one end and the time i n which the combustion zone travels a measured distance is determined. A review of solid and liquid propellants used i n cartridges, gun charges, and rockets has been prepared by Wheeler, Whittaker, and Pike [I%).
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2CO $- COS
with a n energy of activation of 90 kcal.; it is of zero order and accomqanied by ultraviolet radiation i n the range 2500 to 2003 O A. The authors suggest the mechanism
- 2co +2co
+ 202 co; + CaOa 3c
C304
4
co: COZ $- co: 4-
the chain being broken by the emission of a quantum of light. Predvoditelev, Kolodtsev, and cd-workers (96) have studied the combustion of a coal cylinder arranged perpendicularly to the air flow, t h e combustion of a coal particle in air at rest or in motion, and the burning out of a coal channel. T h e results of the investigation are analyzed theoretically. The burning of individual carbon particles has also been theoretically analyzed by Vulis (181). Kolodtsev (70) has investigated the combustion of coal beds made from electrode carbon of particle sizes ranging from 2.6 to 9 mm. Experiments i n which small particles of bituminous coal were dropped in a n air stream through a n electric furnace have been reported by Orning (92). Photographic records were made of the ignition and combustion stages.
FURNACE COMBUSTION I n the literature on fuel beds, i t has been reported that a t the point of the bed where the oxygen concentration vanishes a n unexplained deficiency in the energy balance occurs. The effect has been traced by Arthur (11) t o faults in gas-sampling technique. A study of the mode of combustion of coal on a chaingrate stoker has been made by Marskell and Miller (87). At low combustion rates combustion is confined t o volatile matter and only when this is liberated can the fixed carbon burn. At higher combustion rates each layer of fuel burns out completely as the ignition plane travels down through the fuel. The ignition rate is increased by preheating the primary air. When the air supply is increased the ignition rate increases t o a finite limit. Reference to a down-jet method of combustion which permits high rates
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INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
of heat release is contained in a paper by Townend (166). Several papers (8, 66, 198) have apprarcd on the development of a “cyclone” furnace for burning high-ash low-fu5ion coals. A monograph on factors affecting smokeless operation of underfeed stokers has been published by the Stokpr Manufactuiers’ Association (116). Overfue jets for smoke abatement are describcd by Major (86) and Hurley (68). Under the auspices of the British Ministry of Fuel, Southern (109) has published a paper on the fundamentals of industrial furnace design and operation. Russian investigators report on the application of surface combustion in furnaces. Ravitch (97) has summarized experiments on surface cornbustion carried out a t the Energetics Institution of the U.S.S.R. Academy of Science. The surface catalytic effect of kebriclw can be enhanced by activation with metallic oxides, etc., but some of the natui a1 refIactories, notably dunite, ale many times more effective than firebrick. Very high combustion rates can be achieved by means of surface combustion and the completeness of reaction does not appear t o bcx affected by the presenre of a heat-absorbing surface in the conibustion zone This would enable the principle of sulfate conibustion to be applied to boiler installations, n hich could be m u ~ h reduced in size by the elimination of the large combustion chanibers in use today. Extensive investigations have been made in Elrigland on the open-hearth furnace. The results are summarized by Chestci 9 and Thring (33) and a geneial theory of heat transfer in the open-hearth furnace has been given by Thiing (162). The use of oxygen in open-hearth and blast furnaces IS the subject of numerous reports originating in various countries (14, 60, Z, 65, 69, 7’92, 83,104, 108). The energy transfer from gases to solids has been studied by Kilham (67‘). According to the author, the bulk oi the energy is generally transferred by forced convection ; other transfer processes can become hiportant only M ith certain combinations of gases and solids. Sirnplificd calculations of iadiacion fiom nonluminous furnace gases are described by Trinlis ( I d s ) . G A S BURNERS A laboratory guide to burner design, published by the Amttric.ati Gas Association Committee o n Domestic Gas R,eaearch ( I ) , summarizes work donc at the American Gas Association laboratories. Many of the individual factors influencing design have been corrclated and combined i n empirical relatiorships that are helpful in the construction of burners of predetermined performance. Fraser (46)has determined the flash-back, blowofl and yellow tip limits of 18 different combinations of hi& I3.t.u. gas burning on 50 different burners. Brit’ish manufacturers are giving consideration to replacing aerated flames on gas ranges by nonaerated flames. A favorable report on such burners has been made by Tinbergen (113)for the Ketherlands gas industry. The report covers 2 months of experience. A monograph on fuels and fuel burners has been publiehed by Steiner (115). S U M M A R I Z I N G B O O K S A N D REVIEWS The subject of internal combustion engines is treated bj, Schmidt (103). The topics discussed in this book are: general motor problem-thermodynamics of idealized engine fuels, actual cycle processes, essential factors for efficient motor operation; motor supercharging; special problems of aircraft cnginesnonsuperchal’ged motors, supercharged systems driven by motors, exhaust-driven turbosupercharger, suitability of different motor systems. A considerable part of a book on aircraft engines written by Marchal (86),is devoted to the thermodynamics of fluids and of engines and compressors. Carburetion, ignition, and refraction are dealt with separately. bIanufacturing practices and testing. procedures are considered, and a chapter is devoted to unusual types of engines. Wilkinson (139) presents complcte specificaLions of all the latest aircraft engines.
Vol. 40, No. 9
2 review on combustion of fuels has been prcsented by Xgertorr
(49). The combustion of coal and other solids is discussed, particularly the use of roal dust in reciprocating and turbinv wgines. Consideration is given to the problems of mixing fuel vapors and air and the formation of carbon. Limits of inflammabihty are mentioned, and the intricate process of tht combustion of hydrogen is desciibed. I n the combustion of hydrocarbons, conditions are found at which combustion takeb place as a so-called f‘coo”’ flame. The effect of inhibitors like tetraethyllead in slowing down the reactions in the cool flame region without affecting the ignition region and the phenomenon of h o c k i n g in internal combustion engines are explained. Another review on combustion by Townend (125) deals with recent advances in fundamental knowledge of the combustion of solid, liquid, and gaseous fuels. The work on heats of combustion by the National Bureau of Standards is noted. The greatest general advance has been a knowledge of the mechanism of slow combustion especially in relation to knock in internal combustion engines. Consider ation is given to the application of the general reaction theory and the parts played by atoms, frco radicals, and peroxidic bodies, and to various physical factors. -4t low temperatures, the initial step in the oxidation of coal is the formation of a carbon-oxygen-water complex behaving as a peroxidc. At high temperatures in fuel beds, the initial product is carbon monoxide. Furl “reactivity” is dircussed, and the down-jet method of combustion in fuel beds is briefly described. The effect of various coal characteristics on combustion in steamraising plants is considered. There is a need for fundamental research in the finer points of heat transfer involved.
CONCLUSION On rcviewing the present status of the subject as a whole, considerable progress is noted in the advancement of physicalchemical principles in a field whose practices have in the past been mainly developed as a n art rather than as a sciencc. With many laboratories engaged in investigations of many phases of combustion research it is to be expected that an increasing number of engineers and scientists will gain a comprehensive view of the field and mill learn to undeistand each other’s problems. LITERATURE CITED (1) Ani. Gas hssoc., Committee on Domestic G a s Research. Am. Gas Assoc. Monthly, 29, 10 (1947). (2) Andreev, K. K., J.Phys. Chem. (C.S.S.R.), 20, 467 (1946). (3) Andrew, K. K., and Kostin, J. D., Compt. rend. acad. sci. (U.R.S.S.). 54. 231 (19461. (4) Anon., FZighi,’50,’ 155 (1946j. ( 5 ) Anon., Industrg and Powei., 51, 73 (1946). (6) Anon., Marine Eng. Ship.Rev.,51, 103 (1946). (7) +Inon.,Petrol Processing, 1, 28 (1946). (8) Anon., Power, 91,77, 162, 164, 166 (1947). (9) Anon., P o u e r P l a ? ~Eng., t 51, 134 (1947). (10) Anon., R y . A g e , 122, 488, 497 (1947). (11) Arthur, J. R., .Vatwe, 157, 732 (1946). (12) Audibert. E., Ben. ind. min,bmZe, 223 (1943); Compt. rend., 218, 77 (1944). (13) Audibert, R.. and Raw, C., Ibid., 219, 254 (1944). (14) Bailey, E. T. W’.. Iron Coal Trades Rev.,154,295 (1947). (15) Bayrington, R., Bevis, W. A., and Brook, K., J . Inst. Automobile Engrs. ( L o n d o n ) , 15, 61 (1946). (16) Belyaev,R.F., J.Phus. C‘hem. (U.S.S.R.),20, 613 (1946). (17) Bender, R. J., CIOS File XXXI-78, Items 19 and 30 (1945); .4utomotiwe Aviation Inds., 95, 40, 74 (1946). Comm. Motor, 85, 206 (1947). (18) Bent, R.W.,
(1‘3) Berger, L. B., Elliott, hl. A., Holtz, J. C., andschrenk, H. H.,
C. 5 . Bur. Mines, Izept. Invest. 4032 (1947). ( 2 0 ) Blanc, M . V.,Guest, P. G., von Elbe, Guenther, and Lewis, Bernard, J . Chem. Phus., 15, 798 (1947). (21) Blume, X., Automobiltech. Z . , 46, 36-9 (1943) ; Fuel Abstracts (H.M. Stationery Office), 3, 223 (1946). (22) Bogen, J. S., and Wilson, C. C., Petroleum Refiner., 23,118,130, 132,134,138, 140,142, 146, 148, 152 (1944). (23) Bollinper, L. M., and Williams, D. T., Natl. Advisory Corn. Aeronautics (Washington), Tech. Note 1234 (1947).
September 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
(24) Bowden, F. P., and co-workers, Council Sci. Ind. Research, Bull. 167, 44 (1943) ; 173, 75 (1943) ; Proc. R o y . SOC.(London), A188,291, 311, 329 (1947). (25) Boyle, A. R., and Llewellyn, F. J., J. SOC.Chem. Ind., 66, 99 (1947). (26) Branstetter, J. It., and Meyer, C. L., Natl. Advisory Con:. Aeronautics (Washington), Wartime Rept. E-159 (1943). (27) Brinkley, S. R., Jr., J . Chem. Phys., 15, 113 (1947). (28) Broeze, J. J., Fuel Eron. Conf. World Powel Conf., The Hague. Sect.A3,PuperG (1947). (19) Brooks, D. B., S . A . E . Journal, 54,394 (1946). (30) Caldirola, P., J . Chem. Phys., 14, 738 (1946). (31) Caroselli, H., ALSOS Mission, Klotter File 11C, P B 14554 (1940). (82) Chambadal, P., Tech. moderne, 30, 193 (1946); 38,217 (1946). (33) Chesters, J. H., and Thring, M. W., Iron Steel Industr., Spec. Rept. 37, Sec. 111, Part I, 151 (1946). (34) Childs, J. H., McCafferty, R. J., and Surine, 0. W., Soc. Automotive Engrs., New York, Preprint, October 1946. (35) Cook, H. A., Held, L. F., and Pritchard, E. I., Natl. Advisoi> Com. Aeronautics (Washington), Tech. Note 1117 (1946). (36) Corner, J., Proc. Phys. SOC.,58, 737 (1946). (37) Crawfoid, B. L., Jr., Huggett, C., Daniels, F., and Wilfong, R. E., A n a l . Chem., 19, 630 (1947). (38) Damkbhler, G., Natl. Advisory Com. Aeronautics (Washington) Tech. M e m o . 1112 (1947). (39) Diesel Engine Mfrs. Assoc., Diesel, 24, 1347, 1462 (1946). (40) Dooley, A., and Whittingham, G., Trans. Faraday Soc ,42, 364 (1946). (41) Edelman, L. B., Soc. Automotive Engrs., New Yolk, Preprint, October 1946. (42) Egerton, A. C., Mech. World Eng. Record, 121,29 (1947). (43) Egerton, A. C., and Minkoff, G. J., Nature, 157, 266 (1946). (44) Engelman, H . W., and White, H. J., Natl. Advisory Com. Aeiunautics (Washington), Wartime Rept. E-21 (1944). (45) Fraser, W. R., Eighteenth Annual Joint Conf., Production and Chem. Committees, Amer. Gas Assoc., June 1946. (46) Garside, J. E., Forsyth, J. S., and Townend, D. T. A., Midland Section, Inst. of Fuel, J . Inst. Fuel, 18, 175 (1945). (17) Gaydon, A. G., Eleventh Internat. Congr. Pure and Applied Chem., London, July 1947. (481 Gavdon. A. G.. Trans. Faradau SOC..42. 292 (1946). i49j Gigb, C.,and’Bowden, A. 3:. Engineering, 163, 111 (1947); J . R o y . SOC. Arts, 95, 265 (1947). (60) Golden, J. J., Blast Furnace Steel Plant, 35, 572 (1947). (51) Green, W. P., and Shreeve, C. A., Trans. Am. Soc. Mech. Engrs., 68, 541 (1946). (52) Grunert, A. E., Skog, L., and Wilcoxson, L. S.,Ibid., 69, 613 (1947). (53) Hall, N. A., S.A.E. Journal, 54, 32 (1946); SOC.Automotive Engrs., New York, Preprint, October 1947. (54) IIaIrington, D., and East, J. H., Jr., U. S.Bur. Mines, Injornt. Circ. 7406 (1947). (55) Haven, W. A., Blast Furnace SteelPZant, 35 (11,95 (1947). (56) Hawthorne, E. P., AircraftEng., 18, 330 (1946). (57) Holfelder, O., ALSOS Mission, Klotter File 11 D, P B 15013 (1939). (68) Hurley, T. F., N.W. Sect. Inst. Fuel and Nat. Smoke Abatement Soc., March 1947. (89) Jones, R. E., and Townend, D. T. A,, Trans. Faradall SOC.,42, 297 (1946). (60) Jost, W., “Explosions- und Verbrennungsvorgange in Gasen,” Berlin, 1939. (61) Jost, W., F I A T R e p t . 8 7 3 . ( 6 2 ) Jost, W., ”Self-Ignition of Mixtures of Hydrocarbon and Air Subjected to Very Sudden AdiabaLic Compression”; U. S. Government Technical Oil Mission (TOM) microfilm reel 242, Photoduplication Service, Library of Congress, Washington 25, D. C. (63) Kantrowitz, A., and Huber, P. W., Natl. Advisory Corn. Aeronautics (Washington)’WartimeRep. No. L-21 (1944). (64) Keirn, D . J., and Shoults, D. R , J . Aeronaut. Sci., 13, 411 (1946). (65) Kerry, F. G., Iron Coal Trades Rev., 155,228 (1947). (66) Kettering, C. F., Oil Gas J . , 46, 73 (1947); SOC.Automotive Engrs., New York, Preprint, 1947. (67) Kilham, J. K., Gas Times, 49,314 (1946). (68) Kleinschmidt, R. V., U. S.Navy Dept., Bur. Ships, Research Memo. 1-42, P B 13535 (1942). (69) Knox, J. D., Steel, 120, 106 (June 23, 1947) 86 (June 30, 1947). (70) Kolodtsev, K. I., J . Phys. Chem. (U.S.S.R.),19,417 (1945). (71) Kolomatskii, D. Ya., and Deryabin, A. A., Neftyanoe Khon., 24, No. 5,44 (1946). (72) Kopecki, B. S., I r o n Age, 158, 47 (1946). 173) Kramers, W. J., Bull. Brit. Coal Utilization Research Assoc., 10, 395 (1946). >
I
1595
(74) Laffitte, P., and Pannetier, G., Eleventh Internat. Conf. Pure and Applied Chem., London, July 1947. (75) Leary, W. A., and Taylor, E. S.,Natl. Advisory Com. Aeronautics (Washington), Wartime Rept. W-32 (1943). (76) Lebort, M., and Martin, J., Compt. rend., 222, 1049 (1946). (77) Levi, R., Chimie & industrie, 57, 221 (1947). (78) Lewis, B., and von Elbe, G., “Combustion, Flames and Explo’ sions of Gases,” London, Cambridge University Press, 1938. (79) Lewis, B., and von Elbe, G., J . Chem. P h p . , 11, 75 (1943). (80) Ibid., 15, 803 (1947). (81) Lloyd, P., Proc. Inst. Mech. Engru., 153, 462 (1945). (82) Lloyd, P., Sixth Internat. Cong. Appl. Mech., Paris, Septcnhar. 1946. (83) Lloyd, W. A., Iron A g e , 158, 104 (1946). (84) McKee, L., Mech. Eng., 68, 1045 (1946). (85) Major, W. S., Southern Power a n d l n d . , 65, 121 (1947). (86) Marchal, R., Mech. Eng., 69, 78 (1947). (87) Marskell, W. G., and Miller, J. M., Fuel, 25,4, 50 (1946). (88) Masi, F., Fiock, E. F., and Crosselfinger, R. A., S.A..E. Quart. Trans., 1, 76 (1947). (89) Miller, C. D., S.A.E. Journal, 54, 34 (1946). (90) Mock, F. C., Ibid.,54, 218 (1946). (91) Nash, I.,Ibid., 54, 20 (1946). (92) Orning; A. A., Pulverized Fuel Conf. (Inst. Fuel), June 1947. (93) Pannetier, G., and Laffitte, P., Compt. rend., 221, 469 (1945); 223, 800 (1946). (94) Pinkel, B., and Turner, L. R., Natl. Advisory Com. Aeronautics (Washington), W a r t i m e Rept. E-23 (1945). (95) Predvoditelev, A. S.,and Kolodtzev, IC I., World Powel, Conf., The Hague, Sect. A 4-7 (1947). (96) Propert, R. P., Phil. Mag., 37, 94 (1946). (97) Ravitch, M. B., BulLacad. xi. ( U . R . S . S . ) , Classesci. tech., No. 6, 833 (1946). (98) Ritz, L., et al., B.I.G.S. 112; U. S. Dept. Commerce, O.T.S. PB 46,964 (1946). (99) Roegener, H., Photoduplication Service, Library of Congress, Washington 25, D. C., U. S. Govt. Tech. Oil Mission microfilm reel 2.42. (100) Rothrock, A. M., Spencer, E. C., and Miller, C. D., Natl. Advisory Corn. Aeronautics (Washington), Rept. 704 (1941). (101) Rowley, L. N., and Skrotzki, B. G. A., Power, 90, 667 (1946). (102) Samaras, D. G., Eng. J., 29, 398 (1946). (103) Schmidt, F. A. F., F I A T R e p t . 709; Petroleum Times, 50, 1273 (1946). (104) Shapovalov, M . A., Kislorod, No. 1, 17 (1944) ; Iron Steel Inst., l’ransl. Ser. 312 (1947). (105) Shelkin, K . I., Natl. AdvisoryConi. Aeronautics (Washington), Tech. M e m o . 1110, tr. from J. Tech. P h y s . (U.S.S.B.), 13, NOS.9-10,520, 530 (1943). (106) Shepherd, D. G., Engineer, 181, 268, 300 (1946). (107) ShostakovskiL M. F., and Papok, K. K., J . Applied Chem. ( U . S . S . R . ) , 19,416 (1946). (108) Slottman, G . V., and Kerry, F. G., Steel, 119, 106, 149 (1946). (109) Southern, H., “Fuel and the Future,” Ministry of. Fuel Conf., Preprint (1946). (110) Spencer, R. C., Natl. Advisory Com. Aeronautics (Washington), Rept. 710 (1941). (111) Spencer, R. C., Jones, A. W., and Pfender, J. F., Natl. Advisory Com. Aeronautics (Washington), Wartime Rept. E-16 (1944). (112) Stallechner, K., Deut. Rraf:fahrtforsch., No. 53, 31 (1941). (113) Stanbury, W.A., Coal A g e , 51, 82 (1946). (114) Starkman, E., Trans. Am. Inst. Chem. Engrs., 42, 107 (1946). (115) Steiner, K., Heating P i p i n g A i r Conditioning, 18,92 (1946). (116) Stoker Manufacturers’ A;soc., Sheet Metal Worker, 37 (12), 101 (1946). (117) Tanford, C., J . Chem. Phys., 15,433 (1947). (118) Tanford, C., andPease, R.N., I b i d . , 13,431 (1947). (119) Taub, A., Automotiue Aviation Ind.. 93, 36, 85 (Nov. 1, 1946) ; 34,80 (Nov. 15,1946); 34,74 (Dee. I,1946). (120) Tauschek, M. J., Corrington, L. F., and Huppert, M .C., Natl. Advisory Com. Aeronautics (Washington), Wartime Rept. E-199 (1945). (121) Taylor, J., Hall, C. R. L., and Thomas, H., J . P h y s . Colloid Chem., 51, 580 (1947). (122) Thring, M. W., Iron Steel Inst., Rept. 37, Sect. 111,Part 2, 171 (1946). (123) Tinbergen, D., Het Gas, 67, 50 (1947). (124) Townend, D. T. A,, Chemistry Industyy, 1945, 346. (125) Townend, D. T. A,, Eleventh Internat. Congr. Pure and Applied Chem., London, July 1947. (126) Trinks, W., I n d . Heating, 14, 20 (1947). (127) von Elbe, G., “Kinetics of Flame and Combustion, Frontiers in Chemistry,” Vol. 11, New York, Interscience Publishers. 1943.
INDUSTRIAL AND ENGINEERING CHEMISTRY voii Elbe, G., and Lelria, B., J . Chem. Phys., 10, 366 (1942) von Elbe, G., and LMentser,M., J . Chem. Phys., 13, 89 (1945) von Stein, M., U. 8. Dept. Commerce, QTS, PB 27738, Ma:' 1946. Vulis, L. X.,J . Tech. P h y s , (U.S.S.R.), 16, 83, 89, 98 (1946; Walsh, A. D., Trans. Faraday Soc., 42,269 (1946). Watson, E. A., and Clarlre, J. S ~Flight, 9 51, 552 (1947); J . Tn.,si Fuel, 21, (116)' i (1947). Wear. J. D., Held, L. F., and Slough, J. W., Natl. Advisory Corn. Aeronautic* (TVnshington) Wai.tim,e Rept. E 2 4 (1944). Wheeler, W. PI., Whittaker, IT.* and Pike, FI. H. M., J IWI Fuet, 20, 137 (1947). 120.'299 (1946), Wicker, W. S., Ru' iMsch,
Voll. 40, No. 9
I
RE making of esters is big business: approximate figuIe~ for current production in the United States, i n millions of pounds per yem, are: Ethyl acetate Butyl aoetate Dibutyl phthalate Cellulose acetate
125 (1845) BOO 45 (1945) 280
Alkyd resina
190
Rosin esters
88 700
Cellulose xanthate Plasticizers
170
Alkyd resins are mixed esters from phthalic and other acid:: with pentaerythritol, glycerol, and glycols. Plasticizers are largely phthalates and include dibutyl phthalate. Cellulosc nitrate, glyceryl trinitrste, vinyl acetate, and ethylidene dincetate are in the same class as regzrds amounts produced. EiTcient processes for these established products have been in operation for considerable periods and have beoonie st'andardieed. Changes arc, of course, being made from time to t h e , but t h e j are minor improvements and seldom get into the news. Cellulose acetate and xanthate are not taken up In this brief review. The basic chemistry involved in making them is cornparatively simple, but the details of their manufacture a.re multitudinous.
GENERAL In esterification and in the sapoaificatioii of asters, the alkyloxygen bond usually remains intact but is broken in specia,! caees. Partial racemization in the acidolysis of monophthahtrs oE active alcohols indicates the fission of this bond (I@* The hydrolysis of triphenyl-mothy1 thiobenzoate gives Lriphenj ' _ carbinol instead of the mercaptan (th-bi) : PhCBSCPh,
-+ K20
-+
PhCOGfI
+ PhsCOEP
I
l3r)
! '40) (l4t) ,142) (
143)
(144) Si
154, 157, 158 (1946). L. 8 , Fuel Eoon ~ o i i f World ~, Power Conf., Thb Hague, Sect 6 2 ,Payer 1, Piepiint (1947). Wilkinson, P. H., "Aircraft Engines of the World," London, Pitman and Sons,1947. Willich, N.,A i r Tech. Berv. Command, W r i g h t Field, D a y t o n , Ohio, A A F T ~ a n s l 513 . (1946). Yellott, J. I.,Power Plant E f i ~ .51, , 84, 132 (1947). Yellott, J. I., and Hot,tcarng, 6. F a , Ry. Age, 121, 551, 66(r (1946). Zhorowski, H., TSatl. Advisory Corn. Aeronautics (Washington), Tech. Memo. 1145 (1947). %eldovioh,I.lO.,J. Tech.Phy8. (U.B.S.R.), 17, 3 (1947). \~I~C~XSOII,
( 1%)
-':TVEU
.Tunc 2 4 , 1948.
secund at a lower velocity. The heats of activation are 12,3M1: and 10,800 calories (47). Glycerol (8.8), pentaery'h-itol, and other polyhydric cornpounds (%@ have been esterified under various conditions and the rates and lixits determined. The esterification of 2,3-butylen0 glycol by acetic acid, catalyzed by sulfuric acid, goes in pairr;. of consecutive reactions which do not follow first, second, or third wder equations (187'). I n the esterification of higher fatty acids in the preseuce of catalysts, methanol gives higher velocities and better yields tha;; ethanol (99). The formation of oxonium salts when alcohols are mixed d f u r i c acid is indicated by the sharp rise in viscosities ($8)" This may have to do with the catalytic effect of'the acid in esterification. h number of' kinetic studiee have been made of the hydrolyeis of esters (70, 83, 88, 159). The rates for the ethyl eeters of uubstit,uat,adbenzoic acids have been compared (29). The t e d butyl esters of oxalic, malonic, and succinic acids are hydrolyzed more rapidly in water-dioxane mixture, 1 to 2, than in pure water, t the reverse is true for the glutaric and adipic esters (rej. e temperat,ure coefficient for methyl and ethyl formates is out 1.7 for 10" between 5' and 35' C. (80). The addition of methanol Ion-em the rat,e of hydrolysis i n aqueous mlUtkJn. Ethanol, propanol, and acetone have the samc offect hut t o a, Iwx drgree (150, 161). The use of high boiling uoivents, such as glycerol (130) dielhylene glycol (102),for the potassium hydroxide in the saponlfication of esters is recommended. In tlie presence of hydrochloric acid at 25' C., the esterification cf galacturonic acid is 25 tirnss as fast as glucoside formatioil $17
(83) ~
This niay be attributed to tlie exceptional tendency of tliphenylnicthyl to dissociate (81). In a study of the kinetics of the esterlfication QE butyl alcohol by acetic acid surprieingly low values oE R were found, ranging froni 2.25 to 1.66 according to the raiio of the reactants. The rate was proportional t u the square of the acetic acid concentration (95). For p-iodopropiouic acid amd methanol the valce of K was 4.57 a t 25' C. and 4.42 a.t 35" C. (116). The est,erification velocities of the sulfide acids, RSCH,CO,H, are higher than those for RSCH2CH2C02H,b u t all are loffer than those of the corresponding acids without the sulfur link (117'). The uncatalyxed esterification of glycerol by peanut oil acids has been found to be bimolecular in two successive states, the
Surprisingly cnough, good y+elds QE esters can be obtained by heating animorr,ium salts of organic acids with alcohols. Ammonia and water are given off (.@).
SPEEBlNG UP ESTERlFKATllON The well known, long-used esterification cataiysts, sulfuric. acid, hpdrogcii chloride, and p-toluenesulfonic acid, are still the staid-bgs but oxides and salts of metals are mentioned, particularly in patents. Zinc and tin chlorides are said to be outatandingly activa catalysts, while the chlorides of other heavy metals are relatively inactive (47). Zinc chloride (75, 110), oxide (104, 147), hydroxide (104), and salts (110, 147), as well as Lead (55, 138, 147) and manganese (147) oxides are reconimcndfd.
