Introduction to the conference

CONFERENCE ON OXIDATION PROCESSES Amsterdam, 6th May, 1954

INTRODUCTION TO THE CONFERENCE by Professor H. I. I have pleasure in declaring this conference open. It is the second conference of the type of the Fluidization Symposium held in London in June, 1052. On behalf of the Committee of this Conference and of the Chemical Engineering Group of the Royal Institute of Engineers and also in the name of the Section for Chemical Tcc1mology of the Royal Socicty of Chemistry in the Netherlands, I extend a most hearty welcome to you all, especially to those who have come from abroad. Among these are our friends from Great Britain, members of the Institution of Chemical Engineers and the Chemical Engineering group of the Society of Chemical Industry. These two bodies have been our partners in arranging this Conference. Two years ago, on the proposal made by Dr. VLUGTER at the Fluidization Conference in London, we arranged to have this meeting in Holland and we now feel very happy to be together again. I welcome their presidents SIR HARoLD HARTLEY and Professor GARNER, who have been kind enough to accept our invitation to preside over the meetings of this afternoon and of tomorrow afternoon respectively. It can easily be understood that after the successful conference on fluidization, we now want to discuss an important group of chemical processes, indicated by the name of "Oxidation." It was decided beforehand by the Committee that special attention should be given to the use of oxidation, in order to avoid duplication of the general discussion on .. Oxidation," held by the Faraday Society in London in September 1045, which was attended by about 350 members and visitors. The programme of the meeting proves that it WIIS a good idea, to choose .. Oxidation processes" us a subject for discussion. The choice of two years ago (fluidization) and the present choice (oxidation) demonstrate that chemical engineering is based on physics and chemistry combined. With the additional design of the necessary equipment .. chemical engineering" is the basis for the development of chemical industry. Oxidation is a subject of world interest. Needless to say, many of the authors and participants in the Discussion of 1045 are also present to-day and we are fortunate in having even an author of a paper, Mr. G. H. TWIGG.

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WATERMAN

Even at the meeting of the Faraday Soeiety mueh attention was given to special subjects. The following main items were then considered: Part I, Electron transfer reactions, introduced by Professor 1\1. G. EVANS and Part II, Oxidation of hydrocarbons, introduced by Professor H. 'V. l\IELVJUE. It is evident that the papers of this conference are of a somewhat different nature. More stress has been laid on the process side. It could not be avoided that once more the hydrocarbons should play an important part in our work. In former times oxidation WIIS mostly applied in combustion because of its strong exothermic oharaeter j in so far as oxidation was used for the preparation of chemicals, the generation of heat oCten reduced the efficiency of the process, e.g, in the manufacture of sulphuric acid. Besides, in many cases hydrocarbons werc not oxidized in a direct way but by intermediate reactions, such as chlorination, sui phonation, etc., afterwards, the groups thus introduced in the hydrocarbons were, and sometimes are still, replaced, for example, by hydroxyl groups. Owing to the study of oxidation we are now able to prepare chemicals by direct oxidation of the hydrocarbons. Now referring to the papers, I shall start with that by G. H. TWlGG, who applies the free radical chain mechanism as described by J. L. BOLLAND. Although this scheme was devised for certain oxidations, in which hydroperoxide is the main product, it can be applied to other oxidations in which the bydroperoxide is not the major product. As an example be discusses the oxidation of paraffins such lIS n -decane, The now generally accepted scheme: " initiation, formation of radical (R-), propagation (R02~ R02 -, R02RH ~ RCOOH R-) termination by the removal of radicals from the system by the combination of radicals" has proved to be very successful. TwIGG concludes that, in general, oxidation of 11 paraffin will not lead to anyone major product, unless the structure of the molecule induces preferential attack at one position (for example the 2·5.dimethylhexane of WJBAUT and STRANG). G. WIETZEL, in his paper on " The manufacture of synthetic fatty acids hy oxidation of paraffinic hydrocarbons

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H, I. WATERIIIAN: Introduction to the Conference by molecular oxygen," hopes that a more thorough knowledge of the reaction mechanism will givc higher yields of fatty acids and less contaminating products, 'I'he conclusion of TWIGG docs not seem vcry favourable in this respect, In spite of this conclusion I think that we must persevere in trying to complete oxidation with high yields of one special product. Even in this case heterogeneous catalysis might eventually produce the desired effect. I shall illustrate this with an example from my own practice in the field of hydrogenation. If we have to deal with a mixture of a fatty acid ester (a) with two olefinic double bonds and the samc fatty acid ester (b) with one instead of two olefinic double bonds, it is possible to transform- a into b by hydrogenation, kceping b unchanged, although b alone under the same conditions is immediately hydrogenated. The explanation of this selective hydrogenation in heterogeneous- catalysis is the difference in adsorption of-the two compounds in question and of their hydrogenated products on the surface of the catalyst.. Although this example is not absolutely analogous with the case discussed before, it might nevertheless indicate the possibility of selective catalytic oxidation. The choice of the catalyst, the characteristics of its surface, must give-the selectivity wanted, and in certain cases a favourable position of a part of the molecules to be oxidized. Therc is also a paper by 1\1. B. DONALD and J. R. GROVER, .. The air oxidation of mixtrres of benzene and cyclohexane to phenol." The authors investigated the non-catalytic oxidation at temperatures of (100°C and higher and at atmosphcric pressure. They studied the effect of cyclohexane. The yield of phenol is vcry much dependent upon the cyclohexane concentration and this is of theoretical interest. 'I'he yields and the conversions sccm to be rather poor; the process described therefore is not of technical importance. In my opinion higher and reasonable yields of phenol may be obtained by application of sclcctlve catalytic oxidation also in -this case. P. 1\1ARS and D. W. VAN KUEVELEN, in their paper on .. Oxidations carried out by means of vanadium pentoxide catalysts" give much attention to the oxidation and the reduction process. The substance to be oxidized reduces the catalyst. Therefore the reoxidation of the reduced catalyst must be equal for different oxidation processes at the same temperature. MARS and-VAN KUEVELEN, especially in the oxidation of aromatic compounds, prefer a fluid bed because of the uniformity of the temperature, which also permits the use of higher concentrations of the organic compound. 'I'hey also consider the oxidation of sulphur dioxide and upply in this process their formula for the influence on the reaction rate of thc partial pressure- of the reaction components in the oxidation of aromatics. Practical results arc obtained, which are connected with the' ratio between the amount of catalyst to bc used in thc stages

of a multiple-stage SOa reactor. There are three papers which refer to direct oxidation of benzene derivatives. R.l\I. COLE and A. W. FAIRBAIRN have realized the development of a process for the manufacture of p-tertiary-butylbenzoie acid by blowing air through liquid para tertiary-butylbenzene (Cobalt as catalyst). J. P. FORTUIN and II. I. \VATERMAN in their paper discuss their method for the preparation of cumene hydroperoxide by liquid phase oxidation of cumene with molecular oxygen (Cu as catalyst). Yields of more than 00% are obtained. It is interesting to know that traces of S02 decompose cumene hydroperoxide Into phenol and' acetone. An important factor influencing the oxidation rate is the purity of the feed; small amounts of contaminating substances may break the reaction chains. Stress might be laid on the advantage of preparing cumene hydroperoxide in a solution of cumene [prevention of hazards). COLE and FAIRBAIRN, also discuss precautions to prevent explosion. They protect the reactor with a frangible disc to prevent failure of the vessel in case of a vapour-phase explosion. \Vhercas there is a trend to use molecular oxygen for the direct oxidation of hydrocarbons, as is the case in all the papers referred to, there is one exception. A. F. LINDSAY'S paper tells us about the .. Nitric acid oxidation design in the manufacture of adipic acid from cyclohcxanol and eyclohexanone." Yields of more than 00% arc obtained. (Copper and vanadate as catalyst). L1NDSAY gives much attention to the corrosion problem; in this case J8-8·Ti or, better still, 18-8-Nb austenitic chromium-nickel steel are the most resistant materials of construction. \Ve must be grateful that not less than four papers disclose new methods for the manufacture of chemicals. With the exception of the 'synthetic fatty acids, they were recently discovered. Another very important new process -ls the B.A.S.l? process for the production of acetylene by partial oxidation of gaseous hydrocarbons. 'Ve are ruther surprised to be confronted with such a simple solution for the formation of a tangled and folded flame of a few centimetres thickness; the speed of the gas at any place is higher than the flame velocity of the gas mixture. Professor BARTIIOLOl\IE is to be congratulated on the results obtained. The oxidation 'Is here simply used for the production of heat to support the acetylene formation from methane. In the foregoing I discussed selectivity in oxidation, using as an analogy selective hydrogenation. \Ve meet this selectivity aguin in the usc of oxygen for the oxidation of non-metals in the liquid phase, such as the elimination of the unwanted non-metals silicon, phosphorus, sulphur and carbon in the steel industry. 'V. J. B. CIIATER, In his paper on .. Oxygen processes in the steel industry," discusses these problems

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II. I.

W.A.TER)IAN:

Introduction to the Conference also for the manufacture of hydrogen, is discussed. F. J. DENT'S paper on "The usc of oxygen in gasification" deals with analogous problems, in particular that of facilitating the gasification of low grade fuels and the introduction of other features, such as pressure operations. Ladies and gentlemen, I have come to the end of my introduction and I hope that the papers now laid open to discussion will be the subject of an interesting and succes sful exchange of views, bringing us more knowledge on " Oxidation."

together with the use of oxygen for fuel gas combustion, for application in different furnaces and for the oxidation of solid fuels with oxygen in blast furnaces and for complete gasification of fuel. The paper by A. !II. CLAnK" The provision of oxygen for industrial processes" refers to the manufacture of tonnage oxygen, especially in connection with its usc in the liquid form and the improvement in efficiency of the distillation cycle, so that the air entering the process need only be compressed to a pressure of 5 to G atmospheres. In this paper the usc of oxygen in gasification,

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