Platinum Catalysts in Petroleum Refining
Total Page：16
File Type：pdf, Size：1020Kb
Platinum Catalysts in Petroleum Refining By S. W. Curry, B.s., M.B.A. Universal Oil Products Company, Des Plnines, Illinois Rejbriiiirig processes using platinunz catalysts have beconie oj- major importance in petroleum rejining during the past seven years. The?. enable the octane rating of naphthas to be greatly increased, am1 cue more economicnl than any other rejiningyrocess for the production of high octane gasoline. In this article the general nature of the processes is described and the Platforniing process is considwed iti iiiore rletnil. Platinum in any form was virtually unused years. The end is by no means in sight, in the petroleum industry until 1949. Then since the trend in octane number requirement, Universal Oil Products Company introduced particularly for automobiles, has continued it on an unprecedented scale as the active to creep upward year by year. catalytic agent in its Platforming process for To have advocated the use of 400 ounces catalytically upgrading low octane petroleum of a noble metal, selling at about $70 per naphthas to high quality products. ounce at that time, in a catalyst charge for a Prior to the installation of the first UOP single small commercial refinery unit, would Platforming unit, platinum was found chiefly doubtless have been branded prior to 1949 in laboratories in the oil industry. In sharp as the impractical idea of a dreamer. UOP's contrast with 1949, platinum today may be announcement surprised many in the oil regarded as a most essential item in the pro- industry for that matter. duction of high octane gasoline for automo- Even after the first Platformer had been biles and piston-engine aircraft. Moreover, proven a practical success (it is still operating), substantial portions of the world's benzene, it was over a year before the next Platformer toluene and xylenes are extracted from the was placed in operation. This, of course, is product obtained by catalytically reforming an understandable reflection of the natural petroleum naphthas. These chemicals are in prudence of the industry towards any new large demand as intermediates in the manu- process. Indeed, while catalytic reforming facture of many other chemical products had first been used as early as 1940, and more such as plastics, man-made fibres, explosives, units were installed during the early days of rubber, insecticides and so forth. World War 11, the shortcomings of the From less than 400 ounces of platinum non-platinum catalyst and the complexity of metal contained in the catalyst charge of that the regenerative operation had categorised first Platforming unit, the use of platinum by catalytic reforming in the opinion of the in- the oil industry-as distinguished from con- dustry as too expensive for the peacetime sumption-has climbed to a matter of tons. production of motor and aviation gasolines. Thus the oil industry has risen from It was nearly two years after Universal's insignificance to the rank of one of the Platforming process had shown the industry world's foremost platinum users in seven an economically feasible route to high octanes Platinum Metals Rev., 1957, 1 , (2), 3843 38 and aromatic chemicals from low octane molybdena-alumina, and bauxite catalysts.) naphthas, that the first competitive processes, Two processes employing platinum- also employing platinum-containing catalyst, containing catalysts of undisclosed nature were brought out by several oil companies have been announced during 1956 for the and other engineering research organisations. isomerisation of Cs and Cg hydrocarbons It was 1952 before units employing these (Universal’s “ Penex ” process and Atlantic processes were ready to run. Refining Company’s “ Pentafining ”). No There are now six other reforming pro- commercial units employing either of them cesses in addition to Platforming available to have yet been constructed. the industry. All employ platinum- containing catalyst. Universal also has de- Increase in Octane Rating veloped a variation on the Platforming process, The response of the petroleum industry to called “ Rexforming ”, which is in com- an economically practicable catalytic reform- mercial use and employs the Platforming ing process has thus been enormous, since the catalysts. Similarly, another licensor offers particular forte of the processes is greatly to a variation on his original process. This increase the octane rating of naphthas over brings the total of platinum-catalyst reforming that which can be secured readily and processes to nine. (There are five other economically by other refinery processes. For reforming processes, too, which variously use a time, non-platinum catalyst reforming c hromia- alumina, cobalt- mol yb dena, processes enjoyed popularity because of the The Platforming unit at the Kent Refinery of the British Petroleum Company Ltd. on the Isle of Grain. This has a capacity OJ 6,000 burrels per day Platinum Metals Rev., 1957, 1 , (21, 39 '\ A I f"1oio dingrant of n Plntfonning unit cheaper catalyst they employ and the relative hydrocarbon production) with a given charge insensitivity to poisons. This is no longer an stock. advantage because increased by-product hy- The reactions may be summed up thus for drogen availability has encouraged refiners simplicity: to install facilities to clean up contaminated (I) The naphthenes present in the charge charge stocks, and thus protect the platinum are converted to aromatic hydro- catalyst . carbons by dehydrogenation Most of the reforming processes other than (2) Some of the paraffins are isomeriscd, Platforming employing platinum catalysts other paraffins are converted to utilise regeneration in situ to prolong catalyst aromatics, and still other paraffins are life. Because the catalyst does not require it, hydrocracked Platforming is unique in not employing a (3) Sulphur compounds which may be separate regeneration system. This is one of present are decomposed to hydrogen the reasons why Platforming requires in sulphide and the corresponding general less catalyst per barrel of daily charge hydrocarbon capacity than do most of the other processes. (4) Olefins are saturated and then under- But in doing so, however, it suffers no penalty go any of the reactions previously in effective catalyst life, as measured in barrels mentioned. of charge processed per pound of catalyst The dehydrogenation reaction is par- employed in the reactor system. Moreover, ticularly energy-consuming and is largely the higher initial cost and operating compli- responsible for the decrease in temperature cations of regeneration are avoided. which characterises catalytic reforming. Since the temperature level affects the reaction Reactions in Reforming kinetics and equilibria, heat must be supplied The numerous reactions comprising cata- as the reactions proceed. lytic reforming over platinum are complex, Because the writer is most familiar with it, interdependent and proceed at different rates. the Platforming process is used here to Conditions of temperature, pressure, hydro- illustrate the comrncrcial catalytic reforming gen recycle ratio and space velocity therefore of petroleum naphthas by means of platinum. are chosen to achieve the optimum overall The flow diagrap above illpstrates a typical equilibrium as indicated by the desired octane Platforming process. The raw charge stock is level (in thc case of high octane fuels) or a petroleum naphtha which is prefractionated aromatisation (when running for aromatic to separate for the reactor charge a cut boiling Platinum Metals Rev., 1957, 1 , (21, 40 roughly between 200 and 4m'F (93 to 204OC) Kent Refinery of The British Petroleum from lower and higher boiling hydrocarbons Company Ltd. This has a capacity of 6,000 which may be present. The reactor charge barrels per stream day. A smaller Platforming is then mixed with hydrogen generated in the unit installed in a refinery in Southwestern process and heated to the desired reaction United States is shown below, while the figure temperature, ranging from 850 to 950°F overpage shows a close-up of the heart of a (454 to 51o'C). The hot charge is admitted Platforming unit-the heater and reactor to the first of four (sometimes three) reactors. sections. The platinum catalyst is contained Effluent from the first reactor is con- in the four cylindrical vessels in the centre of siderably cooler than when it entered, as a the picture. consequence of the endothermic reactions Characteristics of Charge and which occur, and is reheated to the operating temperature before it enters the next reactor. Product This is repeated with the material entering the The table on page 43 shows the character- third and the fourth reactors. istics of the depentanised charge to the reactor The final effluent is usually heat-exchanged section of a Platforming unit and the Platfor- against incoming charge, then further cooled, mate product. The reactor chargc had an and finally enters the products separator. octane rating of 48 Research, which probably Enough hydrogen for process requirements is would have increased to 70 octane or so upon compressed and recycled to the charge enter- the addition of 3 ml. of tetraethyl lead per ing the first reactor, while the remainder is gallon. This would not be a suitable fuel for by-product hydrogen of high purity. The a modern automobile. After Platforming, separator liquid is fractionated to the initial however, the octane number was 93 Research, boiling point desired by the refiner, the light unleaded, and upon the addition of 3 ml. of hydrocarbons so separated