US3262886A - Process for naphtha reforming - Google Patents

Process for naphtha reforming Download PDF

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US3262886A
US3262886A US160749A US16074961A US3262886A US 3262886 A US3262886 A US 3262886A US 160749 A US160749 A US 160749A US 16074961 A US16074961 A US 16074961A US 3262886 A US3262886 A US 3262886A
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naphtha
steam
stream
carbon
temperature
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Arnold R Bernas
James George Russell
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Chemical Construction Corp
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Chemical Construction Corp
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Priority to NL285248D priority patent/NL285248A/xx
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Priority to GB39824/62A priority patent/GB1003147A/en
Priority to ES281826A priority patent/ES281826A1/es
Priority to FR914319A priority patent/FR1350692A/fr
Priority to DE19621442991 priority patent/DE1442991A1/de
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    • C01B2203/0844—Methods of heating the process for making hydrogen or synthesis gas by heat exchange with exothermic reactions, other than by combustion of fuel the non-combustive exothermic reaction being another reforming reaction as defined in groups C01B2203/02 - C01B2203/0294
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Definitions

  • This invention relates to the catalytic steam-reforming of naphtha, to produce ammonia synthesis gas.
  • a new approach to naphtha reforming has been developed, in which naphtha is completely converted to a synthesis gas stream by externally fired catalytic steam reform, without concomitant accumulation of free carbon.
  • the formation of lower hydrocarbons by thermal cracking is also controlled and becomes a transient phenomenon, and thus the final process gas stream contains only a negligible proportion of unreacted lower hydrocarbons.
  • Naphtha is relatively volatile petroleum refining product or intermediate, which is generally defined in terms of boiling range.
  • naptha is defined as follows: Na-phtha content (of crude oil) is the total distillate recovered in the U.S. Bureau of Mines routine analysis at a vapor temperature of 392 F.
  • a more detailed definition of naphtha appears in Petroleum Refining With Chemicals, by Kalichevsky & Kobe (1956).
  • a discussion of naphtha on pp. 21-23 of this text indicates that different naphthas may have boiling ranges from a low point of 122 F. to a maximum of 400 F.
  • naphtha is defined as a general term which is applied to fractions boiling in the gasoline or low kerosene range.
  • naphtha is a low-boiling and readily volatilized liquid hydrocarbon cut, derived from crude oil distillation in petroleum refining. This material consists mostly of straight chain paraffinics in the 0-5 to C-9 range, however, up to about 30% naphthenics together with up to 10% aromatics and unsaturates may also be present.
  • naphtha also generally contains a significant proportion of sulfur in the form of COS and mercaptans.
  • Naphtha may be utilized in a variety of ways.
  • crude naphtha may be further refined and upgraded to yield a variety of finished petroleum solvents.
  • naphtha is reformed in the petroleum sense of the term.
  • the crude naphtha is cracked, and hydrocarbon molecules are reassembled in the presence of platinum or other suitable catalyst, so as to yield a substantial proportion of branched chain or aromatics molecules.
  • This material is then blended with other refinery cuts for gasoline usage.
  • the word reforming has an entirely different meaning, as will appear infra.
  • naphtha may also be utilized as a hydrocarbon raw material for the manufacture of hydrogen or ammonia synthesis gas.
  • synthesis gas There are two general approaches to the conversion of the various types of hydrocarbons to synthesis gas, namely, steam reforming and partial oxidation.
  • steam reforming a normally gaseous hydrocarbon such as methane is mixed with steam, and the mixture is then passed through an externally heated bed of nickel-containing reform catalyst. An endothermic reaction takes place between the hydrocarbon and steam, resulting in the formation of a synthesis gas product stream containing principally hydrogen, carbon monoxide and carbon dioxide.
  • a hydrocarbon raw material is reacted with oxygen or oxygen-enriched air at a highly elevated temperature.
  • the product stream is then quenched, to yield a crude synthesis gas stream.
  • a catalyst is not employed in conventional partial oxidation practice, since essentially complete reaction of the hydrocarbon is readily accomplished at the high temper ature levels generated in this process.
  • a variety of hydrocarbons may be employed in partial oxidation, including liquid or even powdered solid hydrocarbons as well as gases.
  • a partial oxidation effect is obtained in a catalytic process by adding oxygen to a stream of hydrocarbon vapor or partially reformed gas, immediately before the stream is passed through a catalyst bed.
  • the bed is not externally heated, instead the process is carried out in a refractory-lined chamber as in conventional partial oxidation. It will be evident that this procedure is subject to the principal economic drawback of all partial oxidation processes, namely, that an air separation plant is required.
  • naphtha is catalytically steamreformed to produce an ammonia synthesis gas.
  • a limited amount of process air is employed in the present invention to assist in the gasification of the naphtha prior to catalytic reform, as well as to provide the nitrogen gas component for subsequent ammonia synthesis.
  • the process of the present invention depends on a unique balance of reaction conditions to achieve the catalytic steam reforming of naphtha, since this is acomplished without accumulated deposition of free carbon. In addition, no significant amount of unreacted hydrocarbon is present in the final synthesis gas.
  • the process is carried out in two stages, a gasification-condition stage and a catalytic steam reform stage.
  • stages of the process are distinctly co-acting and dependent, in that it has been found that the conditioning stage must be of short duration in order to prevent the reactants from reaching equilibrium with resultant deposition of free carbon in the catalyst bed. It has also been found that the reactants must be preheated in order to provide a minimum temperature level in the conditioning stage.
  • process streams of naphtha, steam and air are preheated and mixed. A partial reaction ensues, and the mixed process stream, now containing a variety of intermediate components but not in final reaction equilibrium, is passed through an externally heated bed of reform catalyst.
  • a final process stream is produced by steam reforming of residual naphtha and intermediate lower hydrocarbons.
  • This final process stream consists of a synthesis gas containing principally hydrogen, nitrogen, carbon monoxide and carbon dioxide. The stream is essentially free of unreacted hydrocarbons or solid particulate carbon.
  • the process of the present invention possesses several significant advantages.
  • a primary advantage is that naphtha is catalytically steam reformed to ammonia synthesis gas, without the concomitant accumulation of free carbon or tars, and without the production of lower hydrocarbons as a significant component of the final process stream. Thus, no recycle or side stream disposal is required.
  • the process is continuous rather than cyclic or intermittent.
  • Another object is to reform naphtha in a continuous process, without accumulated deposition of tars or free carbon.
  • a further object is to reform naphtha by catalytic reaction with steam.
  • An additional object is to react naphtha with steam and air by a two-stage mixing and catalytic reform process, whereby naphtha is completely reformed and a gas stream principally containing hydrogen, nitrogen, carbon monoxide and carbon dioxide is produced.
  • Still another object is to gasify and reform naphtha to an ammonia synthesis gas using only air, rather than free oxygen or oxygen-enriched air.
  • stream 1 is a liquid naphtha, derived from petroleum refining or other types of crude oil processing.
  • stream 1 consists principally of paraflinic hydrocarbons in the C to C-9 range, together with naphthenics as well as minor amounts of aromatics and sulfur compounds.
  • the liquid stream 1 is vaporized and preheated in heater 2, to form naphtha vapor stream 3.
  • Vapor stream 3 may be produced at any suitable temperature, ranging from the boiling point of naphtha up to about 1000" F. Above this temperature level the naphtha vapor may become unstable, and certain portions or components will readily crack to smaller molecules with concomitant carbon deposition.
  • Stream 3 thus is preferably produced at a temperature ranging from 400 F. to 800 F.
  • Stream 4 consists of highly superheated steam, preheated usually to a temperature above 1500 F., and preferably to the range of 1500 F. to 1700 F. Although lower ratios are feasible, it has been found that a range of molar steam/carbon ratios between 3 to 1 and 6 to 1 is desirable in proportioning the relative flow rates of streams 4 and 3, in order to prevent accumulated deposition of carbon under normal operating conditions.
  • Stream 5 consists of air, preheated usually to a temperature above 800 F., and preferably to the range of 800 F. to 1200 F.
  • the proportion of air employed in the process is quite small, thus only enough air is used to provide a 3 to 1 molar ratio of hydrogen to nitrogen in the final ammonia synthesis gas.
  • the streams 4 and 5 are preferably combined, to form a mixed steam-air stream 6 at a temperature of at least 1100 F.
  • Stream 6 is now combined with naphtha vapor stream 3, and the mixed stream 7 is immediately passed into residence or gas conditioning chamber 8. It will be appreciated that streams 3, 4 and 5 may be separately passed into chamber 8, however prernixing of the air and steam to form stream 6 is a preferable procedure since this results in better and more rapid mixing of the several streams.
  • stream 3 is more rapidly dispersed and diluted due to the mixing with stream 6, prior to entry of the naphtha vapor into residence chamber 8. Consequently, the possibility of transient carbon formation ordeposition due to cracking of the naphtha is reduced by the pre-mixing step.
  • the unstable lower hydrocarbons are selectively hydrogenated to a certain extent due to the in situ formation of hydrogen, which may possibly be formed in the nascent state.
  • the resultant gaseous stream 9 contains significant proportions of steam, nitrogen, hydrogen, carbon dioxide, carbon monoxide, unsaturated hydrocarbons (mostly ethylene), methane and ethane. It should be understood however, that these components are present on a transient or instantaneous basis. If stream 9 is allowed to reach stable equilibrium under these process conditions, significant formation and accumulated deposition of free carbon will take place.
  • the temperature in unit 8 may be in the range of 1450 F. to 1500 F.
  • the residence time is kept in the range of 0.05 to 0.33 second.
  • unreacted naphtha may pass into the following catalytic stage of the process, however, as will appear infra, the formation of free carbon is readily prevented in the catalyic stage by maintenance of a temperature level above 1600 F.
  • the residence time in chamber 8 must be kept below 1.0 second, and preferably in the range of 0.05 to 0.33 second,'in order to achieve the desired reactions without carbon formation.
  • the instantaneous mix temperature of stream 7 must be kept above 1000 F., since it has been found in practice that the various competing reactions will tend to form free carbon if the initial mix temperature is below 1000 F.
  • This initial or instantaneous mixture temperature should preferably be in the range of 1400 F. to 1700 F., in order to preclude carbon formation due to process upsets.
  • chamber 8 may actually, in terms of apparatus design, consist merely of an insulated pipe section extending between the point of mixing of the reactant streams and the entry of the conditioned gas stream into the catalyst bed section.
  • Reformer 10 may be a unit of conventional design, such as shown in US. Patent 2,660,519.
  • unit 10 is provided with a plurality of reformer tubes such as 11 having a bed or charge of reform catalyst 12, usually consisting of nickel or cobalt deposited on a suitable carrier.
  • Tube 11 is externally heated by such means as combustion of fluid hydrocarbon streams 13 with air streams 14, with flue gas removal via 15.
  • the temperature of the catalyst in bed 12 must generally be kept above 1600 F., in order to prevent carbon accumulation.
  • An exception to this general requirement of 1600 F. minimum temperature during catalytic reforming is the case where stream 9 contains unreacted free oxygen. Free oxygen could be present in stream 9 if residence time in unit 8 is kept very short. Under such circumstances, stream 9 and the initial portion of bed 12 in which free oxygen is present may be maintained at a lower temperature level, down to 1400 F., without concomitant accumulated deposition of free carbon. Of course, after all free oxygen is consumed, the catalyst bed must thereafter be kept at 1600 F. or higher to prevent carbon deposition. As the process stream 9 passes into bed 12, endothermic steam reforming of hydrocarbons immediately takes place.
  • Equivalent linear velocity refers to the gas velocity which would exist at normal operating conditions, if the tube was not filled with catalyst. It has been determined that this linear velocity should preferably be in the range of ft./ sec. to 30 ft./sec., in order to effectively spread out the reforming reaction through the bed 12 and thereby effectively prevent carbon deposition.
  • Various other expedients may be adopted in this respect.
  • the apparatus concept embodied in US. 2,801,159 may alternatively be employed in the present invention in order to more effectively disperse stream 9 into bed 12.
  • Stream 16 contains essentially only hydrogen, nitrogen, carbon monoxide, carbon dioxide and steam.
  • a typical analysis of stream 16 was as follows: 51.4% hydrogen, 22.5% nitrogen, 13.0% carbon dioxide, 12.1% carbon monoxide, 1.0% methane and 0.0% unsaturates. This analysis was on a dry basis, the total product stream generally contained about 50% steam on a total volume basis.
  • stream 16 is now processed by conventional technology, not shown. This will include the usual process steps of CO-oxidat-ion, carbon dioxide removal, etc.
  • the process of the present invention may be carried out with other proportions of air, besides that which will yield a final 3 :1 ratio of hydrogen to nitrogen.
  • the proportion of air will not necessarily be exactly such as to yield a final 3:1 ratio.
  • Somewhat more air may be employed in such cases, since a higher proportion of nitrogen in the final product gas will not be objectionable.
  • Using relatively more air in the process of the present invention is advantageous since lower preheat temperatures are required and further since the possibility of carbon deposition due to process upsets is lessened.
  • operating pressure does not appear to be a significant variable in the process of the present invention.
  • pressure is not critical, an operating pressure in the range of 100 p.s;i.g. to 300 p.s.i.g. is preferable since reform plant equipment size is reduced, and also because subsequent compression costs are reduced.
  • reforming at elevated pressure yields a high pressure process gas which thus may be directly treated for carbon dioxide removal by hot potassium car bonate scrubbing.
  • the required minimum preheat temperatures of the reactant streams prior to chamber 8 will depend principally on the residence time in 8 prior to entry of the mixed stream via 9 into bed 12. With lower residence times in the range of 0.05 to 0.10 second, it has been found that the process may be successfully carried out with a residence chamber temperature in the range of 1450 F. to 1500 F. However, if a longer residence interval up to 1.0 second is required, then the initial streams 3, 4 and 5 must be preheated to higher levels so as to provide a temperature range of 1650" F. to 1690 F. in chamber 8, in order to prevent accumulated deposition of free carbon in actual operation of the process.
  • a minimum steam/ carbon ratio of 3:1 is generally required, in order to satisfy material balance considerations by providing suflicient steam for complete reaction with the naphtha.
  • a steam/carbon ratio in the range of 5:1 to 721 has been found to be optimum in providing complete reaction, satisfactory reaction rate, and minimum tendency for carbon formation due to process upsets. Higher proportions of process air will generally be required if minimum steam/ carbon ratios are adopted, in order to prevent carbon deposition.
  • Table I provides typical optimum conditions for essentially carbon-free operation
  • Table II is a tabulation of various runs in which carbon formation and accumulated deposition was a significant factor.
  • a thin coating of carbon was found on the catalyst in many of the runs in Table I, however, this coating did not result in any accumulated deposition or buildup of free carbon on the catalyst.
  • the steam-carbon reaction rate in these runs was equal to or faster than the carbon formation rate. In any case, it was found that process equilibrium was attained without accumulated deposition of carbon.
  • runs #5 and #6 in Table I infra were carried out under susbtant-ially identical conditions. Run #5 was of 49 hours duration while run #6 was extended to 269 hours duration. Analysis showed no accumulation of carbon in the catalyst after run #6, as compared to the catalyst after run #5.
  • test equipment was modified in order to withdraw a test sample of the gas in the residence chamber.
  • operating conditions of run #7 of Table I were employed, with the gas sample being withdrawn at 0.20 second residence time and quenched.
  • Inlet temperatures of the reactant streams to the residence chamber were as follows:
  • the adiabatic temperature at 0.20 second residence time was in the range of 1630-1690 F.
  • the competing reactions of naphtha combustion, cracking and steam reform are carried out in the first stage of the process of the present invention. It has been determined that, by maintenance of reaction conditions within certain critical ranges, these competing reactions may be carried out without carbon accumulation.
  • the resulting unstable process stream when passed to catalytic steam reforming before further reaction ensues, is successfully steam reformed to yield further hydrogen and carbon monoxide in a second stage without carbon accumulation.
  • the present invention essentially accomplishes the steam reforming of naphtha by a process which partially gasifies the naphtha vapor using preheated air and steam.
  • the resulting mixed gas stream may be successful-ly converted to a synthesis gas by conventional endothermic catalytic steam reforming without accumulater deposition of carbon, if the mixed gas stream is passed into contact with a catalyst bed before final process equilibrium is reached.
  • the critical features of the present invention essentially involve the maintenance of the several inter-related process variables within operating limits in which the new result of the present invention is achieved, namely the continuous steam reforming of naphtha.
  • ' process of the present invention may be employed to produce a reducing gas or other product gas stream with varying proportions of hydrogen and nitrogen, by varying the initial proportion of air.
  • the lower limit of air employable will depend, in any specific instance, on the carbon forming tendency of the particluar naptha to be reformed and thus will be empirically determined in practice.
  • said mixed gaseous stream having a steam/ carbon molar ratio between 5 to 1 and 7 to 1 and containing at least 125 standard cubic feet of air per liquid feed stream gallon of naptha, reacting said mixture non-catalytically for a time interval between 0.05 to 0.33 second, whereby said naphtha is simultaneously oxidized, cracked and reformed without accumulation of free carbon, and catalytically reforming the resulting gas mixture in contact with an externally heated reform catalyst selected from the group consisting of nickel and cobalt deposited on a carrier, said catalyst being maintained at a reaction temperature of at least 1600 F., said gas mixture having a linear gas velocity in the range of 10 to 30 ft./sec. during said catalytic reform, whereby a final reformed gas mixture is produced without accumulation of free carbon, said gas mixture being substantially free of residual hydrocarbons and comprising hydrogen, nitrogen, steam, carbon monoxide and carbon dioxide.
  • a process of making an ammonia synthesis gas mixture principally containing hydrogen and nitrogen in a molar ratio of about 3 to 1 by the continuous reforming of naphtha which comprises vaporizing liquid naphtha, preheating the resulting vaporized naptha to a temperature in the range of 122 F. to 1000 F., preheating an air stream, superheating a stream of steam, combining said stream-s of vaporized naphtha, steam and air to form a mixed gaseous stream at a temperature in the range of 1000 F. to 1700 F., said mixed gaseous stream having a steam/carbon molar ratio of between 3/1 to 7/1, re-
  • said catalyst being maintained at a reaction temperature of at least 1400 F., whereby a reformed gas mixture is produced substantially free of hydrocarbons and comprising hydrogen, nitrogen, steam, carbon monoxide and carbon dioxide, catalytically reacting the carbon monoxide content of said reformed gas mixture with steam to produce further hydrogen by CO-oxidation, and removing carbon dioxide from the resulting process gas stream to produce ammonia synthesis gas, the ratio of said air stream to said vaporized naphtha being proportioned so as to obtain a final hydrogen to nitrogen molar ratio in said ammonia synthesis gas stream of about 3 to 1.

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US160749A 1961-12-20 1961-12-20 Process for naphtha reforming Expired - Lifetime US3262886A (en)

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BE624622D BE624622A (xx) 1961-12-20
NL285248D NL285248A (xx) 1961-12-20
US160749A US3262886A (en) 1961-12-20 1961-12-20 Process for naphtha reforming
GB39824/62A GB1003147A (en) 1961-12-20 1962-10-22 Naphtha reforming process
ES281826A ES281826A1 (es) 1961-12-20 1962-10-24 Un procedimiento para formar una corriente gaseosa de hidrógeno-nitrógeno por reformación de nafta con vapor de agua
FR914319A FR1350692A (fr) 1961-12-20 1962-11-05 Procédé de reformage catalytique à la vapeur du naphte pour la fabrication de gaz de synthèse d'ammoniac
DE19621442991 DE1442991A1 (de) 1961-12-20 1962-11-06 Naphthareformierverfahren

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3351563A (en) * 1963-06-05 1967-11-07 Chemical Construction Corp Production of hydrogen-rich synthesis gas
US3993457A (en) * 1973-07-30 1976-11-23 Exxon Research And Engineering Company Concurrent production of methanol and synthetic natural gas

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8520892D0 (en) * 1985-08-21 1985-09-25 Ici Plc Ammonia synthesis gas
US7335346B2 (en) 1999-08-17 2008-02-26 Battelle Memorial Institute Catalyst and method of steam reforming
US6284217B1 (en) 1999-08-17 2001-09-04 Battelle Memorial Institute Method and catalyst structure for steam reforming of a hydrocarbon
US6607678B2 (en) 1999-08-17 2003-08-19 Battelle Memorial Institute Catalyst and method of steam reforming
US7722854B2 (en) 2003-06-25 2010-05-25 Velocy's Steam reforming methods and catalysts
US8277773B2 (en) 2004-02-13 2012-10-02 Velocys Corp. Steam reforming method

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2135694A (en) * 1930-09-25 1938-11-08 Solvay Process Co Process for the production of hydrogen
US2940840A (en) * 1956-12-31 1960-06-14 Hercules Powder Co Ltd Hydrocarbon conversion process
US3042507A (en) * 1959-03-28 1962-07-03 Hilgers Giovanni Method for cracking and subsequent gasifying of hydrocarbons

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2135694A (en) * 1930-09-25 1938-11-08 Solvay Process Co Process for the production of hydrogen
US2940840A (en) * 1956-12-31 1960-06-14 Hercules Powder Co Ltd Hydrocarbon conversion process
US3042507A (en) * 1959-03-28 1962-07-03 Hilgers Giovanni Method for cracking and subsequent gasifying of hydrocarbons

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3351563A (en) * 1963-06-05 1967-11-07 Chemical Construction Corp Production of hydrogen-rich synthesis gas
US3993457A (en) * 1973-07-30 1976-11-23 Exxon Research And Engineering Company Concurrent production of methanol and synthetic natural gas

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ES281826A1 (es) 1963-03-01
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NL285248A (xx) 1900-01-01
DE1442991A1 (de) 1968-12-19

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