FR2474524A1 - Hydrocarbon conversion processes using mixed phase feed-streams - where heating to reaction temp. is effected in indirect heat exchanger - Google Patents

Abstract

Hydrocarbon conversion processes are claimed in which a mixed-phase feed stream is heated to reaction temp. and partially vaporised by passage through an indirect heat exchange zone prior to passing to the reaction zone. The reaction effluent is separated into vapour and liquid phases and the liquid phase is heated by passage through a direct-fired heating zone to a temp. >=15-20 degrees F above the temp. of the reaction zone inlet. Thereafter, the heated liquid phase is cooled by passing it through the indirect heat exchanger used in heating the original feed stream. Pref. at least part of the vapour-phase effluent is recycled to the reaction zone as part of the feedstream. The technique is claimed for use in the isomerisation of 7-9C aromatics or 4-7C n-paraffins, in hydroprocessing and in the hydrogenation of olefins, but is also disclosed to be applicable to non-catalytic conversion processes, such as the thermohydrodealkylation of toluene or visbreaking, and other processes, such as the dehydrogenation of 8-18C n-paraffins, etc. The problems associated with the maldistribution of mixed-phase feed stream in fired heaters are reduced.

Description

 The present invention relates to a process for treating or refining mineral oils or other hydrocarbon fluids. More particularly, the invention relates to a hydrocarbon conversion process in which a mixed phase feed stream is passed through a reaction zone at an elevated temperature. The invention also relates to the use of indirect heat exchange for recovering heat from the effluent stream of the reaction zone. The present invention can be applied to many processes and, in particular, to hydrodesulfurization, hydrocracking or isomerization processes.

 The present invention has a general character from the point of view of its application and is not limited to a type of reaction or reagent. Thus, it can find application in many processes that are used industrially. These processes include the isomerization of paraffinic and aromatic hydrocarbons and the hydrotreating of black oils for the removal of sulfur and nitrogen.

 Various stages used in the present invention are known in the prior art. For example, it is well known to recover the heat of an effluent stream from a reaction zone by indirect heat exchange of the effluent stream with a feed stream to the reaction zone. It is also a well established practice to pass an effluent from a mixed phase reaction zone into a phase separation zone to recover a vapor stream comprising hydrogen which is then recycled to the reaction zone for reaction. form part of the charging current.

 Another well-known stage in hydrocarbon conversion is to heat a feed stream through a direct flame heating zone.

 Heretofore, it has been customary to heat the feed stream of a hydrocarbon separation conversion unit by first exchanging heat with a hot stream, such as the effluent of the hydrocarbon separation unit. unit and then continue heating in a direct flame heater or other heating unit. The effluent stream from the unit could be sent to another processing unit or cooled.

 The present invention aims to provide a hydrocarbon conversion process which facilitates the treatment of charge currents in mixed phase. The present invention can also, in some specific applications, lower the installation and operating cost of a hydrocarbon conversion process.

 In one of these aspects, the present invention may be characterized as consisting of a) passing a mixed phase charge current through an indirect heat exchange zone and vaporizing a portion of the charge current. in the liquid phase and heating the charging current to the desired temperature; b) passing the feed stream through a reaction zone maintained under the hydrocarbon conversion conditions to obtain an effluent stream of the reaction zone having a higher enthalpy than the feed stream at the moment when this stream charge enters the reaction zone; c) heating the effluent of the reaction zone by passing through a direct flame heating zone; and d) cooling at least a portion of the effluent of the reaction zone by passing through the same indirect heat exchange zone and indirect heat exchange with the charging current.

 The single figure of the accompanying drawing illustrates one of the embodiments of the present invention, applied to a hydrodesulfurization process.

 For the sake of simplicity and clarity a number of device elements necessary for the operation of the process have not been shown.

This concerns the pressure, flow and temperature control systems, as well as the internal parts of the containers, all of which are of common design.

 This description of a particular embodiment of the present invention does not mean that are excluded from the present invention other embodiments described below, or which are the result of a normal and reasonable modification of these modes of production.

 Referring now to the single figure, a mixed phase black oil charge stream comprising a mixture of hydrocarbon-containing sulfur-containing chemical compounds is introduced into the device through line 1. The charge stream is then mixed with a gaseous stream containing hydrogen from the conduit 2, and is passed through an indirect heat exchanger 4 through the conduit 3. The feed stream is then heated to the desired inlet temperature of the desulfurization reactor . This increase in temperature normally results in vaporization of an additional amount of the feed stream. The mixed phase feed stream is then contacted with a catalyst under hydrodesulfurization conditions maintained in the reactor and hydrogen is consumed. for the production of an effluent stream which comprises hydrogen sulfide, hydrogen and hydrocarbonaceous materials in the liquid phase.

 The reactor effluent stream is fed into a vapor-liquid separator 7 via line 6. The liquid phase components of the reactor effluent stream leave the bottom of the separator through line 9 as a flow line. a stream of liquid product. This stream is pressurized by the optional pump 17 and is then divided between the conduits 10a and 10b of the intake pipe of the direct-flame and multi-pass heater 11. The liquid product stream is heated to a temperature greater than that of the reactor effluent stream in the heater and removed from the heater by the outlet pipe constituted by the conduits 12a and 12b. It is then passed through the indirect heat exchanger 4 and cooled by heat exchange with the charging current. The liquid product stream is then removed from the plant via line 13.

 The vapor phase portion of the effluent stream of the reactor is called vapor-liquid vaporizer via line 8 and is sent to a gas purification zone 14. The object of this zone is to eliminate a part of the ammonia, hydrogen sulphide, and light hydrocarbons of the incoming gases. This zone may use one or more partial condensations and an amine wash operation. A resulting stream of condensates which may comprise C5 to C8 hydrocarbons is removed through line 18 and hydrogen sulfide and light gases such as methane and ethane are discharged through line 15. The remaining hydrogen-rich residue is withdrawn through line 20 and is mixed with a stream of supplemented hydrogen fed through line 19. The resulting gaseous stream containing hydrogen is compressed into recycle compressor 16 and then mixed with the charge current supplied by line 1.

 In a large number of processes used in the petroleum, chemical or petrochemical industries, it is necessary to heat a charging current before sending this charging stream to a reaction zone.

 Often, this charge current is a mixed phase stream containing both vapor phase constants and liquid phase components.

 It is also common for ovens or warmers used to carry these charging currents to the proper inlet temperature to be multi-pass heaters. The various problems associated with mixed phase current heating in direct flame and multipass heaters are therefore frequently encountered.

 One of the most important problems in the heaters used for this particular application is the poor distribution of the vapor and liquid phases inside the heater tubes. The result of this poor distribution may be very irregular temperature profiles between or inside the heater tubes and the creation of localized areas with excessive temperature. For example, a large amount of liquid that accumulates at a lower point can block the flow of steam through one or more tubes of the heater, thereby interrupting the normal flow in two phases and possibly leading to periods with little The flow of these fluids through the heater tubes removes heat from the walls of these tubes and, therefore, serves to limit the maximum temperature reached by these tubes.

A flow of fluid that is decreased or interrupted decreases the rate of removal of heat from the tubes by decreasing the heat transfer to the fluids. This leads to higher temperatures in the tubes, which can cause coke deposits or unwanted thermo-cracking of the fluids. Prolonged poor distribution of the liquid flow can lead to weakening of the tubes due to excessive operating temperatures. This leads to rupture of the heater tubes and can cause catastrophic failure of the highly flammable charge line in the heater.

 It is therefore an object of the present invention to provide a hydrocarbon conversion process wherein the problems associated with poor distribution of mixed phase charge currents in direct flame heaters are reduced.

The object of the invention is also to improve the operation of processes using direct-flame and multi-pass heaters. The current.

It is another object of the present invention to provide processes for the hydrotreatment of black oils and the isomerization of C4 to C7 paraffins and C7 to C9 aromatic hydrocarbons. The term hydrotreatment used herein refers not only to the hydrotreatment operations themselves. but also hydrocracking and hydrodesulfurization operations. It is therefore considered to include saturation operations of olefins and diolefins contained in an essence of pyrolysis, hydrodesulfurization of a black oil and removal of small amounts of charge stream nitrogen by hydrodenitrification.

 The present invention utilizes both a heater, preferably a direct flame heater and an indirect heat exchanger. These two apparatuses can be designed and made using the usual standards and methods after adjustment for the temperature and pressure variations used in the present invention.

The term "multi-pass heater" as used herein refers to a heater that has a piping for introducing the fluid to be split along different possible paths through the high temperature heating zone. The term "direct flame heater" as used herein refers to a heater in which a direct flame is maintained. The present invention is used in connection with a reactor or a reaction zone. This zone may be of the fixed bed, moving bed, boiling bed or fluidized bed type. The reaction zone may comprise two or more reactors in series or in parallel. The design and operation of the reaction zone may be the same as those customarily used for the particular conversion procedure that is carried out.

 In the process according to the present invention a mixed phase feed stream is fed to the desired inlet temperature of the reaction zone in an indirect heat exchange zone. Since the quantities of fluid used can be very large, the necessary surfaces in the heat exchange zone may require the use of several heat exchange beams. The use of countercurrent flow in shell and tube exchangers is preferred, but other types of exchangers can be used as well. In addition to being heated in the indirect heat exchange zone, some or all of the liquid of the current can be vaporized. In some conversion processes, such as isomerization, vaporization of the total feed stream prior to reaction is normally required. In other methods, it is desirable or necessary to use mixed phase flow. By way of example, mention may be made of the low temperature hydrotreating of pyrolysis liquids to saturate the olefinic hydrocarbons. High temperatures are avoided in this process because of the excessive polymerization of the olefinic hydrocarbons in the reaction zone.

Mixed phase reagents are also used in hydrocracking or hydrodesulfurization processes for black oils. The term "crude oils" as used herein means a petroleum fraction containing more than 1% by weight of asphaltenes having a boiling range as determined by the distillation method.
Appropriate ASTM that exceeds 3400C. Two of the most common refinery streams, which are normally referred to as black oils, are reduced crudes, that is, a portion of a crude oil boiling above 3400C and containing 1 15% by weight of asphaltenes, and vacuum distillation column residues which normally boil above 52 ° C. and contain from about 1 to 20% by weight of asphaltenes. These very heavy materials can not be vaporized under the required hydrotreatment conditions and thus remain in the liquid phase.

 After being heated in the indirect heat exchange zone, the charging current is sent to the reaction zone. Various streams of gas, recycle or additives may be mixed with the feed stream between the heat exchange zone and the reaction zone, but they are preferably added upstream of the heat exchange zone. A wide variety of reactions can be carried out in the reaction zone. The specific reaction is preferably exothermic, but may also be endothermic. Thus, it is preferred that the effluent from the reaction zone have a higher temperature and enthalpy than the feed stream as it enters the reaction zone. In some cases, for example in hydrocracking, a much larger percentage of the effluent from the reaction zone may be in the vapor phase as compared to the feed stream entering the reaction zone.

 At least a portion of the effluent from the reaction zone passes into a heater. If the effluent from the reaction zone is completely vaporized, it is preferred that the entire effluent passes into the heater and then undergoes exchange with the feed stream.

 A two-phase flow through the heater is then completely avoided. If the effluent from the reaction zone is a mixed phase stream, it is preferred to send it to a vapor-liquid separation zone, as shown in the drawing. The vapor and liquid portions of the effluent from the reaction zone are then separated into individual streams. These two streams or only one of them can be sent to the heating zone. If both streams are heated, they are kept separate for the entire time they are in the heating zone. Preferably, only the liquid phase is heated, if it is present in a sufficient amount. The heated portion of the effluent from the reaction zone is then sent to an indirect heat exchange zone to effect heating of the feed stream.

 To heat the feed stream to the desired inlet temperature in the reaction zone, it is necessary for the heated portion of the effluent from the reaction zone that passes into the indirect heat exchange zone to have a temperature greater than the desired inlet temperature of the reaction zone.

The exact temperature required depends on factors such as the flow rate of the two streams brought to the indirect heat exchange zone and the available area within that zone. The maximum possible amount of the effluent from the heated reaction zone is equal to the flow rate of the feed stream and a temperature difference of at least 8 to 120C is normally required in an indirect heat exchanger. As a result, the heated portion of the reaction zone effluent that passes into the indirect heat exchange zone must have a temperature that is at least 8 to 12 ° C higher than the temperature of the reaction zone. desired entry of the reaction zone.

 The method according to the present invention has several advantages that may not all be present in a particular application. For example, in some processes, the reactor effluent may cause less fouling of the heater tubes than the same load current with a higher temperature. In addition, if the effluent from the reaction zone is a vapor phase stream, there is no risk of poor distribution of the liquid in the heater. A third advantage exists when the effluent from the mixed phase reaction zone is obtained in a process comprising a recycle gas stream. In this case, the pressure drop that occurs in the heater is outside the recycle gas circuit. This reduces the operating cost of the process. An example of this type of process is the hydrodesulfuryl process of black oils shown in the drawing.

 Recycling gas streams are used in many processes, including those involving the isomerization of paraffinic and aromatic hydrocarbons. These recycle gas streams are often rich in hydrogen and contain from 80 to 90 mS or more of hydrogen. The hydrogen can be passed through the reaction zone for several reasons, namely to facilitate the vaporization of the reactants, the maintenance of the catalytic activity and the prevention of excessive coke deposition. In some processes, the desired purity of the recycle stream can be maintained quite easily, such as by using a drag stream, or by judiciously controlling the amount of light material that is removed from the liquid streams. This is normally true for conventional isomerization processes. In hydrodesulfurization and hydrocracking processes, a large number of volatile materials, such as propane, methane and hydrogen sulfide, are often formed. Light hydrocarbons can be removed by partial condensation and adsorption. Acidic hydrogen sulfide is often removed by contact with an amine solution such as monoethanolamine. The operations carried out in the gas purification zones of a desulphurization process may comprise cooling the gas stream to a temperature of about 380 ° C. and bringing the cooled gas into countercurrent contact with an aqueous amine solution in A contacting column. Further details on the purification of recycle gases in desulfurization processes are described in US Patents 3,725,252 and 3,847,799.

 Catalysts suitable for many conversion processes are available. Many hydrotreatment catalysts comprise one or more Group VIII or Group VI-B metals or compounds of these metals, such as oxides or sulfides.

The metal components of group VI-B are generally present in an amount of about 4 to 30% by weight. Group VIII noble metals are preferably present at about 0.2 to 10% by weight.

 All metal concentrations in the catalyst are calculated as the elemental metal.

The metal components of the catalyst are on a porous support material. These supports are generally one of the well-known amorphous refractory mineral oxides, such as alumina, silica or a combination of these two oxides. Zeolite materials such as mordenite, faujacite and A or U molecular sieves may also be used as supports either separately or in combination with amorphous carrier materials. The composition and the specific method of manufacturing the catalysts used in this mode or other embodiments of the invention are not critical and can vary widely. A preferred hydrotreatment catalyst comprises sulphides or oxides of nickel, molybdenum and cobalt, on a calcined support of alumina and silica.

 The conditions maintained within the reaction zone are selected according to factors such as desired reactions, charge composition, and catalyst activity. The operating conditions used during the hydrotreatment normally include a temperature of 260 to 5400C and preferably 315 to 480. A wide range of operating probes is about 14.8105 to 236.105 Ps lower pressures val72.105 tétant preferred.

Hydrogen flows through the reaction zone at a rate of about 35.6 to 4450 m 3 / m 3 of feedstock and preferably at 178 to 2670 m 3 / m 3 of feedstock.

The liquid hourly space velocity of the charge may vary from about 0.25 to 10.0 and preferably from d = 5 to 3.0. Liquid or gaseous cooling streams can be sent to a reaction zone
to limit the maximum temperature reached.

Further details concerning catalysts and
operating conditions of the hydrotreatment can
found in US Patents 3,725,252; 3,730,880;
3,748,261; 3,825,485; 3,847,799; 3,702,237; 3,364,131;
2,717,857 and 3,720,602. A relatively detailed summary
of the hydrocracking technique can be found
in the article starting on page 74 of Industrial
Engineering Chemistry, P oduct Research and Development,
Flight. 14, No. 2, 1975.

The operation of the heater and more speci
the rate at which the fuel is brought to the
heater can be set by one or more measures
temperature at the entrance of the reaction zone or at
inside the reaction zone. Time measurements
used in the reactor control system
driver can also be performed when the
charging current exits the heat exchange area
indirect. The operation of the heater is adjusted to provide the temperature required within the reaction zone for the desired degree of conversion. This temperature varies with aging of the catalyst. Other variables that may require adjustment of the rate of flow of the fuel to the reheater include the flow rate of the charging stream and its initial temperature before entering the zone. indirect heat exchange
The effluent from the reaction zone is not cooled down before passing into the liquid gas separation zone or the heater. If a gas-liquid separation zone is used, it can be designed and carried out in the usual way. There are a large number of types of gas-liquid separators. Examples of such separators are described in US Patents

3,364,657; 3,826,064; 3,853,513; 3,873,283 and 3,900,300.

In many cases, a relatively simple buffer tank with a fog removal device will be sufficient. Guidance on the design of buffer balloons can be found in the article on page 155 of the June 1961 issue of Hydrocarbon
Processing and Petroleum Refiner. Although the use of a vapor-liquid separation zone is preferred when the effluent of the reaction zone is a mixed phase stream, the invention can be implemented in this case without using a gas separation zone. -liquid. This may be due to the desire to cool the effluent stream before separating it into liquid and vapor phases. Moreover, even if a gas-liquid separation is not used, it may be advantageous to use the inventive concept according to When the effluent from the reaction zone contains less material in the liquid phase than the charge stream of the reaction zone.

 In the preferred embodiment of the present invention a C 7 to C 8 aromatic hydrocarbon is isomerized in the vapor phase reaction zone as described in U.S. Patents 2,784,241; 2,976,332; 3,778,318; 3,281,482; 3,304,339; 3,553,276 and 3,996,305.

These documents describe both catalysts and operating conditions. An example of such a process is the isomerization of a mixture of xylene isomers to restore an equilibrium of the isomers. This process is carried out industrially in combination with separation processes that make it possible to separate one or more isomers from a mixture of isomers, the remaining constituents of the equilibrium mixture being recycled to the isomerization zone.

 In the preferred embodiment of the present invention, the reaction zone operates under conditions to induce isomerization of the aromatic hydrocarbons. Except for the presence of a catalyst, these conditions include a temperature of about 0 to 6000C, preferably 320 to about 4500C and a pressure of about 105 to 107i. It is preferred to use a pressure of about 10% by weight. and a single fixed bed reactor operating with downward flow of the vapor phase reagents. The hydrogen circulation rate should be sufficient to maintain a hydrogen to hydrocarbon mole ratio of 1: 1 to 20: 1 in the reactor. This ratio is preferably maintained in the range of about 1.5: 1 to 5: 1. The amount of catalyst charged to the reactor must provide a weight hourly space velocity (weight of hydrocarbons passing through the reactor in one hour per unit weight of catalyst) of from about 0.5 to about 10, and preferably approximately 1 to 5. The exact conditions used vary with the age of the catalyst and are determined by the activity of the catalyst and the effect of these conditions on the selectivity, the conversion rate and the final yield of the isomerization zone. .

 In the center of the isomerization zone the aromatic hydrocarbons is placed an effective isomerization catalyst. Various types of suitable compositions are known and effective catalysts are commercially available. The catalyst typically comprises an acidic mineral oxide carrier such as alumina, silica-alumina mixtures, faujasites and mordenites that have been combined or impregnated with a metal component. An alumina catalyst containing about 0.05 to about 5.0% by weight of a Group VIII metal component and 0.3 to 5.0% by weight of halogen is preferred. comprising about 0.1 to about 1.5% by weight of platinum or palladium and 0.5 to 2.5% by weight of fluorine or about 0.1 to 1.5% by weight of chlorine. This halogen concentration can be maintained by the injection of halogen-containing substances such as carbon tetrachloride into the materials entering the isomerization zone. These composite catalytic materials may further contain about 0.1 to about 1.0% by weight of sulfur to improve their performance. All percentages given herein for catalyst composition are calculated on the basis of the elements. Other catalysts that can be used in the isomerization zone are described in U.S. Patents 3,464,929; 3,409,685 and 3,409,686.

These catalysts comprise an alumina matrix having in the dispersed state less than 20% by weight of finely divided mordenite and containing at least one metal component selected from nickel, platinum and palladium, about 0.001 to 2% by weight of sulfur and about 0.2 to 3% by weight of chlorine or fluorine. Another catalyst described in these documents comprises an alumina matrix in which less than 20% by weight of finely divided mordenite is dispersed and which contains about 0.05 to 5.0 wt.% Platinum or preferably palladium and about 0 wt. 2 to 3.0% by weight of chlorine or fluorine. Other catalytic composite materials may also be used in the reaction zone.

 The preferred embodiment of the invention may be characterized as an aromatic hydrocarbon isomerization process which comprises passing a mixed phase feed stream comprising C 7 to C 6 aromatic hydrocarbons into a hydrogenation zone. indirect heat exchange and vaporization of the liquid phase portion of the charging current and heating of the charging current to a desired inlet temperature in the reaction zone; passing the feed stream through the catalytic reaction zone maintained under the isomerization conditions of the aromatic hydrocarbons so as to obtain an effluent from the reaction zone; heating the effluent of the reaction zone to a higher temperature-by passing through a direct fl ow heating zone; and cooling all the effluent of the reaction zone thus heated by passing through the indirect heat exchange zone and by the corresponding heat exchange with the charging current.

 In another embodiment of the invention a normal paraffin having 4 to 7 carbon atoms per molecule is isomerized in the reaction zone.

This process is described in U.S. Patents 2,938,936.

3,112,351; 3,128,319; 3,131,235; 3,283,301; and 3,755,144. This is done for a variety of applications including upgrading paraffins to motor fuel blend components or producing isoparaffins for Latin-alky processes.

 A preferred catalyst composition for paraffin isomerization comprises an alumina and platinum composite material which is reacted with the hydroxy groups chemically combined on its surface with aluminum chloride or another Friedel-Crafts type halide after calcination of the composite material. Examples of such a catalyst are described in U.S. Patents 2,999,074 and 3,649,704. The alumina-platinum composite material can be prepared by any suitable method, such as coprecipitation or impregnation, and is then moderately calcined at a temperature of about 350 to 700 ° C, and preferably 500 to 6000 ° C to remove the adsorbed water but retain the hydroxy groups on the catalyst surface prior to the reaction with the halide. The isomerization catalyst may also comprise other metals such as germanium or rhenium in addition to platinum.

 In general, satisfactory paraffin isomerization catalysts include refractory inorganic oxides and a platinum group metal.

The solid refractory oxide may be chosen from silica, alumina, titanium dioxide, chromium oxide, or mixtures of these oxides; various refractory oxides found in nature with varying degrees of purity such as bauxite or bentonite, or diatomaceous earth such as kieselguhr. Among the oxides mentioned, alumina is preferred, and in particular substantially anhydrous gamma-alumina prepared synthetically and having a high degree of purity. By platinum group metal is meant a noble metal, excluding silver and gold, selected from platinum, palladium, germanium, ruthenium, rhodium, osmium and platinum. These metals are not necessarily equivalent from the point of view of their activity in the catalyst and among these metals platinum and palladium are preferred. Recent findings indicate that in certain applications of other metals and in particular rhenium and germanium have a beneficial effect and increase or prolong the activity of the catalyst. In these catalysts, a halogen referred to in the art as halogen combined is also normally present and may be from 0.01 to 5% by weight, based on the dry carrier material, which is preferably selected from fluorine and chlorine, chlorine being particularly preferred.

 The conditions necessary for satisfactory operation of the reaction zone during isomerization depend both on the filler material and the specific catalyst used in the reaction zone. For the specific isomerization of C5 and C6 normal paraffins, the inlet temperature to the reaction zone may be from 120 to 204 OC and preferably from 148 to 259 C. The isomerization reaction is exothermic and an increase The temperature range of 1 to 15.degree. C. is normal and depends on the degree of conversion and the amount of benzene contained in the feedstock.

Benzene which is often present due to poor fractionation of the feed exerts a significant effect on the exit temperature of the reaction zone since the hydrogenation reaction of benzene is more exothermic than the isomerisation reaction of the reaction zone. normal paraffin. The reaction zone can be maintained at virtually any pressure and normally the pressure used will be from about 28.105 to 103.105 and preferably from 55.1G5 to 83.105 Pet, especially envlror. 69.li R,
The present invention can also be applied to processes in which the reaction zone does not contain catalytic composite material.

For example, the invention can be applied to a toluene thermohydrodealkylation process or a visbreaking process in petroleum refining.

Another application of the present invention is the dehydrogenation of C8 to C18 normal paraffins as disclosed in US Patents 3,391,218; 3,448,165 and 3,647,719. Other methods that can be practiced using the present invention include but are not limited to: disproportionation of aromatic hydrocarbons; the thermocracking of naphthas; the isomerization of naphthenes such as, for example, the isomerization of methylcyclopentane to cyclohexane; reforming naphthas to produce aromatic hydrocarbons or gasoline mixtures and alkylation of paraffinic or aromatic hydrocarbons.

Claims (7)

 1. Hydrocarbon conversion process consisting of  a) passing a mixed phase charge current through an indirect heat exchange zone and vaporizing a portion of the charging current and heating the charging current to a desired temperature;  b) passing the feed stream through a reaction zone maintained in hydrocarbon conversion con- ditions to obtain an effluent stream from the reaction zone;  c) heating the effluent stream of the reaction zone by passing through a direct flame heating zone; and  d) cooling at least a portion of the effluent stream of the reaction zone by passing through the indirect heat exchange zone and indirect heat exchange with the charging stream.  2. Method according to claim 1, characterized in that all the effluent stream of the reaction zone is sent to the indirect heat exchange zone.  3. Method according to claim 1, characterized in that the charge current is converted into a vapor phase current in the indirect heat exchange zone.  4. Method according to claim 1, characterized in that the effluent of the reaction zone is an effluent stream in mixed phase.  5. Method according to claim 4, characterized in that the effluent stream of the reaction zone is separated into a vapor phase stream and a liquid phase stream in a gas-liquid separation zone.  6. Method according to claim 5, characterized in that the liquid phase stream is heated in a direct flame heating zone.  7. Method according to claim 6, characterized in that at least a portion of the liquid phase stream is cooled by passing through an indirect heat exchange zone and indirect heat exchange with the charging current.