AU611681B2

AU611681B2 - Process for thermally converting methane into hydrocarbons with higher molecular weights, reactor for implementing the process and process for realizing the reactor

Info

Publication number: AU611681B2
Application number: AU15206/88A
Authority: AU
Inventors: Jacques Alagy; Christian Busson; Michel Fouquet
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 1987-04-28
Filing date: 1988-04-27
Publication date: 1991-06-20
Anticipated expiration: 2008-04-27
Also published as: FR2614615B1; EP0289391B1; AU1520688A; DE3860727D1; CA1313885C; NO881814D0; NO881814L; FR2614615A1; EP0289391A1

Description

2 7 APR 1!:I% Melbourne

AUSTRALIA

PATENTS ACT 1952 Form COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: _61 1.68 Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published:

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S. 50

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Priority: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: INSTITUT FRANCAIS DU PETROLE Address of Applicant: 4 AVENUE DE BOIS-PREAU 92502 RUEIL-MAIMAISON

FRANCE

Actual Inventor: *r S

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Address for Service: CLEMENT HACK CO., 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

Complete Specification for the invention entitled: PROCESS FOR THERMALLY CONVERTING METHANE INTO HYDROCARBONS WITH HIGHER MOLECULAR WEIGHTS, REACTOR FOR IMPLEMENTING THE PROCESS AND PROCESS FOR REALIZING THE REACTOR The following statement is a full description of this invention including the best method of performing it known to me:- ME L BO U R N E S Y D N E Y PERTH I" C~jr i 11 c4 3 1 -IA BACKGROUND OF THE INVENTION This invention relates to an improved process for thermally converting methane into hydrocarbons with higher molecular weights, the reactor for implementing the process and the process for realizing the reactor.

Among the methane sources are natural gases and refinery gases. The natural gases can either be gases associated with crude oil or not; their composition varies rather noticeably according to their origin, but they generally contain a volume percentage of methane from to 95%. Methane is normally associated with other alkanes containing up to 6 and even more carbon atoms. Various cryogenic processes permit division of the gases into eooo several fractions once they have been cleared of the water *off and the acid components they contain; nitrogen, liquefied natural gases the propane and butane fraction of which is separated, and a fraction essentially composed of methane •o associated with a low amount of ethane. The latter fraction is either re-injected into the well in order to maintain the pressure which makes the crude oil rise or feed though a gas pipe line as a combustible gas, or else *co subjected to flaring.

oeoo Other sources of methane are refinery gases which •e S have various origins: crude oil first still gases, hydroreforming gases, different hydrotreatment gases, thermal cracking gases, catalytic craKxing gases; all ee *•o I. i 2 these gases contain, in various proportions, methane associated with numerous other gaseous constituents, such as light hydrocarbons, nitrogen, CO=, hydrogen, etc.

For example an effluent gas from a fluidized bed catalytic cracking unit comprises, after washing, about by volume of methane. This gas is often fractionated by cooling under pressure, .hc-a nlors. to obtain two fractions, one containing hydrogen, nitrogen, methane and a low amount of ethylene, the other fraction being 10 composed of the main part of the initial ethylene, ethane, propane and propylene. The latter fraction can be advantageously fed into a DIMERSOL type unit, whereas the first one is fed back into the fuel-gas system of the refinery, where it is used as a fuel.

15 The conversion of methane into hydrocarbons with higher molecular weights is doubtlessly interesting; in distant pools of natural or associated gases the 9 i conversion of methane i- acetylene, ethylene and aromatic compounds can allow, using sequences of well-known 4 20 processes, to obtain liquid fractions that are easier to transport and/or to enhanc o p. /Ue, As an example, after separating the possibly formed solids, the fraction of aromatic compounds can be separated, the gaseous fraction can first be treated in units allowing the oligomerization and/or the cyclization of acetylene, and then, after another gases/liquids separation, the residual gas fraction with a high J ill -1 3 ethylene content can be treated in Dimersol type units to obtain ethylene oligomers.

The conversion of methane, even partially achieved, on the refining scene proper, into products which are easier to increase in value also shows considerable economical advantages.

Different methods for converting methane have already been suggested; for example, U.S. patent 4,199,533 describes a method for obtaining ethylene and/or ethane from methane, which consists in making chlorine at a temperature higher than 700 0 C react with this product.

This process has an important drawback since it uses very corrosive gases at high temperatures, such as chlorine and hydrochloric acid.

Patent FR-A-711,394 describes a process for transforming methane in which the heat necessary for the heating is obtained from starting points of a gas production process.

0 Patent FR-A-1,364,835 describes a process preventing side reactions in the hydrocarbons oxidation.

The previous techniques can also be illustrated by Patents WO-A-8,700,546 and DE-A-1,542,406.

Many processes for catalytic cracking of methane have been described in prior art, using for example zeolitic catalysts, as in Patent EP 93543, but all the 0000 0 *0 0 f0 0

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7 4 catalysts used show a very short life, which is due to coke lays formed in the reaction.

id, th- :_-id.i.ing coupling of methane is a well-known process which can be achieved either in the presence of oxygen or even in the absence of oxygen; in that case, metallic oxides intervene in the reaction by being reduced; US Patents 4,172,810 4,239,658 4,443,644 and 4,444,984 are examples for this type of processes. They are discontinuous since the metallic 10 oxide must be regenerated.

4 4, Among the thermal cracking processes which can transform methane is the "Wulff process", that consists in using refractory contact masses; at first, the refractory mass is heated by the air combustion of a fuel 15 which can be the feedstock itself, then the hydrocarbon to be cracked is decomposed by absorbing the heat accumulated by the refractory material during the previous period; it is thus a discontinuous process.

S* The electric arc and plasma processes are 20 essentially centered on the preparation of acetylene; their high electric power consumption makes them difficult to exploit.

Another type of process, which is sometimes called autothermal, consists in burning a part of the feedstock in order to supply the cracking reaction with the necessary calories; this type of process uses a burner in which about 1/3 of the hydrocarbon is burnt, the rest being cracked. Considering the high thormal lovoln thot have been reached, this type of process essontiaLly produces acetylene and coke.

Patent FR 1,211,695 describes a combined process of hydrocarbon pyrolysis that consists in mixing methane with warm combustion gases which do not contain oxygen in excess, then in injecting into the obtained mixture paraffinic hydrocarbons with more than one atom of carbon; a very low amount of the methane can be transformed in acetylene with this process.

The dehydrogenating thermal coupling of methane is *highly endothermic and requires the obtaining of a very high thermal flow density at high temperatures, from 1,100 to 1,500 0 C. It is necessary that the maximum heat 15 supply is performed in the zone where the endothermic cracking and dehydrogenation reactions take place; pcdueC$ &nhkc&'S uce/ug besides, the obtaining of ,galriazble Product such as 00900N acetylene, ethylene and/or aromatic compounds requires a very short contact time followed by a rapid quenching sr that a "square" temperature profile can be obtained.

There is presently no industrial process available using a controlled heat transfer through a wall, allowing to transform the methane into a I o aB e hydrocarbons th 0 .t CA 60 r-d.c_.lly Ificr $e 1 0E3JECT nIF THE INVNTIflN The object of the present invention is to compensate for this deficiency and propose a process for thermally 6 converting methane into hydrocarbons with higher molecular weights, a reactor for the implementation of this process, leading to an easier, more flexible and better controlled production.

SUMMARY OF THE INVENTION More particularly, the invention relates to a process for thermally converting methane into hydrocarbons with higher molecular weights in a ceramic reaction zone comprising a series of juxtaposed channels 10 grouped in rows and covering at least a part of the length of said reaction zone, parallel to its axis, said W 0t h channel rows being non adjaccnt t- one another, the reaction zone also comprising on one hand a heating zone surrounding said channel rows either on said part of the 15 reaction zone or on a part of the length of said reaction 0* zone when said channels cover the whole length of the reaction zone, and, on the other hand, a cooling zone following said heating zone, comprising circulating a gas containing methane, for example a molar percentage of methane from 10 to 99 in the channels of said rows, heating the heating zone by supplying electric power through successive independant cross sections, substantially perpendicular to the axis of said reaction zone, substantially parallel to the plane of said rows .i e.p tfe r 'fc g aS re f 'ln t and tight to-ard_ /the channels of the reaction zone, introducing a cooling fluid into said cooling zone and collecting said hydrocarbons with higher molecular T8 weights at the end of the reaction zone.

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33 3 3 7 The reaction zone is the heating zone which heats the gaseous mixtures forming the feedstocks as woll as the cooling zone (or quenching zone) which cools the effluents either indirectly through contact with a cold fluid on the walls of the channels or directly through the mixing of the effluents with a cold fluid.

More particularly, said hoating zone is heated by supplying electric power with means such as an electric resistance for instance, which heats through Joule effect 10 the walls of the channel rows through which the gaseous mixtures circulate.

This type of static heating, as compared to a dynamic heating through circulation of a heat-conducting fluid surrounding channels conveying the gaseous reaction 15 mixture, contributes towards an easier and especially better controlled implementation of the process.

The conversion rate of the process is thus increased and the selectivity improved.

Accordinq to one of the major characteristics of the 20 invention, the electric resistances which supply the heating zone with heat are independantly fed with electric power, either separately or in small groups, in order to define heating sections along the heating zone and be able to modulate the energy amount supplied in this whole zone.

The heating zone is generally composed of 3 to heating sections, preferably 5 to 12. In the first part 8 of this zone, the gas containing methane, which has been previously heated up to about 6500C, is generally quickly heated to a maximum temperature at most equal to 1,500 0

C,

advantageously 1,000-1,30COC (the heating zone begins where the feedstock is introduced).

In the second part of the heating zone, which follows the first one, the electric power supplied to each heating section of this part is modulated so that the gases are maintained at a substantially constant 10 temperature, close to the maximum temperature of the first part, in order to obtain a temperature profile which remains substantiallv even all along this second part.

The modulation of these heating sections is achieved in a conventional way; the resistance elements corresponding to the sections mentioned above are generally supplied by modulating units equipped with thyristors. Transformers can optionally allow to adapt the voltages a priori, whereas the modulators allow to 20 perform the fine and continuous regulation of the .4 injected power.

In order to adjust the whole system, the channels in which the feedstock ci-culates are, for example, fitted, at the level of the heating zone and preferably at the level of maximum heating, with at least one sheathed pyrometer with a thermocouple, suited to the temperature level, as for example chromel-alumel or Pt/Pt Rh. These thermocouples are control thermocouples which transmit their informaiticn to the rocju l atur t tctea tthyricvtUr c-,oulator.

In tho fir-ct part of the ht-ating zone, thce electric power is almost exclusively used for bringing the reaction mixture from its initial temperature about 6500C to a temperature of I ,20011C for Qxaniplc, -rc-,nd which the dehydroqenating ondothormic coupling ru,-ctions occur. It is thus at the boginning of th. c ucond pal.rt of the heating zone that it bocorti n 2c2 r- to supply, tha 10 reaction medium with the na- im u i p aw ,r which can bal *-#4easily done by modulating one or sovreu hclat in g a..sections.

a The IEnqth of the first part of the~ heating 7ona generally represents from 5 to 50 of the total length 15 of the heating zone, advantageouFly 10 to '10 Z, nd preferably .15 to 25 of this z'ono.

The electric power providud in this first part of the heating zone j-s such t ha t i t q en r t Ps a hiqh temperature gradient, generally f rom ~'to hu 0 l/cm, advantacgeously 10 to In the s-econd part of the heating zormo. the olctric power whiLch is supplied is modulated at the i tfferomt heating ;r-t ons in this nonE? so t ha t thIif t Frm cera tu re variation remains low in the :one, qvnerall lower than aontt 200 C or 1lQ C arounid t he f i xt-d value?) and advantagPOuLsly lower than about 100C.

The length of the heating zone generally ranqcoi from to 90 of the length of the total reaction zone.

With the heating conditions described above, a considerable thermal flow is obtained at a high temperature level.

The space defined between the rows of channels conveying the feedstock can be occupied by a second series of channels also determining at least one file of channels alternately with those conveying the gaseous mixture. These channels are generally divided into at least two parts not communicating with one another and to Sa. with the channels conveying the charge.

0 According to a first embodiment of the heating zone, the space in the reactor between the plates reserved for 15 the feedstrxk conveyance can be filled with at least one plate generally substantially similar to the plate of the conveying channels, the second series channels of which are substantially perpendicular to the channels conveying •the charge. The heating elements are housed in the second 20 series channels.

According to another embodiment of the heating zone, the second series channels can be substantially parallel to the circulation channels. The heatinq means are then substantially parallel to the plane of the circulation channel plates but in a direction substantially perpendicular to the axis of the channels. The Side walls of the second series i:hannels are therefore hollowed out -9 in orr to~ a l I. w um -to p. nc. and in Or-dr-r d,.F'1 indopondcint heating ?;ctiants 53ubntcin ial Ilpepni .4 to the direction of the feeodstock flow.

The unitary plates serv.;ng to convey the gases of the process are preferably identical to one another. Zi: is also prefvrable that thE- plateS in which the heatinr., elements are placed are similakr to one another; they a be different fromn the platesL convoying the cgavse .4The heating zonke fohl lawid by i c'alinq -nne C.-r quenching zono) 7;c that thc, tomporaturt? c.J the off luunt:, the heating zone? c.-n 'De dorf-ci-id vLrV rapidly' down tc about 300 0 C for example.

According to an embodimont, V)1.t N an i inid i rec,.t.

quenching, the channels conveying the? fuds tock general i 15 cover the whole length of the reaction zone. The ,oconc' series channels, the length of which is. uubs tantially eulto that of the first ons re divided in at leau!t two parts which do not communicate with one another r with the channels conveying the feedstock. The first part (inlet side) corresponds to the heating rono and t ho second part (effluent outlet side) corresponds to the cooling or quenching zone, from which a cooling fluid flows out, generally parallel to the feedcstock f low.

Within the scope of the invention, tho continwoun, heating reactor and quenching exchanger u n it con he acieved ei ther in the form, (if 't rnrnohlock. or by joirntl, Juxtaposing unitary ciumvnt, ti t ~hr iomE, 'orm, which irv cooling zone wflicfl xs an extension ot said heating zone, comprising circulating a gas containing methane in the channels of said rows, heating the heating zone with an electric power supply through successive, independent transverse sections which are substantially perpendicular 7/2 12 assembled together by any appropr-iate means, for example with flanges. The use of reramic withstanding temperatures higher than 1,1500C, and more particularly silicon carbidL-, which is an easily extrudable material, facilitates the implementation of such units or unit elements.

According to one embodiment of the invention, the cooling fluid inflow in the rows of channels constituting the second section and used for conveying the fluid is 10 substantially perpendicular to the axis of these channel rows, thanks to an opening in one of the lateral walls of the concerned channels located on the periphery; the .channels of the same file are linked at the level of the *cooling fluid inlet by means of openings made in their lateral walls, so that the total channels assigned to 'a this purpose are crossed by the fluid.

Numerous ceramic indirect heat exchangers have been cescribed previOuISly; they are essentially used for turbine motors, where the material of the exchanger must 20 be able to withstand temperatures from 1,200 to 1,41000C.

**French patent 2,3,96 us paten t 4,421,702, ~Japanese patent application% 59,046,496~ and 59, 050,09E2 and French patents 2,414,988 and. 2,436,998 (additional to the previous patent) can for example be Cited, the latter~ describing a processi for manufacturing a ceramic indirect heat exchange elIemen t whic~. can be advantageously used within the scope of the invention, after some development% have been carried out..

cooling effluents adapted to cool either Dy cir uu.L.I -s said tight spaces of the second zone of the reactor (indirect quenching) or by direct contact, the effluents leaving said channels (direct quenching) 13 The fluids which can be used for cooling the effluents at the level of the indirect quenching zone can be for example air, alone or mixed with combustion fumes or low-temperature water steam under low pressure.

According to another embodiment, in the case of a direct quenching reaction, the channels conveying the feedstock generally extend over a part of the total length of the reaction zone and the space defined between these channel rows is reserved for the heating zone, the 10 length of which is substantially equal to the length of the channels through which the feedstock goes.

The reaction effluents which leave the heating zone are very rapidly cooled by injection and direct contacting in these effluents, for example with at least 15 one ceramic injector located on the reactor periphery and g• e.cooling fluids such as liquefied petroleum gases, propane or hydrocarbon oils, propane being a preferred quenching gas because it can also be partially cracked and then contribute towards the forming of products such as o 20 ethylene.

The use of ceramic materials, preferably silicon carbide, allows wall temperatures which can reach 1,500 0

C

in continuous use, which exceeds the limits of metallurgy in its present stage and allows to increase the density of the heat flow and the reaction implementation temperature.

L 14 Besides, the use of the different transverse heating sections, independant from one another, at the level of the second part of the heating zone, allows to bring a maximum thermal energy at the place where the most part of endothermic cracking reactions take place, and to maintain an substantially uniform temperature in the rest of the heating zone.

These characteristics, together with the great value of the exchange surface reaction volume ratio, which generally ranges from 200 to 1,000 allow to obtain, thanks to this process, a heat conversion of methane into acetylene, ethylene and benzene products which takes place with a good conversion rate and a high **selectivity.

15 The hydrocarbon feedstocks which can be used within the scope of this invention are gaseous in the normal temperature and pressure cniditions, with a usual methane molar percentage from 10 to 99 for example 20 to 99 7 and preferably 30 to 80 The rest of the feedstock can be composed of aliphatic hydrocarbons, saturated or not, with a number of carbon atoms of at least two, such as, for example, ethylene, ethane, propane or propylene; other gaseous constituents of the feedstock can be nitrogen, carbon dioxide or carbon monoaxide or, preferably, hydrugen, the presence of which al lows to reduce the forming of coke.

The hydrogen molar proportion can range from 1 to 90 It is possible, within the scope of this invention, tco add dilution water steam to the feedstocks defined above; the dilution water steam hydrocarbon feedstock ratio by weight goes from 0.1 to 1.

The feedstocks to be treated generally remain in the reaction zone for a time ranging from 2 to 1,000 milliseconds, preferably 30 to 300 milliseconds.

The invention also relates to the device for implementing the process. This device can also be used for any steamcracking process of a hydrocarbon with at least two carbon atoms.

re m More particularly, the invention relates to a device containing gaseous mixtures supply means and discharge means for the produced effluents, comprising an elongate reactor i, preferably with a square or rectangular section, made of ceramic, with a symmetry axis, connected on one hand to a first end, to said supply means, and on the other hand, to the opposite end, to said discharge means, said reactor being fitted with a series of juxtaposed channels 11, grouped in rows, adapted to the circulation of the gaseus mixture and extending over at least a part of said reactor length, parallel to its axis, said channel rows forming multiple plates 4 which r o, rrow are not adjoining one another and which define te spaces 17 between isaid plates, said reactor also comprising in a first zone (first end side) electric heating means 5, n each said space suited for heating i a e aid channel plates through successive independant i I C1 S U W V L II L- "L rlI of acetylene, and then, after another gases/liquids separation, the residual gas fraction with a high 16 transverse sections which are substantially perpendicular to the axis of said reactor and substantially parallel to the plane of said plates, said heating means thus substantially surrounding said channel plates 4, either S on said reactor part or on a part of the length of said reactor 1 when said channels 11 extend over the whole length of the reactor, said reactor also comprising heating servocontrol and modulation means 7, 8 connected to said heating means, said reactor also comprising in a second zone (opposite end side) which is contiguous to but does not communicate with the first zone, effluent cooling means adapted for cooling either channel plates 4 by circulating a cold fluid in said tight spaces in the second reactor zone (indirect quenching) or the effluents 15 leaving said channels 11 by direct contact (direct quenching).

Each plate generally forms at least one file of unitary channels but, according to a particular embodiment of the process, each unitary channel can be b" 20 subdivided into multiple smaller elementary channels.

The total number of channel rows is not a determining factor in the process; it is obviously S* dependant on the dimension of the whole heating reactor, quenching device and unitary channel dimensions.

Moreover, both external channel or space rows are, within the scope of this invention, preferably taken up by the heating or cooling means.

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17 The number of unitary channels per file is neither a determining factor and depends on the total dimension of the whole and on the dimension of one unitary channel.

The section of a unitary channel generally ranges from 9 to 900 mm 2 advantageously from 25 to 100 mm'. The section can have any form but it is preferably square or rectangular. The length of a channel varies according to the feedstocks to be treated, the process temperature and the desired contact time. The unitary plates are generally parallelopipedic. It is preferable,within this invention, that the unitary plates which are used show the same geometry and an identical number of unitary channels.

Any material showing a satisfactory electric conductibility can be used in the form of an electric resistance within the scope of the invention, providing that it is stable at a temperature of 1,500 1,600 0

C,

for example molybdenum and nickel-chromium alloys.

The plates, be they unitary or grouped in rows, are made of a refractcry material; ceramics such as mullite, iolite, silicon carbide, silicon nitrides, silica or alumina can be used; silicon carbide is preferably used because it shows a good heat conductivity and can be extruded.

The distance between the rows of channels (or plates) which define the spaces destined to receive the heating means or the cooling fluid generally ranges from in order to supply the cracking reaction with the necessary calories; this type of process uses a burner in which about 1/3 of the hydrocarbon is burnt, the rest I *i 9 9 9 9e 9 9 9999

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18 1 to 150 mm, advantageously from 3 to 100 mm. The distance between the various electric heating elements generally goes from 1 to 200 mm, according to the axis of the reaction zone.

With a distance advantageously ranging from 3 to mm, a very good temperature stability has been reached in the maximum heating zone (substantially constant temperature zone).

The invention also relates to a process for realizing the ceramic device for the implementation of the process.

In the first reactor zone, a plate of channels 11 from one series and a plate of channels 28 from a second series are alternately juxtaposed following a substantially adjacent way, heating sections are determined in said plate of channels 28 by introducing heating means 5, S substantially parallel to the plane of said plates, either in the direction of channels 28 from the second series or in a direction substantially 20 perpendicular to said channels 28, said heating means being connected to said heating servocontrol and modulation means 7, 8 said plates of channels 11 and 28 being juxtaposed so that channels 11 from the first series are substantially perpendicular to said sections; if need be, the plate containing said heating means is isolated from said plate of channels 11; in the second reactor zone, either a direct cooling means, preferably close to the outflow of channels 11 effluents, or an OBJECT OF THE INVENTION S/SR The object of the present invention is to compensate 19 indirect cooling means for channels 11 is introduced, following which a plate of channels 11 adapted to receive the effluents in the continuation of channels 11 from said first zone and a plate of channels 18 substantially parallel to channels 11 and adapted to circulate a cooling fluid are juxtaposed in an alternate and substantially adjacent way; if need be, said plate of channels 18 is isolated with a partitioning 32.

3 ,5lo w i n h t ae p l a t e! oi e In the case of indirect cooling, a tightne s ysto is set up between the two parts of the reactor by means such as ceramic flanges.

The use of ceramic and more particularly of silicon .i carbide, which is an easily extrudable material, facilitates the achievement of such wholes or elements of c wholes.

SIt will be easier to understand the invention with the figures which illustrate in a non limiting way the s various embodiments of the process, among which Figure IA represents a longitudinal section of the 20 reactor with direct quenching and Figure IB represents a v* i view of the reactor with indirect quenching, Figure 2 represents a cross section of the reactor vertical reactor I or direct quenching reaction zone, with an elongate form and a square section, comprising a 25g LA_ repsents, accodgo mbdent, introducing a cooling fluid into said cooling zone and collecting said hydrocarbons with higher molecular weights at the end of the reaction zone.

men""I 20 distributor 2 allowing to supply the reactor with the gaseous reaction mixture through an inlet opening 3. The gaseous reaction mixture contains for example 50% of methane and has been preheated in a conventional preheating zone which does not appear on the figure and which is preferably a convection preheating. The reactor is a multiconduit type one with a square section. It has multiple parallelopipedic unitary plates 4 which are substantially parallel towards one another and form rows of channels 11 that are substantially parallel towards one another and through which the gaseous reaction mixture flows. These plates of channels are generally not adjoining and form spaces 17 in which the heating means of the electric resistances are for example located; the latter, which are described hereunder, substantially surround the various plates of channels and are isolated from the feedrtock and the reaction effluents by partitionings 14. The heating zone 9 in which the heating means 5, are housed is set up so that transverse heating sections are constituted, which are substantially perpendicular to the reactor axis defined according to the feedstock flow direction (horizontal sections in the case of Figure These sections are generally independently heated and electrically supplied with a pair of electrodes (15a, 15b, Fig Heating zone 9, the length of which represents for example 90% of the reactor, is set up so that, in its first part (inlet side), the channels conveying the 1* a 0 *0b* 0e *0 ac a. 0 00 a this whole zone.

The heating zone is generally composed of 3 to heating sections, preferably 5 to 12. In the first part 21 gaseous mixture are heated up to a temperature of 1,200 0 C, following a thermal gradiant of 20 0 C per centimeter. To that end, at least one pyrometric probe 8 fitted with a thermocouple, for example chromel-alumel, is housed in at least one channel 11 conveying the feedstock, preferably substantially at the level of the heating zone with the maximum temperature and the probe transmits information to a regulator 7a which operates for example a modulator 7b fitted with a thyristor and connected to the electric resistances 5. The power supplied to each heating section is thus conventionally modulated according to the temperature of each section.

g' The gaseous mixture then continuously flows through the channels 11 which are in contact with the second part 15 of the heating zone, where the temperature is usually kept at a substantially constant value, substantially equal to the temperature reached in the end of the first heating zone, that is, in the case cited above, 1,200 0

C.

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To that effect, the electric power is modulated by 20 means of one or several probes 8 preferably housed along the second heating zone and following the same regulation pattern as above, according to the temperature along said zone of maximum heating, where most endothermic reactions take place, so that the temperature variation in relation to the point fixed is lower by about 5C( in relation to the value fixed.

This second zone of maximum heating corresponds to about 80 of the total heating zone; it ends with a o eit ens wit level of maximum heating, with at least one sheathed pyrometer with a thermocouple, suited to the temperature level, as for example chromel-alumel or Pt/Pt Rh. These thermocouples are control thermocouples which transmit 22 tight.partitioning 14 which can for exampie be made of refractory cement in order to avoid any gas effluent and/or cooling fluid inflow from the following cooling zone.

At the outlet of the heating zone, the reaction effluents leave channels ii and are cooled in a cooling zone 10. They are contacted with a quenching agent such as propane, introduced through quenching injectors 12 located on the periphery of reactor 1 and connected to an exterior propane source (not represented on Fig.1). The total effluent gases and propane are cooled to a temperature of about 500 0 C and gathered through an outlet tool opening 13 at the end of reaction zone 1.

0 I: According to another embodiment with an indirect quenching reactor represented in Fig.18, the rows of channels It conveying the gaseous reaction mixture extend .4 cotinuously all over reactor i. Their length is epsubstantially equal to that of the reactor.

The heating zone in contact with the channels represents for example 60 of the total reactor length.

r "The rows of channels 11 conveying the feedstock are first 5 heated in the upper part (inlet side) in the same conditions as those described above for Figure IA, then cooled in the lower part by the cnoling fluid which flows through space 18, between the plates of channels Ii, cooling the walls of the effluent flow channels.

20 rpreentsforexaple 0 o thetotl racto legth about 20 0 C or 10 0 C around the fixed value) and advantageously lower than about 100C.

t I- S 23 The obturation of channels 17, 18 with a tight obturation device 14 allows to define and insulate the heating zone 9 from the cooling zone 10. Another tight obturation 32 avoids the mixing of the hydrocarbon S effluents with the cooling fluid.

The inflow of the cooling fluid into this space, for Sexample in the rows of channels 18 intended to convey it, can be substantially perpendicular to the a~-of these rows of channels, through an opening 16a in one of the lateral walls of the concerned channels located on the 10 periphery; the channels of the same file are generally connected at the level of the cooling fluid inlet, through openings in their lateral walls, so that the total channels intended to this use are crossed by the

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15 cooling fluid. The withdrawal of the cooling fluid can also take place substantially perpendicularly to the axis of these rows of channels.

The cooling fluid preferably enters the quenching zone 10 through openings 16a connected to a line 19 and located near the partitioning 14. It flows across spaces 18 which are channels parallel to the channels 11 conveying the feedstock, with substant ,lliv the same dimension, in the direction of the reaction offluents, and leaves reactor 1 through openings 16b -ornnected to line If the case arises, the flow direction of the ©cool ng fluid can be reversed; it enters then the quenching zone 1 through line 20 and, after cooling the

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channel plates but in a direction substantial ly perpendicular to the axis of the channels. The side walls of the second series channels are therefore hollowed out 24 reaction effluents counter-currently, leaves zone through line 19.

The reaction effluents which have thus been cooled at a temperature of about 300 0 C are collected at the end of channels 11 and gathered at the outlet opening 13 through collecting line 21, as in Figure 1.

If need be, according to the nature of the feedstocks to be treated, another particular embodiment *999 consists in carrying out a two-stage cooling, the first 10 stage being achieved by indirect quenching in the interplates space up to a temperature from t500 to 700 0 C and l o the second stage being made of a cooling through injection of the cooling fluids intn the effluents of the indirect quenching zone. A direct quenching up to a 15 temperature of about 500 0 C can also be achieved, followed by the cooling of the effluents down to about 2000C with a heat exchanger.

Different ways of producing the reactor for the "9 implementation of the process according to the invention are described hereunder, which only illustrate the heating zone, the quenching zone being direct or indirect as described above with Figures IA and IN.

Fiqure 2 show9 a way of ach evLn] a vertical anl elongate reactor 1, following a horizontal section.

Reactor I i% achieved by juxtaposing in a non dp cm- ay the unitary plates 4a, 4b, whith are placed vertically, each of them containing a file of 11 A$2 heating reactor and quenching a xchang er tin it can be, achieved either in the form of a monoblock or by jointly juxtaposing unitary elements of the same -form, which are unitary channels 11. A~n electric conductor ta, j,'t insulating casing is placed in space 17, h e tv)ec walls of two successive plates, so that it bsa'ly surrounds each plate 4a, 4b, 4Ic, t hu1S-,C df inanq C -1 iat partially a heating section.

Electrodes 15a and 15b allow the electric supply of this heating tape in an independant way. Reac tor I is themiaa~linsulated by insulant 25 and located in a f ram e 4 In order to minimize the power losses, the tape can stick to the wallIs of the next plates 4Ib, 4c so that *the inter-plate space 17 can be smaller than the dimension of a tini tary channe'l.

According to another e-mbodiment illustrated by 1Figure 3, the ;pace 17 in reactor 1, between plates 4 of channels 11 reserved for the fopditock flow, is filled with at least one platp suLbstantially idontical to plate 4, the chainnol% 20 of which, With 5ubstantialty the tsame *dimension, aro placed qubstantially perpendicularly to ,0channels 11, sio that the unitary plates with channelIs alternately set in a vort~cal anid a horizontal pos-ition, thus Gwccessively placed in an orthoclorial way toward% one anothcer, are juxtaposed. ns5i ide chan n e I~ (Fg.) metallit. e1lementq 27 are to be FoundI, in the f orm of wires sipirtals o r tapesi madp mo Iybdenum, s4ubs tan tia ItIy paral I Ie to thO pla,,ne o f plIa tFes 4 Chanrlo '+are adva1ntacJQouc.ly filledC with hoat-COfnd(uCtinq c(ramic powdor ;urh aG Cli arid aru, obtur-atod by a coramic cement 3 1 2 l~~Lad at thoir ends c I ctrodtas 15a anid 1i i tick o t, advantageously used within the scope of the invention, after some developments have been carried out.

26 With such a layout, the partitioning at both ends of the heating zone is achieved by the walls of channels 28.

According to another embodiment, illustrated by Figure B1, the space 17 between the plates 4 of channels S 11 is filled with at least one plate substantially identical to plate 4, the channels 28 of which have substantially the same dimensions and are substantially parallel to channels 11. The different plates are placed Ssubstantially parallel to one another. In each plate of 10 channels 28, multiple heating resistances 22 made of silicon carbide in the form of bars or cylinders (Kanthal resistances, registered trademark)are set substantially parallel to one another and following a plane -the r cectAo a -P substantially parallel to the plates, so thatl their 15 largest dimension is substantially perpendicular to the axis of channels 11. To this end, the walls of channels 28 are laterally hollowed out, to allow their appropriate positioning in the various sections of the heating zone.

The opposite ends of the heating zone are obstructed by ceramic cement partitionings 14 to avoid the inflow of the feedstock and of the reaction effluent cooling fluid mixture into the heatirqg zone in the case of a direct quenching reactor aind to avoid the inflow of the feedstock and of the cooling fluid in the case of an indirect quenching reactor.

These embodiments are of course described for information only, in a not limitating way. It is possible i to change the various heating means described above and 27 to adapt them to the different configuration examples of the heating zone. For example, the Kanthal resistances can be used for the embodiment shown in Fig.3, where the resistances can be sustained by appropriate ceramic hangers or bearers.

There is also an improved form of implementation of the process according to the present invention.

According to this embodiment, the effluent of a plasma flare fed with a plasmagene gas is added to the 10 preheated gas containing methane which constitutes the process reagent. It is well-known that, by passing a gas known as plasmagene through an electric arc, a particular reaction medium is created, which is electrically neutral but rich in ions, electrons, atoms and/or wound a molecules. The plasmagene gas can be for example hydrogen, argon, water steam, nitrogen, methane or any other usual gas, or the mixture of several of them in variable proportions. It can particularly be the total or part of the gas supplying the heating zone.

According to a preferred embodiment of the invention, a part of the gas that constitutes the feedstock can be deducted, before or after reheating, preferably afterwards, and supplied to the plasma flare.

The flare effluent is immediately injected into the reactive fluid rest, just before the tnflow into the pyrolysis zone.

The hydrogen molar proportion can range from 1 to 90 29 To this end, I to 20 7 of the feedstock can be used, but a continuous source of plasmagene gas can also be employed. The effect of this sowing with plasma is to favor the initial heating stages and, thus, to hiqhly facilitate the conversion of methane into hydrocarbons with higher molecular weights.

S

4 SSS

S

4* 4 *64 4* It becomes thus possible to temperature than in the case where that is, for example, an average 10 lower by about i00 0

C.

work with a lower there is no sowing, reactor tempera ture Although the heat transformation ratio is the tendancy to produce whereas the tendancy to compounds is increased.

level is lower, the methane maintained. On the other hand, acetylenic compounds is reduced produce olefinic and aromatic With this reserve, the average heating temperature most often ranges from 600 to 1,3000C. The quenching aims at bringing the temperature of the mixture down under 400 0 C, for example 100-500C or lower.

Besides, a more improved embodimen.t of the process has been discovered, According to this embodiment, the implvmentation of which is easy, at least one priming reagent sielected from the group formed by oxygen, ozone and hydrogen peroxide is added to the preheated gas, in a convenient proportion compared to the reagent amount in the reaction.

comprising in a first zone (first end side) electric Sheating means 5, in each said space suited for heating said channel plates through successive independant 29 The priming rcto is introduced into the preheated gas mixture, preferably in a relatively low amount in relation to methane, before the introduction of the reaction mixture into the heating zone.

Without referring to any theory, one may think that the priming reagent, which has been introduced into the preheated feedstock preferably at less than 300 0 C and generally at 500-600C, favors the formation of radicals, particularly methyl radicals, and thus also favors the 10 starting of the conversion reaction of methane at a lrower temperature, which allows to obtain a higher yield as for the sought products ethylene and aromatic products.

It is therefore not advisable to have too great an amount of priming reagent, because this might lead to the formation of a considerable quantity of radicals and to an excessive formation of secondary products, especially carbon oxides (CO, COQ).

SThe amount of priming reagent introduced into the preheated gas mixture, expressed in percentage of gram atoms of introduced oxygen in relation to the amount of methane expressed in mol, generally ranges from 0.01 to preferably from 0.1 to 1 Accord ing to a preferred embod imen t of the invention, the priming reagent is substantially pure oxygen (that is to say, which less than 1 by volume of impurity), or oxygen diluted with an inert gas such as, for example, nitrogen or argon, or else a more complex r3C~r:!) heating or cooling means.

gas mixture containing oxygen, such as for example air, or air enriched with oxygen or air diluted with an inert gas. It is also possible to introduce the priming reagent by diluting it beforehand in a part of a gaseous mixture to be treated.

If the gas that is used is ozone, the latter can be employed in a substantially pure form or diluted in a gas as mentioned above for oxygen. A mixture of oxygen and ozone or ozonized air can be used.

9 1f0 If hydrogen peroxide is used, the latter can be *employed in a substantially pure form or diluted. It is also possible to use aqueous hydrogene peroxide, sometimes also called oxygenated water, providing that 9 the water amount which is introduced into the reactor 99 15 remains within the limits described above.

It is possible to preheat the priming reagent before introducing it, for example up to a temperature of 150 0

C.

The effect of introducing at least one priming reagent is to highly favor the transformation of methane into hydrocarbons with a high molecular weight. The introduced quantities being relatively low, only a small proportion of carbon oxides is formed. This slight loss is widely compensated for by the beneficial priming effect of the reaction, which allows thus to work with lower temperatures and shorter stays in the reaction zone for the feedstock to be treated.

plates) which define the spaces destined to receive the heating means or the cooling fluid generally ranges from 31 It is therefore generally possible in this case to work with an average temperature in the pyrolysis reactor of about 70 to 1000 lower compared to the case without introduction of a priming reagent. The stay in the S reaction zone can also be slightly shortened by using a priming reagent.

EXAMPLE

An indirect quenching reactor made of silicon carbide is used. The length of the reaction zone, which 10 represents the length of the unitary channels conveying the feedstock, is 3 m. The heating zone is heated by

C

Kanthal electric resistances made of ceramic which are inserted between the plates of unitary channels and *placed in such a way that their largest dimension is perpendicular to the axis of the unitary channels.

The heating zone comprises two adjacent parts; in one part, with a length of 0.5 m, the feedstock, which has been preheated at 600°C, is brought up to 1,2000C; C C this zone, with a high thermal gradient ot 120C/cm, is thermally regulated by thermocouples located in the unitary channels. In the second part, which has a length of 1.5 m, the feedstock is maintained dt L,200°C, more or less 10°C, with the thermal regulation of five heating sections comprising five resistances Ctch, by means of five thermocouples located in the channels. The quenching zone, which is I m loncj and is supplied with air as a cooling fluid, is an extension of the heating none. At isolated from said plate of channels 11; in the second reactor zone, either a direct cooling means, preferably close to the outflow of channels 11 effluents, or an

-~I

32 the outlet of the have a temperature quenching of 250 0

C.

zone, the reaction effluents The feedstock which is used is natural gas, the heaviest fractions of which (LPG) have been removed by compression and cooling at -100 0 C; the remaining fraction, which essentially comprises methane and ethane, is diluted with hydrogen in order to obtain the feedstock to be used, its molar composition being the following 9 f 10 Compound Ha

C

H

C=H.

Mois 100 100 This mixture is heated up to 600 0 C and cracked in the reactor described above, following the cited operating conditions; it remains in the heating zone for 200 ms.

After cooling at room temperature, the gases, the liquids and the solids are separated.

With 205 mols of the mixture which is used, the following products are obtained 1 Figure IA represents, according to an embodiment, a vertical reactor I or direct quenching reaction zone, with an elongate form and a square section, comprising a Products

CH.,

Ben zene Liquid phase without benzene Coke Amoun t 170.25 mols 50 mols 6.25 mols 15.0 mols mol 104 g 4 4 *4 4* *4 4 4 4**4 4.

*4* 44 4 4 44

Claims

1. Process for thermally converting methane into hydrocarbons with higher molecular weights in a ceramic reaction zone with a series of juxtaposed channels grouped in rows and extending over at least a part of the total reaction zone parallel to its axis, said rows of channels being non adjoining with one another, the reaction zone also comprising, on one hand, a heating zone which substantially surrounds said rows of channels either on said part of the reaction zone or on a part of the length of said reaction zone when said channels cover the whole length of the reaction zone, and, on the other hand, a cooling zone which is an extension of said heating zone, comprising circulating a gas containing methane in the channels of said rows, heating the heating zone with an electric power supply through successive, independent S" transverse sections which are substantially perpendicular to the axis of said reaction zone and substantially parallel to the plane of said rows and inc I mGit to the channels of the reaction zone, introducing a cooling fluid into said cooling zone and collecting said hydrocarbons with higher molecular weights at the end of the reaction zone.

2. A process according to claim 1, wherein a first part of the heating zone is heated up to a maximum o temperature at most equal to 1,500 C, in order to obtain a thermal gradient ranging from 5°C/cm to 60°C/cm on a length from 5 to 50% of the total heating zone length, and wherein a second part of the heating zone, subsequent to said first part is heated so that the temperature variation along said second part is less than cooling the walls of the effluent flow channels. I 35

3. A process according to claim 1, wherein said cooling zone comprises a second series of channels alternately with those conveying the gas containing methane, and wherein said cooling fluid is introduced and withdrawn substantially perpendicularly to the axis of the channels of the second series.

4. A process according to claim 1, wherein the cooling fluid is directly contacted with effluents resulting from the heating of the gas, and said hydrocarbons with higher molecular weights are collected, mixed with said cooling fluid.

5. A process according to claim 1, wherein the gas also contains hydrogen.

6. Device for the implementation of the process according to claim 1, comprising means for supplying a gaseous mixture and means discharging the produced effluents, comprising an elongate reactor made of ceramic, with a symmetry axis, connected on one hand, at a first end, to said means of supply and, on the other hand, at the opposite end, to said means of discharge, said reactor containing a series of juxtaposed channels grouped in rows, adapted to the circulation of the gaseous mixture and extending over at least a part of the reactor length, S parallel to its axis, said rows of channels constituting a plurality of plates being nonadjoining with one another .C 't ht and defining _tighte spaces between said rows, said reactor also containing in a fi.rst zone (first end side) means of electrical heating in each said space fitted for heating said plates of channels through successive, independent transverse sections substantially perpendicular to the axis of said reactor and substantially parallel to the plane of said plates, said means of heating thus substantially surrounding said 7 Plates of channels, either on said part of the reactor, or If the case arises, the flow direction of the R. cooling fluid can be reversed; it enters then the S quenching zone 10 through line 20 and, after cooling the W I-- 36 on a part of the length of said reactor when said channels extend over the total length of the reactor, said reactor also containing heating servo-control and modulation means connected to said heating means, said reactor containing in a second zone (opposite end side) contiguous to the first one and not communicating with the latter, means for cooling effluents adapted to cool either by circulating in said tight spaces of the second zone of the reactor (indirect quenching) or by direct contact, the effluents leaving said channels (direct quenching).

7. A device according to claim 6, wherein the section of a unitary channel ranges from 9 to 900 mm 2 preferably from 25 to 100 mm 2

8. A device according to claim 6, wherein the electric heating means comprise at least one heating S element selected from the group consisting of insulating electric tapes, resisting metallic elements and ceramic heating resistances.

9. A device according to claim 6, wherein the heating element is embedded in the ceramic.

10. A device according to claim 6, wherein the spaces S between the rows contain at least one of a second set of plates, the dimensions of which are similar to those of the plates that define the spaces. S.

11. A device according to claim 6, wherein each said space is filled with at least one plate of channels made of ceramic, substantially parallel to one another and placed parallel to said channels conveying the gaseous mixture.

12. A device according to claim 6, wherein each said space is filled with at least one plate of channels made of ceramic, substantially parallel to one another and AZ/\ substantially perpendicular to said channels conveying the fL \gaseous mixture. Reactor 1 is achieved by juxtaposing in a non adj aent-way the unitary plates 4a, 4b, which are -placed vertically, each of them containing a file of 4 37

13. A device according to claim 6, wherein the heating servo-control and modulation means comprise a control thermocouple, a regulation means connected to said thermocouple and a thyristor modulator connected to said regulation means.

14. A process for constructing the device according to claim 6, comprising juxtaposing in a first reactor zone, in a substantially adjacent way and alternately, a plate of channels of one series and a plate of channels of a second series, determining heating sections in said plate of channels of the second series by introducing heating means substantially parallel to to the plane of said plate of chani.els of the second series, either in S the direction of the channels or in a direction substantially perpendicular to said channels, said heating means being connected to said heating servo-control and modulation means, said plates of channels of the first and second series being juxtaposed so that channels of the first series are substantially perpendicular to said heating sections, insulating, if need be, from said plate of channels of the first series the plate of channels of the second series containing said heating means, introducing into a second reactor zone either a direct cooling means, preferably close to the outlet of the effluents of channels of the first series, or an indirect cooling means of channels of the first series following which a plate of channels of the first series adapted to receive the effluents in the extension of channels of said first series is alternately juxtaposed, in a substantially adjacent way, with the plate of channels of the second series 28 are advantageously f illed with heat-conduicting ceramic pow'der such as Csi and are obturated by a ceramic cement 31, and, at their ends, electrodes 15a and 15b stick out. 4 I t 38 substantially parallel to channels of the first series, adapted for circulating a cooling fluid and insulating, if need be, said plate of channels of the second series with a partitioning. DATED THIS 28TH DAY OF FEBRUARY 1991 INSTITUT FRANCATS DU PETROLE, By Its Patent Attorneys: 0, 0 .00. so* GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia. 9 9 99 9 .9 9 9 0* 9* 9. I-v