FR2525212A1 - PROCESS FOR CATALYTICALLY TRANSFORMING ALKANES AS UNSATURATED ALDEHYDES - Google Patents

Abstract

PROCESS FOR THE CATALYTIC TRANSFORMATION OF ALKANES INTO UNSATURATED ALDEHYDES. IN THIS INTEGRATED TWO-STAGE PROCESS, THE ALKANE IS DEHYDROGEN 10, AND THE EFFLUENT, CONTAINING THE CORRESPONDING OLEFINE, H AND BY-PRODUCTS IS SENT DIRECTLY IN A SECOND STAGE 12 OF OLEFINE OXIDIZATION IN L ' CORRESPONDING UNSATURE ALHEHYDE, WITHOUT SIGNIFICANT OXIDATION OF H AND BY-PRODUCTS. THE ALDEHYDE 14 AND THE BY-PRODUCTS 16 CAN BE SEPARATED AND RECYCLED TO THE FIRST STAGE THE INALTERED OLEFINE AND ALKANE. THE EFFLUENT OF THE SECOND STAGE MAY ALSO BE OXIDIZED TO TRANSFORM THE INSATURE ALDEHYDE TO THE CORRESPONDING INSATURE ACID. APPLICATION: TRANSFORMATION OF PROPANE AND ISOBUTANE INTO ACROLEIN AND METHACROLEIN.

Description

The invention relates generally to the preparation of

  In one aspect, the invention relates to the preparation of methacrolein, which is a precursor of methacrylic acid in a two-step process for the manufacture of methacrylic acid. methacrylic acid from isobutylene

or tertiary butyl alcohol.

  In typical processes of the prior art, isobutylene or tertiary butyric alcohol is reacted with

  vapor phase, with molecular oxygen on a catalytic

  to produce methacrolein Then the

  methacrolein and is reacted with molecular oxygen

  Vapor phase on a different catalyst to form methacrylic acid Methacrylic acid can then be reacted with a suitable alcohol to form

an ester of methacrylic acid.

  In another specific aspect, the invention relates to the preparation of acrolein, or acrylic acid, from propane in a process similar to that described

  to obtain methacrolein or methacrylic acid

  crylique. In general, the feed of this process was the unsaturated olefin or the equivalent alcohol. Any saturated hydrocarbon present was considered to be essentially inert since it produced little, if any, oxidation. However, there is an economic incentive for the use of alkanes as raw materials

  raw materials for the preparation of aldehydes and unsaturated

  For example, it is known to dehydrogenate isobutane to form isobutylene for use in its many applications, such as the preparation of tertiary butyl alcohol, methyl and tert-butyl rubber, and butyl rubber. Dehydrogenation processes can be used to prepare isobutylene as raw material for known methacrolein processes However, if isobutylene should be separated and purified, it would be an uneconomical way to prepare methacrolein and acid methacrylic The same comment applies to the conversion of propane into

acrolein or acrylic acid.

  In general, integrated processes are generally not used because the by-products must be separated from the dehy-

  because they can not be present in the use of

  The present process is directed to an integrated process in which the dehydrogenation of isobutane is combined with the oxidation of the resulting isobutylene to obtain methacrolein continuously and without separation. intermediate of isobutylene We can put

  a corresponding process with propane as a food

  and produce acrolein or acrylic acid.

  Processes of interest as back

  Technological plan include a process described in US-A-3,470,239, wherein isobutane is the raw material of a process for preparing methacrylic acid or methyl methacrylate via a tertiary butyl hydroperoxide as Intermediate Isobutane is oxidized to a hydroperoxide and then used to oxidize methacrolein

  methacrylic acid In this oxidation, butyl alcohol

  Tertiary liquefaction is a by-product that can be

  use as raw material to prepare methacrylate

  lein in a classic oxidation process So isobutane

  only indirectly serves as raw material for the preparation

methacrolein.

  In GB-A-1,340,891 isobutane is reacted with

  and oxygen to prepare isobutylene and / or methacrolein on various catalysts based on

  Since the conversion rate of the iso-

  butane is quite weak, we use high concentrations

  isobutylene so that the net amount of isobutylene

  or methacrolein that is produced is sufficient to give a practical process It is also indicated that propane

gives a parallel reaction.

  A recent patent, US-A-4,260,822, discloses a method

  for the direct oxidation of isobutane to methacrylic acid

  than in one step, using this time again from

  large amounts of isobutane to overcome the relative

  low conversion of isobutane into product In this case also, it is indicated that propane is oxidized

  in the same way in acrylic acid.

  The one-step processes above are not economical, since the conversion rates are quite low and require the processing of large amounts of unreacted feed, with recycling for

  produce a high overall rate of isobut conversion

  Similarly, catalysts typically do not have the long useful life required for operations.

satisfactory industrial standards.

  Since isobutylene has a number of uses

  Other than the preparation of methacrylic acid, a number of processes for converting isobutane to isobutylene have been developed and developed. In US-A-3,784,483, a cobalt, iron and phosphorus for the oxidative dehydrogenation of isobutane to isobutylene or propylene to propylene The process of GB-A-1340891 is similar except that high ratios of isobutane to oxygen (about 4/1) In US-A-3,479,416, a method operating in the absence of oxygen uses a catalyst based on a common metal, in particular a catalyst containing chromium, molybdenum and vanadium. In a group of patents of which a typical example is US-A-4,083,883, a precious metal, combined with carrier-promoting metals, is used for the dehydrogenation of

  paraffins, especially normal paraffins.

  Another approach is taken in the US-A patents

  3,692,701, US-A-4,005,985 and US-A-4,041,099.

  transferred, large amounts of steam are used to dehydrogenate butanes on a platinum-tin catalyst on zinc aluminate with a high selectivity for obtaining the corresponding butene, or to dehydrogenate

  propylene propane conversion rates are achieved

  relatively high dehydrogenation of paraffins on zinc titanate catalysts is also

  disclosed in US-A-4,144,277 and US-A-4,176,140.

  In a recently published European Patent Application No. 42,252, isobutylene is prepared by dehydroisomerization of n-butane over a supported catalyst containing an element.

  or composed of a group IIIA, in particular gallium.

  Numerous patents have disclosed processes for the oxidation of isobutylene to methacrolein relative to the present process, that described in GB-A-2,030,885, in which methacrolein is passed with oxygen. and water vapor on a molybdenum catalyst, which gives high values of

  transformation and selectivity for obtaining metha-

  croleine, is of particular interest.

  Numerous patents have described processes for the oxidation of propylene to acrylic acid, such as EP OOQ 663 and US-A-3,954,855. These processes are generally carried out in two stages in order to obtain the best yields of acrylic acid. the first step, propylene is oxidized to the vapor phase acrolein on a promoter molybdenum catalyst and the effluent of the reaction, with addition of oxygen, is passed over a second catalyst

  Molybdenum with promoter to produce acrylic acid.

  Based on the prior art discussed above, a multi-step process could be grouped whereby an alkane was dehydrogenated with or without the presence of oxygen to produce the corresponding olefins which could then be separated and purified, and then In this way, by simply juxtaposing known processes, a "combined" process could be operated which would transform almost all of the alkane to a second step for the oxidation of the olefin to the corresponding unsaturated aldehyde. supply of unsaturated aldehyde

  can not be an economical way to produce aldehyde.

  As will be seen, the present invention relates to an integrated process for converting an alkane to the aldehyde

  corresponding unsaturated without first separating the olefin.

  The dehydrogenation of an alkane produces large amounts of hydrogen and low amounts of lower molecular weight hydrocarbons which would be removed from the product in the case of prior processes (see, for example, US-A-3,479 416), but which must be taken into account in a

  integrated process, during the oxidation of the alkane to the aldehyde.

  Hydrogen and by-products shall not adversely affect the oxidation catalyst or its

  behavior or performance For example, the exposure of sub.

  products under oxidizing conditions can not produce impurities decreasing the quality of the aldehyde Similarly, the presence of hydrogen should not create an explosive mixture

in the oxidation reactor.

  The oxidation step forms carbon oxides as byproducts and certain oxygenated compounds with lower molecular weight and, at the same time, introduces oxygen into 1 Me gas, which is not acceptable in the reactor Thus, the recycling to the dehydrogenation stage of a combined effluent from the oxidation reactor involves particular problems related to the integrated process of the invention. which will be described below,

  problems related to the integration of the process of the prior art

  laughing. According to the invention, alkanes are dehydrogenated to produce the corresponding olefins which are subsequently oxidized.

  unsaturated aldehydes. For example, the metha-

  crolein from isobutane, in an integrated process in which the dehydrogenation of isobutane to isobutylene

  is followed immediately, ie without separating the isobut

  tylene dehydrogenation effluent, by addition

  of oxygen and the oxidation of isobutylene to methacrolein.

  Alternatively, some of the by-products of the dehydrogenase

  This can be achieved by, for example, selective oxidation of hydrogen to water or partial condensation of the water contained in the effluent stream. Methacrolein can be removed before the oxidation step, which concentrates isobutylene. be recovered by washing or fixing the effluent of the oxidation reaction, which also contains unaltered isobutane, isobutylene and oxygen, plus hydrogen, carbon oxides and various sub- hydrocarbon products of dehydrogenation and oxidation reactions. The corresponding method can be implemented using a

food containing propane.

  In certain embodiments of the invention, methacrolein is recovered and then oxygen, hydrogen and oxides of carbon are removed from the effluent of the oxidation reaction by catalytic reactions or reaction techniques. absorption, and the remaining gases, containing isobutane and isobutylene, are recycled to the dehydrogenation reaction. A preferred method of removing oxygen and hydrogen is to react with a suitable catalyst. oxidation under selected conditions to completely remove oxygen, but having substantially no effect on isobutene and isobutane present Suitable catalysts include platinum or other Group VIII noble metals on alumina or other carriers The oxidation of hydrogen is carried out at a

  temperature permitting selective oxidation of hydrogen.

  With platinum on alumina, such oxidation can be initiated at relatively low temperatures, such as ambient temperature. In a preferred embodiment, the rate of addition of oxygen to the oxidation reaction is adjusted by in order to obtain a limited quantity in the effluent, so that the hydrogen produced in the dehydrogenation reaction consumes all of the remaining oxygen

  after oxidation of isobutylene to methacrolein.

  In another embodiment, the alkane and olefin remaining in the effluent gases are absorbed with a suitable liquid, such as C 8 to C 10 paraffin oil, after removal of the aldehyde. We can treat

  gases, if desired, to recover the constituents

  interesting kills, burn the gas or get rid of a

other way.

  In this embodiment, hydrogen and oxygen

  contained in the residual gases and only hydrocarbons

  Unprocessed bures are recycled to the dehydrogenation reactor. In yet another embodiment, the gases

  effluents are partially separated after the dehydration step.

  with the concentrated C 3 or C 4 hydrocarbons,

  that is propylene / propane or isobutylene / isobutane

  tane, sent to the oxidation stage.

  The dehydrogenation of the alkane is carried out in the

  by a vapor phase reaction on a suitable catalyst, which may be platinum / tin on zinc aluminate or on other noble metal catalysts

  and base metals or base metals When cat-

  lyseur is platinum / tin on zinc aluminate, the dehydrogenation will be carried out at a temperature between about 400 and 7000 C and under a pressure gauge

  whose maximum is close to 10 bars.

  The oxidation of the olefin to the aldehyde can be carried out on suitable catalysts, such as oxides

  common metals or mixed bases, in particular catalytic

  based on molybdenum oxide, and in particular a catalytic

  a lysate comprising oxides of molybdenum, bismuth, cobalt, iron, nickel, thallium and antimony,

  silica and one or more of the alkali metals.

  The invention will now be described in more detail, by way of illustration and in no way limitative, with reference to the accompanying drawings in which: FIG. 1 is a block diagram showing the method of the invention;

  FIG. 2 is a simplified diagram showing the pro-

  of methacrolein from isobutane according to one embodiment of the invention, FIG. 3 is a simplified diagram showing the production of methacrolein from isobutane according to a second embodiment of the invention, and Figure 4 is a diagram showing the production of

  acrylic acid from propane according to the invention.

  In one aspect, the invention relates to a method

  combining the dehydrogenation of an alkane, particularly the

  propane or isobutane, to the corresponding olefin,

  propylene or isobutylene, with the subsequent oxidation of propylene or isobutylene to acrolein or methacrolein, but without purification of propylene or isobutylene between the two reactions. The aldehyde product is separated to serve subsequently and, after separation of the by-products, the unreacted olefin and alkane can be recycled, if desired, to the dehydrogenation step. A scheme of such a complete process is

shown in Figure 1.

  Although the process is presented and described specifically

  about isobutane, it goes without saying that this process

  can also apply to propane.

  The process contrasts with those of the prior art because the two reactions are carried out in a manner

  that the effluent from the dehydrogenogenic reaction

  The alkane (optionally with the presence of water vapor (steam (faculty)) can be sent directly to the oxidation reaction 12 for the conversion of the olefin (isobutylene) unsaturated aldehyde (methacrolein).

  well the prior art would expect to separate the isobut

  tylene) of the effluent of the dehydrogenation step, before sending this effluent to the oxidation step Since the dehydrogenation of isobutane involves the production of large amounts of hydrogen, as well as small amounts of hydrocarbons at lower molecular weight, isobutylene (olefin) must be oxidized in the presence of large quantities of hydrogen and by-products without significantly impairing the oxidation of isobutylene to methacrolein or causing oxidation Hydrogen It has been found that isobutylene can be oxidized to methacrolein in the presence of

  of hydrogen and by-products of the dehydrogenation step

  without impairing the oxidation process.

  In another embodiment, partial separation (11) can be carried out by absorption or distillation techniques which is well known to those skilled in the art to obtain a concentrated supply of C 4 hydrocarbon for step (12) According to the composition of the effluent of the dehydrogenation reaction, it may be desirable to remove, in whole or in part, any of the following constituents, or the whole of

  these constituents: hydrogen, light hydrocarbons and water.

  The advantages of the invention are still preserved at least in part, since an impure feed is supplied to the oxidation step.

  concentration, oxidizing the hydrogen to water and / or

  densing part of the water contained in the effluent of the

dehydrogenation reaction.

  In one aspect of the invention, after separation (14) of the aldehyde (methacrolein) from the effluent of the oxidation reactor, the dehydrogenation stage is returned to the dehydrogenation stage.

  gas containing isobutylene and unreacted isobutane.

  Since an excess of oxygen is used to oxidize isobutyl-

  In methacrolein, this recycle stream contains large amounts of oxygen which must not enter the dehydrogenation stage. Any oxygen present may react with the operating temperature and cause loss of C 4 components. processes which admit the presence of hydrogen during dehydrogenation typically only admit minor amounts of hydrogen relative to isobutane. Thus, to form a complete process in which isobutane is converted only 'in methacrolein (plus minor amounts of by-products), it is necessary to remove (in 16) also

  the hydrogen (H 2) formed during the dehydro-

  generating the excess oxygen (O 2) remaining after this oxidation step plus the carbon oxides, and in particular the CO 2 dioxide and other by-products. The proportion of each constituent of the gas at a value tolerable In a preferred embodiment,

  carbon dioxide is removed by washing and the sub-

  purged products, after which the hydrogen is oxidized to water on an oxidation catalyst under conditions such that substantially no losses of C 4 constituents occur. In another embodiment, isobutane and isobutylene are removed by washing the effluent gases and recovered for recycling to the dehydrogenation stage, while the gases are discharged. Thus, the process results from the unsaturated aldehyde (product) and on the other hand, besides the gases t H 2, C 02, light by-products and by-products

heavy (light, heavy).

  The dehydrogenation of isobutane produces a mole

  of hydrogen for each mole of isobutylene and hydro-

  additional gene from the formation of lower molecular weight by-products If, as in the present process, isobutylene is not separated before subsequent oxidation, hydrogen and other byproducts are entrained in the reaction Subsequent oxidation By-product oxidation should be avoided in compounds that contaminate methacrolein Oxidation of hydrogen along with isobutylene would be inappropriate since it would consume oxygen and interfere with oxidation

  Likewise, the oxidation of hydrogen generates

  would generate inappropriate heat and create hot spots in the reactor tubes, and it would lower the productivity of obtaining methacrolein.

  It has been found that the oxidation of the iso-

  butylene in the presence of hydrogen, practically without consuming

  hydrogen, as we will see in the following example.

EXAMPLE 1

  Oxidation of isobutane in the presence of hydrogen A gaseous feed mixture is prepared, simulating

  the effluent that is expected to be obtained by the dehydrogenation

  isobutane in the presence of steam, and this gaseous mixture is introduced into an oxidation reactor to produce methacrolein The gas composition is 7% by volume tertiary butyl alcohol, 15% by weight volume of water vapor, 15% by volume of oxygen, 3.2% by volume of hydrogen, the balance being nitrogen It will be noted that tertiary butyl alcohol dehydrates to form isobutylene, of which it is is generally considered an equivalent in the oxidation reaction The gas is passed at a gas hourly space velocity of 2300 h 1 and at a pressure of about 1.6 bar on 16-0 cm 3 of a The catalyst, about 3.2 mm in diameter, is placed in a 12.7 mm ID tubular reactor. The heat of reaction is removed and the temperature is adjusted using a circulation of molten salt, in the same way usual

  for the realization of such reactions The oxy-

  dation corresponds to the theoretical formula Mo 12 Bi 1 Fe 3 Co 4 Ni 2 T 0.5b 0.3 K 0.3 Cs 0.3 if 7 x The results of the two tests are compared in Table I below L test NO 1 shows the result with presence of hydrogen and test N 02 shows the results obtained after

  stopping the hydrogen supply.

TABLE I

Temperate Temp Rate

the transfor-

  Percentage selectivity

  (OC) ATB * (%) MCHO (1) MAA (2) HOAC (3) CO (4)

-

1,346 85.2 83.4 3.9 2.5 8.9

2,346 86.7 82.1 2.9 2.0 10.3

  * ATB: tertiary butyl alcohol (1) MCHO: methacrolein (2) MAA: methacrylic acid (3) HOAC: acetic acid (4) C Ox: oxides of carbon Tests show differences that are not considered important but are located within the normal range of test measurements The amount of hydrogen consumed was not accurately measured due to the small quantities involved, but it is clear from the analysis of the reactor effluent that very little hydrogen has been oxidized However, the data show

  that this had little or no effect on the oxidation of isobutane

tylene methacrolein.

  Additions of small quantities of other sub-

  C 4 products of the dehydrogenation reaction, such as n-butene, also appear to have little or no effect on

oxidation to methacrolein.

  The separation of methacrolein (14) can be carried out by methods known from the prior art.

  for example, US-A-4,234,519 can be achieved in cooling

  containing and condensing methacrolein, containing water,

  from the effluent of the oxidation reactor of the isomer

  butylene and then washing the resulting gas with a

  The resulting solutions of methacrolein can be stripped at a convenient time to produce a vapor containing methacrolein and intended for subsequent use. Other routes may also be used. separation, such as solvent extraction and

similar operations.

  Although a separation of methacrolein for subsequent oxidation to methacrylic acid (or for other use) is shown, it is possible, provided the catalyst is resistant to the various compounds present, to send the effluent from oxidation step 12 directly to another oxidation step

  intended to convert methacrolein to methacrylate

  We will probably prefer to make the step

  12 oxidation to transform almost all of the iso-

  Butylene methacrolein before oxidation

  resulting in methacrylic acid.

  In its broad form, the invention encompasses the combination of

  its dehydrogenation and oxidation stages carrying out the transformation of isobutane into methacrolein It has been shown that such a combined process, not involving

  an intermediate separation of isobutylene is possible.

  If the resulting by-product stream, which contains high amounts of isobutylene and isobutane, can be used

  for other purposes, gas recycling is not essential.

  In many cases, it will be desirable to recycle

  butylene and unreacted isobutane, so that the integrated process substantially converts the isobutane to methacrylate.

  croleine by producing only minor amounts of

  products and without ever giving a current of isobutylene sensi-

  purely used to recycle gas with high levels of

  isobutane and isobutylene, it will be necessary to

  to the hydrogen formed during the dehydrogenation step, the excess oxygen from the oxidation step, and the carbon oxides formed in the two steps. light and heavy products and impurities from the feed Typically, the carbon dioxide will be removed by washing all or part of the recycle stream with a carbonate or amine solution known in the art, in order to maintain the desired level of carbon dioxide (carbon dioxide) Carbon monoxide will be converted to carbon dioxide in the dehydrogenation reactor Since the presence of these materials is not critical to the dehydrogenation or oxidation steps, they can economically be allowed to accumulate in the recycle stream to a proportion to which they can be conveniently removed.

  and economically Since the boiling points of light and heavy hydrocarbons obtained as by-products, such as methane,

  ethane, ethylene, propane, propylene, pentane and pentene are clearly different from the boiling points of methacrolein or C 4 hydrocarbons, these by-products can be separated by distillation or by purging streams containing the by-products in large quantities or in concentrated form Various processes, such as catalytic oxidation, can be carried out by means of liquid phase absorption or gas phase adsorption, removal of the hydrogen formed by dehydrogenation In a preferred embodiment of the invention, hydrogen and oxygen are removed at the same time by reacting them to form water vapor on a suitable oxidation catalyst under As we shall see, this can be achieved without major losses of C 4 constituents. It is necessary to remove the hydrogen, which must be removed. It is a by-product of the dehydrogenation of isobutane, if the unreacted isobutane must be recycled. As we have seen earlier,

  the oxidation of isobutylene is carried out in such a way that

  IO summed that little or no hydrogen According to a preferred form

  embodiment of the invention, the amount of oxy-

  gene in the diet of the oxidation reaction of the iso-

  butylene so that the effluent does not contain more

  of oxygen that can react with the hydrogen present.

  Of course, neither oxygen nor hydrogen should be

  present in large quantities in the dehydro-

  generation, which should in principle only work with isobutane and water vapor as a feedstock if we want to obtain the best efficiency Oxygen removal is more important, but we can leave It has been found that such selective oxidation of hydrogen can be carried out without loss of hydrogen.

  isobutane or isobutylene which are

  as we will see in the following example.

EXAMPLE 2

  Selective Oxidation of Hydrogen In an oxidation reactor of 12.7 mm ID, containing 75 cm 3 of 3.2 mm pellets or alumina pellets having a contact surface area of about 150 m 2 / g and impregnated with 0.3% by weight of platinum,

  a feed gas simulating the recycle gas is introduced

  obtained after removal of methacrolein.

  The gas is produced at a gas hourly space velocity of 2000 hl and in the vicinity of atmospheric pressure. Its composition is 30% by volume of isobutane, 4% by volume of hydrogen, 3% by volume of oxygen and % in volume

  The reaction is carried out essentially at room temperature

  ambient, and all hydrogen is found to be consumed but there has been virtually no consumption of isobutane. If it is preferred to perform the selective oxidation of the hydrogen in the recycle gas, it is

  feasible to introduce the equivalent step after dehydro-

  generation of isobutane or before the oxidation of isobutylene.

  Although a concentration of isobutylene is achieved, other measures must be

  of oxygen returns to the dehydrogenation stage.

EXAMPLE 3

  Dehydrogenation of Propane A catalyst composed of 0.4% by weight of Pt and 1% by weight of In is prepared by impregnation on a zinc aluminate support.

  catalyst, representing 50 cm 3 in the form of extrusion

  3 mm in a tubular reactor having an internal diameter of 25.4 mm. 250 cm 3 of the zinc aluminate support are added to the reactor above the catalyst bed. gas hourly space velocity of 4,000 h 1 under a

  pressure of 3.5 bar, a gas stream containing

  1 mole of propane per 2 moles of water vapor

  holds at a predetermined temperature the inlet of the catalyst bed, the outlet temperature reflecting the nature

  endothermic reaction of the dehydrogenation reaction The results

  The results obtained are shown in Table II below.

TABLE II

  Tempering test Conversion rate Selectivity for obtaining propylene input propylene (%) (%) C)

1,548 23.6 95.8

2,523 29.7 96.5

  Dehydrogenation of propane produces a mole

  of hydrogen per mole of propylene, and hydro-

  additional gene resulting from the formation of some lower molecular weight by-products If, as in the present process, propylene is not separated before subsequent oxidation, hydrogen and other by-products

  are entrained in the subsequent oxidation reaction.

  The oxidation of by-products to compounds that contaminate acrolein should be avoided. The oxidation of hydrogen along with propylene would be inappropriate since

  would consume oxygen and hinder the oxidation of propylene

  Likewise, the oxidation of hydrogen would generate undesirable heat and create hot spots in the catalyst, it would also lower the productivity of obtaining acrolein. However, it has been found that it is possible to carry out oxidation of propylene in the presence of hydrogen, practically without consuming hydrogen, as will be seen in the following example The presence of propane that has not been dehydrogenated also does not appear to be

  have a great effect on the oxidation of propylene.

EXAMPLE 4-

  Oxidation of Propylene in the Presence of Hydrogen and Propane According to the process described in EP 0000 663, a catalyst corresponding to the reference catalyst A having 80% by weight of K 0.1 Ni 2.5 O 4 is prepared. 5 Fe 3 BiP, 5 Mo 120x and 20% SiO A charge of 220 cm 3 of catalyst, in the form of pellets or pellets of 4.7 mm, is placed in a single tube reactor having

* an internal diameter of 12.7 mm is passed over the catalyst

  at a space hourly space velocity of 1,200 h, a feed gas containing 5% by volume of propylene,% by volume of water vapor and 12% of oxygen. The gauge pressure acting on the catalyst is about 1.76

  bar An analysis, by gas chromatography, of the effluent gases

  ents gives the results indicated in tests 3 to 6 of Table III below:

TABLE III

  Test Time, Temp Conversion rate Selectivity for obtaining no hours ('C) of propylene acrolein and (%) acrylic acid,%

3 78.0 310 91.1 87.4

4 81.0 310 90.6 86.3

93.5 310 90.5 87.7

6 99.5 310 90.1 89.7

7,102 310 94.2 86.6

8,115,309 92.6 88.7

9 124 309 92.5 87.9

139,309 89.3 87.2

he 147 309 91.4 85.6

12,156,310 93.7 86.7

13 180 309 92.9 86.9

  After establishing the catalyst yield with propylene as sole feed, hydrogen is added to the feed gas to partially simulate the conditions.

  which would correspond to the oxidation reaction in case of

  Propylene dehydrogenation produced by propane dehydrogenation 4% by volume of hydrogen

  in the previously introduced mixture The results obtained

  are shown under tests 7 to 10 on the table

  III It can be seen that we obtain substantially the same results

  in tests 3 to 6 It is concluded that there has been practically no oxidized hydrogen, judging from

  according to the operating conditions of the reactor.

  The introduction of hydrogen is stopped and the oxidation reaction is continued with the addition of 4% by volume of propane. The results obtained are presented in the form of tests 11 to 13 in Table III. obtains substantially the same results as for tests 3 to 6, which indicates that propane does not affect

  on the oxidation of propylene and is not itself oxidized.

  These results show that we can oxidize propylene

  in the presence of hydrogen and propane, the two main

  constituents of the mixture resulting from dehydrogenation

  It can be concluded that the integration of propylene

  Dehydrogenation and oxidation reactions are feasible.

EXAMPLE 5

  Oxidation of acrolein in the presence of hydrogen and propane To illustrate the oxidation of acrolein to acrylic acid and the effect of hydrogen and propane additions

  to the feed gas, experiments are carried out which

  correspond to those of Example 1.

  A catalyst corresponding to the composition is prepared

  Example 1 of US Pat. No. 3,954,855, according to the procedure described therein. The composition of the catalyst is Mo 12 V 4.8 Sr, 5 W 2.4 u 2.2 x On place a sample (73 cm 3) of the catalyst in the form of pellets or pellets of 4.7 mm in a tubular reactor having 12.7 mm internal diameter.

  reactor of a thermostated bath ensuring a uniform temperature

  predetermined form The feed to the reactor is initially

  consisting of 6 to 8% by volume of acrolein, 51% by volume of air and 45% by volume of water vapor The volumetric space velocity is 3000 h 1, and the average pressure prevailing in the reactor is slightly above atmospheric pressure. The results obtained are

presented in Table IV.

TABLE IV

  Test Time Tempera Transformation rate Selectivity for obtaining 3 (hours) ture (OC) mation of acro acrilic acid (%) lein (%)

14,126 254 92.8 89.1

126 251 84.5 89.2

16 41 252 86.8 88.4

17 36 251 80.7 87

  As in Example 1, 4% by volume of hydrogen is first added and hydrogen is then replaced by propane. The results obtained are shown in Table IV in the form of Test 16 (H 12). and 17 (propane) Although he

  a certain difference in the rate of transfor-

  In the case of acrolein, it is clear from tests 14 and 15 that the transformation is very sensitive to temperature, and the differences between tests 15, 16 and 17

  are not considered important or significant.

  The selectivity for obtaining acrylic acid is sensitive

the same.

  FIG. 2 is a simplified diagram showing a preferred embodiment of the invention with a method

  complete package to transform almost complete isobutane-

  Methacrolein A diet of fresh isobutane

  is vaporized in an exchanger 22 and combined with a

  The combined stream 26 is then heated in an exchanger 28 to a temperature such that when combined with the required amount of water vapor (30) , the temperature obtained is that

  suitable for the dehydrogenation of isobutane to isobutane

  According to what is shown in FIG.

  water vapor is supplied in the form of a feed stream

  If this is the mode of supply of water vapor, the water produced in the reactions is finally purged from the apparatus and taken from the bottom (49) of the methacroleine stripping apparatus 46. of the process is a production of water, this water can be used to supply the water vapor necessary for the process.

  the other case, a feed stream, containing

  isobutane and water vapor in molar ratios of between 1/1 and 1/10, preferably between 1/2 and 1/5, at temperatures between about 300 and 7000 C, preferably in the vicinity of 650 ° C, and at pressures

  between 2 and 10 bar, preferably

  at around 3 bars, at reactor 32 in which

  about 40 to 50% of the isobutane is converted to isobutane

  with a selectivity equal to or greater than 90%.

  The prior art has described a number of

  lysers for use in this process, and the conditions

  in which the reaction is carried out will depend on the

  A platinum catalyst of the type described in US Pat. No. 4,005,985 is particularly useful for this process. Although platinum and tin arranged on a zinc aluminate support provide a good yield, it can be stated that other catalysts that have proven effective include platinum and rhenium or indium on zinc support aluminate Other noble metals

  Group VIII, singly or in combination on various

  ports known in practice, can be applied to the

  dehydrogenation of isobutane to isobutylene

  Other potential supports may comprise alumina, aluminates of other alkaline earth metals,

  and rare earth aluminates, especially LANTHANE.

  It is possible to use promoters or activators such as tin, lead, antimony and thallium. It is also possible to use catalysts based on common or base metals, such as chromium, zirconium and titanium oxides. magnesium and vanadium as disclosed in US-A-3,479,416 and US-3,784,483 or zinc titanate of US-A-4,176,140 and US-A-4,144,277; 'invention

  is not considered limited to specific formulations

catalysts.

  Those skilled in the art will understand that this type of process

  involves a rapid deactivation of the catalyst and, typically,

  the process will work with multiple reactors allowing frequent regeneration The details of such operations are however not considered

  part of the inventive aspect of the invention.

  The dehydrogenation temperature is endothermic, and the temperature of the mixture exiting the reactor 32 will be about 200 ° C. lower than the inlet temperature. This outlet temperature will be influenced by the amount of water vapor used, the state of the catalyst and the roughness or severity

  selected conditions for the reaction.

  The effluent from the dehydrogenation reactor is cooled

  di in an exchanger 34 to a temperature suitable for its admission into the oxidation reactor 38 and it is

  supplemented with a stream 36 of oxygen to give a feed

  Suitable oxidation of isobutylene to methacrolein is preferred. Substantially pure oxygen is preferred, although less pure oxygen can be used if devices for purging additional inert gases are provided.

  which will normally be present.

  under typical conditions of the prior art, that is,

  that is, temperatures between about 300 and 400 ° C, gauge pressures of about 1 to 8 bar, and gas hourly space velocities of about 2,000 to

  3000 h A suitable catalyst for the oxyhydrogen

  cation, typically a mixture of common or base metal oxides, in particular those based on molybdenum, in particular a catalyst comprising the elements molybdenum, bismuth, cobalt, iron, nickel, thallium, antimony, and one or more of alkali metals The reactor will typically be of tubular type, in which the catalyst is placed in the form of pellets inside the tubes which are surrounded

  by a heat transfer fluid (or heat transfer fluid)

  The process of removing the reaction heat typically 95% of the isobutylene introduced into the reactor will be converted to methacrolein, and will also be obtained.

  minor amounts of methacrylic acid, acetic acid,

  that, and even smaller or less important quantities

  Lighter and heavier by-products

  The amount of isobutylene burns to give oxides of

  If the reactor is operated in such a way as to oxidize almost all the isobutylene, it can

  It may be possible to introduce the effluent from the oxy-

  dation directly in a second oxidation step to further oxidize methacrolein and obtain the acid

methacrylic.

  The resulting gas mixture can be cooled and

  troduced in an absorption tower 42 in which the metha-

  The crolein is absorbed into a stream of recycle water at temperatures of about 15 to 200 ° C. Most of the methacrolein is recovered in a reactor stream.

  solution containing up to about 2 mole% methacrolein.

  This solution can be stored for later use or it can be immediately sent to a methacrolein stripping tower 46 in which, at a lower pressure and with heat application, the methacrolein is stripped from the water and removed in the form of The methacroleine free water is recycled (44) to the top of the methacrolein absorber 42 to be used again. The water produced in the process is removed (49) for disposal or disposal.

  circulating as a vapor in the dehydro-

  The light gases leaving the top of the absorber

  42 of methacrolein contain large amounts of isobutane

  tylene and isobutane with lower amounts of oxides

  carbon, hydrogen, oxygen and light impurities.

  These gases are compressed (48), if they are to be returned as a recycle stream for subsequent conversion of the C 4 compounds to methacrolein - All or a portion of the stream may be washed to remove

  carbon dioxide, as shown schematically only in

  (50), since this represents a technique that the person skilled in the art knows well -for example, one can use

  washing with an amine or a hot solution of carbon dioxide

  nate To avoid an accumulation of light impurities as

  methane, ethane, ethylene, propane and

  can be taken continuously or

  on the recycling stream, as shown, a

  purge stream (51) for light impurities (purged).

  The gas still contains large quantities of hydrogen obtained during the dehydrogenation of isobutane and a

  excess oxygen supplied to the oxidation reactor.

  One feature of one embodiment of the invention is to adjust the amount of oxygen supplied to the reactor 38 so that there is no leftover

  in the effluent no more than can react with the hydro-

  gene produced in the dehydrogenation reaction Such a

  oxidation is shown as being carried out in a reaction

  An oxidizing reactor 52 employs a catalyst capable of oxidizing hydrogen to water at relatively low temperatures, so as not to substantially affect the C 4 components, as indicated in Example 2 above. can be used for this various oxidation catalysts, as

  noble metals or common or basic metals.

  In particular, platinum or palladium on alumina have been found to be particularly useful since the reaction can be initiated in the vicinity of room temperature.

  any convenient temperature can be used,

  At approximately 400 ° C. Alternatively, platinum may be selected from a support zeolite sized to exclude C 4 hydrocarbons. Such catalysts are capable of completely oxidizing hydrogen to water without oxidizing the hydrocarbons.

  In this way, the recycle stream is passed through

  on the selective oxidation catalyst (52) to remove both hydrogen and oxygen, and

  passes the mixture to the dehydrogenation reactor 32

  tion for further processing of this mixture.

  Here is a typical example of a practical way of

  of what is schematically represented on the

figure 2.

EXAMPLE 6

  100 mol / h of a feed stream is sprayed

  containing 95% isobutane, 3% n-butane, 1.5%

  tanes, and 0.5% of propane, and this stream is introduced into the dehydrogenation reactor, as well as 378.3 moles

  hour of a gaseous recycle stream containing 30% iso-

  butane and 37% isobutylene, 16% water and essentially

  no oxygen or hydrogen The currents 26 com

  bined to about 750 C (38) and mixed with 323

  moles / h of water vapor (30) which can be obtained by recycling

  clinking and vaporizing a stream 49 from the stripper 46

  methacrolein The combined current is sent into the reaction

  The effluent stream leaves the reactor at about 520 ° C, and about 45% isobutane is converted to isobutylene. it is cooled to about 130 ° C. in an exchanger 34 and mixed with 171 mol / h of oxygen (36) before being introduced into the oxidation reactor 38, in which about 82% of the isobutylene is transformed The effluent gases leave the reactor 38 at about 342 ° C. at a pressure of about 1.4 bar and are cooled to about 150 ° C. and sent to the absorber 42 in which the methacrolein is recovered by a stream of methacrolein. recycle water sufficient to produce an aqueous solution containing about 1 to 2 mole% methacrolein This solution is then stripped in a stripper 46, with reboiler, which gives a side stream in the form of vapor produced containing 69.7 moles methacrolein hour, 6 moles / h of methacrylic acid and 9.4 moles / h of various by-products such as acetone, acrolein and water.

  coming out of the top of the absorber 42 is sufficiently compressed

  to allow the gas to reach the fresh feed of the dehydrogenation reactor 32 (about 3.9 bar

  pressure) The 429 moles / h of steam containing

  about 23.8% hydrogen, 11.9% oxygen, 21.9%

  isobutane and 17.2% isobutylene. The gas also contains

  oxides of carbon, allowed to accumulate to a desired level and then maintained at this level by washing off the net carbon dioxide obtained at each pass (50). in the selective oxidation reactor (52) in which all the hydrogen and oxygen combine to produce water. The reactor is supplied with gas at approximately 25 ° C. and the effluent leaves it at approximately 175 C because of the

  heat of combustion The gas is returned (24) to the

  freshly vaporized isobutane (20) to

  see the cycle We see in Figure 2 that it is possible-

  It is possible to introduce oxygen (oxygen (faculty)) into the feedstream of the oxidation reactor 52.

  hydrogen if necessary.

  Another embodiment is illustrated in FIG. 3 Dehydrogenation of isobutane to isobutylene in reactor 32, followed by oxidation of isobutylene

  methacrolein in reactor 38 and the recovery

  The sequential methacrolein are the same as in the scheme of FIG. 2. In this embodiment, all gases are purged and only unreacted isobutane and isobutylene are recycled for additional production.

  methacrolein This can be achieved by absorbing hydrocarbons

  C 4 -bures using suitable liquid solvents such as paraffinic or aromatic hydrocarbons, or using solids such as molecular sieves. The process shown in Figure 3 uses a liquid solvent selected to effectively and efficiently separate recover the isobutane and isobutylene from the other gaseous constituents A solvent

  is a paraffin oil containing hydrocarbons

  The carbon dioxide, hydrogen, oxygen and

  light hydrocarbon by-products, in a tower 54 of

  wherein isobutane, isobutylene and heavier materials are absorbed by a liquid stream 56, leaving in the vapor phase the light gases, which are withdrawn (58) from the top of the column for the recovery of useful constituents or to be removed C 4 -rich liquid is withdrawn from the bottom of the column 54 and sent (60) into a stripping column 62 in which the C 4 compounds are removed by stripping. The C 4 poor liquid is withdrawn from the bottom of the column 62, cooled in an exchanger 64 and returned (56) into the absorber (54) to serve again Isobutane and vaporized isobutylene are recycles (24) to the reactor (32) dehydrogenation A small current can be taken from the solvent poor in C 4 and distilled to separate in a conventional manner (not shown)

  high boiling point materials.

  Here is a typical example of practical operation of the

_ _____ _______ 7 __ ____ __

  as shown diagrammatically in FIG.

EXAMPLE 8

  100 mol / h of a feed stream containing 95% of isobutane is vaporized and introduced (26) into the dehydrogenation reactor 32, and 146 mol / h of a recycle gas stream 24 containing 62% of isobutane and 38% of isobutylene. The combined streams are heated and mixed with 461 mol / h of water vapor (30),

  form of fresh or recycled steam from the methacrylate stripper 46

  crolein and vaporized The combined stream 29 is introduced into the dehydrogenation reactor 32 at about 650.degree. C., and

  in this reactor 32 about 45% of the feed isobutane

  The effluent stream leaves the reactor 32 at about 5200 C and is cooled to about 130 C in an exchanger 34 and mixed with 141 moles / h of oxygen (36) before being introduced into the reactor 38. in which about 82% of the isobutylene is converted to methacrolein. The effluent gases exit reactor 38 at about 342 ° C. under a pressure of 1.4 bar and are cooled to about 150 ° C. in a heat exchanger. 40 and sent to the absorber 42 in which the methacrolein is recovered by a stream of water 44 in

  recirculation, in sufficient quantity to give a solution

  The solution is then stripped in a stripper 46 with a reboiler to give a side stream of product vapor containing 69.7 mol / h of methacrolein.

  6 moles / h of methacrylic acid and various by-products

  taking acetic acid, acrolein and acetone.

  The raw recycle gas (43), which comes out of the top of the absorber

  42, is compressed (48) sufficiently to allow the gas to reach the fresh feed of reactor 32 of

  dehydrogenation (gauge pressure of about 3.9 bar).

  The 302 moles / h of steam contain about 28% of hydro-

  7% of oxygen, 30% of isobutane, 19% of isobutylene and 11% of carbon oxides. The gas is passed into the absorption tower 54 in which the quasi-totality of isobutane and The isobutylene is washed out with the stream 56 containing 150 moles / h of a C 8 -C 10 solvent. The C 4 -rich liquid (60) passes to the stripping column 62 in which the C 2 -C 4 compounds are removed. 4 are stripped and returned (24) to the dehydrogenation reactor 32 for

complete the cycle.

  As for the selective oxidation step studied above

  above, the absorption of the C 4 compounds by a solvent can be adapted to achieve a partial separation of the effluent from the dehydrogenation step, so as to introduce into the oxidation reactor only isobutylene and unreacted isobutane As above, some advantages are obtained, but at a higher cost and it is still necessary to remove oxygen and carbon oxides from the effluent gaseous. The above study on processes for

  to convert isobutane to methacrolein can also

  generally apply to a similar process for converting propane to acrolein. The same technique will be used, but the person skilled in the art

  understand that we are going to change the operating conditions

  equipment and equipment to achieve the best results

  but without departing from the broad scope of the invention.

  The usual process practiced on an industrial scale generally produces acrylic acid rather than acrolein. The present invention can be applied to

  the production of acrylic acid, as schematically represented

only in Figure 4.

  The process contrasts with those of the prior art of

  that the effluent from the dehydrogenation reaction

  can be introduced directly into the oxidation reaction 12

  The person skilled in the art, familiar with the prior art, would expect propylene to be separated from the effluent of the dehydrogenation step before introducing this effluent into the reactor. step 12 of oxidation Since the dehydrogenation of

  Propane involves the production of large quantities of hydro-

  low molecular weight hydrocarbons, propylene must be oxidized in the presence of large quantities of hydrogen, propane and It has been shown in the examples above that propylene can be oxidized to acrolein in the presence of hydrogen, propane and by-products of the hydrogenation stage.

  dehydrogenation without affecting the oxidation process.

  tion. After oxidation of propylene to acrolein, all of the effluent from the first oxidation stage 12 (acrolein) can be sent directly to a second stage 14 for oxidation of this acrolein, in which the acrolein is oxidized to Acrylic acid The effluent from the oxidation step 14 is then partially condensed and separated into 16 The acrylic acid is the desired product, heavy by-products are separated ("heavy"), while the lower constituents boiling point are separated into 18 gases in this case little or no interest, for example CO 2 'H 2, 02 and light hydrocarbons ("light"), as well as heavy by-products ("heavy" ") are unloaded, while propane

  unreacted is recycled to steps 10 and 14.

  The effluent from step 12 of the first oxidation can be optionally separated in order to recover acrolein, which is then introduced, with air or oxygen, into step 14 of second oxidation (oxidation

  acrolein) Recovery can be achieved by absorbing

  in suitable liquids, such as water and lower carboxylic acids. Unreacted propane will be

  returned to dehydrogenation step 10, as shown in FIG.

  If a large quantity of non-trans-

  formed, it can possibly be separated and recycled

  ("acrolein") to oxidation step 14, as shown.

  It goes without saying that, without departing from the scope of the invention, many modifications can be made to the method described and shown in particular and as indicated above, the method is applicable to the dehydrogenation of propane, carried out in a ratio of 1 / 0.5 to 1/10 between the propane and the steam, at a temperature of about 400 to 7000 C under a pressure of up to about 10 bar, using a dehydrogenation catalyst based on a Group VIII noble metal or a common metal oxide

on a support.

Claims (7)

  Process for the preparation of an unsaturated aldehyde   from the corresponding alkane, this process being characterized   A process comprising the step of (a) dehydrogenating alkane to the corresponding alkene, optionally in the presence of water vapor, over a dehydrogenation catalyst to form an effluent stream comprising the olefin. hydrogen, carbon oxides, and unreacted alkane; (b) mixing oxygen and possibly   water vapor at this effluent stream from the reaction   dehydrogenation and passing the mixture through an oxidation catalyst under conditions selected to produce the unsaturated aldehyde, and producing an effluent stream comprising the unsaturated aldehyde, the unreacted alkane and the olefin, as well as oxygen and oxides of carbon; and (c) recovering said aldehyde from the effluent of the oxidation reaction.   Process according to Claim 1, characterized in   the alkane is propane and the aldehyde is acrolein.   3 Process according to claim 2, characterized in that the dehydrogenation stage (a) is fed with propane and with steam at a ratio of between approximately 1 / 0.5 and 1/10 and at a temperature of about 400 to 700 ° C and a gauge pressure of about 10 bar, and in that the dehydrogenation catalyst comprises a Group VIII noble metal or a metal oxide current or base on a carrier.   Process according to Claim 1, characterized in   that the alkane is isobutane, and the aldehyde is the metha-   croléine. Process according to Claim 4, characterized in that the dehydrogenation stage (a) is fed with isobutane and with steam at a ratio of approximately 1/1 to 1/10 at a temperature about 300 to 7000 ° C. and a pressure of about 2 to 10 bars, and that the dehydrogenation catalyst comprises a noble metal of group VIII or a common metal oxide or base metal oxide. a support.   Process according to claim 1, characterized in that it further comprises the steps of (d) separating from the effluent of the oxidation reaction (b), after recovery of the aldehyde, the hydrogen produced at dehydrogenation (a), the carbon oxides producing (a) and (b), and the unreacted oxygen in (b), to obtain a depleted effluent, and (e) return this depleted effluent as food   of the dehydrogenation reaction (a).   7 Process according to claim 6, characterized in that oxygen and hydrogen are separated from the effluent of the oxidation reaction (b), after recovering the aldehyde, by reaction with a view to forming the aldehyde. water over an oxidation catalyst under conditions selected to oxidize the hydrogen while substantially non-oxidising the alkane and the corresponding olefin.   8 Process according to claim 6, characterized in that the effluent from the reaction (b) of oxidation, after recovering the aldehyde, the alkane and the unreacted olefin, is separated from the effluent absorbing in a liquid, and that they are then stripped of this liquid for   return as a feed to reaction (a) dehydro-   génation. 9 Process according to claim 1, characterized in that molecular oxygen is mixed with the effluent of the reaction (a) dehydrogenation, and passed over an oxidation catalyst under conditions chosen to oxidize selectively hydrogen while leaving the olefin, the alkane and the other substantially non-oxidized hydrocarbons,   then the oxidation step (b) is carried out.   Process according to Claim 1, characterized in that the effluent from the   reaction (a) of dehydrogenation of the alkane.