DE3415821A1 - Process for the preparation of alcohols from light hydrocarbons - Google Patents

Abstract

According to the invention, a steam reformation reaction being carried out in zone (14) in which, in particular, methane is treated with steam, and a reaction being carried out in zone (20) for the synthesis of alcohols from synthesis gas which is formed in the steam reformation zone are combined. An essential feature of the invention is a recycling of at least a part of the carbon dioxide gas and the light hydrocarbons, which occur in the gas phase withdrawn from the alcohol synthesis zone, through pipe (3) into the steam reformation zone. With the aid of the process according to the invention, methanol and higher homologous alcohols are prepared in a particularly advantageous manner. <IMAGE>

Description

Ι O The invention relates to what is stated in the claims Process for the preparation of a mixture of methanol and at least one in the homologous series linear and saturated alcohol above methanol with e.g. 2 to 10 carbon atoms per molecule, in particular from ethanol, propanol, butanols and pentanols. Some of these alcohols, in general certain such alcohols mixed with one another, are characterized by the fact that they directly to a fuel consisting practically of hydrocarbons, i.e. a normal or super car gasoline, may be added, for example, an automobile fuel of moderate price and excellent quality is obtained.

Process for the production of such alcohol mixtures, which started out from synthesis gas and in one or more Process steps are worked in numerous Documents described, e.g. in FR patent application 82/16 345, GB-PS 21 20 119, FR-PS 25 23 957, the FR patent application 82/11 892 and in the FR-PS 23 69 234 (corresponding to US-PS 41 22 110), 24 44 654 (corresponding to US-PS 42 91 126), 24 53 and 24 41 420.

The process according to the invention takes place in two process stages, whereby the first procedural

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stage is a steam reforming, ie the reaction of water with methane or gaseous light hydrocarbons of the formula CH _n ~, where n = 1 to

η 2η + 2 '

means. During this reaction, carbon monoxide, carbon dioxide and hydrogen and thus a synthesis gas are formed, from which an alcohol or alcohols are produced in a second process stage.

Such a procedure does not appear very much a priori obvious with regard to thermodynamic considerations. So becomes reaction (1), i.e. the reforming of methane with water

CH ₄ + H ₂ O> C0 + 3 H ₂ (1)

accompanied by the equilibrium reaction (2)

A.
CO + H ₉ O = »C0 + H ₉ (2)

^B.

This equilibrium is essentially shifted in the sense of A, due to the excess of water which is used in reaction type (1), this excess being necessary in order to avoid the coking of the reactor and the catalyst caused (by excessive heat generation), which leads to a molar ratio of H ₉ / CO which is very often between 4.5 and 6. The shift in equilibrium (2) in the sense of A is thus expressed in an excessively high content of hydrogen, which in turn results in an excessive formation of methane at the expense of the desired alcohols in the second process stage.

This shift in equilibrium in the sense of A is all the more pronounced than in the case of the ones usually used Temperatures, even in the absence of excess

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of water, the value of the equilibrium constant K (in the sense of A) is favorable for the shift in the sense of A, which at the same time results in a disadvantageous overproduction of C0_.

In the following, different values for K are given for different temperatures:

ρ (in the sense of A)

ρ CO _o .p H.

ρ CO

T ⁰ K T ⁰ C ^L ° 9l0 ^K p ^k p 298 25th 4.992 98175 300 27 4,947 88512 400 127 3.166 1466 500 227 2.114 130.0 600 327 1,429 26.85 700 427 0.952 8.95 800 527 0.603 4.01 900 627 0.341 2.19 1000 727 0.136 1.37

Strictly speaking, however, the invention is based on

Introduction of CO ₃ into the first reactor. As a _{CO 2} source for this introduction, CO "can serve, which is at least partially from a stock of compressed CO ₇ or a similar storage unit (eg from the Ammo

niaksynthesis) or comes from a natural source, or CO », which comes from the gases of the steam reforming furnace

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-δι is obtained, etc., but _{according to the invention at least part of this CO 0} advantageously consists of C0_, which is taken from the synthesis reactor for methanol and / or its homologous alcohols. If the COp is used in this way, which is from the reactor for the alcohol synthesis originates, numerous problems associated with the presence of CO ₂ in the gases withdrawn from the synthesis reactor can be solved. It is indeed advisable to recycle these gases to the synthesis reactor, but the presence of CO ₂ in these gases has disadvantages for the following reasons:

Theoretically, 2 molecules of hydrogen are required to carry out the alcohol synthesis from carbon monoxide and hydrogen for a molecule of CO according to reaction (3):

_n C0 + 2n H ₂ * Q _n H _{2n + 1} OH + (n-1) H ₃ O (3)

For this type of reaction it is therefore generally desirable to use a molar ratio of H- / C0 of around 2 work, e.g. between 1.6 and 2.4 and in particular between 1.8 and 2.2, which is achieved by the method according to the invention is made possible.

In the known processes, the synthesis gas is usually obtained by gasifying e.g. coal, coke, heavy Petroleum residues, bitumen and the like. Obtained and its composition does not correspond to the stoichiometric Composition that is required for the production of alcohols, since this synthesis gas is too low Has hydrogen content; its composition must therefore be adjusted accordingly by conversion of CO with water vapor and subsequent removal the total amount or part of the CO- formed. In this case one has no interest either, too much

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To leave CO ₂ in the synthesis gas, since the alcohol synthesis ■ from CO ₂ requires more hydrogen than in the case of the synthesis from CO, as reaction (4) shows:

η CO ₀ + 3n H ₀ * CH ₀ . OH + (2n-1) H ₀ O (4)

λ 2. η 2η + 1 λ

In the course of the alcohol synthesis, a reaction mixture is produced which contains unconverted gases (CO + H ₀ ), methanol, water, hydrocarbons (methane and higher hydrocarbons with at least 2 carbon atoms per molecule) and homologous alcohols of methanol. All of this effluent is cooled in such a way that most of the methanol and homologous alcohols and most of the water condense. The non-condensed fraction essentially contains carbon oxide, hydrogen, methane, other hydrocarbons and carbonic acid gas. In the known processes, this gas fraction is at least partially recycled as make-up gas to the inlet of the reactor in order to increase the molar ratio H ₂ / CO (at the inlet of the synthesis reactor) to a value of preferably at least about 1.8 to 2.

However, such a method has a major disadvantage, namely the presence of relatively large amounts of carbonic acid gas in the gases withdrawn from the reactor. As stated above, the production of alcohols from CO ₂ requires more hydrogen than their production from CO. Recycling CO ₂ is therefore ultimately a disadvantage. In addition, the recycling of CO ₂ in the reaction zone harms the equilibrium reaction (2), which also prevails in this alcohol synthesis, namely

2, T CO r *

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-ιοί and forms in the reaction zone.

It thus follows that in the prior art there is a very often laborious decarbonation of the non-condensable Gases proving necessary · which obviously result in a not inconsiderable loss of carbon has the consequence.

In certain known processes, such carbonic acid removal has already been practically avoided in the production of methanol. Thus, according to US Pat. No. 3,763,205, a recycling mixture of gas (including C0 "), which is located in the effluent from the methanol synthesis zone, is passed to the steam reforming reactor, specifically only to this reactor, and according to the FR-PS 20 27 392 two recycling of carbon dioxide gas-containing gas are possible, both to the steam reforming reactor and to the alcohol synthesis reactor. According to these two patents, however, the recycled gases contain large amounts of hydrogen, so that, on the one hand, the H ₂ / C0 ratio at the outlet of the steam reforming zone is too high for the stoichiometric ratio of the alcohol synthesis reaction in the second zone to be maintained, and, on the other hand, the excessively high amounts of hydrogen used also result in an excessive formation of methane in the alcohol synthesis reactor at the expense of the desired alcohols.

The method according to the invention is characterized by this from that technology. the gas recycling is significantly improved for the production of alcohols, which are in the homologous series above the methanol.

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The inventive idea is to be seen in the fact that there is no decarbonation of any kind at the exit of the alcohol synthesis zone Make non-condensed gases and a special portion of these gases in the steam reforming reactor while most of the rest of these gases are recycled to the alcohol synthesis reactor will. In this way, the carbonic acid gas, which has not been decarbonated, is used carefully Together with the other gases (CO, H ~) and the remaining methane accompanying them, add the To shift balance (2) in the sense of B, which is one of the aims of the present invention to the for the most part (at least 90%) and up to 100% (if no recycle gas above that illustrated in the figure Line 13 is discharged) of the feed carbon used in the process (CO and CH.) In To convert alcohols. In addition, according to the invention, carbonic acid gas is produced from the steam reforming reactor withdrawn gases originates, to the entrance of the steam reforming reactor recycled. It should be noted that, as a rule, those from the steam reforming zone withdrawn gases are not subjected to cooling before they enter the synthesis reactor.

As the flue gases from the alcohol synthesis reactor at a temperature in the order of 100 are for carrying out the inventive method up to 200 ⁰ C, they are according to the invention in an advantageous manner to a temperature in the order of about 650-950 ⁰ C, preferably to a temperature between 730 and 890 ⁰ C, heated and at least partially recycled to the steam reforming reactor, which between 650 and 950 ⁰ C, preferably between 730 and 890 ⁰ C, works optimally, and they contribute in this way to a for the advantageous postponement of the

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Equilibrium (2) in the sense of B is a favorable K value.

The inventive feature thus resides in a connection of (a) a steam reforming which occurs at high temperature and thus at the chosen temperatures requires a cheap CO ^ charge, and (b) one Alcohol synthesis reaction, which supplies CO "and light hydrocarbons that are detrimental to this reaction, however, their recycling in an advantageous manner takes place both to the steam reforming and to the synthesis reactor. The recycle gases are practical free from water and alcohol. The main advantages of the method according to the invention are thus the following:

- It is no longer necessary to decarbonate the non-condensables leaving the alcohol synthesis reactor To carry out gases,

- the equilibrium (2) of the steam reforming reaction is shifted in the sense of B because that recycled C0_, which is introduced into the steam reforming zone, with which in the steam reforming

Reaction formed hydrogen reacts. This equilibrium shift in the sense of B leads to a reduction in the molar ratio H ₂ / C0 (which is usually too high and has a value from 4.5 to 6) to a value in the order of magnitude from 2 to

(preferably from 2.2 to 2.8) so that in the course of this reaction the first process step, i.e. at of steam reforming, little C0 ~, but essential Amounts of a mixture of CO and hydrogen in a molar ratio of 2 to 3, preferably from 2.2 to 2.8, which is ideal for its use as a synthesis gas for the production of alcohols in the

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Go through the second stage of the procedure. It should be noted that the values for the ratio H / CO, which were discussed above and are necessary for a good operation of a reactor for the synthesis of homologous alcohols of methanol, differ from the high values of this ratio H ₀ / CO, on which is reported in US-PS 37 63 205 and FR-PS 20 2 7 392, differ significantly;

- In the overall balance of the two reactions (steam reforming and alcohol synthesis) there is _{no loss of carbon since the CO 2 present is} not removed but is returned to the first process stage. When both reactions are combined, all of the carbon used is converted into alcohols. Furthermore, the light hydrocarbons which can be formed as reaction by-products concurrently with the alcohols in the synthesis reactor are such that they are advantageously recycled concurrently with the CO 2 to the steam reforming reactor. These light hydrocarbons also include the methane not steam reformed in section (14) of the figure.

The invention is illustrated by the attached figure. The feed material (natural gas, e.g. methane or at least one other light hydrocarbon or a mixture of such gases) is through the lines and 5 fed to the steam reforming zone 14. The supply line for steam and for recovery of the condensate are not shown. Booster carbon dioxide, which comes at least partially from natural gas deposits, is through the lines 2 and introduced. Recyclization carbonic acid gas and the hydrocarbons obtained as reaction by-products are fed through line 3. If necessary, carbonic acid also occurs through line 4

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J4

gas obtained at the exit of the steam reforming zone. The steam-reforming zone preferably operates at a temperature of 730-8 9O ⁰ C under a pressure between 1 and 4 MPa at a rate from 2000 to 10,000 volume of gas (standard temperature and pressure) per volume of catalyst per h.

The effluent from the steam reforming zone indicated by ';' " Line 6 is withdrawn, is passed through lines 7 and 8 into a compressor 19. Possibly is part of the drain through the lines 15 .und

16 passed through a zone 18, whereby usual known appropriate measures a portion of the carbonic acid gas of the steam reforming effluent is isolated, whereupon this Share or at least a part of the same in the steam reforming zone 14 is returned through lines 4 and 26. In this way, it is advantageous for about 3 recycle up to 60 mol% of the carbonic acid gas withdrawn from the steam reforming reactor into this reactor, this recycled amount of carbonic acid gas itself in turn being about 30 to 60 mol% of that in the steam reforming unit imported fresh carbonic acid gas. The effluent from the steam reforming zone after it has reached the pressure required in the alcohol synthesis zone 20 (which is usually between 5 and 20 MPa) was compressed through the pipes

17 and 9 in the catalytic alcohol synthesis zone 20 which operates at a temperature between 200 and 400 ⁰ C, preferably between 250 and 350 ° C.

The effluent drawn off through line 10 from zone 20 is separated in zone 21, on the one hand into a liquid phase, which comprises water and alcohols and is drawn off through line 12, and on the other hand into a gas phase, which essentially contains unreacted gases, includes light hydrocarbons and CO ₂ and the practical

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table is free of water and alcohols and is withdrawn through line 22. At least part of this gas phase, which has optionally been brought to the temperature prevailing in the steam reforming zone 14 recycled to zone 14 through line 3. As a rule, 2 to 15% by volume are preferred in this way 2.5 to 10% by volume of the total volume of the gas phase in line 22 is recycled in such a way that preferably a molar ratio "recycled CH./fresh CH." / between 0.2 and 2, preferably from 0.3 to 1, exists with a view to stabilizing the equilibrium of reaction (2) in the sense of B.

It is also advantageous to pass at least part of the gas phase through line 22 into alcohol synthesis zone 20 the line 11, the compressor 24 and the line 25 to recycle. Advantageously, 85 to 98%, preferably 90 to 97.5% by volume of the total gas phase is recycled in this way. Finally can too a portion of the gas phase can be removed and discharged through line 13, the portion of the in this way removed gas phase makes up a maximum of 10 vol .-% of the total amount of the gas phase in line 22.

The alcohol synthesis is carried out at a pressure between 5 and 25 MPa, preferably between 6 and 20 MPa; the reaction temperature is between 200 and 400 ⁰ C, preferably between 250 and 350 ⁰ C; the hourly space velocity (expressed as volume, at normal temperature and pressure, gas mixture per volume of catalyst per hour) is generally between 1500 and 60,000 hours, preferably between 2000 and 20,000 hours.

Numerous types of catalysts, such as those used for this reaction, in particular those mentioned above at the beginning of the description specified patents are described,

* = or "recycled hydrocarbon / fresh hydrocarbon" *, A

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are perfectly suitable for carrying out the process according to the invention, in particular the catalysts the base of copper, cobalt and various other metals, as in FR-PS 2 5 23 95 7 and the FR patent application 83/05 727, with these preferred catalysts giving the best results allow the present invention when carrying out the recycling operations according to the invention as a task. The higher homologous alcohols obtained according to the invention are involved in particular ethanol, propanol, butanol, pentanol, hexanol, heptanol, etc.

example

The steam reforming of methane (in zone 14) was carried out at a temperature of 880 ^° C. under an operating pressure of 2 MPa, at a volume ratio of water / methane of 2.72 and at an hourly space velocity of 5000 h (normal temperature and pressure) . The steam reforming reactor contains 50 t of catalyst made from nickel-aluminum-calcium-potassium (in% by weight approx. 20% NiO, 5% KOH, 60% aluminum oxide and 15% Ca (OH) ₂ ).

There was no gas discharge (line 13 was not present). After heating to 880 ^° C., part of the gas phase in line 22 was recycled into the first process stage and a further part was recycled into the second process stage. A recycling of CO »took place through

line 4 _.:

The alcohol synthesis reactor section (zone 20) comprised two reactors in series, one of which each had several catalyst beds, with intermediate cooling. The manufactured according to the teachings of FR-PS 25 23 95 7 Catalyst corresponded to the formula (data in atom

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-17-

men) Cu ^ gCo ₀ ^ ₃₅ Al ₁ , τ% _{/ 5} ^La 0, 1 ^Na 0, 2 ' ^{There were 6} catalytic converters per reactor; the operating pressure was 13 MPa and the temperature 300 ⁰ C.

Molar ratio H ₂ / CO. At the entrance to the zone

(on line 5): 1.81

Molar ratio H ₂ / CO at the entrance to the zone (in line 9): 1.97

Percentage of the gas phase recycled in line 3 in relation to the total gas phase in line 22: 3.25%.

Percentage of the CO 3 recycled in line 3 _{in relation to the total CO 2} in line 22: 3.25%.

Percentage of the CO ₂ recycled in line 3 in relation to the total amount of CO ₂ in line 5 (entry into the steam reforming zone): 14.42%. 20th

% of the gas phase recycled into the synthesis zone: 96.74% by volume.

ί - ^ - 2 = 0.51 (molar ratio)% Cb ₂ in line 6

% CO ^ in line 4 _Λί π / τ _ττ ι. ·· -ι j. \ 2 ^a - = 0.4 7 (molar ratio)

% CO "in line 5

Jt_CH ₄ = 0.48 (molar ratio)

% CH ₄ fresh

The following table gives the balance of the invention Procedure in kilomoles; the water vapor partially consumed in zone 14 is not listed.

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O = = = = » LO m
<c O • a · st = - <Yes. I * ϊ Μ - L. I r— t Ln O O - J 4 I tJU O co
TH LO O Ln OJ co :. - - I OJ co co t— * O t-H * « co η ψ% O OJ co r-i O CO OJ O O T-H O O co O O CM UD T-H Ln to O r-H Ln O O CO "* cn cn cn Ln T-H I-H ^ J. to CM 1-H UD co co cn to to to O O O O UD O co co OJ r-H i-H CO OJ I-H σ O T-H rH r-H O co O O O ' ' UD ι — ι σ co O I-H Ln OJ cn T-H t-H UD ■ -ι co to OJ ^ f- I-H O O CG T-H OJ co σ CO co OJ T-H CO O «3- OJ in to O 1-H O O CO T-H cn CO CD «A · in i-H T-H UD CM T-H OJ ro Ln CO CM to UD O O O O O Ln Ln r-H co CM ' cn cn LD CM 1-H «A- O i-H co O cn O r- \ id t — I Ln - O O UD ro Ln I-H to co T-H O O O-j O O LT, rc rc - '"' OJ LT, in «3- OJ O O ο ο O UD OJ T-H O ■ - I ro r-i - O cn O iH rH
rc rc ο LO i-H cn Ln O O cj cj rc to ro LT. OJ Ln i-l UD 1-I Ln OJ OO O σ O CO CM Ln cn cn co co I-H UD OJ UD i-C OJ i-H O r-I Ln approx UD cn O Ln
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co σ
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Claims (7)

INSTITUT FRANCAIS DU PETROLE 4, Avenue de Bois Preau 92502 Rueil - Malmaison France Process for the production of alcohols from light hydrocarbons Claims 1 .J Process for the production of at least one higher homologous alcohol of methanol, in which in two separate zones (14) and (20) a) in a first process stage, a steam reforming is carried out at 650 to 950 ⁰ C in zone (14), which is charged with natural gas consisting mainly of fresh methane, water vapor, refreshing carbon dioxide gas and recycling gas, the water and at least methane to each other Be reacted to form a mixture of carbon oxide and hydrogen according to EPO COPY D-8000 Munich 2 Isartorplatz 6 POB 26 02 47 D-8000 Munich 26 Cable: Telephone Telecopier Infotec 6400 B Telex Muebopat 089/2214 83-7 GII + III (089) 22 96 43 -3-24 - 2 -
Equation (1), which reads for the methane 'CH ₄ + H ₂ O> CO + 3H ₂ (1) and which is accompanied by the equilibrium reaction (2) A.
CO + HO - * CO "+ H ₉ ~ (2) ^Z B * ^Δ so that the reaction (1) and the equilibrium reaction (2) together result in a synthesis gas consisting of a mixture of carbon oxide, carbon dioxide and hydrogen, b) in a second process stage the synthesis at least of a homologous alcohol is carried out in step (20), wherein from the produced in the first process step, through line (9) supplied synthesis gas at least said alcohol is formed, characterized in that one - Treated the effluent from the zone of the second process stage (2 0) in such a way that on the one hand a liquid phase which essentially contains the alcohol or alcohols formed and water, and on the other hand a gas phase which is practically free of water and alcohol (s ) is and carbonic acid gas _; contains most of the unconverted gases and at least one light hydrocarbon, including methane, is recovered, - 2 to 15% by volume of the gas phase at one temperature recycled 650-950 ⁰ C via line (3) to the input of the zone of the first stage (14), wherein the molar ratio recyclisiertes CH _4, CH fresh. between 0.2 and 2 is chosen in order to shift the equilibrium 2 in the sense of B and in the zone the first process stage (14) _{to obtain a molar ratio H 2} / CO between about 2 and 3, which makes it possible at the entrance of the zone of the second process stage (20) at an optimal molar ratio H ₂ / CO between 1.6 and 2 To work 4, - 85 to 98% by volume of the gas phase through lines (.11) and (25) in the zone of the second process stage (2 0) recycle "siert, and - between the two zones (14) and (20), where the first or second process stage takes place, via line (15) Removes carbonic acid gas, which is at least partially via line (4). in the zone of the first process stage (14) recycled. 2. The method according to claim 1, characterized in that one further a maximum of 10 vol .-% of the gas phase from the Process cycle discharges. 3. The method according to claim 1, characterized in that one chooses such process conditions that the volume of the gas phase recycled in zone (14) is between 2.5 and 10%, based on the total volume of the gas phase, the molar ratio of recycled CH. / fresh CH _{4 is} between 0.3 and 1, and the volume of the gas phase recycled in zone (20) is between 90 and 97.5%. 4. The method according to claim 3, characterized in that the first process stage is carried out at a temperature between 7 30 and 890 ⁰ C and the volume of the recycled in the zone of the first process stage (14) Gas phase preheated to 730-890 ⁰ C. 35 EPO COPY ώ I OÖZ 5. The method according to claim 1, characterized in that the second process stage is carried out at a temperature between 250 and 350 ⁰ C and at a total pressure between 6 and 20 MPa. 6. The method according to claim 3, characterized in that the molar ratio H ₂ / CO achieved in the zone of the first process stage (14) between about 2.0 and 3 and the molar ratio E ₀ / CO at the entrance to the zone of the second Process stage (20) selects between approximately 1.6 and 2.4. 7. The method according to claim 6, characterized in that 30 to 60 mol% of the carbonic acid gas withdrawn from zone (14) is recycled into zone (14), so that the amount of recycled carbonic acid gas is 30 to 60 mol% of the refreshing carbonic acid gas introduced into the zone (14), the H ₂ / CO molar ratio achieved in the zone of the first process stage (14) between about 2.2 and 2.8 and the H ₂ / CO molar ratio at the inlet the zone of the second process stage (20) selects between about 1.8 and 2.2.