CA1216864A - Alcohol production from light hydrocarbons - Google Patents

Abstract

The invention relates to the coupling of a vapor reforming reaction carried out in a methane vapor treatment zone in particular and a reaction for the synthesis of alcohols from the synthesis gas produced in the vapor reforming zone. The process which is the subject of the invention is characterized by recycling to the steam reforming zone at least part of the carbon dioxide and light hydrocarbons present in the gas phase of the alcohol synthesis zone. The process which is the subject of the invention applies in particular to the production of methanol and higher homologous alcohols.

Description

lZ ~ 613 ~

The invention relates to a production method.
a mixture of methanol and at least one homogeneous alcohol upper log of methanol, linear and saturated, comprising both for example 2 to 10 carbon atoms per molecule and in particular ethanol, propanol, butanols and pentanols. Either of these alcohols, and generally some of these alcohols used in admixture, have the particularity of being able to be added directly to a gasoline composed essentially of hydro-carbides (i.e. to an automotive type gasoline normal or super type) to be able to obtain, by example, a moderately priced automotive gasoline and excellent quality.
The methods for obtaining such mixtures of alcohols, from synthesis gas in one or more stages, have been widely described in the prior art, by example in French patent no 2,533,554, the patent English No. 2,120,119, French Patent No. 2,523,957, and in French patents n 2,529,544, 2,369,234 (or USP 4,122,110), 2.44 ~. ~ 54 (or USP 4,291,126

2,453,125 and 2,441,420.
The invention relates to a production method.
at least one higher homologous alcohol of methanol, the process consisting in carrying out in two distinct zones:
a) a first steam reforming step carried out in the first separate zone between 650 and 950C, supplied with natural gas (mainly fresh methane), water vapor, make-up carbon dioxide, and gas recycling, stage during which we react together water and at least methane in order to produce a mixture of carbon monoxide and hydrogen in accordance to reaction (1) (written below for processing methane ~
CH4 + H20 ~ CO + 3 H2 (1) ~ f ~ 86 ~
- the -this reaction (1) accompanied by the equilibrium ~ 2) AT

CO ~ H20 - CO2 2 (2) the reaction (1) and the equilibrium (2) giving thus ensernble a mixture of carbon monoxide, carbon dioxide and hydrogen, that is to say a synthesis gas, b) a second step for the synthesis of at least a homologous alcohol, produced in the second zone separate, and during which, from synthesis produced in the first step, we produce at least said alcohol, the process being characterized - in that:
the effluent from the area where the second stage takes place is treated in order to collect on the one hand a liquid phase essentially containing the alcohol (s) produced and water, and on the other hand a gaseous phase, essential-slightly free from water and alcohol (s), containing gas carbonlque, most of the unconverted gas, and at least one light hydrocarbon including methane;
- in that:
2 to 15 ~ by volume of said gas phase are recycled at a temperature between 650 and 950C, at the entrance of said first separate area where the first step, and in that the ratio (in moles) CH4 recycles / fresh CH4 is between 0.2 and 2 so to move the balance (2) in direction (B) in view to obtain in the area where the first stage is carried out, a H2 / CO molar ratio of between approximately 2 and 3, the use of this H2 / CO ratio making it possible to work on the entrance to the area in which the second takes place stage with an optimum H2 / CO molar ratio included between 1.6 and 2.4;
- in that:

~ 2 ~ L6 ~
- lb -85 to 98% by volume of said gas phase is xecycled, in said second separate area where 1 takes place second step;
- and in that between the two distinct zones in which are performed the first and second ~ me steps, we take a carbon dioxide sample, that we recycle at least partially in the area where it takes place said first step.
The method according to the invention therefore comprises two stages;
the first step is a steam-reforming or reforming or steam reforming etc ...) that is to say, the reaction of water with methane or light gases hydrocarbons (LPG) of formula Cn a ~

~ 23L16136 ~

n = 1 to 4. This reaction produces carbon monoxide, carbon dioxide carbon and hydrogen, therefore a synthesis gas ~ from which in a second step, one or more alcohols are produced.

Such a process does not seem a priori very reasonable for thermodynamic considerations. Indeed, the reaction (1) of methane reforming with water:
CH4 ~ H20 ~ CO + 3 H2 (1) is accompanied by balance (2):
AT
CO ~ H20 B C2 + H2 (2) This equilibrium moves essentially in the direction A in due to the excess water used in this type of reaction (1), excPs necessary to avoid coking (by exaggerated heating) of the reactor and of the catalyst, which leads to a very H2 / CO molar ratio often between 4.5 and 6. The displacement of the equilibrium (2) in Direction A thus results in an excessively high hydrogen content which subsequently, in the second stage, leads to training too significant methane, to the detriment of the desired alcohols.

This displacement in direction A is all the more clear, that, at temperatures generally used, even in the absence of excess water, 20 the value Kp (Aj direction of equilibrium is in favor of displacement in direction A, with also, consequently, a surplus production and harmful of CO2.

The various values of Kp for various temperatures:
Kp ~ direction A) = P 2 P 2 _ p CO. p H20 8 ~

rK TC LY10 Kp .____ ... ~ ..... .. ....... __ I
298 25 4.992g8175 300 27 4.947 ~ 8512 400 127 3.1661 ~ 66 500 227 2.11413n, 0 600 327 1.42926.85 700 427 0.9528.95 800 527 0.6034.01 900 627 0.3412.19 101,000 727 0.1361.37 Now precisely, the invention is based, however, on the injec-tion in the first C02 reactor. We can use as a source of C02, for this injection, of C02 coming at least in part from a storage of compressed C02 or a neighboring unit (ammonia synthesis 15 for example) or from a deposit, or C02 recovered from smoke steam reforming furnace etc ~ .. but in accordance with the invention, a at least part of the CO ~ advantageously comes from C02 withdraws from synthesis reactor for methanol and / or its homologous alcohols. And thus use C02 from the alcohol synthesis reactor 20 makes it possible to remedy the numerous problems which generally arise from presence of C02 in the gases withdrawn from the synthesis reactor: it is indeed recommends to recycle these gases in the synthesis reactor but the presence of C02 in these gases presents disadvantages for following reasons:

To carry out the synthesis of alcohols from oxide of carbon and hydrogen, theoretically it takes 2 molecules of hydrogen for a CO molecule, according to the reaction (1 ~:
nCO + 2n H2 ~ Cn H2n + 1 OH + (n-1) H20 (1) ~ L6 ~

Thus, for this type of reaction, it is generally desired table of having to work with a U2 / CO molar ratio close to Z, for example between 1.6 and 2.4 and, more apart; especially, between 1, ~ and 2.2, which will be made possible by the method of the invention.

In prior art processes, generally the synthetic yaz is obtained by gasification, so; t of coal, coke, heavy petroleum residues, bitumens, etc ..., and its composition does does not correspond to the stoichiometric composition for obtaining alcohols, this synthesis gas being deficient in hydrogen; her composition must therefore be adjusted by conversion of CO to steam of water then elimination of all or part of the C02 form. But in In this case, there is no point in leaving too much C02 in the synthesis gas because the synthesis of alcohols from C02 requires more hydrogen than in the case of synthesis from CO (reaction (2)):

2. n H2. Cn H2nr1 OH + ~ 2n-1) H20 (2) During the synthesis of alcohols, an ef ~ luent is recovered reaction which contains unconverted gases (CO + H2), methanol, water, hydrocarbons (methane and heavier hydrocarbons having so at least 2 carbon atoms per molecule) and homologous alcohols methanol. All this effluent is cooled in order to condense the most methanol and homologous alcohols and most part of the water. The uncondensed fraction essentially contains carbon monoxide, hydrogen, methane, other hydro-carbides and carbon dioxide. This gaseous fraction, in the art before, is recycled at least in part at the reactor inlet, at make-up gas to raise the H2 / CO molar ratio (at entry synthesis reactor) to a value of about at least 1, ~ and about 2 preferably.

But the process which we have just described presents an inconvenience.
comes major which is the presence of relatively large quantities carbon dioxide gas in the reactor yaz. We explained higher than the production of alcohols from C02 requires more L6 ~

hydrogen only from C0. A C02 recyclaye is therefore ultimately harmful ~ In addition the recycling of C02 in the reaction zone harms the e ~ balanced reaction (2) which also exists in this synthesis of alcohols, C0 + H20 A ~ C02 ~ H
`B 2 and occurs in the reaction zone.
It follows that in the prior art, it was appropriate to carry out an often tedious decarbonation non-condensable ~ az, or obviously a loss negligible in carbon.
In some prior art methods, already avoided making such a decarbonatat on 70rs of methanol manufacturing essentially: So, in the American patent N 3,763,205, a gas recycling (including C02) present in the effluent from the synthesis zone of methanol is sent to the steam reforming reactor and only to this reactor and in patent No. 2,027,392, two gas recycling operations containing carbon dioxide, are possible to the steam reforming reactor and to the alcohol synthesis reactor. However, in these two patents, the gases thus recycled contain significant amounts of hydrogen so that on the one hand the H2 / C0 ratio at the exit of the steam reforming zone is too high and no longer allows stoechio-metrics of the alcohol synthesis reaction in the second zone and on the other hand, the quantities too large aunts of hydrogen put into play also translate by excessive methane formation in the reactor alcohol synthesis, to the detriment of the desired alcohols Our process improves the techniques of gas recycling, for the production of homologous alcohols methanol.

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- Her -The present invention will be better understood from the reading which follows of a preferred embodiment of it, made with reference to the following drawing:
- The single figure represents the diagram of a installation for implementing the process according to the invention.
The idea of the present invention is not to perform no decarbonation of gases not condensed at the end of the alcohol zynthesis zone and recycle some critical of these gases in the steam forming reactor, the other part of these gases 8 tant er maje the ~. v ,,. ~. ., ~

~ Z168 ~ 4 recycled to the alcohol synthesis reactor So the gas carbonic, which we did not have to decarbonate here is used for good escies with the other gases (C0, H2) and the residual methane which accompany it to move the balance (2) in direction B, one of the bu'cs 5 of the invention being to transform the major part (at least 90%) and even at 100% (when there is no purge of these line recycling gases 13 of Figure j the fresh carbon involved in the process (C02 and CH4) in alcohols. In addition, according to the invention, carbon dioxide from the gases from the steam reforming reactor is recycled to lO the inlet of the steam reforming reactor. Note that generally gases withdrawn from the steam reforming zone do not undergo cooling ~
before they enter the synthesis reactor.

In the present invention, as the effluent gases from the 15 alcohol synthesis reactors are at a temperature of around 100 at 200C or higher, the invention consists in heating them to a temperature of around 650 to 950C approximately (preferably between 730 and 890C) at least partially recycle them to the reactor steam reforming which will operate precisely between 650 and 950C, 20 preferably between 730 and 890C, thus playing on the value of Kp in advantageously deplacani the equilibrium ~ 2) in direction B.

The idea of the invention is therefore to couple (a) a stearn -reforming (steam reforming) carried out at high temperature and requiring 25 thus, at the chosen temperatures, the beneficial contribution of C02 and (b) a syn ~ hese reaction of alcohols providing C02, harmful to this reaction, and light hydrocarbons but which we recycle therefore advantageously both at the steam-reforming reactor and at the reactor of synthesis. The recycled gases will be essentially free of water and 30 spirits. The essential advantages of the present process are thus:
following:

- It is no longer necessary to proceed to decarbonation non-condensable gases from the alcohol synthesis reactor, - the equilibrium (2) of the reaction of the s ~ eam-reforming is moves in direction B since C02 recycles ec injects into the ~ Z16 ~ S9L

steam-reforming reacts with the hydrogen produced in the reaction of steam-reforming. This displacement in direction B will decrease the ratio H2 / CO molar (usually too high, 4.5 to 6) at a value of the order of 2 to 3 (preferably 2.2 to 2.8) so that at during this first stage reaction (steam-reforrning), we will produce little C02 but essentially a mixture of CO and hydrogen in a molar ratio of 2 to 3 (preferably 2.2 to 2.8 days ideal to be used as alcohol synthesis gas during the second stage.
It will be noted that the values of the H2 / CO ratios discussed above and necessary for the proper functioning of a synihese alcohol reactor 10 counterparts of mechanol, differ substantially from high values of these H2 / CO ratios noted in American patent N 3,763,205 and French patent N 2,027,392.

- in the overall assessment of the two reactions (steam-reforming and synthesis of alcohols), the C02 present no longer being eliminated but returned at the first stage, does not cause carbon loss. In the coupling of the two reactions, all the carbon involved is transformed in alcohol. Finally, light hydrocarbons, reaction by-products which can be formed simultaneously with the alcohols in the reactor 20 are thus advantageously recycled at the same time as C02, to the steam reforming reactor. These light hydrocarbons also include non-vapor methane in section (l4) of diagram .

The diagram illustrates the method according to the invention. Load (natural gas, for example methane or at least one other hydrocarbon light or a mixture of such gases) is sent by lines l and 5 in zone l4 of steam reforming. The steam supply line of water and that of condensate recovery are not indicated. Of 30 ga ~ extra carbon dioxide, coming at least in part from the natural gas, is introduced via lines 2 and 26. Carbon dioxide recycling and the reaction byproduct hydrocarbons are introduced via line 3. Optionally, via line 4, arrives also carbon dioxide recovered at the end of the 35 steam reforming. The steam reforming zone preferably works between 730 e ~ 890C, under a pressure between l and 4 Megapascals and ~ L686 ~

with a flow rate of 2,000 to 10,000 volumes of gas (temperature and normal pressure) by volume of catalyst and by hours.
The effluent from the steam reforming zone, withdrawn via line 6, is sent via lines 7 and 8 into a compressor 19. Optionally, part of the effluenk runs through lines 15 and 16 through an area 18 in which part of the gas is recovered by any suitable means carbon dioxide from the steam reforming effluent, which part is at least partially returned to zone 14 of vaporefor-mage via lines 4 and 26. It is thus advantageous to return, in moles, 30 to 60% of the carbon dioxide withdrawn from the vapoforming reactor to this reactor, this ~ quantity recycled carbon dioxide representing itself, in moles, around 30 to 60% of the fresh carbon dioxide injected into the unit of vapoforming. ~ 'effluent from the steam reforming zone, compressed to the required pressure used in zone 20 of synthesis of alcohols ~ pressure generally between 5 and 20 Megapascals), enters via lines 17 and 9 into the 2d catalytic zone for synthesis of alcohols operating between 200 and 400C, and preferably between 250 and 350C.
The effluent from zone 20, drawn off by the pipe 10 is separated in zone 21 into a liquid phase on the one hand containing water and alcohols, this liquid phase being withdrawn through line 12, and on the other hand a gas phase essentially containing unconverted gases, hydro ~
light carbides and CO2, this gas phase substantially free of water and alcohols being drawn off through line 22.
At least part of this gas phase, possibly brought to the temperature prevailing in zone 14 of vapor-forming, is recycled in this zone 14 via line 3. Generally, it is thus recycled in volume 2 to 15% and prefe-2.5 to 10% of the total volume of the gaseous phase of the line 22, so as to preferably have a molar ratio '' CH4 recycles / CH4 fresh '' or '' recycle hydrocarbon / hydro-!, ~ `"

~ 2 ~ 6 ~ 6 ~
8a fresh carbide '' between 0.2 and 2 (pre ~ erence 0.3 to 1), this in order to stabilize the equilibrium of the reaction (2) in direction B.
It is also wise to recycle part at least from the gas phase of the condult 22, towards the synthesis zone 20 /

.
. .

~ 2 ~ i86 ~ L

alcohol, via line ll, compressor 24 and line 25. We will recycle advantageously 85 to 98% and preferably 90 to 97 ~ 5 ~ / 07 volume, of the overall gas phase. Finally a part of the phase gas can also be eliminated (purge) via line 13, this 5 part of the gaseous phase thus eliminated representing a maximum; rnurn 10% in volume of the cotalite of the gas phase of the duct (22).

The synthesis of alcohols is carried out at a pressure included between 5 and 25 Megapascals (MPa) and preferably between 6 and 10 20 MPa; the reaction temperature is included in ink 200 and 400C and preferably between 250 and 350C; hourly volumetric speed, (expressed in volumes TPN of gas mixture per volume of catalyst and per hour) is usually between 1,500 and 60,000hl ei of preferably between 2000 and 20,000h l.
Many types of catalysts described for this reaction, in particular in the patents cited above, to the second paragraph on page l of this specification, convienenc perfectly for the implementation of the present inventi ~ n, and Especially catalysts based on copper, cobalt and various other metals described in French patent N 2,523,957 and which catalysts best allow to observe the best results by operating the critical recycling which is the subject of the invention. Alcohols 25 higher counterparts obtained in the present process are in particular ethanol, propanol, bu-canol, pentanol, hexanol, heptanol, etc ...

EXAMPLE
We operate the methane steam-reforming (zone l4) at a temperature of 880C, an operating pressure of 2 Megapascals, a water / methane ratio of 2.72 (by volume), a volumetric speed 5000h hourly schedule (~ normal empera-cure and pressure). The reactor steam reforming ~ 50 tonnes of ca-talyseur nickel-alumina-calcium-potassium (approximately by weight: 20% NiO, 5% bypass KOH9 60% alumina e ~ lS% lime Ca (OH) 2).

~ a2 ~ 68 ~

There is no purye (absence of the conduike 13). We recycles, after having heated it to 880C, a part of the gas phase from line 22 to the last step and another step towards the second step. A recycling of C02 is carried out via line 4.

The reaction section for alcohol synthesis (zone 20) includes two reactors arranged in series, each of them includes several catalyst beds, with intermediate cooling. The catalyst prepared according to the teaching of French patent N 2,523,957, 10 responds to the formula (in alomes) CuO ~ 8 Co0.3 $ All, l ZnO, 5 aO, l 0.2 there are 6 tonnes of catalyst per reactor; the operating pressure is l3 Megapascals and the iemperature 300C.

H2 / CO molar ratio at the entry of zone l4.
(i.e. in line 5): l, 8l H2 / CO molar ratio at the entry of zone 20 (i.e. in line 9): l, 97 Percentage of gas phase recycled in line 3 by ratio to the total of the gas phase of line 22: 3.25%.

Percentage of C02 recycled in line 3 compared to total C02 from line 22: 3.25%.

Percentage of C02 recycled in line 3 compared to total C02 from line 5 (steam reforming input): 14.42%.

-% of the gaseous phase recycled to the synthesis zone: 96.74% (in volume)--% of C02 lig, ne 4 ~ = 0.5l (molar ratio % of C02 line 6 - ~ of C02 line 4 = 0.47 (molar ratio) % of C02 line 5 3L2 ~ 6 ~ 369 ~

-% of CH4 _ = 0 ~ 48 ~ molar ratio) % of fresh CH4 The following table translates the balance in kilometers from the proceed, the water vapor partly consumed in section 14 has not this indicated.

. ._.
, ~ o = = = = = = = = = = = o .
o Ln O o co Ln C ~ JN ~ ~ coLn ~ Ln O 1 ~ Ln C ~
A ~ rf o ~ _ OO rt OO OO C ~ .l . . . _ _ Ln O OO n OOO
a ~ o ~ ~ I ~ Ln ~ ~ LD
r ~ CO ~ ~ LD LD W LD ~ t OOO
~ DO ~ ~ ~ r ~
_ O LDr ~ O ~ OO dOC) N d a- ^
r- ~
C ~ N CO 1 ~ ~ 9Ln ~, _ ~ o a ~ ~ Ln ~ ~ N r IC ~
O ~ ~) Ln ~ C`J ~ D ~ t OOO
_, oLn Ln Ln ~ ~ ~ t . ...
~ oa ~ o 1` ~ D
OC ~ Ln ~ 1 ~ t Ln OOO ~ D
_ ..

~ ~ ~ o o1 ~
LU ~ OOO
_ ,,, _ _.
Y ~ o cn o 1`
~ ~ Ln ~, Ln ooo L _, ~ L ~ N
Cl:.
- ~
Ln a ~ ~ O Ln co ~
OOD

~ O ~ O
Ln Ln Ln ~ ar ~ - 0O ~ Ln, ~
~ C ~ l ~ ~ ~ ~ OOO ~

~ C ~
_, C ~
O - O
r ~ OO
~ ~) a _ ...
~ e4 ~ i ~

'~ 7 ~ COOO ~ ~) L ~ l c ~ N d- - ~ IIO Lnr ~ O ~, ~ ~
Ng g IC ~ r) ~ t Ln ~ C ~ l O

o Ln Ln r ~ ~

Claims (7)

The realizations of the invention about which an exclusive right of ownership or lien is claimed, are defined as follows: 1. Process for producing at least one higher homologous alcohol of methanol, the process of performing in two separate areas a) a first steam reforming step carried out in the first separate zone between 650 and 950 ° C, supplied with natural gas (mainly fresh methane), in water vapor, in make-up carbon dioxide, and in recycle gas, step to during which water is reacted together and less methane to produce a mixture of carbon and hydrogen according to reaction (1) (written below for methane processing) CH4 + H2O? CO + 3 H2 (1) this reaction (1) being accompanied by equilibrium (2) AT
CO + H2O? CO2 + H2 B

reaction (1) and equilibrium (2) thus giving together a mixture of carbon monoxide, carbon dioxide and hydrogen, that is to say a synthesis gas, b) a second step for the synthesis of at least one alcohol homologous, performed in the second separate zone, and-during which, from the synthesis gas produced in the first step, at least said alcohol is produced, the process being characterized - in that :
the effluent from the area where the second stage takes place is treated so as to collect from a bet a liquid phase essentially containing the alcohol (s) produced and water, and on the other hand a gas phase, essentially free of water and alcohol (s), containing carbon dioxide, most of the gases not converted, and at least one light hydrocarbon whose methane;

- in that :
2 to 15% by volume of said gas phase are recycled to a temperature between 650 and 950 ° C, at the inlet of said first separate zone where the first step, and in that the ratio (in moles) CH4 recycled / fresh CH4 is between 0.2 and 2 so that move the balance (2) in direction (B) in view to obtain in the area where the first step is carried out, a H2 / CO molar ratio of between approximately 2 and 3, the use of this H2 / CO ratio making it possible to work on the entrance to the area where the second takes place step with an optimum H2 / CO molar ratio between 1.6 and 2.4;

- in that :
85 to 98% by volume of said gas phase is recycled, in said second separate area where the second takes place step;

- and in that between the two distinct zones in which are performed first and second steps, we operate, a carbon dioxide sample, that we recyle at least in part in the area where it takes place said first step. 2. Method according to claim 1, characterized in that, in addition, A maximum of 10% by volume of said gaseous phase is eliminated. 3. Method according to claim 1, characterized in that said volume of said gas phase recycled to the first separate zone is included between 2.5% and 10% relative to the total volume of said gas phase, the recycled CH4 / fresh CH4 molar ratio being between 0.3 and 1, and in that said volume of said phase gaseous recycled to the second separate zone is included between 90 and 97.5%. 4. Method according to claim 3, characterized in that the first step is performed between 730 and 890 ° C, the volume of said gaseous phase recycled to the first separate area where the first step is carried out, having been preheated between 730 and 890 ° C. 5. Method according to claim 1, characterized in that the second step is performed between 250 and 350 ° C, at a total pressure between 6 and 20 Megapascals. 6. Method according to claim 3, characterized in that said H2 / CO molar ratio obtained in the first separate area where the first step is performed is between about 2.0 and 3, the H2 / CO ratio molar at the entrance to the second separate area in which takes place the second stage being understood between about 1.6 and 2.4. 7. Method according to claim 6, characterized in that 30 to 60 mole% of the carbon dioxide withdrawn from the first separate area are recycled to this first separate zone, the amount of carbon dioxide thus recycled representing 30 to 60% (in moles) of the gas extra carbon introduced into said first zone distinct, said H2 / CO molar ratio obtained in said first separate area where the first step is performed being between approximately 2.2 and 2.8, the H2 / CO ratio molar at the entrance to the second separate area in which takes place the second stage being between about 1.8 and 2.2.