CH651852A5 - PROCEDURE FOR THE PRODUCTION OF METHANOL MIXTURES AND SUPERIOR ALCOHOLS AND MIXTURES OBTAINED BY THAT PROCEDURE. - Google Patents

Description

The present invention relates to a process for the production of methanol and higher alcohols and the mixtures obtained with said process. The mixtures according to the present invention in particular are useful as a substitute for gasoline and can also be mixed with it in various percentages for use as fuels of internal combustion engines. Many processes are known for the production of methanol in a mixture with higher alcohols. However, they suffer from the drawback of having to operate at rather high pressures, generally between 17,000 and 35,000 KPa and this constituted a considerable disadvantage both for the construction costs of the plant and obviously for the operating costs. On the other hand, the need to work at high pressure is well known from literature, for example Natta in "Catalysis", Vol. V. Reinhold Publishing Corp. New York, 1957, on page 136, clearly says that because of the considerable contraction of volume that occurs in correspondence with the production of higher alcohols it is necessary to operate the synthesis at high pressure; obviously, the more higher alcohols are desired, the more pressure increases should favor their formation. 50 Natta's statements are confirmed by "Table VII of the report presented by PG LAUX to the International Symposium on alcohol fuel tecnology, Wolfsburg, 21-23 / 11/1977 entitled" The catalytic production and mechanism of formation of METHYL FUEL " where the quantity of isobutanol increases from 1.86% at 390 ° C and 179 bar from 6.14% at 390 ° C and 308 bar from 55. The prior art therefore clearly shows that the production of mixtures of methanol and higher alcohols is possible only by operating at high pressure as thermodynamics teaches. • 60

It has now been surprisingly found that the production of mixtures of methanol and higher alcohols is possible even at reduced pressure and that said mixtures have a considerably higher content of higher alcohols than that obtained at the high pressures used in the prior art. The mixtures obtained 65 perform better than the known ones the task of solubilizing the water due to their higher content of higher alcohols and perform the same function as those known when added to petrol, their production cost being on the other hand considerably lower than due to the reduced pressure conditions under which they are obtained. The reason why methanol is not used alone in a mixture with petrol and therefore mixtures of methanol and higher alcohols are produced and these are added to petrol is that a certain amount of water is always present in petrol, deriving from mostly from water used for washing pipes in refineries and from humidity in the air.

When it is alone, methanol mixes with the water present in petrol and mixes with petrol, thus forming two layers, one of petrol and the other of methanol and water, in the car tank. In these conditions the engines come into operation with great difficulty when the methanol and water layer is fed instead of petrol. It is known that the presence of higher alcohols allows the methanol to be solubilized in the presence of water in the gasolines, thus forming perfectly homogeneous mixtures. The mixtures according to the invention have a higher alcohol content of between 25 and 65% by weight and allow the solubilization of methanol even when the concentration of water in the gasoline is very high. With the prior art mixtures, generally at 10% by weight of higher alcohols, it is possible to tolerate, at -18 ° C, 1000 parts per million by weight of water at an alcohol / hydrocarbon ratio of 20/80.

With the same ratio of 20/80 and at -18 ° C the mixtures according to the invention allow to tolerate from a minimum of 2500 to more than 5000 parts per million of water. An object of the present invention is a process for the production of mixtures of methanol and higher alcohols containing from 35 to 75% by weight of methanol on the anhydrous basis consisting of feeding a reaction zone equipped with a catalyst based on zinc, chromium and at least an alkaline metal with H2, CO and optionally CO2 and inert materials with an H2 / CO ratio between 0.1 and 20, preferably between 0.5 and 5, at a temperature maintained in the range between 300 ° C and 500 ° C, preferably between 350 ° C and 450 ° C and a pressure between 2000 and 16000 KPa, preferably between 5000 and 13000 KPa. The catalyst used in accordance with the invention consists, as said, of chromium and zinc and at least one alkaline metal and the weight ratio between Zn and Cr taken as oxides, is preferably between 5/1 and 1/1, the alkaline metal being preferably potassium and the quantity of alkaline metals, taken as oxides, is from 0.5 to 5% by weight of the total of the elements taken as oxides. The preparation of the catalyst can be carried out in different ways.

As an example we mention the precipitation with NH3 from the solutions of chromium and zinc nitrates or the attack with chromic acid of aqueous suspensions of zinc oxide. The catalyst can be dried in a stove or by atomization and subjected to subsequent calcination. The catalyst can be extruded, pelleted or in granules of different size and shape according to the characteristics of the reactor in which it is to be used, by suitably adjusting the porosity.

Alkali metals are introduced by impregnation of the Zn-Cr catalyst already formed with aqueous solutions of hydroxide, carbonate, acetate, formates or other organic salt. Alternatively, the catalyst can be prepared by reacting the zinc oxide with mixtures of ammonium bicromates and alkaline metals in such a ratio that the final catalyst contains the desired amount of alkaline oxides.

Particular attention must be paid to the reduction of the catalyst which is carried out before or after the introduction of the alkali metals by diluting the reducing gas which is preferably hydrogen, with an inert gas, such as nitrogen for example, and controlling the temperature in the catalytic bed so that it does not exceed 350 ° C.

A second object of the present invention consists of the mixtures of methanol and higher alcohols. Mixtures in ac

3

651 852

According to the invention, they have a methanol content ranging from 35 to 75% by weight, an ethanol content from 2 to 5% by weight, a content of n. propanol from 3 to 12% by weight, an isobutanol content from 10 to 30% by weight, the rest consisting of other higher alcohols with 5 or more carbon atoms, having a percentage from 5 to 25% by weight.

All the above percentages are calculated on an anhydrous basis, that is, by neglecting the water present, produced in reaction, as a by-product. It should be noted, with regard to the above concentration ranges, that the lower concentration values of the higher alcohols and correspondingly the higher concentration value of the methanol occur at the higher pressure of the pressure range used in accordance with the invention . Consequently, the higher concentration values of the higher alcohols and the lower concentration value of the methanol are obtained at the lowest pressures.

Here are some examples whose purpose is to better illustrate the invention, since it is understood that the same is not to be considered by them or limited to them.

Example 1

242.5 g of chromic anhydride are dissolved in distilled water so as to obtain a 30% by weight solution. Separately, an aqueous suspension of 736 g of zinc oxide is prepared in two liters of distilled water which is kept under vigorous stirring. The chromic anhydride solution is added under stirring to the zinc oxide suspension and is left under stirring for several hours in order to obtain complete homogenization.

The basic zinc chromate is filtered, dried by atomization and the dry powder is mixed with a binder consisting of zinc stearate and pasted. The tablets, with a diameter of 6 mm, are impregnated with an aqueous solution of potassium acetate in such an amount that on the finished and reduced catalyst the weight content of K2O is around 2.5%. DoTABELLA 1

Pressure KPa

5000

7000

9000.

13000

Temperature ° C

409-415

410-422

400-415

390-410

GHSV h ~ '

5550

11700

14400

14400

Methanol weight%

43.0

46.3

57.2

68.8

Ethanol »

3.7

3.9

3.4

2.9

n Propanol »

9.1

9.7

8.2

6.5

the Butanol »

23.2

22.4

17.4

12.1

- other higher alcohols weight%

21.0

17.7

13.8

9.7

with 5 or more carbon atoms

GHSV = hourly space velocity of the gas

• - the term higher alcohols in the example and in the text also means small quantities of other oxygenated compounds which, for the purposes of uses as fuel for internal combustion engines, are bought as alcohols.

60 The total content of C2 + alcohols present in the liquid next to methanol is equal to 57% at 5,000 KPa, 53.7% at 7,000 KPa, 42.8% at 9,000 KPa and 31.2% at 13,000 KPa.

After having dried to eliminate the impregnation water, the catalyst is ready for the reduction which is carried out in the same apparatus in which the synthesis reaction is carried out.

100 cm3 of tablets are introduced into a 5-tube stainless steel reactor immersed in a fluoridated sand bath and heated up to about 300 ° C in a nitrogen stream containing about 2% hydrogen, making sure that during the reduction the temperature does not exceed 350 ° C. The reduction takes a relatively long time, about 24 hours. Once reduced, the catalyst no longer needs to be exposed to air. Chemical analysis of a sample of this reduced catalyst provides the following results: Zn O = 77.3%; Q2O3 = 19.0%; K2O = 2.4%; loss on calcination at 400 ° C = 1.3%; (percentages are by weight). The surface area is 125 m2 / g. 15 The catalyst thus obtained is used for the preparation of a mixture of methanol and higher alcohols as illustrated in the following example:

Example 2

20 In the reactor described in Example 1 containing 100 cm3 of the catalyst prepared as indicated in this example, a synthesis gas having the following molar composition is fed:

25

H2 = 69 ', 0%

CO = 30.5%

co2 = 0.1%

CH4 = 0.1%

N2 = 0.3%

30 The temperature of the catalytic bed is maintained between 390 and 420 ° C. 4 tests are carried out at 5,000, 7,000, 9,000 and 13,000 KPa. In each of the tests, the liquid reaction product is separated from the gases by cooling and condensation. The analyzes of the average samples collected after 24 hours 35 of test were performed by gas chromatography on the anhydrous product and provided the results reported in table 1.

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Claims (6)

651 852 1. Process for the production of mixtures of methanol and higher alcohols, usable, in particular, as a substitute for gasoline or mixed with it, for use as fuel in internal combustion engines, comprising making H2 and CO react with a molar H2 / CO ratio between 0.1 and 20, and at a temperature from 300 to 500 ° C, characterized in that said mixtures are obtained at a pressure chosen between 2000 and 16000 KPa, and with a catalyst based on chromium, zinc, and at least one metal alkaline. 10 2. Process according to claim 1 wherein the mixtures have a methanol content of between 35 and 75% by weight on the anhydrous basis. 2 3. Process according to claim 1 O 2 wherein the weight ratio between zinc and chromium, taken as oxides, is between 15/1 and 1/1. 4. Process according to claim 1 or 2 wherein the alkali metals taken as oxides are in an amount equal to 0.5-5% by weight of the total of the elements taken as oxides. Method according to one of claims 1 to 4 where the alkali metal is potassium. 6. Mixtures of methanol and higher alcohols prepared according to one of claims 1 to 5 corresponding to the following compositions on the anhydrous basis: methanol from 35 to 75% by weight; ethanol from 2 to 5% by weight; n-propanol from 3 to 12% by weight; 25 isobutanol from 10 to 30% by weight; higher alcohols with 5 or more carbon atoms from 5 to 25% by weight.