DE1268613B - Process for the cleavage of olefins - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN 4fflWW> PATENT OFFICE

EDITORIAL

Int. Cl .:

Number:
File number:
Registration date:
Display day:

C07c

German class: 12 ο -19/01

P 12 68 613.4-42
September 18, 1964
May 22, 1968

The invention relates to a process for the cleavage of olefins which have an olefinic in their molecule Double bond containing ß-carbon single bond using a compound which contains an SH residue, as a cleavage accelerator.

It is well known that certain olefins can be thermally decomposed or cracked with the formation of two or more molecular fragments in the form of corresponding hydrocarbons.

The invention is now based on the object, the general efficiency of a method of the specified Kind that works with hydrogen sulfide to improve and thus a higher yield and to achieve greater throughput per unit of time.

Characteristically, the process according to the invention is carried out in such a way that the cleavage is carried out in the presence of at least 0.005 mol, based on the olefin, of a reaction product of 1 mol of hydrogen sulfide and at least one and not more than 2 mol of an amine, hydrazine or ammonia at temperatures between 500 and 850 ⁰ C and a heating time of 1 to 0.005 seconds.

An expedient embodiment of this process consists in the fact that the cleavage is carried out in the presence an inert diluent, such as. B. water vapor.

According to the invention, compared to the closest prior art (British Patent specification 916 133) has a number of advantages. These consist, among other things, in the fact that hydrogen sulfide or mercaptans are generally gaseous substances or substances with high vapor pressure, see above that the same must be kept in gas-tight containers. Because of the toxicity and the evil Odor, special safety precautions must be taken during storage. Amine salts of Hydrogen sulphide, on the other hand, are solid, odorless substances that can be stored in simple containers. Problems of toxicity and odor nuisance practically do not occur with these salts.

Hydrogen sulfide and mercaptans are hardly soluble in water. When the cleavage reaction is carried out, they must therefore enter the device as gases be pumped in. After the pyrolysis, cooling and separating the cleavage products can be found These gaseous fission accelerators can be found either as a gas in the gaseous fission by-products or in the desired pyrolysis products in dissolved form. In the cleavage of 2-methylpentene-2 z. B. methane and isoprene are produced. Ver process for the cleavage of olefins

Applicant:
5

The Goodyear Tire & Rubber Company,

Akron, Ohio (V. St. A.)

Representative:

ίο Dipl.-Ing. W. Meissner and Dipl.-Ing. H. Tischer, Patent Attorneys, 1000 Berlin 33, Herbertstr. 22nd

Claimed priority:

V. St. v. America September 18, 1963
(309 849)

If hydrogen sulfide is used as a cleavage accelerator for the cleavage, the hydrogen sulfide is partly in methane and partly in isoprene after the pyrolysis. The methane is mostly used as fuel, the proportion of H ₂ S contained in the methane is thus lost, since a separation of the gas mixture into hydrogen sulfide and methane would be much too laborious and too expensive. The fraction of the cleavage accelerator contained in the isoprene must be separated off in order to obtain clean isoprene for polymerization purposes. If, on the other hand, an ammonium salt of hydrogen sulfide is used, the process is much simpler. The water-soluble salt can be added to the water vapor used as a diluent. During cleavage, it dissociates into amine, hydrazine or ammonia and hydrogen sulfide, which acts as a cleavage accelerator. When the pyrolysis products are worked up and separated, the ammonium salt recombines from the dissociation products and dissolves in the condensed water vapor. This makes it possible to return the cleavage accelerator to the initial stage of the process. The losses of accelerator are therefore minimal, and the pyrolysis products are not contaminated. In addition to the technical advantages, there are also economic advantages.
The reaction product of hydrogen sulfide and an amine, hydrazine or ammonia, in the form of an ammonium salt, which is used according to the invention, cannot be considered equivalent to

809 550/476

Hydrogen sulfide should be considered as there is no 1 mole of ammonia. The ammonium sulfide is formed

is to be seen whether such an ammonium salt in by reaction of 1 mole of hydrogen sulfide with

Hydrogen sulfide in the same way as sulfur - 2 moles of ammonia. Ammonium polysulphide is commonly

hydrogen and mercaptans the selectivity and Wir- borrowed by adding sulfur to the conversion

shows the degree of efficiency in olefin cleavage. Furthermore, 5 mixture of ammonium sulfide can be produced,

cannot predict whether this will not be caused by dissociation These materials, water-soluble salts of amines,

the amine formed from the ammonium salt, hydrazine or hydrazines or ammonia with hydrogen sulfide,

Ammonia, the accelerating effect of sulfur, can be produced in various ways.

Hydrogen reduced or switched off completely, since z. B. An embodiment that has proven successful

Amines are known to be free radical scavengers and which has ther- io, is the preparation by conversion of 1 mol

mix olefin cleavage according to the radical mechanism hydrogen sulfide and 1 or 2 moles of an amine

runs. with formation of the corresponding amine hydrogen sulfate

The reaction of 1 mole of hydrogen sulphide with fids or sulphides of the amine used in particular.

1 mole of an amine, hydrazine or ammonia leads to “corresponding hydrogen sulfide” or “corresponding

to a hydrogen sulfide of the corresponding amine, 15 chendes sulfide "is simply meant that the amine and

Hydrazine or ammonia. The implementation of one of the hydrogen sulfide simple addition compounds

MoIs hydrogen sulfide with 2 moles of an amine, hy- gen of the amine used in detail with formation

drazins or ammonia leads to a corresponding a certain amine hydrogen sulfide or certain

the sulfide. With the expression »corresponding hy- ten amine sulfide form. An example of this is the

drug sulfide "or the" corresponding sulfide "is simply a phrase of methylamine [CH ₃ TS [H ₂ ]. When 1 mole

meant that the amine, hydrazine or ammonia and this amine with 1 mol of hydrogen sulfide (H ₂ S) to-

the hydrogen sulfide is a simple addition compound, the end product is methylamine hydro-

form dung. gensulfide [(CH ₃ NH ₃ ) SH]. When two moles

The above term "amine" includes alkylamines, this substance treated with one mole of hydrogen sulfide.

Arylamines, arylalkylamines, ammonia and hydra- 25 are set, the end product consists of methyl

interest. Examples of suitable alkylamines are: methylamine suffide [(CH ₃ NH ₃ ) ₂ S]. Another execution

amine, dimethylamine, trimethylamine, ethylamine, di-form of the accelerator of this invention are those

ethylamine, triethylamine, methylethylamine, dimethyl amine polysulfide. You can implement

ethylamine, diethylmethylamine, n-propylamine, di-n- 1 mole of hydrogen sulfide with 2 moles of an amine and

propylamine, tri-n-propylamine, isopropylamine, Me- 30 adding sulfur to the reaction mixture.

thylisopropylamine, methyl-n-propylamine, ethyliso- are provided. Using methylamine as an example, arises

propylamine, ethyl-n-propylamine, n-butylamine, isomethylamine polysulfide _{[(CH 3 NHg) 2} Sa;], where χ min-

butylamine, methyl-n-butylamine, methylisobutylamine, at least equal to 2 and can increase to about 5, which

Ethyl-n-butylamine, ethylisobutylamine, t-butylamine depends on the excess sulfur added. In

and the like. Examples of suitable arylamines are: aniline, 35 in the same way 2 moles of dimethylamine are added

p-Toluidine ^ -Toluidinjm-Toluidin ^^ - Xylidine ^^ - Xy- 1 mol of hydrogen sulfide with the formation of dimethyl

lidine, 2,6 _: xylidine, 3,4-xylidine, 3,5-xylidine; p-ethyl amine sulfide.

aniline, m-ethylaniline, o-ethylaniline, benzylamine, and the like, those used in practicing the invention

Examples of mixed arylalkylamines are: Phenyl amount of cleavage accelerator is not special

methylamine, phenylethylamine, benzylmethylamine, etc. Like. 4 ° decisive, but it should be ensured that

Hydrazine also reacts with hydrogen sulfide enough cleavage accelerator is used

to form a water-soluble salt. To achieve sufficient acceleration so that

Hydrazine can be simple hydrazine or a sub- which makes sense to add. It has been found that

be substituted hydrazine. Examples are hydrazine, usually about 0.005 mol per mol of olefin to be cleaved

methylhydrazine, diethylhydrazinejPhenylhydrazinjMe- 45 are sufficient. There are none for the amount of accelerator

ethylhydrazine, ethylhydrazine and the like upper limit, but from a practical point of view

Ammonia settles in the same way as the amines do not need more than about 0.5 moles per mole of olefin

or hydrazines can be used with hydrogen sulfide to form

of a water-soluble salt, i.e. ammonium with about 0.5 to about 50 mole percent,

hydrogen sulfide or ammonium sulfide. 5 ° The use of conversion products

A particularly interesting embodiment of the at least one and not more than 2 moles of an invention of this application is the use of an amine, hydrazine or ammonia and 1 mole of sulfur process, which consists in preparing a mixture of cleavage hydrogen as a cleavage accelerator, The (1) of at least one olefin, having a number of advantages over others, catalyzes a carbon-carbon 55 olefin cleavage process in its molecule. Some of these advantages are a single bond, which is in the ^ -position to double the ease of process management and the economic bond, and (2) at least one material. The reaction products of 1 or 2 moles of one that (a) ammonium hydrogen sulfide, (b) ammonium amine, hydrazine or ammonia with 1 mole of schwenium sulfide and (c) at least one ammonium hydrogen sulfide are water-soluble. This means that sulfide can be, this material being present in an amount of this cleavage accelerator in the form of an aqueous solution of at least 0.005 mol per mol of olefin, solution can be introduced into the process, and the carbon-carbon single bond, the water is then heated and forms steam which is in the / 5-position to the double bond of the olefin and serves as a cleavage diluent. Because of the cleavage by the mixture suitable temperature water solubility of the reaction products from amiperature conditions of about 500 to about 850 ⁰ C and 65 nen, hydrazines or ammonia and H ₈ S, the residence times of about 1 to about 0.005 seconds can be unnecessary amounts easily measured and without throws. The ammonium hydrogen sulphide arises from difficulties in handling as well as being stored for an unlimited time reaction of about 1 mole of hydrogen sulphide. According to the invention as a cleavage

5 6

accelerator compounds used are cheap, too. Examples of such diluents which results in considerable economic efficiency. are non-fissile heat-resistant olefins and ge-these Compounds can also be recovered paraffinic hydrocarbons that are present in the im because they are not used in the application as a cleavage cleavage process temperatures faster practically not destroyed and attacked in 5. In fact, any diluent can be water-soluble Shape can be regained. Means to be used on the procedure They are not soluble in the hydrocarbon phase, so they have no adverse influence. Of these will that the problem of cleaning is eliminated. This usually involves the use of steam in the process of the invention Accelerators used require further development of the invention for reasons of convenience no expensive building materials for the cleavage furnace (the accelerator is water-soluble) and the host and the quenching device, as it favors less corrosiveness. That in the implementation of the are dative, so that less costly alloys use the ratio of dilution used in the invention can be. In addition, the agent can form an intermediate accelerator to form an olefin within wide limits of this invention no by-products, see about 0.5: 1 and about 15: 1 or more moles of Verdie 15 thinners per mole of olefin are removed again in the purification stage. However, if a would have to and make cleaning more expensive. Ratio greater than about 15: 1 is used,

The cleavage of the olefins according to the procedure tends to become uneconomical,

of the invention can in general in any conventional- It is preferred to use a ratio of diluent

be carried out in the same way as used in the tech-

nik of olefin cleavage is applied. The conditions. The olefins can also be used without a diluent

conditions that can be used according to the invention can be split.

In general, within wide limits, the implementation of the invention is modified by the following will; they depend on a number of factual experiments explained. The results and beguiling away. These conditions depend on the special conditions of the splitting attempts in tables olefins to be cleaved, shown by the desired pro form.

products, the type and amount of the diluent used. carried out at the desired conversion rate, which is derived from a "hairpin" ability of the implementer to the products, the snake consisted of a pipe made of stainless steel the desired conversion efficiency to the steel with an outside diameter of 6.35 mm desired Products and the type and quantity of what was manufactured. This snake reactor was turned into a bed turned away accelerator. made of flowable heat transfer powder

The cleavage temperature can be between, for example, that consists of microspherical silicic acid clay

between about 500 and about 850 ° C, where the earth-cleavage catalyst existed. The heat transfer

Range between about 600 and about 800 ⁰ C preferred.

will. A preferred range is between about 625 35 heating devices and by burning a natural

and about 775 ° C, and the most preferred gas flame is heated in a flowable powder bed. Of the

is between about 650 and about 725 ° C. Temperature gradient from the top to the bottom of the rich

The pressures at which the olefins are split in bed was at no point greater than 5 to 6 ⁰ C, and

The gradient from the flowable bed to the walls of the bed can range from about 1 mm Hg to about 35 atmospheres

are sufficient. Preferably, however, a pressure between 40 tubes was about 5 to 6 ⁰ C. The temperatures within

about 100 mm Hg and about 17.5 atm. A cheaper half of the fluidized bed as well as the temperatures in the

Range is between about one atmosphere and about fission zone were created by conventional thermocouples

7 to 10.5 atm. measured. The procedure consisted in the thermal

The conversion time in which the olefins are split into transmission powder by the electrical resistance, is usually referred to as the dwell time. 45 heaters to about 500 ° C, whereby The residence time is defined as the length of time that 1 mole of the heat transfer powder can flow into the air Gas, regardless of whether it was made of pure gas. Then a natural gas burner became an olefin, Olefins in a mixture with other hydrocarbons switched to the heat transfer powder on the substances, other olefins or diluents to the desired cleavage or working temperature acts, bring for passage through the cleavage zone 50. The cleavage accelerators that are water soluble needed. In the practice of the invention, the water used to generate it may have been added Residence times from about 1 to about 0.001 seconds were used as the dilution vapor. That was held with a preferred range between, including the accelerator, and the olefin see about 0.75 and about 0.01 seconds and the am were at the appropriate speed that most preferred range between 0.5 and 0.05 Se-55 for adjusting the ^ O-hydrocarbon ratio lies. nisses and the desired amount of accelerator and

Those used for carrying out the invention to achieve the desired residence time of the mate olefins are supplied to the cleavage reactor as pure olefins, rialien in the cleavage zone or the cleavage reactor in a mixture with other olefins, in a mixture with is required, pumped. After all variables are different Hydrocarbons or in a mixture with 60 were made, so that the desired Arbeitsbedininerten Diluents or a mixture with compounds prevailed, were the decomposition products, if they were a combination of these substances supplied. When they were liquid, collected in chilled templates and, Use of an inert diluent - if it was gaseous, it appears to be atmospheric and spatial, diluents such as steam, temperature conditions measured. The products were nitrogen, carbon dioxide, methane, ethane or water - the content and yields according to customary analytical substances, be used. Other hydrocarbons, see methods analyzed. Conventional reverse at the temperatures used non-fissile guiding methods were applied to the end, Can also be used as a diluent to determine yield or effectiveness.

For example

In this example, various experiments were carried out in which 2-methylpentene-2 was _{continuously pyrolyzed using methylamine sulfide [(CH 3} NH ₃ ) ₂ S] as a cleavage accelerator. A control experiment was carried out in which no cleavage accelerator was present; This control experiment represents the thermal pyrolysis of 2-methylpentene-2. The diluent used was steam in a ratio of 3 moles of steam per mole of 2-methylpentene-2. The pressure applied

was atmospheric. The conditions, such as temperature, time and amount of accelerator, as well as the yield and Effectiveness are summarized in the following table. In column 1 is the test number, in column 2 the mole percent of accelerator used, in column 3 the residence time in seconds, in column 4 the Temperature in degrees Celsius, in column 5 the mole percent of isoprene obtained per pass and in Column 6 get the reaction effectiveness in percent-

One isoprene listed per mole of pyrolyzed 2-methylpentene-2.

Ver
search
No. Mole percent
accelerator Ver
because
Time Tempe
rature Mole percent
Isoprene Really
sam
speed 1
2
3 6th
6th
O
(Control) 0.15
0.20
0.15 650
640
626 18.4
11.9
7.5 54.1
52.4
44.9

Example II

In this example a series of experiments were carried out in which 2-methylpentene-2 was used in various Temperatures using various amounts of ammonium sulfide as a cleavage accelerator was continuously pyrolyzed. at Control tests were run at each of the various temperatures at which no cleavage accelerator was present; these control attempts represent the thermal pyrolysis of 2-methylpentene-2. As an inert diluent, steam was used in a ratio of 3 moles of steam per mole of olefin is used. The pressure was about atmospheric. The results are summarized in the table below, in which column 1 shows the test number, in column 2 the average cleavage temperature in degrees Celsius, in column 3 the average residence time in seconds, in column 4 the cleavage accelerator and the amount used in mol percent, if used (no accelerator was used in the control experiments), in column 5 the yield in Mol percent of isoprene that was obtained per passage through the cleavage zone, in column 6 the reaction efficiency in percent isoprene listed under Using the recycle technique and represents the number of moles of isoprene that per mole pyrolyzed 2-methylpentene-2 is obtained.

attempt temperature Dwell time Accelerator and amount, Isoprene yield Reaction effect No. ⁰ C in seconds based on 2-MePe-2 per round
in mole percent sameness 1 2 3 4th 5 6th 1 600.5 0.192 thermal (control) 3.65 46.12 2 606.7 0.146 (NH ₄ J ₂ S (2.54) 4.22 48.40 3 625.7 0.154 thermal (control) 7.45 44.88 4th 630.3 0.146 (NHAS (2.54) 8.30 55.32 5 660.5 0.150 thermal (control) 10.70 53.15 6th 661.6 0.145 (NHJ ₂ S (3.71) 19.06 56.71 7th 675.4 0.149 thermal (control) 13.56 51.26 8th 681.9 0.140 (NH ₄ J ₂ S (3.71) 25.94 55.99 9 682.2 0.141 (NHJ ₂ S (6.06) 29.79 58.41 10 707.5 0.188 thermal (control) 25.82 40.90 11 702.3 0.138 (NH ₄ J ₂ S (6.06) 38.14 57.84

As can be seen from the results of the above experiments, there is a remarkable improvement in the yield per pass and the reaction efficiency by using the invention Received catalyst. This is especially true when there are optimal conditions in terms of isoprene yield can be achieved per round. It can thus be seen that the cleavage accelerators of this invention not only have an extremely good acceleration activity, but also have the advantage of sit to be water-soluble and recoverable, so they are in this relationship to the economy contribute to the demerger proceedings.

Similar results can be obtained using the general procedures outlined above Examples and the techniques given in the description can be used.

In the list of olefins below, which is meant to be illustrative, there are olefins which, when they are cleaved or pyrolyzed according to the invention, improved results both in terms of yield as well as the effectiveness compared to the thermal cracking of these olefins. These are olefins so summarized that olefins which form the same main products on decomposition are in one group stand.

Examples of olefins which, upon decomposition, are mainly 2-methylpentadiene-1,3 and 4-methylpentadiene-1,3 are: 2-methylhexene-3, 2-ethylpentene-l, 2,3-dimethylpentene-1, 2,4-dimethylpentene-2, 2-methylheptene-3,4,4-dimethylhexene-2,2 Propylpentene-2,2-methylheptene-3, 4,4-dimethylhexene-2, 2-propylpentene-2, 2-methyl-3-ethylpentene-1,2,6-dimethylheptene-3,2-propylhexene-1 and witches-3.

Examples of olefins which mainly form 3-methylpentadiene-1,3 on decomposition are: 3-methylhexene-3, 3-ethylpentene-2, 3-methyl-2-ethyl-butene-1, 3-methylheptene-3, 3,4-dimethylhexene-2, 3-methyl-2-ethylpentene-1 and 3,6-dimethylhepten-3.

Examples of olefins which mainly form 2,3-dimethylbutadiene-1,3 on decomposition are: 2,3-dimethylpentene-2, 3-methyl-2-ethylbutene-1, 2,3,3-trimethylbutene-1, 2-isopropylpentene-1,2,3,3-trimethylpentene-1 and 2,3-dimethylheptene-2.

Examples of olefins which mainly form 2-ethylbutadiene-1,3 on decomposition are: 2-ethylpentene-2, 3-ethylpentene-2, 3-methyl-2-ethylbutene-l, 3-ethylhexene-2, 3-methyl-2-ethylpentene-1 and 3-methylhexene-3.

Examples of olefins which mainly form 1,3-butadiene on decomposition are: pentene-2, hexene-2,

3-methylpentene-1, cyclohexene, 3-methylbutene-1, 2

3-methylpentene-1, cyclohexene, 3-methylbutene-1, 2-heptene, 3-methylhexene-l, 5-methylhexene-2, 2-octene, 5-methylheptene-2, 3,5-dimethylhexene-1, 3,4,4-trimethylpentene-1, 6-methylheptene-2, nonene-2 and 3-methyloctene-1.

Examples of olefins which mainly form isoprene on decomposition are: 2-methylpentene-2, 3-methylpentene - 2, 2 - ethylbutene -1, 3,3-dimethylbutene -1, 2,3-dimethylbutene-l, 2-methylhexene-2, 3-methylhexene-2, 2-ethylpentene-l, 2,3-dimethylpentene-l, 3,3-dimethylpentene-1, 2-methylheptene-2, 3-methylheptene-2, 2-ethylhexene-l, 3,3-dimethylhexene-l, 2,5-dimethylhexene-2, 3,5-dimethylhexene-2, 4-methyl-2-ethylpentene-1, 2,3,4-trimethylpentene-1, 3,3,4-trimethylpentene-2, 2-Methylocten-2, 3-Methylocten-2, 3,3-Dimethylhepten-1, 2,5-dimethylhepten-2, 2,6-dimethylhepten-2, 5-methyl-2-ethylhexene-1, 3,3,5-trimethylhexene-1 and 2,5,5-trimethylhexene-2.

Examples of olefins which mainly form piperylenes on decomposition are: hexene-3,4-methylpentene-2, Hepten-3, 4-methylhexene-2, octene-3, 4-methylhepten-2, 6-methylheptene-3, 3-ethylhexene-l, 4-methyl-3-ethylpentene-2, 4,5-dimethylheptene-2 and 4,5,5-trimethylhexene-2.

Examples of olefins which form ethylene as the main product on decomposition are: pentene-1 and 2-methylpentene-1.

Examples of olefins which form propylene as the main product on decomposition are: pentene-1, hexene-1, 4-methylpentene-1, heptene-1, 2-methylhexene-1, 4-methylhexene-l, 5-methylhexene-l, 2,4-dimethylpentene-1, 4,4-dimethylpentene-1, octene-1, 4-methylheptene-1,5-methylheptene-1, 6-methylheptene-1 and 4-ethylhexene-1.

Examples of olefins which form isobutylene as the main product on decomposition are: 2-methylpentene-1, 2-methylhexene-l, 5-methylhexene-l, 2,4-dimethylpentene-1 and 4,4-dimethylpentene-1.

Examples of olefins that decompose butene-1 and / or butene-2 as main products are: heptene-1, 4-methylhexene-1, 2-methylheptene-1 and 2,4-dimethylhexene-1.

Examples of olefins which, on decomposition, 2-methylbutene-1 and / or form 3-methylbutene-1 and / or 2-methylbutene-2 as main products are: 5-methylheptene-1, 6-methylheptene-l, 4,4-dimethylhexene-l, 4,5-dimethylhexene-1 and 2,6-dimethylhepten-1.

Examples of olefins which form pentene-1 and / or pentene-2 as main products on decomposition are: 4-methylheptene-l, 4-ethylhexene-l and 2-methyloctene-1.

Examples of olefins which, on decomposition, are 2,3-dimethylbutene-1 and / or 2,3-dimethylbutene-2 as the main ao products are: 4,4,5-trimethylhexene-1 and 2,5,6-trimethylheptene-1 or -2.

These olefins are usually desired to be cleaved by the process of this invention of 2-methylpentene-2, 3-methylpentene-2, 2-ethylbutene-1, To produce 3,3-dimethylbutene-1 and 2,3-dimethylbutene-1 using the isoprene cleavage accelerator according to the invention.

Although various exemplary embodiments have been shown for the purpose of illustration are, it is self-evident for the person skilled in the art that various changes and modifications can be made without departing from the scope of the invention.

Claims (3)

Patent claims: 1. Process for the cleavage of olefins which have an olefinic double bond in their molecule ^ - carbon single bond contained using a compound that contains an SH radical, as a cleavage accelerator, characterized in that the Cleavage in the presence of at least 0.005 mol, based on the olefin, of a reaction product from 1 mole of hydrogen sulfide and at least one and not more than 2 moles of an amine, hydrazine or ammonia at temperatures between 500 and 85O ° C and a heating period from 1 to 0.005 seconds. 2. The method according to claim 1, characterized in that the cleavage in the presence of a inert diluent. 3. The method according to claim 2, characterized in that the inert diluent is used Steam used. Considered publications:
British Patent No. 916 133;
Römpp, Chemie Lexikon, 6th edition, Vol. I,
Column 266. 809 550/476 5.68 © Bundesdruckerei Berlin