EP0118805A2 - Motor fuel - Google Patents

Abstract

The invention relates to fuels based on methanol and / or ethanol which contain additions of mixtures of saturated C5 hydrocarbons and mixtures of saturated C4 hydrocarbons.

Description

The invention relates to fuels based on lower alcohols, which contain additions of mixtures of saturated C _S hydrocarbons and mixtures of saturated C ₄ hydrocarbons.

Distilled methanol, so-called pure methanol, has been intensively investigated as an alternative fuel for several years. (Chemical technology, Winnacker-Küchler, Vol. 5, Organic Technology I, 4th edition, 1981, p 517.) Also additives such as. B. higher alcohols and water to methanol for use as fuel are known. (N. Iwai, The combustion of methanol mixed with water, Second Nato-Symposium; Nov. 4-8, 1974, Düsseldorf.)

In an older patent US Pat. No. 23,65,009, combinations of alcohols with 1-5 C atoms with saturated and unsaturated hydrocarbons with 3-5 C atoms are described. Furthermore, 2,404,094 (Conti nation U.S. Patent No. 2,365,009 in Part) is described a fuel by the same applicant in US-PS, either of absolutely pure methanol or commercially available distilled anhydrous methanol is (column 6, lines 8-11) and aliphatic C ₃ -C ₅ contains hydrocarbons. This application also claims a methanol fuel containing 2-20% of a C ₄ or C ₅ aliphatic hydrocarbon. According to column 5, lines 22-27, hydrocarbons in highly pure form are preferred. Furthermore, the hydrocarbons used can also be partially unsaturated or consist of unsaturated hydrocarbons (column 5, lines 28-34). In the examples (Table 1) n-petane, isopentane and a C _{4 cut} which contain up to 20% butenes are indicated as additional components. According to claims 5 and 6 can also Mixture of saturated C _S hydrocarbons are used for the special case of fuel for aircraft engines. US Pat. No. 2,365,009 also describes mixtures of ethanol with aliphatic C ₃ -C _S hydrocarbons, where the aliphatic hydrocarbons can be both saturated and unsaturated, and preferably isopentane (Claim 8 and Table 1) is admixed as the hydrocarbon. Further examples of ethanol / hydrocarbon mixtures are described in DE-OS 2,806,673 and DE-OS 3,211,775. In particular, experts are aware of the efforts to be made in countries where ethanol is abundant, such as. B. in Brazil, use this both pure and in mixtures with hydrocarbons (petrol) as fuel (e.g. Chemical Engineering Process, April 1979, p. 11).

On the other hand, the experts are aware of important fuel-specific disadvantages of the lower alcohols. B. the poor cold start behavior, the driving behavior at low outside temperatures, unsatisfactory miscibility with hydrocarbons, especially at low temperatures and the wide explosion range when mixed with hydrocarbons. The cold start problems are to be found in the low ignitability of the alcohols methanol and ethanol. A measure of the ignitability is the vapor pressure of a fuel, which is measured at 37.7 ° C according to the so-called Reid test.

For comparison, gasoline in the Reid test has a vapor pressure of 700 mbar, methanol on the other hand 350 mbar. At outside temperatures below 15 ° C, the vapor pressures of methanol and ethanol are so low that a gaseous, ignitable mixture is no longer possible. The explosion limits of pure methanol in air are 6.75 to 36.7 vol.%, So that there is an explosive fuel-air mixture in the vehicle tanks between + 15 ° C and + 25 ° C. Additions of 6-9% by weight isopentane reduce the upper explosion limits to -7 ° C in summer and -20 ° C in winter, so that the safety problems are largely eliminated.

Isopentane is also characterized by excellent solubility in both methanol and ethanol, especially at low temperatures. The best setting data for the vapor pressure of pure methanol turned out to be the upper vapor pressure values of the fuel standard DIN 51 600 with 700 mbar for summer and 900 mbar for winter fuel (Reid test).

In view of the problems described and the state of the art as well as the more recent investigations, isopentane (2-methylbutane) was therefore regarded as the optimal admixing component to date.

The fuel from distilled methanol and isopentane, which is known as M-100 fuel, has been tested in several auto fleet tests and has been used in municipal auto fleet tests for years, especially in the Federal Republic of Germany (see H. Müller; 27th DGMK main conference, 6 - October 8, 1982). Although methanol containing iso-pentane to some extent meets expectations for a usable motor fuel, the studies unexpectedly have shown that there are still significant disadvantages to this fuel.

In summer operation in particular, the steam pressure when using pure methanol is too high, despite the reduction of the isopentane content to 5 to 6% by weight, with undesirable outgassing of the isopentane occurring as a result, while in winter operation up to 9% by weight despite the isopentane content at low temperatures Vapor pressure drop occurs, which means that the cold start properties leave something to be desired in winter cold weather below -10 ° C.

It has been shown that a further major disadvantage of the fuels contained in isopentane are the different amounts of isopentane which, depending on the summer or winter quality, have to be added both in the case of methanol and ethanol. This means that corresponding fluctuations in the calorific value of the fuel have to be accepted, which in turn necessitates a corresponding readjustment of the engine.

It was therefore an object of the present invention to find fuels based on methanol and ethanol which, on the whole, have to be changed without the total amount of lower-boiling components added, i.e. with the same calorific value, better cold start behavior, better driving behavior, in particular at relatively high and relatively low Provide outside temperatures, as is required in practical motor vehicle operation, with perfect solubility even in winter operation and lower outgassing in summer operation, and at the same time ensure safe operation without an explosive mixture occurring in the fuel tank.

• a) die Gesamtmenge an C₄- und CS-Kohlenwasserstoffen im Kraftstoff 0,1 bis 15 Gew.-% beträgt und
• b) das Verhältnis von C₄ : C_5' 1 : 500 Gewichtsteile bis 3 : 1 Gewichtsteile beträgt, sowie durch Kraftstoffe auf Ethanolbasis mit gegebenenfalls bis zu 25 Gew.-% Wasser im Kraftstoff, dadurch gekennzeichnet, daß dem Ethanol ein Gemisch aus gesättigten C₄-Kohlenwasserstoffen und ein Gemisch aus gesättigten C_S-Kohlenwasserstoffen zugesetzt wird,
• a) die Gesamtmenge an C₄- und C₅-Kohlenwasserstoffen im Kraftstoff 0,1 bis 15 Gew.-% beträgt und
• b) das Verhältnis von C_{4 :} C₅₁ 1 : 500 Gewichtsteile bis 3 : 1 Gewichtsteile beträgt,

bzw. durch Gemische der erfindungsgemäßen Kraftstoffe auf Methanol- und Ethanolbasis.This object was achieved according to the invention by means of fuels based on methanol, optionally with up to 15% by weight of water in the fuel, characterized in that a mixture of saturated C ₄ hydrocarbons and a mixture of saturated C ₅ hydrocarbons is added to the methanol,

• a) the total amount of C ₄ - and CS hydrocarbons in the fuel is 0.1 to 15 wt .-% and
• b) the ratio of C ₄ : C _{5 '} 1: 500 parts by weight to 3: 1 parts by weight, and by fuels based on ethanol with optionally up to 25 wt .-% water in the fuel, characterized in that the ethanol is a mixture of saturated C ₄ hydrocarbons and a mixture of saturated C _S hydrocarbons is added,
• a) the total amount of C ₄ and C ₅ hydrocarbons in the fuel is 0.1 to 15% by weight and
• b) the ratio of C _4: C _{51 is} 1: 500 parts by weight to 3: 1 parts by weight,

or by mixtures of the fuels according to the invention based on methanol and ethanol.

It has surprisingly been found for the person skilled in the art that mixtures of saturated C ₄ and C ₅ hydrocarbons with pure methanol and with undistilled technical methanol, so-called raw methanol as well as with ethanol or technical water-containing ethanol, all of the above in an excellent, previously unattained manner Meet requirements, as will be explained in detail. It was particularly surprising that the combination of the desired properties, i.e. sufficiently low outgassing at high outside temperatures, in particular also safe explosion limits was achieved despite the addition of a relatively low-boiling C ₄ component, even with a relatively high water content, and therefore also in a very humid climate, there is no phase separation in the fuel mixture. In particular, it was surprising that technical cuts on C ₄ - and C _S hydrocarbons, such as those found in the refinery and primary chemicals production area, e.g. B. ethylene and benzene / toluene (BT) systems, are excellent despite different compositions of individual hydrocarbons, but in contrast to the prior art, only minor additions of unsaturated aliphatic compounds according to the present invention should be present.

The total amount of saturated C ₄ and C ₅ hydrocarbons can be 0.1 to 15% by weight, but a constant total amount of 1 to 12% by weight is preferred for summer and winter qualities. The ratio of C ₄ to C _S hydrocarbons can be 1: 500 to 3: 1. A ratio of C ₄ : C ₅ of 1: 1 to 1:20 is preferred.

Small amounts of non-C ₄ or non-C hydrocarbons, e.g. B. C ₃ -, C ₆ -, C ₇ -hydrocarbons, as they are necessarily contained in technical fractions, can be contained in the fuel, regardless of whether it is non-aromatic or aromatic hydrocarbons.

Suitable fractions of C ₄ and C _S mixtures are given as examples in the following analyzes:

It is possible with the fuel according to the invention, as with numerous known alternative fuels, to admix certain amounts of other customary components, for. B. C ₃ -, C ₄ - and higher alcohols, ethers, such as. B. methyl tert-butyl ether, and other available ethers, also ketones, such as. B. acetone and aromatics such as benzene, toluene and xylenes can be mixed.

The methanol quality previously used for methanol-based fuels is methanol processed by distillation, so-called pure methanol (absolutely pure or refined methanol). It is known to the person skilled in the art that high demands are made with regard to the purity of this methanol quality, a correspondingly high level of operational effort being required, particularly in the distillation area. Since certain technical problems occur in particular with methanol fuel, such as. B. Corrosive and dissolving effects of methanol on motor vehicle parts such as lines, tank linings, engine parts and engine materials and, in addition, high demands are placed on complete combustion with regard to environmental pollution, and further deposits, especially in the carburetor and engine, must be avoided methanol that has not been worked up by distillation, as occurs in low, medium or high-pressure synthesis plants (so-called crude methanol (non-refined methanol »not considered suitable.

As is well known, raw methanol contains up to approx. 5% by weight of water numerous impurities, such as. B. formaldehyde, methyl formate, formic acid, dimethyl sulfide, formaldehyde dimethyl acetal, iron pentane carbonyl and other carboxylic acids and their esters.

It was an unpredictable result of the investigations by the applicant that, in contrast to the prejudice according to the prior art, undistilled methanol is also outstandingly suitable for the fuels according to the invention, in particular with regard to the vehicle parts which come into contact with the fuel and In terms of emissions. It has surprisingly been found that the emissions of CO, NO and hydrocarbons are lower than those when using pure methanol. The following table shows this:

According to the invention, a crude methanol can also be used which is not distilled, but is topped off with removal of non-volatile impurities.

• Fig. 1 beschreibt die Abhängigkeit des Dampfdrucks (absolut) eines erfindungsgemäßen Kraftstoffs von der Temperatur für Sommer- und Winterqualität bei Einsatz von Reinmethanol.
• Fig. 2 beschreibt das Gleiche bei Einsatz von Rohmethanol.
• Fig. 3 gibt die Dampfdrucke für Winter- und Sommerqualität eines erfindungsgemäßen Kraftstoffs auf Ethanolbasis wieder.

1 and 2 serve to explain the excellent properties of the methanol-based fuels according to the invention in more detail.

• Fig. 1 describes the dependence of the vapor pressure (absolute) of a fuel according to the invention on the temperature for summer and winter quality when using pure methanol.
• Fig. 2 describes the same thing when using raw methanol.
• 3 shows the vapor pressures for winter and summer quality of an ethanol-based fuel according to the invention.

In Fig. 1 the vapor pressure is shown in mbar in a temperature range from +30 ° to - 30 ° C.

For comparison, vapor pressure curves with added isopentane are shown. The quantities added are the desired Reid steam pressures (DIN standard) of 700 mbar for summer quality and 900 mbar for winter quality (at approx. 38 ° C), after which 5.5% by weight isopentane for summer quality and 8 for winter quality , 5% by weight of isopentane are to be added. In contrast to this, according to the invention, a total hydrocarbon amount of 7% by weight is used in the case of pure methanol and that of 5% by weight for summer and winter qualities in the case of raw methanol (see Table 2).

Looking at the curves for summer quality, it is found that when isopentane is added in the temperature range from +10 ° C to higher temperatures, an undesirably high steam pressure rise occurs, which as a result leads to poor starting behavior due to outgassing of the isopentane. Outgassing also leads to driving problems in continuous operation.

On the other hand, in the range of temperatures below 0 ° C, the vapor pressure of the winter quality drops undesirably strongly when isopentane is added, so that the required starting behavior at low temperatures is deteriorated. In contrast, the admixture of the C ₄ / C ₅ mixture according to the invention shows, surprisingly, significantly improved properties in both areas with perfect solubility of the components in one another and a required upper explosion point of -13 ° C. for summer quality and -25 ° C. for winter quality.

While in the case of the addition of isopentane, different amounts of hydrocarbons are required, resulting in a summer calorific value of 21.35 MJ / kg and a winter calorific value of 21.98 MJ / kg, so that changed settings on the engine are required when using this fuel. The fuel according to the invention has a uniform calorific value for summer and winter quality of 21.30 MJ / kg (see Table 3).

As FIG. 2 shows, the behavior of the fuel according to the invention is when crude methanol and C ₄ / C ₅ carbons are used Adding hydrogen compared to adding isopentane to raw methanol is also much cheaper.

Another unpredictable result of the present invention (Table 1) relates to the surprising environmental friendliness of the fuels according to the invention, with the use of raw methanol unexpectedly achieving significantly better results than when using pure methanol.

Table 4 shows an example of the data for summer and winter quality of an ethanol fuel according to the invention with a total hydrocarbon content of 8% by weight, the vapor pressure again being 700 mbar for summer quality and 900 mbar for winter quality.

As can be seen from Table 5, summer and winter quality have the same calorific value, so that it is not necessary to readjust the motor. The explosion limits are between -20 ° C and -25 ° C. Furthermore, there is also excellent solubility with a cloud point of -25 ° C.

The vapor pressure curves for winter and summer quality are shown in Fig. 3.

Also in the case of the ethanol / C4 / C5 hydrocarbon fuel according to the invention, a fuel is hereby made available which excellently fulfills all the requirements described at the beginning.

The fuels according to the invention can be additized, as is customary in the case of alcohol-based fuels. Suitable corrosion inhibitors include a. e.g. B. those based on triazole, imidazole or benzoate.

As an ignition control additive such. B. tricresyl phosphate, but also others can be used.

If necessary, emulsifiers such as glycols or their mono- and diether and others can be used.

Other additives are also possible according to the invention.

Undoubtedly, the interaction of the components according to the invention to form the new fuels based on pure, raw methanol and ethanol with previously unattainable properties, which can be produced if necessary from domestic raw materials, namely from coal synthesis gas or bioalcohol, is of the greatest economic importance.

As the extensive years of investigations carried out by the applicant, which were carried out at great financial expense, in particular with isopentane additives, the use of which was to be regarded as particularly suitable on the basis of the prior art, it is an unexpected result of the present invention that the fuels according to the invention meet all the requirements in the Practice put on a fuel to meet in such an excellent way.

Claims (5)

1. Fuels based on methanol with optionally up to 15% by weight of water in the fuel, characterized in that a mixture of saturated C ₄ hydrocarbons and a mixture of saturated C ₅ hydrocarbons is added to the methanol, a) the total amount of C ₄ and C ₅ hydrocarbons in the fuel is 0.1 to 15% by weight and b) the ratio of C _4: C ₅ , 1: 500 parts by weight to 3: 1 parts by weight. 2. Fuels according to claim 1, characterized in that the methanol used is undistilled technical methanol. 3. ethanol-based fuel, optionally with up to 25% by weight of water in the fuel, characterized in that a mixture of saturated C ₄ hydrocarbons and a mixture of saturated C ₅ hydrocarbons is added to the ethanol, a) the total amount of C ₄ and C _S hydrocarbons in the fuel is 0.1 to 15 wt .-% and b) the ratio of C _4: C ₅ , 1: 500 parts by weight to 3: 1 parts by weight. 4. Fuel according to claim 3, characterized in that the ethanol used is technical water-containing ethanol. 5. Fuel according to claims 1-4, characterized in that it consists of mixtures of the fuels based on methanol and ethanol.

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