EP0014992B1 - Application of polyethers and acetals based on methanol and/or ethanol as fuels for diesel engines and fuels for diesel engines comprising these compounds - Google Patents

Description

The present invention relates to the use of polyethers and acetals based on methanol and / or ethanol as fuels for diesel engines and fuels containing these components for diesel engines.

It is well known that alcohols, including methanol and ethanol, are useful fuels for gasoline engines. However, these alcohols are not suitable for diesel engines, since they only produce cetane numbers of around 8-10, and trouble-free driving is only guaranteed with cetane numbers from around 20. Although the effect of such mixtures for improving the ignition behavior can be increased by adding ignition enhancers or ignition accelerators, these aids are either expensive or have considerable disadvantages. Alkyl and cycloalkyl nitrates, which are mainly used for this purpose, are not toxicologically harmless or technically difficult to manufacture and, since they tend to explode, are not safe to handle. Above all, however, as a result of the water still contained in the alcohols, they can hydrolyze to form the corrosive nitric acid.

Because on the one hand fuels based on mineral oil are becoming increasingly expensive and the sufficient supply of crude oil is known to be at risk, but on the other hand methanol is becoming increasingly competitive, albeit to a limited extent and ethanol can be made available in large quantities to plant origin in numerous countries The invention has the general object to replace the mineral oil diesel fuels with economical and environmentally friendly fuels based on these alcohols.

From DE-OS 2 753 027 it is known to use mixtures of predominant amounts of methanol and polyalkylene glycol ethers as fuels for diesel engines. However, methanol is essentially only available cheaply where natural gas or coal is available, so this proposal does not satisfactorily solve the problem of greater independence from natural gas or oil producing countries. It is also a disadvantage of these blends that they are immiscible with conventional diesel fuels.

wobei Rund R' C₁-C₄-Kohlenwasserstoffreste und R" Wasserstoff oder einen C₁-C₄-Kohlenwasserstoffrest bedeuten, einerseits und einen Äther

wobei n für 0 bis 4 steht, andererseits als Hilfsmittel für den Kaltstart von Dieselmotoren bekannt. Die Eignung eines Stoffes oder Stoffgemisches als Kaltstart-Hilfsmittel für Dieselmotoren, die im übrigen mit herkömmlichem mineralischem Dieselöl betrieben werden, läßt jedoch keine Rückschlüsse auf die Eignung für den Dauerbetrieb zu. Beispielsweise ist ein gebräuchlicher Kaltstart-Hilfsstoff, nämlich Diäthyläther, für den Dauerbetrieb offensichtlich nicht brauchbar, und außerdem werden die Kaltstarter getrennt vom Dieselöl in die Ansaugluft des Motors eingesprüht. Die Lehre der US-PS vermag daher keine Anregungen hinsichtlich der Eignung von Stoffen als Kraftstoffe für Dieselmotoren für den Dauerbetrieb zu geben.Mixtures of an acetal are also known from US Pat. No. 2,842,432

where R _{1 is} C ₁ -C ₄ -hydrocarbon radicals and R "is hydrogen or a C ₁ -C ₄ -hydrocarbon radical, on the one hand and an ether

where n stands for 0 to 4, on the other hand known as an aid for cold starting of diesel engines. However, the suitability of a substance or mixture of substances as a cold start aid for diesel engines, which are otherwise operated with conventional mineral diesel oil, does not allow any conclusions to be drawn about the suitability for continuous operation. For example, a common cold start aid, namely diethyl ether, is obviously not suitable for continuous operation, and the cold starters are also sprayed into the intake air of the engine separately from the diesel oil. The teaching of the US PS is therefore unable to provide any suggestions regarding the suitability of substances as fuels for diesel engines for continuous operation.

Accordingly, it was the object of the invention to replace conventional diesel fuels wholly or in part with fuels based on methanol and especially ethanol.

• a) Polyäther der allgemeinen Formel
  
  in der A eine Äthylen- oder 1,2-Propylengruppe bedeutet, R¹ für einen C_l-C₈-Alkylrest und R² für Wasserstoff oder einen C_i-C₄-Alkylrest steht und n einen Wert von 1-5 hat, und/oder
• b) Acetale der allgemeinen Formel II
  
  in der R³ Wasserstoff oder eine C_l-C₁₂-Alkylgruppe und R⁴ für die Methylgruppe oder die Äthylgruppe steht und m einen Wert von 0-5 hat,

allein oder in Mischung mit

• c) bis zu 45 Vol.-% Äthanol (III) und/oder Methanol (IV) und/oder
• d) bis zu 30 Vol.-% Wasser (V) und/oder
• e) bis zu 85 Vol.-% von Dieselkraftstoffen auf Mineralöfbasis (VI)

hervorragend als Kraftstoffe für Dieselmotren eignen.It has been found that

• a) polyether of the general formula
  
  in which A represents an ethylene or 1,2-propylene group, R ^{1 represents} a C ₁ -C ₈ -alkyl radical and R ^{2 represents} hydrogen or a C _i -C ₄ -alkyl radical and n has a value of 1-5, and or
• b) acetals of the general formula II
  
  in which R ^{3 represents} hydrogen or a C ₁ -C ₁₂ alkyl group and R ^{4 represents} the methyl group or the ethyl group and m has a value of 0-5,

alone or mixed with

• c) up to 45 vol .-% ethanol (III) and / or methanol (IV) and / or
• d) up to 30 vol .-% water (V) and / or
• e) up to 85 vol.% of diesel fuels based on mineral oils (VI)

excellent as fuels for diesel engines.

• i) 15-90 Vol.-% eines Polyäthers (I) oder Mischungen solcher Polyäther und/oder 15-90 Vol.-% eines Acetals (11) oder Mischungen solcher Acetale,
• ii) bis zu 45 Vol.-% Äthanol (III) und/oder Methanol (IV),
• iii) bis zu 30 Vol.-% Wasser (V) und
• iv) bis zu 85 Vol.-% von Dieselkraftstoffen auf Mineralölbasis (VI).

Well-suited fuels of this type are characterized by the following composition:

• i) 15-90% by volume of a polyether (I) or mixtures of such polyethers and / or 15-90% by volume of an acetal (11) or mixtures of such acetals,
• ii) up to 45% by volume of ethanol (III) and / or methanol (IV),
• iii) up to 30 vol .-% water (V) and
• iv) up to 85% by volume of mineral oil-based diesel fuels (VI).

These mixtures exclude those from the protection request who are known as such from US Pat. No. 2,844,232, that is to say mixtures which contain a dialkoxyalkane (II with m = 0) and additionally a polyethylene glycol ether (1), but neither ethanol (III ), Methanol (IV) or water (V).

The rule here is that the quality of the polyether (I) and the acetal (11) defined by the cetane number increases with increasing degree of polyetherification, which means that the proportion of components (III) to (V) can be increased accordingly.

The degree of polyetherification n is understood to mean the average degree of polyetherification.

Since the polyethers (I) and the acetals (11) become more expensive as the degree of etherification increases, but on the other hand can be blended with the larger quantities of the much cheaper alcohols (III) and (IV), the economic mix is based on the price of these Components. The monomethyl and monoethyl ether of ethylene glycol and propylene glycol as compounds (I) are less suitable as fuels for diesel engines on their own, but as components in amounts of around 85% by volume in mixtures with the higher molecular weight compounds (I) and (II).

Among the polyethers (I), preference is given to those in which A represents ethylene units, since most of these can be prepared from ethanol as a raw material by dehydrating ethanol to form ethylene, which is then oxidatively converted into ethylene oxide, which is then added to methanol in a polyaddition reaction .

Although the quality of the acetals (II) increases with increasing degree of etherification m and increasing C content of the radicals R ³ and R ⁴ , formaldehyde and acetaldehyde dimethyl acetal is preferred for economic reasons, since these acetals can be obtained entirely from methanol and ethanol. In a weakened form, this also filters out those aldehydes which are obtainable via the aldol condensation of acetaldehyde, such as crotonaldehyde. The relatively inexpensive ethyl hexanal should also be emphasized here. In general, the alkyl radicals can be branched or unbranched, but preference is given to the compounds (11) with straight-chain radicals.

The acetals (II) offer the advantage that they can be mixed with diesel fuel based on mineral oil in any ratio and used in the form of these mixtures. This also applies to polyether (I) in which R ² ≠ H. The mixing ratios for the other polyethers (R ² = H) are easy to determine.

The polyethers (I) and the acetals (11) are known or are easily accessible by known, large-scale processes.

The engine power is surprisingly not reduced by the relatively high water content. Although the absolute energy content in water-containing mixtures is lower in accordance with their water content, the efficiency of the motors is increased by the water because the heat losses are reduced.

The fuels according to the invention for diesel engines, to which the auxiliaries customary for diesel fuels based on mineral oil can be added, but as a rule need not be added, are not only excellent for their purpose in terms of engine performance and driving behavior, but are also particularly environmentally friendly, since they burn practically completely to carbon dioxide and water and because the exhaust gases therefore contain very little carbon monoxide, hydrocarbons, nitrous gases and soot contain. An additional advantage of the fuels according to the invention for diesel engines is that they become more stable to cold than the conventional fuels with increasing content of the polyethers (I) and the acetals (11). Particularly noteworthy here are the polyethers with R ² = H, which in their pure form remain operational down to (-50 ° C).

The energy content of the fuels according to the invention for diesel engines is 60-90% of the conventional petroleum-based fuels per unit weight. As a result, some technical changes, such as the enlargement of the pump elements in the fuel injection pump, are caused on the diesel engines of conventional design. These changes can easily be taken into account in the manufacture of the motors and can be retrofitted to conventional motors. Otherwise there is no difference to conventional engines, neither in terms of design nor in terms of driving behavior.

Examples

Using a test engine with a compression ratio of ₆ = 22, the cetane number (CZ) of various fuels according to the invention for diesel engines was measured under practical conditions, ie in each case with a full air filling. The reference fuels were x-methynaphthalene (CZ = 0) and cetane (hexadecane) (CZ = 100). The results are shown in the following tables.

Claims (2)

1. Use of

a) polyethers of the general formula I

where A is an ethylene or 1,2-propylene group, R¹ is C₁-C₈-alkyl and R² is hydrogen or C₁― C₄-alkyl, and n is from 1 to 5, and/or

b) acetals of the general formula II

where R³ is hydrogen or C₁-C₁₂-alkyl and R⁴ is methyl or ethyl, and m is from 0 to 5,

used individually or mixed with

c) up to 45% by volume of ethanol (III) and/or methanol (IV) and/or

d) up to 30% by volume of water (V) and/or

e) up to 85% by volume of petroleum-based diesel fuels (VI)

as fuels for diesel engines.

2. Fuels for diesel engines, having the following composition:

i) 15-90% by volume of a polyether (I) or of a mixture of such polyethers and/or 15-90% by volume of an acetal (II) or a mixture of such acetals,

ii) up to 45% by volume of ethanol (III) and/or methanol (IV),

iii) up to 30% by volume of water (V) and

iv) up to 85% by volume of petroleum-based diesel fuels (VI),

excluding mixtures containing a dialkoxyalkane (II where m is 0) as well as a polyethylene glycol ether (I), but not ethanol (III), methanol (IV) or water (V).