NEW OXYGENATED COMPONENTS FOR FUELS AND PREPARATION THEREOF

The present invention relates to a new process for preparing glycerin ethers which can be used as oxygenated components for fuels, in particular mono, di and tri sec- butyl, 2-sec-pentyl and 3-ser-pentyl ethers. Thccc ethers are new and are a further object of the present invention, as also their mixtures and the compositions of fuel or components of fuel containing them.

The trend and forecasts of the European market in general and the Italian market in particular, relating to products for motor vehicles, are characterized by a constant increase in the request for gasoil and a reduction in the consumption of gasoline. In order to satisfy the market demands, various alternative fuel sources have been taken into consideration, among which those used in the production of biodiesel. Biodiesel normally consists of esters of fatty acids and is commonly obtained by transesterification of triglycerides

of a vegetable origin with methanol. Glycerin is obtained as by-product (about 10% by weight) whose use is an important aspect for improving the production process of biodiesel. One of the possible uses of glycerin is the formation of glycerin ethers (mainly di-ter-butyl ethers) , by means of an etherification reaction with olefins to give the corresponding ethers. The olefin mainly used and object of numerous patents is isobutene. The reaction with isobutene leads to the formation of terbutyl ethers of glycerin, of which the most interesting is di-ter-butyl ether.

The patent US 5,578,090 describes a biofuel consisting of a mixture of several components, among which fatty acid esters and glycerin ethers. The invention comprises the esterification of fatty acids, mainly from animal fat, with an alcohol and the etherification of the released glycerin with an olefin. Olefins which can be used are all linear, branched and cyclic olefins having from 2 to 10 carbon atoms, among which ethylene, propylene and isobutene are preferably used due to their low cost, or highly substituted olefins which form more stable carbocationic intermediates . The mixture obtained is considered as being not fully suitable for being mixed with a traditional diesel and is

therefore subjected to a subsequent hydrocracking or thermal cracking phase to lower its viscosity in order to make it compatible with traditional diesels. Even if not described, under these conditions, the glycerin ethers are obviously degraded.

US patent 5,476,971 describes the synthesis of diterbutyl ether of glycerin starting from glycerin and isobutene in the presence of a sulfonic acid as catalyst. The continuous process for the production of ether starting from glycerin coming from the transesterification process of the corresponding triglycerides, is also described.

Patent application WO 2005/093015 describes, among other things, the synthesis of terbutyl ethers of glycerin by reaction with isobutene in the presence of an ion exchange resin Amberlyst type as heterogeneous acid catalyst. In US 6,015,440 terbutyl ethers of glycerin are prepared by reaction with isobutene in a continuous process in the presence of anionic resins of the type Amberlyst 15 used as heterogeneous catalyst.

EP 0649 829 describes the synthesis of glycerin ethers with branched olefins in the presence of heterogeneous acid catalysts such as Y zeolite and β zeolite . WO 94/01389 describes the preparation of ethers of

various polyhydroxyl compounds, among which glycerin, in the presence of acid catalysts. All olefins having the general formula R1-C(=CH ₂ ) -R2 are claimed, wherein Rl can be an H or an alkyl group and R2 an alkyl group, but only isobutene is cited as an example.

In EP 323135 olefins are transformed into iso- olefins by means of a catalytic process. As these are more reactive than the starting olefins, they are used in a subsequent passage to form branched ethers by reaction with alcohols.

From what is specified above, it seems evident that the disclosure relating i ^~ o the synthesis of glycerin ethers to be used in fuels is oriented towards the use of branched olefins capable of supplying glycerin ethers with the highest possible branchings. Linear olefins, on the other hand, are not taken into consideration, both due to their lower reactivity with respect to branched olefins and to the fact that the resulting products are ethers with fewer branchings . The reaction products with these linear olefins, on the other hand, are more appropriate as components for gasoil, in particular for use in motor vehicles, because the cetane number of a compound is generally inversely proportional to the branching degree of the molecule. In addition, these compounds can be used as additives for

gasoline. The necessity is therefore felt for finding a process which facilitates the etherification reaction of glycerin with suitable linear olefins, leading to sufficiently high conversions from an industrial point of view.

The applicant has now found that by using strong acid catalysts and suitable reaction conditions, the etherification process of glycerin with particular linear olefins can be performed obtaining considerably high conversions.

A first object of the present invention therefore relates to a process for preparing glycerin ethers by the reaction of glycerin with a linear olefin selected from 1-butene, 2-butene, 1-pentene, 2-pentene and mixtures thereof, in the presence of a strong acid catalyst, at a temperature selected from 80 to 18O ⁰ C. The olefins can be used individually or mixed with each other. Refinery streams can be well used, for example, containing mixtures of 1- and 2- isomers of the same olefin or mixtures of isomers of both types of olefin, butene and pentene . A stream which can be conveniently used contains butenes, of which 1-butene as main component, deriving for example from synthesis plants of MTBE.

The resulting products are mixtures of mono, di and tri-substituted glycerin ethers, of which the first in a

quantity preferably not higher than 20%. A mono- substituted ether refers to the product resulting from the etherification of the hydroxyl in position 1 of glycerin, having the formula RO-CH ₂ -CHOH-CH ₂ OH, wherein R is selected from sec-butyl, 2-sec-pentyl and 3-sec- pentyl . Di-substituted ether refers to the etherification product of the hydroxyls in position 1 and 3 of glycerin, having the formula RO-CH ₂ -CHOH-CH ₂ OR, wherein R is selected from sec-butyl, 2-sec-pentyl and 3-sec-pentyl, whereas the tri-substituted product is that in which all the hydroxyls of glycerin have been etherified, having the formula RO-CH ₂ -CHDP-CH ₂ OR, wherein R is selected from sec-butyl, 2-sec-pentyl and 3-sec-pentyl.

In particular, in the case of 1-butene and/or 2- butene, the main component is 1, 3-di-sec-butyl ether of glycerin (hereafter indicated as DSBE) . When 1-pentene is used, the main products are 1-mono-2-sec-pentyl ether and 1, 3-di-2-sec-pentyl ether of glycerin. When 2-pentene is used, the main products are l-mono-3-sec-pentyl ether and 1, 3 -di-3-sec-pentyl ether of glycerin. The mono-, di- and tri-substituted isomers can be easily isolated and separated from each other by distillation.

These reaction products, object of the invention, individually or mixed with each other, can be used as components for fuel, in particular gasoil, especially for

use in motor vehicles, and as additives for gasoline. The addition to gasoil or gasoline of ethers obtained by the reaction of glycerin with linear olefins having four or five carbon atoms allows, among other things, a significant reduction in particulate emissions.

For this purpose, 1, 3-di-sec-butyl ether of glycerin and the mixture of 1-mono- and 1, 3-di-2-sec-pentyl ether of glycerin are preferably used.

All the ethers obtained with the process of the invention are new and are a further object of the present invention.

The mixtures consisting of at ltJd.sc two ot these ethers are also new, as also the mixtures of fuel and fuel components containing one or more of these ethers. The ether or ethers are added to the fuel in a total quantity that can vary from 0.1 to 30% by weight with respect to the total weight of the fuel composition. From 3 to 30% by weight of ether or ethers is preferably used in diesel compositions, and from 0.1 to 3% by weight of ether or ethers in gasolines.

The process, object of the present invention, is catalyzed by a strong acid catalyst. Strong acid catalysts suitable for the purpose are preferably selected from strong soluble organic acids, very strong soluble organic acids, strong solid heterogeneous acids

and very strong solid heterogeneous acids. As a strong soluble organic, and therefore homogeneous, catalyst, it is possible to use, for example, methanesulfonic acid or toluenesulfonic acid. Very strong soluble, and therefore homogeneous, acids are preferably used, such as, for example, trifluoromethanesulfonic acid, which allows higher yields to be obtained.

Strong solid acids which can be well used as heterogeneous catalysts can be polymers with acid groups and resins with acid groups. Very strong solid acids are, for example, polymeric materials with very strong acid groups .

Examples of polymers or resins with acid groups are

Amberlyst 15, Amberlyst 35 and Amberlyst 39. These resins are commercial products which can be supplied for example by Rohm and Haas Co., USA.

A polymeric material with very strong acid groups which can be conveniently used is Nafion SAC-13, a polymeric resin functionalized with trifluoromethanesulfonic groups. Nafion SAC-13 is a product of Engelhart, Italy or commercialized by Sigma-

Aldrich.

It is preferable to operate at an acid concentration ranging from 0.02 milliequivalents/litre (meq/1) to 1.0 meq/l.

The reagents can be introduced into the reactor in any sequence. The reaction can be carried out either in a closed reactor under continuous stirring (CSTR, Continuous Stirred Tank Reactor) or in a reactor fed in continuous.

It is preferable to operate at a temperature ranging from 100 to 16O ⁰ C. The pressure preferably ranges from 8 to 35 bar. The glycerin and olefin are reacted in a relative molar ratio which varies from 1:2 to 1:8. At the end of the reaction, according to one procedure, the excess non-reacted olefin is evaporated, water and a non-miscible organic solvent, such eta heptane or diethyl ether, for example, are added. The organic phase is separated, anhydrified and evaporated under reduced pressure. The liquid residue is distilled to separate the mono-ether from the di-ether and from the tri-ether . Example 1 Reaction of glycerin with 1-butene (linear olefin) and a strong homogeneous acid catalyst

55 g (0.98 moles) of 1-butene and 1.0 g of methanesulfonic acid (0.01 moles) were added to 29 g

(0.32 moles) of glycerin. After 6 hours at 140 ⁰ C and a pressure of 28 bar, under stirring (1,200 rpm) , the excess unreacted 1-butene was evaporated. 10.0 g of

product were obtained, containing sec-butyl ethers of glycerin in the percentage ratio in moles indicated in the following Table:

The final conversion was 10% in moles with respect to the starting glycerin. The products (butene) ₄ are the oligomerization compounds of butene. Example 2

Reaction of glycerin with 1-butene (linear olefin) and a very strong homogeneous acid catalyst

63.0 g (1.12 moles) of 1-butene and 1.5 g of trifluoromethanesulfonic acid (0.01 moles) were added to 30.3 g (0.33 moles) of glycerin. After 6 hours at 14O ⁰ C and a pressure of 30 bar, under stirring (1,200 rpm) , the excess unreacted 1-butene was evaporated. 33.0 g of product were obtained, containing sec-butyl ethers of glycerin in the percentage ratio in moles indicated in the following Table:

The final conversion was 43% in moles with respect

to the starting glycerin. The products (butene) ₄ are the oligomerization compounds of butene.

Example 3

Reaction of glycerin with 1-butene (linear olefin) and a very strong heterogeneous acid catalyst

55 g (0.98 moles) of 1-butene and 49.0 g of very strong anionic exchange silica Nafion (acid equivalents 0.007 moles), functionalized with trifluorosulfonic groups, were added to 29.3 g (0.31 moles) of glycerin. After 6 hours at 140 ⁰ C and a pressure of 30 bar, under stirring (1,000 rpm) , the excess unreacted 1-butene was evaporated. 27 g of product were obtained, containing sec-butyl ethers of glycerin in the percentage ratio in moles indicated in the following Table:

The final conversion was 36% in moles with respect to the starting glycerin. As can be observed, the main reaction product is 1, 3-sec-butyl diether. The oligomerization products are much lower than those obtained in Example 3 using trifluoromethanesulfonic acid, which can be considered the acid equivalent in homogeneous phase of Nafion. Example 4

Reaction of glycerin with Raffinate 1 (containing 1- and 2-butene, linear olefins) and a strong homogeneous acid catalyst

113 g of Raffinate 1 (C4 mixture, containing 1- and 2-butene, coming directly from a synthesis plant of MTBE, methyl-terbutyl ether) , instead of the pure 1-butene of the previous examples, and 1.57 g of methanesulfonic acid (0.016 moles), were added to 30.1 g (0.32 moles) of glycerin. The composition of Raffinate 1, indicated in the following Table, shows that the main components are 1-butene and 2-butene:

ComOositi on of Raffir.ate 1

compound %, weight isobutane 2,03 n-butane 9

2-butene, cis 16,65

2-butene, trans 11 ,3

1-butene 60,7 isobutene 0,19

1 ,3-butadiene 0,07 propane 0,05 propylene 0,01

After 20 hours at 140 ⁰ C and 29 bars of pressure, under stirring (1,200 rpm) , the excess unreacted gas was evaporated. 12 g of product were obtained, containing

glycerin sec-butyl ethers in the percentage ratio in moles indicated in the following Table:

The final conversion was 21% in moles with respect to the starting glycerin. Under these conditions the 1- butene is substantially more reactive than 2-butene, as indicated by analysis of the composition of the gaseous phase after the reaction. Example 5

Reaction of glycerin with Raffinate 1 (containing 1- and 2-butene, linear olefins) and a very strong homogeneous acid catalyst

The reaction of Example 4 was repeated using Raffinate 1 having the same composition.

116 g of Raffinate 1 and 1.6 g of trifluoromethanesulfonic acid (0.01 moles) were added to 30 g (0.32 moles) of glycerin.

After 20 hours at 140 ⁰ C and 28 bars of pressure, under stirring (1,200 rpm) , the excess gas was evaporated. 45.0 g of product were obtained, containing glycerin sec-butyl ethers in the percentage ratio in moles indicated in the following Table:

The final conversion was 68% in moles with respect to the starting glycerin. It should be noted that the oligomerization products are almost absent.

The conversion obtained is higher than that of Example 4 as under these conditions, in Raffinate 1 the reactivity of 1-butene and 2-butene is comparable, as indicated by analysis of the composition of the gaseous phase after the reaction. Example 6 Reaction of glycerin with Raffinate 1 (containing 1- and 2-butene, linear olefins) and a very strong heterogeneous acid catalyst

The reaction described in Example 4 was repeated using Raffinate 1 having the same composition indicated in the Table of Example 4, in which it is indicated that the main components are 1-butene and 2-butene.

102 g of Raffinate 1 and 50.1 g of very strong anion-exchange silica Nafion (acid equivalents 0.007 moles), functionalized with trifluorosulfonic groups, were added to 30.7 g (0.33 moles) of glycerin. After 20 hours at 140 ⁰ C and 30 bars of pressure, under stirring (1,000 rpm) , the excess gas was evaporated. 46.5 g of product were obtained, containing glycerin sec-butyl ethers in the percentage ratio in moles indicated in the following Table:

The final conversion was 76% in moles with respect to the starting glycerin. As can be observed, the main reaction product is 1, 3 -sec-butyl diether. The oligomerization products are almost absent.

The conversion obtained is higher than that of Example 3 as, in Raffinate 1, not only does 1-butene react but also 2-butene. The mixture of reaction products obtained was treated in order to isolate the DSBE ₇ i.e. 1,3-di-sec- butyl ether of glycerin. Aftpr eliminating the excess butene under reduced pressure, 50 ml of water and 80 ml of heptane were added to the liquid obtained. After extracting the aqueous phase 3 times with heptane, the solvent of the organic phase was evaporated. The colourless liquid remaining was distilled at 115°C, 3-4 mmHg . A distillation fraction was obtained (about 22 g) whose composition in percentage moles, determined by gas- chromatography, is indicated in the following Table:

This product, corresponding to 1, 3-di-sec-butyl ether of glycerin, called DSBE, was used as component for fuels for motor vehicles in the physico-chemical

characterization tests of the following example 9.

Example 7

Reaction of 1-pentene (linear olefin) and glycerin

100.0 g of 1-pentene (1.42 moles) and the acid catalyst in such a quantity as to reach 0.018 moles of acid equivalents, were added to 40 g of glycerin (0.43 moles) . The reaction was terminated after 6 hours of reaction at 160 ⁰ C under stirring (1,200 rpm) , at a pressure of 19 bar. After evaporating the unreacted 1- pentene under vacuum, the reaction products were analyzed via gas chromatography. The followinq Table indicates:

- the relative composition of each mixture obtained, in terms of 2-sec-pentyl ethers of glycerin, and

- the conversion with respect to the glycerin for each reaction, with the variation in the catalyst used, both homogeneous and heterogeneous:

The data of the table are expressed in percentage moles:

As can be observed, the very strong acids are better catalysts than the corresponding strong sulfurated acids, both homogenous and heterogeneous . Example 8 (comparative) :

Reaction of glycerin with isobutene (branched olefin) and a strong homogeneous acid catalyst

55 g (0.98 moles) of isobutene and 0.99 g of methanesulfonic acid (0.01 moles) were added to 29 g (0.32 moles) of glycerin. After 6 hours at 70 ⁰ C under stirring (1,200 rpm) , the excess unreacted isobutene was evaporated. 67 g of product were obtained, containing ter-butyl ethers of glycerin in. the percenlcige ratio in moles indicated in the following Table:

The final conversion was 93% in moles with respect to the starting glycerin. Oligomerization by-products of isobutene were also formed, mainly that with 4 monomers [ (butene) ₄ ] .

100 ml of water and 100 ml of heptane were added to the mixture of reaction products, after evaporating the excess isobutene. The aqueous phase was extracted 3 times with heptane. The extract was anhydrified with Na ₂ SO ₄ and the solvent was evaporated under reduced pressure. The

colourless liquid remaining was distilled at about 110 ⁰ C, 4 mmHg of pressure. A distillation fraction was obtained (about 34 g) whose composition in percentage moles, determined by gas-chromatography, is indicated in the following Table:

This product, called DTBE, was used as component for fuels for motor vehicles in the physico-chemical characterization tests described hereunder. Example 9 Physico-chemical characterization of mixtures of DSBE and

DTBE in gasoil

The products DTBE and DSBE, obtained from the synthesis of the processes described in example 8 and 6, respectively, were used as components for gasoil for motor vehicles . The tests performed and results obtained are indicated hereunder.

The products DSBE and DTBE were added in a quantity of 20% by weight to two types of commercial gas oil for motor vehicles, indicated as gasoil 1 and gasoil 2.

The main characteristics of the mixtures obtained are indicated in the following table:

* Cold Filter Plugging Point, CFPP

From the data, it can be deduced that the addition to the gas oil of 20% by weight of these glycerin ethers does not significantly alter the viscosity, density and distillation curve of thp sa ^m e gaεcil. The ceLciπe numoer of the mixture with DSBE is on an average 5 points lower than the gasoil as such and therefore it cannot be said that the DSBE excessively jeopardizes the product with respect to the ignition quality, whereas the cetane number of the mixture with DTBE is 14 points lower than that of the base gasoil, which represents a substantial penalization. The cetane characteristics of these ethers were examined in greater detail in a second experiment in which a commercial gasoil for motor vehicles was mixed with both 10% of DSBE and 10% of DTBE.

In this case, the DSBE reduces the cetane number by only 2 points and the DTBE by 3 points. The addition of a

cetane improver additive (ethyl hexyl nitrate) , at levels which do not exceed those of current use (400 ppm) , proves to be sufficient for bringing the cetane characteristics of the mixture containing DSBE back to the starting levels.

Levels of additive outside those of current use, and equal to 1,600 ppm, on the other hand, are necessary for bringing the cetane number of the mixture with DTBE back to the starting levels.

From the data indicated, it is evident that it is possible to add even considerable quantities of etherification products of glycerin with linear olefins to the gas oil, thus allowing an excellent exploitation of this by-product of the production of biodiesel, with a consequent improvement in the same production process of biodiesel, whereas, to the contrary, the addition to gasoil of etherification products of glycerin with

branched olefins substantially jeopardizes the cetane quality.

Example 10

In this example, the emissions of a gas oil containing 10% of DSBE, prepared as described in Example 6, are compared with those of a "base" gas oil, within the specification EN590, and with those of a gas oil containing 10% of DTBE, prepared as described in Example 8.

The "base" gas oil, containing 10 ppm of S as indicated in the following Table 1, was used for the experiment-ation together v;ith two gas υiia formulated by adding 10% of DSBE and 10% of DTBE respectively to the same base gas oil.

The main characteristics of the gas oils used are indicated in Table 1 and compared with the specification limits . Table 1

The emissions were evaluated on a Diesel Common rail vehicle without an anti -particulate filter with a 1.3 litres engine, following the NEDC homologation cycle (EC Regulation Nr. 692/2008 of the European Commission of 18/7/2008) and the Artemis cycle, the motorway part (Real-world driving cycles for measuring cars pollutant emissions - Part A: The ARTEMIS European driving cycles" Report INRETS-LTE 0411 - June 2004) .

The results listed in the following Tables 2 and 3, are the average of at least 4 repeated tests. In the following tables, PM refers to the particulate mass collected on a sppr-ific filter accordiuy to che standard homologation method (EC Regulation Nr. 692/2008 of the European commission of 18/7/2008) .

Table 2 : Emissions detected in the NEDC homologation Cycle

Table 3 : Emissions detected in the motorway part of the Artemis Cycle

From the experimentation, it can be observed that:

• A decrease in the cetane number is observed, which however remains within t-he specification Iimics in the case of DSBE, whereas it is critically below the specification limits in the case of DTBE.

• DSBE, mixed at 10% in gas oil, brings slight improvements with respect to the PM emissions.

• The emission of HC and CO are correlated to the cetane number of the gas oil and are therefore better for DSBE with respect to DTBE.