The invention concerns oxygenated gasoline components and gasoline oxygenates. In particular, the invention concerns a high-octane oxygenated gasoline component and a method of producing thereof.

Oxygenates are oxygen-containing organic compounds added to gasoline to enhance the combustion reactions of gasoline in an engine and, due to this, to reduce carbon monoxide and hydrogen carbon emissions. Commonly used oxygenates are alcohols (Cx-O-H) and ethers (Cy-O-Cz) containing 1 to 6 carbons. Methyl tertiary butyl ether (MTBE) is the most widely used oxygenate in motor petrol. However, a new environmental problem relating to MTBE has arisen. Since MTBE is very soluble in water, it has been found in ground water causing poor smell and taste of the water. For this reason, the use of MTBE in gasoline will be prohibited in California from the beginning of 2003.

However, even after prohibition of MTBE, the reformulated gasoline should contain 2% oxygen. It is therefore evident that new, MTBE free, high-octane oxygenated gasoline compositions are needed to comply with the regulations on gasoline in connection with air quality and to meet the requirements set by current automotive engines. Proposed suitable substituting chemicals of MTBE are alcohols and ethers, such as ethanol, methanol, tert-butanol and other tertiary alkyl ethers. A very realistic alternative is ethanol, which has good octane numbers. It can be predicted that the use of ethanol as a component of automobile gasolines will increase in near future. However, ethanol increases the vapour pressure of the gasoline and it is water-soluble.

Finnish Patent Application No. 20001679 concerns gasoline containing an oxygenate and a method of producing a suitable oxygenate of gasoline, namely 2,4, 4-trimethyl-2- pentanol. According to the application the total oxygenate concentration of the gasoline

is 2-20 vol-% and the oxygenate consists of one or more of following compounds: 2,4, 4-trimethyl-2-pentanol, 2,4, 4-trimethyl-2-metoxypentane and ditertbutyl ether.

The research octane number (RON) and the motor octane number (MON) of the gasoline thereof is more than 90 and 80, respectively.

The present invention concerns a method of producing an oxygenated, MTBE free, gasoline component and the gasoline component product. The invention is based on the idea that ethanol and/or heavier ethanol ethers are used as oxygenates in gasoline.

Further, the invention is based on the idea of converting at least a part of the ethanol, which may remain as an oxygenate in the final gasoline, to water-insoluble ethers.

Water-insoluble heavier ethers can be obtained via reacting isooctenes, in particular a mixture that consists essentially of 2,4, 4-trimethyl-1-pentene and 2,4, 4-trimethyl-2- pentene, with ethanol.

The basic raw materials suitable for the new gasoline component produced according to the present invention are field butanes and ethanol. The overall process has three steps: - isomerisation of n-butane to isobutane and dehydrogenation of isobutane to isobutene -dimerisation of isobutene to a mixture of isooctenes etherification of isooctenes with ethanol.

The recovered mixture is suitable for a gasoline component as such or as blended with the product recovered from the dimerization unit. A remarkable advantageous feature of the process is that it is unnecessary to remove the remaining ethanol from the etherification product. Excess of ethanol can be used in the etherification step to increase the ether conversion.

In the first step, n-butane is isomerised to isobutane with known isomerisation catalysts, such as platinum supported on alumina or zeolites. For the dehydrogenation of isobutane to isobutene there are available at least four dehydrogenation processes: Catofin, Oleflex, Phillips and Snamprogetti-Yarsynthesis. The catalysts used are based

either on supported chromia or on supported noble metal. The other difference between the processes is the way how the heat required for highly endothermic dehydrogenation reaction is supplied.

In the next step, isobutene is converted to isooctenes on an ion-exchange resin catalyst.

The reaction is carried out typically under pressure in a liquid phase. A small amount of an oxygenate such as methanol, tert-butyl alcohol (TBA) or MTBE, is added to improve the reaction selectivity to dimers. The isooctene product consists of mainly two isomers, viz. 2,4, 4-trimethyl-1-pentene and 2,4, 4-trimethyl-2-pentene, which both have a carbon atom attached to a methyl group and a double bond. This type of carbon has been shown to be reactive in the etherification reaction.

In the last step, the isooctenes react with ethanol forming the ether, 2-ethoxy-2,4, 4- trimethyl pentane. This reaction is also carried out in a liquid phase using a strong cation-exchange resin as a catalyst. Also other acid catalysts can be used. The etherification temperature is typically less than 100 °C, since the thermodynamic equilibrium for the exothermic reaction decreases with an increase in temperature. The equilibrium conversion can be improved by applying excess of ethanol in the reaction mixture.

The reaction product contains unreacted isooctenes, unreacted ethanol and the formed ether, and it can be used directly as a gasoline blending component without any further separation steps. The formed 2-etoxy-2,4, 4-trimethylpentane has excellent properties as a gasoline component. It is almost insoluble in water, its vapour pressure is low and it has high octane numbers.

If ethanol is not wanted in the gasoline, the unconverted ethanol can be separated from the reaction product and the remaining mixture can be used. In that case, the oxygenate- containing mixture is completely insoluble in water.

The present invention provides remarkable advantages. The liquid mixture produced according to the process of the present invention is an excellent gasoline component having high octane numbers and lower vapour pressure compared to a mixture, where only pure ethanol is used as an oxygenate. The olefin content of the gasoline component decreases and the octane number increases as the result of etherification. The boiling point of the used ethers is higher than that of MTBE. Furthermore, the solubility in water of the used ethers is crucially lower than the solubility of MTBE.

The process for producing the gasoline component is advantageous. The moderately low conversion of the ether can be improved by using excess of ethanol and the ethanol can remain in the final gasoline component. Thus, the expensive process step for separating the ethanol from the product is avoided. For instance, when MTBE is produced, the overall process contains the step for removing alcohol from the product.

Ethanol is a favourable raw material of the process, since it can be produced from biomass via fermentation and therefore it is a renewable compound.

If 2-methoxy-2,4, 4-trimethylpetane were produced according to the present invention, the use of excess methanol in the etherification would result in a situation where the separation step of the methanol from the final product would be needed. Furthermore, the water solubility (around 100 mg/kg), boiling point (149 °C) and octane numbers (RON 110, MON 98) of the mentioned methanol ether are inferior to that corresponding ethanol ether.

It is known that etherification reactions of heavier ethers are clearly slower that those of lighter ethers, such as MTBE or TAME. Therefore, it is particularly advantageous to use an excess of alcohol in the etherification process producing 2-ethoxy-2,4, 4- trimethylpetane.

In the context of the present invention, "an oxygenated gasoline component"means a liquid mixture of hydrocarbons and one or more oxygen-containing organic compounds

that enhance combustion reactions of gasoline and/or reduce carbon monoxide and/or hydrocarbon emissions of automobiles.

Figure 1 shows the process flow chart of the process according to the present invention.

Flow 1 consists essentially of isobutene. Flow 2 is the dimerised product flow of flow 1, i. e. mainly di-isobutene. Flow 3 contains ethanol and flow 4 is the reaction product mixture of the etherification unit 6. The product contains ether, ethanol and di- isobutene. In unit 7 the product from the etherification is mixed with a basic gasoline, such as non-oxygenated gasoline 95. Optionally a part of the dimerised product of unit 5 is separated to an other flow and mixed with the etherified product of unit 6 in unit 7.

The method of producing an oxygenated gasoline component according to one preferred embodiment of the present invention comprises the following steps in the indicated order: - feeding n-butane into an isomerising unit, - recovering an isomerised reaction product consisting essentially of isobutane, - feeding the recovered reaction mixture from the isomerisation unit into a dimerisation unit, - recovering a reaction product consisting essentially of the isomers of isooctene, - feeding the reaction product recovered from the isomerisation unit and ethanol into an etherification unit, - carrying out the etherification in a liquid phase in the presence of an acid catalyst, and - recovering a reaction product.

N-butane is introduced into the isomerisation as a feed, which essentially consists of n- butane.

The method according to a preferred embodiment may comprise a step of blending the recovered reaction product of the etherification step with the product recovered from the dimerization unit.

Further, the process may, when needed, comprise a step of separating the ethanol from the etherified product before bleinding it to the final gasoline product.

To speed up the etherification process and to improve its conversion the molar ratio of ethanol to isooctenes that are fed to the etherification unit ranges preferably between 1 and 8.

The etherifcation is preferred to be carried out at a temperature below 200 °C, especially the temperature between 70 and 90 °C is preferred.

The preferred ether to be produced in the etherification is 2-ethoxy-2,4, 4-trimethyl pentane. Thus, the preferred feed to the etherification unit contains hydrocarbon feed consisting essentially of 2,4, 4-trimethyl-1-pentene and 2,4, 4-trimethyl-2-pentene.

Further, to avoid unnecessary isomerisation during the etherification, the molar ratio of 2,4, 4-trimethyl-1-pentene to 2,4, 4-trimethyl-2-pentene in the hydrocarbon mixture that is fed to the etherification unit corresponds to the thermodynamic equilibrium of the mixture.

The oxygenated gasoline component produced according to the present invention typically consists of 2-ethoxy-2,4, 4-trimethyl pentane in a quantity ranging from 2 to 20 % by weight, methyl tertbutyl ether less than 1 % by weight, ethanol in a quantity ranging from 1 to 65 % by weight, and isooctenes in a quantity ranging from 15 to 85 % by weight.

The oxygenated gasoline component can be blended with any type of gasoline, typically with lead-free gasoline, such as 95 and 98 type gasolines.

According to the present invention, 2-ethoxy-2,4, 4-trimethyl pentane is a suitable oxygenate in a reformulated gasoline. When the ether is used as oxygenate of a gasoline the amount of the ether is below 20 vol-%, preferably from 1 to 5 vol-%. The ether can be blended with a lead-free gasoline, such as 95 and 98 type gasolines.

Example 1 In the etherification process according to the present invention 2-ethoxy-2,4, 4- trimethylpentane is formed. The properties of the ether and MTBE were compared by measuring octane numbers and water solubility. Oxygenates were blended with a typical gasoline and RON and MON values were determined. In following (table 1) characteristics of 2-etoxy-2,4, 4-trimethylpentane and MTBE are compared.

Table 1 2-etoxy-2,4, 4- MTBE trimethylpentane Blending-RON 115... 116 117 Blending-MON 100 101 100 Solubility in water (mg/kg) 60 43000 Purity (%) 97 >95 Density (kg/m3) 794 745 Boiling point (°C) 160 55 It can be clearly seen that 2-etoxy-2,4, 4-trimethylpentane has extremely high octane numbers and that it is almost completely insoluble in water.

Calculated Example Di-isobutene was etherified with ethanol in an etherificaiton unit. The feed of the etherification unit had the ethanol to di-isobutene (DIB) molar ratio of 4, i. e. the DIB content of the feed was 37. 8 wt-% and the ethanol (EtOH) content was 62.2 wt-%.

At 50 °C the conversion of DIB was 9.0% At 70 °C the conversion of DIB was 5.5% At 90 °C the conversion of DIB was 3.9%.

The product composition (calculated with a conversion of 10%) was roughly DIB 34.1 wt-%, EtOH 60.6 wt-% and ether 5.3 wt-%, when the etherification temperature was 50 °C. The mixture had an oxygen content of 21.6 wt-%.

With a reactive distillation the conversion of DIB can be increased to 30%, the product composition would be: DIB 26.5 wt-%, EtOH 57.5 wt-% and ether 16.0 wt-%.