FR2799201A1 - Process for the separation of sulfur-free components from motor fuels for applications in mobile systems such as touring coaches and utility vehicles - Google Patents

Abstract

The invention exploits the notion that sulfur-containing components generally have higher boiling points than sulfur-free components, and aspiration is effected by a vacuum evaporation of the initial fuel supply. The separation process of sulfur-free components is effected by vacuum evaporation produced by a gas transport pump, and the separated components are condensed under increased pressure into a separate reservoir.

Description

The invention relates to a method for separating substantially sulfur-free components from a motor fuel on board a motor vehicle.

Motor fuel desulfurization is usually done by industrial chemical processes in refineries during fuel production. Methods known for this purpose are extraction, adsorption, distillation or microbiological processes. Commercial fuels for commercial engines in Europe currently have a residual content of about 200 ppm. This content is problematic in view of the sulfur compatibility of modern aftertreatment systems, which contain adsorbers and catalysts. To account for this, efforts should be made to obtain residual sulfur levels of less than 10 ppm.

The object of the invention is to provide a method of separating substantially sulfur-free components from an engine fuel which is suitable for application in mobile systems. In particular, its implementation must only require a small footprint and a low weight.

According to the invention, this result is obtained by a process which is characterized in that the separation is carried out by vacuum evaporation. Advantageous embodiments of the invention will emerge from the following.

The process according to the invention exploits the fact that the sulfur-containing fuel components generally have a higher boiling point than the substantially sulfur-free fuel components.

According to the invention, the separation on board the vehicle components substantially free of sulfur and boiling point is therefore by evaporation by vacuum. For this purpose, it is exerted, by means of a pump, a suction inside the fuel tank, in which is the initial fuel, in order to create a depression. The low-boiling fuel components, substantially free of sulfur, evaporate and are pumped out of the tank. The sulfur-free components can then be condensed under increased pressure (relative to ambient or atmospheric pressure).

All of the fuel components separated from the initial fuel are hereinafter also referred to as "low sulfur fuel fraction". All remaining fuel components in the initial fuel are therefore also referred to as "sulfur-rich fuel fraction".

The use of the low sulfur fuel fraction significantly extends the life of modern aftertreatment systems.

The apparatus necessary for carrying out the process according to the invention is reduced. An essential advantage of the process according to the invention is the fact that evaporation by vacuum can take place at room temperature. Additional heaters, such as heatable evaporation structures, with resistance heating elements, are therefore not necessary. As a result, the size and weight of the apparatus can be kept low. The method according to the invention is therefore very suitable for use in all mobile systems such as passenger cars or utility vehicles or in rail vehicles.

Another advantage of the process according to the invention is that the fraction of sulfur-poor fuel is immediately available on board when the engine is started. It is therefore possible to dispense with an additional tank for sulfur-poor fuel provided especially for the cold start phase.

The process according to the invention is applicable to all motor fuels, in particular those for spark ignition engines (Otto cycle engines) or for diesel engines, with kerosene or methanol.

A gas transport pump, in particular a membrane pump, can be used for evaporation by vacuum. The condensation under increased pressure (relative to the ambient or atmospheric pressure) can then advantageously be effected at the outlet of the pump in a pressure vessel connected to the outlet of the pump, so that the condensation by pressure does not require additional expense of apparatus.

As already mentioned, evaporation by vacuum can be carried out at room temperature. However, according to a particularly advantageous embodiment, it is also possible to produce the evaporation at increased temperature and use for this purpose heat sources anyway present in the motor vehicle to heat the fuel to be fractionated. For this purpose, it is possible to use in particular the engine oil (whose temperature is generally greater than 100 C) or the coolant (at about 80 C) for cooling the engine. In such a case, to heat the fuel, it is placed in thermal contact with the engine oil or engine engine coolant.

The condensation of the separate components, which are substantially free of sulfur, can also be carried out at room temperature. <B> It is however also possible to carry out the condensation at temperatures below room temperature.

The low sulfur fraction separated by evaporation by vacuum can either be used directly for combustion in the engine (in gaseous or liquid form), or can be collected and stored in a tank.

In particular, the low sulfur fraction is suitable for addition to the engine feed during the cold start phase G or in the lean burn mode of a spark ignition engine (Otto engine).

In the case of a diesel engine, the addition of low sulfur diesel fuel also reduces the emission of particulates into the exhaust gas.

Another application of the low sulfur fraction obtained by the process according to the invention is its use in the desulfurization of a catalyst in the aftertreatment system of an engine exhaust gas. In such an aftertreatment system, sulfur accumulates from time to time on the catalyst surface, and is removed by regeneration (desorption). This regeneration can be carried out only with low sulfur exhaust gas.

In addition to its use as an engine fuel, the low sulfur fuel fraction is also applicable as a low boiling point reductant for lean exhaust gas denitrogen catalysts.

Vacuum evaporation, to separate the low sulfur fraction, can be carried out both from the vehicle fuel tank and from an additional intermediate vessel. The sulfur-rich and higher boiling fraction remaining in the recipe

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In the KV fuel tank there is an enrichment of the higher boiling fuel components containing sulfur. It is possible and advantageous to perform both evaporation and subsequent condensation by pressure on the discharge side of the pump at room temperature, so that the method according to the invention can dispense with additional provisions for heating. or cold.

Depending on the type of pump, the desired sulfur content of the fraction to be obtained can be adjusted by the design of the pump (pressures on the suction side and the discharge side), as well as the required fractionation time by the pumping capacity. Maintenance-free (oil-free) diaphragm vacuum pumps, which have a long service life and are insensitive to substances condensing inside the pump, are particularly suitable for this purpose. The electrical power requirement of such a diaphragm pump is also very low.

Very low boiling point compounds, such as butane, which can only be condensed during the distillation by a very high cooling (<0 ° C.), can be obtained by a relatively low die by means of the process according to the invention.

Fuel fractionation for spark ignition engines (Otto engines) was carried out according to the method described with reference to FIG. 1. From <B> 1000 </ B> ml of the fuel used, 350 ml of low sulfur boiling point fraction and 650 ml of higher boiling fraction, rich in sulfur. The pressure was 100 to 300 mbar on the suction side and 1 to 2 bar on the discharge side. On the discharge side of the pump, the low-boiling components, substantially free of sulfur, are highly enriched, while higher boiling fuel components, containing sulfur (including aromatics), are not highly enriched. practically more content. Fuel remaining in the fuel tank enriches the higher boiling fuel components containing sulfur.

The different sulfur contents were as follows: Sulfur content of the initial fuel (ROZ95): <B> 128 </ B> ppm Sulfur content of the low boiling point fraction, low in sulfur: 14 ppm Sulfur content of the higher boiling fraction, high in sulfur: 177 ppm Figure 2 shows the effect of fuel sulfur on the NOx conversion of an aftertreatment system. The operating time (in hours) is indicated on the abscissa and the NOX conversion (in) is indicated on the ordinate. Two series of measurements were made for sulfur contents of 31 ppm and 130 ppm with the same type of catalyst. The tests were carried out with a spark ignition engine (Otto engine) and direct injection in a mixed lean mixture (30 seconds of lean mixture with k = 1.5 and 2 seconds of rich mixture with? , = 0.75).

 As can be seen from a comparison of the series of measurements, the life of the catalyst decreases considerably when the sulfur content is higher.

Claims (15)

<U> CLAIMS </ U> A method of separating substantially sulfur-free components from a motor fuel on board a motor vehicle, characterized in that the separation by vacuum evaporation is carried out. 2. Method according to claim 1, characterized in that it condenses under increased pressure (psur separate components, substantially free of sulfur. 3. Method according to claim 1 or 2, characterized in that a transport pump (PU), in particular a diaphragm pump, is used for evaporation by vacuum. 4. A process according to claim 3, characterized in that the condensation of substantially sulfur-free components at the outlet of the gas transport pump (PU) is produced. 5. Method according to one of the preceding claims, characterized in that the fuel is fuel for spark ignition engines (Otto engines) or for diesel engines, kerosene or methanol. 6. Method according to one of the preceding claims, characterized in that evaporation is carried out by vacuum and / or condensation at room temperature. 7. Method according to one of claims 1 to characterized in that it carries out evaporation vacuum at increased temperature. 8. A method according to claim 7, characterized in that, for heating the fuel, it is in thermal contact with the engine oil or the engine engine coolant of the motor vehicle. 9. Method according to one of the preceding claims, characterized in that one directly uses the fuel components separated substantially free of sulfur, or is collected in a reservoir (DG). 10. Method according to one of the preceding claims, characterized in that the substantially sulfur-free fuel components are added to the supply of the engine in gaseous or liquid form. 11. Method according to one of the preceding claims, characterized in that the low-boiling fuel components, substantially free of sulfur, are added to the engine supply in the cold start phase. The method as claimed in one of the preceding claims, characterized in that substantially sulfur-free fuel components are added to the engine feed in the lean-burn engine or during the desulfurization of the engine aftertreatment system. engine exhaust. Process according to one of the preceding claims, characterized in that substantially sulfur-free fuel components are used as the reducing agent for lean exhaust denitrogen catalysts. 14. Method according to one of the preceding claims, characterized in that it carries out evaporation by vacuum in an intermediate container provided in addition to the fuel tank (KV) in the motor vehicle. 15. Method according to one of the preceding claims, characterized in that sulfur-containing, non-evaporated fuel components are added to the engine feed in operating phases at stoichiometric or full load conditions.