WO2003018717A1 - Improvements made to the treatment used to reduce sulphur in catalytic gasoline and in intermediate crude distillates by means of silica gel - Google Patents

Abstract

The invention relates to an improvement made to the chemical treatment used to reduce the sulphur content of catalytic gasoline and intermediate crude distillates using at least one filter filled with silica gel. Said improvement consists in regenerating the silica gel by washing same with water at a temperature that is at least equal to the boiling temperature.

Description

IMPROVEMENTS IN TREATMENT FOR REDUCTION OF SULFUR IN CATALYTIC GASOLINES AND IN INTERMEDIATE CRUDE DISTILLATES, WITH GEL SILICA

TECHNICAL FIELD

The present invention is related to production processes of catalytic gasoline and intermediate distillates of crude oil. More particularly, the invention relates to processes for reducing the sulfur content in catalytic gasoline and in petroleum intermediate distillates; and specifically, with the purification of the silica gel filter used in said processes.

BACKGROUND OF THE INVENTION In Mexican patent application No. 99/2593, filed on March 18,

1999, in the name of the inventors herein, a chemical treatment is described to reduce the sulfur content of catalytic gasoline and intermediate crude distillates. In said treatment the sulfur is absorbed in at least one filter packed with silica gel, which operates at the outlet pressure of the processes of production of catalytic gasolines and distillation of intermediate crudes. A step of capital importance in the treatment referred to in said pending patent application is the regeneration of the silica gel used for the filtering step.

Said regeneration, as clearly specified in the aforementioned Mexican patent application, is necessary since the silica gel is saturated with sulfur and, correspondingly, decreases its effectiveness. The regeneration is carried out by washing with hot air to ensure that the sulfur is oxidized to SO2 and thus removed from the silica gel; for which the filter is isolated, temporarily removing it from the production line, and heated air is injected through it at a temperature of around 450 ° C, until the regeneration of the silica gel is completed, as specified clearly in said patent application. The filter is subsequently cooled and when it reaches the temperature of the refinery's service air, the gel-packed filter is in a position to be reconnected to the production line to be used again in the filtration.

OBJECTIVE OF THE INVENTION

It has now been discovered that the regeneration step, which in the Mexican application 99/2593 is carried out with heated air at an elevated temperature, can also be carried out, in an easier, faster and less complicated manner, using a procedure called closed cycle, and that involves the steps of: washing the filter with water at a temperature at least equivalent to the boiling point, until the water comes out clear and without traces of sulfates; dry the filter at 115 ° C; and purify the wash water, to remove traces of sulfur derivatives thereof. The wet water vapor, produced, can be reused by drying it previously. This way of regenerating the filter forms the basis for the improvement patent referred to in this description.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the improvements of the invention, and its connection with patent application 99/2593, filed on March 18, 1999, a detailed description of the novel aspects included in these improvements will be given, and for this purpose reference will be made thereto to the attached drawings, in which they are illustrated. In these drawings:

Figure 1 is a conventional flow chart of the process, in which the situation of two filters packed with silica gel is shown; filters to be regenerated in accordance with the present invention. Figure 2 is a conventional diagram of the assembly for the regeneration of the silica gel contained in the filters of the present invention; Y

Figure 3 is a conventional diagram of the sulfur absorption process in the filter loaded with silica gel, and the subsequent regeneration process thereof. PORMENORIZED DESCRIPTION OF THE INVENTION

As stated in the aforementioned Mexican patent application, and whose total content is incorporated herein by reference, the crude oils are subjected to a series of operations in combined plants, which essentially comprise atmospheric towers, in which products such as primary gasoline, turbosine or naphtha and diesel are obtained; and vacuum distillation towers, in which high vacuum diesel oils are obtained, which are recovered as charges for catalytic plants.

In catalytic plant reactors, catalytic gasoline is obtained as the main product, by means of a catalytic thermal cracking operation of high-vacuum diesel fuels from, among other sources, the vacuum distillation towers referred to in the preceding paragraph. It is in this environment that the invention of the Mexican patent application is used cited above, and where the improvement referred to in this application will apply.

Referring first to Figure 1, oil from the oil fields, with high sulfur content, is sent to a fractional tower

1, from where it passes to the catalytic tower 2.

In the operations carried out in them, the hydrocarbon stream does not substantially lose its sulfur content, so it is normally sent to a desbutanizing tower (not shown), in which, in addition to eliminating light hydrocarbons, such as butane, propane, etc., it is about removing as much sulfur as possible, subjecting the current to a treatment known as "Merox", which is indicated in 3. However, the reduction of sulfur in treatment 3 is limited.

These high sulfur contents in the catalytic gasolines that leave on line 6 limit production. For this concept, the losses of catalytic gasoline production are currently around 10%. However, as time goes by, this loss of production increases since the crude oils that are currently being processed are becoming heavier and contain a higher percentage of sulfur.

To obviate these inconveniences, the aforementioned Mexican application taught the installation of two filters 4 and 5, loaded with silica gel, at the exit of catalytic gasoline from the chemical treatment Merox 3. The purpose of these filters is to absorb the non-eliminated sulfur in treatment 3, by passing the gasoline through silica gel. The pair of filters 4 and 5 works alternately; that is, one of them (4) is put into operation until the silica gel is close to the saturation point with sulfur, at which point the other filter 5 is connected, while the filter 4 is regenerated by hot air. It is necessary to note that, although only two filters 4 and 5 have been illustrated, each of them can be replaced by a train of filters, so their number could be greater.

With reference to Figure 2, the number 7 represents the line through which the regeneration means of the filters 4 and 5 are passed countercurrently, when that operation should be performed; while the number 9 identifies the upper filter regeneration valve that, through line 8, connects with a sulfur plant (not shown).

Figure 3 is a flow chart, much more detailed, illustrating the regeneration system referred to in the present improvement. The dry hot steam inlet (without moisture) has been identified with "A"; with "B", the sulfur-containing water outlet to the bitter water recovery plant; and with "C" the entrance of virgin demineralized water.

As clearly shown in Figure 3, in this improvement also filters 4 and 5 (corresponding to the filters of equal number illustrated and claimed in the Mexican application mentioned above) are arranged in the same relation with respect to the towers 1 , 2 and 3 also defined in said previous application. Where the improvement of the invention lies is in the way of regenerating filters 4 and 5. As explained above, one of the filters 4, 5 (which can be representative of a train of filters) is put into operation. As the silica gel contained in the filter retains the sulfur contained in the stream of filtration, is saturated with the result that the sulfur content in the product is increasing. At this point, the filter is removed from the line, replacing it with the other (5, 4) (which can also be representative of a filter train). While this other filter is in operation, the filter removed from the line is subjected to the regeneration steps.

The filter to be regenerated is first subjected to a washing step, as shown with the dotted lines, until the moment the outlet water is clean and clear, without yellow color. At that time it will be free of sulfur. The absence of sulfates is checked visually or (preferred) by a test commonly used with cadmium acetate. If it is verified that the water is clear and clear, the water will be used again for regeneration, in a closed cycle.

The water used will be at an elevated temperature, preferably equivalent to at least the boiling point. This will produce, as usual, wet steam, which can be used repeatedly, drying it. Preferably, the steam is reheated. Once the silica gel has been washed with the water at a temperature at least equivalent to the boiling point, as stated above, it is dried, preferably at a temperature of about

115 ° C Once the silica gel dries, the filter is able to be used again in the filtration of gasoline or other sulfur-containing product.

EXAMPLE A catalytic gasoline, with an initial sulfur content of 0.17% by weight, was subjected to purification on a filter of the invention, based on a bed of silica gel. Filtration was maintained until the silica gel showed negative results. of filtration At that point the silica gel was washed countercurrently with superheated steam, until the resulting wash water was clear and clear. This cycle of operations was repeated twice, performing a backwash operation and drying the silica gel after each saturation of the filter. The results of the three filtration operations were the following:

TABLE I FILTRATION RESULTS

Although only three times the filter was used in this example, it should be noted that the regeneration step allows the silica silica to be reused practically without limits; as long as the practice of regenerating it is observed every time it is saturated. The results will invariably remain within the scale of indicated reductions, always below 0.1%.

From the foregoing it will be seen that in all cases the gasoline filtered in the regenerated filter according to the present invention reduced the sulfur content by about 50% with respect to the initial content; thereby demonstrating the effectiveness of the regeneration operation performed in accordance with the present invention.

Even when the inventive concept has been described in detail in the foregoing, it will be understood that it has only been done for the benefit of clarity, and not as a limitation on the scope of the invention.

Claims

Claims 1.- In a procedure to reduce the sulfur content in catalytic gasolines and in intermediate distillates of crude, by filtration in at least one filter packed with silica gel, where the silica gel of the at least one filter is subjected to a regeneration step The improvement characterized in that the regeneration includes the steps of: washing the at least one filter with high temperature water until the washing water is substantially free of sulfur derivatives and is clear and transparent to the eye; Dry the at least one filter at elevated temperature and treat the wash fluids to recirculate them to a subsequent regeneration operation. 2. Improvements according to claim 1, further characterized in that the water is introduced to the counter current filter, and is at least at the boiling temperature. 3. Improvements in accordance with claim 1, further characterized in that the drying step is carried out at about 115 ° C. 4. Improvements in accordance with any of the preceding claims, further characterized in that the water is at least partially in the form of water vapor. 5. Improvements in accordance with any of the preceding claims, further characterized in that the entire regeneration operation is carried out as a closed cycle.