JPS6041644B2 - Aromatic hydrocarbon purification method - Google Patents

Description

[Detailed description of the invention] The present invention is directed to aromatic hydrocarbons, particularly C6-C.

The present invention relates to an improvement in a refining method for obtaining components by removing impurities from raw oil containing a large amount of these components. According to , in addition to improving product yield and unit consumption, it also reduces energy consumption. C0~ of benzene, toluene, xylene, etc. (hereinafter collectively referred to as "BTX")
C8 aromatic hydrocarbons are contained in large amounts in cracked gasoline, which is produced as a by-product during the thermal decomposition of naphtha, for example. This type of raw material oil contains polymerizable diolefins and styrenes as well as organic sulfur compounds as impurities. In order to remove these impurities and obtain purified BTX, conventionally, these hydrocarbons have first been added at relatively low temperatures using a catalyst that is active at low temperatures, such as palladium, while avoiding the polymerization of diolefins. Group VIB elements of the periodic table (Cr, MO, W) and iron group elements (Fe, CO, Ni
) The organic sulfur compound is further catalytically hydrogenated at elevated temperature using at least one catalyst selected from the group consisting of A two-step purification method is adopted in which organic nitrogen compounds, if present, are simultaneously converted to ammonia and removed.

Unreacted hydrogen containing hydrogen sulfide and ammonia that flows out together with the reaction product after the secondary hydrogenation is washed with water to separate and remove at least ammonia, and then returned to the secondary hydrogenation step for use. When carrying out the above process, it is necessary not only to completely remove impurities, but also to minimize the loss caused by hydrogenation to the nucleus of aromatic hydrocarbons (hereinafter abbreviated as 1-nuclear hydrogenation). This is required.

Conventionally, it has been considered that a high degree of purification and a high yield are incompatible; for example, when processing a raw material containing about 100 ppm of organic sulfur compounds to reduce the residual sulfur content to 1 ppm or less, BTX is used. The loss due to conversion to nuclear hydrogenated cyclohexane or its derivatives is 3
It was allowed to reach ~5% as unavoidable. However, the recent rise in oil prices and the tightening of the supply-demand relationship demand that such losses be kept to a minimum. Recent research has shown that nuclear hydrogenation during secondary hydrogenation can be significantly reduced by subjecting the catalyst to specific pretreatment and appropriately selecting reaction conditions, resulting in a BTX yield of 9.
It has become easier to increase the ratio to 9% or more. Avoiding unnecessary nuclear hydrogenation also means that the amount of hydrogen required as a raw material can be saved by that amount, which is preferable from the point of view of basic unit consumption. By the way, in the secondary hydrogenation operation for removing organic sulfur compounds using the above-mentioned catalyst, a considerably high temperature of 200 to 4000C is considered appropriate.

In the two-step refining process, pyrolyzed gasoline is distilled to produce C6~
The temperature at which the C8 aromatic component is distilled is about 100°C, whereas the temperature for primary hydrogenation using a conventional palladium catalyst has been 50 to 80°C. Therefore, the feedstock oil must be cooled from around 100°C to 50-80°C, and in order to undergo secondary hydrogenation, it must be heated to the above-mentioned 200-400°C. . Such operations naturally result in the consumption of a large amount of thermal energy or require the installation of extra heat exchangers, and therefore, as an industrial process, savings should be made. The present inventors conducted research from this perspective and surprisingly found that hydrogen containing hydrogen sulfide produced in the secondary hydrogenation process can be recycled in the primary hydrogenation process, and that sulfide in the hydrogen can be recycled. Depending on the hydrogen content, the preferred temperature for primary hydrogenation using a palladium catalyst is higher than when using only conventional fresh hydrogen. The present invention was achieved by establishing favorable conditions between the hydrogen sulfide concentration and the feedstock oil supply rate. As mentioned above, the method for refining aromatic hydrocarbons of the present invention involves first treating a feedstock oil mainly composed of C6 to C8 aromatic hydrocarbons with a relatively low-temperature catalytic hydrogenation treatment using a palladium catalyst. That is, by primary hydrogenation, diolefins and styrenes therein are removed by hydrogenation, and then they are removed from group IB elements of the periodic table (Cr
, N4O, W) and iron group elements (Fe, CO, Ni) by relatively high temperature catalytic hydrogenation treatment, that is, secondary hydrogenation, using at least one catalyst selected from the group consisting of
In a method for purifying C6 to C8 aromatic hydrocarbons, which involves converting the contained organic sulfur compounds into hydrogen sulfide and then separating and recovering aromatic components, hydrogen sulfide separated from the reaction product of secondary hydrogenation. Hydrogen gas containing
Alternatively, only a part of the hydrogen sulfide is removed and recycled to primary hydrogenation, and used together with newly supplied hydrogen for catalytic hydrogenation, and the concentration of hydrogen sulfide in the total hydrogen supplied to primary hydrogenation (Volume Ppm) and feedstock oil supply rate m (volume per catalyst volume, per hour) to the primary hydrogenation, the temperature T (°C) at the inlet of the catalyst bed for primary hydrogenation is determined so that the following formula is satisfied. It is characterized by control.

(However, 0.8≦m≦5) The above formula is valid in the range of 50≦T≦200°C.

That is, primary hydrogenation is performed at a temperature range of 50 to 200°C. In addition, secondary hydrogenation is carried out at 200 to 400°C, generally at 25°C.
It is carried out at a temperature of 0-350°C. If the standard purification method of the present invention is explained with reference to the drawings, as shown in Figure 1,
Pyrolysis gasoline CG is fractionated in a fractionating column 1, and a fraction mainly containing C6 to C8 components is separated and passed to a primary hydrogenation column 2.

The C6 to C8 components distilled from the fractionating column 1 are 97 to 102
It has a temperature of 'C. If the suitable temperature for primary hydrogenation is, for example, 130°C, then the feedstock may be heated slightly (achieved by recycling a portion of the primary hydrogenation product to the organic sulfur compound system) to the primary hydrogenation step. There, diolefins and styrenes are hydrogenated using hydrogen containing hydrogen sulfide over a palladium catalyst. Depending on the amount of these unsaturated components present, considerable heat generation and associated temperature rise are observed. The products of the primary hydrogenation enter the secondary hydrogenation tower 3 together with hydrogen, and enter the periodic table group VIB (Cr, MO
, W) and a catalyst containing at least one selected from the group consisting of iron group (Fe, CO, Ni).

Among these catalysts, the one most commonly used at present is CO.
-MO type, Ni-MO type and Ni-CO-MO type. Optionally, a portion of the product of the primary hydrogenation is
As described above, the temperature may be controlled by circulating it back into the catalyst bed for primary hydrogenation. In this case, the circulating portion is not included in the calculation of m. The appropriate temperature for secondary hydrogenation is
The temperature is preferably 250 to 350°C. The product is cooled and condensed, added to water, washed, and separated from the gas phase components and wash water in a separator to remove the C6-C8 components, which are then directed to further final purification and fractionation steps if desired. The feedstock oil usually contains organic nitrogen, and secondary hydrogenation produces ammonia, which is removed by the water washing described above. Hydrogen containing gas phase components, ie hydrogen sulfide, is recycled to the primary hydrogenation step to replenish the consumed hydrogen.

Although some hydrogen sulfide in the circulating hydrogen is removed by washing with water,
If this is insufficient and the amount accumulates in the circulating gas, and as a result, the optimum value exceeds 200°C, the amount can be actively reduced by re-washing with water or alkaline washing. When the hydrogen sulfide in the circulating hydrogen is 1100 ppm, if the same amount of new hydrogen is added, the hydrogen sulfide concentration X in the total hydrogen supplied to the primary hydrogenation will be 550 ppm, m = 1
According to the above equation, the suitable temperature in this case is 131±10° C., so there is no need to intentionally remove hydrogen sulfide. The temperature may be gradually raised at startup, when the concentration of hydrogen sulfide in the circulating hydrogen gas is low, or in accordance with the concentration. In this way, the present invention circulates the hydrogen sulfide concentration in hydrogen without worrying about it as long as it does not become too excessive, and smoothly circulates the hydrogen sulfide concentration in hydrogen by providing a catalyst layer inlet temperature that corresponds to the concentration. The operation can be continued or the degree of hydrogen sulfide removal can be easily adjusted to provide the appropriate primary hydrogenation temperature.

Alternatively, by adjusting the feedstock feed rate,
It is also possible to create desirable operating conditions. For example, when the concentration of hydrogen sulfide entering the catalyst layer is X=300 ppm and the raw oil supply rate is m=1, the appropriate temperature for primary hydrogenation is 98±10° C. from the above equation.

This relationship is as shown in FIG. 2, which graphically shows the relationship between temperature T and hydrogen sulfide concentration X for several values of m. The temperature of the primary hydrogenation of 98° C. means that the C6-C8 components from the fractionation column can be fed to the primary hydrogenation without heating or cooling. If the C6 component is also recovered in addition to C6 to C8, the fractional distillation temperature will be higher, but since the secondary hydrogenation is carried out at a relatively high temperature, the primary hydrogenation may also be carried out at a high temperature. When the feedstock has a low sulfur content and the circulating gas has a low hydrogen sulfide concentration, the optimum primary hydrogenation temperature is lower than the fractionation temperature and may require some cooling; The temperature gap tends to be higher than that in the case where hydrogen does not exist, so the temperature gap is not small. In any case, X. ．． m
As long as the relationship in the above formula holds true between Almost no hydrogenation occurs.

Furthermore, no gum is produced due to polymerization of diolefins or styrenes.

At temperatures below this range, hydrogenation is insufficient overall, while at temperatures that are too high, hydrogenation is almost complete, but the aromatic nuclei are also attacked, reducing the amount of alcohol to less than 1%. If you stop, you will not be able to achieve your goals. Therefore, in carrying out the purification method of the present invention, in addition to controlling the temperature of the primary hydrogenation, it is necessary to adjust the hydrogen sulfide concentration in the circulating hydrogen, change the raw material supply rate, or all three. It is concluded that favorable operations should be continued by finding the optimal conditions by correlating the factors.

This allows refining to the desired high level, and
Loss of aromatic components and hydrogen consumption can be minimized, and energy consumption can be expected to be saved. In addition to the operating conditions for primary hydrogenation in the refining method of the present invention, the temperature should be in the range of 50 to 200°C and the feedstock oil supply rate should be in the range of 0.8 to 5/Hr. The ratio is in a molar ratio of 0.01 to 5, usually 0.4 to 2.0. Pressurization is naturally advantageous since it is a hydrogenation reaction, but according to experience, the magnitude of the pressure has almost no effect on the above-mentioned temperature equation related to the present invention. It is sufficient to select from ~80k9/CItG, and usually 30-60kg/C7lfG is appropriate. Examples 1 to 4 and Comparative Examples 1 to 4 In the primary hydrogenation using a palladium catalyst, hydrogenation to the side chain of styrene, that is, conversion to ethylbenzene, which is to be performed at a high rate as possible, and benzene, which is to be avoided as much as possible. The following experimental example shows how the hydrogenation of the core, that is, the conversion to cyclohexane, changes depending on the catalyst temperature, circulating hydrogen sulfide concentration, and feedstock feed rate. This confirms the formula.

A mixture of styrenes/benzene 20/80 (volume ratio) was used as a raw material, and it was supplied together with hydrogen containing hydrogen sulfide to a reactor filled with an alumina-supported palladium catalyst, hydrogen/feedstock oil = 1/1 (molar ratio), and pressure Hydrogenation was carried out at 60k9/DGl and under the conditions listed in the table.

The conditions of each example and comparative example are also shown in the graph of FIG. The reaction product was analyzed by gas chromatography and the conversion rate was calculated.

The results are also shown in the table. Example 5 A cracked gasoline with a diene number of 2\sulfur content of 240 ppm was used as a raw material oil, and primary hydrogenation was carried out using an alumina-supported palladium catalyst under conditions where the feed rate was kept constant at m = 1/Hr.

Since the hydrogen sulfide concentration in the circulating hydrogen gas was X = 550 ppm (volume), the temperature range at the inlet of the catalyst layer to be adopted was (132 ± 10) °C from the above formula.
It was calculated that

Therefore, when the operation was carried out at a temperature of T=130°C, the diene number of the product decreased to 0.8 or less, and hydrogenation to the benzene nucleus was only a trace (a). 1% or less).

[Brief explanation of the drawing]

FIG. 1 is a flow chart for explaining the aromatic hydrocarbon purification method of the present invention. FIG. 2 is a graph showing the relationship between the central value of the catalyst bed inlet temperature T for primary hydrogenation to be adopted in the refining method of the present invention and the hydrogen sulfide concentration, depending on various feedstock oil supply rates. . 1... Fractionation column, 2... Primary hydrogenation,
3...Secondary hydrogenation.

Claims (1)

[Claims] 1. A feedstock oil mainly composed of C_6 to C_8 aromatic hydrocarbons is first subjected to relatively low-temperature catalytic hydrogenation treatment (primary hydrogenation) using a palladium catalyst to remove diolefins and styrenes therein. These are then removed by hydrogenation of the elements of Group VIB of the periodic table (Cr, Mo,
W) and at least one catalyst selected from the group consisting of iron group elements (Fe, Co, Ni) is subjected to relatively high temperature catalytic hydrogenation treatment (secondary hydrogenation) to sulfurize the contained organic sulfur compounds. After converting into hydrogen, the aromatic components are separated and recovered, and the hydrogen gas containing hydrogen sulfide separated from the reaction product of the secondary hydrogenation can be used as is or with only a portion of the hydrogen sulfide removed. In the method for refining C_6 to C_8 aromatic hydrocarbons, which consists of circulating the hydrogen into the hydrogen and using it in catalytic hydrogenation together with freshly replenished hydrogen, the hydrogen sulfide concentration X (volume p) in the total hydrogen supplied to the primary hydrogenation is
pm), feedstock oil supply rate m to primary hydrogenation (volume per catalyst volume, per hour, and temperature T (
℃), and controlling the other one so that the following relationship is established between the measured value and the other one. T=(2-1/m)(30X+600)^1^/^2±
10 (within the range of 0.8≦m≦5, 50≦T≦200) 2. The refining method according to claim 1, which uses pyrolysis gasoline as the raw material oil. . 3. The purification method according to claim 1, wherein X is controlled in advance within a limit value so that the primary hydrogenation temperature according to the above formula is in the range of 50 to 200°C.