JPH0362753B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for efficiently liquefying coal by a direct hydrogenation liquefaction method, particularly a two-stage hydrogenation method, and more specifically, a method for efficiently liquefying coal by increasing the deashing efficiency of solvent refined coal (SRC) after primary hydrogenation. The present invention relates to a coal liquefaction method that incorporates deashing technology that effectively brings out the effects of secondary hydrogenation. This type of deashing technology includes (1) mechanical separation methods such as filtration, centrifugation, gravity sedimentation, and distillation;
(2) Two types of solvent separation methods are known in which a special solvent is added to accelerate the sedimentation rate. However, after comprehensively evaluating both deashing efficiency and equipment economy, it was determined that the solvent separation method is more advantageous, and the solvent separation method is now becoming the mainstream in the development of deashing technology. Representative examples of those that have already been developed include Lummus' anti-solvent method and Kerr-McGee's anti-solvent method.
Critical Solvent Method
solvent method). First, in the anti-solvent method, the high-boiling fraction of the primary hydrogenated solvent is used to dissolve
A petroleum-based deashing solvent (anti-solvent) with a boiling point of 170 to 400°C is mixed with the SRC solution, and after it is sufficiently dissolved, it is sent to a sedimentation tank where it settles and separates.The purified SRC solution is collected from the top, and the sludge and ash are collected from the bottom. The solutions rich in SRC are separated and sent to a distillation column for rectification and separated into solvent, purified SRC and demineralized sludge. However, this process is characterized by the use of a petroleum-based deashing solvent with a relatively high boiling point, and because it employs a solvent separation method by distillation, there are problems with economic efficiency and the amount of solvent used is limited. There are limits of course. Therefore, the viscosity of the solution in the sedimentation tank is higher than that in the critical solvent method described below, which results in a lower sedimentation rate of the sludge and a disadvantage that the apparatus becomes larger. Furthermore, since petroleum-based solvents are used, there is a problem in that there are restrictions on where commercial plants can be constructed. On the other hand, in the critical solvent method, a monocyclic aromatic compound such as pyridine, benzene, or toluene is used as a deashing solvent, and the ash is separated by precipitation near the critical point of the solvent, and then the temperature and pressure conditions of the solution are adjusted. By adjusting the temperature to the critical point, the solvent can be separated and recovered without imparting latent heat of vaporization. This process has the advantage that solvent recovery does not require large amounts of energy, so large amounts of solvent can be used. Moreover, because the solvent itself has a low molecular weight and the deashing operation is carried out at a high temperature close to the critical temperature, the settling speed of the sludge in the settling tank is extremely fast, and the settling tank is also extremely small. There are advantages to being able to do so. However, due to the characteristics of the process, the residual amount of asphalt in the deashing SRC increases, which reduces the efficiency of secondary hydrogenation, and makes it difficult to adjust the temperature and pressure at the critical point as described above. The effects of the two-stage hydrogenation method have not yet been effectively demonstrated. Furthermore, in any of the above methods, a portion of the SRC is lost along with the separated sludge, which poses a problem in terms of yield. The present invention was developed in view of these circumstances, and its purpose is to be able to increase the separation and sedimentation rate without any particularly difficult operations, and at the same time, it is difficult to perform secondary hydrogenation, such as with asphaltenes. large molecular weight substances (fused polycyclic aromatic compounds, etc.)
The purpose of the present invention is to provide a coal liquefaction method that incorporates deashing technology that enables the separation of coal, facilitates secondary hydrogenation, and effectively exhibits the effects of the two-stage hydrogenation method. However, the coal liquefaction method of the present invention that has achieved these objectives involves subjecting the slurry obtained by mixing raw coal with a solvent to primary hydrogenation at high temperature and pressure in the presence of a catalyst. , the SRC obtained here is
In the coal liquefaction method for obtaining light oil by removing the ash content in the SRC by sedimentation in a solvent, and then subjecting it to secondary hydrogenation in the presence of a metal catalyst with high hydrogenation separation ability and under high temperature and high pressure. The key point lies in the recycling and use of the naphtha fraction distilled at a temperature of 180°C or less among the fractions obtained by distilling the primary hydrogenated product as a solvent to be added to the ash removal process during SRC. do. The configuration and effects of the present invention will be clarified below based on the flowchart showing the examples, but the scope of application and embodiments of the present invention will not be limited by these explanations, and the purpose of the above and below will not be limited. All modifications that do not violate the scope of the present invention are included in the technical scope of the present invention. Figure 1 is a block flow diagram showing an outline of the process of the present invention, with square frames representing processing details and parentheses representing substances. That is, a slurry obtained by mixing raw coal such as lignite with a solvent is preheated as necessary and subjected to primary hydrogenation at high temperature and pressure in the presence of a catalyst. The type and amount of slurry-forming solvent, preheating and
The conditions for the subsequent hydrogenation reaction, the type and amount of the catalyst, etc. are not limiting requirements of the present invention. After primary hydrogenation is carried out,
If necessary, gas-liquid separation is performed under reduced pressure, followed by distillation (1), in which the equilibrium solvent is recovered,
At the same time as SRC is produced, naphtha (generally a mixed oil consisting of aromatic compounds, naphthenes, paraffins, etc. having a boiling point of 180°C or less) is obtained. Conventionally, this naphtha was simply recovered as a product, but the key point of the present invention is that a portion of it is recycled and used as a deashing solvent. That is, as mentioned above, the SRC obtained by distillation (1) contains ash, which has a negative effect on the efficiency of secondary hydrogenation, so research on deashing technology as mentioned above is being carried out. The present invention is based on a method of sedimentation separation of ash in a solvent, and a part of the naphtha obtained in distillation (1) is added to SRC as a deashing solvent.
In addition, when performing distillation (2) again after deashing and adding a step to recover the naphtha added during deashing, the recovered naphtha can be supplied to the deashing process as a deashing solvent, and the A closed system as shown by arrow A is formed. Therefore, in the actual operation of this process, it is necessary to initially supply the deashing solvent only with the naphtha obtained from distillation (1), but once a certain running state is reached, the closed system A
Distillation (1)
The supply of naphtha from can be considered as mere replenishment. The conditions for distillation (1) and distillation (2) do not need to be interpreted in a restrictive manner in the present invention, and any method may be used as long as it is a method that can efficiently recover naphtha components with a boiling point of 180°C or less. However, as can be understood from FIG. 1, it is desirable that the product can be fractionated into at least a naphtha fraction (low temperature fraction), an equilibrium solvent (medium temperature fraction), and SRC (high temperature fraction). Further, there are no particular restrictions on demineralization conditions, but after various studies, the following condition range can be recommended as the optimum range. Temperature: 150 to 400°C, more preferably 280 to 350°C Pressure: 20 to 60 Kg/cm ² Amount of deashing solvent: 2 to 20 times the amount of SRC, more preferably 2.5 to 4 times (weight ratio) Above recommended range This does not mean that it is impossible to carry out the present invention even if the temperature and pressure are outside the range, but due to the relationship between temperature and pressure, deashing is carried out near the critical point of the solvent, and the solution is removed during distillation (2). It is best to employ a combination of adjusting the temperature and pressure to a critical point and recovering the solvent. However
At temperatures below 150℃ and pressures above 60Kg/ ^cm2 , the settling speed of the sludge in the settling tank becomes slow;
If it is less than 20 Kg/cm ² , there is a tendency that convection of the solvent occurs and prevents the settling of the sludge. In addition, if the amount of deashing solvent is less than twice the amount of SRC, it will be treated as sludge.
Separation of SRC is insufficient, and conversely, even if the separation capacity exceeds 20 times, the separation ability between the two will not be improved any further, and the cost of recovering naphtha in distillation (2) will only increase, which is not desirable. Next, the hydrogenation conditions are not a limiting requirement of the present invention, but include the properties of the coking coal, the type and amount of the equilibrium solvent, the consumption of _H2 ,
Various considerations should be made, taking into account the type of catalyst, etc.
Typical conditions are as follows. <Primary hydrogenation> Temperature: 430~480℃ Pressure: 150~280Kg/ ^cm2G Catalyst: Fe ₂ O ₃ Hydrogenation degree: 3~4% <Secondary hydrogenation> Temperature: 400℃ or less Pressure: 150~ 280 Kg/cm ² G Catalyst: Metal catalyst such as Co-Mo type or Ni-Mo type Hydrogenation degree: 3 to 4% Next, examples of the present invention will be described. 15% by weight in SRC obtained by primary hydrogenation
In cases where a considerable amount of ash is contained, this
Naphtha was obtained by introducing SRC into a 50 mm diameter settling tank and distilling it at 180°C in distillation (1) or distillation (2) (the distillation curve of this naphtha is as shown in Figure 2; Distillate up to 180℃)
was added in an amount four times that of SRC (weight ratio), and deashing was carried out at a temperature of 300°C, a flow rate of 70/hr, and a sedimentation rate of 61 cm/min. For comparison, deashing was carried out under the same conditions by replacing naphtha with toluene, benzene, and kerosene (all reagents). The amount of ash contained in SRC after deashing was as shown in Table 1.

[Table] That is, in the case of using naphtha, the deashing efficiency has been sufficiently improved, and this greatly contributes to improving the secondary hydrogenation efficiency. In particular, the fact that the ash content is reduced by 200 ppm compared to toluene, benzene, or kerosene is effective for separating benzene-insoluble components and hexane-insoluble components (including fused polycyclic aromatic compounds such as asphaltene). This means that, from this point of view, it greatly contributes to improving the secondary hydrogenation rate. Since the present invention is configured as described above, the product produced during the process can be used cyclically as a deashing solvent, which not only reduces running costs but also improves the deashing efficiency during SRC. Moreover, it was possible to contribute to improving the secondary hydrogenation efficiency.

[Brief explanation of drawings]

FIG. 1 is a block flow diagram showing the process of the present invention, and FIG. 2 is a diagram showing the distillation curve of naphtha used in the present invention.

Claims (1)

[Claims] 1. A slurry obtained by mixing raw coal with a solvent is subjected to primary hydrogenation at high temperature and pressure in the presence of a catalyst, and the ash content in the solvent-refined coal is removed from the solvent. After sedimentation and removal in
In the method of liquefying coal to obtain light oil by subjecting it to secondary hydrogenation, 180% of the fraction obtained by distilling the primary hydrogenation product is used as the solvent added in the ash removal step from the solvent-refined coal. A coal liquefaction method characterized by recycling naphtha fraction distilled at temperatures below ℃.