WO2025182551A1 - Method for producing higher silanes - Google Patents

Abstract

To provide a method for producing higher silanes that has high selectivity for disilanes even when a lower silane and a catalyst are reacted for a long time.　The present invention includes a method for producing higher silanes in which a porous oxide and a lower silane are brought into contact to convert the lower silane into a higher silane having more silicon atoms, wherein the higher silanes include disilanes, the estimated reaction time is from more than 200 hours to 10,000 hours, the temperature at which the porous oxide and lower silane are brought into contact is 100-400°C, and the retention time represented by formula (1) is from 5 seconds to less than 80 seconds.　Retention time [sec] = amount of porous oxide [L] × ((pressure [MPaG] + 0.101325)/0.101325) × (273.15/(temperature [°C] + 273.15)) × (3600/amount of gas supplied [NL/h]) … (1) (In formula (1), the amount of porous oxide represents the amount of porous oxide brought into contact with the lower silane, the pressure and temperature each represent the pressure and temperature at which the porous oxide and lower silane are brought into contact, and the amount of gas supplied is the amount of raw material gas containing the lower silane supplied per unit time during contact with the porous oxide.)

Description

Method for producing higher silanes

The present invention relates to a method for producing higher silanes.

With the development of the electronics industry, there has been a rapid increase in demand for silicon-based thin films for semiconductor manufacturing, such as thin films of polycrystalline silicon or amorphous silicon. Higher silanes (Si _n H _2n+2 ; n is an integer of 2 or more), such as monosilane (SiH ₄ ) and disilane (Si ₂ H ₆ ), have recently become increasingly important as raw materials for producing such silicon-based thin films for semiconductor manufacturing, and demand for disilane in particular is expected to increase significantly in the future as a raw material for silicon-based thin films for semiconductor manufacturing, which are becoming increasingly miniaturized.

In the production of silicon-based thin films used in semiconductors and other applications, technology is being developed that will enable stable and efficient production of high-grade silanes on an industrial scale, as well as being economical.

For example, Patent Document 1 discloses a catalyst for producing higher silanes from lower silanes using a catalyst having specific pores, and an example of producing higher silanes by reacting the catalyst with the lower silane for 10 to 200 hours.
Patent Document 2 discloses a production method for producing oligosilanes from hydrosilanes using a continuous reactor equipped with a predetermined catalyst layer, and discloses a production example in which the catalyst layer is reacted with hydrosilane for 1 to 10 hours.

International Publication No. 2015/060189 International Publication No. 2016/027743

In order to stably and efficiently produce disilane on an industrial scale, it is necessary to carry out the reaction continuously while keeping the equipment as small as possible. However, through research by the inventors, they discovered a new problem: when the catalyst and lower silane are reacted continuously for a long period of time, exceeding the reaction times disclosed in Patent Documents 1 and 2, for example, the selectivity for disilane decreases.

In consideration of the above circumstances, the present invention provides a method for producing higher silanes that achieves high selectivity for disilane even when reacting lower silanes with a catalyst for a long period of time.

The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved by providing the following configuration, which has led to the completion of the present invention.
That is, aspects of the present invention relate to, for example, the following [1] to [9].
[1] A method for producing higher silanes by contacting a porous oxide with a lower silane to convert the lower silane into a higher silane having a higher silicon number than the lower silane,
the higher silanes include disilanes;
The cumulative reaction time is more than 200 hours and not more than 10,000 hours,
the temperature at the time of contacting the porous oxide with the lower silane is 100°C or higher and 400°C or lower;
The residence time represented by the following formula (1) is 5 seconds or more and less than 80 seconds.
Methods for producing high-grade silanes.
Residence time [seconds] = porous oxide amount [L] × ((pressure [MPaG] + 0.101325) / 0.101325) × (273.15 / (temperature [°C] + 273.15)) × (3600 / gas supply rate [NL/h]) (1)
(In formula (1), the amount of porous oxide represents the amount of porous oxide to be contacted with the lower silane, the pressure and temperature represent the pressure and temperature, respectively, when the porous oxide is contacted with the lower silane, and the gas supply rate represents the amount of raw material gas containing the lower silane supplied per unit time when contacted with the porous oxide.)
[2] The method for producing higher silanes according to [1], wherein the residence time is 40 seconds or more and less than 80 seconds.
[3] The method for producing higher silanes according to [1] or [2], wherein, before contacting the porous oxide with the lower silane, the temperature of the lower silane is adjusted to 0°C or higher and 30°C or lower, and the pressure of the lower silane after temperature adjustment is increased to set the temperature of the lower silane to 40°C or higher and 200°C or lower.
[4] A method for producing higher silanes according to any one of [1] to [3], wherein the porous oxide has at least regularly arranged pores, is composed mainly of silicon oxide, and has an alkali metal and alkaline earth metal content of 0.00% by weight or more and 2.00% by weight or less.
[5] The method for producing higher silanes according to [4], wherein the pore diameter of the porous oxide is 0.4 nm or more and 0.6 nm or less.
[6] The method for producing higher silanes according to any one of [1] to [5], wherein the porous oxide has a crystalline zeolite structure made of aluminosilicate or metallosilicate.
[7] The method for producing higher silanes according to any one of [1] to [6], wherein the porous oxide is an aluminosilicate and the SiO ₂ /Al ₂ O ₃ molar ratio in the porous oxide is 10 or more and 3,000 or less.
[8] The method for producing higher silanes according to any one of [1] to [7], wherein the porous oxide is MFI-type zeolite.
[9] The method for producing higher silanes according to any one of [1] to [8], further comprising separating and recovering disilanes from the higher silanes.

The present invention provides a method for producing higher silanes that has high selectivity to disilane even when reacting lower silanes with a catalyst for a long period of time.

Furthermore, since disilane can be produced with high selectivity, industrial production of disilane can be carried out efficiently, and even if by-products such as trisilane are not reused, unnecessary waste can be reduced, making disilane economical to produce.

FIG. 1 is a diagram showing a schematic diagram of the production flow of the present invention when monosilane is used as a raw material.

The following describes a preferred embodiment of the present invention. Note that the embodiment described below is an example of a typical embodiment of the present invention, and should not be construed as narrowing the scope of the present invention.

<Method of producing higher silanes>
The present invention provides a method for producing higher silanes, which comprises a step of contacting a porous oxide with a lower silane to convert the lower silane into a higher silane having a higher silicon number than the lower silane,
the higher silanes include disilanes;
The cumulative reaction time is more than 200 hours and not more than 10,000 hours,
the temperature at the time of contacting the porous oxide with the lower silane is 100°C or higher and 400°C or lower;
The residence time represented by the following formula (1) is 5 seconds or more and less than 80 seconds.
This is a method for producing higher silanes.

Residence time [seconds] = porous oxide amount [L] × ((pressure [MPaG] + 0.101325) / 0.101325) × (273.15 / (temperature [°C] + 273.15)) × (3600 / gas supply rate [NL/h]) (1)
(In formula (1), the amount of porous oxide represents the amount of porous oxide to be contacted with the lower silane, the pressure and temperature represent the pressure and temperature, respectively, when the porous oxide is contacted with the lower silane, and the gas supply rate represents the amount of raw material gas containing the lower silane supplied per unit time when contacted with the porous oxide.)

[Porous oxide]
The porous oxide used in the method for producing higher silanes of the present invention is a catalyst that, when in contact with lower silanes, converts the lower silanes into higher silanes having a higher silicon number than the lower silanes.

The porous oxide used in the present invention is primarily composed of silicon oxide, and its content is preferably 60% by weight or more and 100% by weight or less. Components other than silicon oxide that may be included are not particularly limited as long as they are components typically included in catalyst supports, and examples include aluminum oxide, titanium oxide, zirconium oxide, zinc oxide, magnesium oxide, iron oxide, boron oxide, and gallium oxide. These components may be included in a state where they are physically mixed with silicon oxide, or may be included in a state where they are chemically combined (in the form of a composite oxide).

The porous oxide of the present invention, which is primarily composed of silicon oxide, has uniform pores. Uniform pores are those that are regularly arranged, and the diameter of these regularly arranged pores is preferably 0.4 nm or more and 0.6 nm or less. The pore size of the porous oxide can be determined by nitrogen adsorption. In the examples, the values used are those listed in the International Zeolite Association's Atlas of Zeolite Framework Types, Sixth Revised Edition (Elsevier). In cases where there are multiple diameters, and at least one diameter is within the range of 0.4 nm or more and 0.6 nm or less, this is listed.

The pores of the porous oxide, whose main component is silicon oxide, are formed by repeated silicon-oxygen bonds and oxygen bonds with other elements (e.g., aluminum, titanium, zirconium, magnesium, zinc, etc.) that are optionally incorporated into the framework formed by the silicon-oxygen bonds. If the bond configuration is the same, the pore diameter can be expected to be the same. In the present invention, if the number of oxygen atoms is 8 to 12, i.e., an 8- to 12-membered oxygen ring, the pore diameter will be approximately the target size. Therefore, it is preferable that the pores of the porous oxide are pores composed of 8- to 12-membered oxygen rings. Furthermore, if multiple types of rings are present in a single compound, it is preferable that the ring with the greatest number of oxygen atoms is an 8- to 12-membered oxygen ring.

The content of alkali metals and alkaline earth metals contained in the porous oxide used in the present invention is 0.00% by weight or more and 2.00% by weight or less, preferably 0.00% by weight or more, preferably 1.00% by weight or less, and more preferably 0.5% by weight or less. Note that the above values are the content of alkali metals and alkaline earth metals in terms of metals contained in the catalyst, and can be measured by methods such as ICP optical emission spectrometry, ICP mass spectrometry, and atomic absorption spectrometry.

For example, when silicon oxide contained in the porous oxide used in the present invention is produced using a raw material containing silicates such as alkali metal silicates or alkaline earth metal silicates, the raw material contains alkali metals and alkaline earth metals as ions, so the silicon oxide may contain alkali metals or alkaline earth metals. When this silicon oxide is treated with acid, the alkali metal ions or alkaline earth metal ions are removed and replaced with hydrogen ions to maintain electrical neutrality. These hydrogen ions function as a Bronsted acid, and by controlling their amount, it is possible to control not only the acidity distribution but also the acid strength.

As described above, the porous oxide used in the present invention has uniform and regular pores. However, it is preferable that the porous oxide be crystalline and have regularly arranged pores due to its crystalline structure. In this case, it is possible to form crystals from silicon oxide (silicon-oxygen bonds) alone, but if aluminum or other metals are coexistent, the crystals may also be formed by incorporating these metals. Known examples of such crystalline porous oxides containing primarily silicon oxide include aluminosilicates containing aluminum and silicon, and metallosilicates containing silicon and metals other than aluminum (e.g., titanium, zirconium, zinc, iron, boron, gallium, etc.). Among these crystalline silicon oxides, crystalline zeolites are preferred because of their uniform pores.

The crystalline zeolite preferably used as the catalyst of the present invention generally has a composition represented by the following formula (2):
(M ¹ , M ² _1/2 ) _m (Al _m Si _n O _{2 (m+n)} ) xH ₂ O... (2)
In the above formula (2), M ¹ represents an alkali metal ion such as Li ⁺ , Na ⁺ , or K ⁺ or a hydrogen ion, M ² represents an alkaline earth metal ion such as Ca ²⁺ , Mg ²⁺ , or Ba ²⁺ , m and n are integers satisfying n≧m, and x is an integer.

The zeolite has a composition in which the cations ^M1 and ^M2 compensate for the negative charge of the aluminum silicate framework formed by _{AlmSinO2 (m+n)} . The basic unit structure of zeolite is a tetrahedral structure of _SiO4 or _AlO4 , which are connected infinitely in three dimensions to form a crystal. The zeolite _may also have a metallosilicate framework in which at least a portion of the aluminum element in formula (2) is replaced with another element such as zinc, iron, boron, gallium, or phosphorus. Zeolites having a framework in which at least a portion of the silicon element of the zeolite is replaced with another element may also be used.

The above-mentioned zeolites include natural zeolites (natural zeolites), but from the perspective of use as catalysts, highly ordered synthetic zeolites are preferred. Synthetic zeolites are generally produced by hydrothermal synthesis in an alkaline aqueous solution, using water glass, sodium silicate, colloidal silica, etc. as a silica source, mixing this with an alumina source and compounds that serve as oxide sources of elements such as iron, boron, titanium, gallium, and phosphorus. Zeolites produced by hydrothermal synthesis still contain alkali metals such as sodium and potassium, as shown in formula (2) above. Even if lower silanes are brought into contact with this zeolite in this state and a reaction to convert them to higher silanes is carried out, the catalytic activity is low.

In the present invention, as mentioned above, even in the zeolite represented by formula (2) above, all or at least some of the alkali metal ions and alkaline earth metal ions must be replaced with hydrogen ions by ion exchange or the like, so that the alkali metal and alkaline earth metal content is 0.00% by weight or more and 2.00% by weight or less. This is thought to result in the development of acid sites on the surface of the silicon oxide (typically zeolite), which then gives the silicon oxide catalytic activity.

The skeletal structures of the above zeolites are compiled into a database by the International Zeolite Society and are represented by a structural code consisting of three capital letters. Examples of the above zeolites include BEA zeolite, FER zeolite, LTA zeolite, MFI zeolite, MOR zeolite, MWW zeolite, LTL zeolite, FAU zeolite, ERI zeolite, CHA zeolite, and OFF zeolite.

Among the above zeolites, BEA-type zeolite, FER-type zeolite, LTA-type zeolite, MFI-type zeolite, MOR-type zeolite, and MWW-type zeolite are preferred in terms of their favorable conversion reaction of monosilane to higher silanes, including disilane, with MFI-type zeolite being more preferred. These zeolites are presumed to have an appropriate acid distribution and acid strength for the above reaction.

Examples of the BEA-type zeolite include β-type zeolite. Examples of the FER-type zeolite include ferrierite. Examples of the LTA-type zeolite include A-type zeolite. Examples of the MFI-type zeolite include ZSM-5 and TS-1. Examples of the MOR-type zeolite include mordenites. Examples of the MWW-type zeolite include MCM-22. Examples of the LTL-type zeolite include L-type zeolite. Examples of the FAU-type zeolite include X-type zeolite, Y-type zeolite, and faujasite. Examples of the ERI-type zeolite include erionite. Examples of the CHA-type zeolite include chabazite. Examples of the OFF-type zeolite include offretite. Of these zeolites, ZSM-5 and TS-1 are more preferred, with ZSM-5 being especially preferred.

When the porous oxide used in the present invention is a crystalline oxide containing an aluminosilicate or metallosilicate, it is preferable that some or all of the alkali metal ions or alkaline earth metal ions that compensate for the negative charge of the framework in the aluminosilicate or metallosilicate in the porous oxide be substituted with hydrogen ions. The amount of hydrogen ions contained in the aluminosilicate or metallosilicate can be calculated by subtracting the total amount of alkali metal ions and alkaline earth metal ions contained in the aluminosilicate or metallosilicate from the total amount of ions necessary to compensate for the negative charge of the aluminosilicate or metallosilicate framework and maintain electrical neutrality. Because hydrogen ions function as an acid as described above, the calculated amount of hydrogen ions is the amount of acid contained in the porous oxide.

In addition to the above-mentioned ion exchange method, other methods for obtaining crystalline oxides (typically zeolites) containing aluminosilicates or metallosilicates substituted with hydrogen ions include using finely powdered silica, colloidal silica, tetraethoxysilane (TEOS), etc. as a silica source, mixing this with an alumina source such as metallic aluminum, aluminum sulfate, aluminum nitrate, or sodium aluminate, or with compounds that serve as oxide sources of elements such as iron, boron, titanium, phosphorus, and gallium, and adding an organic structure-directing agent such as a quaternary ammonium salt and water to carry out hydrothermal synthesis.

When the silicon oxide contained in the porous oxide of the present invention contains aluminum, typically when it contains an aluminosilicate, the _SiO2 / _{Al2O3 molar} ratio can be any value, but is usually 5 or more, preferably 10 or more, more preferably 20 or more, and usually 5,000 or less, preferably 3,000 or less, more preferably 2,000 or less. Having the _SiO2 / _{Al2O3 molar} ratio within the above range tends to provide an acid strength suitable for the reaction to produce higher silanes such as disilane. The _SiO2 / _{Al2O3 molar} ratio can be determined, for example, by fluorescent X-ray analysis.

As described above, the amount of hydrogen ions can be calculated by subtracting the total amount of alkali metal ions and alkaline earth metal ions contained in the aluminosilicate or metallosilicate from the total amount of ions required to compensate for the negative charge of the framework and maintain electrical neutrality. A specific example of this calculation method will now be described. Consider, as an example, a ZSM-5 zeolite with _{a SiO} /Al _{O molar} ratio of 1500 containing 0.01 wt % Na. The amount of Al contained in 1 g of ZSM-5 zeolite is 83.8 micromoles, which is the total amount of ions required to compensate for the negative charge of the framework and maintain electrical neutrality. Meanwhile, the amount of Na contained in 1 g of ZSM-5 zeolite is 4.3 micromoles. As a result, the amount of hydrogen ions contained in 1 g of ZSM-5 zeolite is calculated to be 79.5 micromoles.

The specific surface area of the porous oxide used in the present invention, as measured by the BET method (source: Science and Applications of Adsorption, by Yoshio Ono and Isao Suzuki, edited by Kodansha Scientific), is preferably 100 m ² /g or more, more preferably 200 m ² /g or more, and is preferably 1,000 ^{m 2} /g or less, more preferably 800 m ² /g or less.

In order to further improve the performance and characteristics of the catalyst, suitable transition metal elements with catalytic function, such as platinum, palladium, ruthenium, rhodium, copper, silver, molybdenum, nickel, iron, and cobalt, may be introduced into the porous oxide used as the catalyst of the present invention as needed, using methods such as ion exchange or impregnation.

If it is necessary to shape the porous oxide, it can be shaped by a variety of methods, either known or equivalent. For example, a suitable binder such as alumina, silica, silica alumina, zirconia, magnesia, titania, or a clay mineral can be mixed with the porous oxide, and the resulting mixture can be shaped by a method such as extrusion molding. Alternatively, the porous oxide can be shaped by compression molding without using a binder. By shaping in this way, it is possible to obtain an appropriate size and shape, which can be adapted to the reaction type and process used to produce higher silanes in the present invention.

[Low-grade silane, high-grade silane]
The lower silanes used as raw materials in the production method of the present invention include monosilane. Higher silanes having a higher silicon number than the lower silanes obtained by the production method of the present invention include silanes such as disilane and trisilane (Si _n H _2n+2 ; n is an integer of 2 or more).

In the manufacturing method of the present invention, the lower silane used as the raw material may be used as is without dilution, or may be diluted with another diluent gas to form a mixed gas. When diluted, the diluent gas is not particularly limited, as long as it is a gas inert to the lower silane, such as nitrogen, hydrogen, argon, or helium. The concentration of the lower silane in the raw material gas is typically 1 vol% or more, preferably 10 vol% or more, and more preferably 20 vol% or more, and is typically 95 vol% or less, preferably 90 vol% or less, and more preferably 80 vol% or less. However, a higher concentration is preferred because it allows for more compact manufacturing equipment. Furthermore, when considering the need to compact manufacturing equipment, the concentration of the lower silane in the raw material gas is preferably 50 vol% or more, and preferably 100 vol% or less. In non-catalytic systems, a method of making hydrogen coexist in the raw material gas is sometimes used to suppress the precipitation of solid silicon, but in the present invention, there is little need to make hydrogen coexist in the raw material gas, and productivity can be improved compared to non-catalytic manufacturing methods, such as by reducing the size of the manufacturing equipment and reducing manufacturing costs.

The lower silanes used in the present invention may contain impurities as long as they are inert to the reaction. However, impurities such as oxygen, carbon dioxide, carbon monoxide, nitrogen-containing compounds such as amines and nitriles, oxygen-containing compounds such as water, alcohols, aldehydes and ketones, olefins such as ethylene and acetylene, and phosphines may inhibit catalytic activity, so it is preferable to reduce their presence as much as possible.

[Contacting Porous Oxide with Lower Silane]
In the production method of the present invention, the contact between the porous oxide and the lower silane is carried out in a reactor containing the porous oxide as a catalyst, for example, as exemplified in FIG.

(temperature)
The temperature at which the porous oxide is brought into contact with the lower silane is usually 100° C. or higher, preferably 120° C. or higher, more preferably 140° C. or higher, and usually 400° C. or lower, preferably 350° C. or lower, more preferably 300° C. or lower, and even more preferably 250° C. or lower. Within this temperature range, the temperature will not be too low to result in an insufficient conversion rate of the raw material lower silane, nor will the reaction temperature be so high that the above-mentioned solid silicon precipitation becomes significant and solid silicon adheres or accumulates on the inner walls and piping of the reactor, making stable operation difficult.

(Residence time)
The residence time is a concept corresponding to the time during which the lower silane contacts the porous oxide, and in the example of FIG. 1 , it indicates the contact time between the porous oxide serving as the catalyst in the reactor and the monosilane raw material introduced into the reactor after temperature and pressure adjustment of any lower silane described below.

The residence time is calculated by the following formula (1).
Residence time [seconds] = porous oxide amount [L] × ((pressure [MPaG] + 0.101325) / 0.101325) × (273.15 / (temperature [°C] + 273.15)) × (3600 / gas supply rate [NL/h]) (1)

In formula (1), the amount of porous oxide refers to the amount of porous oxide brought into contact with the lower silane. In formula (1), the pressure and temperature refer to the pressure and temperature within the reactor when the porous oxide and lower silane are brought into contact, respectively, and can be measured using the respective sensors installed in the reactor. In formula (1), the gas supply rate refers to the amount of raw material gas containing the lower silane supplied per unit time to the reactor when it is brought into contact with the porous oxide, and is measured using a flow meter at the inlet of the reactor. If it is difficult to install a flow meter at the inlet of the reactor, the gas supply rate may be measured using a flow meter installed upstream or downstream of the inlet of the reactor. If the gas supply rate measured using the flow meter is not a value under standard conditions, the gas supply rate may be calculated by converting it to standard conditions based on the measurement conditions. In formula (1), L refers to liters, and NL refers to normal liters.

The residence time is usually 5 seconds or more, preferably 40 seconds or more, more preferably 60 seconds or more, and usually less than 80 seconds, preferably 77 seconds or less, more preferably 75 seconds or less. If the residence time is within this range, the selectivity of disilane can be increased, and the selectivity of trisilane and the like can be lowered, reducing unnecessary waste and increasing the production efficiency of disilane (production amount per unit time).

(pressure)
The pressure when contacting the porous oxide with the lower silane is not particularly limited as long as it satisfies the above-mentioned reaction temperature range and residence time range, but is usually 0.1 MPaG or more, preferably 0.2 MPaG or more, more preferably 0.42 MPaG or more, and usually 1.0 MPaG or less, preferably 0.8 MPaG or less, more preferably 0.6 MPaG or less. Within the above-mentioned lower limit range, the size of the reactor and associated equipment can be reduced, and within the above-mentioned upper limit range, the production of the solid silicon due to high pressure can be suppressed.

(cumulative reaction time)
The cumulative reaction time is the time required from the introduction of lower silanes into a higher silane production apparatus, including a reactor used to contact the lower silanes with the porous oxide, to the separation of the resulting higher silanes, including disilane, in a separator, while the reactor is kept within the above-mentioned residence time, temperature, and, preferably, pressure ranges, after circulating the lower silanes within the production apparatus and continuously contacting them with the porous oxide within the reactor. In other words, the operating time of the production apparatus under these conditions may also include a feed heater, compressor, and feed preheater for adjusting the temperature and pressure of the lower silanes, as described below. For example, in the production flow shown in Figure 1, monosilane is optionally diluted with a diluent gas and introduced into a production apparatus, and then optionally passes through a raw material heater, compressor, and raw material preheater. The monosilane is then brought into contact with a porous oxide in a reactor, unreacted monosilane is recovered in a separator, and the unreacted monosilane, or a mixed gas mixed with optionally added monosilane or diluent gas, is again brought into contact with the porous oxide in the reactor, and this cycle is continuously repeated until the final reaction product, higher silanes including disilane, are separated.

However, if the temperature and pressure inside the reactor are outside the above temperature range, and preferably outside the above pressure range, the time until they are returned to within the above temperature range, and preferably within the above pressure range, is not included in the cumulative reaction time. Furthermore, if contact between the porous oxide and lower silanes inside the reactor is stopped, the time until contact is resumed is not included in the cumulative reaction time. Furthermore, if hydrogen gas or the like is passed through the reactor to perform catalytic activation treatment of the porous oxide in order to remove lower silanes and higher silanes from the porous oxide inside the reactor, the cumulative reaction time is reset to 0 hours.

The cumulative reaction time is usually more than 200 hours, preferably 500 hours or more, more preferably 1,000 hours or more, and usually 10,000 hours or less, preferably 8,000 hours or less, more preferably 6,000 hours or less. If the cumulative reaction time is within the above range, higher silanes can be obtained with high selectivity to disilane for a long period of time.

[Temperature and pressure adjustment of lower silanes]
In the production method of the present invention, it is preferable to adjust the temperature of the lower silane to 0°C or higher and 30°C or lower before contacting the porous oxide with the lower silane, and then increase the pressure of the lower silane after the temperature adjustment to set the temperature of the lower silane to 40°C or higher and 200°C or lower.

The equipment used to adjust the temperature of the lower silanes to between 0°C and 30°C (hereinafter referred to as "temperature adjustment 1") is not particularly limited, but can be, for example, a raw material heater such as a double-pipe heat exchanger. The temperature adjusted in temperature adjustment 1 is usually 0°C or higher, preferably 5°C or higher, and more preferably 10°C or higher, and usually 30°C or lower, preferably 28°C or lower, and more preferably 25°C or lower. The temperature adjusted in temperature adjustment 1 can be measured, for example, with a thermometer installed on the outlet side of the raw material heater. By adjusting the lower silanes to the above temperature range in temperature adjustment 1, it is possible to prevent problems such as equipment freezing in the compressor used to increase the pressure of the subsequent lower silanes due to the temperature dropping below 0°C.

Next, the pressure of the lower silane whose temperature has been adjusted in Temperature Adjustment 1 above is increased (hereinafter, this pressure increase will also be simply referred to as "pressure adjustment"). There are no particular limitations on the device used for pressure adjustment, but a compressor such as a diaphragm compressor can be used, for example. The pressure of the lower silane adjusted by pressure adjustment is typically 0.1 MPaG or higher, preferably 0.2 MPaG or higher, and more preferably 0.42 MPaG or higher, and typically 1.0 MPaG or lower, preferably 0.8 MPaG or lower, and more preferably 0.7 MPaG or lower. The pressure adjusted by pressure adjustment can be measured, for example, with a pressure gauge installed on the outlet side of the compressor. By adjusting the pressure of the lower silane to within the above range by pressure adjustment, raw material supply to the reactor becomes smoother and the contact conditions between the porous oxide and the lower silane in the reactor become easier to control.

Then, the temperature of the lower silane whose pressure has been adjusted by the above pressure adjustment is adjusted to 40°C or higher and 200°C or lower (this temperature adjustment is also referred to as "temperature adjustment 2" hereinafter). There are no particular limitations on the method for adjusting the temperature in temperature adjustment 2, but for example, heating to the desired temperature can be done using a heat exchanger. The temperature of the lower silane adjusted in temperature adjustment 2 is usually 40°C or higher, preferably 80°C or higher, and more preferably 100°C or higher, and usually 200°C or lower, preferably 180°C or lower, and more preferably 150°C or lower. Adjusting the lower silane to the above temperature range in temperature adjustment 2 makes it easier to adjust the temperature of the lower silane introduced into the reactor.

[Manufacturing method]
The production method of the present invention is preferably carried out by a continuous flow system using a fixed bed, fluidized bed, moving bed or the like.

In the case of a fixed bed, it is preferable to continuously pass a lower silane or a mixed gas containing, optionally, a diluent gas through a tubular reactor packed with a porous oxide appropriately shaped as described above. Only one reactor may be used, or when multiple reactors are used, they may be connected in series or in parallel, or a combination of these may be used.

If the conversion rate of lower silanes decreases due to the passage of production time, etc., the conversion rate of lower silanes can be improved by subjecting the porous oxide to catalytic activation treatment. The catalytic activation treatment can be performed by removing the porous oxide from the reactor, or by leaving the porous oxide in the reactor. However, since this simplifies the number of steps, it is preferable to perform the catalytic activation treatment while the porous oxide is still in the reactor. While there are no particular limitations on the method of catalytic activation treatment, it is preferable to stop the flow of lower silanes or a mixture of lower silanes and a diluent gas such as hydrogen gas while the flow of lower silanes is in progress, and then to flow a gas containing hydrogen gas. The gas flowed during the catalytic activation treatment is preferably 100% hydrogen gas, but it may be diluted with an inert gas such as nitrogen or argon, if necessary. The temperature during catalyst activation treatment is not particularly limited, but is preferably 20°C or higher, more preferably 50°C or higher, even more preferably 100°C or higher, and preferably 600°C or lower, more preferably 400°C or lower, and even more preferably 300°C or lower. The pressure during catalyst activation treatment may be reduced pressure, normal pressure, or increased pressure, but is preferably 0.01 PaG or higher and 1.0 MPaG or lower. This catalyst activation treatment restores the catalytic activity of the porous oxide, resulting in an extended catalyst life.

[Separation and recovery]
The reaction product discharged from the reactor may be separated and recovered into unreacted lower silanes and the resulting higher silanes, including disilane, by known methods such as cooling or distillation, or the disilane may be separated and recovered from the higher silanes, including disilane. By separating and recovering the disilanes in this manner, disilane can be obtained efficiently. Furthermore, after separation into unreacted lower silanes and the resulting higher silanes, the lower silanes, which serve as raw materials for the higher silanes, can be recovered and recycled, and reused to produce higher silanes, including disilane.

The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples and can be modified as appropriate within the scope of the present invention.

The concentrations of monosilane, disilane, and trisilane were analyzed using a gas chromatograph. Gas chromatography measurements were performed as follows:

Analysis target: monosilane Analysis equipment: Gas chromatograph GC-8A (Shimadzu Corporation)
Column: Porapak-QS (Waters), length 1 meter, diameter 3 mm
Retention time of the analyte: monosilane = 7.5 minutes Carrier gas: helium (40 ml/min)
Column temperature: 70°C, held for 5 minutes, then increased to 180°C at 16°C/min. Injection port temperature: 200°C
TCD detector temperature: 200°C
TCD detector current: milliamps

Analytical object: disilane, trisilane Analytical equipment: Gas chromatograph GC-2030 (Shimadzu Corporation)
Column: TC-BOND Q (GL Sciences), length 30 m, diameter 0.32 mm
Retention time of analyte: disilane = 5.1 minutes, trisilane = 9.5 minutes Carrier gas: helium (3.4 mL/min)
Column temperature: 70°C
Inlet temperature: 150℃
BID detector temperature: 180°C
BID detector: discharge gas

Quantitative method for raw materials and products: The contents (mol %) of monosilane (MS), disilane (DS), and trisilane (TS) contained in the reacted gas were determined from the results of the gas chromatographic measurements described above. From the MS supply amount per hour (mol/min) and the contents of each of the above components, the amount of DS produced per hour (moles/min equivalent to Si atoms), the amount of TS produced per hour (moles/min equivalent to Si atoms), and the amount of remaining unreacted MS (moles/min equivalent to Si atoms) were determined after the reaction. Note that in no case were any silanes higher than tetrasilane detected.

From these values, the MS conversion rate (mol %), DS selectivity (mol %), and TS selectivity (mol %) were calculated as follows.
MS conversion rate (mol%) = (DS production amount (mol) x 2 + TS production amount (mol) x 3) / MS supply amount (mol)
DS selectivity (mol%) = DS production amount (mol) × 2 / (DS production amount (mol) × 2 + TS production amount (mol) × 3)
TS selectivity (mol%) = TS production amount (mol) × 3 / (DS production amount (mol) × 2 + TS production amount (mol) × 3)

The experimental equipment and production flow used in this invention are shown in Figure 1. The reactor was filled with catalyst, and the reactor was heated to a specified temperature in an electric furnace. The flow rate of the raw material gas was controlled by a mass flow meter.

[Example 1]
A 284 mm inner diameter reactor tube was filled with 132 L of ZSM-5 ( _SiO2 / _{Al2O3 molar} ratio = 1500, Na content [wt%] = 0.01, alkali metals other than Na and alkaline earth metals below the detection limit, pore diameters = 0.51 nm, 0.53 nm, 0.55 nm, 0.56 nm (0.4 nm to 0.6 nm), shape: 3 mm pellets, binder type: alumina), and the catalyst was pretreated by heating at 200°C under a nitrogen flow. A mixed gas of monosilane gas and hydrogen gas (monosilane concentration: 80 vol%) was introduced into the reactor and circulated within the production equipment at 120°C and 0.5 MPaG for 2028 hours to produce higher silanes. The gas supply rate was appropriately controlled with a control valve from the start of the reaction, and the gas supply rate was changed as shown in the table below. The reaction product at the time of 952 hours of cumulative reaction time was introduced online into gas chromatographs GC-8A (manufactured by Shimadzu Corporation) and GC-2030 (manufactured by Shimadzu Corporation), and the contents of monosilane, disilane, and trisilane were determined. Furthermore, no solid silicon deposition was observed visually on the wall surface of the reaction tube. From these values, the results of MS conversion, DS selectivity, TS selectivity, etc., and each condition are shown in Table 1 below. The reactor temperature in Table 1 indicates the temperature at the time the reaction product was obtained.

[Example 2, Comparative Examples 1 and 2, Reference Examples 1 and 2]
The contents of monosilane, disilane, and trisilane were determined, and the MS conversion, DS selectivity, and TS selectivity were calculated in the same manner as in Example 1, except that the conditions were changed to those shown in Table 1. The results are shown in Table 1. No solid silicon deposition was visually observed on the wall surface of the reaction tube.

Claims (9)

1. A method for producing higher silanes, comprising contacting a porous oxide with a lower silane to convert the lower silane into a higher silane having a higher silicon number than the lower silane,
the higher silanes include disilanes;
The cumulative reaction time is more than 200 hours and not more than 10,000 hours,
the temperature at the time of contacting the porous oxide with the lower silane is 100°C or higher and 400°C or lower;
The residence time represented by the following formula (1) is 5 seconds or more and less than 80 seconds.
Methods for producing high-grade silanes.
Residence time [seconds] = porous oxide amount [L] × ((pressure [MPaG] + 0.101325) / 0.101325) × (273.15 / (temperature [°C] + 273.15)) × (3600 / gas supply rate [NL/h]) (1)
(In formula (1), the amount of porous oxide represents the amount of porous oxide to be contacted with the lower silane, the pressure and temperature represent the pressure and temperature, respectively, when the porous oxide is contacted with the lower silane, and the gas supply rate represents the amount of raw material gas containing the lower silane supplied per unit time when contacted with the porous oxide.) The method for producing higher silanes described in claim 1, wherein the residence time is 40 seconds or more and less than 80 seconds. The method for producing higher silanes described in claim 1, wherein the temperature of the lower silane is adjusted to between 0°C and 30°C before contacting the porous oxide with the lower silane, and the pressure of the temperature-adjusted lower silane is increased to set the temperature of the lower silane to between 40°C and 200°C. The method for producing higher silanes according to claim 1, wherein the porous oxide has at least regularly arranged pores, is composed primarily of silicon oxide, and has an alkali metal and alkaline earth metal content of 0.00% by weight or more and 2.00% by weight or less. The method for producing higher silanes described in claim 4, wherein the pore diameter of the porous oxide is 0.4 nm or more and 0.6 nm or less. The method for producing higher silanes according to claim 1, wherein the porous oxide has a crystalline zeolite structure made of aluminosilicate or metallosilicate. 2. The method for producing higher silanes according to claim 1, wherein the porous oxide is an aluminosilicate, and the _SiO2 / _{Al2O3 molar} ratio in the porous oxide is 10 or more and 3,000 or less. The method for producing higher silanes according to claim 1, wherein the porous oxide is MFI-type zeolite. The method for producing higher silanes described in claim 1 further comprises separating and recovering disilanes from the higher silanes.