Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
  • C01B33/021—Preparation
  • C01B33/023—Preparation by reduction of silica or free silica-containing material
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F5/00—Compounds of magnesium
  • C01F5/02—Magnesia
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F5/00—Compounds of magnesium
  • C01F5/02—Magnesia
  • C01F5/04—Magnesia by oxidation of metallic magnesium
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/12—Surface area

Definitions

• the invention relates to processes for the production of silicon by means of magnesiothermic reduction of silica.
• Silicon is part of a wide variety of products with great economic growth potential, especially in the electronic field, for example in semiconductors, lithium-ion batteries or solar cells, so that the demand for silicon is steadily increasing. Therefore, there is a continuing need to further improve processes for producing silicon.
• An established chemical method for obtaining silicon is the reduction of silica with magnesium (magnesiothermic reduction), which is illustrated by the following reaction scheme:
• Chlorides, sulfides or nitrates Chlorides, sulfides or nitrates. Highlighted inert materials are sodium chloride or alternatively magnesium oxide, for example, in a proportion of 72 wt .-% (MgO, Riedel-de-Haen # 13138, BET: 42 m 2 / g) and 65 wt -.% (NaCl) on the Starting mixture are used.
• WO 2011/042742 Al recommends sodium chloride or alternatively Calcium chloride as moderators for the reduction of Si0 2 with magnesium.
• the invention relates to processes for the production of silicon by means of magnesiothermic reduction of silicon dioxide, characterized in that a mixture (educt mixture) is used for magnesiothermic reduction comprising silica (Si0 2 ), magnesium (Mg) and magnesium oxide (MgO) as moderator a BET surface of ⁇ 40 m 2 / g.
• the silica may be in amorphous or crystalline form. It can be of synthetic or natural origin. Examples of silica are fumed silica, precipitated silica, quartz, tridymite, christobalite, diatomaceous earth or silica-bonded SiO 2 , such as forsterite or enstatite. Preference is given synthetic, amorphous silicic acids, fumed silica is particularly preferred.
• the volume-weighted particle size distribution D 50 of the SiO 2 particles is, for example, 10 nm to 500 ⁇ m, preferably 100 nm to 100 ⁇ m and particularly preferably 500 nm to 50 ⁇ m (determination method: static Li scattering, measuring instrument Horiba LA 950, water as dispersion medium ).
• the specific surface area (BET) of Si0 2 is, for example, 1 to 500 m 2 / g, preferably 10 to 300 m 2 / g and particularly preferably 15 to 200 m 2 / g (determined according to DIN 66131 (with nitrogen), for example with Measuring device Sorptomatic 1990 of the company Porotec).
• Magnesium can be used, for example, in the form of wire, preferably in the form of chips, and more preferably in the form of powder. the.
• the particle size of the magnesium is for example 1 ⁇ to 10 mm, preferably 5 to 5 mm and more preferably 10 ⁇ to 500 ⁇ .
• the stoichiometric ratio of silica to magnesium (SiO 2 / Mg) in the educt mixture is preferably from 0.3 to 1, more preferably from 0.4 to 0.7, and most preferably from 0.4 to 0.6.
• the magnesium oxide which is contained in the reactant mixture is also referred to below as a moderator.
• the magnesium oxide used as a moderator may be of natural or synthetic origin.
• the volume-weighted particle size distribution D 50 of the MgO particles is for example 1 ⁇ to 1 mm, preferably 5 ⁇ to 500 ⁇ and more preferably 10 ⁇ to 200 ⁇ .
• the specific surface area (BET surface area) of magnesium oxide is 40 m 2 / g, ⁇ preferably 35 m / g, more preferably ⁇ 30 m 2 / g, particularly be ⁇ vorzugt ⁇ 25 m 2 / g, and most preferably ⁇ 20 m 2 / g.
• the BET surface area of the magnesium oxide is preferably> 0.01 m 2 / g.
• the BET surface area is determined in accordance with DIN 66131 (with nitrogen), for example with the Sorptomatic 1990 measuring instrument from Porotec).
• the bulk density of the magnesium oxide is preferably 0.05 to 3 g / cm 3 , more preferably 0.08 to 2.5 g / cm 3 and most preferably 0.1 to 2 g / cm 3 (determined according to DIN ISO 697).
• the magnesium oxide has a purity of preferably about 85% by weight, more preferably> 90% by weight, most preferably 95% by weight.
• the purity is determined by means of ICP (inductively coupled plasma) emission spectrometry (Optima 7300 DV, Perkin Elmer).
• the magnesium oxide is digested acidic.
• the ICP determination is based on ISO 11885 Water quality - Determination of inductively coupled plasma atomic emission spectrometry (ICP-OES) (ISO 11885: 2007); German version EN ISO 11885: 2009.
• “Other moderators” may be used in addition to magnesium oxide, examples of further moderators are (earth) alkali halides, such as sodium chloride or calcium chloride, or magnesium oxide with non-inventive BET surface area 60% by weight, more preferably 80 80% by weight and particularly preferably 90 90% by weight of magnesium oxide, based on the total weight of the moderators Any other moderators are in the starting material mixture, for example, at 40% by weight, preferably 20% by weight % and more preferably ⁇ 10% by weight, based on the total weight of the moderators, Most preferably, in addition to magnesium oxide, no further moderators are used.
• Silicon dioxide and magnesium are also collectively referred to as reactants.
• the weight ratio of the reactants to the moderator is preferably 0.05 to 1, more preferably 0.2 to 0.7, and most preferably 0.3 to 0.6.
• the educt mixture may contain further optional constituents, for example dopants, such as diborontrioxide. In the course of the magnesiothermal reduction, for example, diboron trioxide can be reduced to elemental boron and serve as a dopant for the resulting silicon.
• the proportion of optional constituents is for example up to 5 wt .-%, preferably 1 ppb (parts per billion) to 5 wt .-%, based on the total weight of the educt mixtures.
• the silica and the magnesium may be separately or preferably in the form of a mixture be used.
• the moderator may be added to a mixture of silica and magnesium, or preferably mixed together with silica and magnesium.
• Silicon dioxide, magnesium and the magnesium oxide used as a moderator are thus generally mixed prior to carrying out the magnesiothermic reduction, that is generally mixed before introduction into the reactor.
• the mixing is preferably carried out at ambient temperature, for example at room temperature, more preferably at 15 to 35 ° C. In any case, the mixing is carried out at temperatures of preferably ⁇ 400 ° C, more preferably 390 ° C and more preferably ⁇ 350 ° C.
• mixers customary therefor, in particular industrial mixers.
• mixers are free-fall mixers, such as container mixers, cone mixers, drum roll mixers, wheel mixer mixers, tumble mixers or push and throw mixers, such as drum mixers and screw mixers.
• suitable mixers are given in "Blending of Solids" by R. Weinekotter and H. Gericke, Springer 1995.
• the magnesiothermic reduction can be carried out in conventional reactors, in particular furnaces, such as, for example, tube furnaces, rotary kilns, chamber furnaces, belt furnaces or furnaces.
• the reactors can be operated batchwise or continuously.
• the reactors may be cooled in a conventional manner. In general, however, the reactor is not cooled.
• the educt mixtures can be introduced into the reactors, for example in the form of pellets, granules or preferably in the form of powder beds.
• the magnesiothermic reduction is preferably carried out at 400 to 1200 ° C, more preferably at 500 to 1100 ° C and most preferably at 600 to 1050 ° C.
• the magnesiothermic reduction is generally initiated thermally, that is to say by heating the educt mixture to a temperature within the aforementioned temperature range.
• the pressure in the reactor is preferably 0.5 to 10 bar abs ., More preferably between 0.7 to 5 bar abs. and most preferably between 0.8 to 1.5 bar abs,.
• the magnesiothermic reduction is preferably under a
• Inert gas atmosphere in particular under an argon atmosphere or an argon / hydrogen atmosphere, in particular with a hydrogen content of - ⁇ 5 vol .-% performed.
• the residence time of the mixture in the reactor is preferably 1 second to 12 hours, more preferably 1 second to 6 hours, and most preferably 1 second to 3 hours.
• the mixture leaving the reactor generally contains silicon, magnesium oxide and optionally one or more further constituents, such as magnesium silicate, magnesium silicide or optionally boron.
• additional constituents such as magnesium silicate, magnesium silicide or optionally boron.
• unreacted educts may also be present, such as magnesium, silicon dioxide or, if appropriate, titanium. boron trioxide.
• the product mixture preferably contains from 1 to 40% by weight, more preferably from 2 to 35% by weight, and most preferably from 5 to 30% by weight.
• Silicon preferably 45 to 99 wt .-%, particularly preferably 50 to 96 wt .-% and most preferably 55 to 94 wt .-% of magnesium oxide, preferably 0 to 40 wt .-%, particularly preferably 0 to 30 wt. %, and most preferably 0 to 20% by weight of other ingredients, wherein the data in% by weight each relate to the total weight of the product mixture and add up to 100% by weight for each product mixture.
• the work-up of product mixtures can be carried out, for example, by adding one or more acids.
• acids are hydrohalic acids, such as hydrochloric acid or hydrofluoric acid, carboxylic acids, such as acetic acid, or oxygen acids of phosphorus, such as phosphoric acid. Preference is given to acetic acid or hydrochloric acid. When using several acids, these can be used as a mixture or preferably nachei- each other.
• the workup can therefore also be carried out in two stages with different acids, for example by a first acid treatment with hydrochloric acid and a second treatment with hydrofluoric acid.
• the acids are preferably incorporated in the form of sets ⁇ w ssrigen solutions.
• the concentration of the acids used is preferably 0.01 to 10 mol / L, more preferably 0.1 to 8 mol / L, most preferably 1 to 5 mol / L.
• the molar ratio of the protons of the acids to the magnesium oxide of the product mixture to be worked up is preferably at least 2 to 1.
• the silicon thus obtained can be dried, for example at temperatures from 0 ° C to 200 ° C, preferably at 20 ° C to 150 ° C and particularly preferably at 40 ° C to 100 ° C.
• the pressure during drying is preferably from 0.01 to 1 bar abs . and preferably 0.1 to 0.5 bar abs .
• the product thus obtained preferably contains from 50 to 100% by weight, more preferably from 60 to 100% by weight and most preferably from 70 to 100% by weight of silicon, based on the total weight of the product.
• the silicon produced according to the invention can be used in all common applications for silicon, for example in electronic Applications. Particularly noteworthy here are semiconductors, solar cells, thermoelectric generators and in particular as an active material for lithium-ion batteries.
• magnesium oxide according to the invention as a moderator in the magnesiothermic reduction of its heat of reaction and thus the process can be controlled - and this even when carrying out the process on an industrial scale.
• the use of magnesium oxide with BET surface according to the invention leads to higher silicon yields. Fortunately, the formation of the by-product magnesium silicate was pushed back and sales of educts were increased.
• magnesia oxide used as a moderator chemically corresponds to the by-product of the magnesiothermic reduction, so that the moderator can be separated together with the magnesium oxide formed during the reaction without a separate washing step being necessary for separating the moderator ,
• the calculation of the product compositions was prepared starting from the element contents (Si, O, Mg) under the over XRD demonstrated he ⁇ filled constraint that magnesium oxide was tung completely removed in the aqueous workup and the isolated product of Si (0) Mg 2 Si0 4 and Si0 2 was composed.
• the Mg content of the isolated product was used to calculate the magnesium silicate content and, consequently, the Si0 2 and Si (0) contents of the isolated product.
• the amount of MgO present before the aqueous work-up was determined via the dissolved amount of magnesium in the filtrate of the washing solution.
• magnesium oxide according to the invention as moderator (Examples 3 and 4)
• significantly higher yields of elemental Si (O) were obtained, based on the silicon used in the form of SiO 2 , and the proportion of by-product was markedly reduced.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Silicon Compounds (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Silicates, Zeolites, And Molecular Sieves (AREA)

Applications Claiming Priority (2)

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• 2016
  • 2016-02-24 DE DE102016202889.8A patent/DE102016202889A1/de not_active Withdrawn
• 2017
  • 2017-02-15 CN CN201780013193.6A patent/CN108778995A/zh not_active Withdrawn
  • 2017-02-15 KR KR1020187027531A patent/KR20180116373A/ko not_active Application Discontinuation
  • 2017-02-15 US US16/077,502 patent/US20190031516A1/en not_active Abandoned
  • 2017-02-15 JP JP2018544471A patent/JP2019506360A/ja not_active Withdrawn
  • 2017-02-15 WO PCT/EP2017/053427 patent/WO2017144328A1/de active Application Filing
  • 2017-02-15 EP EP17707491.1A patent/EP3419933A1/de not_active Withdrawn

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