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
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/90—Carbides
  • C01B32/914—Carbides of single elements
  • C01B32/956—Silicon carbide
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28D—WORKING STONE OR STONE-LIKE MATERIALS
  • B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
  • B28D5/0058—Accessories specially adapted for use with machines for fine working of gems, jewels, crystals, e.g. of semiconductor material
  • B28D5/007—Use, recovery or regeneration of abrasive mediums
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working

Definitions

• the invention ' relates to a non-chemicai method and a system for recovering silicon carbide (SiC particles and glycol, and- in- particular, to a non-chemicai method and a system for recovering SiC particles and glycol that have been used in suspension in a cutting medium for the cutting or sawing, of silicon wafers for solar cells and electronic objects often called slurry.
• particles of silicon carbide (SiC) of specific grit sizes such as FEPA classes F500, P60O, and F800, are dispersed in an organic liquid, thus forming a suspension, which is used as a cutting medium, or slum'.
• Common dispersing agents -are -organic giycolic liquids such as polyethylene glycol (PEG), dipropylene glycol (DPG), diethylene glycol (D-EG-), and propylene glycol (PG).
• surfactants that reduce surface tensions are added to the slurry * .
• the sawing is usually conducted by a wire saw, wherein the abrasive slurry is earned by a thin, hardened iron wire with brass on the surface, towards the "sawing z mT where it performs its "cut grinding '' ' process and cuts the silicon (Si) block into a series of thin wafers.
• the slurr ' becomes contaminated with Si from the Si block, iron (Fe) ' from the cutting wire, and SiC lines (i.e. fine particles) -from the breaking down of abrasive grains.
• the Si wafers are used for the manufacture of electronic or microelectronic devices, or for the .manufacture of solar cell panels for the production of electr ic power.
• the cleanliness requirement of these Si wafers is typically so high that, 5» practice, only Si free and Fe free slurry have been used for the cutting.
• the requirement for particle size distribution is precisely specified in. order to obtain smooth surfaces on the Si wafers. SiC particles for sawing lies within a narrow grain size range, i.e. that there is little or minimal difference between the size of the largest and the smallest grains .
• the properties of the glycol are also precisely specified in order to ensure a consistent sawing performance from the start to the end of the sawing process..
• FEPA FS00, F600 and F800 microgrits are commonly used in. the sawing of Si. wafers and it is important that the grains of SiC conform to the standards of harrow particle size distribution, and low impurity levels- to obtain a good result.
• the conventional practice is to dilute the slurry with large quantity of water and separate the solid and liquid fractions by physical means.
• the solid fraction consisting of SiC particles, SiC fines, Si and Fe particles* is first cleansed by centrifugal separation process, which makes use of the fact that the SiC particles have larger diameters than the contaminants of SiC fines, Fe and Si.
• This step is capable of achieving the narrow particle size distribution requirement, hut is usually unable to meet the low impurity levels. This is especially prevalent with smaller SiC grit sizes such as F800, where the SiC particles are much closer in diameter to the contaminants, hence making it more difficult to separate, Therefore, ⁇ a chemical treatment step is required, in which caustic soda and acid -are used to chemically reduce Si and Fe respectively to the required levels.
• the liquid fraction consisting of glycol, water, fine particles and dissolved ions, is recovered through a series of processes— filtration, colour removal (using chemicals directly), deionizaiion (using , chemicals indirectly), and evaporation.
• the use of chemicals in the recycling process not just adds to the cost, but also presents an environmental problem in terms of disposal.
• a method for recovering silicon carbide (SiC) particles and glycol from a slurry wherein the slutty comprises a mixture of SiC, Si, and Fe particles suspended in glycol, by physically removing fine grain, particles.
• the method may include: separating in a slurry filter press the .slurry into a first, solid phase stream and a first liquid phase stream, wherein the first solid phase stream comprises essentially the SiC, Si, and Fe particles and wherein the first liquid phase stream comprises essentially glycol, water, suspended fine particles, and dissolved ions;
• liquid purification stage comprises:
• a system for recovering silicon carbide (SiC) particles and glycol from a starry wherein the slurry comprises a mixture of SiC, Si, and Fe particles suspended in glycol.
• the system may include: a slurry filter press for separating the slurry into a first solid phase stream and a first liquid phase stream, wherein the first solid phase stream comprises essentially the SiC, Si, and F particles and wherein the first liquid phase stream comprises essentially glycol, water, suspended fine particles, and dissolved ions;
• the solid purification stage comprises:
• hydrocyelone system to obtain an underflow stream comprising recovered SiC particles in water and an overflow stream comprising essentially fine particles of SiC, Si and Fe suspended .in water, wherein the hydrocyelone system comprises one or more hydroeyations;
• liquid purification stage comprises:
• a water distillation column t obtain, a first residue and a first distillate comprising water; and a glycol distillation, column to obtain a second distillate comprising glycol.
• Figure 2 A shows a SEM (2000x magnification) of the recycled F50O grit size SiC particles recovered from present method according- t the operating conditions given in Table 1. la this ease. Si content is about 0, 13 wt% and e content is -about 0,05 wt%.
• FIG. 2B shows a SEM (2000x magnification) of the recycled JIS2000 grit size SiC particles recovered from present method according to. the operating conditions given in Table 1, In this case, Si content is about 0.43 wt% and Fe content is about 0.63 wt%.
• Figure 2C shows a SEM (2000x magnification) of the recycled F80G grit size: SiC particle recovered from presen method according to the operating conditions given- in Table 1. In this case. Si content is about 0.14 wt -and Fe content is about 0,65 wt%.
• Figure 3 shows a photograph of the product glycol, specifically, PEG,. DPG, DEG, and PG, .recovered by the present liquid purification stage.
• the : method allows recovery of SiC of a narrow grain size range by physically removing (i.e. without involving use of chemicals) from the SiC particles smaller particles such as, but not limited to, iron (Fe), silicon (Si) and SiC fines.
• the method also allows recovery of glycol properties to its desired levels by means of distillation (i.e. again without involving the use of chemicals).
• the method and system can. be applied cost-effectively on an industrial scale and at the same time have minimal negative impacts on the environment.
• FEPA Federation of European Producers of Abrasives
• microgrits are obtainable.
• FEPA is the- international standard to which these kinds of materials- have to comply.
• the relevant, standard - is FEPA standard 42-6B 1 84, R 1 93. (The same definition is incidentally defined fay ISO 6344-3 1 68, part 3;.
• a method for recovering silicon carbide (SiC) particles and glycol from a slurry wherein the slarry comprises a mixture of StC, Si, and Fe particles suspended in glycol.
• the method comprises die following steps: separating in a slurry filter press the slurry into a first solid phase stream and a first liquid phase stream, wherein the first solid phase stream comprises essentially the SiC, Si, and Fe particles and wherein the first liquid phase stream comprises essentially glycol, water, suspended fine particles, and dissolved ions;
• treating the first liquid phase stream, to a liquid purification stage comprises: feeding the firSi liquid phase stream to a water distillation column to obtain a. first residue and a first distillate comprising water;
• Used slurry which is essentially made up of the solid particles suspended in glycol, is fil tered to separate the solid stream from the liquid stream. Water may be added to the used slurry for dilution before tire separation.
• diluted used slurry is separated into solid and liquid i a slurry filter press.
• Pressure filtration, improved cake washing and air blowing help to enhance tlie solid- liquid separation, achieving low water content -and trace glycol (as the organic liquid medium) levels in the solid content.
• the solid phase, stream may include essentially the SiC. Si, and Fe particles.
• The. liquid phase stream may include essentially glycol, water, suspended fine particles and dissolved ions. This liquid stream is further purified in a separate sequence of liquid purification steps to be. described later,
• Water may be added to the solid phase stream obtained from the slurry filter press to obtain a suspension of SiC, Si, and Fe particles of a predetermined solid-liquid ratio.
• the suspension of SiC* Si, and Fe particles is then fed to a hydrocyclone system to obtain an underflow stream and. an. overflow stream.
• Hydrocyclone is a form of wet centrifugal separation ⁇ f the particles into coarse and fine .fractions.
• the feed enters the h drocyciofle &nge3 ⁇ 4tiafly s after which the heavy or coarse particles start to spiral down the conical bottom section and leaves as an "underflow".
• the fine fraction leaves via the to section of the hydrocycione as an. "overflow",
• the hydrocycione system may include one or more hydrocyelones.
• 0033j The hydrocycione system may include one or more hydrocyelones.
• the hydrocycione system may include 4 to 8. hydrocyations.
• the hydrocy graduates may be connected in series. Other forms of connecti on of the hydioeyclones. may also be possible.
• hydrocyations such as 4 to 8.
• hydrocyations including 4, 6, or 8 hydrocyations May be connected in series and operate in a counter-current arrangement, in suc arrangement* each hydrocycione may produce an overflow stream and an underflo stream.
• Bach underflow stream of an upstream hydrocycione: m y be fed to
• Each overflow stream of a downstream hydrocycione may be fed to an upstream, hydrocycione.
• the inventors have surprisingly found that in the operation of the present hydrocycione system, a combination of feed pressure, solid content in the feed to the hydrocycione system, temperature, and use of ultrasonic may be useful in aiding the separation and SiC recovery process.
• the temperature may be set in the range of 45 °C .to 60 °C.
• the ultrasonic frequency may be set at more than 24 kf x.
• the feed ressure may be set at 3.5 ⁇ 0.5 bar.
• the solid ..concentration in the feed may be set at between 11 wt% and 15 wt3 ⁇ 4.
• f 0041 In one example, by treating a -slurry with JIS20Q0 grit size using a temperature range of 45 °C- to 60 "C and ultrasonic frequency at more than 24 kHz, the Si impurities can be further reduced by at least 60% while the Fe impurities can be further reduced by at least 20%, as disclosed in copending international Application No. PCT/IB2013/O5 60i filed on October 24, 2013, the contents of which are- incorporated herein in its entirety.
• Figure. 2 A shows a SEM (20Q0x. magnification) of the recycled F5Q0 grit size SiC particles recovered from present ' method according to the operating conditions given in Table 1. in this case, Si content i about 0.13 wt% and Fe content is about 0.05 wt%.
• Figure 2B shows a SEM (2Q00x magnification) of the -recycled J.IS2OG0 grit size S iC particles recovered from present method according to the operating conditions given in Table I . in this case, Si content is about 0.43 wt% and Fe contest is about 0,63
• I004SJ Figure 2C shows a SEM (2000x magnification) of the recycled FS00 grit size SiC particles, recovered from present method according to the- operating conditions given in Table 1 , this- case, Si content: is about 0.14 wt% and Fe content is about 0.65 wt%. :
• the underflow from the last hydrocyclone is separated into solid and liquid via a product .filter press. Pressure filtration, cake wasliing and air blowing ensure the solid-liquid separation, achieving low water content in the solid. Optimum reflux time prior to filtration and quality of filter cloth also play vital roles in filtration -.efficiency.
• the solid is then transferred for drying and the filtrate is recycled within the process.
• ki the next step continuous drying of the solid from product filter press takes place in a product dryer under atmospheric pressure, using either heat or microwave.
• heat or microwave is applied to achieve .uniform drying. This allows the powder to be dried in a continuous and even manner, without over- dryin -Of "baking".
• the condensate is exhausted out of the -dryer through a bag filter. Dried powder is discharged and conveyed pneumatically to the next step.
• the solid from product filter press are dried in the product dryer at a drying. temperature of 150 °C to 200 °C.
• the water content in the solid from the product filter press is ⁇ 20 wt%. With the right range of temperauue, final moisture, content of ⁇ 0.30-wt% can be achieved. The same effect can be achieved by using I fcW of microwave for ever 1 kg water/hour to be dried. 10049 After the drying step, the dried powder may -be fed to a product sieve.
• the purpose of ultrasonic .. sieving is to separate any agglomerates or large particles (overs) in the dried SiC.
• the overs retained on the 42 ⁇ mesh screen are being collected and returned to the process as rework material 005O] in various embodiments, after the hydrocyclone system treatment, (lie overflow from the first !iydroeyefone is separated into solid and liquid in HC fines filter press. Pressure filtration and air blowing ensure the solid-liquid separation, achieving low water content in the solid. Optimum re-flux time prior to filtration and quality of filter cloth also playvital role in filtration efficiency. The solid is transferred for drying and the filtrate is recycled within the process.
• the solid from HC fines filter press are dried in the HC fines dryer at a drying temperature of 120 *C to 160 °C .
• the water content in the solid from the product filter press is ⁇ 30 wt%.
• a final moisture content of ⁇ 5 wt% can be achieved.
• the same effect can be achieved by using 1 kW of microwave for every 1 kg water/hour to be dried.
• the water distillation column is operated at between 110 °C and 120 °C and at a vacuum, pressure of 70 ⁇ 10 mbar.
• the feed composition may-include water content: 52 wt% - 60 wt%, and glycol content : 40 wt% - 48 wt%; With the righ t range of operating : temperature and vacuum pressure, a final moisture content of ⁇ 0.50 wt% can.be achieved.
• Glycol recovery is done by processing the water distillation column residue through a glycol distillation column. Under vacuum condition, it decreases the boiling point of glycol resulting in a significant reduction of utility required and prevents any risk of glycol cracking. In this step, glycol will be evaporated, condensed and collected as a distillate while the residue, which is made up of minimal amount of glycol, fine particles, and dissolved ions, will be disposed as waste.
• Figure 3 shows photograph of the product glycol, specifically, PEG, DPG, DEC, and PG, recovered by the present liquid purification stage, corresponding to Table 4,
• a system for recovering silicon carbide (SiC) particles and glycol from a slurry wherein the slurry comprises a mixture of SiC, Si, and Fe particles suspended in glycol.
• the system may include:
• a s irty filter press for separating the slurry into a first solid phase stream and a first liquid phase stream, wherein the first solid phase stream comprises essentially the SiC, Si, and Fe particles and wherein the first liquid phase stream com rises: essentiall glycol, water, suspended fine particles, and dissolved ions; a solid purification stage, wherein the solid purification stage comprises: a hydrocyclone system to obtain an underflow. Stream comprising recovered SiC particles in water and an overflow stream comprising essentially fine particles of SiC, Si and Fe suspended in water, wherein the hydrocyclone system comprises one or more hydrocyck es.;.
• the hydrocyelone system comprises more than one hydroeycione.
• the hydro ' cyclone system comprises 4 to 8 hydrocyclones.
• the hydrocycloues are connected 1 ⁇ 2 series.
• the hydrocyclones cormected in -series operate in a counter-current asxangerrseni, whexemeach hydrocyelone produces an overflow stream and an underflow stream, wherein, each: underflow Stream of an upstream .hydrocyelone is fed to a downstream hydro eye lone, and wherein each overflow stream of a downstream hydrocyclone is fed to an upstream hydroeyelone.
• the system comprises a product dryer downstream of the product filler press for drying the recovered SiC particles and may further comprise a product sieve downstream of the product dryer for sieving the dried S C particles to separate any agglomerates or large particles (overs). 3 ⁇ 4 ⁇ >70]
• the system ma further comprise ' fines filter press configurable, to receive the overflow from the hydrocyclone system.
• system may further comprise a fines dryer downstream, of the fines, filter press for drying the fines products from the fines filter press.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
• Separation Of Solids By Using Liquids Or Pneumatic Power (AREA)
• Cyclones (AREA)

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• 2015
  • 2015-01-27 SG SG11201706012RA patent/SG11201706012RA/en unknown
  • 2015-01-27 EP EP15708592.9A patent/EP3250507A1/de not_active Withdrawn
  • 2015-01-27 WO PCT/IB2015/050612 patent/WO2016120663A1/en active Application Filing
  • 2015-08-26 TW TW104127877A patent/TWI562816B/zh not_active IP Right Cessation

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