How are high and low boiling points substances handled in the polysilicon purification stage?
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Please share how the high and low boiling points substances generated in the purification stage during polysilicon production are handled.
Some are sold abroad; as far as I know, some factories actually give them away for free, yet no one wants them! But who knows in the future! Some factories recycle SiCl4 for reuse; for example, they react it with SiCl3 and H2 to produce SiHCl3, which can then be utilized!
The high-boiling substances are mainly silicon tetrachloride, and in most cases it is necessary to have someone transport them away; however, it is also important to verify whether that party has the appropriate qualifications to handle them. The treatment of low-boiling substances is currently a troublesome issue; I hear that incineration is used for this purpose.
The high-boiling substance is mainly silicon tetrachloride, requiring a purity of over 98%, and it can be exported from the Jiangsu and Zhejiang regions. Low-boiling substances should be sent back to the silicon trichloride manufacturer for re-purification, as some of the boron remaining in them is not allowed to enter the reduction process.
We’re literally paying to have our high-boiling substances taken away by others. As for those with low boiling points, they are recovered and reused. We operated 7 towers separately; the low-boiling fraction was then subjected to distillation. The resulting trichlorosilane was not reused but sent straight for disposal, as its impurities of boron and phosphorus were too high!
Part of our silicon tetrachloride was leached by itself, and part was sold off (3500 per ton to buyers)
Currently, high-boiling substances are mainly used to produce ethyl silicate or fumed silica. The amount of truly hydrogenated material is extremely small, and there is also some that cannot be prevented from undergoing hydrolysis.
It is generally recycled; if that’s not possible, it is hydrolyzed