One of the most common commercial methods to produce pure silicon that is to be

Question

One of the most common commercial methods to produce pure silicon that is to be used for the manufacture of semiconductors in the Siemen's chemical vapor deposition (CVD) process is shown below. A chamber contains a heated silicon rod, and a mixture of high purity trichlorosilane mixed with high purity hydrogen that is passed over the rod. Pure silicon (EGS electronic grade silicon) deposits on the rod as a polycrystalline solid. Single crystals of silica are made later by subsequently melting the EGS and drawing a single crystal from the melt. The reaction is H2 (g)+ SiHC, (g)-) Sí (s) + 3 HCl (g) the rod initially has a mass of 1460 g, and the more fraction of Hz in the exit gas is 0.223. The more fraction of Hz in the feed to the reactor is 0.580, and the feed enters at the rate of 6.22 kg moles per hour. What will be the mass of the rod at the end of the process? Gas HCl Hz Hz

Explanation / Answer

mole fraction of H2 in feed gas =0.58

feed rate = 6.22 kmoles/h

H2 in feed = 3.6076 kmoles/h

SiHCl in feed = 2.6124 kmoles/h

let 'X' moles of SiHCl react in process

so moles of SiHCl in exit= 2.6124-X

as 1 mole of hydrogen react with 1 mole of SiHCl

moles of hydrogen in exit = 3.6076-X

1 mole of hydrogen after reacting produces 3 moles of HCl

therefore HCl in exit stream = 3*X

therefore mole fraction of H2 in exit stream =(3.6076-X)/(2.6124-X+3.6076-X+3*X) =0.223 (given)

(3.6076-X)/(6.22+X)=0.223

3.6076-X=0.223*(6.22+X)

3.6076-X=1.38706+0.223X

1.223X=2.22054

X=1.815650041

moles Si got deposited = X = 1.815650041 kmol/h

mass of Si deposites every hour =28*1.815650041 =50.83820115 kg/h

if the process runs for t hours

si deposite at end of process = deposition rate*time in hr=50.83820115*t

at the end mass of rod = initial mass + Si deposition

=1.46+50.83820115*t                        ....ans.

comp. inlet outlet   kmol/h HCl 0 3*1.815650041=5.4469 SiHCl 2.6124 2.6124-1.815650041 =0.796749959 H2 3.6076 3.6076-1.815650041=1.791949959

Related Questions

Navigate

• Browse (All)
• Browse O
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.