Tugas Kelompok.docx

TUGAS KELOMPOK TRK Lanjut Kelompok 4 Laily Fitri Pelawi (1806154116) Muhammad Arif Darmawan (1806

Example 10.4 The general treatment of the problem predicting the global rate at given bulk conditions accounts for both mass and heat-transfer effects. Let us treat the generalization of example 10-2 by supposing that we know Tb = 452oC = 725 K and the bulk concentrations given for 10% conversion level in Table 10-2. We also presume that the intrinsic rate equation [Eq. (K) of example 9-2] is available. The objective is to calculate a global rate. It is known from the data in Table 10-2 that the answer is rp = 0.0956 gmol/h.gcat. However, to illustrate this type of problem, we will pretend that we don’t know the rate, just as we did in example 10-2. Solution: As in Example (10-2), one method of solution is to assume a rate. Then calculate Ts and Cs (for each component) from the left-hand-side equalities in Eqs (10-21) and (10-22). Finally, check the assumed rate by using these values of Ts and Cs in the expression of the intrinsic rate. We assume r = 0.0956 and evaluate kmam and ham from Eqs (10-9) and (10-11), using Eq.(10-10) with jD = jH. Substituting these results in Eqs. (10-21) and (10-22) we obtain Ts – Tb =

r𝑝 (−H) ℎ𝑎𝑚

= 28𝑜 𝐶

Ts = Tb + 28 = (452 + 273) + 28 = 753 K (Cb – Cs)SO2 = 1.40 x 10-5 lb mol/ft3 or (pb – ps)SO2 = 0.0139 atm The numerical values shown are those already determined in examples (10-3) for T and (10-1) for C. Similar C values for oxygen and sulfur trioxide are also available from Example 10-2. In summary, the corresponding ps values are (ps)SO2 = 0.0603 – 0.0139 = 0.0464 atm (ps)O2 = 0.201 – 0.0045 = 0.196 atm (ps)SO3 = 0.0067 + 0.0150 = 0.0217 atm We check the assumed rate by using these surface partial pressures and Ts in the intrinsic rate equation rp =

This result agrees well with assumed value. In the normal case where a good initial estimate for rp is not available, iterative calculations would probably be required. The initial estimate for rp could be that value calculated from the intrinsic rate equation assuming ps = pb and Ts = Tb. “Constants” in the intrinsic rate equation are temperature dependent. Thus, in the normal case it is necessary to know how A and B in Eq. (A) vary with temperature and to use the values corresponding to the calculated surface temperature. In our calculations this was unnecessary because A = 0.176 and B = 12.9 were the correct values for Ts = 753 K (480oC). Another method of calculation of Ts and Cs values may be used for first order reaction. This is to employ the equality of the left-and right-hand terms in Eqs. (10-21) and (10-22) are solved simultaneously for Ts and Cs.