Page 238 - Elements of Chemical Reaction Engineering Ebook

Chap. 4 Questions and Problems 209

P4-7, The elementary gas-phase reaction
(CH3),COOC(CH3),+C2H6 + 2CH,COC-H3
Hall of
is carried out isothermally in a flow reactor with no pressure drop. The spe-
cific reaction rate at 50°C is 10-4 min-1 (from pericosity data) and the acti-
vation energy is 85 kJ/mol. Pure di-tert-butyl peroxide enters the reactor at
10 am and 127°C and a molar flow rate of 2.5 moYmin. Calculate rhr: reactor
volume and space time to achieve 90% conversion in:
a CSTR (~ns.: 4700 dm3)
a FFR (Am.: 967dm3)
If this reaction is to be carried out at 10 atm and 127°C in a batch mode
with 90% conversion, what reactor size and cost would be required to
process (2.5 moYmin X 60 min/h X 24 h/day) 3600 mol of di-tcsrt-butyl
peroxide per day? (Hint: Recall Table 4-1.)
Assume that the reaction is reversible with Kc = 0.025 mo12/dm6 and
calculate the equilibrium conversion and then redo (a) through (c) to
achieve a conversion that is 90% of the equilibrium conversion.
What CSTR temperature would you recommend for a 500-dm3 CSTR to
obtain -the;maxiaRukn msion if WRX = - 100,000 cal~ mol?
(Hint: Remember that the equilibrium conversion will be different for a
flow reactor and a constant-volume batch reactor for a gas-phase reaction
that has a change in the total number of moles.)
A liquid-phase isomerization A + B is carried out in a 1000-gad CSTR
that has a single impeller located halfway down the reactor. The liquid enters
at the top of the reactor and exits at the bottom. The reaction is second-order.
Experimental data taken in a batch reactor predicted tne CSTR conversion
should be 50%. However, the conversion measured in the actual CSTR was
57%.
(a) Suggest reasons for the discrepancy and suggest something that would
give closer agreement between the predicted and measured conversions.
Back your suggestions with calculations.
(b) Consider the case where the reaction is reversible with K, := 15 at
300 K, and AHm = -25,000 cal/mol. Assuming that the batch data
taken at 300 K are accurate and that E = 15,000 cdmol, what CSTR
temperature do you recommend for maximum conversion?
P4-9 Sargent Nigel Ambexromby. Scoundrels Incorporated, a small R&D clompany
has developed a laboratory scale process for the elementary, solid-cata-
lyzed-gas-phase reaction A + B + C + D (names coded for proprietary rea-
sons). The feed is equal molar in A and B with theentering molar flow rate
of kis 25 mol/min and the volumetric feed is 50 dm3/min. Engineers at
Scoundrels calculated that an industrial scale packed bed reactor with 500 kg
of a very rare and expensive metal catalyst will yield a 66% conversioln when
run at 32°C and a feed pressure of 25 atm. At these conditions the specific
reaction rate is 0.4 dm3/mol .min kg catalyst. Scoundrels sells this process
and cxtalyst to Clueless Chemicals who then manufactured the packed bed.
When Clueless put the process onstream at the specifications provide4 by
Scoundrels, they could only achieve 60% conversion with 500 kg catalyst.
Unfortunately the reaction was carried out at 31.5"C rather than 32°C. The