Ivan Flashcards
definition of a catalyst
a substance that, by chemical interaction with reactants, increases the rate of a chemical reaction without being consumed to any significant degree. Doesn’t affect the thermodynamics
for a volcano plot what do values at lower temp mean?
= higher catalytic activity
homogeneous vs heterogeneous catalysis?
homo = same phase, usually liquid
hetero = different phases, usually solid catalyst,
physical causes of catalyst deactivation?
sintering - metal particle growth in metal catalysts at high temp
attrition - break up of catalyst pellets
chemical causes of catalyst deactivation?
- poisoning by impurities (electron acceptor elements S, Cl, C)
- poisoning by reagents or products (coke deposition)
eq for catalyst deactivation?
R (t) / R (0) = exp -k_d t
where R (0) = initial reaction rate
R(t) = rate at any time t
k_d = first-order deactivation constant
what is catalyst lifetime?
a period of time during which a set of reaction conditions (temp, contact time) can be kept constant without loss of catalytic activity or selectivity
how to prevent catalyst deactivation and improve lifetime?
- purification of reactor feeds and catalysts
- using guard beds to protect the catalyst from poisons in the feed
SiO2-Al2O3 adsorbs basic impurities NH3, Zno adsorbs H2S - temp ramp to maintain constant conversion
- catalyst regeneration - burning off coke to emit CO, CO2 and H2O
Es?
Activation energy of surface reaction
To be feasible for uphill reactions (100% conversion) what is deltaG
Delta G <40
For not 100% conversion deltaG < 0
Eq for K
K = k2/k1
K = exp (-E/R) * (1/T1 - 1/T2)
Rate eq for PFR
C = Co exp (-kt_r)
Conversion for PFF
X = (Co - C) / Co
t_r eq
v/u
Rate eq for DPFR
r = (Co-C)/t_r
= XCo/t_r
