ΔHR1;298  K  ¼ — 1240 kJ=mol ð1Þ

are bulk catalysts typically made by pressing the active powder

into a pellet with the desired dimensions (Cavani et al., 2006).  The

resulting catalyst pellets therefore have a bimodal pore   structure,

i.e. the micro-porous structure from the chemical synthesis of the active powder and the macro-porous region between the powder formed by the pelleting process. Due to diffusion limitation, the global reaction rate of the catalyst pellet in the reactor can be different from the intrinsic reaction rate measured for the active powder (Sharma et al., 1991). Hence, the real performance of the VPP  catalyst  pellet  in  a  technical fixed-bed  reactor  is  an overall

ΔHR1;298  K  ¼ — 2092 kJ=mol ð2Þ

C  H  O       2O  ½r3 ]2CO       2CO     H  O

ΔHR1;298  K  ¼ — 852 kJ=mol ð3Þ

The intrinsic rate expressions and kinetic parameters were taken from Guettel and Turek (2010), and the parameters are given in Table 1:

.    Ea;j.

result of the chemistry nature of the active component and the pore structure of the pellet. Most of current research on n-butane oxidation focusses on improving the catalytic chemistry of the  VPP

catalyst  (Benziger  et  al., 1997;  Centi, 1993;  Trifirò  and  Grasselli,

2014).  New   synthesis   methods   are   continuously   proposed to

increase the intrinsic activity of the VPP precursors (Glaum et al.,

2012; Hutchings, 2004). To the best of our knowledge, the pore structure optimization of the VPP catalyst for n-butane oxidation is not explored yet.

r2 ¼

k2pC4 H10 pO

1 þK1pC4 H10 þ K2pH2 O

k3pC  H  O p0:25

ð6Þ

Early studies have shown that an optimal pore structure of   the

catalyst pellet can be of great importance (Keil, 1999; Wei, 2011;

  4     2     3      O2

3 ¼

þ  1   C4 H10 þ  2   H2 O

ð7Þ

Coppens et al., 2001). With the development of experimental techniques, rational design and synthesis of catalyst pellets with desired pore structure for better performance is nowadays    possi-

Since the aim of the present paper is to investigate the effect of the pore structure of the catalyst pellet on the reactor perfor- mance, the above-mentioned reaction rates rj  which are in units of

ble (Liu et al., 2013; Luss, 1990). The effect of the pore structure

parameters of the VPP catalyst pellet on the reactor   performance

mol=ðkg

cat

U sÞ were  converted  to  the  surface  area  based  reaction

rate  rj;s    which  is  in  units  of  mol=ðm2 U sÞ  with  assumed  active

for n-butane oxidation in a fixed-bed reactor is investigated in this work by means of detailed mathematical modelling. If the overall yield of maleic anhydride can be improved by 1% with altering the catalyst  pore  structure,  this  may  open  up  a  new  direction   for

surface per catalyst mass Sg