Page 99 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

P1: GKD Revised Pages
Encyclopedia of Physical Science and Technology EN002C-86 May 17, 2001 20:36

Catalysis, Industrial 497

The rate law for the hydrogenation of esters to alcohols Oxychlorination of ethylene is highly exothermic, and
shows a dependence on the square of the hydrogen pres- heat removal from reactors must be efficient. Graded-
sure. activity catalysts are used in fixed-bed reactors, or fluid-
18. Ammonia. The rate law for ammonia synthesis, bed reactors are used to control heat generation and trans-
3 2
a fer. Inert substances can be used to moderate conversion
Rate = k 1 + pN 2 x p H 2 p NH 3
in a bed, or the KCl loading on the catalyst can be var-
2 3 ied to control reaction rates. Advances have been made
1−a
− k 2 p NH 3 p H 2
using oxygen instead of air. Catalyst life has been im-
takes the forward and reverse reactions into account. proved significantly by changing the catalyst shape (rings
Potassium oxide, alumina, and calcium oxide are promot- and spheres) to decrease carbon formation in the interior
ers for iron, which is the basic catalytic material. The of the alumina catalyst matrix.
promoters increase basicity, stabilize surface area, and in-
crease reaction rate. Chemisorption of nitrogen (dissocia-
tive) is the rate-limiting step. The product ammonia com-
petes for active sites, so the reaction is run at relatively IV. INDUSTRIAL CATALYSIS RESEARCH
low conversion. Catalysts have been improved, allowing
operations at lower pressure and longer catalyst lifetimes. A. Research For Profit
19. Ethylene oxide. The oxidation of ethylene to ethy- Industrial catalysis research can be both fundamental and
lene oxide is exothermic (∼117 kJ/molH), and further oxi- applied. The long-term objective must be to make a profit
dation to carbon dioxide and water is even more favorable
using the knowledge of catalysis acquired through re-
thermodynamically. The reaction must be run under ki-
search. Different project evaluation schemes are used to
netic control to prevent total oxidation.
assess the potential profit of catalysis-related research.
Oxygen and ethylene adsorb on a supported silver cata-
Such factors as company size, business philosophy, com-
lyst. A Rideal-Eley mechanism is favored for the adsorp- petition, and economic conditions affect the ratio of ap-
tion. Chloride is a promoter/modifier for the catalyst and plied to fundamental catalysis research.
reduces the surface oxygen content. Silver(I) on the sur- The high cost of industrial research has prompted
face tends to increase ethylene adsorption, which explains industry-government, inter-industry, and industry-uni-
why small levels of chloride increase the rate of reaction. versity alliances to fill the research void.
20. Methanol. Methanol can be synthesized from mix- Examples of industry-government alliances are the
tures of carbon monoxide, carbon dioxide and hydrogen: National Institute of Standards and Technology Advanced

CO + 2H 2 → CH 3 OH Technology Program, the Japanese Agency of Industrial
Science and Technology which operates 15 laboratories,
CO 2 + 3H 2 → CH 3 OH + H 2 O the National Center for Scientific Research in France, and
The shift reaction equilibrium is also important: the Italian National Agency for New Technology.
Industry-university alliances are illustrated by Centers
CO + H 2 O ↔ CO 2 + H 2 for Catalytic Science and Technology such as those at the
University of Delaware and Delft Department of Chemical
The rate expression can be simplified if the assumption
Technology.
is made that methanol desorption is the rate-limiting step
Illustrative of intercompany alliances in catalysis is the
on a Cu/ZnO/Al 2 O 3 catalyst:
hydroprocessing MAKFining Technologies. This com-
2 0.7
Rate = k p H 2 (pCO) bines technologies and expertise from Mobil, Akzo Nobel,
M. W. Kellogg, and Fina. The goals of the alliance include,
21. Oxychlorination of ethylene. Knowledge of the role
“to create innovative approaches and optimum solutions
of copper chloride and the mechanism of oxychlorination
to the industry’s changing product demands and to make
has evolved. Current theory suggests that Cu(II) chloride
a more effective use of each company’s research and de-
chlorinatesethylene,whichischemisorbedonthecatalyst. velopment resources.”
1
C 2 H 4 + O 2 + 2HCl → CH 2 ClCH 2 Cl + H 2 O Another way to leverage the scarce research and de-
2
velopment funds is to hire a catalyst-consulting group.
Ethylene chemisorption should be enhanced at Cu(I) Several catalyst-consulting companies exist to work on a
sites, which result from the chlorination of ethylene. confidential basis on projects sponsored by clients with
Cu 2 Cl 2 is reoxidized by HCl and oxygen to CuCl 2 : an interest in business development, market strategy anal-
ysis, technological benchmarking, and new product and
1
Cu 2 Cl 2 2HCl + O 2 → 2CuCl 2 + H 2 O
2 process innovation.