Lloyd L. Handbook of Industrial Catalysts

Подождите немного. Документ загружается.

428

Process

ICI

Lurgi

Topsoe

Mitsubi

ICI, Pi

Lurgi,

Topsoe,

Mitsubi

nitrate

onate

and de

roduc

laine

ferent

Figure

ermis

Chapter 10

TABL

a. I

to and Rogerson,

Supp, Nitrogen

Dybkyaer, Chem

shi, Takahashi an

. With the n

particles, pre

icient in zinc.

ed large parti

why the cata

izes and deac

10.9. Lurgi rea

ion from Lurgi

10.13. Low P

cto

ed quench l

ubular.

team raising (adv

-cooled tubula

ee radial flow rea

ltibed with inte

hem. Eng. Prog.

6-40 (1977) 109.

Econ. Eng.

evi

Tado, Chem. Ec

w three comp

ipitated in th

The final sta

les of carbon

lysts had a va

ivated rapidly

tor for a low-

ktiengesellsch

essure Methano

zenges.

nced radial conc

tors with water c

ed steam generati

(July 1977) 95;

w 13(1981) 149.

n. Eng. Review,

onent catalyst

acid solution

es of precipita

te which wer

iable compos

during operat

ssure methanol

aft.

l Converter Typ

pt).

oolingat outlets..

on.

itrogen (July-Au

(1974) 79.

s this meant

, were large,

tion, under al

e deficient in

tion, containe

on.

synthesis plant.

es.

50–150

40–100

50–90

50–200

1995) 32.

hat the first c

ich in alumin

aline conditio

copper. This

d crystals of

Reproduced w

ar-

if-

Pressure (bar))

Figure 10.10.

methanol syn

quench distrib

ature control.

inspected thro

the pressure v

– no internal c

C: the ICI lo

ensure good

the free passa

and dischargi

of catalyst per

maintenance

from Catalyst

y M. Twigg,

ermission of

Ammon

A modern lo

hesis converter

tors for cataly

: catalyst is ch

ugh these man

ssel is of a sim

atalyst basket is

enge quench d

as distribution

e of catalyst fo

g; D: gravity

its rapid prep

r recharging.

Handboo

, 2

. Twigg.

a and Methanol

-pressure

showing

t temper-

arged and

holes; B:

le design

required;

stributors

nd allow

charging

discharge

ration for

eprinted

ed., Ed.

) by kind

Synthesis

430 Chapter 10

TABLE 10.14. Byproduct Formation in Methanol Production.

Composition ppm (vol) Process

High Pressure Low Pressure

Methanol wt% 90–94

Water wt% ~10 ~20

Dimethyl ether 7800 <300

Ethanol 2500 150–650

n propanol 1200 <100

2700 <50

<400 <150

Acetone <30 <10

Methyl formate 900 <1000

Other esters <200 <20

Other ketones <250 <20

Hydrocarbons 20–80

Methane < 20 m

/te product

Total (excluding H

O)wt% 2–5 <0.5

A novel way to precipitate small particles was introduced to overcome the

problem.

By continuous mixing of reactants in a jet, the carbonates could be

precipitated at pH 7 so that the precipitate contained uniformly small, well-

mixed crystals and provided catalysts with a long, stable life. Continuous opera-

tion at 50-bar pressure was possible for three years in a 300 tonnes per day plant.

By-product formation was significantly decreased in comparison with the zinc

oxide-chromia catalysts as outlined in Table 10.14.

As the demand for large, 1000 tonnes per day capacity plants increased, the

operating pressure was optimized at 100 bar. The original catalyst was less sta-

ble at this pressure. However, by combining the alumina with a proportion of the

zinc oxide, possibly in the form of a spinel, before precipitation of the copper

component, an even more stable catalyst was produced.

Catalyst activity was

proportional to the surface area of the metallic copper reduction, which also con-

trolled the stability of the catalyst during use. Continuous improvement of pro-

duction techniques and a better understanding of the catalyst precursors could

increase catalyst life increased to about five years.

10.2.2.3 Precipitates Forming During Production

A mixture of basic copper and zinc carbonates is formed during the precipitation

of the metal nitrates. These have general formulae similar to malachite—

(OH)

(CO

)—in which some of the copper is replaced by varying propor-

tions of zinc. The amorphous mineral georgeite, with the formula Cu

(OH)

has been identified in the precipitate. As the precipitate ages other minerals,

such as aurichalcite and hydrozincite, form depending on the proportions of

copper and zinc. Free aluminium ions in the solution can be incorporated in a

+ alcohols

i-propanol

complex basic carbonate M

(OH)

.4H

O, hydrotalcite, which is related

Ammonia and Methanol Synthesis

431

• Amorphous copper/zinc georgeite (Cu,Zn)

(OH)

forms during pre-

cipitation.

• Aging gives low zinc (15%) malachite (Cu/Zn)

(OH)

and high zinc

(36%) aurichalcite (Cu/Zn)

(CO

)

(OH)

• Further aging gives finely divided copper enriched (70+%) malachite

(Cu,Zn)

(OH)

The very small copper crystals that form after careful drying, calcination

and reduction are very stable and the catalyst remains active for several years of

plant operation. It has been suggested that the reduced copper is stabilized as

clusters of copper atoms at the oxygen rich (001) surface of the zinc oxide. In

turn, the zinc oxide is stabilized by small zinc aluminate particles or other re-

fractory oxides. The addition of small amounts of magnesium oxide enhances

the stabilizing effect of zinc oxide. Zinc oxide can also absorb any traces of

sulfur or chlorine in synthesis gas.

10.2.2.4 Operation with Copper Catalysts

It is clear that the mixed copper oxide/zinc oxide/alumina formulation is an ex-

cellent catalyst in the low-pressure methanol process. There has been much de-

bate in explaining the role of copper in the reaction and how methanol is pro-

duced. The group that invented the catalyst examined a number of possibili-

ties:

• Was methanol synthesized from carbon monoxide or carbon dioxide?

• Was the copper oxide reduced or oxidized during the synthesis process

and what active sites were formed?

• What reactions were taking place on the active surface and how did this

affect the process?

It has been concluded from experimental work with catalysts containing

alumina that methanol forms from carbon dioxide and that the catalyst activity is

proportional to the copper metal surface area. The presence of carbon dioxide in

the gas increases the synthesis rate. The zinc oxide and alumina play little part in

the actual reaction apart from stabilizing the reduced copper and protecting it

from the effect of any poisons. On the other hand, with catalysts containing

chromia, the carbon dioxide leads to a decrease in the reaction rate.

to the Feitknecht compounds. The mineral azurite can also be formed by ageing

the precipitate at slightly elevated pressures.

taking place has been summarized as:

A vital stage of the catalyst preparation is the aging period, in which the

structure of the precipitate changes, to produce the appropriate copper zinc and

aluminium distribution in the final catalyst. During aging, it is significant that

the initial blue precipitate changes color to blue-green. The sequence of changes

432 Chapter 10

10.2.2.5 Reaction Mechanism with Copper Catalysts

During operation, the reduced copper metal surface is partly covered by mobile

oxygen atoms and carbon dioxide is adsorbed on the ‘oxidized’ copper. Carbon

dioxide is then able to react with hydrogen adsorbed on the reduced copper sur-

face. A formate intermediate is reduced first to a methoxy group and then to

methanol. Oxygen remaining on the copper surface can either react with ad-

sorbed carbon monoxide to form carbon dioxide or to react with hydrogen to

form water which also provides more carbon dioxide by the water gas shift reac-

tion with carbon monoxide. Depending on the ratio of carbon dioxide to carbon

monoxide in synthesis gas, up to 30% of the reduced copper can be covered with

adsorbed oxygen. The proportion of adsorbed oxygen also depends on the ox-

ides in the support. These reactions are summarized as follows:

O ↔ H

+ O(ads) (H

O + CO ↔ CO

+ H

) (10.1)

→ 2 H(ads) (10.2)

→ CO

(ads) (10.3)

(ads) + H(ads) → HCOO(ads) (10.4)

HCOO(ads) + 2 H(ads) → CH

O(ads) + O(ads) (10.5)

H(ads) + CH

O(ads) → CH

OH (10.6)

O(ads) + CO ↔ CO

(10.7)

It is important to emphasize that the mobile, active sites are formed from

adjacent copper atoms and surface oxide. Much of this work has been the sub-

ject of a review by the ICI group.

10.2.2.6 Selectivity

Mixed oxide methanol synthesis catalysts containing copper are very selective

and the selectivity of the conversion of carbon oxides to methanol exceeds 99%.

This is simply explained because there is no splitting of carbon-oxygen bonds

when carbon oxides are adsorbed on the copper surface.

Consequently, the methane and higher alcohols formed with zinc oxide-

chromium oxide catalysts are no longer major by-products. Formaldehyde and

methyl formate form only in small, equilibrium amounts.

Ammonia and Methanol Synthesis

433

Although dimethyl ether could be produced with an acid catalyst by a sim-

ple dehydration reaction, the alumina component of the catalyst has low acidity

and less than 200 ppm ether is found in crude methanol. This is most probably

due to the neutralizing effect of the basic zinc oxide.

10.2.2.7 Low-pressure Methanol Reactor Types

The first low-pressure methanol process was designed to produce 300-600

tonnes per day of methanol, at about 50-bar pressure with a copper oxide-zinc

oxide-alumina catalyst. This was the maximum size of plants being used at the

time. By using a simple process design, based on a centrifugal compres-

sor/circulator, a novel quench converter with heat exchanger cooler and catch-

pot, the ICI process eliminated the costly high-pressure equipment and recipro-

cating compressors of the old process. The cost of making methanol was cut to

The process was further optimized to operate at 100 bar pressure as demand

for methanol increased and plants producing 1000 tonnes per day were devel-

oped. A more stable and efficient version of the original catalyst was also intro-

duced. As methanol demand continued to increase in the 1970s, other similar

processes were developed using more energy-efficient designs. Apart from the

first, quench cooled converters, tube cooled, radial flow and steam-raising con-

verters have all been used.

Catalyst life and activity have also been improved. For various reasons the

catalysts used in some of the later processes were based on copper oxide-zinc

oxide-chromia catalysts.

10.2.2.8 Catalyst Reduction

The copper oxide component of low-pressure methanol catalysts must be re-

duced to copper metal, with a dilute stream of hydrogen in nitrogen, before use.

Careful temperature control is essential during this procedure in which a large

volume of water is evolved, depending on the copper content of the catalyst

used.

Reducing gas contains up to 1% hydrogen at about 10-bar pressure and is

circulated through the converter. The catalyst temperature is increased slowly

and reduction should begin between 150°-160°C. The reduction of the catalyst is

extremely exothermic and the progress of the reduction can be monitored by

observation of a high-temperature zone passing down the bed as reduction pro-

ceeds. To prevent damage to the catalyst the inlet temperature is restricted to

180°C with a maximum bed temperature of 230°C. If necessary, the maximum

temperature can be controlled by changes to the hydrogen concentration as the

hot spot passes down the catalyst bed. After condensing water from the outlet

gas, the nitrogen is simply re-circulated after the addition of more hydrogen.

about 25-30% at that current level of the time.

434 Chapter 10

Any carbon dioxide, formed from the decomposition of residual carbonate in the

catalyst, can be purged from the system if the concentration exceeds 2-3%.

When the peak catalyst temperature reaches the bottom of the reactor, the

inlet temperature can be increased to 220°–240°C and the hydrogen concentra-

tion to 10-20%. It can take about two to five days to reduce the 100–200 tonnes

The catalyst is most stable at low temperatures, and the purity of the

product methanol decreases as the temperature of the converter is increased. For

these reasons, the process is usually operated at the lowest possible temperature

and pressure, consistent with achieving the design production rate. As the cata-

lyst becomes deactivated, it usually becomes necessary to increase the reaction

temperature to maintain production capacity. The inlet temperature to the bed is

usually about 220ºC in the initial stages, gradually increasing to 250ºC over a

three to five year period.

10.2.3 Novel Catalysts

The possible use of palladium as a potential catalyst for the synthesis of metha-

nol received much of attention during the 1980s.

56,57,58

These catalysts were nev-

er commercialised because the rate of reaction was relatively low, a significant

amount of methane was always produced and the high cost of palladium made

this approach too unattractive.

A much more radical approach was first proposed by Baglin and co-

workers, who showed that careful oxidation of a range of copper/thorium in-

termetallic compounds gave rise to a new generation of extremely active cata-

lysts. Thorium, however, is weakly radio-active and would not be acceptable for

large scale use on safety grounds. A similar range of catalysts based on interme-

tallic compounds derived from copper and rare earth elements was then devel-

oped by workers from ICI, who also discovered that the pure rare earth metal

could be substituted by the much cheaper mixed alloy, Mischmetal, with no loss

in activity. Addition of a little aluminium metal to the molten cop-

per/Mischmetal mixture improved the stability of the catalyst towards deactiva-

tion. Methanol could be prepared over this generation of catalyst at tempera-

tures as low as 70ºC and pressures in the range 5–10 bar. The mechanism of

methanol synthesis over this catalyst is quite different to that of the conventional

copper/zinc oxide/alumina catalyst. It was demonstrated by radioactive labelling

experiments that the methanol was produced directly from carbon monoxide,

rather than carbon dioxide, in strong contrast with the conventional catalyst.

Indeed, carbon dioxide was even shown to be a poison for this catalyst. It is be-

lieved that the active component of this catalyst is extremely small particles of

copper metal, perhaps even in the atomic state, supported on an oxide matrix, on

the basis of in situ x-ray diffraction analysis of the evolution of the catalyst from

the intermetallic precursor. This approach has not been commercialised at the

of catalyst required for large plants.

Ammonia and Methanol Synthesis

435

present time. The mains reasons were that poisoning by carbon dioxide and wa-

ter, meant that purification of the synthesis gas was very difficult and costly.

Furthermore, the catalyst expanded in volume greatly during the in situ activa-

tion procedure, and this led to poor gas distribution through the converter. These

problems have yet to be overcome.

REFERENCES

1. S. J. Green, Industrial Catalysis, Benn, London, 1928, p. 334.

2. Larson and Richardson, J. Ind. Eng. Chem., 17, (1925)971; Larson and

Brooks, J. Ind. Eng. Chem., 18 (1926) 1305.

3. C. Ernst, The Fixation of Atmospheric Nitrogen, Chapman and Hall, Lon-

don, 1928; J. B. Allen, Chem. Eng. Progress (Sept 1965) 1; S. Strelzoff and

L. C. Pan, Synthetic Ammonia, Chemico, 1962.

4. ICI European Patent Application 78302769 (March 7 1979); Nitrogen

(Nov-Dec 1979) 122; S. A. Topham, S. A. Hall, and D. G. Heath, Devel-

opment of ICI Low Pressure Ammonia Synthesis Catalyst, ICI/CFDC

Technical Symposium, Shanghai (April 1989).

5. J. R. Jennings, ICI, US Patents 4654320 and 4668657.

7. S. J. Green, Industrial Catalysis, Ernest Benn, London, 1928, p. 343.

8. S. J. Green, Industrial Catalysis, Ernest Benn, London, 1928, p. 349-352;

British Patent 153254 (1921); Thompson et al., Chem. Eng. Prog. 48,

(1952) 468.

9. Chem. & Met. Eng. 30 (1924) 198; USP 1408987 (1922); 1478549-50

(1923).

10. British Patent 197199 (1922); 218237 (1923); Canadian Patent 229485

(1923).

12. L. B. Nelson, History of the US Fertilizer Industry, Tennessee Valley Au-

thority, 1990, p. 201.

13. R. S. Tour, Chemical & Mech. Eng., Parts 1-5, (June–Oct 1922).

14. L. B. Nelson, History of the US Fertilizer Industry, Tennessee Valley Au-

thority, 1990, p. 227.

15. L. B. Nelson, History of th US Fertilizer Industry, Tennessee Valley Au-

thority, 1990, p. 229.

16. Chemico US Pat. 3041151 (1962).

19. F. Uhde British Pat. 259230 (1926).

20. V. E. Parke, Billingham – The First Ten Years, ICI Ltd, Billingham, 1957.

6. British Petroleum US Patents 4142993 (1979) & 4453775 (1979).

11. L. Casale, J. Ind. Chem. 17 (1925) 971; Bitish Pat. 227491 (1923).

17. I. Cedersberg, British Patents 153290 (1920); 168902 (1921); USP 1452027

(1923); Can Pat 219825; 223453 (1922).

(1925-6).

18. F. Uhde, German Patent 493793 (1925); Br Pat 273735; 253122; 247225

436 Chapter 10

21. A. Mittasch, Advances in Catalysis, Vol. 2, Academic Press, NY, 1950, p.

82.

22. J. R. Jennings and S. A. Ward, Catalyst Handbook, 2nd edition, Ed. by M.

V. Twigg, Wolfe, London, 1989, p. 397; R. Schlögl, Catalytic Ammonia

Synthesis, Ed. by J. R. Jennings, Plenum, New York, 1991, p. 39.

23. G. Ertl, Catalytic Ammonia Synthesis, Ed. by J. R. Jennings, Plenum, New

York, 1991, p. 39.

24. D. R. Strongin and G. A. Somorjai, Catalytic Ammonia Synthesis, Ed. by J.

R. Jennings, Plenum, New York, 1991, p. 39.

25. W. Turner, Kellogg International Corporation: Ten Years of Single Train

Ammonia Plants, Paper 1, AMPO 74, ICI Operating Symposium, Amster-

dam (1974).

Beinlich, Thompson, Chem Eng Prog, 43 (1947) 291.

27. Topsoe’s New Ammonia Process, Topsoe Topics (March 1976); I.

Dybkjaer, Fertilizer Nitrogen, British Sulfur International Conference,

London (January 1981).

28. Quartulli & Wagner, Why Horizontal Ammonia Converters?, Hydrocarbon

Processing, (December 1978); Le Blank, Retrofit Ammonia Plants to Save

Energy, Hydrocarbon Processing, (Aug 1986) 39.

30. Kellogg US Patent 4568531-2.

31. A. K. Rhodes, Oil Gas Journal, (Nov 18 1996) 37.

32. Canadian Pat. 1094532; S. R. Tennison, Catalytic Ammonia Synthesis, Ed.

by J. R. Jennings, Plenum, New York, 1991, p. 39. Angew Chem. Int. Ed.,

40 (2001) 1061.

34. Jahn, Berichte, 13 (1880) 983.

35. German Pat. 293379 (1913); British Pat. 20488 (1913); US Patent 1201850

(1914).

36. German Pat. 415686; 441433; 462837 (1923); US Patent 1558559; 1569775

(1923).

37. Fiat Reports No 888, (Aug 1946) p. 7-8; British Pat. 227147.

38. French Pat 540343 (1921).

39. Patart, Comptes Rendus, 179 (1924) 1330.

40. Patart, Chimie et Ind. (Nov 1926).

41. Italian Pat. 267698 (1928); French Pat. 670763 (1930); G Natta, Catalysis,

Vol. 3, Ed. byEmmett, Reinhold Pub Corpn, N.Y., 1955, p. 349.

42. Natta and Corradini, Proceedings Int. Symposium on the Reactivity of Sol-

ids, Gothenberg, 1952, p. 619.

43. Lazier and Vaughan, J. Am. Chem. Soc., (1932) 3080.

44. Molstead and Dodge, Ind. Eng. Chem., 27 (1935) 134.

26. Slack, Allgood, Manne, Chem. Eng. Prog., 49 (1953) 393; Bridger, Pole,

29. S. R. Tennison, US Patent 4163775 (1979).

33. S. Stalica, Hydrocarbon Processing, (July 1999) 85.

Ammonia and Methanol Synthesis

437

45. C. L. Thomas, Catalytic Processes & Proven Catalysts, Academic Press, N.

Y., 1970, p. 150.

46. US Patent 1746783 (1930).

47. Fenske and Frohlich, Ind. Eng. Chem., 21 (1929) 1052; Frohlich and Lewis,

Ind. Eng. Chem., 20 (1928) 285.

48. W. Katowski, Chem. Tech., 15 (1963) 204.

49. G. W. Bridger, MacRobert Award Lecture, Manufacture of High Activity

Catalysts (November 25, 1975).

50. M. V. Twigg and M. S. Spencer, Topics Catal. 22 (2003) 191.

51. M. S. Spencer, Catal. Letters 66 (2000) 255; A. M. Pollard, M. S. Spencer,

R. G. Thomas, P. A. Williams, J. R. Jennings and J. Holt, Appl. Catal. A 85

(1992) 1.

52. Methanol the ICI Way, Chemical Week, (Jan 6 1968) 34.

53. Marschner and Moeller, Applied Industrial Catalysis, Vol. 2, Ed. by B. E.

Leach, Academic Press, N.Y., 1983, p. 215.

54. M. S. Spencer, Applied Catalysis A General, 85 (1992) 1; M. S. Spencer,

Topics Catal. 8 (1999) 259.

55. Doesburg, Hoppener, de Koning, Xiaoding, and Scholten, in Preparation of

Catalysts, Vol. 4, Ed. By Delmon et al., Elsevier, Amsterdam, 1987, p. 767.

56. Chinchen et al., ACS Div. Fuel Chem., 29(5) (1984) 178.

57. Blaziak and Kotowski, Prez. Chem. 43 (1964) 657.

58. G. C. Chinchen, P. J. Denny, J. R. Jennings, M. S. Spencer and K. C.

Waugh, Appl. Catal. 36 (1988) 1.

59. M. L. Poutsma, L. F. Elek, P. A. Ibarbia, A. P. Risch, and J. A. Rabo, J.

Catal. 52 (1978) 157.

60. E. K. Poels, P. J. Mangnus, J. van Welzen, and V. Ponec, Proc 8

Int Con-

gress Catal 2 (1984) 59.

61. R. F. Hicks and A. T. Bell, J. Catal. 91 (1985) 104.

62. E. G. Baglin, G. B. Atkinson, and L. J. Nicks, Ind. Eng. Chem., Prod. Res.

Dev. 20 (1981) 87.

63. G. D. Short and J. R. Jennings, ICI, European Patent 117944 (1984).

64. J. R. Jennings, R. M. Lambert, R. M. Nix, G. Owen, and D. G. Parker, Appl.

Catal. 50 (1989) 157.

Catal. 106 (1987) 216.

65. R. M. Lambert, R. M. Nix, T. Rayment, J. R. Jennings, and G. Owen, J.