Progress in the partial oxidation of methane to methanol and formaldehyde

Catalysis Today, 8 (1991) 305-335 Elsevier Science Publishers B.V., Amsterdam

305

PROGRESS IN THE PARTIAL OXIDATION OF METHANETO METHANOLAND FORMALDEHYDE

M.J.

Brown and N.D.

British Station,

Parkyns

Gas plc, Research and Technology London SW6 2AD, tireat Britain

Division,

London Research

SUMMARY The recent literature on the direct partial oxidation of methane to methanol and formaldehyde is reviewed, both for nominally heterogeneous and for homogeneous reactions. Emphasis is placed on the interaction of surface and gas phase chemistry in the reactivity of methane. At present, reported yields of oxygenates are only a few per cent at most for catalysed reactions : much higher yields have been claimed for homogeneous or heterogeneouslyinitiated reactions. The review concludes with some remarks about the economic viability of direct oxidation processes and some future directions of research.

INTRODUCTION The existence methane

is

the

possibility

of

The need

for

location

of

gaseous

fuel

hydrocarbon (ref.

this

to

arises, natural

over

both

has

synthesis

in

copper-based

route

followed

this

from

well

established

methane

by the highly sway.

but

A method

of

be devised.

is

derived

This

aspect

product

or

fuel.

formaldehyde breaking of

costly

will

as well

transport

of

synthesis

conversion

the

chemicals,

produce

a relatively

direct

of

transporting

Besides

the method

selective

it

of

as a valuable

to

the

and chemicals.

remoteness

to methanol

At present,

1) on to

fuel

liquids.

of

MTG process

convert

of which

costliness

with

and as a source

to

gas, (ref.

of

the

relative

as compared

is

natural

forms

partially,

the Mobil

holds

could

to other

and the

perceived.

process.

of

attention

it

methanol

down over

and

would

be highly

be dealt

with

later

in

Review.

has been however,

reviewed

6),

of at

all

these

a high

formidable

extensively

and Lijffler (ref.

least

a process

gas,

As a result

are,

for

been

if

at

own right

catalyst

attractive,

directly

methanol its

for

it

distances,

long

energy-intensive

this

long

reserves

has focussed

gas wells

material

The need directly

World-wide

converting

the

source

vast

constituent,

liquids,

21,

as the

of

chief

(ref. the

4),

0920-5861/91/$10.85

level

for

the mid-1980s

by Foster two reviews

interest

more than

and no clear

in

latter

pressures,

(ref.

path

is

the

a decade. yet

by Pitchai 5),

in

and Klier

specifically

0 1991 Elsevier Science Publishers B.V.

oxidation

The chemical

visible.

and by Gesser.

concentrating

direct

problems

The subject (ref. Hunter

31,

was

by Garcia

and prakash

on methanol

306 Scurrell

formation. of

methane

(ref.

8)

conversion

have

a summary of

of

this

afresh,

referring

to

but

earlier

Interaction

of

a review,

extensive

face

subject

heterogeneous

work,

to get

reasonable

either

at

initiate

CH.

conversions

CH,

case

of

homogeneous

place

in

the

reactions

+

provides

20 years. propose

amplify

to

the

review

past

5 years,

a point.

need

to activate even

temperatures

(450

Generally, in the

gas

a carbon-hydrogen

for

gas-solid - 65O’C)

radicals

phase

are

are

and are

used

generated

able

to

HO,

gas

entirely

Just

or

and Krylov as it

reactions

reactant.

reactor

subject

reaction

*

governed

of

the

0,

In the takes

of

high

Korshak

made over

to mean that,

relatively

the

valuable,

we do not

to

and the

tended

Sinev,

at progress

necessary,

methane has

considered

the past

and heterogeneous

of

surface

further

+

where

reaction reactions,

the

literature, look

have

especially

work over

homogeneous

initiate

is

Russian

to

8)

Recently,

which

impressive rather

The low reactivity bond to

7) and Mimoun (ref.

more generally.

published the

In the the

(ref.

( 1) oxidation

phase.

of

methane the

Thereafter,

by a series

of

radical

as for

the

oxidative

coupling

leading

to

insertion

of

to methanol, course

reactions,

this

the

reaction

reaction

as described

of methane,

oxygen

of

may also

to

give

is

later.

ethane

be initiated

at

and ethene, the

surface.

CH.

+

Thereafter, catalyst

surface,

to activate

101

The energy

diagram

consequence

to

is is,

reactions it

in all

given

stages

and that

poor

selectivities.

may take

the

gas

phase

place,

either

on the

, and it may be difficult

to

reactions

is

the

compared

to

relatively the

ease

high with

energy

which

required

subsequent

i.e.

[g’

HCHO

+

CO

(Fig.

1)

refers

below

true

naturally,

in

molecule,

place,

also

( 2)

alternatives.

CH,OH

+

same tendency

desired

feature

may take

to

these

the methane

reactions

[surface.Hl

radical

or near

between

A general

CH, +

CH, +

subsequent

distinguish

leads

+

[surface1

for

supposedly

that

it

any attempt This

is to

+

H,

to gas

phase

heterogeneous

difficult drive

aspect

( 3)

is

to the

stop

reaction

clearly

reactions

reactions. at

the

the

earlier,

to high

shown in

but The

the

conversions literature.

307

0

Enthalcw

(kJ/mol)

-200

-400

-600

-800

-

-1000 Fig.

1.

Enthalpy

changes,

at

298 K, for

successive

oxidation

reactions

of

methane

A slightly

surprising

oxygenated

products

and formaldehyde above, methanol found .

and the to

separately, fact

that

formaldehyde,

The formation

as an intermediate, during

formation

is

conclusive.

not

feature has been

of

of

the

that

it

reasonably

would

suggest

formaldehyde

formaldehyde,

is

to find

selective

seem possible

that

catalysts

are

a mixture

might

be expected

sometimes

reported

although,

as will

to

catalysts

produce

The energy

selectively.

many MO-containing

and methanol of

attempts does

of

diagram

known to

oxidise

products

would

to go through in varying

be discussed,

for

methanol shown

be

methanol

amounts the

evidence

308 HOMOGENEOUS GAS PHASE OXIDATION The chemistry to

that

of

most

that

studies

have,

reasons

why methanol

like

other

active

an

phase

optimisation

of

effect

.

use

of

modelling

.

use

of

novel

.

photochemical

of

to

for

selectivity

well

mixed.

direct trap

this

jets 16).

high

full

phenomenologicallyThe conversion

research

overall

(or

in the

process

removal area

of

of

on :

reaction

either

13).

mechanism

at

stages

the

encouraged

Recent

remains

to

the

gases

should

from

products.

are

the

prior

used

High methane

optimum

reached,

All

the

of

find

has been

to

methane

reactor,

to

point.

studies

reactor

for

if

the

to oxygen

ratios

either a cold are

from

>C, hydrocarbons)

by finger

used

oxygenated is

observed

products at

to

increasing

coupled

species

temperatures

(ethane, because

and

the

:

( 4)

The equilibrium concentration, conversion

is

dependent

parameters

on temperature,

which

pressure

are , accordingly,

and oxygen

important

in governing

the

to methanol.

There

diameter

to

to

ethene of

CH, + 0, +CH,O,

conditions,

are

oxidation.

A switch

conversions,

14,

air

reactants

analysis,

or by using

used

(refs.

to a cent.ralised

be comparable

methods

products

formation

tried

consensus

a disputed

add preheated

results

the

work has

and a general

premixing

However,

of

pressures

ref.

to methanol

any condensable

equilibrium

that

tias chromatographic

sampling

prevent

the

Methane,

conversion

the

conversion,

reactors,

(ref.

of

12).

conversion

example,

for

or using

reviews,

similar

design

bar)

though

15).

determine

found

conditions

flov

(ref.

and termination

has concentrated

is

Combustion

initiation

(>lO

(see,

flov-tube

methane

understanding

at all

conditions.

propagation

high-pressure

reactor

studies

the

the

the basic

formed

in a number of

previous

of

10,111.

additives

High-pressure

methanol

the

are

reaction

oxidation

oxidation (refs.

much of

react

on the step,

Since

gas

.

Early

will

partial

processes

produced

depending

species).

the

or formaldehyde

initiation

homogeneous .

accordingly,

ways,

in

combustion

hydrocarbons,

different involves

occurs

general

are,

however,

discrepancies

when comparing Pyrex-lined the

results

tube. differ

results Table

in methanol

selectivities

from apparently 1 shows

markedly

how,

under

similar

and methane studies

closely-related

in two different

laboratories.

in a 4-mm

309 TABLE 1 Comparison

of

conversion

studies

Temp. I’C

results

Pressure /atm

450 450 450 451 452 456

97.5 93.4 50.0 93.3 89.3 94.9

from ref. from ref. from ref. from ref. calculated

There example, only

16).

placed

the

15).

and the always

reaction

of

diameter

reactor, Other the the

ratios

(S/V)

to

mixture.

active

surfaces

break

up laminar

plug-flow

it

to

the

reactors

Calculations

of

extremely

annular

(ref.

Reynolds

the

these

reactors

is

is

gas

the

use

the

et

17)

or,

-5 -

10.

the

to

to

1.0

the

been

the

reactor

from

4 - 20 mm It

cm-*.

transfer

a needle-valve

is

in the external

to

immediately

a thermocouple 14) will

and also chemistry.

use

The valve

is

thought

data

that

do,

purely

to

akin

more back-mixing.

accordingly, recover

the extra

environment,

known experimental

quickly

mm diameter

perturb

may provide

introducing

is,

in contact

an 0.8

both

a more turbulent

The flow

should

for

reaction have

ranges

heat

This

possibly

Number from

profile

temperature,

(ref.

tube.

phase

a problem,

temperature. of

character

gas

used

For

of

oxidation

externally

from 5.0

mentioned,

and produce

discrepancies.

temperature

efficient

(a> (a) (b) (cl (d) (c)

gas

something

the

reactors

40 36 38 76 55 83

ideal

temperature of

the measured

reactor

by a valve,

valve.

explain

range

actual in

flow

patterns

low values,

disturbed of

the

influence

flow

assuming

or mounted

there

Yarlagadda

into

n.t.p.)

reaction

the

that

as previously

giving

if

that

reactor,

flow

downstream

14)

may lie

laminar

and even

(ref.

CH,OH sel. /mol(%)

5 5 5 9.5 13.3 8.0

(e) (e) (e)

a full

the

of

approximates

reaction

to flow

diameter

CH, conv. /mol(B) ca. ca. ca.

exothermicity

explanations

inserted

give

in

to ensure

or,

(at

reasons

the

course,

200 200 300 208 75 232

characterise

zone

tubes

thermocouple

to

rates

to measure

The internal

possible,

before

to

account

surface-to-volume

smaller

with

into

high-pressure

Residence time fs

0 0 47.5 0 2 0

measurement

Thermocouples

in

(ref.

Table 1 Figure 3(a) Table 2 Table 1 given flow

attempting

taking

(X) N*

2.5 6.6 2.5 6.7 8.7 5.1

may be a number of

one study

(ref.

the

15 15 14 14 from

temperature

reactor,

two methane-to-methanol 14,151

Feed Composition CR, 0,

49 49 49 50 25 65

(a) (b) (c) (d) (e)

from (refs.

however, laminar

characteristic

310 On the

other

such

that

the

tube

than

that

dimensions so that

in

the

may have

there

are

from

conversion the

amount of selectivity

al

(ref. that

without yield

15)

find

oxygen

in

(ref.

mixture

no oscillations

a temperature dynamic

of If

will

partial as

oxidation

(ref.

15),

(ref. noted. effect

of

adding

(NTP).

(ref.

natural

small 22)

In both

is

phenomena,

the

temperature

were have

With oxygen

observed

been

production

410 - 45O’C levels

selectivity

at for

lower

suggesting

effect

25 -

a than

to methanol

oscillations,

of

study

the

oxygen

or

gas

the

of

50°C, order

(ref.

22)

has

sensitisers,

to

was at

that

on selectivity.

The effect

than

to methanol

of

to methane a ‘real’

1OO’C lower no benefit

looked

these

reactant (refs.

lowers

natural than

in

are

the

20,21). conversion

of

a

selectivity way at

called.

an unsensitised

10 atm and a flow-rate was found

on

pure methane

terms

sometimes to

of

methane

gas has

in a more systematic

as they

it

amounts

hydrocarbons

the

pure methane

ethane

of

commercially, small

them to

while

was made relative at 45O’C,

be utilised contains

by adding

rather

studies,

mixture

is

gas which

studied

these

sensitisers

The selectivity

methane

amounts

by about

of

additives, of

methane/IO%

: thus,

oscillations

an adverse

as methane.

has been

or by using

A recent

evaluation

they

occurs

of methane

range

The highest

natural

as well

temperature

21).

of

feedstock,

process

For example,

conversion

remark,

to methanol

temperature

may have

14)

Burch

low.

Similar

to eliminate

sort

(ref.

this

conversions

to cool-flame

8% oxygen.

observed.

this

is

favourable

the

containing

et whereas

50% but

oxidation

18).

are

in

selectivity

As Burch et than

profile. of

of

Yarlagadda

low methane

partial

(ref.

which

oxidation

its

hydrocarbons

the

temperature

work

low enough of

the

trend

for

additives

the

take,

higher

just

behaviour

Effect

of

the

gas.

dependence.

attributed

were

feed

sample

selectivity

concentration-dependent,

and at

They occur

19).

in

profile

characteristics.

the velocity

the

the

velocity

flow

of

of

in

reactor

mass-averaged

because

the

in

on this

an accurate,

by conversion)

feature

conditions

different

can be larger

consumption

some early

under

methane-oxygen 5X,

a slight

Oscillations,

at 400 bar

in

oxygen

multiplied

oscillations.

effect

a discrepancy

present

only

large

profile

time

differences

in the magnitude is

residence

quite

conditions,

there

to a marked velocity

Small

have

taking

selectivities

(selectivity

35 bar

these

strongly

An interesting

reported

in

leads

has a longer

flow.

reactors

oxygen

methanol

full

flow

wall

the

difference

to methanol,

the

et

of

under

find

find

centre

problems

the

with

laminar

reactor

similar

chromatography Apart

highly the

a disproportionately

apparently

Moreover, gas

hand,

gas near

to be between

of

is the

The 90%

40 -

80 ml/min

41 and 52X,

the

311 selectivity

to

formaldehyde

conditions

were

deliberately

An extensive

selection

cyclic,

unsaturated

thiols,

amines.

assess

these

* the

of

to

than)

the

than

may have

methanol

In recent more widely the

used

This

to

reaction

to

is

some extent,

of

in

the

in

to

behaving

may be the major

be

sensitiser

equivalent

additive

problems

and many

A few produced

percentage sometimes

the

causes

(MTCR).

to methanol. the

present,

(or

more like

calculation

source

of

of products.

:

high

methanol

beneficial

selectivity

by reducing

the

action

in

terms

of

overall

oxidation

reactions

occurring,

view

contribute

significantly

conditions

are

was used

have

model

no longer

the dependence pressure

the

18 species.

wall wall to

the

fit

Eight

isothermal

ignition of

extra

experimental

assumes

the

though

oxygen.

delay

has become

methane produced

4 of

With all

reaction

that

model

oxidation

the

vhich

reaction.

the

at

pressures

containing

61

61 reactions

have

are

these

may be minor

reactions data

were

initial

not

and it

if

assumes

(ref.

13).

they

that This

as temperature

added

on ignition

conditions on the

are

6

no specified

The model

experiments

in

data.

a model

Within

phenomena

may be an over-simplification

overall

whereas

them.

by ensuring

experimental

reactions, reactions

reactions

experimental

predicting

at partial

involving

of

phase

scheme

They have

small.

of

and of

looked

discrepancies,

to

gas

explaining

23 - 26).

isothermal,

are

model

of

to validate

heterogeneous

may introduce

complex

some already-established

(refs.

This

of

as a method

necessary

workers

approximate

partial

ketones,

selectivity;

the MTCR to

level

sensitiser

modelling

both

describes

elementary

variations

aldehydes, The criteria

complete

selectivity However,

a slight

chemistry

50 bar

products.

years,

is

Russian above

for

reduced

attain

methane

used,

it

correctly

saturated,

selectivity.

partial

of

ethers,

These

maximum selectivity.

including

formaldehyde)

the

oxygen

appear to

sensitisers.

temperature;

* additives

Modelling

(and

a sensitiser.

may help

operating

of

peroxide.

10% and this

points

of

:

to

as the

be those

hydrocarbons,

additives

amount of

absence

was tested,

formaldehyde.

selectivity,

* additives

terms

the

reached

The general

models,

were

improvements

some experiments

methanol

to

on the minimum temperature

selectivity

greater

not

the

and di-t-butyl

on the methanol

gave

co-reagent

in

sensitisers

and aromatic

The majority

high

of

sensitisers

- the effect

zero

chosen

and water,

effect

apparently

being

(ref.

delay

26)

(ref.

was used

temperature

when the

27). to

The

investigate

and the

initial

a

312 Simplified proposed

reaction

elsewhere

a whole

are

important

is

the

formaldehyde,

+

is

and that

very

four

If

et

in

competition

should

alter

not written,

of

the major

source

donor,

methane,

of

:

the

sole

source

of

methoxy

:

by hydrogen

fate

of

the

abstraction

atoms

to

hydroxyl

from

the

which

is

balance,

but

converted

can.form

increase

u’,per the

is

from

there

some hydrogen

a theoretical

could

This

principally

a hydrogen

carbon

there

radical.

form water,

of

and in methanol,

all

methyl

are

must be

methanol. limit

of

selectivity

2/3

limit

+

as the methoxy

radicals

two radicals

only

the

always

through

slightly.

debate

is

are

radicals

hydroxyl,

amount of

CH,OO + CH,OO

Also,

and their (ref.

other

channels

reaction

methylperoxy

is

methane,

this

exist

importance

Another of

and there

with

relative

28).

self-reaction

small

reaction

is

that radicals

for the could :

CH,O + CH,O + 0,

are

reaction

dominant limit

these

with

selectivity

This

is

and hydroxyl-radicals.

hydroxyl

selectivity

of methyl

the

as

( 71

of

a certain

the

formed

the

methane

are

for

the

reaction

selectivity

models

CH,OH

concentrations

were

species

In terms

A reaction

direct

it

that

a hydrogen

hydroperoxide

hydrogen

Hence,

combination

methanol.

is

excess.

in both

equations

As the

of

dispute with

that

methyl

is

debate

large

selectivity.

increase

of and

radicals. of

atoms

CH, + OH +

focus

little

radical

propose

of

hydroperoxide

form water.

direct

some features

been

( 6)

at abstracting

present

the

but

have

may be over-simplified

or other

14).

efficient

balanced

the

(ref.

point

the

features

( 5)

decomposition

by methylperoxy

for

is

methoxy

peroxide,

The major

to

14),

chemistry

There of

ref.

major

CH,O + OH

hydrogen

used

omitted.

the methyl

methane,

explain

CH,OH + R

the

CH,OOH +

to

example,

as the

reaction

Yarlagadda radicals

for

hydrogen

CH,O + RH

methane

(see.

questionable,

features

methanol

mechanisms

bypasses

source

could

then

of

reach

( 8)

able

to

the

production

methoxy 100X.

react

radicals,

The Russian

further of

with

hydroxyl

then

the

modelling

CH, to

produce

radicals

and if

theoretical study

(ref.

23)

313 takes the

account

of

all

of

optimum conditions We are

for

on one used methanol

in

methanol the

(ref.

29).

modelling

(ref.

30).

times,

predicts

(CH,OH) added.

experimental of

are

about

needed

to

a maximum selectivity

a model

form of

about

to

find

the

(ref.

15)

amounts

40 - 50% for

the

optimum

mechanism

Russian that

of

is

reactions

methane-to-oxygen

significant

try

find

some extra

resembles

observations

4OO*C, high

to

The reaction with

It

not

production.

formulating

production

the

but does

formaldehyde)

of

ignition

, temperatures

residence

(or

course

points,

methanol

for

predicts

>20 bar

based of

model,

and

pressures

ratios

of

and short

methanol.

It

a flow-reactor

in plug

mode. Some mechanisms

conversions

with

CH, + 0,

+

the

is

occur

This

at

though

of

methyl

formaldehyde

radicals

at

lov

and 0,,

:

into

two parts

: first,

by a re-arrangement

reaction

has been widely

radicals

with

+

+ 0

this

formation

( 9)

split

the

CH, + 0,

(4)

followed

reactions,

methyl

the

between

reaction

low temperatures

coupling

explain

a reaction

addition

often

radical,

products.

to

HCHO+ OH

The reaction peroxy

attempt

by postulating

competing

of

above-mentioned

and hydroxymethyl

correctly

flow

for

ourselves

conditions

the

CH,O

reaction

is

(ref.

31).

reaction

postulated

Even at

may not

molecular

an addition,

but

is

to

used

the not

to

in oxidative

important.

The

possible

route

has another

form a give

now thought

temperatures

be at all

oxygen

to

and decomposition,

reaction :

(IO)

very

slow

at

these

temperatures,

as it

is

highly

endothermic.

Novel

reactor Since

of

the

reactor

chemistry. design

small-scale However,

systems

can alter

32),

flow

to

reactors

nature

experimental

work has used

methanol

has been alternating

of

produced electric

has been apparent oxygenates

production

the critical

through

it

selectivity

on methanol

the high-pressure of

(ref.

the

The influence

of

evidence

mixture

and reaction

work by Brockhaus

(refs.

reactor

in

of

either small

fields

static yield produced

the

by influencing

small

14.15)

design.

that

differences

design the in

the

may be further

The majority or flow-tube by passing in a 0.06”

of reactors.

a methane-oxygen (1.5

mm) gap

314 between (ref.

cylindrical 34)

a tube

has also

through is

to

ignited

quenched with

been

which

mixture this

plates

ignited

at

involve

the

18%.

in

of of

selectively.

It

- air

flows.

mixture

ethane)

is

tube,

methane

The reaction though

along

vater

of

vapour

consists

subsequently

the up to

of

This added

reaction

may be

6.1% are

quoted,

different

paths

with

involved

the

studies

at atmospheric

air

is

photolysis

between

to

air

of

are

3 and

ESR and radical those

at higher

may be questioned.

to whether

are

be added.

and formaldehyde

using

similar

schemes

and

The reactions can also

of methane

37)

of

carried

pressure,

source. but

but methanol

(ref.

published

is

are

conversions

according

reaction

conversion

These

vapour,

detected

the

photochemical

as a radical

products,

been

of

100°C,

and water

mechanism

parts

the

35 - 38).

50 -

amounts,

have

studied

(refs.

methane

high

radicals

The common initiation

H,O

have

many different

relatively

temperature, proceeds

of

reactor

29%.

compounds

photolysis

Methoxy

light

of

(or

down the

Conversions

low temperature,

yields

trapping.

further

co-workers

on mixtures

The reaction formed

methanol hydrogen)

and methane

Still

gas.

oxygenated

relatively

performed

produce

combustion

conversion

Ogura and his

out

to

(typically

selectivities

Photochemical

A quenched-pulsed

33).

by a spark,

mixture.

methanol

to

used

a fuel

by an inert

methane

(ref.

is

water

present vapour

It or

not.

by 185 nm UV

:

H + OH

+

In the

absence

methane, produce

to

(11)

of

air,

produce

the major

both

methyl product,

methanol.

In this

oxidation,

the magnitudes

radicals

are

relatively

large

fast.

reaction

of

methyl

radical

with

of

ethane,

reaction

enough Other radical

methane

the

resulting

radicals. or

system, of

the

to

ensure

reactions with

radicals

hydrogen

radicals

can couple,

react

hydroxyl

radicals

unlike

with

the high-pressure

concentrations that quoted water

abstract

The methyl

the

of methyl rate

as sources

vapour,

for of

and the

this

from to

to

form

flow-tube and hydroxyl process

methanol reaction

is

are of

the

hydroxyl

:

CH, + H,O

l

CH,OH + H

(12)

CH, + OH

l

CH,OH + H

(13)

315 but

these

reactions

conditions

used

When air

(or

ethane

is

is

the

to hydroperoxy

occur,

to any great

the

present,

hydrogen

atoms

and methylperoxy

prevented

methylperoxy

almost

radicals

significant

not

extent,

at

the

operating

here.

oxygen)

since

radicals,

will

is

dominated

and the methyl

radicals

completely

will

amounts

chemistry

produce

when air

is

methanol

of

equations

by a combination

radicals

respectively.

both

by peroxy will

be converted

The formation

present.

Self-reactions

and formaldehyde (8)

of of

in

and (4).

CATALYTIC OXIDATION Production

of

methanol

Attempts one, the

aiming other,

literature results

to at

oxidise

the

high

1985186

extensive,

earlier

have

the

al

the

best

included

Cu/SiO,,

time

for

et

al

22)

over

is

like

have

of

led

at

quartz

although

was little

both

from

the

in general,

over-oxidation,

there

by Burch

methanol

looked

are,

in

work.

group

the yield

metals

the

ambiguities

and the

of

>40 bar,

Co/Al,O,,

Hopcalite pressure

a fact

times

have

various

a constant

and residence

should

also

groups

difference agree

or Pyrex,

is

examined

that

a

necessary

effect

of

to

passing These

solids.

manganite),

30 atm.

17 - 50 sets.

be borne

the

catalytically-active

(a copper of

in an empty reactor that

catalytically-active Copper,

(ref.

mixtures

the mixture

conditions,

that

reaction;

yield.

Gesser

They used

247 - 407°C

22).

improving

Nonetheless,

surface,

two classes

case

the

Both groups

pressures

into

oxidation

In neither some of

some degree

steel.

fallen

by the more recent

and concluded least

non-metallic

the methane/oxygen

SnO,.

for

of

reaction.

at

have

homogeneous

(ref.

problem

wall

and stainless

inert

Hunter,

the

to

that,

resolved

and co-vorkers

reactor

claim

Pyrex

been

homogeneous

as leading

relatively obtain

Gesser addressed

pressure of

Burch et

the

although

undesirable

betveen

from

reaction.

have

influence

catalytically

yield

since

Both Hunter, 151,

the

at a fully-heterogeneous

reported

(ref.

methane

improving

TiO,

temperatures

in

(By comparison,

was 174 seconds

under

in mind in making

aerogel the

and

range

the

residence

the

same

comparisons

with

the

reactor.)

between

reaction

and the

although

the

reaction

(8%)

300 -

selectivity

conversion at

longer

of

35OOC. had little towards methane

residence

methanol was lower

time.

effect

on the

remained (621,

very

compared

course high to

of at

the

the 92 - 96X,

gas

phase

316 Of the obtained

oxide

at

catalysts,

2470C,

gave

only

conversion.

Moreover,

the

irreversibly,

shortly

after

produced

only

oxides

Burch et reacting

conditions

to

yield

they

quite

unambiguously,

obtained,

cent

the methanol

of

the methanol conclude, entirely

could

CH,

+

H+

To this

end,

they

by incorporation

of

form was measured

temperatures oxides

C,H,,

of

C,H,,

for

of

If

temperature

well

the

(ref.

was taken

methanol

formation,

step

not

put

the

suggest but forward.

of above

of

39)

has

methane

(<10X)

even

the

best

have

produced

They believed

protonation

‘superacid’ of

however,

being

conversion

al is

production

some that

:

(HM) and increased

of

to

this

oxide,

there

both

rather

acidity the

at formation

oxidative the

coupling, products.

HM and HMF mordenites, reactivity, -1.0%

formation

although at 425’C of

the it

for

HMF.

CO + CO, increased

products. that

there

a reaction One has

is

a link

mechanism to

comment,

H?iF

than

occurred

10% of

was only

value,

of

was little

were due.to

increase

methane

function

methane

constitute for

the

region.

nitrous

conversion

was similar

fluorination

et

claims,

from methane.

The Hammett acidity

the

decomposed

Burch

(14)

by the use

of

stable! a few per

hand,

methanol

although

the H-form

in

did,

other

lower

showed,

more than

mordenite.

H,

the

surprisingly

earlier

through

under

for

results

despite

and Moffat

+

in

methanol

and low conversions

methane

(HXF).

be -13,

products

and dominated

The authors

off,

used.

selectivity,

of

mordenite

but most

that

fell

conditions

direct

a highly-acidic

CH,’

are

on the

the

products

be noted

result,

catalysts

Their

to make methanol

Kowalak

: methanol

should

was

+

of

to decompose

copper,

c 1 bar)

reasonable

and appreciable

of

best 4% CH,

accounted

group.

carbon, C,/C,

the

only

other

stability

Below 400°C,

main influence

rapidly

the

as low as 350 - 425aC.

The distribution

the

attempts catalysts

was encouraged

as oxidant,

activity

turnings,

of

of

fluorine

to

Selectivity dioxygen

use

activation

used

the All

mixtures

under

the

by using

[CH,]’

the

failed

Copper

encouraging.

+

but

83% at

decomposition Canadian

reactor

(preactants

encourage

the

that

in

results

they

to

at

its

T > 400°C

to maintain not

interesting

of

for

low pressures

looked

methanol/oxygen

work on use

in an attempt are

whether

present.

inappropriate

The other

results

have

see

surprisingly,

not

that

started.

of

carbon.

a Pyrex-lined

entirely

remark

reaction

15)

that

5OO’C.

to methanol

authors

compared

Even at

used

of

(ref.

SnO, showed any promise

a selectivity

between beyond

superacid

the

however,

initial that

sites

and

activation a radical

317 mechanism

cannot

be dismissed.

oligomerisation

of

that

radical

oxygenated

participate

in

CH, and the

the

Il’chenko partial

(700°C)

(70

even under

- 80%).

these

together

lowest

temperature amounts, somewhat,

Their

coupling

Anderson zeolites

for

discourage

been

partial

replaced

oxide of

was,

0.25

-

carbon.

Small

comment that very this

bulk

of

to

mordenites

of

methane

the

products

methanol

two sets

was

rest.

(0.1

However,

- 0.9%)

formaldehyde.

C, hydrocarbon

of

as

at much higher

methanol

of

dominant,

were

At the

yield

fell

to

and formaldehyde

however. of

results.

are

formed,

increased

does,

however,

but,

The Russian although

the

yield

group

they

of

seem to have

CH,,

to with

of

the

to have

of

which

of

of

do

oxygenated

been

in

the

at

were

also

to aromatics

of

low acidity,

to

hydrocarbons.

structural

Al”+

A

ions

properties. 510 -

balance

615 K conversions obtained,

being

oxides

observed,

of

and the

of methanol

attribute

to

had Nitrous

was characteristic

The formation

and Tsai

possibilities

78 - 38% MeOH were the

C, and C, olefin

Anderson

the

and,

formaldehyde,

these

one of

to aromatic

selectivity

Cu-FeZSM5.

the

the appropriate

selectivities

to convert

of

case,

methanol

where most

improve

amounts

investigated

in this of

was found

used

failure

have also

conversion

amounts

combination,

ensures

stable

- 25%) made up the

oxygenates

41)

oxidation

small

low acidity

examined

- 3.0%)

mordenites

FeZSM5 zeolite,

1.52%

of

temperature

sufficiently

As a result,

the

these

interest

further

again,

with

of

(ref.

by Fe’*,

together

those

products.

and Tsai

copper-exchanged

are

as oxidant

amounts

(0.8

selectivity

compare

principal

the

small

as to how the

de-alumination

oxidative

(12

investigated, the

also

dioxygen

+‘C,H,

CO + CO, remaining to

have

15 - 25% and the

amounts

while

difficult

product.

40)

very

larger

make no suggestions

reaction

and Hoffatt.

of

C,H,

(600aC)

increased

comment that

order

vhile

vith

negligible

is

(ref.

conditions,

found,

It

the

lov

products

as CH,O, are

They used

than Kovalak

of

the

scheme.

catalysts.

were

co + co,

such

and colleagues

temperatures

of

relatively

species,

reaction

oxidation

conversions

The bulk

authors of

was unique

some kind

the to

of

synergism. The earlier already mentioned methanol

been

vork

discussed

that

they

of

Somorjai

(ref.

length

in the

at

investigated

and formaldehyde

the more recent

work

at

received

above.

different

catalyst

who exchanged

ionisable

groups

transitional

metal

ions.

and of

previous

levels Nitrous

system

oxide

but

oxide

carbon

(ref.

43)

it

may be

catalysts,

conversion

was used

on a Russian As seems

of

Lunsford

reviews

MO- and V-based similar

A rather

of

42)

obtain

and selectivity

was used

(AP-3) the

to

as oxidant.

by Il’chenko

to be invariably

to

has

et

with case,

(ref.44),

a whole the

series

least

318 active

catalyst

CH,/N,O

gave

ratio

carbon

gave

of

-

similar

(small)

amounts

of

reported

single

in

direct

would

the

3).

Sinev the

Nearly

of

as,

methanol

Fez*

-

and Fe’*

and lower methanol,

on the methane

currently, to

yields

46)

of

while

Cu2* gave

methane

and has

catalysed to

complete

formaldehyde

around

formaldehyde

9),

surfaces

for

in a

a half

of

use

the

to

of

the

fact

formaldehyde

(ref.

47).

MO, Cr and its and other used

specific

with

in

the paint

it

is

congener, oxides, with

unless

are not

of

pursued

some success.

exceed

5 -

able

Pure metals

to

45). inhibit

to

the

for

the CH,/O,

This 3). of

be of

but and

complete feed.

At the

production,

work was

and it the

use,

Pd/ThO,,

formaldehyde

selectivity. (ref.

to using

are

is

a little

catalytic

activity

of

further, industrial

either

surprising their

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1986

inhibitors

oxidation

modification

standard based

in

in mind,

do not

catalysts.

largely

and Klier

type

W, into for

46)

position

subject work

gas-phase

halocarbons

was very

34% (ref.

that

Russian catalysts

complete

were

the

the

added.

oxide

towards

by adding

been

extensive

are

be industrially

reviewed

Keene and Trimm (ref.

Pd/Al,O,,

this

would

two exceptions,

on stable

methanol,

by Pitchai that

has not

In view

yields

Cullis,

7.5% HCHO at

find

with

activity

extensively to

that

one or

compounds)

completely residual

of

with

work has used

that

(ref.

the

a yield

and,

30% for

to be too

almost

been

goal converted

useful

or

remember

surprising

also

studies

the

(ref.

published

felt to

same time,

silica

slow

practical

all

Mann and Dosi

system

during

towards

very

halogen-containing

methanol

of

of

Mn*+,

combustion

et

formaldehyde,

(generally

metal

incomplete

and Klier

8% for

discussed

13.8%

Cr’*,

conversions

same as when Pitchai

that

with

is

progress

remark

oxidation

Tib+-exchanged

of

CO,.

amounts

conversion

be a desirable

production

much the

generally

helium.

a

and formaldehyde.

during

quantities

has been

one has

produced

trace

However,

remains

higher

773 K, with

industries.

attractive

(ref.

is

methanol

and polymer

being

smaller

methanol

Industrially,

stage

World’s

with

at

formaldehyde

Formaldehyde

oxidation.

but

gave

reaction

a selectivity

products

methanol,

of

with

CH,,

remaining

of

for

substantially

of

Zn** and Bi*+

Production

been

selectivity

diluted

the

yields

selectivities; equal

1.33,

best

1.8% conversion

no formaldehyde gave

the

catalysts

on silver

that

several

experimental

changes

in valence

for

or on the workers

have

catalysts. state

oxidising

Fe/MO/oxide incorporated However,

are

not

easy,

have

319 Otsuka oxides,

and Hatano

and tried

cation.

to

in

Fig.

2

required

step

2,

which

active

out

have measured

it

that

imply

with

the

of

activity

scheme

hydrogen

quite

the

of

electronegativity

a conceptual

abstraction

would

for

in step

different

of

methane 1.

a range

but

properties

the

of

respective

oxidation

shown

insertion

of

oxygen

in catalytically-

sites.

CH+

CH,_x$-HCHO

Fig. 2. Reaction Otsuka and Hatano

One might, little

sequence for (ref. 48)

therefore,

of

highest vas

48)

correlate

The pointed

is

(ref.

the

expect

character

activity

for

at a maximum for

electronegativity minimising

Ca,O,

plot.

the

rate

that

both

step

3,

other

to

with

might

ail

products,

which

lay

maximising

with

in

step

by

sites

be best.

hand,

compared

by the most

proposed

oxide

steps

conversion

and Bi,O,,

*

oxidation,

a compromise

for

On the

of

HCHOwas encouraged

methane

needed methane

-co,co

CO and CO,,

of

the

HCHO yield and the

highly-electronegative

a

the

including

the middle

2.

having Thus,

implies

selectivity

oxides,

those

for of

W, B

and P. Arguing binary of

on these

oxide

CH,/O,

semi-empirical

mixture 3.0,

2.8% methane

of

they

for

Be with

obtained

a W/F of

lines,

Otsuka

B supported

up to

0.42

g.

data

are

results

is

1% yield

hr.

and Hatano

on silica.

L-l,

of

HCHO with

a not

developed

a

At 873 K and a ratio a conversion

untypical

value

for

of oxide

catalysts. Some selected cases, with

where the

a range

highest

considerable between

recent

range

3 - 0.2,

973 K as at

the

is

49)

touched

relatively

are

of

lover

tends

to

exceptional

on later. narrow

some work

(ref.

was used,

probably

with

become

range

of

spanning

because

of

the

an order where

are

used

the high time of

magnitude,

Schvank’s

low temperature

with

employed

those a

723 -

873 K, CO

results used,

also

high

range

above

temperatures

an extremely

is

varying the

while

(mass/flow)

i.e.

there

within

slow

In most

2.

stoichiometry

much more dominant.

because

on Cr,O,/Ai,O,,

data

been kept

extremely

The pseudo-contact

49)

best

CH,/oxidant

is

in Table

As can be seen,

have

reaction

here

the

yield.

temperatures

value

together

quoted,

or best

conditions

although

and CO, formation (ref.

of

selectivity

gathered

but

clusters the

exception

mass/flow (593

K).

this

in a

ratio

of

H

hf. 18 -

0.6

1.0

813

0.19

1.0

m

0.23

0.0

1.0

m

0.B

2.9

1.0

123

0.56

0.08

1.0

m

0.56

0.45

0.66 0.66

2

0.33

0.33

E 0.66

863

E 0.33

E :.:. .. ::: i.:. * * 3.0 n.a.

Kz “.a.

U.0

0.34

n...

al.0

0.6

“A.

a.0

O.Ol

“4.

8.0

II

Es?

( 0.P hdar) Infed

-

02 68

-

z

li El 17

f---t-

1.0 1.m

73 2:

2:

1.0 8.4

:

1.0

787

0.7

1.3

10

1.0

2:

t 1.0

2.2

z ::: z :::

2

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l.2 3.6

58 10 -

E 82

69 -

66.1

64

-

321

On the whole,

the

necessary

compromise

molecule

and the need

only

a few cases

converted

to

cases,

between

restrictive

the energy

to minimise

do the yields

to desired

attempts

relatively

force

higher

self-defeating,

yields

of

selectivity

(mole

products.

cent

Tabie

of

In

methane

2 demonstrates

conversion

sharply

the

the methane

per

methane

falls

represent

desirable

I - 2 per cent.

by increasing

used

to activate

formaldehyde

exceed

as the

needed

over-oxidation

of

product)

conditions

is,

under

how

in most

such

conditions. The use the

case

of

oxidising

of

nitrous

attempted

power

partially

of

he used rather

with

There

of

that

NE0 does

oxidation

:

actually

on silica oxygen

to note give

hoped that

slight

that

hand,

of that

to

on MOO, and that for

support

these

51,52),

these

vhere

he obtains

groups

53)

partial

to

almost

other

(ref.

milder

may tend

(refs.

the

as in

possibly

low Na content,

any of

was active

the

used

Spencer

very

Just

dioxygen,

evidence

Barbaux _et

O- species

other

that

of

have been

In the work of

supported

on the

Ox-,

very

HCHOwith

It may be pertinent

N,O.

is

some comment.

is to

catalysts

N,O as oxidant.

yields

, it

compared

oxide-containing

a MOO, catalyst higher

requires

formation

oxides,

products,

Molybdenum

exclusively

as oxidant

methanol

surface

oxidised

hopes.

oxide

have lead

do with commented

to

oxidation

total to

formaldehyde. In a contribution co-feeding 523 K,

the

passing with

the

advantage

Spencer’s MoO,/SiO, great

[ref.

level, 51).

inversely

over

the

of

0,

(ref.

52)

vith

methane.

purity

of

should

be reduced

show very to methane

N,O,

of is

silica

In the

the

reaction

The degree

is

99.51

used

clearly conversion

then that

compared

with

conversion

at

overwhelming.

mixtures

as support,

how selectivity (Fig.

3).

the

obtained,

over

a

among the more successful.

as much as possible,

by

run at

claim

selectivity

scarcely

CH,fO,

of

in situ first, mixture

The authors

much greater

the

55)

on oxidation

formaldehyde the

N,O was produced series.

HCHO is

(ref.

vhich

The results

of

and despite

on the

proportional

in

at 673 - 723 K.

oxidation

to give

541,

ammonia into

reactor

however,

direct

work

(ref.

two reactors

the yield

reaction 0.1% CH,,

catalyst

stress

sodium

second

catalyst,

oxidation only

converts

the

a V,O,/SiO,

723 K is

and CH, into

catalyst

through

direct

by Krupa et

0,

NH,,

He lays

and especially preferably to

the
formaldehyde

ppm. is

322

. . . . . . . . . . . . . . ..-f

,.(_...,..

(a)

4 5 2 3 % Methane Conversion

1

0

(b)

Fig. 3. Selectivity/conversion relationship for formation oxidation of methane with oxygen at different temperatures (b) Catalyst V,O,/SiO, (a) Catalyst MoO,/SiO, (ref. 52).

In the plotted

V,O,

case

of

catalyst

showed

A number of

activity

than most

up to

relatively

of

high

contact

interesting

point

the

reactor higher

but

alumina

CO,,

confirming

vork

surface

texture 20 rnp g-1.

they

of

results

not

clear, silicas

Carbon

atoms

that

K),

for

at

were

obtained

formaldehyde products

by use

of

produced

partial by Guliev

compared

to

need

reasonable

bulk

silicic

only

CO and

(ref.

hr-r

authors

-1800),

selectivity. great

stress

to maintain

the

surface

surface

were

59)

space

lay

on the

C,H.)

CH, radicals.

et higher

the

formation.

oxidation.

a rather

873 K at

deposited

of

no

walls

(mainly

Using

(6000

and the

the

by N,O gave

for

be enhanced

shown

An

or quartz

production

of

866 K at

(8X).

oxygen

level

561 have at

Vycor,

coupled

silica

although

(ref.

the

same temperature

57)

has measurable at a lower

poor

substituting

KSM and KSK-2. (ref.

itself

is

activity

could

3(b)).

can be converted

noted

(s893

the of

their

intermediates.

that

57)

and only

(Fig

, albeit

selectivity

be

a silica-supported

and Moffat

0,

could

velocity,

silica

to a significant

at

conversions

are

is

used

points

good

Schwank et

this

the

selectivity,

silicas,

much higher for

with

had a discernible

specificity

remarkably

reasons

reaction

the

two Russian than

but

and magnesia

that

KaszteIan

(ref.

vhich

but not

acid

obtained

their

tubing,

also,

The activity,

above

from

temperatures

observed

velocity

times,

space

By contrast,

formaldehyde

co-fed

data

on temperature

out

to

catalysts.

the methane

of

3(a)).

pointed

methane

Schwank et

At the

Quite

other

4.5%

formaldehyde.

using

of

independent

dependence

have

conversion

of HCHO during : (ref. 55)

selectivity/conversion

(Figure

a marked

authors

for

were

being

temperature-dependent

activity

that

the

MoO,fSiO,,

on a common curve,

slightly

of

Y

6

invoked

they The

on the area as being

323 The effect

of

silica-supported that

(ref

had

the

591,

Na* in

found the

that

been

remarked

effects

less

allowed

sodium

and molybdena

at

lower

high

recent

selectivity

of

all

clear-cut,

of

may cause

undesirable

functions

and

MacGiolla

that

the

strong

interfere

Coda et N,O as

small

levels

without

co-workers

60)

between

the Ho~~/Mo~~

of losing

(ref.

interactions

with

found but

using

catalyst

and his

521,

a catalyst

K) and

suggesting

Spencer

and


as

(<873

of MOO, in

levels

silica

Spencer

silica

levels.

temperatures

work

of

on.

behaviour

of HoO,/silica

the

support

and

on the

on slightly

The most

suggests

already

effect

selectivity

selectivity.

silica

little

working

oxidation,

on reactivity

MOO, has

sodium

reduced

sodium

the

oxygen

shuttle

mechanism. There

are

approaches reactor

or

three exceeds

design

specified

to

of

per

products

relatively

rose

to

efficiency

extensive

42% for

iron the

former

5 bar

were

Optimum

partially

occurring

The last in a Japanese describes methane

catalysts at

600°C.

(ref.

for

the

the

be a

Although

catalysts

reviewed

CO and CO, being

both

yield

a

seem to

8).

of

not

to AS-37,

(ref.

conversion

of

and yield.

space

velocity

HCHO from

recycled

ratio,

gas,

while

just

yield

.

of

so-called

greatly.

a commercial

of

-2% to

the

the

increased of

the

was

former

in

vital the

gas

to

Whether

process,

(ref. giving

64).

This

a selectivity

The patentees

lay

the

is,

conversion. diluted

(1:9)

notably

almost

although

yields,

the

is

yields

somewhat of

stress

part

argon.

to

total of

region

that

the

may be (ref.

formaldehyde

economical

3 -

and MOO,,

catalysts

66% at a conversion on the

with

Pe,O,

reaction

of

although between

exclusively

that

high

reported

non-stoichiometric

in a quasi-cool-flame giving

that

Pressures

leading

good

is

selectivity,

catalysts,

obtain

phase

Both

pass

HCHO in high

heavily

suggests

to catalysts

a single

49).

Other

investigation

are

for

methane

oxygen

-7OWC.

results,

reference patent

the

were

Subsequent formulation

basis

and WO, gave

active

although

temperatures

oxidation.

from

and yield

and Schwank

was much more

gave much inferior

correct

conversion

Fe,O,(MoO,),.,,

used,

the

are

matter.

Tsigdinos

molybdate

refers

many of

the

catalyst/hour)

The outstanding by Kastanas.

removed

form

a manipulation

973 K and an overall

(gHCHO/volume could

62)

but with

same recycle

recycle

uses

many years

the

a different

however,

over

of

formaldehyde

The work would

50 increased

When CO and CO, were

38%.

(ref.

of

The catalysts

shown to depress

temperature of

Patent

recycled

are

yield

really

61).

as low as for

extensively

ratio

these

(ref.

out

probably

high

the

catalyst.

carried

as these

a recycle

formaldehyde reactor

is are

removed,

8000 hr-‘,

such

pass

of

yield

a relevant

a programme

above,

selectively

The first

aluminosilicate

conversion the

to work where

the

but

Russian

follow-up

under

10%.

increase

explicitly

commercial

At the

references

with

details

of

10.5%

water

plays

64). appear but

in

324 achieving which

high

it

does

For example,

this.

by saturating

the

methane/air

The best

temperature, of

Fe (IIX), a silica

sense

that

90.3%

my

lead

(ref.

to

65)

catalysts centre

without under

of

elements

which

plays

reaction

nmol.

details

were

0.07

nmoi.

of

well

becomes increased relatively proceed,

0,

pointed

that

leads

understood,

may yet

+

need

f

more important mass action less

out

to

1.5% methane

recently

appeared,

partial generation

and Rooney

from

The result group,

700°C using

which

oxidation an Maa0

was a series

supported

formation

of

the

on series

from methane,

a 1~1 methane/air

CH,/hour. of

selective

excitation

by UV light

oxidation

of methane

As low a temperature of

hr.

mol-1, the

hr-*

carbon

being

CH,fO,

ratio

g-1

of

3.0.

67)

923 R (ref.

or

Other

Under these

was noted.

catalyst

This

and compares

catalyst

under

-3 m mol.

hr-1

TV

as 450 R gave

observed.

formaldehyde,

a 3X MoO,lSiO,

that

with

a

conventional,

g-1,

using

0,

52).

the mechanism

oxygenated

although

further

CH,

species,

some of the kinetic

refinement.

for

the

homogeneous

and especially data

The initiating

for

step

gas

methanol, some of

is

the

:

HO,

t 11

as the

pressure

effect,

important.

controlling

the

oxidation

already

reaction

at

v/w)

in

conditions.

The best

3% of

for

phase

reaction.

a very

843 K (ref.

of each) (50%

Amir Ebrahimi

a combination

m mol.

g-1 at

catalyst

partial

We have

0.2

hr-1.

a 1.8% Mo/SiO,

Mechanism

to

conditions

g.

room

(10% v/v

formaldehyde

catalyst.

about

by

be obtained

catalyst

only

an alkyl

at

no oxides

WfF 0.62

first,

radical

the

m mof,

obtain

have

is

at

to be the active

R is

for

used

HCHO/hour,

corresponds

non-activated

+

to

some methanol,

of

5.35

66)

over a 5% MoO,fSiO, -5

HCHO yield

CH,

(ref.

temperatures

conditions,

fairfy

in

activity

of

of

phase

part

the

catalysts.

where

rate

formaldehyde

steps

an important

oxides

of

developing

methyl

a conversion

a yield

over

of

80% selectivity

and moderate

figure

of

the

same reaction

metathesis

on MoCl,/R,Sn,

paper

vapour

of

In the

with

The second

can only

water

the MOO,, gave

20% conversion

mixture,

above

with

implied

problem

ideas

olefin

the mechanism

given

communications

the

had exceptional

what

remainder

the

research.

the

of

based

catalysts

giving

of

de novo,

and combining

catalysts,

silica of

new avenues

with

are

catalyst,

preliminary

examine,

mixture

selectivity

Two interesting

results

was a mixture

MO oxides

support.

at

the

Mg and MO, the

Bi,

a similar

conversion

suggesting

reaction

catalyst

Ni (II),

being

without

selectivities,

the

is

and partly Thereafter,

overall

increased, because

the

chemistry,

chain

partly

surface

because

reactions

propagation

as shown in Fig.

of

reactions 4.

the

become

325

CH

4

WWW02~02

Fig.

4.

It

Schematic

is

difficult

heterogeneous Only,

block

there

in a very few cases

sub-atmospheric

highest

I968

has

comparisons

of gap’

in order

have

been

This

case.

(ref.

gas phase

to

measurable

obtain

in have

at other

>6OO*C (873 partial

the

K),

than

conversions, far

above

the the

volume

inferior

can be attributed

to

to

at high

those

the

obtained

over-oxidation

mechanism’

by Dowden,

Schnell

for

selective

and Walker

(fH3

CH 4teci-”

(ref.

oxidation 711,

ads

of

methane

shown in Fig.

(+ ~&+CO’+

ads

vas

presented

5.

CO, 1 HCHO,,,

+ OH

I

ads

P

Fig. 5. catalyst

‘Virtual (slightly

A-

-0orO

Z(Q)

in of

15).

A ‘virtual

0

the

gap’.

oxidation.

reaction

been

work with

and a ‘temperature

done

gas phase

results

the

mechanism.

work been

been

included

the

oxidation

a ‘pressure

generally

in purely

in every

product

both

used

15,21,?2),

absence,

the desired

is

and,

used

Where catalysts (refs.

the methane

has catalytic

pressures

temperatures

pressure

of

to make direct

because

minimum temperature

their

diagram

0

I

II

ads

ads

ads

I OCH,

0

I

I

ads

ads

mechanism* for partial oxidation adapted from Dowden et al (ref.

of methane 71).

over

oxide

in

326 This

is

a classical

take

place

methane quite

on the

and the

Hatano

sites,

(ref.

48)

bi-functional Stroud

(ref.

73).

re-generate

with

in

account

thinking

in

not

area

increasing

easily

progress

in

be trapped

the out

temperatures

field from

as lov

over

Li/MgO

formation than

surfaces

depends

the

equivalent

CH, radicals

react

hydrocarbons) (ref.

76)

surface

also

and in

the

hydrocarbons, If dioxygen with

the

at

gas

Oads -species oxides

the in

the

is

the

cycle to

also

a

formation

production

-OCR,.

would

Whether

of

require

methanol

an unresolved

over

a

is

question,

methyl

that

an

and

the

(ref.

quite

Lin _et

to

form

the

>700°C.

nominally

react

have

to

detect

75)

is

like have

products

in

CR, may MgO, at used

CH, generated energy

considerably

phase

Garibyan

of

oxides,

(ref.

rBle of

further

reviewed

yields

over

but

coupled

important

74)

al

gas

drastically

may be produced to

activation

Li sites

however,

been

reasonable

methane

for

not,

The whole

has

radicals

Ionisation)

of

does

may desorb

The apparent

mol-1)

5,

may occur.

surfaces

they

besides

generating

Dowden mechanism,

by a Rideal-Eley of

catalytic

reaction (C,

for

CH, lower

(1).

The

and higher

and Margolis

radicals,

heterogeneous

both oxidation

on the of

methane.

surface, to

kJ.

temperatures

phase

and

9)).

bypasses

that

by passing

other

emphasised

72)

-OH groups,

(ref.

as in Fig.

For example,

(206 each

including oxide

according

more often,

with

observed

have

out

phase

concentration

value

it

and Lunsford

400 - 6OO*C.

on the

et

vith

that

Multi-photon

at

of

The possible

, is still

and that

as 4OO’C.

the

formaldehyde

methanol

reactions

and pointed the gas

that

reactions

Campbell

REHPI (Resonance-Enhanced

is

scheme,

reaiisation

Driscoll,

use

and

answer.

phase

on a catalyst,

phase.

by Otsuka the

that

for

by Sinev

production

methane

of

require

them (ref.

dissociation.

hydrogen

reaction

of

suggest

suggests

in fact,

a clear

gas

to

reactions

dioxygen)

differently

by both

species

review

and,

give

possible

the

by the

relatively gas

(see

the

the dissociation of

from neighbouring

oxygen

adsorbed

simple

of

water

the mechanism

of

A relatively

the

for

formaldehyde

work does

changed

of

interaction

intermediate

take

work

all

success.

of

sites

feature

them

Dowden mechanism

as an intermediate

reductive

led

-OCH, as a precursor

subsequent

Another

current

active

that

slightly

developed

some slight the

by elimination

of

of

This

out

dissociation

re-stated

subsequently

of

the

participation

methanol

a point

point

probable

more recently.

be closed

feature

(and

catalysts

Consideration could

The authors

surface.

activation

different

mechanism , where

Langmuir-Hinshelwood

carbon.

mechanism,

methyl then to

the

radicals,

can activate

gas

CH, may react

produce

phase desired

products

or,

321 We do,

therefore,

occur

in

phase

and surface

the

region

have 600 -

to

consider Over

7OO’C.

initiation

possible

c

0,

+

CH,

+

HO,

‘X

i-

COlsurf +

CH,

f

COHlsurf

In the

case

of

gas

relatively

phase

low rate

reactivity,

may ensure to

the

Once formed,

emphasises

CH,

+

the

that

K, for

for side

that

higher

place

the

of of

of

the

their

place

at

ways,

high a boundary

according

The flow

diagram

to (Fig.

the

is

may occur

The value

of

scheme on the

This

treatments

reactions

hydrogen

particular

peroxide,

products

for

try

is

where more work needs

favour to

C,H,,

the

the C,H,

and

to

take

account

processes

that

available,

and combustion some time.

that

into

more longer-lived

studies

to be done.

take

although chemists of

and hydroperoxy

studies

step,

will

The fates

radical

Most combustion

interactions

to

increases

readily

in a termination-type We suggest

the

700 K.

involving

methylperoxy

products.

an area

4 to

do exist

the actual

at

products.

not

characterise

hence,

equilibrium

begins

coupled

possible is

in models

importance.

species

the

surface,

the

the

on temperature,

radicals

oxygenated

catalyst

and, radicals

500 K and 10.6

shown in Fig.

of

of

increasingly

to

information

Approximate

at

of methyl lead

radicals

oxygen-containing

dependent

16.4

equilibrium

an understanding

such

of

strongly

300 K,

expense

reaction

these

4)

:

the methylperoxy

reactions

concentration

at

the

including

are

gas

spontaneously

with

take

in different

equilibrium

reactions

hydroperoxide,

radicals

(4)

T ) 700 K,

bimolecular

which

destruction

coupled

concentration.

and formaldehyde.

at

desirable.

methyl

the

atm-i

requires

been

of

equation

on the catalyst.

highly

the

may

( 4)

30.4

homologues,

species,

rale

and the

To extend reactions

appear however,

reactions

may react

and oxygen

to methanol

being

extent

radicals

of subsequent

constant,

Thus,

ideally

initiation,

radicals,

subsequent

the concentration

course

logarithm

left-hand

all

the

both

CH,O,

may lead

have

methyl

controls

the whole

that

of

range,

that

:

radicals

surface

reactions

surface.

vital

0, *

as this

For

diffusion

temperature

the pressure,

, the

volume.

of

layer

close

initiation

reaction

phase

temperature

may occur

CH,

over the vhole

this

processes

gas

assume

and few try of

surface

to

radical/surface

328 The amount of

mechanistic

but some common features already

mentioned,

over-oxidation

N,Q has

of

dissociative

adsorption

that

catalysed

N,O is

active

it

is

in the

oxidation

the

oxidation

being

of

whereby of

methane

atoms.

(Fig.

to

a switch

in

methanol

to

with

not

species

this

over

14.5

the

very

>90% of

m mol.

hr-1

for

to O*-,

this

between

the

g-l, at

SO

600°C

suggested

was responsible

species

corresponding

78) shows

as an intermediate

MO‘“/Mo”L

to

(ref.

vere

Yang and Lunsford

between

by

leads

MoO,/SiO,,

and converted

observed

formaldehyde,

formally

O,,

at 203*C vas

formaldehyde. valence

that

The catalysts

than 0,.

limited AS

control

form 0-

Work by Yang and Lunsford

rate is

to to

to formaldehyde,

especially

methanol

to attempt believed

has been catalysts.

to be a consensus

selective

conversion

a bridging-oxygen,

be used

seems

processes

Ho-containing

generally

methanol

oxidation,

that

for

53,67,77). of

less

: the

to is

there

(refs.

surprising

mechanism

It

but

far

methanol

at 350°C

not

tended

oxidation

actually

for

reactant

discernible

products.

CO and CO, production on the

work done on surface

are

a for

oxidation two Ho(V)

6).

“\\ /-go\ do MO

/

/Mo<

\

0

0

0

I

CH,OH

Fig. (ref.

6. Interaction 78)

The other

of

feature

catalysts

is

Kasztelan

and Moffat

molybdenum ordinary (ref.

53)

the

in

the

that

attempted (refs.

form of

Moo,-catalysts, have

silicomolybdates

methanol

correlated

molecules

seems

of have

phosphomolybdic supported increasing

(SMA) on HoO,/SiO,

MOO, catalyst

common to alf

correlation 67,771

with

surface.

the work on MO-containing

structure

with

published

selectivity-

a series

of

and silicomolybdic

on silica, selectivity catalysts,

both

they

with

papers acids.

and Barbaux

the

formation

as characterised

on For et of

by XPS and

step

329 Raman spectroscopy.

They attribute

stabilisation

SMA-phase

0-

on the

on bulk

pointed

MOO,, which

out

that,

products

of

together

with

reaction of

leads

at high

the methane traces

of

intermediate

the

overall

Fig. 7. catalysts

determined

consideration towards

with

different

space

velocities,

He was unabfe

the

-

catalyt

the

rate

Thiele

to

(ref. the

say whether

or not.

52)

to

has

primary

a secondary

HCHOy

product, methanol

A simplified

was a scheme

CO 2

ic

oxidat

were

any degree

ion

of

k %, k,

constants

modulus,

at

as opposed

Spencer

7.

k,

for

products

Oz- species,

CO being

formaldehyde

shown in Fig.

[CH,OH]

to

HCHO and CO, are

methanoi.

for

selectivity

the desirable

reaction,

Reaction scheme (ref. 52).

Data were

the

and oxygen

is

02

4-

of

increasing

to CO and CO, formation.

on the way to

reaction

CH 1

the

able

of

methane

and k,,

to

over

MoO,/SiO,

which,

taken

the

selectivity

predict

methane

conversion

review,

much of

(ref.

into

79).

STRATEGIC AND PROCESS IMPIJCATIONS Economic

assessments

As was stated for

work

in this

the

steam

reforming

example,

Shell’s

which

currently

is

non-selective encourage

(ref.

methanol wider-pore

with

synthesis

the route

recently-announced under

catalyst,

in this

process synthesis, zeolite

stage

chain

offers

the

with

stage

Mobil’s

driving-force for For

products.

distillates

(SMDS),

a relatively

and catalyst

selected

to

by a highly-selective

is

kerosine-type

still

syngas rather

steam

methanol

ZSM5.

the

an alternative

or other

uses

conditions

to

to

middle

oxidation

an alternative

than

for

followed

by partial

and then catalyst

to methanol,

the desired

first

need

in Malaysia,

growth,

to produce

case,

perceived

process

construction

Nonetheless,

gas,

of this

beginning

Fischer-Tropsch

60).

The Shell

the

has come from

hydrocarbon

hydrocracking

natural

at area

product. production

than

reforming,

to distillate

steam

from reforming.

followed stage,

by using

a

330 A process would

look

that

could at

attractive,

(ref

El> set

cost

of

out

to

try

of

catalytic assumed

gas

partial

oxidation

that

such

of

oxidation greater

than,

Pure oxygen because

of

as being

but of

the

quite

the

other

$172.

tonne-z, rose

on the

The extra

costs

is

oxidation

of

selectivity

an evaluation Department

partial

of methane

of

(OCM) to

of

route

showed

would

be 70X,

heat

transfer

of Mobil

process

athene that,

methane

per

considerable compared plant

81).

to

needed

pass

to

basis

over

65X for

the

to

be under

77X,

equal.

CO, removal falling and increased

other

for

nor

do they

hand,

(refs.

the

14,171

been

three

used

the

partial

for

the basis

sponsored

cases

give

best

as the

the Ilunter-Gesser Finally,

the

conversion/

R and D in a study

of

by the

: one using data

oxidative

for

a

coupling

gasoline. of

the Hunter-Gesser

at 90% selectivity

savings

the

and Foster,

They compared

and hence

of

were

consnmption,

and have

(DPOM) and,

on the

for stage,

investigated

On the

one using

The

process.

and co-workers

to methanol,

oxidation

They concluded conversion

some promise,

(ref.

gas

yet

do so.

Gesser

Energy

plant

to

be

at a value

two routes

converter

any way near

Hunter,

route

the

provide

on the

do have

by Kuo and Ketkar

conventional

direct

of

reaction

to

until,

of

by Edwards to

methane

route.

the methanol

postulated developed

of

stage,

conventional

natural

comes

oxidation

fell

air

oxide

approximate, the methane

for

costs

of

nitrous

to

no catalyst

to methanol,

being

results

homogeneous

from

methanol.

use

was calculated

the

is

purposes.

in

total

of the

and of

a

of

as it

methanol

need

increased

means,

admittedly

selectivity

the

duty

that

a

They

heat

synthesis

commercial

the

the

dismissed loop,

this,

tonne-z,

the

the

recycle

for

of

study,

to

water

requirements of

the

of

of

and Foster

course,

heat

clear

methane

much prospect published

remove

immediately

the beat

from

cost

from

leading

demand to It

the

arise increased

process),

by conventional

as selectivity

the

using

that

as,

$248

plant,

in one stage.

4OO*C, and with

in

of

linearly

made in

efficiency

energy

U.S.

less

to

a conceptual methanol

the

expensive

also,

importance

the

a rather

bar),

arose

being,

and Foster They compared

10 MPa (100

expensive

critical

of

from methane

They assumed,

: Edwards

that

as opposed

more or

that

reactor

nitrogen

feature

assumptions

thermal

of

100% selectivity,

(Benfield

the

same order

side-reaction

With

cost

the

as feed,

producing

run at

from

advantages.

using,

pass.

unrealistically

was the

co,.

per

as oxidant

build-up

One important cost-study

might

be removed

was used

plant

directly

and Edwards

possible

reactor

a stage

in one stage

superficially,

MJ-*I with

($3.5

10% methane

could

methanol

quantify

methanol

natural

conversion

least

to

a conventional

source

produce

the

other

conventional a halE.

at

data,

50 bar

two. route

7.5%

pressure,

The thermal and the

Kuo and Ketkar,

the

DPOM

efficiency investment

like

their

in

331 Australian

counterparts,

selectivity further the

in work

the

stressed

partial

to confirm

absence

of

such

liquefaction

costed

it

at

oxidation

plant

process

developments

the

year.

The reactor of

results

fit

(ref.

15).

natural

process solar

are

comes

prospects It

is

prospect single

pass. for

are

needed.

still

thoughts high

are

to apply As the regime, which

the

other

In the

two such

name implies, initially

very

field

with

fed

over

These

Burch

directly

et

into

al

the

formation.

is

especially

research

at

so for

preliminary

potential

present

to

35 - 50% 60%).

of

developments the

present

be so unquantifiable

This

promising

that

in Russia

between

hydrate

has

200 tonnes/

oxygen

studies

seem to

route

results

of

applications

of

this

of

type

of

on harnessing

areas so far,

methane

that

oxidation

absence

of

of

are

but

reactor pressure

performance

no catalysts yield

pressures

where

10%) in a

holds

the

laboratory

in present

designs

in

(say,

still

confirmatory

a breakthrough

best

data

technology,

low conversions

at

used.

in their

Department

the

are

in high

at high

reactor

a Pressure

there

to methanol

developments,

projects

at high

has some proven

partial

of

being

is

attempt.

on commercial

to novel

U.K.,

concept

100 atm,

methane

the

gas

typically

routes the

despite

progress,

process

at Bath University,

and Foster

by future

a capacity

process

prevent

may be more effectively

At least

an

fruition.

now turning

selectivity

In

from

oxidation

a remote

with up to

as some of

convert

future

at

direct

reactor

of

The homogeneous

prospects

scale

one feels

clearer

from

will

this

flow-tube

to be worth

and research

clear

that

supplied

reducing

here , the

by this

dependent

to

oxygen

Edwards

products

to

Especially,

become

power

the

which,

totally

further.

in abeyance.

conceptual

organic

used

economics as not

light.

of

to

by recommending

proceeding

their

selectivity

liquid

produced

and is

processes

will

Future

and methanol

The methanol

66),

pure

of

prospects

at pressures

with

time

of

a flow-reactor

qualitatively

photocatalytic (ref.

is

to

present

before

expensive.

described

selectivities

gas pipeline

visible/UV

are

operates

- 3.0X,

use

costs

on a development

The potential the

fixed

cost

technology.

The plant

2.5

the

process

work remains

excessively

reservations

83.84).

total

that

not

of

They concluded

data

further

total

separation

(refs.

(with

is the

had some application

a level

Hunter-Cesser

and there

in

Despite

the

remarking

+30X of

sensitivity process.

confirmation,

It may be worth air

the

oxidation

of

initial

Chemical

Engineering,

Swing Reactor operates in (refs.

the

under

to

enhance

an alternating

presence 72,73),

stages.

of for

In one, are

attempting

methanol

yields.

pressure

an oxidising methanol

workers

catalyst

formation.

The

332 reactor

will

also

desired

product,

contain

from which

depressurisation of

Chemical

a porous

of

Engineering

A ceramic

proposed.

at

tube

In one variant,

Bath work,

migrate

would

the

to

rates

with

pores

for

of

be recovered

outside

of

of

tube

no catalyst

purely

the

envisages as

using

is

to

envisaged

tube

at all

it

4 - 5 nm is

:

that

methanol

by surface

homogeneous

Department

between

similar

catalyst,

the

U.S.A.,

size

the

on the

the methanol

inside the

adsorb

from

Colorado,

controlled

oxide

on the

the

of

preferentially

proposal,

to separate

Of course,

reported

might

University 85)

the

would

A second

(ref.

a mixed

continuously.

reaction

cycle.

be coated

preferentially

collected

the methanol

the

membrane reactor

produced.

the

stage

which

a zeolite.

need

reaction

in

would

diffusion

and be

be used,

as the

(ref.

14)

are

and no results

are

yet

very

high. Both

these

available, others

products

but are

it

also

three

it

oxidation

different

selectivity. but

careful example, reactor

groups

These

is

clear

offer

that

and critical obtain which

at a very

certainly

early

stage

seem that

this

will

be the

direction

that

taking.

The catalytic or

are

would

to

design

their

good of

results the

yields

opportunities

obtaining

quenches

formaldehyde

claiming

for results

reactors. only

looks

of

more encouraging,

more than

10% per

exploitation is

not

easy

Schwank eE

products

two

and optimising

yields very

631,

catalysts

immediately

with

at high

and may require (ref.

on carefully-prepared

reaction

pass

after

for and using

contacting

a

the

catalyst.

ACKNOWLEDGEMENTS The Authors this

paper.

and with

Professor

Dr.

Spencer

N.D.

would

They also J. also

like

to

thank

acknowledge

British

helpful

Schwank.

who provided

provided

material

Gas plc

for

discussions details

in advance

permission

with of

of

Professor

unpublished

to publish R. results.

publication.

REFERENCES N.D. Parkyns, Chem. Br., 26 (1990) 841. L. Morton, N. Hunter and H. Gesser, Chem. Ind., (1990) 457. R. Pitchai and K. Klier, Catal. Rev.-Sci. Eng., 28 (1986) 13. E.Y. Garcia and D.G. Ldffler. Rev. Latinoam. Ing. Quim. Quim. apl. 14 (1986) 267. N.R. Foster, Appl. Catalysis, 19 (1985) 1. H.D. Gesser, N.R. Hunter and C.B. Prakash, Chem. Rev., 85 (1985) 235. M.S. Scurrell, Appl. Catalysis, 32 (1987) 1. H. Mimoun. New Journal of Chemistry, 11 (1987) 513.

Burch

333 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24. 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

41 42

M. Yu. Sinev, V.N. Korshak and O.V. Krylov, Russ. Chem. Rev., 58 (1989) 22. R.J. Hucknall, "Chemistry of Hydrocarbon Combustion", Chapman and Hall, London (1985). B. Lewis and G. von Elbe, "Combustion, Flames and Explosions oE Gases", Academic Press, New York, 2nd Edition (1961). I.A. Vardanyan and A.B. Nalbandyan, Int. J. Chem. Kinet., 17 (1985) 901. G.L. Bauerle, J.L. Lott and C.M. Sliepcevich,J. Fire Flammability, 5 (1974) 190. P.S. Yarlagadda, L.A. Morton, N.R. Hunter and H.D. Gesser, Ind. Eng. Chem. Res., 27 (1988) 252. R. Burch, G.D. Squire and S.C. Tsang, J. Chem. Sot., Faraday Trans. I, 85 (1989) 3561. O.T. Onsager, R. Ledeng, P. Saraker, A. Anundskaas and B. Helleborg, Catal. Today, 4 (1989) 355. H.D. Gesser, N.R. Hunter and L. Morton, U.S. Patent No. 4618732 (1986). J.L. Lott and C.M. Sliepcevich, Ind. Eng. Chem. Proc. Des. Dev., 6 (1967) 67. P.S. Yarlagadda, L.A. Horton, N.R. Hunter and H.O. Gesser, Combust. Flame, 79 (1990) 216. N.R. Hunter, H.D. Gesser, L.A. Morton, P.S. Yarlagadda and D.P.C. Fung, Proc. VII Int. Symp. Ale. Fuel Technol., Paris, Oct. 20 - 23, (1986) 620. N.R. Hunter, H.D. Gesser, L.A. Morton and D.P.C. Fung, Proc. 35th Can. Chem. Eng. Conf., CaLgary, (1985). N.R. Hunter, H.D.Gesser, L.A. Morton, P.S. Yarlagadda and D.P.C. Fung, Appl. Catal., 57 (1990) 45. V.I. Vedeneev, M. Ya. Goldenberg. N.l. Gorban and M.A. Teitelboim, Kinet. Catal., 29 (1988) 1. V.I. Vedeneev, M. Ya. Goldenberg, N.I. Gorban and M.A. Teitelboim, Kinet. Catal., 29 (1988) 8. V.I. Vedeneev, M. Ya. Goldenberg, N.I. Gorban and MA. Teitelboim, Kinet. Catal.. 29 (1986) 1121. V.I. Vedeneev, M. Ya. Goldenberg, N.I. Gorban, A.A. Kamaukh, and M.A. Teitelboim, Kinet. Catal., 29 (1988) 1126. A. Melvin, Combust. Flame, 10 (1966) 120. A.M. Dean and P.R. Westmoreland, Int, J. Chem. Kinet., 19 (1987) 207. M.3. Brown, D.R. Dowdy and D.3. Smith, Unpublished results (1989). I.A.B. Reid, 6. Robinson and D.B. Smith, 20th Symp. (Int.) on Cornbust., The Combustion Institute, (1984) 1833. 11.Batt, Int. Rev. Phys. Chem., 6 (1987) 53. R. Brockhaus and H-J. Franke, U.K. Patent No. 2,006,757, (1982). R.G. Mallinson, C.M. Sliepcevich and S. Rusek, ACS Div. Fuel Chem. Prepr. 32 (1987) 266. M. Lancaster, D.J.H. Smith and N.J. Stewart, U.K. Patent No. 2159153 A. (1985). K. Ogura, C.T. Higita and .hi. Fujita, Ind. Eng. Chem. Res., 27 (1988) 1381. K. Ogura and M. Kataoka, J. Mol. Catal., 43 (1988) 371. C.T. Migita, S. Chaki and K. Ogura, J. Phys. Chem., 93 (1989) 6368. K. Ogura, C.T. Migita and T. Yamada, .I.Photochem. Photobiol., 52 (1990) 241. S. Kowalak and J.B. Moffatt,. Appl. Catalysis, 36 (1988) 139. N.X. Il'chenko, V.G. Ilyine, L.N. Raevskaya, N.V. Turutina, A.D. Onishchenko and A.I. Bostan, React. Kinet. Catal. Lett., 38 (19891 141. J.R. Anderson and P. Tsai, J. Chem. Sot., Chem. Commun., 1987 1435. K.J. Zhen, M.M. Khan, C.H. Mak, K.B. Lewis and G.A. Somorjai, J. Catalysis, 94 (1948) 501.

334 43

44 45 46 47

48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

72 73 74 75 76 77 78 79 80

H-F. Liu, R-S. Liu, K.Y. Liew, R.E. Johnson and J.H. Lunsford, J. Amer. Chem. Sot., 106 (1984) 4117. N.I. Il'chenko, A.I. Bostan, V.M. Luk'yanchuk and I.A. Tarkovskaya, Katal. Katal.. 25 (1987) 42. C.F. Cullis, D.E. Keene and D.L. Trimm, J. Catalysis., 19 (1970) 378. R.S. Mann and M.K. Dosi. J. Chem. Technol. Biotechnol., 29 (1979) 467. H.R. Gerberich, A.K. Stautzenberger and W.C. Hopkins, h 'Concise Encyclopaedia of Chemical Technology', ed. H.F. Mark et al, Wiley, New York, 1990, p.528. K. Otsuka and M. Hatano. J.Catalysis, 108 (1987) 252. G. Kastanas, G. Tsigdinos and J. Schwank, 1989 Spring National AIChe Meeting, Houston, Texas, April 1989, Paper 52d. E.Y. Garcia and D.G. Lgffler, React. Kinet. Catal. Lett., 26 (1984) 61. N.D. Spencer, U.S. Patent 4, 607, 127 (1986). N.D. Spencer, J. Catalysis, 109 (1988) 187. Y. Barbaux, A.R. Elmrani, E. Payen, L. Gengembre, J-P. Bonnelle and B. Grzybowska, Appl. Catalysis, 44 (1988) 117. A.A. Krupa, I.V. Ogorodnik and L.P. Chernyak, Khim. Technol. (Kiev), No. 1 (1988) 36. N.D. Spencer and C.J. Pereira, J. Catalysis, 116 (1989) 399. S. Kasztelan and J.B. Moffat, J. Chem. Sot., Chem. Commun.. (1987) 1663. G.N. Kastanas, G.A. Tsigdinos and J. Schwank, Appl. Catalysis, 44 (1988) 33. I.A. Guliev, A.Kk. Mamedo and V.S. Aliev, Azerbaijan Khim. Zhur., (1985) 35. E. MacGiolla Coda, E. Mulhall, R. van Hoek and B.K. Hodnett, Catalysis Today, 4 (1989) 383. N.D. Spencer, C.J. Pereira and R.K. Grasselli, J. Catalysis, 1990 (in press). I.A. Zuev, A.R. Vilenski and I.R. Mukhlenov, Zhurnal Prildadnoi Khimii (English version), 61 (1988) 2607. A.R. Vilenskii, I.A. Zuev, I.P. Mukhlenov and A.E. Prokopenko, Russian Patent 1479450, (1989). J. Schwank, Personal Communication. T. Yamaguchi, E. Echigoya, S. Sai and M. Sueyoshi, Japanese Patent JP 62-212336, (1987). V. Amir-Ebrahimi and J.J. Rooney, J. Molec. Catalysis, 50 (1989) L17. T. Susuki. K. Wada, M. Shima and Y. Watanabe, J. Chem. Sot., Chem. Commun., (1990) 1059. S. Kasztelan and J.B. Moffatt, J. Catalysis, 106 (1987) 512. S. Ahmed and J.B. Moffatt, Catalysis Letters, 1. (1988), 141. S. Kasztelan, E. Payen and J.B. Moffatt, J. Catalysis, 112 (1988) 320. K.J. Zhen, C.W. Teng and Y.L. Bi, React. Kinet. Catal. Lett., 34 (1987) 295. D.A. Dowden, C.R. Schnell and G.T. Walker, Reprints of papers for IVth International Congress on Catalysis, Moscow 1988, ed. - J. Hightower, The Catalysis Society, Houston, p.1120. D.A. Dowden and G.T. Walker, U.K. Patent 1, 244, 001, (1971). H.J.F. Stroud, U.K. Patent 1, 398, 385, (1975). D.J. Driscoll, K.D. Campbell and J.H. Lunsford, Advances in Catalysis, 35 (1987) 139. S-P. Lee, T. Yu and M.C. Lin, Int. J. Chem. Kinet., 22 (1990) 975. T.A. Garibyan and L. Ya. Margolis, Catal. Rev.-Sci. Eng., 31 (1989-90) 355. J.B. Moffatt and S. Kasztelan, J. Catalysis, 109 (1988) 206. T-J. Yang and J.H. Lunsford, J. Catalysis, 103 (1987) 55. N.D. Spencer and C.J. Pereira, AIChE Journal, 33 (1987) 1808. S.T. Sie. M.M.G. Senden and H.M.H. van Wechem, Catal. Today, 8(1991)371.

335 81

J.H. Edwards and N.R. Foster, Fuel Science and Technology International,4 (1986) 365. 82 J.C.W. Kuo and A.B. Ketkar, U.S. Dept. of Energy Report, DOE/PC/90009-3, Aug. 1987. 83 U.V. Bak, A.D. Bondar, V.I. Veneneev. S.A. Egorov and P.M. Shcherbakov, Khim. Prom., (5) (1988) 272. 84 U.F. Budymka, S.A. Egorov, N.A. Gavrya, A.S. Mochaev, G.A. Khomenko and V.E. Leonov, Khim. Prom., (6) (1987) 330. 85 J.N. Armor, Appl. Catalysis, 49 (1989) 1.