Characterisation of organic coal structure for liquefaction

Fuel Processing Technology, 15 (1987) 257-279

257

Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

CHARACTERISATION OF ORGANIC COAL STRUCTURE FOR LIQUEFACTION C.E. SNAPE National Coal Board, Glos. GL52 4RZ (UK)

Coal

Research

Establishment,

Stoke

Cheltenham,

Orchard,

SUMMARY Studies relating the behaviour of coals in direct liquefaction to compositional properties are revlewed. No one single property adequately predicts conversions for all coals but correlations with sulphur, reactive maceral and volatile matter contents, vitrinlte reflectance and H/C ratios have been established for coals from particular geological reglons. At short residence times, bituminous coals give higher conversions than lower rank coals but, under typical hydroliquefaction processing conditions, distillate yields are often higher from lower rank coals. Lack of information on the nature of aromatic, aliphatic and heteroatomic groups and on the concentrations of low molecular weight constituents in coals has prevented more precise structural correlations with liquefaction behaviour being established. Analytical results from techniques that show potential to improve our understanding of the way organic coal structure affects liquefaction are assessed.

INTRODUCTION Since

the renewed

interest

during

the early

1970s in the production

liquid fuels and chemical feedstocks by direct coal liquefaction

(refs.

of

1-3),

there have been a number of studies relating coal reactivity to compositional properties:

a number of configurations for hydroliquefaction have been used in

process development units (PDUs) and in pilot plant work (refs. 4-6), pressures being considerably (refs.

4,7).

lower than those used in the German processes of the 1920s

Two-stage

processes

have been developed

to optimise

both

coal

dissolution in a suitable process-derlved solvent and subsequent hydrocracklng of the primary products to low boiling distillates (refs. 8,9). The

correlation

complicated because, are

heavily

of

coal

properties

with

liquefaction

behaviour

is

for a given coal, both the rate and extent of conversion

dependent

on

the

conditions

and

process

configuration

used.

Consideration must be given not only to the yields of the primary products and distillates, but also to the quality of recycle solvent. are still considered recycle

solvents

strive

to

to be

the most

for particular

improve

our

effective way

processes

knowledge

of

(refs.

coal

behaviour can be predicted more accurately.

Microautoclave tests

to assess both

10,11).

structure

so

coals and

However, we should that

liquefaction

258 Attempts

to

correlate

back to the 1920s (ref. 13,

14)

is

containing severe

properties

liquefaction

and that

studies.

dissolution

parts

because

it

liquefy

readily.

The characteristics is carried

in

the

absence

less evident with increasing

This review focuses the possible

of

relatively

hydrogen);

mild

the use of carbon

for coal liquefaction.

advance

structural our

bshaviour

systems

and chemical

are

of

the

important

conditions

differences

as

there have been

in

role

(i.e.

short

conversion

are

assessed way

(ref.

(ref.

15).

16)

techniques and

coal

such as pyrite,

their

the

Nor does it

as reducing

media

capable of providing future

structure

integration

affects

to

liquefaction

is considered.

COAL PROPERTIES Tables plant

information

1970s

of coal minerals

monoxide/water

understanding

(albeit under

of the organic part of coal and does

effect

Analytical

coals

process severity.

on the behaviour catalytic

the early

catalytic effect of which is reasonably well understood

detailed

that

today be classified

of the coal play a more

out under

generally

cover

Since

date

in 1940 (rafs.

demonstrated

of coal which would

time

discuss

behavlour

The work of Storch and co-workers noteworthy

residence

not

with

up to 87% dmmf C give high yields of soluble products

and exinite

numerous

12).

particularly

conditions)

vitrinlte

when

coal

AND LIQUEFACTION

1 and

(continuous)

properties

recent

laboratory

studies correlating

conversions

(refs.

17-54).

Details

conditions,

basis of calculating

Processing

conditions

according

BEHAVIOUR

2 summarlse

have

of

and

plus

investigated,

and principal

designated

PDU

in hydroliquefactlon

coals

conversions

been

(batch)

low,

pilot

to coal

processing

findings are listed.

moderate

or

high

severity

to the following criteria:

mild

no hydrogen

used

or

short

moderate hydrogen pressure

residence

time

(100-200 bar),

(
with

temperatures

less

than 430°C moderate

-

long residence

time (>30 mln.)

severe

-

same as moderate but with added catalyst.

temperatures up

in hydrogen,

to 475°C

A distinction yields

of

similar

overall

distillate 50, 52).

has to be made between overall

insoluble

conversions

are

matter)

conversions

yields Thus,

organic

upon

conversions

distillate

hydroliquefaction

hydrocracklng

laboratory not

in

and

the

primary

but

relevant

Coals vastly

dissolution

studies which have been concerned

particularly

(determined

yields.

to PDU and pilot

may

from give

different

products

(refs.

only with overall plant

operations.

Rank effect A number

of investigators

(refs.

3,17,24,28,29)

have

found

that at short

259

residence

times US low-rank coals

(lignites and sub-bituminous

coals)

liquefy

less readily than their bituminous counterparts while at longer residence times conversions

are often

fairly

similar

(refs.

3,17,24).

Hydrogen

consumptions

and the yields of benzene-solubles at the longer residence times (>30 min.) are roughly inversely proportional to rank (ref. 1,17,40), which is in accord with the

potential

of

lower

rank

coals

to

give

higher

distillate

yields

than

bituminous coals under typical process conditions (see Table 2). Baldwin

and

co-workers

(ref.

26)

have

proposed

that

to

highlight

differences in reactivity, coals should be compared by means of rate constants derived from conversions at a number of residence times rather than by single conversion values. residence

times

bituminous

They found that, whilst conversions to THF solubles at long (60 min.)

coals,

were

conversions

fairly

similar

for

at short residence

eleven

US

high-volatile

times were vastly different

and did not correlate with sub-rank. Whitehurst

(refs. 3,24) reported that, for US coals containing 75-90% daf

C, short residence time conversions correlated with fluidity and with pyridine extractability, Figure

i.

85-87%

dmmf

all of which reached a maximum at about 85% daf C as shown in

Clarke C

and

with

co-workers

high

(ref.

swelling

39)

numbers

anthracene oil, a poor hydrogen-donor

found gave

solvent.

that high

UK

coals

containing

extraction

yields

to swell is vastly reduced by the removal of chloroform soluble material 55,56),

these

constituents

findings

suggest

(mobile phase)

that

phenomena

the concentrations

of relatively

(ref. low MW

in coals have a marked effect on coal dissolution

under relatively mild conditions. swelling

in

Since the propensity of coals

suggests

that

The application coals

with

of polymer

85-87%

theory to coal

dn=nf C and

the highest

chloroform and pyridine extractabilities have the minimum cross-linking density in their macromolecular

structure

(refs.

57-60).

The fact that lignites and

sub-bltuminous coals cannot be liquefied to the same extent as bituminous coals at

short

residence

cross-linked density. example, higher

the initial concentrations

therefore

have

Alternatively,

times

could

also

be

attributable

to

their

higher

However, other explanations are equally plausible. dissolution of

polar

inherently

retrogressive

products groups

lower

from lignites

than

those

solubilities

For

contain considerably

from bituminous in

organic

coals

and

solvents.

free radical polymerisation reactions could occur

due to the inability of the donor solvent or molecular hydrogen to penetrate coals and cap free radical sites in the early stages of liquefaction. Physical effects. These are extremely important under mild liquefaction conditionsj e.g. the ability

of

conversions.

H-donor

solvents

to

penetrate

coals

has

a

marked

effect

on

Narain et al (ref. 61) found that trapping process solvent within

the coal matrix

by treatment

at about

200°C prior

to liquefaction

increased

260 conversion,

presumably because

in the early found

stages were

to be better

disrupt

retrogressive

reactions such

should

have

effects

as

coal

another

a beneficial

are not

times,

penetration

rate

limiting

step

coals and lignites times

(refs.

28,

must

(ref.

obtain

ability

presumably

64,65). (ref.

aromatic

one

retrogressive

conversions

part

of

reactions,

Particle 17),

size

suggesting

short

residence

fast as this appears

to be the

to increase

because

from

(refs.

Demineralisation

found

polynuclear

tetralin

to

and prevent

coal fairly easily at liquefaction

high

be relatively

66).

have been

to their

hydrogen

limit

with

can solvate

to

have been 67),

therefore

on conversions

large molecules Nevertheless,

due

and

transfer

in liquefaction

temperatures. solvent

Phenols

can

and

effect

observed

that relatively

62,63). that

reactions

and indollne

presumably

the coal matrix more effectively

(refs. pyrene,

to

free radical combination

Tetrahydroqulnoline

than tetralin

penetrate

hydrocarbons, depolymerising

limited.

solvents

hydrogen bonds,

retrogressive

at

and drying conversions

hydrogen-donor

of sub-bituminous at short

solvents

residence

are

then

in

better contact with the organic matter. Maceral composition It has been established vltrinite

and

bituminous

coals are generally more reactive

37,41-44).

exinite

that under a wide range of liquefaction

Reactive

conversions

(liptinite)

maceral

For

anthracene

example,

Clarke

oil decreased

with

the same rank (ref. 39). Hemisphere,

contribute

correlations liptinite

and

have

been

found

reported inertinite

concentration

contents

are obtained.

and

19,20,36,

correlate

with

regions

(refs.

yields

in

for UK coals

of

coals from the Southern

semi-fusinite

to overall

South

to

extraction

conversions

that when semi-fusinite for

(refs.

geological

that

particularly

38) found

sub-bituminous

African

with

(refs.

a

22,36,37).

is included

coals,

For brown coals,

low

in the

much

better

correlation

with

(hydrogen rich) and huminite macerals have been found (refs. 34,50).

Parkash macerals

from

than inertinites

in non-carboniferous

significantly

with conversions

al

increasing

macerals,

Gray et al (ref. maceral

et

However,

inertinite

reflectance

reactive

contents

macerals

for coals of similar rank from particular

31,38,39).

Indeed,

group

conditions

et al

(refs.

in short residence

consequently

the

43,

44)

have

reported

time liquefaction

liquefaction

synergistic

effects

between

for Canadian sub-bituminous

behaviour

of

whole

coals

was

not

coals always

consistent with that for maceral concentrates. Bulk properties It is clear from the data presented property Overall and

can predict conversions

therefore

analysis

has

conversions

and distillate

are dependent been

used

to

or oil yields

on different derive

in Tables

1 and 2 that no one single

and oil or distillate

yields

are not necessarily

coal characteristics.

expressions

for all coals.

predicting

related

Multi-variant

conversions

or

oil

261 yields

(refs.

other

term

contents. one

18,20,52):

for

these

reflectance,

contain

and

for

a term

for

carbon,

sulphur

volatile

and

or

at

Cluster analysis was used by Given et al (refs. 21,22)

hundred

US

bituminous

tetralln extraction

coals

on

the

basis

on

into three sets with differing

least

reactive

their

one

maceral

to group over

conversions

using

carbon and sulphur contents.

For the high sulphur coals of intermediate

carbon content that gave the highest

conversion,

and

promoted

it

was

found

that

pyritic

organic

sulphur

Oil yields,

particularly

increase with increasing

for Southern Hemisphere

coal H/C ratio

coals, have been found to

(refs. 31-33,35,68).

oxygen contents of low-rank coals tend to limit oll yields. al showed that the correlation improved formed

if the oll yields during

ratlonallsed

the

(see

dissolution

of

Figure

of

allphatic

brown

rich

2 and

as

relationship

between

such as reflectance, for

their

coals

"guest"

in

processing, 78-83%

distillate

dmmf

carbon

oll yields

and H/C

Hemisphere

49,53).

decreasing

rank under

the overall In

the

literature

catalysts vacuum

typical

conversions

(refs.

on

concentrations Distillate

of

it should he pointed

mineral

matter

Kohleol and

added

Recycle

solvent

recycle

structure

will

solvents.

For

pyrite

(ref. 53) i.e. when there and

(refs. may

is much

disposable

out that in processes

catalysts

to

employing

48,49), be

high

detrimental.

of the residues are too

product composition

composition

is largely governed by processing

and sub-bltumlnous

solvents

of

example,

solvents

contain

significantly

influence n-alkane

derived

coals tested

acceptable

undoubtedly

recycle

bituminous coals

of

yields increase with

inherent

process

severe

coals containing

Although

of

of

coals

pumping.

solvent and intermediate

There

the

moderately

conditions

effects

weakly

indicative

addition

rank independent.

beneficial

as

In

yields have to be limited if the viscosities

all US bituminous giving

the

differing or

for US and European

distillate

SRC-II processing largely

such

high for satisfactory Recycle

are

16,69),

separation,

or parameters

after

low-rank coals to increase overall conversions,

of

workers

"host" material.

for bituminous

However,

coals is

These

physically

counterparts.

yields are at a maximum (refs.

35). terms

molecules

is not as straightforward

Southern

the high

for the carbon dioxide

ref.

chemically bound to the more aromatic macromolecular The

However,

Indeed, Redllck et

for brown and other low-rank Australian

and H/C ratios are corrected

hydrollquefaction

concentrations

rank,

independently

conversion.

from

higher

quality the

(refs.

compound

concentrations

low-rank

coals

concentrations

conditions,

in the SRC and EDS processes

classes are

since of

13,54).

present

likely these

long

However,

to

in recycle be

coals

alkyl

coal

high

in

generally

chains

than

(refs. 70,71).

are many

studies

relating

the

composition

of primary

liquefaction

262 products,

particularly

structure

of

the

asphaltenes,

parent

coals

increasingly more aromatic, less oxygen, with

to

processing

(refs.

71-78).

conditions

Products

and

to

generally

the

become

containing more condensed aromatic structures and

increasing

process severity

(refs.

74-77).

Indeed,

in the

SRC-I process, bituminous coal products resemble those from lignltes (ref. 72). However,

when mild

liquefaction original

conditions

products

coals

sub-bitumlnous

are used,

is a valuable

(refs.

71,

77

the characterisatlon

approach

and

to probe

78).

coals are generally more

Asphaltenes

aliphatic

of

the primary

the structures from

and contain

of the

lignites

and

less condensed

aromatic structures than those from bituminous coals, (refs. 77,78).

ORGANIC COAL STRUCTURE AND LIQUEFACTION BEHAVIOUR The following discussion considers how variations and

hetaroatomic

behavlour. spectrometry tetralln

environments

Data

on

(MS) and

(refs.

(refs.

low

and

FTIR have

extractions

characterlsation

and

aromatic

MW

affect

groups

These

that

and

show

liquefaction pyrolysis-mass

with

conversions

other

promise

allphatlc

from

been correlated

79-81).

82-116)

constituents

allphatlc

already

in aromatic,

methods for

of

in

coal

advancing

our

understanding of liquefaction behaviour are summarised in Table 3. Aliphatic ~roups (i)

total concentrations

The increase

hydroliquefactlon

with

(Tables

is probably

I and

2)

generally

in maximum attainable

increasing

to a large

concentrations of allphatic groups.

H/C

extent,

ratio

and

attributable

Although solld-state

oil yields

decreasing

in

rank

to increasing

13C NMR and FTIR have

proved the most popular methods for estimating aliphatlc carbon concentrations and aliphatic

to aromatic

hydrogen

ratios

respectively,

there

is still

some

uncertainty concerning the accuracy of these techniques (refs. 82-92, Table 3). Nevertheless, found

that

bituminous

they highlight yields

of

structural

ethylacetate

trends.

solubles

Senftle et al

in

tetralin

(ref. 83) have

extractions

of

coals correlate better with the intensity of the band at 2853 cm

US -I

in the IR spectra of the coals rather than with the total intensity of all the C-H stretching vibrations (il) h~droaromatic

(2750-2995 cm-l).

~roups.

These probably play an important role both during

the early stages of llquefaction limiting studies

retrogressive by Reggel

and in the absence of a H-donor

reactions

et al.

(ref.

(refs.

I,

3).

Catalytic

solvent by

dehydrogenation

93) using Pd/CaCO 3 in boiling

phenanthrldine

(b.p. 330°C) indicate that the concentration of hydroaromatic groups decreases with increasing carbon content and, for the US coals containing about 83% daf C, the hydroaromatlc

groups account

40% of total H or 15% of total C). dehydrogenation

(refs.

94,95);

for 30-35 H atoms per I00 C atoms However,

results

secondary

vary with

reactions

the metal

used

(about

can affect (ref.

94),

263

palladium giving the highest yield of hydrogen.

In contrast, NMR analysis of

coal extracts indicates that hydroaromatic groups account for a maximum of half of

the aliphatic

carbon in a UK bituminous

about 10% of the total C (ref. 71).

coal containing 82% dmmf C, i.e.

The hydroaromatic groups probably consist

of i or 2 rings (ref. 96) with dihydro species predominating

(ref. 97) and not

highly condensed structures as proposed by Farcasiu (ref. 73). The

observation

that bituminous

coals

with

about

80%

daf

C apparently

contain the highest concentration of hydroaromatic groups (ref. 93) and do not give the highest

conversions,

either in short residence

time liquefaction or

anthracene oil extraction,

suggests it is not the total concentration but the

mobility

groups

of

hydroaromatic

liquefaction.

The

that

distribution

of

is

important

in

hydroaromatic

the

early

groups

stages

of

also

be

could

important, model compound studies indicating that dihydro groups, e.g. in 9,10 dihydrophenanthrene tetrahydro groups,

are

reasonably

condensed

could

the

aid

generally

e.g. in tetralin aromatic

hydrogen

more

117).

structures

transfer;

effective

(ref.

hydrogen-donors

In addition,

in the low MW constituents

pyrene

increases

the

than

the presence of

rate

of

of coal hydrogen

transfer from tetralin to coal via the formation of dihydropyrene (ref. 118). (iii)

alkyl/alkylene

groups.

Long

alkyl

groups

are

significantly higher concentrations in low-rank coals carbon) for

than in bituminous

the

paraffins

polyarylalkanes,

found

such

coals in

as

(refs.

70,71)

liquefaction

dibenzyl,

has

generally

present

in

(up to 10% of the total

and are obviously responsible

oils.

The

received

thermal

much

behaviour

attention

of

(see,

for

example ref. 119) because the cleavage of short alkylene bridges was thought to be important in coal dissolution. wide

variety

containing

of

aliphatic

hydroaromatic

However, other studies have indicated that a

structures

rings,

cleave

linking under

two

(ref. 120) probably by 8-bond scission mechanisms in

accord

with

the

generally

decreasing

aromatic

typical

groups,

liquefaction

(ref. 121).

concentrations

of

many

conditions

This finding is aliphatic

groups

found with increasing liquefaction severity (ref. 74-77).

More information is

needed

bridges

on

the

concentrations

of

short

alkylene

(C2-C4)

present

in

coals, though some inferences have been made from ruthenium tetroxide oxidation (refs. 100-102) and trans-alkylation studies (ref. 103). Aromatic groups. Durfee the

mass

and co-workers

range

ethylacetate

70-180

solubles

in

(refs.

reported

extractions of fifty one

79,80) have correlated peak intensities

Curie-point by

pyrolysis-MS

Yarzeb

et

US bituminous coals.

al.

with

the

(ref.

21)

gave

positive

correlations

alkylbenzenes and naphthalenes

with

for

in to

tetralin

Five factors were included in a

regression equation which gave a correlation coefficient of 89%. phenols

conversions

conversions,

gave negative ones.

while

Peaks due to those

due

to

Whether there is any real

264 chemical

significance

in these correlations

sulphur coals were included (ref.

81)

spectra

found

of

However, 122)

that

US

coals

and

therefore

The

correlated

the

Winans

such

bituminous

with

increase

yields

OH

in

in

tetralin

decreasing

could

Senftle et al.

bands

carbon

well

the

FTIR

extraction. content

reflect

found with decreasing

and

coals

as

co-workers

the

(ref.

aromatic

(ref.

II0)

of aromatic

(refs.

and

suggests

structures

104-106)

structure

have

carboxylic

much

used

Three

were

of

the

material

in

ring

found

13C NMR analysis

that are too highly condensed

becoming selective

acids.

benzonaphthofurans

Solld-state

that

coal rank and H/C

to the aromatic

into low MW aromatic

phenanthrenes

coals but not in lignltes.

concentrates consists

observed

Nevertheless,

phenolic

conversions

increase

distillate

to convert

structures

with

the

I and 2) may also be related

condensed.

oxidation

of

to be seen since some high

less condensed.

increasing

(Tables

less

in the investigation. intensities

the OH concentrations

structure becoming

ratio

the

remains

in

of maceral inertinites

to be liquefied

easily. Heteroatomic Model linkages,

linkages compound

studies

particularly

those

liquefaction

conditions

generated

the

derived

by

that

aliphatic

(refs.

cleavage

from certain

indicate involvSng

thioethers

thioethers

free radical chain reactions. for U.S. coals, but

the

lignites

distribution

increasing

concentrations

of

organic

sulphur

sulphur

counterparts

sulphur with conversion bituminous

been

numerous

used

to estimate

ether

108,126), groups

Illinois

titration,

to

hydrolysed

coal

are play

increased

present an

that, coals

significantly

113).

the

(ref. 35).

at

(ref.

have

and

of hydroxyl been

114-116).

made

Thus,

with

the

high

correlation

of

(refs. 21,22)

organic

for some US

Liotta

the concentration

in

low

significant role

in

groups

in bituminous

have coals of

et al.

that oxidation

of

found

of aliphatic

giving

ethers

(ref.

115)

effect on liquefaction. in

liquefaction.

127) and to significant

methods

concentrations

concentrations

their

temperatures

spectroscopic

to determine

to have a deterimental

important

(cleaved)

extraction yields decalin

explain

derivatisation

concentrations

few attempts

(Table 3, refs.

No.6

Esters

would

indicates

than bituminous

of labile sulphur groups than their

found by Given and co-workers

and this would be expected

appear

this

radicals

125) can promote

coals.

Whilst

(refs.

and

sulphide

(ref.

vary

(ref.

thioether

sulphide

reduction

not

and

hydrogen

and

sulphur

does

sulphur coals contain higher concentrations low

124)

and disulphides

groups

ether

are labile under mild

Moreover,

(refs.

less thiophenic

sulphur

of

groups,

Temperature-programmed

contain

of

number

120,122,123).

of

thiols,

a

rise

brown Esters

to

coals are

increased

and

easily solvent

oil yields on liquefaction with

265 Low MW constituents As

previously

extractable factor

affecting

fluidity

is

solvents,

closely

as

that,

material

be

in

and

trapped

to

to

the

the

low-temperature

residence

the

appear

times.

extract

129).

Not

obtained 128).

material, components

with

polar

There

is

the

some

low

MW

of

coals

and

Although most of this material has

of low MW components

(ref.

the major

surprisingly,

yield

extractable

solvent

to be

(ref.

macromolecular

(ref.

as consisting

from ultra-filtratlon

of would

dlmethylformamlde

within

to the mobile phase

in coals

short

at

addition

generally been perceived evidence

concentrations phase')

related

pyrldine

complication may

('mobile

conversions

also

such

contribute

discussed,

material

130)

(< ~I000),

that pyrldine

extracts

dispersed matter with weight average MWs of approximately

100,000.

there is

contain much

CONCLUSIONS i.

Maceral

composition

liquefaction

and certain

performance

different

criteria

distillate

or oil yields.

2.

being

At short residence

molecular

hydrogen,

dependent

on

However,

the

for

bulk properties

coals

required

from

to

ratlonalise

times or in the absence

the

extent of

amount

trapped material

of

coal

relatively

is also

indicators

geological

overall

appears

extractable

to be important

of

regions,

conversions

of a hydrogen-donor

dissolution low MW

likely

are useful

particular

and

solvent or be

strongly

material

to

present.

and

further work

is

needed to define the exact nature of the low MW species in coals. 3.

Inertinites

needed

to

are

define

generally

chemically

difficult such

seml-fusinlte

with low reactivity

and

with

those

non-carboniferous 4.

Distillate

increase More

with

detailed

concentration aromatic

higher

liquefy

material,

e.g.

and the

further

differences

from Northern Hemisphere

reactivities

from

some

studies

between

carboniferous Southern

are

coals

Hemisphere

coals. yields

increasing

in

relatively

severe

hydroliquefaction

H/C ratio and with decreasing

characterisatlon of

to

allphatlc

may establish

carbon

or

with

other the

vltrlnlte

correlations

proportions

of

generally reflectance.

e.g. with 1 and

the

2 ring

structures.

ACKNOWLEDGEMENT The author thanks British Coal for permission

to publish this paper.

expressed are those of the author and not necessarily

The views

those of the Board.

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129

130

R.J. Pug-mire, W.R. Woolfenden, C.L. M a y ~ , J. Karas and D.M. Grant, Application of 2-D and dipolar dephasfng --C NMR techniques to the study of structural variations in coal macerals, Proc.lnt.Conf. on Coal Science, Pittsburgh, USA, August 15-19, 1983, lEA, pp. 667-670. M.I. Burgar, J.R. Kalman and J.F. Stephens, A new NMR method for estimating aromatic ring condensation in coals, Proc.lnt.Conf. on Coal Science, Sydney, Australia, October 28-31, 1985, Pergamon, pp.780-783. M.J. Trewhella, I.J.F. Poplelt and A. Grlnt, Structure of Green River oll shale ~erogen, Fuel, 65 (1986) 541-546. A. Attar and F. Dupols, Data on the distribution of organic sulphur functional groups in coals in: M.L. Gorbaty and K. Ouchi (Eds.), Coal Structure, Am.Chem.Soc.Adv. in Chem. Series 192, 1981, pp.239-256. B.S. Ignasiak and M. Gawlak, Polymeric structure of coal. 1.Role of ether bonds in constitution of hlgh-rank vltrinlte, Fuel, 56 (1977) 216-222. R. Liotto, G. Brons and J. Isaacs, Oxidative weathering of Illinois No.6 coal, Fuel, 62 (1983) 781-792. R.J. Baltisberger, V.I. Stenberg, K.J. Klabunde and N.F. Woolsey, Chemistry of lignite liquefaction, Report for US/DOE, EC/02101-23 (1983) pp.7-9. M. Le Roux, D. Nicole and J.J. Delpuech, Performance indices for coal liquefaction solvents, Fuel, 61 (1982) 755-760. F.J. Derbyshire, P. Varghese and D.D. Whitehurst, Synergistic effects between light and heavy solvent components during coal liquefaction, Fuel, 61 (1982) 859-864. D.S. Ross and J.E. Blessing, Possible hydride transfer in coal conversion processes in: D.D. Whitehurst (Ed.), Coal Liquefaction Fundamentals, Am. Chem. Soc. Symp. Series 139, 1980, pp.301-314. B.M. Benjamin, V.F. Raaen, P.H. Maupin, L.L. Brown and C.J. Collins, Thermal cleavage of chemical bonds in selected coal-related structures, Fuel, 57 (1978) 269-272. S.E. Stein, A fundamental chemical kinetics approach to coal conversion in: B.D. Blausteln and M.J. Constock (Eds.), New Approaches in Coal Chemistry, Am.Chem. Soc. S3~p. Series 169, 1981, pp.92-129. Y. Kamiya, T. Yao and S. Oikawa, Thermal treatment of coal-related aromatic ethers in tetralln solution in: D.D. Whitehurst (Ed.), Coal Liquefaction Fundamentals, Am.Chem. Soc.Sump. Series 139, 1980, pp,lll-129. R.H. Schlosberg, T.R. Ashe, R.J, Panclrov and M. Donaldson, Pyrolysis of benzyl ether under hydrogen starvation conditions, Fuel, 60 (1981) 155-157. J.S. Youtcheff and P.H. Given, Dependence of coal liquefaction behavlour on coal characteristics, 8. Aspects of the phenomenology of the llquefaction of some coals, Fuel, 61 (1982) 980-987. C.B. Huang and L.M. Stock, On the role of sulphur compounds in coal liquefaction, Am.Chem. Soc.Prepr.Div. Fuel Chem., 27(3-4) (1982) 28-36. P. Zhou, O.C. Dermer and B.L. Crynes, Oxygen in coals and coal-derived materials in: M.L. Gorbaty, J.W. Larsen and I. Wender (Eds.), Coal Science Vol.3, Academic, New York, 1984, pp.253-300. B. van Bodegom, J.A. Rob van Veen, G.M.M. van Kessel, M.W.A. Sinnige-NiJssen and H.C.M. Stulver, Action of solvents at low temperatures I. Low-rank coals, Fuel 63 (1984) 346-354. J.W. Reasoner, C.L. Reagles, C.P. Clark, J.M. Whltt, J.C. Hower, L.P. Yates and E. Davis, Predictors of isothermal fluid properties of coals, Am. Chem. Socl. Prepr.Div. Fuel Chem., 19(i) (1984) 207-212. P.H. Given, A. Marzec, W.A. Barton, L.J. Lynch and B.C. Gerstefn, The concept of mobile or molecular phase within the macromolecular network of coals: a debate, Fuel, 65 (1986) 155-163. H.P. Hombach, Particle size and molecular weights of derivatives from coal, Fuel, 61 (1982) 215-220.

Mainly tetralin

7 US

207

I001

400 440, ~55 427

Tetralin HAD

104 US mainly high vol.bit.

Tetralln/ 3801-methyl413 naphthalene mixtures 400

400, 425

Synthetic mixtures

Tetralin

2 coalderived samples

US lignite to Iow vol.bit.

US lignite sub-bit, and bit.

ii US low pyrite high vol.blt.

4 US Wyodak sub-blt.

Whltehurst et a l

Gorln et al

Baldwin et al

30, 60

276 max.

M

L/ M

L

I0

560

L/ M

H

L

M

M

L

Severity

390

SC

60

60

40

2 50

Res. time min.

139

3 8 5 , 241 400

Anthracene oll

Various lithotypes

Given et al

103

Tetralin

449

400

H p~. bar

17 US

lignite to low vol.blt.

Coals

Reaction Conditions

Epperley

Neavel

(us)

Investigators

T°C

THF,cyclohexane + dist.

TRF benzene

Benzene, cresol

Pyridine

Ethylacetate

Benzene, n-pentane + flit.

Cyclohexane

Pyrldine, benzene

Solvents in product work-up

3, 24

I, 25

26

27

Conversion dependent on amount of H transferred from solvent. Variations between coals in conversion ~ H transfer relationship, no clear trend with increasing rank. Kinetic ranking of reactivity indicated no clear trend with increasing coal sub-rank (A, B and C). Distillate yields correlate with C, S and reactive maceral contents.

2123

Coals grouped into 3 subsets from conversion data according to C and S contents, high S and intermediate C content coals giving the highest conversions. At 3 mln., lowest conversions obtained for low rank coals and maximum conversion for bit. coal containing 85% daf C. Similar conversion for all coals obtained at longer residence times.

19, 20

18

17

Ref. Nos.

High conversions generally for vitrinite and liptinite macerals. Lower reactlvltles for inertinltes dependent on geological area.

Significant variations in conversions for coals from Appalachian region. Conversions predicted from S and VM contents.

coals.

Conversions to benzene-solubles inversely proportional to rank. 90% conversion to pyrldine solubles obtained after 2 mln. for bituminous

Principal Findings

St"m-ry of laboratory studies relatln~ coal characteristics to liquefaction behaviour

Solvent/ Catalyst

TABLE I

bO

Coals

US sub-bit. and bit.

US lignite and 4 bit.

Illinois and 3 Kentucky

13 Australian 67-93% daf C

219 brown coal samples

Brown coal and 3 llthotypes

27 Australian coals of varying rank

Australian inertinite concentrates

20 S.Afrlcan

Investigators (US, Australia and S.Afrlca)

Winans et a l

Naraln et al

Waiters et al

Cudmore (Australia)

Perry et al

Nomura et al

Jackson and co-workers

Shlbaoka et al

Gray et al

350475

405

400

400, 425

400

450

300450

419

Anthracene 450 oil/ZnCl 2

Tetralln

Tetralln

Tetralln/ ZnCI 2

Tetralln

Tetralln

Tetralln/ HDS cat.

Hyd. creosote oll

Tetralin

T°C

250

981

601

981

411

801

1401

751

-

H p~. bar

60

60

180

120

240

60120


6

Res. time mln.

H

M

M

M/ H

M

M

M/ H

L

L

Severity

Reaction Conditions

Toluene, hexane

Benzene, n-hexane

Dichloromethane, n-pentane

Benzene, n-hexane

Toluene with filt.

Toluene + filt.dlst.

Pyrldlne, toluene

THF n-pentane

Pyridine, benzene/ ethanol

Solvents in product work-up

Principal Findings

to liquefaction behavionr

Conversions correlate with reactive macerals including semi-fusinite, H/C ratios and VM contents.

Inertinltes, particularly semi-fuslnlte contribute significantly to hydrogenation products. Higher T needed to react inertlnltes compared to vltrlnite and exlnlte.

Good correlation between H/C ratios and oil yields (both corrected for C09). Brown coal liquefaction explained in ter~s of guest (allphatlc rich) and macromolecular host material.

Without ZnCIg, conversion correlates with humodetrlnlt~ content.

H/C gave best correlation with conversion. Exchangeable cations increase yields of heavy products.

Distillate yields and overall conversions correlate with H/C. Conversions correlate with reactive maceral contents for similar rank coals.

Similar conversions obtained.

Lignite gave lowest conversion.

Demlnerallsation increased conversions for sub.blt.coals. Yields of benzene/ethanol soluhles decreased with increasing C content.

Summa*7 of laboratory studies relatin~ coal characteristics

Solvent/ Catalyst

TABLE i (Contd)

38

36, 37

35

34

32, 33

31

30

29

28

Ref. Nos.

551

30, 400 430

380460

450

Tetralin

Recycle solvent/ Na~S+ re~ mud Creosote oil/Pe203 -S Naphthalene 400 phenanthrene/ Ni

Maceral concentrates

German and Turkish lignites

Australian brown, Japanese

7 vitrinite concentrates

Parkash et al (Canada)

Oelert et al

Morl et al

Ouchi et al

i001

15

60

1560

30

i0

240

60

Res. time min.

M/ H

M/ H

H

M

L

L/ M

L

Severity

Pyridine, benzene, n-hexane

Pyridlne

Benzene, Cyclohexane

THF

Dichloromethane

Pyridlne, benzene

Quinoline

Solvents in product work-up

45

46

47

Varying T for maximum conversions of different lignites. Wax contents considered to have only a secondary effect on conversion. Generally poor correlations of conversions with H/C ratios, VM and reactive maceral contents. Authors propose volatile carbon c o n t e n t gives best correlation. High conversions for all the samples but H consumptions and yields of benzene solubles decrease with increasing C content.

Conversions for whole coals not consistent with those of maceral concentrates.

4244

For sub-bituminous coals, reactivltiy is lip.> vit.>inertinlte. Higher T needed to liquefy inertinltes.

39

40

85-87% dmmf C with highest conversions. For coals of inertinite contents residue yields.

Ref. Nos.

Higher conversions for carboniferous coals than corresponding cretaceous coals. Conversion to benzene solubles decreased with increasing C content.

Coals containing PSI gave highest the same class, correlated with

Principal Findings

to liquefaction behavlour

pr. = pressure L/M/H = low/moderate/high - see text for classification of reaction conditions I = initial pressure Res. = residence bit.= bituminous VM = volatile matter SC = semi-contlnuous vlt. = vitrinite lip. = liptinite filt. = filtration vol. = volatile HAO = hydrogenated anthracene oll Hyd. = hydrogenated HDS = hydrodesulphurlsation FSI = free swelling index dist. = distillation

Abbreviations used

(Japan)

601

220300

201

390

Tetralin

21 Canadian

(UK)

Clarke et al

Ignasiak et al (Canada)

H p~. bar

Anthracene 400 oli, phenanthrene

Coals

Reaction Conditions

35 UK

Japan)

Investigators (UK, Canada, W. Germany and

T°C

Summary of laboratory studies relatin~ coal characteristics

Solvent/ Catalyst

TABLE i (Contd)

Kohleol

HVB (brown coals)

SRC-II

SRC-II

SRC-II

EDS

Strobel et al (W. Germany)

Lenz et al (W. Germany)

Wright (US)

Hoover (us)

Tomlinson et al (US)

Trachet et al (us)

IWB = H y d f i e r e n d e V e r f l u s s i g u n g yon B r a u o k o h l e SRC - S o l v e n t R e f i n e d C o a l

A b b r e v i a t i o n s used

Name

M

M/H

M

M/h

H

M/H

Process Severity

54

53

52

51

50

48,49

Ref. Nos.

EDS = Exxon Donor Solvent M,H = see text for classification of reaction conditions

Solvent quality is not dependent on coal rank.

Bituminous coals with pyritic S >1.5% and reflectance of of 0.65-0.75 process well. Addition of pyrite increases oil yields for sub-blt, coals and lignites. Maximum attainable oll yields increase with decreasing rank.

Empirical relationships derived to predict overall conversions and oil yields based on reflectance levels and pyritic S, VM and reactive maceral contents. Conversion drops signlflcantly for coals containing less than 1% pyritic S.

Without pyrite, conversion for lignites and sub-bit. coals lower than those for bituminous coals. Pyrite addition gives both higher co,verslons and distillate yields for the lower rank coals~

Petrographic composition of Rhenish brown coal has virtually no effect on conversion.

Maximum yields of distillate (<350°C) obtained for coal containing about 80% daf C and 10-12% daf O.

Principal Findings

Summary of pilot plant studies relating liquefaction behaviour to coal characteristics

Investigators

TABLE 2

Alkyl groups give largely mono-carboxylic acids

Alkyl groups transferred from coal to toluene

Trifluoroperoxyacetic acid and ruthenium tetroxide oxidation Transalkylation

-arylmethyl and other short alkyls

Suggests dihydro species are major type present in Illinois No.6 coal

Trlfluoroperoxyacetic acid oxidation

13C NMR analysis of soluble products is preferred to that of coals because long alkyl peaks are much better resolved in solution state spectra.

Distribution of aliphatie carbon in extract and tar fractions determined

NMR structural analysis

NMR analysis of coals, extracts and tars. Olefin yields from flash pyrolysis.

Pd/CaCO~ gives highest yields of hydrogen To avoid secondary reactions, use of lower boiling solvents than phenanthridine recently recommended

Aromatic and aliphatic H bands partially resolved in high resolution spectra

Also, solid state IH NMR Catalytic dehydrogenation

Accuracy of data for coals assessed by Painter and co-workers, errors may be considerable

Review of determination Reviews on use of solid state 13C NMR First application to coal Problems concerning quantification~ only about 50% of the carbon in some coals being observed Recent application of an alternative technique

COF~ENTS

Mainly FTIR

Pressure DSC

Mainly solid state 13C NMR

METHOD

Some methods for characterisln~ allphatic~ aromatic and heteroatomic groups in coals

-long alkyls

-hydroaromatic groups

-ratio of aliphatlc H to aromatic H

-total concentration of aliphatic carbon

Aliphatic

GROUP

TABLE 3

103

97 100-102

98,99

70,71

97

71,96

95

93,94

82

90-92

86-88 89

82 83,84 85

REF.NOS

Na/NH~ treatment

- ethers

HBr reaction BBr 3 reaction

TPR

s o l i d s t a t e 13C N ~ - s p i n n i n g sideband analysis -peak s y n t h e s i s

- S groups

Heteroatomlc

- p r o p o r t i o n of b r i d g e h e a d carbons

-dipolar dephasing

Solid state 13C NMR

-ratio of aromatic H to aromatic C

See text Cleaves allphatlc ethers only Method only applied to coal liquids

Sulphur groups are reduced at characteristic temperatures. Non-thlophenlc groups account for much of S in US coals

With quantification problems (see above), these methods can probably only identify major differences.

Despite problems concerning quantification (see above), results Indicate generally increasing ratio with increasing rank. Highlights differences between macerals.

Estimates include adjacent allphatic carbons and heteroatoms

Aromatic groups converted to low MW carboxyllc acids, NaoCr~Ov oxidation probably gives highest converslofls But these have not been reported.

Selective oxidation methods X-ray diffraction

Useful indicator but, as yet, little on quantification

CO~ENTS

Pyrolysis - MS

METHOD

Some methods for characterlsln~ aliphatic~ aromatic and heteroatomlc ~roups in coals

-average size

groups

-distribution of

Aromatic

GROUP

TABLE 3 (contd)

114 115 116

113

112

iii

109,110

107,108

104-106

79,80

REF. NOS

278

80

60

CONVERSION WT. %

z.0

20

20 PYRIOINE EXTRACTABILITY WT % 10

104 OtESELER FLUIDITY (div/min) 103

102

101

70

I

!

75

80

85

90

% dat COAL

Fig.l

Comparison of conversions in short residence time liquefaction with pyrldlne extractabilities and Gieseler fluidltles for a range of US coals (adapted from ref. 24)

-5

Fig. 2

0

10

20

3O

% OIL YIELD

~0

50

6o

I .7

I .8

HIC

13

i -9

I 1.0

I 1.1

i 1"2

Correlation between oil yield (n-pentane solubles, C09-free, dmmf basis) and H/C ratio (CO 2 free basis) for Australian coals; {~ , medlum-hlgh volatile sub-bltumlnous and bituminous; • , low volatile sub-bituminous; A , brown (from ref. 35)

I "6

13

n

[3

~i~ A

•