CA1111796A - Liquefaction of calcium-containing sub-bituminous coals and coals of lower rank - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process for the treatment of a calcium-containing sub-bituminous coal and coals of lower rank to form insoluble, thermally stable calcium salts which remain within the solids portions of the residue on liquefaction of the coal, thereby suppressing the formation of scale, made up largely of calcium carbonate, e.g., vaterite, which normally forms within the coal liquefaction reactor (i.e., coal liquefaction zone), e.g., on reactor surfaces, lines, auxiliary equipment and the like. An oxide of sulfur, in the vapor phase, is contacted with a coal feed sufficient to impregnate the pores of the coal.
The impregnated coal, in particulate form, can be liquefied in a coal lique-faction reactor (reaction zone) at coal liquefaction conditions without sign-ificant formation of vaterite or other forms of calcium carbonate scale on reactor surfaces, auxiliary equipment and the like.

Description

1 It was ~no~n prior to the tur11 of the century that hydro-

2 carbon gases and liquids, tars and chell1icals could be~obtained not

3 only rom potroleum, but from coal. Very early ~rocesscs employe(l

4 destructive clistillation, coal being transforn1ed into gases and S petroleum-like liquid products. Other coal conversion processes 6 involved the formation and extraction of a s]urry with a hydrocarbon 7 solvent, catalylic hydrogenation and hydrogenolysis. The use of 8 coal liquids as refinery feedstocks and as petrochemical raw materials 9 on commercial scale in this country now seems a virtual, or at least an eventual certainty in view of the demands now being made OJI
11 petroleum reserves.
12 A coal liquefaction process of particular interest now 13 under development is one W]liC]l utili~es a hydrogen transfer, or 14 hydrogen donor solvent to hydrogenate and liquefy the coa~. In such a process, crushed coal is contacted with a selective solvent which 16 ac~s at least in part as a hydrogen donor to supply hydrogen to the 17 hydrogen-deficient coal to convert the coal solids to liquids. The 18 product includes petroleum-lilce liquids, i.e., lO00~F- liquids, and 19 heavier products. The heavy products are characterized generally as ~0 "liquefaction bottoms," and consist of 1000F~ organics, inorganics 21 and carbon residue (fusinite). This material, whicl1 analyzes about ~2 60-70 wt. % carbon, and about 20 wt. % ash, lS less useful than the 2~ 1000F- liquid, and generally contains 40-50 wt. % of the original . . .:
24 feed coal to the process.

Coal is not a pure hydrocarbon, but is a material com-26 prised of carbon, hydrogen, oxygen, sulfur and nitrogen. It con- ', 27 tai~s a considerable amount of volatile matter. Principally, how-28 ever, it is a material in ~hich the orgaJ1ic ma~ter ma~es up an ~ ~ssentiall~ continuous phase within which mineral, or inorganic .
~ ~ matter îs dispersed. The Or~flniC mate~ial is co~1prised o~ bituMen `:

7~i 1 and humin whicl1 havc large, f~at, aromatic, lamellar structures that 2 differ in molecular weight, degree of aromaticity, oxygcn, sulfur 3 and nitrogen contcnt and degrce of crosslinking. Structurally, the 4 organic portion of the coal is constituted of condcnsed aromatic rings of high molecular weight, about 70% of the carbon atoms being 6 within the aromatic rings. Oxygen, sulfur and nitrogen are combined 7 in chemically functional groups, e.g., hydroxyl, ~eto, carboxyl, amino, sulfide, and the like ~11ich occur in various parts of the 9 molecules. The inorganic material COllSiStS of fusane, sulfur, e.g., pyritic sulfur and inorganic sulfates, and other mineral matter.
11 Various metals, notably calcium is present as complexes of large 12 organic acids known as humic acids; and perhaps, also as calcium '3 ions.
14 The mineral matter in coal is not necessarily inert in coal llquefaction reactions; nor is its presence necessarily benign.
16 The presence of calcium) in particular, as learned many decades ago by the ~erJnans, is quite detrimental. At ~Yesseling, near Cologne, `
18 Germany~ e.g. when the Germans operated a high pressure coal lique-19 factlon process for producing liquids from lignites they ~ound that the~ir reactors all too rapidly plugged solid with a hig]i ash-containing 21 scale whic11 they termed caviar , because it had the appearance of 22 agglomerated balls, or spherulites. The spherulites, which are ~3 Indictative of the vaterite form of calcium carbonate,were found to 24 be comprls~ed of calcium carbonate containing hexagonal crystals of iron sulfide. Deposits of the scale initially caused decreased 26 prodaction because of the necessity to lower throug11put, and all too 27 soon completc shutdown was necessary. Preheater tubes, on occasion, 28 burst due to bloc~age. Attemp-ts by the Germans to solve thls 2~ problem largely involved engineering techni~lles to prevent scale ~fo~mation. In one technique a small slip stream was withdrcL~L f~om : : : ` :
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, 1 an initial reactor of a series in a process called ''dcsclnding''. Ihe 2 initially formed small particles were continuously withdrawn and 3 removed, and the slip s~ream then returnecl to the reactor. This 4 aided in suppressing further crystal growth, and sloi~ed down the rate of scale formation within the reactor. l`his technique was 6 subsequently abandoned due to high gas losses and high erosion rates 7 within auxiliary equipment. In another me~hod, a first reactor was 8 provided with a concentric bottom mounted ;nlet tube through which 9 the coal feed was introduced, an objec~ive being to eliminate calcium carbonate growth in the product passed down stream. ~he 11 problem of calcium carbonate scale formation yet persists resulting, 12 inter alia, in intermittent operation. Further improvements are 13 highly desirable in coal liquefaction processes to eliminate, or 14 suppress, the formation of calcium carbonate scale in reactors, lines, and auxiliary equipment.
.
1~ It is, accordingly, the primary objective of the present `

17 invention to supply this need.

18 A particular object is ~o provide a process for the vapor . .
19 phase pretreatment of calcium-containing sub-bituminous coals and coals of lower rank to render such coals amenable to liquefaction 21 wl~ile suppressing the formation of calcium carbonate deposits as ; 22 scale, within the coal liquefaction reactor, lines, and auxiliary ~ 23 equipment.
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` 24 A more particular object of the invention is to provide a process of such character wherein the calcium is converted into a ,.
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26 ~molecular species ~]iich is innoc~ous as regarc1s the formation of 27 scale, the calcium forming particulate residual solids, on lique-28 factlon, thatare easily~disposed of with the coal liquef~ction bottoms.

A furtl1er ob~iect i~s to provide, as an artieLe oI manufac~

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ture, a pretreated particulate calcium-containing coal feed which has been rendered amenable to direct liquefaction by pretreating with a gaseous agent to form therein a molecular species of calcium, and the impregnated coa:l. then sent directly to a coal liquefact:Lon reactor (or zone) and liquefied withou~ the normal tendency to form calcium c~rbonate scale wi~:hin the reactor, lines and auxiliary equipment at coal liquefaction conditions.
These obJects and others are accomplished in accordance with the present invention characterized generally as a process for liquefying a coal feed, sub-sequent to a pretreat~ent, or preconditioning of a sub-bituminous coal, or lowerrank coal by contact with an oxide of sulfur, in the vapor phase, t:o Eorm an insoluble, thermally stable molecular species which remains as particulate solids within the residue, and within the liquefaction bottoms, on liquefaction of the coal. The added sulfur oxide reacts with the calcium of the coal to form a molecular species which deposits within the pores of the coal. The molecular species is thermally stable and does not decompose at liquefaction conditions, and during liquefactlon it remains as particulate solids and thereby does not form, or it at least suppresses the formation of scale, or calciu~ carbonate deposlts. The insoluable form of calcium remains within the liquefaction botttoms, or ash, and is conveniently disposed of, after liquefaction, wlth the liquefaction botto~s.
In the practice of thi.s invention, in a pretreatment step, an oxide of sulfur which is characterized by the formula S0 , wherein X is 2 or 3, is con-tacted in the vapor phase, is maintained in contact with a coal feed, suitably ;
: a particulate coal feed, for a period sufficient for impregna~ion of said sulfur : oxide into the pores of the coal, preferably for a period rangîng from at ~ least about 0.01 hours to about 24 hours, more preferably at least about : ~ ' ,:

-, . , :
~ ' ,~ , . ' ' ' 1 0.l hours to c2bou~ 4 hours. I'refcrably, the imprcgnation of the coal is carried ou-~ at elevatod prcssure, sui~ably from about 0 to 3 about 200 psig, preferably from about S to about lS0 psig. ~fter 4 the ;mpregnat:ion, the coal can then be liquefied, without any additional treatmel1t, at liquefaction conditions to produce petroleum-6 like liquid products.

7 The rate of impregnation of the coal depends to a large - 8 extent on coal particle si~e, and condition of the coal. In general, 9 the smaller the particle size of the coal the grea~.er the rate of impregnation, and conversely, the larger the particle size the 11 slower the rate of imprcgnation. Generally, however, particulate .- . , ~-- ~
12 coal of size ranging from about -8 mesh to about l inch particle 13 size diameter, and more suitably :Erom about -8 ~esh to about 20 mesl 14 ~Tyler series), can be adequately impregnated within the above ` 15 defined time periods by treatment, or contact with the gas, or a 16 mixture of gases, containing one or more of the~oxides of sulfur, 17 viz. sulfur dioxide or sulfur trioxide; or compound 11hich can be ç

18 decomposed in situ to generate one or more of tlie sulfur oxides, : : :
19 Preferably, the coal is treated on an as received ~or as mined) basis and is not dried prior to impregnation. In this regard it has .

21 been found that dr~ing of the coal is deleterious in that it reduces 22 the~amount of sulfur oxide gas that can be absorbed by the coal, and ~ : ~ . :
23 retards the rate of impregnation. It is believed that the drying causes~tl1e gel structure of the coal, and consequently the pores ,: : .
25 w1thin the strocture, to collapse. Also, ~hen the coal is dried, 26 ~the volume once occupied by~water is displaced by gas; this possibly 27 ~ dccreaslng~tho rnte at which the sulfur o.~ide gas can be absorbed ~ -2~ ~into the interior Or the coal. Thus~ it is believcd that the suliur ; 29 oxidc~gases dissolve in the water contained ~Jithin the pores to form ,: :
a sul~ate, or indirectly Q sulate is formed, e.g., by ox:idation in ~ 6 -`::: :
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1 situ from sul~ite; or, possibly an entiroly di-fEercnt insoluble 2 n1olQc~ r spcc:ies is formed.
3 1Yhile Applica11t does not desire to be bound by any spe-4 cific theory of mecl1anism, the present inventi.on is nonetlleless susceptible to reasonable explanation. Calci~.m1 is known to exist in 6 coal largely as a humate, or organocalciu1n complex 1~hich presumably 7 was introduced in nature via an ion exchange mechanism. Coal is 8 thus a fossili~ed prehistoric form of plant life formed in the carth 9 by partial decomposition, and gradual c11emical transformation of vegetable matter under almost anerobic conditions, ~ith the aid of 11 microorganisms, and in the presence of water. Over the ages, as the 12 gro~nd water drained a~!ay the conversion of the plant matter took 13 place, very slowly, leading first to t~le formation of lignite, then ~:
1~ soft sub-bituminous coal, and then anthracite. During some early portion of this period, ground water percolated through the forma- .
16 tion of coalifying, or coalified biomassj to deposit calcium.
17 1)uring normal liquefaction of the coal, it is the humates that are 18 decomposed to calcium carbonate, this giving rise to scale formation, 19 or deposits of calcium carbonate whicil form on reactor \~alls, t li.nes, auxiliary equipment and the like. In accordance with Appli-21 cant's process, however, the calcium is precipita.ted internaly ¦~
22 within the pore~s of the coal as thermally stable molecular species, 23 insolubie at liquefaction conditions, the calci.um forming partic- ~ :
2A ulate residual solids whicl1 becomes a part of the liquefac*ion bottoms~. The calcium, is thus separated after liquefaction from the 26 valuable petroleum-like llquic1.s as a port.lon of the liquefaction 27 ~bottoms ~ ~ -28 One thlls vis~1alizes the pores vf mined coal as :Eilled.
29 wit11 ~a~er, and calcium hun1ate as constituting a portion of the 0 molocular structare of the coal. ~ho c,1lcium 11umate can thus be ': -~ 7 ~ : ' .'7~?~

1 considered as compriscd of two anionic sites, e.g., carboxylate ~nd 2 phenolate functional groups, one each of which projects outwardly 3 into the liquid of the pore, and thus as having two electronegative 4 groups which are counterbalanced by a Ca2+ ion also contained in solution within the liquid of the pore. On addition of a sulfur 6 dioxide or sulfur trioxide gas, or admixture containing one or more 7 of these compounds within the gaseous admixture, an anion is formed 8 which combines with the calciurn to form a molecular species whic]l 9 percipitates within the pore as an insoluble molecular species of calcium, perhaps CaS04, a molecular species which is thermally 11 stable and substantially inert at coal liqueiaction conditions. The 12 insoluble CaS04, or other molecular species, in any event, forms 13 particulate solids which remains as a part o the residue of the 14 liquefaction bottoms, innocuous as to scale formation. Though the CaSO~ species, ho~Yever, is inert in the liquefaction reaction, the 16 presence of the calcium may be particularly beneficial where the 17 liquefaction bottoms are to be gasified~ since the calcium may 1~ constitute an effective gasiication catalyst.
19 ln the treatment of a subbituminous coal or coal of lower .
ran~ essentially 80 to lOO percent of the Ca2+ ions originally 21 present in a coal can be converted into insoluble thermally 22 stable CaSO~, or other insoluble molecular specie, which remains 23 within the coal and is released during liquefac~ion as particulate ,~ .
24 ~ so]ids which are recovered with the liquefaction bottoms. This can be accomplished with an undried coal at ambient, or essentially 26 ambient conditions wlthout any necessity of heating the gas or ~27 supplyiog a vacuum.
~ 28 In t1le best mode of practicing tbe present invention~ a ; 29 sub~ituminous or lower rank coal feed is contacted at ambicnt con-;: :
ditions wit1i a sulfur oxide gas and thereby impregnated 1he coal .
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can then be reduced in size and dried (if not previously done) and then sent direc~ly to a liquefaction reactor. In such process, schematically illustrated by reference to the figure, the required process steps preferably include (a) a elrst zone 0 wherein coal, sultably particulate coal, is contacted with a sulfur oxide gas, and if desired, the coal can then be drled, (b) a mixing zone 10 within whlch the particulate impregnated coal i'3 slurrled with an internally generated or indigenous liquids fractlon, (c) a coal llquefactlon zone 20 withln which a slurry of the impregnated coal and hydrogen are fed, and the coal liquefied, (d) a distillation and solids separation zone 30 within which a sol-vent Eraction, a 1000F-~ heavy bottoms fraction, and liquid product fraction are separated, (e) a catalytic solvent hydrogenation zone ~-~0 wherein the solvent fraction is hydrogenated prior to its being recycled to said coal liquefaction zone 20.
In coal impregnation zone 0, a particulate subbituminous or lower rank coal of size ranging up to about 1/8 inch particle slze diameter, suitably 8 mesh (Tyler), is contacted with a sulfur oxide gas as previously characterized, e.g., SO2, SO3 or the like, at àmbient conditions for a period of generally less than two hours, and impregnated.
The impregnated coal is then preferably admixed in zone 10 with a recycle donor solvent. The total solvent and coal are preferably admixed in a solvent-to-coal ratio ranglng from about 0.8:1 to about 4:1, more preferably about 1.2:1 to about 1.6:1, based on weight. The solvent is preferably one which boils with-; in the range of about 250 F to about 850 F, more preferably ~rom about 290 F to about 700P. ~he coal slurry is then fed, preferably with molecular hydrogen, into the coal liquefaction zone 20.
Within the coal liquefaction zone 20, preferred liquefaction conditions .~ ~

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.: : . . . '. , , . . , ~ .-include a temperature ranging from about 700 F to about 950 F, more preferably from about 800 F to about 850 F, with preferred pressures ranging from about , 300 psia to about 3000 psia, more preferably Erom about 800 psia to about 2000 psia. Preferably, molecular hydrogen is also addecl to the liquefaction zone 20 at a rate Erom about 1 to about 6 weight percent: (MAF coal basis~, preferredliquid residence times range from about 5 to about 130 minutes, and more pre-ferably from about 10 to about 60 minutes.
The product from the coal liquefaction zone 20 consists of gases and liquids~ the liquids comprising a mixture of undepleted hydrogen-donor solvent~
depleted hydrogen-donor solvént, or compounds, dissolved coal, undissolved coal and mineral matter. The liquid mixture is transferred into a separation zone 30 wherein light fractions boiling below 400F useful as fuel gas and naphtha are recovered, and intermediate fractions boiling, e.g., from 400F to 700~' are recovered for use as a hydrogen donor solvent. ~leavier fractions boiling from about 700F to 1000P are also recovered, and bottoms fractions boiling above 1000 F, including char, mineral matter and ash are withdrawn for use in a gasi-fication process or for coking, as desired.
The solvent fraction, or 400-700F fraction, is introduced into a catalytic solvent hydrogenation zone 40 to upgrade the hydrogen content of that fraction.
The conditions maintained in hydrogenation zone 40 hydrogcnate and, if desired, conditions can be provided which produce substantial cracking. Temperatures normally range from about 650 F to about 850 F, preferably from about 700 F to about 800F, and pressures suitably range from about 650 psia to about Z000 psia, preferably from about 1000 psia to about 1500 psia. The hydrogen treat rate ranges generally from about 1000 to about 10,000 SCF/B, preferably from about 2000 to about 5000 5CF/B. The :: :
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1 hydro~enation catalysts ~nployed are conventional. Typically, such 2 catalysts comprise an alumina or silica-al~lmina support carrying one 3 or more Group VIII nol1-noble~ or iron group metals, and one or more 4 Group VI-B metals of the Periodic Table. In particular, combinn- '~
tions of ol1e or morc Group VI-B metal oxides or sulfides with one or ~t 6 more Croup VIII metal oxides or sulfides are preferred. Typical 7 catalyst metal combinations incluc1e oxides and/or sulfides of cobal~-8 molybdenum, nickel-molybdenum, nic~el-tul1gsten, nickel-molybdenw~
9 tungsten~ cobalt-nickel-molybdenum and the li~e. A suitable cobalt molybdenum catalyst is one comprising from about l to about lO
11 weight percent cobalt oxide and from about 5 tc7 about 40 weight 12 percent molybdenum oxide, especially about 2 to 5 weight percent 13 cobalt and about lO to 50 weight percent molybdenum. ',~lethods for 14 the preparati.on of these catalysts are well known in the art. The active metals can be added to the support or carrier, typically lb alumina, by impregnation from aqueous solutions followed by drying 17 and calcining to activate the composition. Suitable carriers nclude, for example, activated alumina, activated alumina-silica, 19 zirconia, titania, etc., and mixtures .hereof. Activated clays, such as bauxite, bentonite and montmorillonite, can also be employed.
21 These and other features of the present invention will be 22 better understood by reference to the following demonstrations of 23 prior art runs conducted by liquefaction~of the coal 1~ithou~ benefit 24 of treatment with a sulfur oxide comyound, and to comparative data set forth in subsequent examples obtainecl on liqllefyil1g the coal 2~ slurries in accordance wit11 this in~el1tion. All uni-ts are in terTns , 27 of weiglit unless otherwise specified.
EX~IPLE l ~a -- : ' 29 l~ifty gram portions of "as receivec1" 1~yodak coal ~con-tain]ng 30% moisture) of si~e rangril1g from -8 to 20 mesh, werc each : .
- 11 - I ' ', -.

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1 separately pre~r~ated ~ith sulfur d1oxide ~as for a period of five 2 minutes at 30 psig. A~ the end of the fivc minute period "~hen the 3 pressure had droppec1-to zero, another charge of sulfur diox;de was 4 added to 30 ps:ig, and anot11er, until the ra-te of pressure drop had S slowed. ~ slight exotl~erm ~as noted at each addition, but otherwise 6 the treatme]1t was conducted at ambient temperatures. Tl1e specimens, - 7 after about one-half hour of similar treatment, were each then 8 removed from the autoclave, driec1 at 220F for sixteen hours, and : 9 then analyzed by x-ray. These data, when compared with a raw u11treated sample, showed that calcium sulfate was present only in 11 the treated coal specirnens.
i ~2 It would appear that the sulfur dioxide on contact ~ith 13 the moisture ~ithin tl1e pores of the coal forms sulfurous or sulfuric 14 acid and tha~, these acids, in turn reacts with calcium to form sulfites, bisulfites, sulfates, bisulfates or the like; but, in any 16 event, an insoluble, thermally stable species, or species which does 1~ not decompose at coal liquefaction conditions is formed.
18 From the elemental analyses of the raw and treated coals, 19 the amount of sul:Eur fixed by the coal was calculated. I`he fixed sulfur is nearly constant for the several runs using as-received 21 coal, being about 2 moles of sulfur per mole of calcium. (~he 22 sulfur fixed by previously dried coal is variable and depends on time of treatment,-and hence it~is preferred to treat coal on an as .: : : , , 24 recelved basis~.
The portions of sulfur dioxide-treated coal, and a raw ~6 ~Wyoda~ speci1nen usecl as a control, were liquefied in ba~ch tube !
~autoclaves at 8~0F; lS00 psig; in the presence of a hydrogenated ~ 28 ~croosote oll solvont (2:1 ratlo ~olvent:coal) "~ith 3 weig11t per~ent : ~ ~ 2~ added 1nolecular hyclrogen, based on coal. ~-ray diffraction patterns ~ ~ 30 of tho res.idues of the sulfur dioxide treated syecimens s1~owed the ~, , ~ 12 - i .

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1 pr-sence of calci~m sulfate, but an absence o~ calclurll carbonate.
~ 'I`hermogravimetric analyses showed a sevenfold rcductioll of carbonate 3 in tlle res;duc of sulfur dioxidc treated coal as compared Wit]l thc 4 rcl~Y coal.
S _~A~IPLE 2 6 T~YO hundred pounds of as-received lYyodak coal ~crushed to pass a 3/4 inch screen) was placed in a 55 gallon drum fitted with 8 an inlet tube and a 50 psig blowout patch. Gaseous sulfur dioxide 9 was allowed to enter the drum throug}l the inlet tube; the pressure being kept at 12 psig by means of a gas regulator. The coal ~Yas 11 treated in this way for 6 days, then the drum vented and the coal 12 dried on a fluidized bed drier.
rL , 13 Next a slurry of dried coal and donor solvent, (hydro-14 genated creosote oil) ~Yas prepared, in a solvent to coal ratio of 1.6 and fed, with hydrogen, into a ~0 foot tubular reactor, held at ~ ~16 800F and 2000 psig. The noininal residence time was 60 minutes.
;~ 17 The product ~as collected periodically and distilled. Analysis of 18 ~ the residue by x-ray dif-fraction indicated little if any calcium 19 carbonate was present, and chemical analysis showed a seven fold ; 20 reductiorl in carbonate contellt compared to the residue from an 21 untreatcd Wyodak coal liquefaction.
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22 The run was terminated due to a reàctor plug, which was :: .
23 sbown to be due to.coke and not reactor scale. When the reactor was ~ 24 opened, no sign of scale was found.
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; ~ 25 ~ It is apparent that varlous modifications can be made 26 ~ wltllout departing the spirit and scope of the invention. Various 27 analyses, ta~en togethcr, sl~ggest~that coal contains a limited 8 nulDber of exchange sites, and that under varying conditions of time 2g ~ concentratiol~, SO~ treating gas conccntr;ltiorl, the e.Ychallge of the sulfur oxides into the coal can be substantially quantitative.

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1 Essentially all of the caleium of a subbituminous or eoal of lower 2 ranlc, can thus be eonverted ~o a fornl of ealcium whieh is essen- ¦
3 tially innocuous in ~he coal liquefaction reaction.

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Claims (26)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the treatment of calcium-containing sub-bituminous coals and coals of lower rank to form an insolubic, thermally stable calcium salt which remains within the pores of the coal on liquefaction comprising contacting said coal in vapor phase with one or more compounds characterized by the formula SOX, wherein X is 2 or 3, to form within the pores of said coal a water insoluble, thermally stable calcium compound, and then recovering said impregnated coal.

2. The process of Claim 1 wherein the compound SOX is sulfur dioxide.

3. The process of Claim 1 wherein the compound SOX is sulfur trioxide.

4. The process of Claim 1 wherein the compound SOX is a mixture of sulfur dioxide and sulfur trioxide.

5. The process of Claim 1 wherein the compound SOX is contained in a gaseous admixture with other gases.

6. The process of Claim 1 wherein impregnation of the coal with the compound SOX is conducted at pressures ranging from about 0 to about 200 psig.

7. The process of Claim 6 wherein the pressure ranges from about 5 to about 150 psig.

8. The process of Claim 1 wherein contact between the particulate coal and the SOX compound is maintained for a period ranging at least about 0.01 to about 24 hours.

9. A process for the treatment of calcium-containing sub-bituminous coals and coals of lower rank to form an insoluble, thermally stable calcium salt which does not form scale during coal liquefaction comprising contacting said coal in vapor phase with one or more compounds characterized by the formula SOX, wherein X is 2 or 3, to form within the pores of said coal a water insoluble, thermally stable calcium compound, and then liquefying said impregnated coal at liquefaction con-ditions to produce petroleum-like liquid products.

10. The process of Claim 9 wherein the compound SOX is sulfur dioxide.

11. The process of Claim 9 wherein the compound SOX is sulfur trioxide.

12. The process of Claim 9 wherein the compound SOX is a mixture of sulfur dioxide and sulfur trioxide.

13. The process of Claim 9 wherein the compound SOX is contained in a gaseous admixture with other gases.

14. The process of Claim 9 wherein impregnation of the coal with the compound SOX is conducted a pressures ranging from about 0 to about 200 psig.

15. The process of Claim 14 wherein the pressure ranges from about 5 to about 150 psig.

16. The process of Claim 9 wherein contact between the particulate coal and the SOX compound is maintained for a period ranging at least about 0.01 to about 24 hours.

17. The process of Claim 9 wherein the coal is liquefied in a liquefaction zone at temperatures ranging from about 700°F to about 950°F, at pressure ranging about from about 300 psia to about 3000 psia by contact with a hydrogen donor solvent.

18. The process of Claim 17 wherein the temperature of liquefaction ranges from about 800°F to about 850°F, and the pressure ranges from about 800 psia to about 2000 psia.

19. The process of Claim 17 wherein the hydrogen donor solvent is one which boils within a range of from about 400°F to about 850°F, and contains at least about 30 wt. % hydrogen donor compounds.

20. As an article of manufacture useful for liquefying at coal liquefaction conditions, without the formation of significant amounts of calcium carbonate scale, subbituminous coal or coal of lower rank which contains within its pores an insoluble, thermally stable calcium salt formed by the steps comprising contacting said coal in vapor phase with one or more compounds characterized by the formula SOX, wherein X is 2 or 3.

21. The article of manufacture of Claim 20 wherein the compound SOX is sulfur dioxide.

22. The article of manufacture of Claim 20 wherein the compound SOX is sulfur trioxide.

23. The article of manufacture of Claim 20 wherein the compound SOX is a mixture of sulfur dioxide and sulfur trioxide.

24. The article of manufacture of Claim 20 wherein the compound SOX is contained in a gaseous admixture with other gases.

25. The article of manufacture of Claim 20 wherein impreg-nation of the coal with the compound SOX is conducted a pressures ranging from about 0 to about 200 psig.

26. The article of manufacture of Claim 24 wherein the pressure ranges from about 5 to about 150 psig.