CA1117453A - Liquefaction of calcium-containing subbituminous coals and coals of lower rank - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process for the liquefaction of a calcium-containing sub-bituminous or lower rank coal; wherein the coal is first treated to form a water-insoluble thermally stable calcium compound which remains in the pore of the coal on liquefaction, by (i) contacting the coal in particulate form with single compound MX, in an aqueous solution, capable of forming the said water-insoluble, thermally stable calcium compound, M being H+, an ammonium ion or a monovalent or multiple cation selected from the group consisting of the Group IA, IVA, VIB, and VIII metals of the periodic table of the elements, and X being sulfate, carbonate or phosphate, and (ii) maintaining the contact for a period of time sufficient for impregnation of the compound into the pores of the coal; and wherein the thus single compound impregnated coal is then recovered and subjected to coal liquefaction conditions. On separation of the impregnated particul-ate coal from the solution, the coal can be liquefied in a coal liquefaction reactor (reaction zone) at coal liquefaction conditions without significant formation of vaterite or other forms of calcium carbonate scale on reactor surfaces, auxiliary equipment and the like.

Description

1 A coal liquefaction process of particular interest

2 now under development is one which utilizes a hydrogen trans-

3 fer, or hydrogen donor solvent to hydrogena~e and liquefy

4 ~he coal. In such a process, crushed coal is contacted with S a gelective solvent which acts at least in part as a hydro-6 gen donor to supply hydrogen to the hydrogen-deficient coal 7 to convert the coal solids to liqulds. The product includes 8 petroleum-like liquids, i.e., 1000F. liquids, and heavier 9 products. The heavy products are characterized generally as "liquefaction bottoms," and consist of 1000F.+ organics, ll inorganics and carbon residue (fusinite). This material, l2 which analyzes about 60-70 wt. % carbon, and about 20 wt. %
13 ash, is less useful than the 1000F- liquid, and generally l4 contains 40-50 wt. % of the ariginal feed coal to the process.
16 Coal is not a pure hydrocarbon, but is a material l7 comprised of carbon, hydrogen, oxygen, sulfur and nitrogen.
18 It contains a considerable amount of volatile matter. Prin-19 cipally, however, it is a material in which the organic mat-ter makes up an essentially continuous phase within which 21 mineral, or inorganic matter is dispersed. The inorganic 22 materlal consists of fusane, sulfur, e.g., pyritic sulfur 23 and inorganic sulfates, and other mineral matter. Various 24 metals, notably calcium is present as complexes of large or-ganic acids known as humic acids; and perhaps also as cal-26 cium ions.
27 The mineral matter in coal is not necessarily in-28 ert in coal liquefaction reactions. The presence of calcium, 29 in particular, is quite detrimental. Thus, it is known that in high pressure coal liquefac~ion processes for producing liquids from lignites that the reactors rapidly become plugged solid with a high ash-containing scale which has been termed "caviar", because it had the appearance of agglomerated balls, or spherulites.
The spherulites, which are indicative of the vaterite form of calcium carbonate, were found to be comprised of calcium carbonate containing hexagonal crystals of iron sulfide. Deposits of the scale initially caused decreased production because of the necessity to lower throughput, and all too soon complete shutdown was necessary. Preheater tubes, on occasion, burst due to blockage.
The problem of calcium carbonate scale formation yet persists re-sulting, inter alia, in intermittent operation. Further improve-ments are highly desirable in coal liquefaction processes to eliminate, or suppress, the formation of calcium carbonate scale in reactors, lines, and auxiliary equipment.
The invention is concerned with meeting this need.
This invention therefor relates to a process for the pretreat-ment of calcium-containing subbituminous coals and coals of lower rank to render such coals amenable to liquefaction while suppress-ing the formation of calcium carbonate deposits as scale, within the coal liquefaction reactor, lines, and auxiliary equipment.
Thus the present invention provides a process for the lique-faction of a calcium-containing subbituminous or lower rank coal;
wherein the coal is first treated to form a water-insoluble therm-ally stable calcium compound which remains in the pore of the coal on liquefaction, by (i) contacting the coal in particulate form with a single compound MX, in an aqueous solution, capable of forming the said water-insoluble, thermally stable calcium compound, ? ~ ~
I ? j M being H+, an ammonium ion or a monovalent or multiple valent cation selected from the group consisting of the Group IA, IVA, VIB, and VIII metals of the periodic table of the elements, and X being sulfate, carbonate or phosphate, and (ii) maintaining the contact for a period of time sufficient for impregnation of the compound into the pores of the coal; and wherein the thus single compound impregnated coal is then recovered and subjected to coal liquefaction conditions.
The present invention can be characterized generally as a process for liquefying a coal feed, subsequent to a pretreatment, or preconditioning, of a subbituminous coal, or lower rank coal by contact with a compound or salt which forms 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 compound, or salt, 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 liq~e-faction it remains as particulate solids and thereby does not form, or it at least suppresses the formation of scale, or calcium carbonate deposits. The insoluble form of calcium remains within the liquefaction bottoms, and is conveniently disposed of, after liquefaction, with the liquefaction bottoms or with the ash. Pre-ferably, additional 1000F- liquids are recovered from the lique-faction bottoms by pyrolysis in an additional step, and the 1000F+
materials, or char, which now contains a molecular species is then subjected to gasification.

. ~
,i ~L1174S3 In the preferred practice of this invention, in the single pret:reatment step, within a solution, there is dispersed a single compound or salt which is characterized by the formula MX, wherein M i6; H+ (proton), an ammonium ion, or a monovalent or multiple valent cation, suitably a proton provided by a mineral acid such as sulfurious acid, sulfuric acid, phosphoric acid or the like, or a monovalent or multiple valent cation selected from Groups IA, IVA, VIB and VIII of the Periodic Table of the Elements (Sargent-Welch Scientific Company, Copyright 1968), suitably iron, cobalt, nickel, tin, molybdenum, lithium, sodium, potassium, cesium and the like, and X is an anion which is capable of forming insoluble, thermally stable calcium compounds, exemplary of which are sulfite, carbonate, phosphate, most preferably the anion is sulphate or carbonate, and the solution, preferably an aqueous solution, is maintained in con-tact with a coal feed, suitably a particulate coal feed, for a period sufficient for impregnation of the compound or salt into the pores of the coal, suitably for a period ranging from at least about 0.01 hours to about 24 hours, preferably at least about 0.5 hours to about 4 hours. After the impregnation, the coal is removed from the aqueous solution, and then liquefied at lique-faction conditions to produce petroleum-like liquid products.
The rate of impregnation of the coal depends to a large extent on coal particle size, and condition of the coal. In general, the smaller the particle size of the coal the greater the rate of impregnation, and conversely, the larger the particle size the slower the rate of impregnation. Generally, however, particulate coal of size ranging from about -8 mesh to about 1 inch particle size diameter, and more suitably from about -8 mesh to

- 5 -~17'~53 about 20 mesh (Tyler series), can be adequately impregnated within the above defined time periods by treatment, or contact with the aqueous solutions of the compounds or salts, suitably by solutions containing from about 0.1 to about 20 percent, preferably from about 0.1 to about 10 percent of the compounds or salts, based on the weight of the solution. Preferably, the coal is treated on an as received (or as mined) basis and is not dried prior to impreg-nation. In this regard it has been found that drying of the coal is deleterious in that it greatly reduces the amount of the com-pounds or salts which can be absorbed by the coal, and retards therate of impregnation. It is believed that the drying causes the gel struc-- Sa -~i ~ - ~

~ 4 ~ 3 1 ture of the coal, and consequently the pores within the 2 structure, to collapse. Also, when thR coal is dried~ the 3 volume once occupied by water is displaced by gas; thus de-4 creasing considerably the ability of the solution with which the coal is contacted to wet the interior surface of

6 the coal. The wetting properties of the pore surfaces are

7 thus adversely affected on drying.

8 While Applicant does not desire to be bound by

9 any specific theory of mechanism, the present invention is nanetheless susceptible to reasonable explanation. Calcium 11 i8 known ~o exist in coal largely as a humate, or organocal-l2 cium complex which presumably was introduced in nature via 13 an ion exchange mechanism. Coal is thus a fossilized pre-4 historic form of plant matter formed in the earth by partial decomposition, and gradual chemical transformation of veg-16 etable matter under almost anerobic condltions, with the aid 17 of microorganisms, and in the presence of water. Over the l8 ages, as the ground water drained away the conversion of 9 the plant matter took place, very sl~wly, leading first to ~ the formation of lignite, then soft subbituminous coal, and 21 then anthracite. During some early portion of this period, 22 ground water percolated through the formation of coalifying, 23 or coalified biomass, to deposit calcium. During normal 24 liquefaction of the coal, it is the humates that are de-composed to calcium carbonate, this giving rise to scale 26 formation, or deposits of calcium carbonate which form on 27 reactor walls, lines, auxiliary equipment and the like. In 28 accordance with the present process, however, the calcium 29 is precipitated internally within the pores of the coal as thermally stable molecular species, insoluble at liquefac-1~ ~7 ~ ~ 3 1 tion condltions, the calcium forming particulate residual 2 solids which become a part of the liquefaction bottoms.
3 The calcium, is thus separated after liquefaction from the 4 valuable petroleum-like liquids as a portion of the mineral S matter in liquefaction bottomsO
6 One thus visualizes the pores of mined coal as 7 filled with water, and calcium humate as constituting a por-8 tion of the molecular structure of the coal. The calcium 9 humate can thus be considered as comprised of two anionic sites, e.g., carboxylate and phenolate functional groups, 11 one each of which projects outwardly into the liquid of the 12 pore, and thus as having two electronegative groups which 13 are counterbalanced by a Ca2+ ion also contained in solu-14 tion within the liquid of the pore. On addition of the salt or compound MX, M in effect replaces the Ca2~ ion and X
16 combines with the calcium to form a molecular species which 17 precipitates within the pore as insoluble CaX, a molecular 18 species which is thermally stable and substantially inert 19 at coal liquefaction conditions. The insoluble CaX forms a particulate solids species which remains as a part of the 21 residue of the liquefaction bottoms~ innocuous as to scale 22 formation. Though the CaX species, however, is inert in the 23 liquefaction reaction, the presence of the calcium may be 24 particularly beneficial where the liquefaction bottoms are 2s to be gasified, since the calcium may constitute an effec-26 tive gasification catalyst.
27 Improvements in liquefaction yields, and rates 28 of conversion of the coal to useful petroleum-like liquids 29 can also be obtained by the judicious selection of certain ~ species of compounds and salts of the MX variety as opposed ~117453 to others. For example, soluble compounds and salts wherein the cation portion of the compound and salt is cesium, potassium, sodium, iron, nickel or tin are preferred to other cation species because these species provide more active catalytic effects in liquefaction of the coal, and hence such compounds and salts of such species are preferred on a cost effectiveness basis, parti-cularly inasmuch as there is no impairment or loss in the function of the anion in forming the insoluble molecular species, CaX. Cobalt and molybdenum are also preferred cations for use in the formation of the insoluble CaX species. The preferred soluble compounds and salts are those which contain a sulfate or carbonate either of which forms an insoluble molecular species comprised of CaSO4 or CaCO3. Exemplary of species which contain both a preferred cation and anion for such purposes are sodium sulfate, potassium sulfate, potassium carbonate, ferrous sulfate, ferric sulfate, nickel sulfate, stannous sulfate and the like. Generally, in the treat-ment of a sub-bituminous coal or coal of lower rank essentially 80 to 100 percent of the CA2+ ions originally present in a coal can be converted into an insoluble thermally stable CaX molecular 2~ species, particularly to CaSO4 or CaCO3 which remains within the coal and is released during liquefaction as particulate solids which are recovered with the liquefaction bottoms; and an essent-ially equivalent amount of a catalytic cation can be conveniently added to the coal to enhance the coal liquefaction reaction. And, this can be accomplished with an undried coal at ambient, or at essentially ambient conditions without any necessity of heating the solution or supplying a vacuum, though a vacuum can be used to .
~ , i increase the rate of impregnation of a dried coal if desired.
In the best mode of practicing the present invention, a subbituminous or lower rank coal feed is contacted at ambient con-ditions with a solution of a single compound or salt as character-ized by the formula MX, supra, and impregnated. The solution is then separated from the coal as by centrifugation or filtering, and if desired, the coal can then be reduced in size (if not pre-viously done) and then dried. In such process, schematically illustrated by reference to the figure, the required process steps generally include (a) a first zone 0 wherein coal, suitably particulate coal, is contacted with a solution of the single com-pound or salt characterized by the formula MX, then separated from the solution and dried (by additional steps not shown), (b) a mixing zone 10 within which the particulate impregnated coal is slurried with an internally generated or indigenous liquids fraction, (c) a coal liquefaction zone 20 within 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 solvent fraction, a 1000F+ heavy bottoms fraction, and liquid product fraction are separated, (e) a catalytic solvent hydrogenation zone 40 wherein the solvent fraction is hydrogenated prior to its being recycled to said coal liquefaction zone 20, (f) a pyrolysis zone 50 wherein the 1000F+ heavy bottoms fraction from zone 30 can be pyrolyzed to produce additional 1000F- liquids, and char, and (g) a gasification zone 60 wherein the char can be gasified in a catalytic reaction.
In coal impregnation zone 0, a particulate subbituminous or lower rank coal of size ranging up to about 1/8 inch particle size diameter, suitably 8 mesh (Tyler), is slurried in an aqueous 111'~453 solution containing a single MX compound or salt, as previously characterized, e.g., Na2SO4, K2SO4, NiS04, FeSO4, Fe2(SO4)3 or the like, added to the water in concentrations ranging from about 1 to about 20 weight percent, preferably from about 1 to about 10 weight percent, at ambient conditions for a period of about 30 minutes to 2 hours. Thereafter, the impregnated coal is separated from the coal by filtration, and dried.
The impregnated coal is then admixed in zone 10 with a recycle donor solvent. The total solvent and coal are admixed in a solvent-to-coal ratio ranging from about 0.8:1 to about 4:1, preferably about 1.2:1 to about 1.6:1, based on weight. The solvent is one which boils within the range of about 250F. to about 850F., pre-ferably from about 290F. to about 7000F. The coal slurry is then fed, preferably with molecular hydrogen, into the coal liquefaction zone 20.
Within the coal liquefaction zone 20, liquefaction conditions include a temperature ranging from about 700F. to about 950F., preferably from about 800F. to about 850F. with pressures ranging from about 300 psia to about 3000 psia, preferably from about 800 psia to about 2000 psia. Preferably, molecular hydrogen is also added to the liquefaction zone 20 at a rate from about 1 to about 6 weight percent (MAF coal basis), liquid residence times ranging from about 5 to about 130 minutes, and preferably from about 10 to about 60 minutes.
The product from the coal liquefaction zone 20 con-\

~ J~4 5 3 1 sists of gases and liquids, the liquids comprising a mixture 2 of undepleted hydrogen-donor solvent, depleted h~ rogen-3 donor solvent, or compounds, dissolved coal, undissolved 4 c081 and mineral matter. The liquid mixture is transferred into a separation zone 30 wherein light fractions boiling 6 below 400F. useful as fuel gas or naphtha are recovered, 7 and ~ntermediate fractions boiling, e.g., from 400F. to 8 700F. are recovered for use as a hydrogen donor solvent.
9 Heavier fractions boiling from about 700F. to 1000F.
are also recovered, and bottoms fractions boiling above 1000F., including char, mineral matter and ash are with-12 drawn for use in a gasification process or Lor coking, as 13 desired.
14 The solvent fraction, or 400-700F. fraction, is lS introduced into a catalytic solvent hydrogenation zone 40 l~ to upgrade the hydrogen content of that fraction. The con-17 ditions maintained in hydrogenation zone 40 hydrogenate and, l8 if desired, conditions can be provided which produce sub-19 stantial cracking. Temperatures normally range from about ~ 650F. to about 850F., preferably from about 700F. to 2l about 800F., and pressures suitably range from about 650 2~ psia to about 2000 psia, preferably from about 1000 psia to 23 about 1500 psia. The hydrogen treat rate ranges generally 24 from about lO00 to about 10,000 SCF/B, preferably from about 2000 to about 5000 SCF/B. The hydrogenation catalysts 26 employed are conventional. Typically, such catalysts com-n prise an alumina or silica-alumina support carrying one or 28 more Group VIII non-noble, or iron group metals, and one 29 or more Group VI-B metals of the Periodic Table. In par-~ ticular, combinations of one or more Group VI-B metal oxides 1 1~7~ ~ 3 1 or sulfides with one or more Group VIII metal o~ides or sul-2 fides are preferred. Typical catalyst metal combinations in-3 clude oxides and/or sulfides of cobalt-molybdenum, nickel-4 molybdenum, nickel-tungsten, nickel-molybdenum-tungsten, cobalt-nickel-molybdenum and the like. A suitable cobalt 6 molybdenum catalyst is one comprising from about 1 ~o about 7 10 weight percent cobalt oxide and from about 5 to about 8 40 weight percent molybdenum oxide, especially about 2 to 9 5 weight percent cobalt and about 10 to 5Q weight percent molybdenum. Methods for the preparation of these catalysts 11 are well known in the art. The active metals can be added 12 to the support or carrier, typically alumina, by impregna-13 tion from aqueous solutions followed by drying and calcin-14 i~g to activate the composition. Suitable carriers include, for example, activated alumina, activated alumina-silica, 16 zirconia, titania, etc., and mixtures thereof. Activated 7 clays, such as bauxite, bentonite and montmorillonite, can 18 also be employed.
1 Suitably, the 1000F~ liquid bottoms from zone 30 2 is next pyrolyzed in a pyrolysis zone 50 and pyrolyzed at 21 temperatures ranging from about 900F. to about 2200F., ~a preferably ~rom about 900F. to about 1200F., at pressures 23 ranging from about ambient to about 200 psig, preferably 24 from about 10 psig to about 150 psig, to recove~ additional ?5 1000F- liquids, and the 1000F+ material, or char, is then 26 fient to a gasification zone 60.
27 The residual 1000F+ material, or ch~r, is gasi-28 fied with steam in zone 60 at temperatures ranging from about 900F. to about 1800F., preferably from about 1200F.
to about 1500~F., at pressures ranging from about ambient 1 to about 200 psig, preferably from about 10 psig to about 2 150 psig, to recover gaseous products, carbon monoxide, 3 hydrogen and the like.
4 These and other features of the present inven~ion will be better understood by reference to the following 6 demonstrations of prior art runs conducted by liquefaction 7 of the coal without benefit of treatment with the MX com-8 pounds and salts of this invention, and to comparative data 9 ~howing liquefaction of coal pretreated with MX compounds and salts in accordance wi~h this invention. Comparative 11 data are also given which show the gasification of char ob-12 tained from untreated coal, and coal pretreated pursuant to 13 this invention. All units are in terms of weight unless 14 otherwise specified.

16 Two 50.0 g. portions of "as received" Wyodak coal 17 (30% moisture), a sub-bituminous coal comminuted to pass a 18 20-mesh screen, were each mixed, respectively, with 450 g.
19 portions of a 0.2% nickel sulfate solution and a 1.0% nickel ~ sulfate solution (g/100 ml.). The mixtures were allowed to 21 stand at ambient conditions for 10 days, and filtered.
22 Nickel analyses were obtained on the starting solutions and 23 on the filtrates. These data tabulated immediately below, 24 clearly show that the nickel is taken up by the coal.
25 Specimen Description of % Metal gm metal/lOOg 26 No.~ _ Solution (Mg/ml.~ (as received~
28 1 NtiaS04 Sgolution 3600 1.19 29 1 Filtrate from 3a 1% NiS04 Solution 2275 31 2 Starting 0.2% 720 32 NiS04 Solution 33 2 Filtrate from 0.2%
34 NiS04 Solution 124 0.54 ~ J~ 5 3 1 The specimens of coal were washed with water, 2 dried at 220F. in an oven, and then subjected to liquefac-3 l:ion in an autoclave, at the conditions given in Table I.

840F; 1500 p9ig; 2/l Hydrogen~ted Creosote Oil 6 solvent/coal; 40 minutes residence time; 3 Wt. %
7 H2 treat, based on coal 8 Z Cyclohexane Insolubles 9 (Wt. % DAF Coal)l _

10 Sample Based on Autoclave Based on

11 No. Material Balance Ash Balance -

12 0 Raw Wyodak Coal 42 38

13 l Wyodak Coal Treated 34 32

14 with 1% NiS04 2 WYodak Coal Treated 37 36 16 with 0.2% NiS04 17 X-ray diffraction patterns taken on the cyclohex-18 ane insolubles clearly demonstrate that the nickel sulfate 19 i9 readily absorbed into the coal to react with the calcium humate. Essentially the only calcium carbonate in the form 21 of vaterite was present in the residue of ~he untreated coal 22 None was found in the residue from liquefaction of the 23 treated sampLes.
24 The treatments of the coal with aqueous solutions of metal salts were successful in preventing formation of 26 calcium carbonate scale during liquefaction of the impreg-27 nated coal.
28 The following examples are further illustrative 29 of the benefits of such treatments, and additionally show the advantages achieved during liquefaction by the use of 31 compounds or salts which contain a species of cation which 32 is catalytic in the liquefaction reaction.

Jl ~l.1~7~S~

1 I~XAMPLES 3-5 2 Fifty gram portions of an as received (A.R.) 3 Wyodak coal, i.e., coal containing about 30 weight percent 4 moisture, crushed to particle size ranging -8 to 20 mesh, was treated with aqueous solutions of me~al sulfates by con-6 tact of the portions of coal therewith under nitrogen for 7 a continuous period of one week to assure essentially com-8 plete reaction in forming the insoluble calcium species g within the pores of the coal, ater which time the portions of coal were separated from the solution, washed with water, 11 oven dried at 220F for 16 hours and then liquefied in an 12 autoclave, or bomb~ The identity of the solutions used to 13 treat the portions of coal on an as received basis, the 14 conditions of liquefaction, and the results of the liquefac-tion in terms of percent conversion for the treated portions 16 of coal vis-a~vis raw coal, are given in Table II, belowO

18 840Fo~ 1500 psig; 2/1 Hydrogenated Creosote Oil 19 solvent/coal, 40 minutes residence time; 3% by weight of molecular hydrogen treat gas added, 21 on coal 22 Conversion 23 Treated With (W~% DAF Coal) 24 Specimen _ Solutions Ash Balance Raw Wyodak Coal ~ 62 26 Nickel Sulfate 1% NiSO4 68 27 Treated Wyodak Coal 28 Ferrous Sulfate 5% FeSO4 69 29 Treated Wyodak Coal Ferric Sulfate10% Fe2(So4~3 72 31 Treated Wyodak Coal 32 The data thus show that only 62 percent of the 33 raw Wyodak coal is converted to 1000F~ liquids, plus water 34 and gasesO However, nickel sulfate and both ferrous and 1~74S3 1 ferric sulfate treated coals showed DAF (dry, ash free 2 basis~ liquid conversions improvements spanning the 6-lO
3 percent range. Analysis of the ash residue showed that 4 calcium carbonate as vaterite was present only in the un-treated, or raw Wyodak coal residue.

7 Two hundred pounds of as-received Wyodak coal 8 (crushed to pass a 3/4 inch screen) was mixed with 20 gal-9 lons of water and one gallon of 96% sulfuric acid, and the slurry allowed to stand for seven days. The slurry was drained, the coal washed with water and then dried in a 12 fluidized bed drier~ Next a slurry of dried coal and donor 13 solvent, in this case a hydrogenated creosote oil, was pre-14 pared, in a solvent to coal ratio of 1.6, and fed, with hydrogen, into a 40 foot tubular reactor, held at 800F.
16 and 2000 psig The nominal residence time was 60 minutes.
17 The product was collected periodically and distilled. The 18 bottoms from the distillation were analyzed by x-ray diffrac-19 tion~ No calcium carbonate was detected. (Calcium carbon-ate was detected in ~he residue of a similar run which used 21 an untreated Wyodak coal.) 22 After six days of continuous operation, the run 23 was voluntarily terminated3 and the reactor brought down to 24 ambient conditions in a controlled manner1 Dissection of the reactor along the vertical axis showed tha-t no scale 26 had formed within the reactorO
In contrast, in a similar run using untreated 28 Wyodak coal, the reaction was terminated voluntarily after 29 four days. Dissection of the reactor along the vertical axis showed that considera~le scale had formedc Analysis ~ 16 -~ ~7 ~ 3 1 showed the scale to be made up largely of calcium carbonate.
2 The following data demonstrates that an as rec-3 ceived coal can be satisfactorily impregnated even with 4 relatively dilute solutions of the salt to form thermally stable, insoluble calcium species at very mild conditions 6 within relatively short periods of times.

8 In a series of tests portions of as received 9 Wyodak coal, i.e., coal containing 30 weight percent mois-ture, were admixed and immersed in aqueous solutions of 11 metal sulfates, and these mixtures allowed to stand at am-12 bient conditions for ~pecified periods, after which t~e coal 13 was separated from the liquid by filtration and the coal 14 then analyzed by atomic adsorption analysis for determina-tion of the amount, or quantity of metal absorbed by the 16 individual portions of coalO Data for one percent nickel 17 sulfate and zinc sulfate solutions, expressed as moles of 18 metal taken up per 100 grams of as received (A.R.) coal are 19 given in Table III, below.
rABLE III
21 Exchange of Metals onto as Rec_ived Wy~dak Coal 22 Mole Metal Taken g Calcium (As 23 Up per 100 g. CaSOL) in 100 ml.
24 Solution A oR~ Coal~l) FI~TRAT~2) 1% NiS04 oOo~o 0.17 26 1% Zn$04 0 025 0.17 ..
27 (1) 100 g. A.R. Coal has 00020 mole calcium.
28 (2) Solubility of CaS04 in water is 0~20 gllOO mlO

1~7~.S3 1 From these it can be seen that 100 grams of as received coal 2 absorbed 0.02 mole of the respective metal, which amount of 3 metal is directly related to the calcium content of the coal.
4 It is found that there are a limited number of ex-change sites, that ~he exchange can be quantitative by us-6 ing adequate concentrations of salts within the impregnat-7 ing solutions, and by allowing adequate solution to coal 8 ratios for sufficient periods. For example, with a nickel 9 sulfa~e solution used for the treatment of as received Wyodak coal it has been found that with a 0~2% nickel sul-11 fate, nearly 82% of the nickel in solution is abscrbed, 12 amounting to 0.009 mcle of nickelO Using a l~/o solution, 13 the data shows tha~ about 35~/O of ~he nickel is taken up~
14 amounting to 0.020 moleO The follcwing series of data given in Table IV below illustra~e the rate of exohange of nickel 16 onto an as received Wyodak coal of different parti~le sizes 17 from a five percent nickel sulfate solut:ion~ the amount of 18 take up being measured over different time periods in terms 19 of the grams of nickel sulate per 100 grams of the coalO
TABL~ IV
21 Exchan~e of Nlckel S~lfate (5% ~olution) 22 ~
23 Grams NiSO4 24 Coal Time Period~ Absorbed per ~ ~Hours ~ 100 ~ Coal 26 8 to 20 Mesh ~ 0~5 105 28 20 ~0O
29 48 4~0 (0 026 moles) 31 ~ 20 Mesh ~ 0O5 3.8 33 20 4O0 (0.026 34 moles) 1~ ~7 ~ ~ 3 1 It is thus quite apparen~ that the coal can be ad-2 equately treated at ambient condi~ions, generally within 3 periods ranging from about one-half to about four hours to 4 provide essentially maximum uptake o the impregnating metals.
6 EXAMPLES 9-lO
7 Two fifty gram portions of -20 mesh Wyodak coal 8 (Samples Nos. l and 2), on an as received basis and contain-9 ing 30 weight percent moisture, were each contacted and im-lo mersed, respectively, in a 150 ml. portion of a solution, 11 (a~ one of which was formed by dissolving 5 grams of K2C03 12 in 250 ml. of distilled water, and (b) the other of which 13 was formed by dissolving 5 grams K2S04 in 250 ml. of dis-tilled water. Each of the two portions of coal were al-lowed to stand for a 24 hour period, after which time the 16 portions of coal were separated by filtration from the two 17 different solutions, washed with distilled water and then 18 dried in a vacuum oven at about 220F.
19 Five gram portions from each of the two larger portions of alkali-metal salt treated coal specimens, and 21 a third five gram specimen of -20 mesh as received, or un-22 treatçd (raw) Wyodak coal (Sample No. 0), similarly dried, ~3 were then each separately admixed, or slurried with lO grams 24 of tetralin in a tubing bomb. Hydrogen was then added to 2s each tubing bomb, and each bomb sealed at 400 psig.
26 The bombs were then placed in a sandbath heated 27 to 770F. for a period of l hour and 45 minutes to liquefy 28 the specimens of coal. The bombs were then rapidly quenched 29 in cold water. In a series of separate manipulations, each of the bombs were then separately opened and the contents ~ 4~ 3 1 of each poured into cyclohexane, washed with hexane, and the 2 washings combined with the rest of the cyclohexane. After 3 the several washings, the cyclohexane specimens were centri-4 fuged, and the recovered solids washed several times with additional hexane taking care in each instance to recover 6 as much of the solids as possibleO These manipulations 7 completed, the three solid specimens were dried in a vacuum 8 oven at 220F. Ash analyses were then obtained, from which g the conversion for each specimen was then calculated. The percent conversion of each specimen of coal to 1000F- liq-11 uid is given in Table V, below 13 Percent Conversion t 14 Sample No. _ Specimen 1000F- Coal Liquids~l) 0 Raw Wyodak Coal 70O0 16 1 K2C03 Treated 7401 17 Wyodak Coal 18 2 K2S04 Treated 63~3 19 Wyodak Coal (1) Average of two runs 21 Analyses, after completion of the liquefaction, showed the 22 presence of vaterite in the residue from the raw, or un-23 treated coal. No vaterite was found in the residue from 24 either of the other specimensO
Atomic absorption analyses showed that 0.023 mole 26 Of K2CO3 was absorbed onto 100 grams of as received Wyodak 27 coal, whereas, in contrast, only 0cOO9 mole of K2S04 was ab-28 sorbed on a similar specimen of ~Iyodak coalO This reflects 29 the importance of the solubility of the anion, i.e., C03=
vis-a-vis S04', to wit:
31 Ca+2 + K2X = K2+ + CaX

1 where X - S04 , solubility of CaS04 is 0~2go/100 ml.
2 X - C03~, solubility of CaCo3 is 0.0014g~tlO0 ml.
3 The greater insolubility of CaC03 drives the exchange 4 equilibrium, as shown by the equation, to the right, giv-ing more potassium incorporation.
6 Next, 80 milligram specimens of each of the three 7 samp~ s obtained from the liquefaction residue, respectively, 8 were placed in a thermogravimetric analyzer, then heated to 9 about 1560F. until a constant weight was obtainedO
Steam was then introduced, and the weight change 11 was measured with time. These data were used to calculate 12 instantaneous rates of gasification vis-a-vis % burnoffO
13 The data are shown in Table VI, belowO

Char Gasification Rates at 1560Fo 16 ~a~R~ RrDi~
17 Sample Before Steam Percent Rate 18 NoO Added(l) Burnoff(l~ mg/minO!mg~l) 19 32~9 809 0~203 29~ 0~170 21 5()~2 0~057 22 1 (K2C03) 2603 7~9 0~383 23 23-6 0~60 24 4~O7 0.391 2 (K2S04) 28O9 8~6 0 148 26 ~0.3 0.153 27 49.~l 0~126 28 (1) Average of two runsO
29 These data thus show that the alkali metal cations are carried through and are contained within the 1000F-31 liquefaction bottoms. Where a sufficient amount of the al-32 kali metal cations are present additional 1000F- liqùids 33 can be produced and then, on gasification the cations can 34 act as catalysts in the gasification reaction to increase the reaction rate, as compared with untreated coal. The ;~.1. 1'7~ -j3 1 advantage gained, if desired, could be translated into lower 2 gasification temperatures. Suitably also, ~he catalyst can 3 be recovered by existing technology and recycled.
4 It is apparent that various modifications can be made without departing the spirit and scope of the inven-6 tion. Various analyses, taken together, suggest that coal 7 contains a limited number of exchange sites, and that under 8 varying conditions of time, concentration, and solution to 9 coal ratio, the exchange of the metal salts into the coal can be substantially quantitative. Essentially all of the 11 calcium of a subbituminous or coal of lower rank, if it is 12 not dried prior to treatment, can thus be converted to a 13 form of calcium which is essentially innocuous in the coal 14 liquefaction reaction, and the calcium which remains in the coal may be beneficial in a coal gasification reaction 16 Moreover, by judicious selection of a metal cation species ~7 which is catalytic the performance of the coal gasification 18 process can be improved; and by selection of cations on the 19 basis of their cost and effectiveness is catalyzing the gas-ification reaction considerable improvements can be made 21 from a cost-effectiveness standpoint~

Claims (12)

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

1. A process for the liquefaction of a calcium-containing subbituminous or lower rank coal; wherein the coal is first treat-ed to form a water-insoluble thermallystable calcium compound which remains in the pore of the coal on liquefaction, by (i) contacting the coal in particulate form with a single compound MX, in an aqueous solution, capable of forming the said water-insoluble, thermally stable calcium compound, M being H+, an ammonium ion or a monovalent or multiple valent cation selected from the group consisting of the Group IA, IVA, VIB, and VIII metals of the periodic table of the elements, and X being sulfate, carbonate or phosphate, and (ii) maintaining the contact for a period of time sufficient for impregnation of the compound into the pores of the coal; and wherein the thus single compound impregnated coal is then recovered and subjected to coal liquefaction conditions.

2. A process according to claim 1 further characterized in that M, of the compound or salt characterized by the formula MX, is iron.

3. A process according to claim 1 further characterized in that M, of the compound or salt characterized by the formula MX, is cobalt.

4. A process according to claim 1 further characterized in that M, of the compound or salt characterized by the formula MX, is nickel.

5. A process according to claim 1 further characterized in that M, of the compound or salt characterized by the formula MX, is tin.

6. A process according to claim 1 further characterized in that M, of the compound or salt characterized by the formula MX, is potassium.

7. A process according to claim 1 further characterized in that M, of the compound or salt characterized by the formula MX, is sodium.

8. A process according to claim 1 further characterized in that M, of the compound or salt characterized by the formula MX, is molybdenum.

9. A process according to claim 1 further characterized in that contact between the particulate coal and the solution of the salt or compound is maintained for a period ranging at least about 0.01 to about 24 hours.

10. A process for the liquefaction of a calcium-containing subbituminous or lower rank coal; wherein the coal is first treat-ed to form a water-insoluble thermally stable calcium compound which remains in the pore of the coal on liquefaction, by (i) contacting the coal in particulate form with a single compound MX, in an aqueous solution, capable of forming the said water-insoluble, thermally stable calcium compound, M being H+, an amonium ion or a monovalent or multiple valent cation selected from the group con-sisting of the Group IA, IVA, VIB, and VIII metals of the periodic table of the elements, and X being sulphate or carbonate and (ii) maintaining the contact for a period of time sufficient for im-pregnation of the compound into the pores of the coal; and wherein the thus single compound impregnated coal is then recovered and subjected to coal liquefaction conditions.

11. A process according to claim 1 further characterized in that 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.

12. A process according to claim 11 further characterized in that 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.