CA1138800A - Solids precipitation process for coal- derived liquids using recycled solvent fractions - Google Patents

Abstract

SOLIDS PRECIPITATION PROCESS FOR COAL-DERIVED LIQUIDS
USING RECYCLED SOLVENT FRACTIONS

ABSTRACT
A solids removal step for coal liquefaction-hydrogenati processes utilizes the addition of a selective solvent liquid fraction to coal-derived liquids to produce rapid precipitation of solids and thereby achieve a high percentage of solids removal from the coal-derived liquids. It uses a selected solvent additive liquid fraction which is convenient obtained from the coal liquefaction process by distillation, without need for additional hydrogenation steps or the addition of any extraneous liquids.
The solvent liquid used is a coal-derived liquid fraction boiling between about 300-550°F, which has a Watson characterization factor (K) in the range of 9.5-11, and also has a Kauri-butanol value exceeding about 40 and preferably is 50-130. Following mixing of the two hydrocarbon liquids together, the resulting settling time for particulate solids in the liquid mixture is relatively short, usually less than about 45 minutes and under certain conditions may be about 15-30 minutes.
The resulting clarified overflow liquid portion from this solids precipitation step contains less than about 0.1 W %
ash and unconverted coal solids, while the underflow liquid portion contains 30-50 W % solids and may receive further processing as desired, such as coking. Although this solids precipitation step is useful with various coal liquefaction processes, it is preferably used with catalytic hydrogenation processes such as the H-Coal? process wherein between about 2 and 4 W % hydrogen is chemically combined with the coal derived liquid.

Description

~`
1138l~0 BAC~'G~OUND OF 'rl~E INVENTIO.~
.

FIELD O~ TIIE INV~NTIOr~
This invention relates to the li~uefaction of coal and more specifically relàtes to the removal of unconverted coal, ash, and other particulates from a coal liquefaction reaction product.
DESCRIPTIO~ OF THE PRIOR ART:
Processes for the removal of particulate solids for example unconverted coal and ash, from the coal-derived liquids by the addition of a promoter or solvent liquid to produce precipi-tation of such particulate solids are well kno~m in the prior art.
U.S. Patent 3,687,837 discloses that the solids in a coal liquefaction product can be caused to agglomerate, thereby in-creasing ease of separation through fil;ration or centrifugation, by adding a process derived solids-f~ee liquid boiling between 100F to 700F or an ash.containing liquid boiling a.bove 1000F.
The agglomerating agent boiling between 100F and 700F is pro-duced by the do~stream hydrocracking of a clarified coal liquid.
The 1000F plus material is essentially bottoms liquefaction product. The aforementioned process su~fers from the disadvan-ta~es that the agglomerating agent (boiling between 100-700F) must be produce~ by costly hydrogenation, while the 1000F plus material is quite viscous and while promoting ag~lomeration, makes separation by, for example,filtration or centrifugation, ~ore difficult. ~ similar process is disclosed in U.S.Patent 3,790,467.
U.S. Patent 3,791,956 to Gorin, et al., ~iscloses ~ coal li~ucEaction process in ~Jhich ~ precipitatinq solvent which is an aliphatic or naphthenic hydrocarbon solvent having ~ boilin~

~388~0 range of 75-200C, such as cycloll~xane, n-dccane,"DecaLi~' etc., is add~d to a stirred agglomeration zone maintained at a telllperat~lre between 250-370~C and a pressure bet~een 5-200 psig.
It is rccog~ ed thaL such liquid fracti~s ~o not normally occur in the coal liquefaction product, but must be recovered following 'subsequent hydrocracking steps.
U.S.Patents 3,852,182 and 3,856,675 to Sze et al., disclose the removal of solids derived liq~ids by a promoter liquid having a characterization factor (K) of 9.75-11.0 and boiling between 0 250F and 750F. However, these processes required added pro-cessing steps, such as hydrocracking to produce the promoter liquid and the residence time for the solids to settle is rela-tively long (0.5-6 hours). This re;quires large and expensive pressurized settler vessels to æhieve satisfactory solids removal from product liquid streams.
Because of these problems, the use of more effective solven~
liquid fractions, which can be conveniently derived from the coal-liquefaction process and require significantly shorter settling times, has been souc,ht. I

.

*Trademark for decahydronaphthalene 3 8 ~

Sl~ 'u~R~ OF T~IE l~!VE~!TIOM

This invention per.ains to the removal by precipitation of a~sll ~nd other insol~lble m~terials from coal-derived liquids, and utilizes the addition of a~specific internally-generated liquid fraction to promote solids precipitat-ion in the coal-derived liquid and to achieve a higher percentage of solids removal. The solids removal step uses a selected additive solvent liquid which is derive~ from the coal liquefaction process through simple fractionation and without need for further processing. The ,, solvent liquid used in this process is a coal-derived naphtha liquid fraction, boiling between about 300-600~JF and having a characterized factor (K) in the range of 9.5-11, as defined by the equation:

K = ~

wherein TB is the average molar boiling point of the liquid (K), and G is the specific gravity of the liquid ( 60 F/60F) .
The solvent liquid used is preferably a 350-550F fraction o~
"H-Coal" process catalytic hydrogenation procesS naphtha fractionated from the atmospheric still overhead liquid and mixed with the hydrogenated coal liquid in sufficient amounts to produce the :L~ precipitation of solids in a settling zone, but not in excessive amounts or in a ràtio to produce exoessive settlina of val ~ le heavier coal products. The'~-Coal"process is described in U.S.Patents Re. 25,770 and 3,519,555.

ratio of solvent to coal liquid should be at least about 0.6/1 and preferably bet~7een 0.8/1 and 1.5/1. Also, because of the greater effectiveness of this solvent fraction for causinn rapidprecipitation of particulate solids in the settler, the required solids settling time is relatively sllort, usually less than abou~ 45 minutes and *Tradem~rk 8~3~0 1~
. .
certain conditions, 10-30 minu~es. Such rapid precipîtation of solids l~laterial permits the use o~ smaller and less expensive vessels.
'lhe resulting cl~ri.ied o~erflow licl~lid ~Jithdrawll froln the solids settler vessel contains less than 0.1 weight percent ash ~and unconverted insoluble coal solids. The remaining underflow liquid portion contains increased solids of between about 40-50 weight percent. Such underflow liquid stream may be further processed as desired, such as vacuum distillation, coking, or ~o gasification.
It is an important feature of this invention that the solvent precipitating agent used is a special solvent fraction deri~ed entirely from the coal liquefaction process, and that no further hydrogenation treatment of this fraction, other than fractionation recovery, is required. This solvent liquid fraction is usually produced from atmospheric still overhead liquid and is also recovered by fractionation from reduced solids overflow stream from the settler, The conditions in the settler vessel should be maintained at sufficient pressure to avoid evaporatilon of the light liquid fraction and at suficient temperature to maintainthe liquid viscosity within a desirable low range to facilitate solids settling. Usually the settler pressure should be between about 50-200 psig and the t~r~ atur~e should be a~out 500-6Q0F and preferably 530-580F.

DESCRIPTION OF THE DRAI~INGS

Fi~ure 1 is a schema'ic diagram showing tl~e essential proccss stcps of the invcntion incor~orated into a coal liquefaction process.

~388~0 Figure 2 is a graph of weight percent ash in coal liquid against settling time for various ratios of solvent to liquefaction product.
Figure 3 is a graph of weight percent solids against ratios of solvent to liquefaction product.

DESCRIPTION OF THE PREFERRED EMBODIMENT

_ _ _ . _ _ . . .
This invention will now be described as employed in a catalytic ebullated bed type coal hydrogenation process and illustrated by Figure 1. As shown, a bituminous or semibituminous coal enters the system at 10 and is first passed through a preparation unit generally indicated at 12.
In such unit the coal is dried of substantially all surface moisture, ground to a desired mesh size, and screened for uniformity. For our purposes, it is preferable that the coal have a particle size of about 50 to 375 mesh (U.S. Sieve Series).
The coal fines are discharged into transfer line 13 and pass to slurry tank 14 where the coal is blended with a slurrying oil indicated at 15, which is conveniently made in the system. To establish an effectively transportable slurry, it is found that the ground coal should be mixed with at least about an equal weight of slurrying oil.
The resulting coal-oil slurry is pressurized by pump 16 to superatmospheric pressure, such as 500-5000 psi, and is then passed through heater 18 to bring the clurry to a temperature in the order of 600F to 850F. The heated coal-oil slurry is then discharged into reactor feed line 25, wherein it is supplied with recycled hydrogen from line 19.
Fresh makeup hydrogen is added as needed at 17.

~f i~388GO
.

The entire mi~ture o~ coal-oil slurry and hydrogen then cnters reactor 20, passing upwarclly from the bottom at a rat~, under pressure and at a temperature to accomplisll the desired hydrogenation~ In addition, particulate hydrogenation catalyst 5may be added to reactor 20 at connection 21 in the ratio of about 0.1 to 2.0 pounds of catalyst per ton of coal. Such a catalyst would be from the class of cobalt, iron, molybdenum, nickel, tin, or other hydrogenation catalysts kno~t in the art deposited on a base of the class of al~nina~magnesia, silica, o or similar materials.
By concurrently flo~ing liquid and gasiform materials up-wardly through a vessel containing a mass of solid particles o~
a contact material, which may be a specific catalyst as indicated above, and expanding the mass of solid particles at least 10%
and usually by 20-100% over the volume of the stationary mass, the solid particles are placed in random motion within the vesse~
by the upflowing streams. A mass of solid particles in this state of random motion in a liquid medium may be described as "ebullated". The characteristics of the ebullated mass at a ~o prescribed degree of volume expansion can be such that finer, lighter particulate solids ~ill pass up~7ardly thro~gh the ca~alyst . m~ss, so that the contact p~rticLcs constit~lting the eb~llated mass are retained in the reactor and the finer, lighter matexial may pass from the reactor. The catalyst bed upper level 22 above which few, if any, contact particles ascend, is called the uppcr level of ebullation.
In general, the gross density oE the stationary mass of con~tct ma~erial ~i]l be bet~Jeen about 25 to 200 pounds per cu~ic foot, the ~lo~ rate of thc liquid will be between about 5 and 120 gallons p~r minute pcr square foot of horizontal cross-section area of tlte ebullatcd mass, ancl the e~panded volume o~ the ebullatcd mass usually will be llOt more than double the volume of thc scttl~d mass. To main~ain ~he desired superficial upward liquid velocity 113~8(~0 in the reactor, a portion of the liquid slurr~ is usually re-cycled to the reactor, such as a portion of liquid stream 24 which is removed from about the upper level of ebullation 22 and recycled via conduit 38 and pump 39 to the bottom of the reactor 20. Alternatively, thîs recycled liquid stream may be located within the reactor, as will be understood by those skilled in this art. Spent catalyst may be removed ~y drawoff at connection 23 to maintain the desired catalytic activity within the reaction zone.
Reactor operating conditions are in the range of 700-950F temperature and 1000-4000 psi partial pressure of hydrogen, prefera~ly 750-900F and 1000-3000 psi hydrogen partial pressure. Coal throughput or space velocity is at the rate of 15 to 150 pounds coal per hour per cubic foot of reactor volume, so that the yield of unreacted coal as char is between 5 and 15 weight percent of the quantity of moisture and ash-free coal feed. The relati~e size of the coal and catalyst particles and condition of ebullation is such that catalyst is retained in the reactor, while the ash and unreacted char particles are carried out with the liquid reaction products.
From reaction zone 20 and effluent stream 24, which is virtually free of solid particles of contact material, is withdrawn, cooled at 26: and then passed to a first phase separator 28. From separator 28, a light gas stream is removed at 29 and passed to hydrogen purification step 30.
A medium-purity hydrogen stream 32 is recovered from purification step 30, warmed at 26, and recycled through heater 34 to reactor 20 to proYide most of the hydrogen requirements therein as heated hydrogen stream 19. Also, a liquid stream 36 is recovered from separator 28 and is passed , . . .. . . . , ., . .... . , ., . . ,, , ,, , ., . ,, .. , ~ ~, . . . .

~138~0 at reduced pressure to intermediate phase separator 40.
This separator operates at 500-650F temperature and permits removal of a substantially gaseous stream at 41 and a liquid stream at 42.

- 7a -... ... . .... . . ..... . .
.

1~388~0 From phase separator 28, liquid stream 36 is withdrawn and passed to phase separator 40. ~ hydrogenated coal liquid is withdrawn at 42 containing unconverted or insoluble coal and ash solids from the reaction step 20 and is passed to hydroclone separation step 46. An overflow liquid stream containing a reduced concentration of solids is removed therefrom at 47 and returned to reactor 20 to help control the solids concentration in the reactor. An underflow liquid stream, containing an increased concentration of solids, is withdrawn at 48. If desired, a portion 49 may bypass hydroclone 46 for control purposes.
In addition, the hydroclone can be eliminated to permit passage of stream 42 directly to settler 50.
This hydroclone underflow liquid stream 48 is mixed at 44 with a solvent liquid 45 derived from the process by fractionation. It has been found that the ratio of solvent liquld 45 to stream 42 should be between 0.6/1 and 1.5/1.
The resulting mixed stream is then passed to settler 50, which is maintained at a temperature between about 550-600F
and pressure conditions sufficient to avoid vaporization of the precipitating solvent, generally about 50 psig and usually not exceeding about 200 psig. Rotary rake 51 or equivalent mixing means is used to provide sufficient mixing and continuous agitation to prevent premature settling of the precipitated solids component. Because of the effectiveness of the combination of the liquids to produce precipitation of solids, the residence time in the settler to achieve significant solids settling is usually less than about 45 minutes and is preferably 15-30 minutes.
From settler 50 r o~erflow liquid 52 is continuously withdrawn and contains less than about 0.1 weight percent - B -.. , .. . ~ . .

1~388~0 solids and usually less than about 0.07 weight percent solids comprising fine particles of uncon~erted coal and ash.
This overflow liquid 52 contains some sol~ent liquid fractions and is passed to recovery ~0 - 8~ -. . . . . .. . . ..

1~3~ 0 , tower 51~:ror sut~;tantial recovery of the solvent mater:ial by ~list~ t:ion. 'rhe ~Inderrlo~! liq~lid strec~ 56, c~ontaitlin~, an increased solids concentration, is removed from settler 50 by pun-ping and with the aid o~ internal rotary 51, reduced in pressure by passage to fla~h dr~m 58 which is maintained at a pressure of at least 5 psig and a temperature of 550F which pr~vents vapor-i~ation o~ solvent, and passed to vacuum distillation at 60. The resulting overhead liquid 61 from the vacuum still is joined wit~h stream 52 and passed to the recovery distillation tower 54. The bottoms stream 62 from vacuum still 60 may be urther proeessed by, ~or e~am~le, coliing or gasification to produce the makeup hydrogen needed in the process.
The li.gllt fraction removed overllead at 55 from recovery tower 54 is a 350-600~F fraction, ~7hicll is ef~ective in produeing precipi tation of ash and unconverte~l coal solids from the hyclrogenated coal l~ uicl. Thi~; liquid ~raction is p<~ssed ~o holding tank 70 for recycl~. to tlle solvent preeipi.tat-ioll m:ixin~ ~ank as n~ecled.
Al~o froln ~o~er ~4 c~ ~uel oil Eraetion 56a is rcrnoved as produet.
If des-ire(l, a port:ion of stream 56a ean be used as slurry;ng oil 15.
Ret~lrn:i-nt, no~ to pllase seyarator l~0, overl~eacl streaTn 41 is passcd Lo c~ )he2^;c d:ist:illclLioll to~Je-- G'~. The reslllt~ cr ~itluicl product streanl is withdrawn at 66 and providcs an int~ mediate liqu:id product. I:E desired, a portion 72 o~ ~his liqui~ stream 66 ca~ e used for slurrying oil 15. ri~l~e light overhead liquid stream 65 is passecl to a fract~ionation tower 68 for production o~
a portion 69 oC t:he prccipitating solvent liqui~ needecl ~or tl~e solverlt: pr~ci p.~ tC'ttiO11 step. This solvent liquicl ~r~c~ion renlovecl c-lt 69 is passed to ilolding tanli 70. The coln~ined l~e~ solvent 69 arl(l recovere(l solvetlt 55 is withdra~n from tank 70 at the desire(l rctte, to prov:id~ solvellt s~r~c-tm ~5 for aclclition to eoal-derived ~ r~c~ 2 clt lllix;~c, ~ int ~ cle~iir~d, cl cp~c:tal ~

: ( ( mi.xinr, Lanlc mcly be provic~ed at 44, desirned for achieving intimate ie:i.t~ 0~ e sol~ent: alld l):ro<luc l: l:i.clui(ls s u:l~.L icicnt to a(:lLieveagglomer~tion and subseq~2n-t rapid settling of solicls in the ~settlinr vessel 50.
The invention will be lurther illustrated by reference to the exan~ples which follo~

EX~MPLE I

~ continons run was made in accordance with the inventionin a settler hav:i.ng a capacity for receiving 30 lbs of material per hour.
The settler utilized is a pipe 56 inches in length and 8 inches in diameter. The feed ~Jas a hydroclone underflow containing 27 weight percent solids, (1~ weigh, percent ash). The precipitating solvent had the characteristics noted i.n Table 1 below.

_~`a Gravlty, ~Pt 2 Dist:i.llcltion ~

~ , 3~, 3() , 350 ~96 ..
; 90 4l~8 ~P 538 ~ e res~llts of t~,is r;in are sho~n in Table 2 belo~/ whic~h sho~v tl~at t-lle ash colltent~ .s red-lced to between .006 wei,llt percen~
and .093 ~ei.~ el^cent.

;

~13~380(1 ;

. Tal)l~ 2 ' Coal l.iquid flow Rate, lbs/hr 13.1 Precipitclting Solvent Flow Rate, lbs/hr 11.9 Ratio Solvent to Coal Liquid .91 Set-tler Conditions Temperature F 550 ~ressure, psig 200 Run Duration, hours 16 _____________________________________ _________ ___________________ __ __._____________________________________________________________ Set~ler Ovcrflow ~ettlcr Under~low Ash,~ % - llour Flow Rate Flow ~a-te 8.9 7.2 1 0.016 6.91.

2 0.()28 0.76

3 0.0~.9 0.83 ~ n. o/,o 1 2.32 ~ 0.0~1 2.77 ; 6 0.036 9.06 7 0.076 7.32 0.03~ _ 9 0.006 lo n. 093 10 86 11 ~.0~.0 15.9 .2 0.0~ .9 01 ~.2.83 1(~ . 0. 0~ 13.26 0. 06 35.44 16 0. 07 29.60 2~
2?76 3n 'ro~ll, L~;. 138.

I~388QO

f'L~ I t 13c-se(l on the r~ sults in ~xallnle I, calculations for scale up t:o 3¢)0 ~ ,c~re -n~?.d~ ~?roj ect:incr, the or)erclt;on in accord~nce ~:ith l i~ re 1. 'l`lle results ~re sho~Jn in Tabl~ .3 be:Low. ~e~erence - to stream number in the ~able corresponds to Figu~e I.

Table 3 Cornponent:, Lbs/Hr Stream Total Anti- Solid~
umber Lbs/llr Solvent Distillate F~es-iduum olicls I~TCr/o llydroc lone ~`eed ~'~2 644.5 87.4 13.6 Ilydroclone Over~low 47 394.5 39.8 10.
llydroclone linderf1O~J L'~S 250.~'~ 3.2 118.~ 81.2 47.~ 19.0 Anti-Solvent 300-400I~ l~5222.1 222.1 0.0 0.0 0.0 0.0 Settler ~ccd ~72.5 225.3 118.~ 81.2 ~7.~ 10.
~et~lcr Overfl o;.~ 52 283.G 171.0 1 70.5 42.0 0.1 0.0 SJl~-cLltl-~É;0~7 56188.9 5~.3 ~7.9 39.2 ~7.5 25.
IJnclcr~lo~
l'`l~';h C)verl~r2acl 5059.2 S1.2 8.0 0.0 0.0 0.0 I'.ol:to~ . 591.~'). / 3.1 39 9 39. 2 ~/ . ', 3G.~' Vacuuill ()verhead 6l3l~. 7 3.1 31.6 0.0 0 ~ o.o ~'acuum ~o~l:orns 6295.0 0.0 8.3 39.2 47.5 50.
I) i s t~ l. I. a t: ion ~ec-~d 52377.5 225.3 110.1 ~2.0 0.1 0.0 An ~ So lven~
l~ecovr ry 55222 .1 222.1 0. O O. O 0. O 0 O
~uel. ()i1 I'ro~uct: 56155.ll 3.2 110.O ~2.0 0.1 0.0 ~ 1138800 EXAMPLE III
A one-liter capacity stirred autoclave unit was used to determine solids settling rates for various mixtures of separator bottoms liquid and selective sol~ent liquid derived from coal. Numerous batch runs were made at conditions of 550F temperature and 200 psig pressure, using freshly produced hydroclone underflow slurry liquid mixed with 350-600F "H-Coal"* process naphtha fraction as the solvent liquid. Ratios of solvent~slurry liquid of 0.3 to 1.0 were tested. The operation consisted of charging the autoclave with the desired quantity of slurry liquid and solvent liquid, then heating and stirring the mixture until the desired temperature and pressure was obtained. The agitation was then stopped and liquid samples withdrawn through an internal tube at a fixed level in the autoclave at 15 minute intervals for analysis to determine the solids ; concentration in the samples. Typical data obtained at 15 minute intervals after autoclave agitation was stopped are shown in Figure 2.
It is noted that the weight percent ash in the coal liquid sample declined with increased settling time from 8-11 weight percent initial to less than about one weight percent solids after 30-90 minutes. With increased ratios of solvent/slurry liquid, shorter settling times were required to achieve desired low percent solids in the liquid samples, with desired ratios exceeding about 0.3 and ratios of 0.6 - 0.8 being the most effective. Surprisingly, where the ratio of solvent to slurry liquid is at least or greater than 0.8 a vast improvement in settling takes place.

* Trademark EXAMPLE I~
To confirm the solids settlin~ data from the above autoclave experiments by usin~ continuous process ~low runs, an online continuous 30 lb~hr solvent precipitation step was incorporated into an experimental "H-Coal" liquefaction process handling about 250 lb/hr coal feed. The precipitation equipment was used to produce solids settling and determine the settling rate for mixtures of coal-derived liquid slurry and selective solvent naphtha fraction additive liquid produced in the "H-Coal" liquefaction process. The slurry feed was hydroclone underflow liquid containing about 18 weight percent ash (27 W% total solids). The ratio of solvent liquid to slurry liquid ranged between 0.3 and 1.1.
The resulting overflow liquid from the settler contained ash concentration below 0.1 weight percent and ranged between 0.006 - 0.093 weight percent. The benzene-insoluble material rejected in the underflow from the settler contained as much as 30 weight percent ash (45W~ solids) on a continuous basis. The liquid residence times in the settler ranged from about 40 to 90 minutes. Results of average weight percent ash in the overflow and underflow streams at equilibrium settler conditions are shown in Figure 3.
It is noted that the average ash concentration in the overflow liquid from the settler decreases from 0.11 to 0.03 weight percent as the ratio of solvent/slurry liquid is increased from 0.4 to 0.9.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A liquid-solids separation process for removal of unconverted coal and ash particulate solids from hydrogenated coal-derived liquids by solvent precipitation, comprising (a) adding to said coal-derived liquid a solvent derived from the coal liquid without further hydrogenation, said solvent being a coal-derived naphtha fraction having a boiling range between about 300-600°F and having a characterization factor (K) in the range of 9.5 - 11; (b) mixing the two liquid streams together upstream of a settling step and providing sufficient settling time to produce substantial precipitation of the solids, so as to provide a clarified overflow liquid portion and an underflow liquid portion having increased solids concentration; (c) with-drawing the clarified overflow liquid stream containing a sub-stantially reduced concentration of solids as liquid product;
and (d) withdrawing the underflow liquid stream.

2. The process of Claim 1 wherein the additive solvent liquid fraction has a boiling range between 350°-550°F.

3. The process of Claim 1 wherein a portion of the solvent additive liquid is derived by fractionation of an atmos-pheric distillation overhead liquid fraction, and the remainder is recovered by fractionation of the settler effluent streams and recycled to the mixing step.

4. The process of claim 1 wherein the settling step conditions are in the range of 50-200 psig pressure and 500-600°F
temperature, and internal rake means are used to prevent excessive settling of the bottoms stream.

5. The process of Claim 1 wherein the ratio of the added solvent liquid to separator bottoms liquid to provide the settler feed liquid is between about 0.6 and 1.25, the solids settling time in the settling step is less than about 45 minutes, and the settler overflow liquid product contains 0.1 to 1.0 weight percent unconverted coal and ash solids.