CA1146095A - Process for the separation of contaminants from feed streams using magnetic beds - Google Patents

Abstract

ABSTRACT

PROCESS FOR THE SEPARATION OF CONTAMINANTS
FROM FEED STREAMS USING MAGNETIC BEDS

The invention relates to the removal of con-taminants from fluid streams in a continuous process by adsorption on solid adsorbents, particularly small particle size adsorbents, which also include a mag-netizable component, wherein the adsorption and desorp-tion are carried out at substantially the same pressure.
The adsorbent particles and magnetizable component which flow or move through the vessel are stabilized against fluid by-passing and solids back-mixing and recirculation generally associated with fluidized beds (except for the flow or movement of the solids through the contacting vessels) during adsorption and desorp-tion by the use of an applied magnetic field.

Description

1146~3S

PROCFSS ~OR TH~ SEPARATION OF COl~P~ ~ NA?~rs PRO~ F:E:ED STREA~IS USING ~GNrTIC BEDS (MS~3-69) FI ~ LD OF THE I~NTIOl~

2 The present invention relates to a process for

3 the separation of com?onents or mixtures from feed streams

4 using magnetically stabilized beds~ ~ore particularly, .he invention relates to the removal Oc cont2minants from fluid 6 streams in a continuous process by use of soli~ adsorbents 7 capable of adsorbing the contaminant(s) from the fluid 8 streams. The adsorbents include a magnetizzble com~onent.
9 The adsorbent particles and magnetizzble compo~ent which flow or move through the vessel are stabilize~ by the use 11 of an applied magne.ic Sield against gas ~y-passing and 12 solids back-mixing and recirculation generally associated 13 with fluidized beds (except for the flow ~r movement of the 14 solids through the contacting vessels) du~ing ~dsorption 1~ and desorption. The use of the applied magnetic field en-16 zbles one to use small size adsorbent particles without en-17 countering high pressure drops as with fixed bed processes.
1.8 The small adsorbent particles give faster transfer of the 19 contar.inants than with large particles which allows 'or a closer approach to equilibri~m, the use o~ smaller beds 21 thzn would be needed in a fixed bed process an~ the pos-22 sibility of using one adsorption bed rather th~n a multi-23 plicity of- beds as with fixed bed processes. The invention 24 allows many separation stages to be obtained in a single 2; vessel without incurring high gas-side pressure drop.
26 DESCRIPTIO~ OF THE ~RIOR ART
27 In conventional separation processes, vapors 28 oS the gases to be .reated are contacted with adsorbents 29 in fixed beds, a plurality of beds being used so that one or more beds will be undergoins a regeneration step while 31 one or more other beds are being used in the absorption step 32 of the cycle. I. is readily evident that cyclic fixed 33 bed operations have a number o~ inefficient aspects, in-34 cluding the need for extensive valving znd mani~olding, 3; as well 2S ?ressure swing-product lQss, considerable , ~

~1~6~5 1 waste of heat in heating up and later cooling down the 2 various flow lines, vessel walls and internal components 3 of the vessel. Although in theory only two vessels nee2 4 be used for a cyclic operation, one for adsorption and one for regeneration, in actual practice use of more than two 6 vessels is advantageous to reduce the size of the vessels, 7 to reduce stripping gases (product gas loss~ and to minimize 8 adsorbent inventory. However, as the number of vessels 9 increases, the time available for regeneration becomes critical, so that there must be provision made for suf-11 ficient time intervals to go through all of the regenera-12 tion steps, including switching of valves, ~epressuring, 13 heating, holding at high temperature, cooling ana repressur-14 ing. See H. M. Barry, Chemical Engineering t pages 105-120, February 8, 1960; E. Kehat et al, I & EC Pr~cess 16 Design and Development, 4: 217-220 (1965); J. I Nutter 17 et al, A I.CH.E. Journal, Pages 202-206, March, ~963;
18 G. J. Griesmer et al, Hydrocarbon ProcessinG, 44: 147-19 150 (1965); W. J. Schumacher et al, I & EC Process Design 20 and Development, 6: 321-327 (1967)i and D. M. R~thven et 21 al, C ical Enqineering Sciences, 26: 114~-115 (1971~.
22 Because of the large plant invest~ent required 23 in fixed bed adsorbent processes, as well as high operat-24 ing costs, the desirability of employing a conti~uous countercurrent adsorption process for separating com~onents 26 in feedstreams has long been recognized. The fl~idized 27 solids technique is an attractive approach to such a con-28 tinuous process, because it eliminates the r~eed for valving, 29 manifolding and other facilities required for a ~ixed bed cyclic operation. A number of patents and publications 31 have disclosed the concept of separating hy~rocarbon mix-32 tures by fluidized or simulated fluidized beds. Fluidized 33 bed drying has also been described in the patent literature.
34 For example, see U.S. Patent Nos. 3,494,046 and 3,104,806 35 which are concerned with processes for drying particulate 36 matter. However the advantages inherent in the use of 37 fluidized beds for such operations as catalytic cracking 38 and hydroformin~ of hydrocarbons, namely, comple~e mixing 1146~

1 Of solids so as to insure isothermal conditions and maxi--2 mum heat transfer is a disadvantage in an adsorption pro-3 cess wherein back mixing of solids is not desirable. For 4 this reason, when the use of fluidized solids for adsorp-tion processes has been undertaken, it has required a 6 plurality of vertically spaced shallow fluidized beds 7 providing stagewise contacting of gas and adsorbent. See, 8 for example, L. B. Etherington et al, Chemical Engineering 9 Progress,Pages 274-280, July,1956; and E. D. Ermenc, Chemical Engineering, Pages 87-94, May, 1961.
11 In the present invention, the adsorption and 12 desorption of the contaminant(s) in a feed stream takes 13 place in a fluidized (i.e., expanded and levitated) bed 14 accomplished without the need for a plurality of vertically spaced shallow beds by employing an applied magnetic field 16 to stabilize or structure the fluidized bed. The result 17 is that true countercurrent staged flow of solids with 18 respect to the flow of the fluids, e.g., fluids contain-19 ing product and contaminants,that fluidize the bed can be obtained with greatly reduced overall investment and 21 operating cost, as compared with what was heretofore pos-22 sible. The process of the present invention preferably 23 takes advantage of the use of a magnetically stabilized 24 fluidized bed, such as disclosed in U.S. Patent No.4,115,927 ~
25 to R.E. Rosensweig, with particular reference to column 21, t 26 lineS 16-28.

28 The present invention is directed to a process 29 for the separation of contaminant components from a feed-30 stream containing the same, within an external force field, 31 said process comprising the steps of:

32 (a) adsorbing a portion of the contaminant 33 from said feedstream by countercurrently contacting said 34 feedstream with a bed comprising adsorbent particles 35 capable of adsorbing said contaminant components from 36 said feedstream;

~146Q95 1 (b) desorbing at least a portion of said 2 contaminant from said adsorbent particles to regenerate 3 at least a portion of said adsorbent particles;
4 (c) providing a magnetizable component with said adsorbent particles and applying a magnetic field 6 to said magnetizable component and adsorbent particles 7 along the direction of said external force ~ield and at a 8 strength sufficient to prevent and/or suppress gross solids 9 circulation and back mixing;
~d) fluidizing, expanding or levi~ating said 11 adsorbent particles and magnetizable component by counter-12 currently contacting said adsorbent particles and magneti-13 zable component with said feedstream; and 14 (e) carrying out said adsorption and desorption steps at substantially the same pressure.
16 An essential feature of the present invention 17 involves carrying out both the adsorption and desorption 18 steps at essentially the same pressure, i.e~, the pressure 19 dif~crcntial will vary b-7 only about 70 psi or ~ess.
Preferably, in some low pressure processes, ~he pressurc 21 differential will be less than about 25 per~ent from the 22 adsorber pressure but never more than about 70 psi from 23 the adsorber pressure.
24 Thus, in its broadest sense, the p~esent inven-tion can be defined as a process for separating contami-26 nant components from a feed stream which com~rises feeding 27 the feed stream to a bed of adsorbent particles which are 28- admixed or composited with magnetizable particles by counter-29 current contacting these particles under fluidization con-ditions (or where the bed is expanded or levitated by the 31 feed stream) wherein said bed is stabilized by the appli-32 cation of a magnetic field, and recovering the feed stream 33 aepleted of said contaminants.
34 The term "contaminant" as used herein is to be 3~ taken in the broadest sense as being substances, molecules 36 or compounds which make "impure" the final product one 37 desires to obtain. Obviously, the contaminant removed . .

~6~5 1 from a feedstream in the process of the pres~nt invention 2 may itself be valuable Thus, t~e term "contaminant"
3 merely refers to the subs~ances,molecules or compounds 4 one wishes to remove from a feedstream, irres~ective o'

5 the value or lack thereof for the "contamina~ts".

6 Examples of some contaminants whic~ may be re-

7 moved from the feedstreams utilizing the pro~ess of the

8 present invention include the acid qases and ~olar or non-

9 polar-type compounds.
Typical polar-type compounds ~some of which 11 are also acidic) include: CO, COS, NP.3, H2S, SO2, H2O, 12 HCN, RS~ (wherein R is an organic radical, e~'g., mercaptans), 13 RS ~wherein R is an organic radical, e.g., C~4S), etc.
14 Typical non-polar acid gases include CO2 and ~S2.
Typical non-polar compounds includ~ hydrocarbons, 16 e.g., methane, ethane, propane, butane, substituted 17 hydrocarbons, etc.
18 The process of the invention is preferably carried 19 out by fluidizing, expanding or levitating t~e adsorbent particles and magnetizable components under countercurrent 21 substantially plug flow conditions by subjecting the ad-22 sorbent particles and magnetizable component to a magnetic 23 field, preferably a uniform applied magnetic field having 24 a substantial component along the direction ~f the external force field ~e.g., gravity) such that the mag~etizable com-26 ponent has a component of magnetization along the direction 27 of the external force field and wherein a po~tion of the 28 bed of particles is fluidized by a flow of fPuid opposing 29 said external force field at a superficial fluid velocity ranging between:
31 (a) a lower limit given by the normal minimum 3~ fluidization-superficial fluid velocity requ~red to fluidize 33 said bed in the absence of said applied magnetic field, and, 34 (b) an upper limit given by the superficial fluid velocity required to cause time-varying fluctuations 36 of pressure difference through the stably fluidized be~
37 portion during continuous fluidlzation in the presence of 1~46~95 1 said applied magnetic field.
2 Preferably, the strength of the magnetic field 3 and its deviation from 2 vertical orientation are main-4 tained so as to prevent and/or suppress the formation of bubbles in the fluidized or expanded or levitate~ medium 6 at a given fluid flow rate and with a selected f~uidi-7 zation particles makeup.
8 The magnetically stabilized fluidized adsorbent-9 desorbent beds have the appearance of expandedbacked beds with substantially no gross solids circulation or recircu-11 lation (except for the plug flow movement of the solids 12 through the vessels) and very little or no fluid by-passing.
13 The application of the magnetic field enables one to employ 14 superficial fluid flow rates 2, 5, 10 or 2~ or ~o~e times the superficial fluid flow rate of the fluidized bed 16 at incipient fluidization in the absence of the a~plied 17 magnetic field, concomitant with the absence of bubbles.
18 In other words, as the superficial fluid velocity is in-19 creased, the pressure drop through the bed is similar to that which would be expected from a normal fluidized bed 21 without the application of a magnetic field; it increases 22 to the bed weight support value at the min~m~m fluidization 23 velocity, and then remains relatively constant as the fluid 24 velocity is increased. This stably fluidized be~ condition persists even as the solids are continuous-y moved in a 26 descending, substantially plug flow manner through the 27 contacting vessels.
28 BRIEF DESCRIPTION OF THE D~A~INGS
29 Fig. 1 represents a vertical cross-sectional view of the magnetically stabilized adsorber and desorber 31 (regenerator) wherein the adsorber and desorber are 32 positioned side-by-side.
33 Fig. 2 represents a vertical front cross-sectional 34 view of the magnetically stabilized adsorber and desorber (regenerator) wherein the desorber is positioned above 36 the adsorber.

1146~)9S

1 DESCRIPTION OF T~E PRE~ERRED ~BODIMENTS
2 As indicated previously, the present in~ention 3 relates to a process for preferentially adsorbing con-4 taminants, e.g. polar or non-polar compounAs from a feed-stream containing at least one other component which co~-6 prises contacting said feedstream under adsorption con-7 ditions for said contaminants with a bed co~taining ad-8 sorbent particles and desorbing said adsorbe~ contaminants 9 from said adsorbent particles whereby a stream enriched in said preferentially absorbed contaminants is obtained, 11 said process being carried out in t.he presen~e of a ma~-12 netizable component and an applied magnetic ield to 13 stabilize or structure the bed containing the adsorbent 14 particles and magnetizable component. By the present 15 proces-s, the separation can be staged.
16 The adsorbent particles may be used as admix-17 tures or as composites with a ferromagnetic or ferrimag-18 netic component or substance. All ferromagnetic and ferri-19 magnetic substances, including, but not limi~ed to, magnetic Ee3O4, y-iron oxide (Fe2O~), Cerrites of the form ~O.Fe2O
21 wherein ~ ls a metal or mixture of metals such as Zn, ~n, 22 Cu, etc.; ferromagnetic elements including i~on, nickel, 23 cobalt and gadolinium, alloys of ferromagnetic elements, 24 etc., may be used as the magnetizable and fl~idizable par-ticulate solids which are used in admixture or com~osited 26 with the adsorbent particles. Alternatively the adsorbent 27 may itself contain a ferromagnetic or ferrimagnetic sub-28 stance in its makeup. In this case, the adsorbent 29 is already magnetic; no additional magnetic ~aterial need be admixed or composited with the adsorbent.
31 ~he adsorbent ~articles are-generally chosen 32 to suit the particular feed to be treated a~d the contam-33 inent substance(s) that is to be removed from the feed-34 stream. Inorganic, organic or high moleculaI weight in-organic or organic adsorbents may be used.
36 Examples of adsorbents suited for ,he separation 37 process of the present invention include activated carbons, 1~6~5 1 treated activated carbons, molecular-sieving carbon; non-2 stoichiometric carbon-sulfur compounds, (e.g., CxS compounds 3 such as disclosed in U.S. Patent No. 4,201,665, selected 4 artificially synthesized zeolites, such as those having some particular ratio of principal components identified 6 as: "Type A"; "Type L"; "Type X"; "Type Y"; "Type ZSM";
7 mordenite faujasite, erionite; and the like, those zeo-8 lites which have particular silica-alumina ratios and those 9 in which the original sodium cations are exchanged to other cations; selected silica-gels, such as those having some 11 particular relative components of silica, alumina and ferric 12 oxides, those which have particular steric properties as 13 the average pore diameter, specific surface area, pore 14 volume and others; selected activated aluminas such as those having particular components of aluminum oxide and 16 water, those hydrated forms, some particular crystal forms, 17 those which have a particular structure; activated clay or 18 selected acid clays such as montmorillonite in which case 19 the base is exchanged holloysite or attapulgite; aluminas;
layered clays.
21 The aforesaid adsorbents comprising carbon, 22 silica, alumina, metal oxides, iron, magnesium, hydrated 23 oxidesand/or other elements are characterized as:
24 (1) having several different structures, or (2~ having different components, and 26 (3) such that some composing elements are sub-27 stituted by others, followed by further chemical or physi-28 cal treatment.
29 Most of the aforesaid adsorbents are readily ' available in the commercial market. Also the adsorbents 31 similar to those which are commercially available can be 32 generally synthesized without very elaborate technique and 33 many adsorbents can be prepared by chemically or physically 34 treating commercially available adsorbents. A further description of the zeolites mentioned above, and their 36 methods of preparation are given, for example, in U.S.
37 Patent Nos. 2~882,243; 2,882,244; 3,130,007; 3,410,808;

g ' 1 3,733,390; 3,827,968 and patents mentioned therein.
2 Other adsorbents suitable in the practice of the 3 invention include cation-exchange resins with exchange 4 groups of benzene sulfonic acid, carboxylic acid ! phos-5 phoric acid; strongly or weakly basic anion-exchange resins;
6 high molecular weight particles of styrene-divinylbenzene 7 copolymer, or its halomethylated, or cyano-ethylated 8 polymers; acrylonitrile copolymers; high molecular weight 9 compounds having several functional groups such as cyano, cyanomethyl, chloromethyl, thioether, sulfone, iso-11 cyanate, thiocyante, thiourea, allyl, acetyl-acetone, 12 aldehyde, ketone, aliphatic, anhydride, ester, halogen, 13 nitro and others.
14 The most suitable adsorbents for achieving high adsorption-desorption rates are activated carbons, molee-16 ular-sieving carbon, synthetic zeolites and high molecular 17 weight organic materials. These adsorbents generally show 18 a high exchange rate of adsorbing components, due to their 19 chemical affinity for various contaminant substances such as acid gases, and polar and non-polar-type molecules in 21 the case Oc high molecular weight materials, and because 22 of the macropores in case of activated carbons, molecular 23 sieving carbon and synthetic zeolites which comprise minute 24 crystals smaller than a few microns, and clay or other 25 binding material.
26 Typical examples of suitable adsorbents are 27 synthetic zeolite "TypeA " for the separation of various 28 polar molecules from gaseous feeds. Type A zeolite has 29 a typical oxide formula Na20.A1203.2SiO2.4 1/2 ~2O,a typical 30 unit-cell formula Nal2[(AlO2)12(SiO2)12].27.~2 ~ Y
31 of 1.99 g/cc, a unit cell constant of 12.32-24.64 Angstroms, 32 a void volume of 0.47 cc/cc, a free aperture of 2.2A(~
33 4.2A(~), and a kinetic diameter of 3.6-3.9A.
34 Synthetic zeolites include a useful class of in-35 organic adsorbents because the adsorption power of the 36 molecules selected for adsorption on zeolites can easily 6~95 1 be altered by exchanging sodium ions which usu~ly come 2 from the oricin21 production steps into some other cation~s 3 to change tnei_ crystal structure or electron confiaura-4 tions ,o the desired 'orms. Usually Group I metal ions such 2S lithium, potassium, rubidium, cesium, silver, 6 copper; Grou? II metal ions such as bery'lium, magnesium, 7 calcium, strontium, barium, zinc, ca~ium, mercury, ti-8 tanium, vanadium, chromium, nickel, cobalt, iron, manga-9 nese; rare earth metals, uranium; and lead cations or their mixtures are used to replace sodium ions originally con-11 taine~ in the zeolites. The more elfective se~s of cations 12 are: potassium and lithium; potassium anA calcium;
13 potassium and cadmium; potassium an~ ircni potassium and 14 nickel; potassium and cobalt; potassium a~d barium;
potassium a~d magnesium; calcium znd ma~nesium; calcium 16 and mznganese; lithium and m2ncanese; barium and sodium;
17 barium and lead; iron and uranium; and o~hers. Given 18 a ~zrticular feed stream, the most suitable set of 19 cations, their relative compositions, or most effective activation t eatments can be easily selected through various 21 experiments, since cation-exchange ~roced~a~e is readily 22 repea,ed many times. Gener211y, ~vpe A synthe.ic zeol~tes 23 are exchanged with calcium or masnesium or ~.heir mixtures 2~ for separating the polar or non-polar molecules from the 'eed strea~.
26 The adsorbent, i.e., the synthe~ic zeolite, 27 typically contain 75-98~ of the zeolite component and 2-25 23 of a matrix,(e.g., binder), compone~t. The zeolites will 29 usually be exchanged with sufficient cations to reduce the 30 ~so~ium level of the zeolite .o less than 5 wt. ~, preferably 31 less than 1 wt. ~. Reference in this rec2rd i5 made to the 32 following U.S. Patents: 3,140,2~9; 3,140,251; 3,140,252 33 and 3,1~0,253.
34 When the magnetizable component is aGmixed ~ith 3i no~ma~ne-ic zdsorbent particles, it is pre.'erred that the 36 volume fraction of the masne.izable component exceed 25 37 volume percent, more preferably it should exceed 50 volume 1146Q!~5 1 pe-cent, an~ p-e erably ~.o_e than 60 volume percent, to 2 ~btein the greatest bed sta~ility at the lowest applied 3 magnetic field strength.
4 In case of a com?osite OL the magnetizable com-ponent and the adsorbent, the fe-romagnetic and/or ~erri-6 magnetic material will com?rise 1 to 25, pre~erably ~ to 7 15 volume percent based on the total volume of the com?osite 8 adsorbent. In any event, the composite should have a 9 magnetization of at least 50 gauss, preferably greater than 250 gauss.
11 One example o~ prep2ring the com?osites o~ the 12 magnetizable component and the adsorbent i5 described as 13 follows: the ~agnetic com?onentsuch as 40~ Series stain-14 less steel, particles and the adsGrbent, e.g., the zeolite sieve, are admixed with a base (matrix or binder) for the 16 adsorbent and a relatively homogeneous gel is formed. The 17 adsorbent base m2y be comprised of, for examPle, silica, 18 alumina or silica-alumina. The gel may then ~e dried, cal-19 cined and/or sized. Suitable techniques for sizing and shapin~ the composite adsorbent are extrusion, pilling, 21 beading, spray drying, etc. The magnetizable c~mp~nent may 22 also be com~osited ~ith the adsorbent by impregnation, co-2' gelling, coprecipitation, etc.
24 The bea particles (composites or admixtures) 25 will typically have an average mean particle di2meter 26 ranging from about 50 to about 1500 microns, preferably 27 rom a~out 100 to about 1000 microns, an~ more pre~erably 28 from about 175 to about 850 microns. The particles may be 29 of any shape, e.g., spherical, irregular shaped or elongzted.
~he a?~lication ol a magnetic field to '.he flui~-31 ized, expznded or levitated particles containing the mas~eti-32 za~le particles in the adsorption or desorption zones in 33 accordance with the invention is not limited to any speci~ic 34 method of producing the ma~netic field. Conventional 35 permanent magnets and/or electromagnets can be employed ~o 36 provide the magnetic field used in the practice of the 37 present invention. The positioning o the magnets will, 1~46Q9S

1 of course, vary with the solids used, degree of fluidization 2 required and the effects desired. In the preferred em-3 bodiment of the present invention, a toroidally shaped 4 electromagnet is employed to surround at least a portion 5 of the fluidized bed as this provides the most uniform 6 magnetic field and consequently the best stability throug-7 out the bed. The electromagnets may be energized by alter-8 nating or direct current, although direct current energized 9 magnetic fields are preferred due to lower costs of opera-

10 tion. Such electromagnets when powered by direct current

11 with the use of a rheostat are particularly ~esirable for

12 applying a magnetic field to the bed particles and to

13 provide an excellent method of stabilizing the fluidiza-1~ tion of the bed particles in response to the flow of the 15 fluidizing medium.
16 The invention is not limited by the shape or 17 positioning of the magnet employed to produce the magnetic 18 field. The magnet can be of any size, strength or shape 19 and can be placed above or below the bed to zchieve special 20 effects. The magnets employed can be placed within or 21 without the vessel an~ may even be employed as an integral 22 portion of the vessel structure itself. The proces~ is 23 not limited to any particular vessel material and it can 24 be readily adapted for use in contactinq vessels currently 25 employed by industry.
26 The amount of magnetic field to be applied to the 27 fluidized solids in the contacting zones ~adsorption and 28 desorption æones) will, of course, depend on the desirecl 29 magnetization for the magnetizable particles and the amount 30 Qf stabilization desired. Particles having relatively weak 31 magnetic properties, e.g., cobalt, nickel, e~c., will 32 require the application of a stronger magnetic field than 33 particulate solids having strong ferroma~netic properties, 34 e.g., iron, to achieve similar stabilization effects. The 35 size and shape of the solids will also obviously have an 36 effect on the strength of the magnetic field to be employed.
37 ~owever, since the strength of the field proauced by an ~146~5 1 electromagnet can be adjusted by adjusting the field stren~th 2 of the electromagnet, an operator can readily adjust the 3 Cield strength employed to achieve the desire~ degree of 4 stabilization for the particular system employed. Specific methods of applying the magnetic field are also described 6 in U.S. Patent Nos. 3,440,731; 3,439,B99, 4,115,927 2nd 7 4,143,469; British Patent No. 1,1~8,513 and in the published 8 li.erature, e.g., M.V. Filippov, Applied Magnetohydro-g dynam.ics, Trudy Instituta Fizika Akad.Nauk., L~tviiskoi S~R 12:215-236 (1960); Ivanov et;al, Kinet. Kavel, 11 11 (5):1214-1219 (1970); Ivanov et al, Zhurnal Prikladnoi 12 Khimii, 45:248-252 (1972); and R.~. Rosenweig, Science, 13 2 :57-60 (1979). The most preferred applied magnetic field

14 will be a uniform magnetic field such as described in U.S.

15 Patent No. 4,115,927. Typically, the empty vessel applied

16 magnetic field, as taught in U.S. Patent No. 4,115,927,

17 will range from about 50 to about 1500 oersteds, preferably

18 from about 100 to about 600 oersteds and more preferably

19 from about 125 to about 400 oersteds.
The process operating conditions to ~e employed 21 in the practice of the present invention may ~ary widely 22 and will include those treating conditions typically em-23 ployed in the adsorption-desorption separation processes 24 known in the art. As well known, these conditions will generally vary depending on the feedstream bei~g treated, 26 the adsorbent beins used, etc. An essential feature of 27 the invention, however, is to carry out the~adsorption and 28 de~or~,ion at essentiailv ~ne ~t"e nressure, ie., t~e 29 pressure differential between the adsorption and desorp-tion zones will vary by no more than about 25 ~ercent, 31 preferable no more than 10-20 percent. As an additional 32 constraint, the pressure differential in magnitude will 33 not exceed about 70 psi. The zones will only vary from 34 about 1 to about 70 psi and preferably the pressure dif-ferential will only vary between 10 and 50 psi. Thus, 36 the regeneration (desorption) is done thermally at the ~146Q95 1 same or essentially the same total pressure as in the 2 adsorption zone. The temperatures used in t~e adsorption 3 zone will be those at which the contaminant~s) to be ad-4 so`bed are preferentially a~sorbed with the particular 5 adsorbent being used. These temperatures may range from 6 about -200DC to about 350C, preferably from about 0CC
7 to about 300~C, especially preferably from ~bout 10 to 8 about 200~C, and more preferably from about 15~C to a~out 9 150C. The temperatures during desorption will be at least about 100C greater than those at adsorption, prefer-11 ably 200C and more preferably 300C greater than the 12 tem~eratures used during adsorption. The pressures used 13 during the adsorption and desorption steps may range 14 from about 0.1 to about 2000 psi, preferably from about 1 to about 750 psi, and more preferably from about 1 to 16 about 650 psi. The feed stream to be treate~ in accor~ance 17 with the process of the invention may be eitner in a gaseous 18 or liquid state. The superficial fluid velocity ~f the 19 fluidizing fluid in the case of gas may range from about 0.01 to about 3 m/sec, more preferably from about 0.08 m/
21 sec to about 1.5 m/sec. The superficial fluld velocity 22 of the fluidizing fluid in the case of a liquid may range 23 from about 0.001 cm/sec to about ~.3 cm/sec, ~ore prefer-24 ably from about ~.008 cm/sec to about 0.15 c~/sec. The 25 bed particles preferably move countercurrently in a sub-26 stantially plug-flow manner against the asce~ding feed or 27 stripping gas by the action of gravity or pressure in the 28 contacting vessel~s). The solids movement rate may vary de-29 pending on the level of contaminants in the ~eed, the 30 size of the vessel(s), the feed gas velocity, etc.
31 The adsorption can take place in any suitable 32 vessel as earlier mentioned. The vessel may be e~uipped 33 with internal supports, trays, etc. In the lower portion 34 of the adsorption vessel there will be disp~sed a suitable 35 grid means for distributing the incoming feea. The bottom 36 or lower portion of the adsorption vessel will ha~e means 1~4~ 5 1 for removing spe~. solids 'rom the adsorp_ion vessel. This 2 o~eni~g may be e, the si~e of the ~essel or a' its bot~om 3 A pipe sr~ may be u,ilized for feeding ~he g2seous fee~, 4 i.e,, per'orated pi~es. 3y use of a pipe ~rid the spent solids may flow past the grid by gravity to the regenera-6 tor or desorber.
7 The Ceed mi~ture applicable t~ the process o-8 the present invention may come from a ~ariety of sources, 9 for example, the p-ocess of t~e invention is ap?licable to ,he following separation processes: Drying ~f natural 11 gzses prior to licueCaction for LNG; drying o' natural gases 12 prior to cryogenic fractionation ir.~o hish BTU pipeline gas, 13 ethane, etc.; drying steam cracXer off-gzs prior to cryo-14 genic dis~ill2tion in ethylene plants; dryins cat21ytic l; cracking off-g2s prior to c-yogenic distillatio~s; dryins 16 o' air prior to liquefaction and distillation t~ make 17 oxyaen and nitrogen; ~ryins of air Cor various zpplications ;8 such 25 instrument control systems; dryins of recycle c hydrogen ~as for cat21ytic refor~ins Cor making gasoline an~ other related dryinc, and separation processes;
21 removal oS polar compouncs, such as H20; Y,2C, SC~2, N~3, 22 COS, RSH, etc. Crom non-?012r gases such as natural C2S, 23 hydroc2rbon gases, e.g., 'rom refineries, ~vdro~en enc 24 mixtures thereof; removzl of C02 or ~1~0 from non-~012r g2ses; removal of C02 rom cryogenic plant ee~ g2ses;
26 removal of sulfur compounds from na'ural C25; hydrogen 27 purific2tion processes, e.g., 28 (1) from demethanizer o'f-gas contai~ing hydro-29 gen, CH4, C0, C2H4, C~H2, C02 and N2;
~2) from steam re-ormer hy~roaen containinq 31 C02, ~2~ CH4, C0 and nitrogen, 32 (3) from off sas from a catalytic reformer con-33 taining hydrogen, CH~, C2H6, C3Hg, C4Hlo, and trace 34 amounts of C~ hyc~oc2rbons;
(4) from refinery and chemical pl2nt fuel g2s 36 streams containing hydrogen, CH4, C286~ C3H8~ C4~10~ C2~4 37 C3H6, C4Hg, along with trace amounts of Cs+ hydrocarbons, 38 C02, C0, N2 and H20.
, 1146~S

1 (;) from hycrcfiners co~taining hydrogen, 2 CP.~" C2~6~ C3~B~ C~10~ C2~4~ C3H6, C4Hg, along with trace zmounts of Cs+ hydrocarbons, H25, C02, CO, N2~ N~3 and :~ O;
(6) from electrolytic off-gas contain~ng N2, 6 CO2 2nd ~2;
7 (7) from dissociated N~.3 from N2 and ~3; and 8 (8) from NH3 reactive loop purge containing g CX4, A, ~2~ an~ NH3; methanol reactor loop purge containing lQ CO, C02, CH4, and N2; removal of orgznic solvents from 11 air; solvents recovery wi,~ activated carbon; a2sorption 12 c hydrocarbo~s from gas streams, e.~., pro~ane a~d higher ~ hydrocarb~ns from naturzl oas; ethane from methzne/ethane 1~ r..ixtures; and Kry~.on 80 removal from air; and (9) methane from air.
16 The followins Table illustr2.es ex2mples of 17 processes whereby minor amoun LS o polar molecules and 18 CO2, CS2 and the like may be removed from gaseous streams lg u~ilizing the process of the present invention.

1146~)95 ~ 17 --~) D g o C~ O O O O
f~
~ o ~
C E ._ U~ 'O
~ ~ ~ C C ~ C
O f~
~ _ E ~ ~ r~ X
o o ~ g -~ z ~n O
~'I ' E
V O O ~ U~ ~ E _~
~ ~ o ~ ~
~ O ~ O QJ ~ ~ S~ C ~
V~ O ~ ~ z r~ I o rl ~ ;~ O O S~ O
~ ~ ~ LO ~o r ~ ~) ~ G ~
o ~) r o o ~ ~ O r~ O
O O C~ ~ ~ O~ -- O o~ ~ ~.
Cl ~-I h :~ _~ F ~ ~) h ~ c~ L~
_I P~ C ~:1 o ~
5~ 1-1 t~ ~) P I ~ O a) ~, ~ I dP ~ O
C_ .~ G~
E~ o ~ .:J ~ u~ c~ I u7~1;) X ~
rl C ~ ~ ~ ~ Q~) O h Oc)E u-~ X
3 Q) E~ ~ I = E O ~I z ~,) ~ I ~ O I `10 7 ~ Z = tr, ~! ~J C~ ~ h h U~
C) C~
O . U~
E~ u~
O
C
o C U~
O ~ V ~ ~ ~ C
) F

~.LJ~-- C ~

ns O ~.~ ~ 5 ,~ ~ o ~ s --I~ ~a ^
u~ u~ h ~ o o ;;.
,1 ~ C ' ~ C ~ ~ U) G) ` v o I ~o ~ ~u) h1~ ~ ~ '~
o ~ ~ :~ C~ )O 1~ ~ z -C) 5 ',~
.~, ~ ~ ~ :~ ) 3 ~
C~ H~ ~ _)-- , , _ Z-- z-- ~ ~ _ .

.. . . . .

1~46~95 1 The adsorbed contaminant molecules are desorbed, 2 as mentioned above by the thermalswing process, i.e., 3 the process which involves heating the spent particles to 4 a temperature where the adsorbent's adsorptive capacity for the contaminant compounds or molecules is reduced to a 6 low level. The removal of the contaminant compoun~s or 7 molecules trapped between the sorbent particles is en- ;
8 hanced by a suitable purge gas stream, e.g., steam, ammonia, 9 hydrogen or low molecular weight hydrocarbon gases or product gas from the absorber, etc.
11 A specific generalized example of the process 12 of the present invention comprises contacting a bed of 13 particles of a Type 4A zeolite molecular sieve containing 14 a ferromagnetic component countercurrently with a eed ~ of vapors, e.g., a natural gas and water vapors in the 16 magnetically stabilized adsorption zone. The solids leave 17 the adsorption zone with the water loaded virtually at 1~ equilibrium with the feed vapors. The nature of the mole-19 cular sieve structure preferentially adsorbs the polar molecules ~e.g., water) from the natural gas components.
21 By use of the magnetically stabilized bed, it is possible 22 to use smaller particles than in fixed bed processes and 23 by use of these small particles, reduced diffusion resis-24 tance can be realized. ~lso, the size of the adsorption bed is relatively small compared to a fixed bea of con-26 ventional sized sieve particies. The sieve particles 27 flow from the adsorption zone to the magnetically stabil-28 ized desorption zone where they move downward counter-29 current to the ascending hot purge gas stream. The hot gases heat the spent particles to a temperature ~here the 31 sieve's adsorptive capacity for the water is reduced to a 32 low level and water is conseauently desorbed from the adsor-33 bent. As in the adsorption step, the small particle size 34 reduces diffusion resistance and results in a very close approach to equilibrium betwee~ vapors and solids at any 36 given point. As mentioned before, pressures are nearly 37 the same in all the zones, whereas the temperature in the ~1461~95 -- lg --1 desorption zone is subs.antially sreater than that in the 2 adsorption zone, 3 Referring now to the drawings, Fi~. 1 is shown 4 for explanation of the principles of separation in the present invention. Fig. 1 shows a basic embodiment of 6 the present invention wherein the feed comprisin~ the 7 gaseous mixture is supplied to the lower portion of vessel 8 1 containing a selectively adsorbing material an~ magneti-9 zable component 3, A solenoid or magnetic means ?5 is arranged to supply a substantially uniform magnetic fiel~
11 on the solid particles charged in vessel 1. The gaseous 12 feed mixture is supplied to the adsorber vessel via line 7.
13 The feedstream from line 7 is fed directly to grid 9 at a 14 superficial fluid velocity sufficient to levitate or fluid-ize the bed particles. The bed particles leave vessel 1 16 in a descending manner via stzndpipe 13. The solids in the 17 standpipe can be controlled by valve means in the standpipe 18 (not shown). These bed particles are then transerred to 19 desorber 21 via line 17. A lift gas from line 15 assists the transfer of the solids in line 17, whereupon the par-21 ticles empty into desorber vessel 21 via inlet 19. The 22 particles in desorber 21, in a fluidized st~te, move in a 23 descending manner against the up-flowing gas stream (pre-24 ferably hot dry gas) provided ~ia line 23. ~he hot dry gas is fed directly un~er grid 25. The spent ~ed particles 26 3a are stabilized by a solenoid or magnet means 5a. The 27 desorbed or regenerated bed particles flow out of vessel 28 21 countercurrently and preferably in a plug flow manner 29 into standpipe 29. The regenerated bed particles are then transferred to the adsorber vessel 1 via the standpipe 29 31 and transfer pipe 31. Transfer of the bed particles may 32 be facilitated by a lift gas via line 15a. The ~ed 33 particles are returned to vessel 1 via inlet 33~ The 34 nature of the selective adsorbent utilized in the process 35 will permit the gases devoid of polar moIecules to 36 leave vessel 1 via line 11 while the polar molecules are 1146~95 1 adsorbed by the bed pzrticles. The adsorbed ~olar mole-2 cules on .he other hand are desorbed in desorber 21 and 3 are emit~ed fro~ the desorber via line 27 ~long with the 4 hot purge gas. The regenerated particles may be cooled ; by heat eY.changer means (not shown) during ?assage through 6 line 31 prior to being returned to the top ~f the adsorber 7 at inlet 33.
8 Referring to Fig. 2, there is sh~wn a separation 9 unit of the present invention which is a-study design of a natural gas drying unit preceding liqui~ction for 11 ~NG. In Fig. 2 there is shown a vertically disposed 12 vessel 1 containing therein a fluidized or expanded or 13 levitated bed 3 of descendins sorbent particles which in-1~ clude magnetizable particles. The descendi~g sorbent and l; magnetizable particles are preferably composi,es of Type 16 4A zeolite molecular sieve ~hich has been composited with 17 a 400 Series stainless steel. Surrounding vessel 1 i5 an 18 arrangement of electrical coils ; for im~osing z magnetic 19 field upon the fluidized bed. A stream o. moist gas that is to be dried in the vessel is ~ntroduced ~elow the bed 21 through line 7 zt a rate sur'icient to sus_ain the bed in 22 z fluidized con2ition, and dry gas is remo~ed from the 23 vessel above the dense ph2se of the bed vic line 11. The 2~ particles that are to be regenerated are removed from the bed via solids outlet 13 controlled bv sli~e valve la or 26 its e~uivalent. The removed solids are carried u?ward 27 through transfer line 17 to regeneration vessel 21. The 2~3 solid particles 3a in vessel 21 are levitated in the bed 29 by a suitable rate of flow of regenerating gas introduced through inlet 23. An arrangement of elect_ical coils 31 5a surrounds vessel 21 so thct 2 uniform magnetic field 32 can be imposed upon the luid bed of particles 3a.
33 ` ~1oisture-laden spent regeneration gzs leaves 34 the upper portion of vessel 21 via line 27, is co~led in heat exchanger ao and passes to se?arator ~1. Separated 36 water leaves through line 42, and the dew2tered ~zs ~asses 37 through line 43 to compressor 4~.

.

~146~9S

1 Regenerated solids are trans erred by grzvity through 2 line 29, the rate of solids îlo~7 beins controlled by 3 slide valve 3~ or its equivalent.
Altho-lgh any suitable dry gzs could be used for regenerating the solids in vessel 21, it is most adva~-6 taseous to employ a portion o~ the dry gas in line 11, 7 leading it into line 34 through valve 35 and heating it 8 in urnace 37. The hea.ed gas is transferred to inla~t 23 g through line 38.
lQ Most of the dewatered regeneration gas entering 11 co~pressor 45 is used to convey descending solids from 12 vessel 1 to vessel 21 via transfer line 17, being intro-13 duced into that line via vzlve 15a. Since there would be 1~- a net bUild-u? Oc gzs in the circulating sys,em comprising l; lines 17 and 47, by virtue of the gas added to line 38, 16 an equivalent amount of gas is removed throush line 50, 17 con_rolled by valve 51.
18 In a -epresen'2tive exam?le usin the apparatus 19 Oc Fig 2, the temper2ture and pressure in ~Tessel 1 are 70F (21.1C) and 625 ?sio, respectively, and in regener-21 ation vessel 21 they a-e 600P (315.5C) anc 595 ?sig, 22 respectively. The particles h2ve a censity of 1.6 s/c~3 23 and an average ?article size cT 300 microns. To dry 24 5~6,000 stand2rc cubic 'eet ?er s.ream ~ay o' natural gas containing 1,020 pounds Oc wa.er per hour to a dew 26 poin~ o. -90F (-67. RC), the bed height is 6 ~eet, the 27 the bed diameter is 12 feet, and the superficial gas 28 velocity is 0.7 feet/sec. in the vessel 1; and a bed 29 height of 15 feet, a bed diameter of 3 eet and a super-3G ficial gas velocity of 0.9 eet/sec are used in the re-31 generation vessel 21. The solids circulation rate through 32 the system is 1,000 pounds per hour. The appliea magnetic 33 ,ield is such 2s to provide a void fractio~ in both the 34 adsorption and desor?tion vessels of about 0.35 to about 0.7 or greater. The sorbent particles are a composite of 36 75 wt. % of the 4A molecular sieve Com?onent and 25 wt.
37 ~ o~ the ferromagnetic compone~t, the latter being 400 . ..

~1~6~9S

1 Series s.ainless steel which is 95 volume percent to 5 2 volume percent, respectively.
3 ~7hile a sinsle zdsor?tion and deso-ption vessel 4 is shown in the Drawinqs, it will ~e a~reciated .hat multiple ~Tessels may ~e employed if desired. ~owe~er, 6 the use Oc '.he smzll ?articles in the process Oc ,he 7 present invention enakles one to use fewer or smaller 8 vessels.

Claims (16)

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

1. In a process for the selective separation of contaminants from a mixture in a feedstream containing the same within an external force field, said process comprises the steps of:
(a) adsorbing a portion of said contaminants from said feedstream by contacting said feedstream with a bed comprising adsorbent particles capable of adsorbing said contaminants from said feedstream; and (b) desorbing at least a portion of said con-taminant from said adsorbent particles in step (a) to re-generate at least a portion of said adsorbent particles;
the improvement which comprises:
(1) providing a magnetizable component with said adsorbent particles and applying a magnetic field to said magnetizable component and adsorbent particles along the direction of said external force field and at a strength sufficient to prevent and/or suppress gross solids back-mixing and fluid by-passing;
(2) expanding or levitating said adsorbent parti-cles and magnetizable component by countercurrently contact-ing said adsorbent particles and magnetizable component with said feedstream; and (3) carrying out said adsorption and desorption steps at substantially the same pressure.

2. The process of claim 1 wherein said applied magnetic field is substantially uniform and said adsorption and desorption steps are carried out in separate vessels.

3. The process of claim 1 or 2 wherein said adsorbent particles and magnetizable component flow in a descending, substantially plug flow manner.

4. The process of claim 1 or 2 wherein the tem-perature in the adsorption step ranges from about -200°C to about 350°C and the pressure in the adsorption and desorp-tion step ranges from about 0.1 to about 2000 psiq.

5. The process of claim 1 or 2 wherein said adsorbent particles and magnetizable component have an average mean particle diameter ranging from 50 to about 1500 microns.

6. The process of claim 1 or 2 wherein said adsorbent particles and magnetizable component are composited.

7. The process of claim 1 or 2 wherein said adsorbent particles and magnetizable component are admixed.

8. The process of claim 1 or 2 wherein said adsorbent particles include zeolite molecular sieve parti-cles.

9. The process of claim 1 or 2 wherein said adsorbent particles include activated carbon, treated acti-vated carbon or molecular-sieving carbon particles.

10. The process of claim 1 or 2 wherein said adsorbent particles are selected from non-stoichiometric carbon-sulfur compounds and layered clays.

11. The process of claims 1 or 2 wherein said adsorbent particles are comprised of alumina.

12. The process of claim 1 or 2 wherein the de-sorption step is carried out by heating the adsorbent parti-cles.

13. The process of claims 1 or 2 wherein a purge stream is utilized during said desorption step and wherein the desorption step is carried out by heating the adsorbent particles.

14. The process of claim 1 or 2 wherein the contaminant loaded adsorbent particles and magnetizable component leave the adsorption zone virtually at equilibrium with the incoming feed-stream.

15. The process of claims 1 or 2 wherein said feed stream comprises natural gas and water vapor and the water vapor is preferentially adsorbed during the adsorption step, and wherein the adsorbent particles are comprised of alumina.

16. The process of claims 1 or 2 wherein said feed stream comprises a mixture of methane and ethane and the ethane is preferentially adsorbed during the adsorption step, and wherein said adsorbent particles include activated carbon, treated activated carbon or molecular-sieving carbon particles.