CA2185264C - Upgrading heavy oil by ultrafiltration using ceramic membrane - Google Patents

Abstract

A large pore (500 - 2000 .degree.A) ceramic membrane is used to separate asphaltenes from heavy crude oil. Permeate is recycled to the feed for an initial period, during which the pores are deliberately fouled to reduce pore size. This reduction eventually levels off, at which point recycling is terminated and ultrafiltration is continued thereafter at good flux rates with effective asphaltenes removal.

Description

~ 21~5264 FIELD OF THE INVENTION

2 The invention relates to a process for the selective removal of

3 aspl, " 1es and metal complexes Acsrjri~pd therewith from heavy oil by ulIIa~ lio

4 using permeable ceramic ~ b~dnes.
BACKGROUND OF THE INVENTION
6 The present invention was developed in connection with ~ lb 7 carried out to investigate removal of asl,halIt1nes and metals (Ni and V~ from heavy 8 crude oil using ceramic m~",b,d"es.
9 Heavy crude oil is one form of heavy oil. Heavy oil is defined herein as having a density of about 1000-934 kglm3 (10~ API to 20~ API gravity) and a viscosity 11 of about 100-100,000 m Pa. s. The heavy oil may be heavy crude oil, atmospheric and 12 vacuum residue, heavy fuel oil or used heavy oil.
13 The particular oil used in the ~ Ot:l il l Itn lla was heavy crude oil produced 14 in the Cold Lake area of Alberta. This crude oil typically has the following properties:
PHYSICAL PROPERTIES
16 Density ~API 10.1 17 Viscosity at 40~C, m Pa. s8,887 18 Viscosity at 80~C, m Pa. s 425 Asl,l,alI~n~s, wt. % 17.4 21 Nickel, llglg 59 22 Vanadium, ,Lg/g 154 2 ~ ~2~4 As indicated, this crude oil is high in as,ul, " .le and metal 2 conc~ Lr ls. This is typical for many heavy oils. It is these oils that the present 3 invention addresses.
4 In the case of heavy crude oil, certain disadvd"lages arise from these properties. More pariicularly:
6 ~ The high viscosity commonly requires that a diluent must 7 be added before the oil can be pipelined;
8 ~ Thea~,ul,dll~nesagglo,,,e,dLeanddepositonthesurfaces 9 of p,uces~i"g equipment;
~ The asphaltenes lead to undesired coke formation during 11 hydl ui l u~.es~ y, and 12 ~ The metals will contribute to catalyst dea.,~
13 Much research effort has therefore been carried out by the industry to 14 develop useful techniques for reducing the asphaltene and metal contents of heavy oil, particularly crude oil.
16 Selective separation with permeable ~elllLndnes is one technology that 17 has been investigated for this purpose. This technique is commonly referred to as 18 "ulllaiillldlio~
19 According to i3altus and Anderson, in their paper titled "Hindered 20 Diffusion of Asphdllt:"es through Microporous Mulllbldll~s", Chem. Eng. Sci., 38, 21 1959-1969 (1983), the size of the molecules making up the a~,ul,alLt:,les varies 22 between about 10-1ûû0~A.

2t ~26~

This suggests that the membrane used for separation of asplldlle:n~s 2 should have an average pore size less than 1000~A. In cunsid~,i"9 what pore size to 3 use, one will weigh that a smaller pore size will increase as~Jl,dlL~"e separation but 4 reduce permeate flux. The literature commonly r~uullllllend~ an average pore size of about 250~A or less, if a product of pipeline quality is to be produced. By "pipeline 6 quality" is meant that the oil viscosity will be less than about 500 m Pa.s at 40~C.
7 Most of the research reported on in the literature has focused on the use 8 of polymeric IlltllllL,ldlles for separating asphalle,l~s from heavy oil. As an example, 9 O. Kutowy, P. Guérin, T. A. Tweddle and J. Woods in their paper entitled "Use of Mt""b~dnes for Oil Upgrading' published in the P~uceudi~y~ of the 35th Canadian 11 Chemical Engineering Conference, Volume 1, pg 26-30,1985, reported that Cold Lake 12 crude oil diluted with 34~~O naphtha and processed using a 3-30nm pore size polymeric 13 membrane, operated at 45~C at a pressure 3 MPa, could reduce the oil viscosity from 14 90 to Z cp and V and Ni contents from 125 ppm to 5 ppm and from 41 ppm to 0.6 ppm" ~:.,ue~iti ~oly.
16 However,polymeric",e",L,,d,1esarelimitedtolowtemperature(<100~C) 17 operation, if long membrane life is needed. They are also subject to chemical 18 dey,addLiu" when exposed to light hyd,u.,a,bùns.
19 Given the high viscosity of heavy crude oil, it is desirable to practise ull~ dLion at relatively high temperature and diflerential pressure. One needs to 21 reduce the viscosity as best one can and increase the pressure to improve flux rate.
22 Additionally, it may be desirable to add a light l,yd,oudlbun diluent to further improve 23 flux rate. For these reasons, polymeric " ,e" ,brd"es have not won application 24 co"""~ !y for ullldiillldliul1 of heavy crude oils.

2 ~ 8 526~
Some research has been directed to the use of alumina - based ceramic 2 membranes for ulll "" 'icn of heavy crude oils. These ",e,~ dnes can operate at 3 high temperature and pressure and are quite immune to chemical deyldddlion~
4 In this connection, the following relevant patents in the literature have been noted.
6 U.S. Patent No. 4,411,790, issued to Arod et al on October 25, 1983, 7 teaches:
8 ~ practising high temperature ulll '" dlion on a viscous oil 9 containing asphaltenes, to separate a:".l,altenes from the oil;
~ using a non-organic membrane (for example, alumina-coated 11 ceramic) operated at a temperature of 100 - 350~G at a pressure 12 differential of 1 - 20 relative bars;
13 ~ the membrane having a radius of per",ed",e:l,y in the order of 50 - 250~A.
U.S. Patent No. 5,256,297 issued to Feimer et al on Octo~er 26,1993, 16 teaches:
17 ~ practising high temperature u~ " dlion on a viscous oil 18 containing metals and a~ es, to lower the metal and 19 as~,l,dll~ne contents thereof;
~ using a non-organic membrane operated at a temperature of 21 100 - 500~C at a pressure differential of 20 - 500 psig;
22 ~ the membrane having a pore size of 5 - 1000~A, preferably 10 -23 100~A;
24 ~ using two sequential stages of separation, each equipped with the same ",e",b,dl,e, 2 ~ 85~

~ optionally using a diluent to assist in reducing the feed viscosity;
2 and 3 ~ optionally recycling the retentate from the second stage to the 4 feed to the first stage.
In summary then, the prior art teaches that temperature and pressure-6 resistant non-organic " ,~, l Ib, dl ,es can be used to remove as~,l ,all~nes and metals from 7 heavy oil to reduce viscosity and upgrade the oil However, as previously stated, it is 8 indicated that fine pore size (< 250~A) is preferred.
9 There are problems inherent in using ceramic " Itl I fbl dl ,es having a pore 10 size in the order of 250CA. For example, the membrane is expensive to fabricate.
11 Furthermore, the flux rate through the membrane is low. And finally, the small pores 12 tend to plug quickly. It is belleved that these factors have combined to discourage 13 cu,l""~,uial application of ceramic membrane in the heavy crude oil upgrading field.
14 It is therefore desirable to develop a ceramic membrane ulLIdlilll ~ic:1 15 process in which flux rate, as~,hdlL~3ne reduction and cost are all improved. Preferably, 16 itwouldbedesirabletodevelopaprocesswhereinthea~-l,all~necontentoftheheavy 17 crude oil is reduced sufficiently so that the product viscosity meets pipelining 18 gl 1.
19 It is the objective of the present invention to provide such a process.

~ 2185264 SUMMARY OF THE INVENTION
2 As previously indicated, the invention is concerned with upgrading heavy 3 oil containing aspl, " ,es and associated heavy metal co",~ ,xes by reducing 4 asph " ,e and metal contents using ulII '" c.Iion.
The invention is based on using a large pore, initially non-fouled, ceramic 6 Illtlllb,dne and operating it for an initial period during which substantially all of the 7 permeate is recycled to the feed and the membrane is deliberately fouled to reduce the 8 effective Illt""b,dne pore size. Following this period, recycling is terminated and 9 penneate with reduced asphaltene and metal contents and reduced viscosity is thereafter continuously recovered with a minimal rate of flux decline.
11 By 'large pore' is meant that the membrane has an initial average pore 12 size greater than about 500~A, preferably in the range 500 - 2000~A and most 13 preferably in the range 1000 - 2000~A.
14 As stated, the process ill~,UI~Oldl~s an initial period of operation under conditions of permeate recycle to the feed. During this period the membrane partially 16 fouls and the effective pore size is gradually reduced, with accompanying improvement 17 in separation of a~ es and metals. It has been discovered that the diminution 18 of pore size (evidenced by di" ,il li:,l ,ing flux rate) eventually substantially levels off. The 19 pel",- ' "ty condition of the membrane at this levelling off point is such that flux rate is reasonably high and a~l, 'I ,e separation is good enough to yield a product that 21 can be pipelined. At about the levelling off point, recycling of permeate is terminated.
22 Thereafter ulLIdfillldlio,l is continued for a prolonged period without recycle, until finally 23 the pores become too small to enable viable operation and backflushing or other 24 ,t,ge,1e,.A~;ol1 is required to restore the membrane to a substantially non-fouled 25 condition.

By using a membrane with such large pores, the cost of membrane 2 fabrication is siy,,~ cu,Lly reduced and high flux rates are attained.
3 In summary then, the following benefits are obtained by the practice of 4 the invention:
~ the viscosity of the oil is reduced, to render it suitable for pipeline 6 conveyance;
7 ~ the metal and asphaltene contents are reduced, to improve the 8 refinery ac~,e~-td"~,e of the upgraded oil; and 9 ~ the cost is reduced by providing increased overall flux rate and lower membrane fabrication cost.
11 Broadly stated, the invention is di rected to a process for upgrading heavy 12 oil feed containing asph " 1es, co~ Jlisiny subjecting the feed to ulll~ilLI 'ion by 13 feeding it at elevated temperature and pressure through a substantially non-fouled 14 ceramic membrane having a large average pore slze to produce pemmeate and 15 retentate products; recycling a major portion of the permeate product to the feed 16 entering the membrane for sufficient time so that rapid diminution of permeate flux rate 17 begins to substantially level off and the asphaltene content of permeate product being 18 produced is reduced by at least 30~/O compared to the feed content; and then 19 l~ illdLillg recycling and continuing to subject additional feed to ulLId~ilLl 'i~n.

DESC~IP I ION OF THE DRAWINGS
2 Figure 1 is a schematic showing the laboratory circuit used in the 3 e~ e,i",e"ts underlying the invention;
4 Figure 2 is a simplified sectional side view showing the membrane module of Figure 1;
6 Figure 3 is a plot, based on Example V, showing flux rate and permeate 7 a~lldlI~Ile content values over time during a run conducted in acc-"dd"ce with the 8 invention - the curves show a period of initial rapid diminution followed by a period 9 where the values only slowly change or substantially level off. Recycling of permeate is terminated at the interface of these two periods.

11 Dt~CR I ION OF THE PRt~t~RED EMBODIMENT
12 In accordance with the process heavy crude oil is first heated and then 13 pumped through a permeable ceramic membrane unit at high differential pressure 14 using a cross-flow alldllg~lllt:lll. Useful conditions are as follows: ~ pore size: 500 - 2000~A
16 ~ feed temperature: 90~C to boiling temperature of the oil or 17 upper limit of membrane capability 18 ~ differential pressure: 40 psig to maximum allowable 19 differential pressure of the membrane 21 ~ fluid velocity through membrane tube: 1 to 15 ms~' 22 ~ feed flow rate: depends on total surface area of the 23 membrane unit and will be about 1 - 10 24 liters/hr. per m2 of available membrane surlace ~ 21 8~26~
~ membrane~a, - operable at trans-membrane 2 pressure of 1450 psig and 3 temperature up to 480~C.

4 The expe,i"~"ts underlying the invention were carried out in the batch

5 ulll dli.,n unit shown s~l,elll~li~ J in Figure 1. The unit included a membrane

6 module 1 shown in Figure 2 and comprising a 5.08 cm O.D. x 1.9 cm l.D. tubular steel

7 housing 2 containing a 25 cm long x 1 cm O.D. single tube ceramic membrane element

8 3. The membrane elements used were obtained from United States Filter Corporation g of l/Vdl I ~ndale, PA and are identified by the trade mark MEMBRALOX. The membrane elements were single tube asymmetric ceramic m~"~ dlles composed of alumina.
11 Each element comprised layered co, ll,uosiltlx with the outer layer having the smallest 12 pores.
13 The membrane element 3 was inwardly spaced from the housing wall to 14 form an annulus 4. The open ends of the annulus and housing were closed by ferrules 5 carrying O-ring 6 O-ring 7 and end plates 8 9. The end plate 8 formed an inlet 10 16 for feed and the end plate 9 formed an outlet 11 for retentate. The housing side wall 17 12 formed an outlet 13 for the permeate and an outlet 14 for collecting a permeate 18 sample or draining the permeate side of the module. A first reservoir tank 18 19 containing heavy crude oil feed was equipped with a stirrer 33 and was externally heated by an electrical heating band 32. The heavy crude oil feed was delivered 21 through valve 19 to the feed pump 20 and pumped to the internal retentate recycle line 22 35 through the filter 21 using line 22. A second reservoir tank 15 containing toluene 23 was also connected to the feed pump through valve 16 and shut-off valve 17. The 24 heavy oil feed and the internal retentate recycle were pumped through the membrane ~ 21 ~5264 tube at high velocity using the recycle pump 23. The Internal retentate recycle rate 2 was monitored using flowmeter 34. During nommal operation shut-off valve 29 was 3 closed and the retentate was mostly recycled through line 35 to ensure a high cross-4 flow velocity in the membrane tube. A small portion of the retentate also flowed 5 through the relief valve 30 that was used to control the pressure in the membrane.
6The penmeate flowed through valve 25, filter 26, flowmeter 27, valve 28 and was 7 recovered at point P of Figure 1. In additlon, a permeate sample could be withdrawn 8 through valve 24. During the initial part of the operation, permeate was recycled to the

9 feed tank by switching valve 28 so that the permeate was returned to the reservoir tank 10through line 36 and valve 31. Once the permeate asphalLt,l1e content was at the 11 desired level, valve 28 was switched so that permeate was recovered at point P.
12In the operation of the unit, heavy oil was heated in tank 18 and the 13 membrane unit filled with this oil wlthin 1 minute using the feed pump 20. The unit was 14 purgr d of trapped air by opening valve 29. Subsequently valve 29 was closed and the 15 recycle pump 23 was started. The relief valve 30 was then adjusted to obtain the 16 desired pressure In the ",e",l,ld"e tube. Valve 25 was opened and valve 28 was 17 switched so that permeate was directed through line 36 back to the feed tank.
18 Permeate samples were also withdrawn through valve 24. Once the initial permeate 19 recycle period was complete, valve 28 was switched such that the permeate flow exited 20 at point P.
21Most comparisons made in the Tables are based on initial flux. That is, 22 for the case of no permeate recycle initial flux is the flux measured as soon as the 23 membrane unit has reached steady state (about 20 minutes) and for the case of 24 permeate recycle the flux is that flux measured after about 3 hours once the permeate 25 recycle has been stopped.

~ 2 1 8J264 As shown in Figure 1, permeate can be recycled to the front end of the 2 membrane unit. Recycling is c~ c~d when a non-fouled membrane is placed in 3 operation and is continued until there is a sharp change in diminution of flux rate. At 4 about this point, (identified by the numeral 100 in Figure 3~, recycling is terminated 5 while ~" '" 'ion is continued.
6 I,,ler,,,iLl~l,L back-pulsing can be practised by '~ .,9 penmeate 7 through the membrane wall to clear the gel layer when it accumulates.
8 A small amount (~ 10 wt. ~/0) of a diluent, such as benzene or toluene, 9 can be added to the feed to reduce viscosity, if desired.
The invention is disclosed and supported by the following examples.

11 Exam~le I
12 This example compares the results obtained in the first stage of the 13 operation, each conducted under the same conditions with the exception that in one 14 run no permeate was recycled and in the other nun all of the permeate was recycled 15 for a preliminary period of 3 hours. The membrane used had an average pore 16 diameter of ~ 1 000~A.

~ 21 ~5264 The conditions and data are set forth in Table 1.

3 feed temperature: 120~G
4 inlet pressure: 97 psig fluid velocitythrough ~lb~dlle 7- 9 m/s 6 Run 1 Run 2 7 duration of recvcle l~eriod. hrs. Nil 3 8 feed - Cold Lake crude oil 9 a~ h " ~ne, wt. ~~O 18.3 18.3Ni, ppm 76 76 11 V, ppm 190 190 12 viscosity Zg 40~C, cps 5,825 5,825 13 API gravity 10.1 10.1 14 initial ~ermeate samde flux, kg/m2/day 105 64 16 asph " ,e, wt. ~/O 12.6 5.3 17 Ni, ppm 60 35 18 V, ppm 151 85 19 viscosity ~Z 40 C, cps 1,525 710 API gravity 11.8 13.8 21 ~526~

~~0 reduction in:
2 as~ es 31 71 3 Ni 21 54 5 Example ll 6 This example shows the improvement obtained by permeate recycle in 7 the context of a membrane having an average pore diameter of 500~A.
8 The conditions and data for two runs carried out at the same conditions, 9 except for recycling, are set forth in Table ll.

TABLE ll 11 feed temperature: 120~C
12 inlet pressure: 95 psig 13 fluid velocity through ",~",I.,d"e. 7 m/s 14 Run 1 Run 2 duration of recycle Period (hrs) Nil 4 16 feed - Cold Lake crude oil 17 da~Jhdl~ e1 wt. ~~0 18.3 18.3 18 initial permeate sample 19 asphaltene, wt. ~/0 13.9 5.1 ~~0 reduction in aa~ halL~nes 24 72 Exam~le lll 2 1 8 5 2 6 4 2 This example compares the results of a run carried out using a 200~A
3 average pore size ceramic membrane, without recycle, and a run carried out with a 4 1000~A average pore size ceramic membrane, with recycle.
The conditions and data are set forth in Table lll.

6 TABLE lll 7 feed temperature: 120~C
8 inlet pressure: 95 psig 9 fluid velocity through ~ lbldil~. 7 - 9 m/s membrane ~ore size: 200~A 1000~A
11 duration of recvcle: Nil 3 hrs.
12 feed: Cold Lake cnude oil 13 asphaltene, wt. ~/O 18.3 18.3 14 initial oermeate sam~le flux, kg/m2/day 34 61 16 a~l.llallt"le, wt. ~/O 3.4 3.7 17 ~/O asphaltene reduction 81 80 ~ 2 1 8~264 The data of Table lll shows that the 1000~A membrane, operated with 2 an initial recycle period, had the same degree of separation as that obtained with the 3 200~A ~"~""L,,d"e. However, the flux rate was 61 kglmZ/day with the 1000~A4 membrane whereas it was only 34 kg/m21day with the 200~A ~"e""L,rd"e. Otherwise stated, operatlon with the large pore membrane using recyc!e attained a significant 6 increase in permeate flux without loss in abpl ,alLe"e separation, when compared to the 7 results achieved with the 200~A pore size membrane.

8 Example IV
9 This example assesses the rate of diminution of flux rate during and after the initial recycle period.
11 A nun was carried out on Cold Lake crude oil having ab~l,altt"~e content 12 of 18.3 wt. ~/O. The ceramic membrane used had an average pore size of 1 000~A. The 13 oil was at a temperature of 120~C and pressure of 97 psig when introduced into the 14 membrane. The fluid velocity through the membrane tube was 9 m/s. The pemmeate was recycled for 2 hours. The run was continued for a total of 8 hours. Table 4 sets 16 forth the permeate flux rates in kglm~/day, measured at the end of each hour of the 17 run.

~ 2 1 ~5264 TABLE IV
2 Time-on-stream Permeate flux 3 hrs ka/m2/dav 4 0.2 360 6 0.6 301 7 0.9 314 8 1.1 88 9 1.6 61 2.6 51 11 3.1 49 12 4.0 53 13 4.9 59 14 5.6 60 6.5 55 16 8.1 58 17 Thls example shows that within 3 hours the flux rate diminution had 18 levelled off and remained generally constant thereafter.

19 Exam,~le V
This example d~lllon~L,dl~s how to determine the duration of the 21 permeate recycle period.

~ 21 ~5264 A run was carried out using Cold Lake crude oil having as~,l,alLt"le 2 content of about 19 wt. %. The run was carried out at a temperature of 120~C and an 3 inlet pressure of 97 psig. The fluid velocity through the membrane was about 9 m/s.
4 The ceramic membrane had an average pore size of 1000~A.
The run was conducted without permeate recycle. The results are 6 tabulated in Table V.

8 Time-on-Stream Permeate flux Permeate ~/O
g (hrs) rate a~.h 't ,e Reduction (kg/m~/day) content 11 (wt. o/o) 13 0.25 383 18.6 0.5 14 0.43 301 18.9 0.5 0.62 251 18.9 0.5 16 0.93 220 18.2 4 17 1.3 223 18.8 1.
18 1.8 188 17.3 9 19 2.8 58 16.4 14 3.9 49 10.6 44 21 4.9 53 4.2 78 22 6.1 57 4.2 78 23 7.1 56 24 7.9 52 3.8 80 2 1 8526~
The data shows that, after an initial period of about 4 hours, the 2 membrane had operated to achieve an a~ dll~ne reduction of about 70~/O. The 3 r~co"""~"ded permeate recycle period would be 4 hours in such a case.

4 Exarnple Vl Thisexampledt"l,o,l~l,dl~thataceramicmembranehavinganaverage 6 pore size of 2000~A can perform as well as one of 1000~A.
7 Runs were carried out using 1000~A and 2000~A Illelllbl'dn!::S fed with 8 Cold Lake crude oil at a temperature of 160~C with a pressure of 95 psi. The 9 permeate was recycled for an initial period of 2 hours. The results are reported below.

TABLE Vl 11 pore size: 1000~A 2000~A
12 flux (kglm2/day) 65 70 13 as~lldll~:lle reduction (~/0) 75 80 14 The data of Table Vl are reported for a time of 3 hours recycle plus 3 hours operation (total 6 hours).

Claims (5)

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

1. A process for upgrading heavy oil feed containing asphaltenes, comprising:
subjecting the feed to ultrafiltration by feeding it at elevated temperature and pressure through a substantially non-fouled ceramic membrane having a large average pore size to produce permeate and retentate products;
recycling a major portion of the permeate product to the feed entering the membrane for sufficient time so that rapid diminution of permeate flux rate begins to substantially level off and the asphaltene content of the permeate product being produced is reduced by at least 30% compared to the feed content; and then terminating recycling and continuing to subject additional feed to ultrafiltration to recover heavy oil permeate reduced in asphaltenes.

2. The process as set forth in claim 1 wherein:
the average pore size of the membrane is greater than about 500°A.

3. The process as set forth in claim 1 wherein:
the average pore size of the membrane is greater than about 1000°A.

4. The process as set forth in claim 1 wherein the average pore size of the membrane is in the range of about 1000° - 2000°A.

5. The process as set forth in claims 1, 2, 3 or 4 wherein:
the feed is heavy crude oil.