GB2190398A

GB2190398A - Oil deasphalting process

Info

Publication number: GB2190398A
Application number: GB08711349A
Authority: GB
Inventors: Gerard Hotler
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 1986-05-14
Filing date: 1987-05-14
Publication date: 1987-11-18
Also published as: NL8701097A; GB8711349D0; FR2598717A1; FR2598717B1; DE3715983A1

Description

GB2190398A 1

SPECIFICATION

Deasphalting process This invention relates to a deasphalting process for hydrocarbon oils. 5 Processes for deasphalting an oil containing asphaltenes have long been known which involve treating the oil with a deasphalting solvent. Two phases are formed which are then separated; a light phase containing the major part of the solvent and the deasphalted oil, and a heavy raffinate phase substantially containing the asphalts and a little solvent. Each of the phases obtained is then subjected to an operation for the removal of the solvent. In this way, separate 10 collection of the deasphalted oil (DAO) and an asphaltic phase is achieved.

US Patent No. 2 940 920 describes the separation of the light extract phase (comprising the mixture of deasphalted oil and deasphalting solvent) into a crude raffinate phase comprising a heavy fraction referred to as---resins-and a little deasphalting solvent, and a crude extract phase comprising a heavy fraction of deresined and deasphalted oil and the major part of the 15 deasphalting solvent, in conditions close to the critical point of the solvent. The expression -critical point of the solvent- is used in the Patent to refer to a critical pressure-critical temperature pairing. The critical temperature of a pure substance is the maximum temperature at which that substance can be liquefied by isothermal compression, while the critical temperature of a mixture is the maximum temperature at which the whole of that mixture can be liquefied by 20 isothermal compression. The critical pressure of a pure substance is the maximum pressure at which it is possible to observe boiling or condensation by an isobaric variation in temperature, and the critical pressure of a mixture is the maximum pressure at which it is possible to liquefy the whole of the mixture by an isobaric reduction in temperature. The expression "conditions close to the critical point- is usually employed to indicate a temperature such that T=0.95 to 25 1.05 Tc (on an absolute temperature scale) and a pressure P such that P=1. 05 to 1.5 Pc (on an absolute pressure scale).

For example, in Example IV, columns 25 and 26, lines 30 to 35 of US 2940920, the separation of a resin fraction on the one hand and a mixture of deresined deasphalted oil and pentane on the other hand, at a temperature of 0.96 to 1.04 Tc and at a pressure of 0.86 to 30 1.48 Pc when the critical pressure and temperature of pentane are respectively 19WC and 33.3 bars is described.

Subsequent separation of the crude extracts and the crude raffinates from the deresining step from the solvent with which they are still mixed, may be effected under markedly supercritical conditions: thus, in US 2940929 the deresined deasphalted oil is separated from the pentane at 35 215C and 38 bars (column 18, line 20), while in US 4305814 the resin- pentane mixture is separated at 240'C and 46 bars.

US 4502944 describes three-phase separation under slightly subcritical conditions, T=0.95 Te, P=1.5 Pc; and subsequent separation operations for products and solvent also take place in the supercritical range. 40 French Patent Application No. 85/15 552 describes a process which seeks to further improve energy recovery in DAO-solvent separation by effecting at least two supercritical separation stages at different temperatures with heat recovery by exchange in relation to different flows and optionally by effecting either a vapour recompression operation or three supercritical separa tion operations with recycling in the case of retrograde condensation, specifying for the whole 45 procedure very precise ranges of operating conditions. For example, when the solvent is pen tane, the temperature will be between 224'C and 26WC and the pressure will be between 38 and 68 bars.

Another technique for economic separation of a solvent and a Qolute is known: that is, effecting separation operation by tangential filtration over a membrane. 50 In a paper presented at the National Meeting of American Institute of Chemical Engineers in Seattle, 25th to 28th August 1985, Kulkarni, Funk and Li described the separation of deas phalted oil and pentane with an organic membrane at temperatures of between 25C and WC and at pressures of the order of 7 to 20 bars. A result which was considered as being typical of the series of experiments described, starting from a mixture with a weight ratio of solvent to 55 solute of 4 (20% by weight of DAO and 80% by weight of pentane), produced from 300 to 800 1 per M2 of membrane per day of a mixture with a weight ratio of solvent to solute of 16 (6% by weight of DAO and 94% by weight of pentane); the ratio of the flow rate of permeate to the input flow rate is of the order of 0. 1. There are two main disadvantages to the process described: 60 1) the fraction of recycled oil with respect to the separated oil is far from being negligible:

15%.At would be necessary correspondingly to increase the amount of deasphalting solvent and the size of the reactor in order to maintain the operating yields of the deasphalting operation; 2) the temperature that the organic membrane can withstand does not exceed 75C and in addition the degree of selectivity drops substantially as the temperature rises from 250C to 500C.65 2 GB2190398A 2 Since the deasphalting operation takes place at between 170 and 2MC, it would be necessary to have a series of heat exchangers with the filtration unit in order not to have to supply energy for heating the regenerated solvent to be recycled to restore it to the proper conditions for the deasphalting operation.

As regards ultrafiltration processes using mineral membranes which aim to separate hydrocar- 5 bon substances in the liquid state by operating at a temperature of higher than 80'C, mention may be made of French Patent No. 2482975. That patent uses mineral ultrafiltration barriers coated with a sensitive layer of at least one metal oxide having a permeametry radius of between 5 and 25nm; it is intended for the regeneration of waste oils by the removal of impurities therein which are retained by the barriers used, and it can also be used for reducing 10 the proportion of asphaltenes in hydrocarbon feedstocks. In the latter use, the process is found to be unsatisfactory as the level of removal of the ashphaltenes remains low, as is shown by the example in the French patent.

We have now found it possible to provide a deasphalting process utilising deasphalted oil deasphalting solvent separation which makes it possible to minimize the energy required for the 15 separation operation.

Thus, the invention provides a process wherein a hydrocarbon oil containing asphalt is treated with a deasphalting solvent to produce a light oily phase (crude extract) and a heavy asphaltic phase (crude raffinate) which are separated one from the other, and the solvent of each of said phases is at least partially separated therefrom, and wherein solvent is separated from the light 20 oily phase in at least three steps:

a) a first step in which the light oily phase is subjected to supercritical conditions for the solvent so as to cause separation into two phases, a light solvent- enriched phase and a heavy oil-enriched phase, and said two phases are separated one from the other, the operating conditions being moderate supercritical conditions, that is to say such that the light solvent- 25 enriched phase forms a liquid phase or dense supercritical phase (i.e. of a density higher than the critical density of the pure solvent); b) a second step in which the light solvent-enriched phase separated in step a) is subjected to controlled tangential filtration by circulation on an upstream side of a porous inorganic mem brane, the operating conditions on a downstream side of the membrane comprising a pressure 30 lower than on the upstream side but the pressures nonetheless being sufficient for a permeate to be formed as a vapour or light supercritical phase (that is to say, of a density lower than or equal to the critical density of the pure solvent), and there are thus collected separately, on the downstream side of the membrane, the solvent-rich light supercritical phase and on the upstream side of the membrane a retentate comprising the residual phase has not passed through the 35 membrane containing solvent-reduced deasphalted oil; and c) a third step in which the heavy oil-enriched phase separated in step a) is fractionated to produce separately a solvent phase and a hydrocarbon phase containing resins.

The process of the invention thus generally involves effecting a preseparation operation in -liquid-liquid- conditions on the deasphalted oil-solvent mixture and then passing a solvent- 40 enriched phase along a porous or semi-permeable inorganic membrane, substantially under the same conditions, so as to form a permeate essentially comprising solvent and a retentate from which the residual solvent may be removed and which comprises a deasphalted and deresined oil, which may, if desired, be recycled to the pre-separation step. The heavy phase of the preseparation operation can be subsequently substantially freed of solvent and will constitute an 45 oily phase: either a simply deasphalted oil (if recycling of the retentate occurs) or a resin.

It is thus possible to save energy compared to a conventional supercritical separation oper ation since the maximum temperature to which the solvent is raised is preferably 15'C to 50'C lower than that of a conventional supercritical separation step. In addition, the pressure condi tions used in step b) of the process of the invention make it possible to achieve a higher degree 50 of selectivity than in separation operation using a conventional membrane; these conditions correspond to a -supercritical pervaporation- procedure.

The viscosity of the permeate is generally scarcely higher than that of a gas and the viscosity of the mixture to be filtered is conventionally reduced by an increase in temperature and a reduction in the concentration of deasphalted oil. 55 The level of selectivity is greatly improved compared with a conventional separation operation using a membrane, when a liquid phase is to be found on each side of the membrane, with an identical pore diameter. Finally, the pervaporation step taking place in the supercritical range, the energy required for vaporization of the permeate is very much lower than that for the supercriti cal range. To sum up, separation with a membrane under supercritical conditions, in accordance 60 with the present invention, provides a degree of selectivity which is substantially the same as that of a conventional supercritical separation operation but, because it is possible to operate at a lower temperature, the amount of energy involved and the heat exchange surface area are thus lower.

The deasphalting solvent conveniently comprises at least one hydrocarbon having 3 to 6 65 3 GB2190398A 3 carbon atoms and may be selected from, for example, nC3, nC4, nCs, nC6, iC4, Cr, neo C5, isos C6 hydrocarbons as well as propylene, butenes, pentenes and hexenes. If desired, the hydrocar bon may be in the form of commercial propane, butane, pentane and hexane, as well as a C.

Cut, C4 Cut, C5 Cut, C6 cut, propylene cut and butene cut which are formed as mixtures.

A deasphalted oil may be obtained either from the deasphalting operation or from the deas- 5 phalting operation followed by deresining of heavy petroleum substances such as, for example, atmospheric residua, vacuum residua, topped heavy crudes, catalytic cracking residues and coal or petroleum tars, by means of any of the above-mentioned solvents.

The ratio by volume of solvent to oil, which is referred to as the solvent ratio, in a deasphalt- ing or deresining operation, is generally from 3:1 to 10A. 10 In the process of the invention:

1) the supercritical pre-separation step may be regarded as a---liquidliquid- diphasic step, wherein the two separated phases may be considered either as a heavy liquid and a light liquid or as a heavy liquid and a dense supercritical phase (density higher than the critical density of the pure solvent). The term -supercritical- relates here to the deasphaiting solvent. The condi- 15 tion -slightly supercritical- therefore excludes the formation of a heavy liquid and a vapour phase. It is preferable to avoid involving three phases.

2) the final separation step trhough the membrane may be regarded as a supercritical pervapo ration step: the fight liquid or the dense supercritical phase from the pre-separation step consti tutes the -chargefor the mineral membrane, the permeate is formed by a - vapour- or light 20 supercritical phase (density lower than or equal to the critical density of the pure solvent), the retentate may be either singe-phase and thus simply solvent-reduced, or dual-phase involving a heavy liquid and a light liquid of a composition and properties substantially the same as those of the charge.

Operation will preferably be in the following manner: the crude extract from deasphalting is 25 subjected to conditions of temperature and pressure such that T, and P, are preferably in the ranges Tb>T,>T, and P,>Pb to cause separation into two liquid phases, a heavy oil-enriched phase (A) and a light solvent-enriched phase (B), and those two phases are separated. For the sake of economy, P, will preferably be chosen such that PL>P1>Pb.Tb,TJL and Pb. are as defined hereinafter: 30 Ts: the minimum liquid-liquid separation temperature is preferably equal to TIA+15'C wherein T,, is the temperature at which the crude extract issues from the deasphalting unit, and P,: is a -technological limit- pressure, resulting from calculations in respect of economy, and embodying the fact that beyond a certain pressure the increase in capital investment costs cannot be compensated by a drop in operating cost or by enhanced flexibility in operation of the 35 unit.

Thus, PL can be set at 85 bars in the case of a deasphalting operation using propane, 75 bars in the case of a deasphalting operation using butane, 68 bars in the case of a deasphalting operation using pentane and 65 bars in the case of a deasphalting operation using hexane.

Tb and P, respectively represent the bubble temperature and pressure of the deasphalted oil- 40 deasphalting solvent mixture: in a very rough approximation, the pair Tb, Pb is given by extending the vapour pressure curve of the solvent beyond the critical point. Some characteristic values are set forth in Table A:

4 GB2190398A 4 TABLE A

P=C n-Butane n-Pentane n-Flexane Pb(bars) Tb(OC) Pb(b=s) Tb(O0 Pb(bars) Tb(OC) Pb(b=) Tb 0 C) 43 990C 40 161C 40 212PC 35 25dC 47.5 1040C 45 169PC 45 22dC 40 26f'C 10 112C'C 50 1760C so 2289C 45 271C 62.5 121C 55 18lc ss 2360C 50 28CPC 70 1290C 60 19fC 60 2450C 55 289PC 15 77.5 137PC 65 1980C 65 251C 60 2980C 1449C 70 2030C 68 2530C 65 3040C 75 209PC 20 For the pressures Pb indicated, the values of "Tb" set forth in the Table represent an estimate of the maximum value that the actual Tb can attain. Clearly, the actual bubble temperature 25 depends on the proportion of oil in the mixture and the nature of oil on the one hand and the composition of the deasphalting solvent which will generally be a cut and not a pure substance on the other hand. The invention is not limited to the foregoing values and the man skilled in the art will be able to make any adaptations required.

In order to provide the conditions for the second step, that is to say to allow for supercritical 30 pervaporation through the membrane and in general to avoid involving downstream of the membrane a light liquid phase or dense supercritical phase, the mode of operation used is preferably as follows: the first light solvent-enriched phase (B) is passed in tangential filtration mode along a porous inorganic membrane at a tangential speed V, while a pressure drop AP is imposed across the membrane without the supply of additional heat to the permeate so that it 35 expands adiabatically. V is preferably between two limits V,>V>V2 and AP is also preferably between two limits AP1>AP>AP2. The permeate comprises a solvent phase which may be recycled to the deasphalting step after any appropriate heat exchange. The retentate is formed either as one or two liquid phases, the whole being enriched with oil in relation to the first phase (B), and if desired the retentate can be recycled to the liquid- liquid supercritical presepara- 40 tion step.

The preferred values Of V1NDAP, and AP2 are defined below:

The maximum tangential speed V, is conveniently 30m.sec-1, it being considered that beyond that value the polarization layer which is formed is excessively thin, which gives rise to a drop in selectivity. The minimum tangential speed V2 is conveniently 0.3m.sec-1, below that it is consi- 45 dered that the polarization layer which is fomed is excessively thick and the permeate flow rate becomes excessively low.

The maximum pressure difference AP, between the two sides of the membrane generally depends on the mechanical strength of the carrier for the membrane, and the upper limit will conveniently be between 12 and 80 bars, depending on the design configuration of the carrier. 50 The minimum pressure difference AP2 is arbitrarily considered to be 3 bars, the permeate flow rate becoming excessively low below that value. The pressure on the permeate side will nor mally be chosen so that downstream of the membrane there is a supercritical phase correspond ing to the density condition of step (b) of the process.

Preferably, the process uses an inorganic membrane with a pore radius of 2 to 10 nanometres 55 and in a particularly preferred embodiment, a pore radius of 2 to 4 nanometres. The porous ultra-filtration membrane may be as described in the prior art, for example in US Patent Nos.

4060488 or 4411790 or French No. 2550953. Thus, the membrane may comprise a porous metal, ceramic or equivalent carrier on which there has been deposited a fine material comprising at least one metal compound, for example one of the oxides of the following elements: titanium, 60 zirconium, magnesium, silicon, aluminium, yttrium, hafnium, and mixed oxides of a plurality of those metals with or without silica, or boron oxide, or an alkali or alkaline-earth metal fluoride, a silicon carbide or a silicon nitride, and the like.

Depending on the particular application of the process, it may be appropriate to combine the membranes in variable numbers in ultrafiltration modules. Those modules may be disposed in 65 GB2190398A 5 series or in a parallel. It will be appreciated that the number of such modules depends on the selectivity of the mineral ultrafiltration membranes, the nature of the feedstock, the degree of enrichment desired in respect of the two fractions, the respective viscosities of the feedstock and the permeate, and the selected temperature and pressure conditions.

The term -membrane- is used herein for the sake of simplification to refer to a single 5 membrane or an assembly of membranes.

Embodiments of the invention will be hereinafter described by way of nonlimiting example with reference to the accompanying drawings in which:

Figure 1 shows a first embodiment of the process of the invention in which only asphalt and deasphalted oil are produced; and 10 Figure 2 shows a second embodiment of the process of the invention which involves the production of asphalt, resin and deresined and deasphalted oil.

Referring to Fig. 1, the feedstock oil is fed by line 30 and the solvent by line 29 into the deasphalting reactor or series of reactors as indicated by 1 operating under preferably slightly subcritical conditions. The heavy fraction comprising asphaltenes and a little solvent is discharged from line 24 to the solvent recovery step 25 comprising a low pressure (flash) evaporation operation and a final vapour entrainment (stripping) operation. The asphalt is collected at 26 and the recovered solvent is discharged by line 27 for recycling through lines 28 and 29. The light fraction comprising deasphalted oil and the major part of the solvent (generally at least 90%) is discharged by line 2 and is heated in exchanger 3 and furnace 4 so as to be at 20 supercritical conditions T1 and P, The mixture, which is then a dual- phase mixture, undergoes settlement in the separator 5.

The light liquid solvent-enriched phase comprising, for example, at least 83% of solvent and in most cases at least 88% of solvent and at most 93.5% of solvent is discharged by way of the line 6 to the filtration assembly 9. It passes in tangential filtration relationship along the mem- 25 brane 7 at a speed V. The part which has not passed through the membrane, i.e. the retentate, is overall impoverished is respect of solvent; it is either single-phase or dual-phase and its overall solvent content depends on the tangential filtration conditions. It has a solvent content which is preferably approximately equal to the solvent content of the mixture which is dis charged from the deasphalting reactor at line 2. The retentate is combined with the flow in the 30 line 2, downstream of the furnace 4. The part which has undergone pervaporation through the membrane, i.e. the permeate, is obtained under slightly supercritical conditions: P,-AP and T2, T2 resulting from adiabatic expansion of the permeate. AP represents the pressure difference between the two side of the membrane. The composition of this supercritical phase is preferably at least 94% by weight of solvent and in most cases at least 97% of solvent, and that flow is 35 discharged by way of the line 8.

The heavy liquid phase which issues from the separator 5 comprises at least 45% by weight of deasphalted oil and in most cases approximately 55% by weight of deasphalted oil. It is taken by line 11 and reheated in exchanger 12 and furnace 13, the dual- phase mixture which is then obtained is allowed to separate under supercritical conditions (as defined in French Patent 40 Application No. 8515552) in the separator 14. The light or vapour phase which preferably comprises at least 97.5% solvent is discharged into the line 8 by way of line 19. The combined solvent stream is then pumped via 20 through exchanger 3 where it undergoes cooling, giving up heat to the mixture in line 2. The cooled solvent is then discharged (21) to the buffer tank 22 for hot solvent, before being combined again with the solvent intake 29, by line 23. The 45 liquid phase which preferably comprises at least 80% of deasphalted oil is discharged by way of line 15, giving up heat in exchanger 12 before being passed to solvent recovery step 16 which involves low-pressure (flash) evaporation and vapour entrainment (stripping). The deasphalted oil issues through 18 and recovered solvent is discharged by line 17- the cooled solvent in lines 17 and 27 are combined with the solvent feed at 29 by way of the line 28. 50 It will be appreciated that, instead of separating the solvent from the deasphalted oil (line 11) by supercritical settling (14) followed by evaporation (16), it is possible to operate with simple distillation by passing the mixture in line 11 directly into evaporation unit 16. The thermal efficiency of the operation is however markedly less advantageous so that the embodiment as shown in Fig. 1 is preferred. 55 Referring to Fig. 2, the feedstock oil is supplied by line 30 and the solvent by line 29 to the deasphalting reactor or series of deasphalting reactors as indicated by 1 operating under prefera bly slightly subcritical conditions. The heavy fraction comprising asphaltenes and a little solvent is discharged from line 24 to the solvent recovery step 25 comprising a low-pressure (flash) evaporation operation and a final vapour stripping operation. The asphalt is collected at 26 and 60 the recovered solvent is discharged by line 27.

The light fraction comprising deasphalted oil and the major part of the solvent (preferably at least 90%) is discharged by line 2 and heated in exchanger 3 so as to be at supercritical conditions T, and P, The mixture, which is then a dual-phase mixture, undergoes settlement in the separator 5; the furnace 4 shown in Fig. 1 is generally not necessary in this embodiment. 65 6 GB2190398A 6 The heavy liquid phase which preferably contains at least 50% of resin and in most cases at least 57.5% of resin is discharged by line 11 to the solvent recovery step 31 formed by a low pressure (flash) evaporation operation and a vapour entrainment (stripping) operation, the resin being collected at 32 and the recovered solvent being discharged by line 33.

The light liquid phase which preferably comprises at least 75% of solvent and in most cases 5 at least 80% of solvent and at most 90% of solvent, is discharged by line 6 to the filtration assembly 9. It passes in tangential filtration relationship at a speed V along the membrane 7.

The part which has not passed through the membrane, i.e. the retentate, is either single-phase or dual-phase and its overall content is at least 30% by weight of oil and in most cases at least 37.5% of oil. The retentate is discharged through line 10 and heat exchanger 12 and furnace 10 13, the mixture, which is then a dual-phase mixture, undergoes settlement in the separator 14 under supercritical conditions.

The light phase which preferably comprises at least 97.5% of solvent is discharged by line 19 to line 8. The combined solvent stream is then pumped via 20 through exchanger 3 where it undergoes cooling, giving up heat to the mixture in line 2. The cooled solvent is then discharged 15 by line 21 to the buffer tank 22 for hot solvent, before being combined with the solvent feed 29 through line 23.

The liquid phase which preferably comprises at least 80% of deasphalted oil is discharged through line 15 and gives up heat in exchanger 12 before going to the solvent recovery step 16 comprising a low-pressure (flash) evaporation operation and a vapour entrainment operation 20 (stripping). The deasphalted and deresined oil issues through 18 and the recovered solvent is discharged by line 17. The combined cold solvent in line 17, 27 and 33 is added to the solvent feed 29 by way of the line 33.

In this embodiment it is possible not to use the supercritical separator 14 and to pass the flow in line 10 directly to evaporator 16; thermal efficiency in this case is less good. 25 The following non-limiting Examples serve to illustrate the invention.

Examples

Examples 1 and 2 are set forth respectively to explain the liquid-liquid pre-separation step (a) and the subsequent tangential filtration step (b). 30 Examples 3 to 6 describe a complete mode of operation of embodiments of the invention:

without production of a resin fraction (Examples 3, 4 and 5) by using respectively pentane, butane and propane as the extraction solvent; and with the production of a resin fraction (Example 6) by using pentane as the solvent.

By way of example, analyses in respect of the crude charge, the deasphalting solvents and 35 representative deasphalted oils are set out below. 1 7 GB2190398A 7 All percentages are by veight.

Le,M Arab vacuum residue (A) 5 d 15 - 1.037 4 Asphaltenes C7 = 15.25% Cbmadson carbcn - 22.95% 10 96 mlpi= = 5.42% nickel = 50 ppm vanadium = 167 ppm 15 Pentane cut (B) d 15 m 0.630 20 4 CS m 0.21% wt. ics - 23.40% wt. nC, 75.74% wt, 0.65% wt 25 Butane cut (C) d is a 0.580 (nmasured at 3 bars absolute) 4 30 C4 - 1.38% wt. iC4 = 31.23%. but-l-ene + isobutene 15.67% wt nC4 n 34.88%, trans-but--2-ene = 9.14%, cis-but-2-ene 7.18% m 0.52% 35 Pre cut (D) d is = 0.505 (masured at 10 bars absolute) 40 4 C3 m 1.47% wt$, propylene a 16.22%# 80.17%; + C3 C 2.14% Oil deaSPhalted with pentane (E) 45 d 15 = 0.995 Yield in relation to 50 Asphaltenes C5 = 0.42% Asphaltenes = 0.040% Resi&e A m 68.30% C7 8 GB2190398A 8 carbm 11.6% Vanadium = 39 ppm Nick41 = 6 ppm 5 Sulphur = 4.57% D 20 = 1.543 10 Oil deasphalted with butane (F) d4- = 0.987 Asphaltenes Cs = 0.085% 15 It C7 = 0.007% Conradson carbon = 7.85% Yield in relaticn to Vanadium 20 28 ppn, Residue A 53.15% Nickel 5 ppm Sulphur 3.38% n 1.529 25 D 20 Oil dhalted with propane (G) 30 d is m 0.982 4 Asphaltenes C5 ' 0-009% 35 Conradsoncarbon - 4.05% Yield in relation to Vanadium = 12 ppm Residue A g 34.64% Nickel a 2 ppim Sulphur - 2.94% 40 nD 20 - 1.507 45 Example 1

Vacuum residue (A) is contacted with pentane cut (B), the proportion of solvent by volume (expressed at ambient temperature) being 4m3/M3. Operation is carried out in a column in which 50 the head temperature is 18WC, and the pressure is 40 bars relative. That produces the deas phalted oil (E) and an asphalt with a ring-ball point of 16WC.

The crude extract (23.4% by weight) mixed with the solvent (76.6% by weight) leaving the extractor head is subjected to different conditions in respect of temperature and pressure (202 to 205'), at 45 to 50 bars, so as to effect liquid-liquid separation. That produces on the one 55 hand a light liquid phase comprising solvent and deasphalted and deresined oil and on the other hand a heavy liquid phase comprising 50 to 55% of resin and 50 to 45% of solvent (see Table 1, lines 1 to 4).

In a second series of tests, the preliminary deasphalting operation is carried out with a solvent content of 6.7M3/M3, with all the other variables remaining identical. The crude extract (15% by 60 weight) mixed with the C, cut (85%) leaving the head of the extractor is brought to a pressure of 55 bars and to different temperatures (between 201 and 21 1'C). This mode of operation also produces a liquid-liquid separation effect, and characteristics of which are set forth in Table 1 (lines 5 to 7).

Vaccum residue (A) is contacted with butane cut (C), the proportion of solvent by volume 65 9 GB2190398A 9 (expressed at ambient temperature) being 5M3/M3. Operation is carried out in a column in which the head temperature is 13WC and the pressure is 40 bars relative. That produces deasphalted oil (F) and an asphalt with a ringball point of 122C.

The crude extract (17.5% by weight) mixed with the solvent (82.5%) is subjected to different conditions in respect of temperature, 143C and 147'C, and pressure, 52 to 56 bars absolute, 5 so as to produce liquid-liquid separation. That gives on the one hand a light liquid phase which comprises solvent and deasphalted and deresined oil and on the other hand a phase forced by 57% to 62% by weight of resin and 40 to 45% by weight of butane cut, see Table 2.

k 0 Tab] e 1 T p Resin % oil. % resin Resin Oil (OC) bars DAO % light phase heavy phase A C 7 A C 5 C.C A C 7 A C5 C.C 202 0 45 27% 19.5% 50.8% 0.085% 1.5% 16.2% 0.011% 0.08% 9.0% 204 0 45 43% 16.4% 53.7% 0.065% 0.8% 14.1% 0.008% 0.05% 8.1% 202 0 50 9.4% 22.5% 51.5% 0.19% 3.9% 19.1% 0.017% 0.18% 10.7% 205 0 50 20.8% 20.4% 52.6% 0.14% 2.9% 16.8% 0.014% 0.10% 9.8% 0 55 3% 14.65% 50.4% 0.3% 4.8% 22.2% 0.018% 0.25% 11.4% 201 206 0 55 18. 5% 12.85% 56.7% 0.12% 2.9% 16.8% 0.012% 0.10% 10.0% 211 0 55 34% 10.90% 54.95% 0.08% 1.2% 15.0% 0.009% 0.07% 8.8% C.C.: Conradson carbon AC 5: Asphaltenes with pentane DAO: Deasphalted oil AC 7: Asphaltenes with heptane Table 2

0 W (D 00 T p Resin % % oil % resin Oil Resin (,C) bars DAO light phase heavy phase A C 5 C.C A C 1; C.C 143 0 56 18% 15.65% 59.80% 0.012 5.65 0.60 10.7 147 0 56 46% 10.85% 61.50% 0.005 4.50 0.25 9.05 147 0 52 66% 7.35% 61.15% 3.80 0.12 8.70 GB2190398A 11 Example 2(Table 3) This example examines the performances of different filter elements from the point of view of selectivity and permeate flow rate; is also demonstrates the benefit of supercritical pervaporation compared to subcritical pervaporation or liquid ultrafiltration upstream and downstream of the membrane. 5 The filter elements are tubes which are 0.75m in length and 7mm inside diameter. The interior of the tubes is covered with a filtering layer in which the pore radius may be 2nm, 3nm or 4nm.

The permeate flow rate is expressed in terms of 1 /h for 1 element and M3 /day/M2, while selectivity S is expressed by (H charge/(1 -H charge))/((H permeate/(1 -H permeate)) where H charge is the fraction by weight of oil in the feed and H permeate is the fraction by weight of 10 oil in the permeate.

A first subcritical pervaporation test is carried out by circulating 600 1/h at 22 bars effective pressure and at 180C of a mixture of 23.5% of deasphalted oil E and C, cut B, the tangential speed along the filtering media with a pore radius of 21nm is 4m.sec-l. The pressure drop across the membrane is set at 8 bars and the permeate is collected in gaseous form. It is then 15 condensed at 14WC and then either passed into the tank which contains the mixture to be filtered or cooled to ambient temperature and expanded for measurements of flow rate and for analysis. Under those conditions, 1.675 1/h of permeate containing 1.5% by weight of oil is measured.

Two upstream liquid-downstream liquid filtration tests are then carried out by circulating 600 20 1/h at 32 bars effective pressure and 1800C of the above-indicated mixture, firstly in an element with a pore radius of 2nm and then in an element with a pore radius of 4nm. The pressure drop is also set at 8 bars. The measurements in respect of flow rate and analyses are as follows:

pore radius 2nm: 0.186 1/h of mixture containing 0.18% by weight of oil pore radius 4nm: 1.49 1/h of mixture containing 12.45% of oil. 25 The advantage of supercritical pervaporation is demonstrated in the following two tests:

The above described mixture is passed at an identical flow rate by weight (that is to say in this case 680 1 /h) under a pressure of 48 bars and at 210'C into an element with a pore radius of Sinm. The pressure drop across the membrane is fixed at 8 bars. Under those conditions, 10.17 1/h of mixture containing 5.9% of oil is collected. 30 720 1/h at 48 bars and at 21WC of a mixture containing 12.85% of deasphalted oil and 87.15% of C5 cut is passed through a filter element with a pore radius of 3nm. The pressure drop across the membrane is again 8 bars. Under those conditions, 13.80 1/h of mixture containing 3.10% of deasphalted oil is collected.

The order of magnitude of flow rate and selectivity is retained when there is a change of 35 solvent.

A filter tube with a pore radius of 3nm is again used. 540 1 /h under a pressure of 50 bars at 1450C of a mixture composed of 7.35% of deasphalted oil and 92.65% of butane cut is passed through the filter tube. A pressure drop of 6 bars across the membrane is selected. Cooling to ambient temperature is effected and the permeate is expanded at 3 bars for flow rate measure- 40 ment and then analysis. Under those conditions, 9.78 1/h of mixture containing 1.57% of oil is collected.

N.) Table 3

Pore Charge Linear Permeate Flow rate Permeate radius flow rate speed flow rate 3 oil Selectivity T p Type of 2 nm at T and P m/sec (20% 1 bar) /day/m content oC bars separation m 3 600 1/h 4 1.675 1/h 2.44 1.5% wt 20.2 180 22 Subcritical.

pervaporation 2 600 1/h 4 0.186 1/h 0.27 0.18% 170.4 180 32 Upstream-downstream liquid 4 600 1/h 4 1.49 1/h 2.17 12.45% 2.16 180 32 Upstream-downstream liquid 3 680 1/h 4.53 10.17 1/h 14.82 5.90% 4.87 210 48 Supercritical ------------------------------------------------------------------- pervaporation 3 720 1/h 4.8 13.80 1/h 20.10 --------------- --------- Supercritical 4.61 210 48 pervaporation 3 540 1/h 3.6 9.78 1/h 14.25 1.57% 4.97 145 50 Supercritical pervaporation (butane, A P = 6 bars) 0 W CD 00 13 GB2190398A 13 Example 3 (Figure 1) Line 30 is used to inject 3 t/h of the vacuum distillation residue A and line 29 is used to inject 8.48 t/h of a mixture of 97.8% by weight of C. cut B and 2.2% by weight of recycled deasphalted oil, into a mixing zone followed by a settlement zone, the combination being referred to as the deasphalting zone 1. The pressure is 53 bars and the mean temperature is 5 1900C. Under those conditions, the mixture forms two phases. Line 24 is used to take off 1.56 t/h of a mixture comprising 61.5% by weight of asphalt and 38.5% of solvent which is subjected to low-pressure evaporation (flash evaporation) and then entrained (or stripped) by steam in zone 25. From that zone issues 0.96 t/h of asphalt (26) and 0.6 t/h of solvent (27) which is passed to line 28 and then line 29. The line 2 is used to take off 9.921 t/h of light 10 phase formed by 22.45% by weight of deasphalted oil and 77.55% by weight of C. cut. That mixture is heated to 20WC in the exchanger 3 and then to 2115.WC in the furnace 4; at that time the pressure has fallen to 48 bars due to a pressure drop. There is then added to that flow, 5.895 t/h of a mixture from line 10, comprising 22.45% by weight of deasphalted oil and 77.55% by weight of solvent. The mixture settles in the separator 5 to form two liquid phases. 15 The light liquid phase (12.084 t/h) which is formed by 12.469/6 by weight of deasphalted and deresined oil is discharged by line 6 to filtration assembly 9. That phase passes along the membrane 7 at an initial tangential speed of 4m.sec-1. The permeate, that is to say 6.174 t/h, is discharged by way of the line 8, comprising 2.92% by weight of deasphalted and deresined oil and 97.08% by weight of solvent, its temperature has fallen to 210'C and its pressure to 40 20 bars. The temperature drop has only been 5.WC, which shows the advantage of pervaporation under supercritical conditions. The selectivity factor 12.46/87.54 S= =4.74. 25 2.92/97.08 The mean specific flow rate of permeate of 18.1M3/day/M2 (expressed at ambient temperature and pressure) implies a total area of membrane of 16. 1M2. To make up the membrane 7, assemblies formed by a series of elementary tubes (as described in Example 2) with a pore 30 radius of 3nm are arranged in parallel. The retentate which is discharged by way of the line 10 is recycled to the separator 5.

The heavy liquid phase (3.747 t/h) formed by deasphalted but nonderesined oil (54.6% by weight) and solvent (45.4% by weight) is carried by the line 11 to the exchanger 12 where it is heated to 233'C and the furnace 13 where it reaches 25WC, at which point the pressure has 35 fallen to 40 bars due to the pressure drop. The mixture which is then a dual-phase mixture, under supercritical conditions, undergoes settling in the separator 14. 2. 319 t/h of heavy phase formed by 87.97% of deasphalted oil and 12.03% of solvent are taken off by way of the line 15. That phase is cooled to 227'C, giving off its heat to the flow in the line 11 in the exchanger 12, and then passes into the zone 16 where it undergoes low- pressure evaporation 40 (flash evaporation) followed by vapour stripping. 2.04 t/h of deasphalted oil is discharge by way of the line 18 and 0.279 t/h of solvent is passed by way of the line 17 to the lines 28 and 29.

1.407 t/h of light phase (supercritical vapour) composed of 99.6% by weight of solvent and 0.4% of deasphalted oil is discharged by way of the line 19. The flows in the lines 8 and 19 go to the pump 20. Downstream of the pump the pressure is 40 bars and the temperature is 45 2118.WC after adiabatic compression, the flow is at 22WC and 55 bars, it then passes through the exchanger 3 from which it issues at a temperature of 204'C, having given up its heat to the mixture in the line 2; the line 21 carries it to the buffer tank 22 from which the line 23 carries it to the solvent injection at 29.

50 Example 4 (Figure 1) Injected into the deasphalting zone 1 are 3 t/h of vacuum residue A and 9. 745 t/h of a mixture of 98.8% Of C4 cut (C) and 1.2% of recycled deasphalted oil, under a pressure of 57 bars and a mean temperature of 13WC. Two phases settle out:

- The heavy phase which is treated in the assembly 25 produces 1.5 t/h of asphalt (line 26) 55 and 0.9 t/h of solvent (line 27).

- The light phase (10.345 t/h) of a mixture with 15.63% of deasphalted oil and 84.37% Of C4 cut is heated to 142'C in the exchanger 3 and then to 15O.WC in the furnace 4. Combined with that flow is 3.975 t/h of recycled retentate containing approximately 15. 70% of deresined and deasphalted oil and 84.30% Of C4 cut. The mixture settles in the separator 5 under a pressure 60 of 52 bars. The light liquid phase (11.823 t/h) composed of 6.27% by weight of oil and 93.73% by weight of butane cut is directed towards the filtration assembly 9, the initial tangential speed along the membrane 7 being approximately 4m.sec-1. The permeate (7.848 t/h) which is composed of 98.5% of C, cut and 1.5% of deasphalted and deresined oil is discharged to the line 8, its temperature has fallen to 146' and its pressure to 44 bars. The drop in 65 14 GB2190398A 14 temperature has been only 5.WC, the selectivity factor has been 6.27/93.73 S= =4.39, 1.5 /98.50 5 while the mean specific flow rate of permeate (expressed at ambient temperature under a pressure of 3 bars) is about 12.2M3/day/M2. The retentate is recycled is recycled by way of the line 10 to the separator 5. The heavy liquid phase (2.496 t/h) which is composed of 60% of deasphalted oil and 40% of C, cut is heated to 178' in the exchanger 12 and then to 195' in 10 the furnace 13 when the pressure has fallen to 44 bars, due to the pressure drops. That mixture undergoes settlement in the separator 14. The heavy phase gives up its heat in the exchanger 12 from which it issues at 16WC to be treated in the assembly 16 from which issue 1.5 t/h of deasphalted oil (18) and 0.204 t/h Of C4 Cut (line 17). The light phase, 0.792 t/h Of C4 Cut, is combined by way of the line 19 with the line 8 and then the pump 20. The temperature and the 15 pressure are 44 bars and 15O.WC upstream; after a diabatic compression the downstream conditions are 161' and 59 bars. That flow is cooled to 144' in the exchanger 3 and is then passed to the buffer tank 21 before being recycled to the line 29.

Example 5 (Figure 1) 20 3 t/h of vacuum residue (A) is treated in zone 1 under a pressure of 68 bars and at a mean temperature of WC, by 15.115 t/h of a mixture of 0.83% of recycled oil and 99.17% of C, cut (D). 3.3 t/h of heavy phase is treated in the zone 25 from which 1.95 t/h of asphalt (26) and 1.35 t/h of solvent (27) issue. 14.814 t/h of light phase (7.94% of deasphalted oil and 92.06% Of C3 cut) are heated to 101'C in the exchanger 3 and then to 1 WC in the furnace 4. 25 Combined with that flow is then 17.226 t/h of recycled retentate (7.97% of deasphalted and deresined oil and 92.03% Of C3 cut). The mixture undergoes settlement under a pressure of 63 bars in the separator 5. The light phase, 29.94 t/h (5.01% of oil and 94. 99% Of C3 Cut) is passed to the filtration assembly 9; the initial tangential speed along the membrane 7 is 4m.sec-l. The permeate (12.714 t/h: 1% of oil and 99% Of C3 Cut), is collected at 105' and 55 30 bars and then discharged by way of the line 8. The fall in temperature has only been 5' while the selectivity 5.01/94.99 S 5.22 35 1/99 is a little greater than with the other solvents, whereas the mean specific flow rate of permeate (expressed at ambient temperature and under a pressure of 10 bars) is a little lower than with the two solvents: 9.1M3 /day/M2. 40 The retentate is recycled by way of the line 10 to the separator 5.

- The heavy liquid phase (2.1 t/h: 50% of oil and 50% Of C3 Cut) is heated to 124' in the exchanger 12 and then to 145' in the furnace 13. The mixture is allowed to settle under a pressure of 55 bars in the separator 14. The heavy phase (1.236 t/h) gives up its heat in the exchanger 12 from which it issues at 125', and it is separated at 16 into 1.05 t/h of 45 deasphalted oil (18) and 0.186 t/h of C, cut (17). The vapour phase (0. 864 t/h Of C3 Cut) rejoins the line 8 and then the pump 20: the upstream conditions are 55 bars and 108'. After adiabatic pumping that flow is raised to 117' and 70 bars. It is cooled to 99' in the exchanger 3, and the line 21 carries it to the buffer tank 22 from which it is recycled to the line 29.

50 Example 6 (Figure 2) The line 30 is used to inject 3 t/h of vacuum distillation residue (A) and the line 29 is used to inject 8.862 t/h of a mixture of 96.34% by weight Of C5 cut (B) and 3.66% by weight of recycled deasphalted oil, into a mixing zone followed by a settlement zone 1, the combination being referred to as the deasphalting zone; the pressure is then 50 bars and the mean tempera- 55 ture is 17WC. Under those conditions, the mixture settles as two phases. The line 24 is used to take off 1.32 t/h of a mixture formed by 61.36% by weight of ashpalt and 38.64% of solvent which is subjected to low-pressure evaporation (flash evaporation) and then entrained (stripped) by means of steam, in the zone 25, from which issue 0.81 t/h of asphalt (26) and 0.51 t/h of solvent (27) which is returned towards line 28 and then line 29. The line 2 is used to take off 60 10.362 t/h of light phase formed by 24.20% by weight of deasphalted oil and 75.80% by weight of C. cut. That mixture is heated to 201.50C in the exchanger 3; at that time the pressure has fallen to 45 bars due to a pressure drop. Two liquid phases are allowed to settle in the separator 5 where supercritical conditions obtain.

The heavy liquid phase, 0.546 t/h, formed by 54.95% of resins and 45.05% of solvent, is 65 GB2190398A 15 discharged by way of the line 11 to the zone 31 where it is subjected to low-pressure evaporation (flash evaporation) and steam entrainment (stripping). 0.246 t/h of solvent is reco vered by means of the line 33 and 0.3 t/h of resins is discharged by way of the line 32.

The light liquid phase (9.816 t/h) comprising 22.49% of deasphalted and deresined oil is discharged by way of the line 6 to the filtration assembly 9. That phase passes along the 5 membrane at an initial tangential speed of 4m.sec-1. The supercritical permeate, that is to say 4.908 t/h of mixture consisting of 6.3% by weight of deasphaited and deresined oil and 93.7% of C5 cut, is cooled to 197.WC and its pressure has fallen to 37 bars. The drop in temperature has only been 4'C, which shows the advantage of supercritical pervaporation. The selectivity factor was 10 22.49/77.51 S= =4.32.

6.3/93.7 15 The mean specific flow rate of permeate of 12.4M3/M2/day (expressed at ambient temperature and pressure) implies a total area of membrane of 23.75M2. The retentate which is discharged by way of the line 10 (also comprising 4.908 t/h), consisting of 38.7% of deasphalted and deresined oil and 61.3% of solvent is carried to the exchanger 12 where it is heated to 21WC and the furnace 13 where it reaches 25WC, at which point the pressure has fallen to 37 bars as 20 a result of the pressure drop. The mixture which is then a dual-phase mixture undergoes settlement in the supercritical separator 14. 2.124 t/h of heavy phase consisting of 88.98% of deasphalted oil and 11.02% of solvent is taken off by way of the line 15. That phase is cooled to 216', giving up its heat to the flow in the line 10 in the exchanger 12, and it then passes into the zone 16 where it undergoes low-pressure evaporation (flash evaporation) and then 25 steam entrainment (stripping). The line 18 is used to discharge 1.89 t/h of deasphalted oil, while the line 17 passes 0.234 t/h of solvent towards the fines 28 and 29. 2. 784 t/h of light phase (vapour) composed of 99.6% of solvent and 0.4% if deasphalted oil is discharged by way of the line 19. The flows in the lines 8 and 19 go to the pump 20. Downstream of the pump the pressure is 37 bars and the temperature is 216.WC; after adiabatic compression, the flow is at 30 226'C and 50 bars, and it then passes through the exchanger 3 from which it issues at 192o after having given up its heat to the mixture in the line 2, the line 21 carries it to the buffer tank 22 from which the line 23 passes it to the injection of solvent at 29.

Claims

CLAIMS 35

1. A deasphalting process wherein a hydrocarbon oil containing asphalt is treated with a deasphalting solvent to produce a light oily phase and a heavy asphaltic phase which are separated one from the other, and the solvent of each said phases is at least partially separated therefrom, and wherein solvent is separated from the light oily phase in at least three steps:

a) a first step in which the light oily phase is subjected to supercritical conditions for the 40 solvent so as to cause separation into two phases, a light solvent- enriched phase and a heavy oil enriched phase, and said two phases are separated, the operating conditions being moderate supercritical conditions such that the light solvent-enriched phase forms a liquid phase or dense supercritical phase; b) a second step in which the light solvent-enriched phase separated in step a) is subjected to 45 controlled tangential filtration by circulation on an upstream side of a porous inorganic mem brane, the operating conditions on a downstream side of the membrane comprising a pressure lower than on the upstream side but the pressures being sufficient for a permeate to be formed as a vapour or light supercritical phase, and there are thus collected separately, on the down- stream side of the membrane said solvent-rich light supercritical phase, and on the upstream 50 side of the membrane a retentate comprising the residuais phase which has not passed through the membrane containing solvent-reduced deasphalted oil; and c) a third step in which the heavy oil-enriched phase separated in step a) is fractionated to produce separately a solvent phase and a hydrocarbon phase containing resins.

2. A process according to claim 1 wherein step c) is effected by supercritical fractionation 55 comprising heating of the heavy oil-enriched phase from step a) so as to separate it into two phases, separation of the phases and the removal by evaporation of the residual solvent contained in the heavier phase.

3. A process according to claim 2 wherein the supercritical fractionation operation is carried out by subjecting the phase to supercritical conditions which are more severe than those of step 60 a) and such that the resulting solvent-rich phase is gaseous or of a density lower than the critical density of the pure solvent.

4. A process according to any one of claims 1 to 3 wherein the retentate containing deasphalted oil and residual solvent is subjected to a solventdeasphalted oil fractionation oper- ation so as to yield a heavy phase of deasphalted and deresined oil which has a reduced solvent 65 16 GB2190398A 16 content and a light solvent phase.

5. A process according to claim 4 wherein the solvent-deasphaltedderesined oil fractionation operation is effected by subjecting the phase to supercritical conditions which are more severe than those of step a) and such that the light solvent phase produced is gaseous or supercritical with a density lower than the critical density of the pure solvent. 5

6. A process according to any one of claims 1 to 3 wherein the retentate is mixed with the light oily phase and then subjected to the supercritical conditions of step a), the hydrocarbon phase produced in c) then being a hydrocarbon phase containing both deasphalted oil and resins.

7. A process according to any one of claims 1 to 6 wherein the moderate supercritical conditions of step a) comprise a temperature T1 and a pressure P, such that Tb>T1>T., and 10 Pl>P, wherein Ts is the minimum liquid-liquid separation temperature and T, and P, respectively represent the bubble temperature and pressure of the light oily phase which is subjected to step a).

8. A process according to any one of claims 1 to 7 wherein the flow along the porous inorganic membrane in step b) is effected at a tangential speed of from 0. 3 to 30m.sec-l. 15

9. A process according to any one of claims 1 to 8 wherein the inorganic membrane has pores of radius of from 1 to 10 nanometres.

10. A process according to any one of claims 1 to 8 wherein the inorganic membrane has pores of a radius of from 2 to 4 nanometres.

11. A process according to any preceding claim substantially as herein described. 20

12. A deasphalting process substantially as herein described with reference to the accompanying drawings.

13. Each and every novel product, process, method, apparatus, feature and combination substantially as herein described.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.

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