Brief Description of the Invention

Hard asphalts exhibiting a penetration of less than 100 and commensurate low temperature properties, preferably the properties of an 85/100 asphalt, can be made from vacuum residua which ordinarily cannot be used to produce such asphalt under normal vacuum tower operating conditions, preferably vacuum residua derived from Arab light or similar crude or feeds substantially comprising Arab light crude or similar crudes by ultrafiltering the vacuum residua through a membrane. The permeate obtained, of substantially reduced metals content, is useful as cat feed. The retentate is harder than the pitch fraction produced under normal vacuum tower operating condi¬ tions. In refineries which are not equipped with sophisticated vacuum distillation equipment, oxidizers, or propane deasphalters, it would not be possible to produce acceptable hard asphalts from such vacuum residua by typical refinery distillation.

Thus, ultrafiltration of this vacuum residua preferably Arab Light-type vacuum residua permits the production of acceptable hard asphalt directly without resort to sophisticated vacuum distillation procedures, oxidizers, or propane deasphalters. A collateral benefit is an increased production of reduced metals content cat feed as permeate.

Background of the Invention

Treating hydrocarbon charges by ultrafiltration is a process known in the art.

Japanese 4013509 describes the purification of oils such as lubricating oil or naphtha by filtering the oil through an ultrafil¬ tration membrane made from polymers such as acrylonitrile styrene copolymer or polysulfone polymer. The oils treated can be lube oil, naphtha (e.g., residual oil from vacuum distillation), spent lube oil, or carbon-containing spent wash oil for engines. The process involves

filtering the oil through an ultrafiltration membrane at a pressure of 1-20 kg/cm^, a flow rate of 2-4 m/sec and a temperature of 5.50°C.

US 4,411,790 describes the use of inorganic membranes for high temperature ultrafiltration of oils. The process can be used to regenerate used lube oil or to reduce the asphaltene content of heavy oils such as vacuum residua. The membrane is an inorganic ultra¬ filtration barrier having a pore radius of 50-250A coated with a metal oxide layer. The process is run at temperature above about 100°C. Membrane plugging is prevented by periodically applying back pressure.

US 4,797,200 describes separating heavy oil by diluting the oil with a solvent such as chloroform or toluene and ultrafiltering the diluted oil through an ultrafiltration membrane such as cellulose or polyvinylidene fluoride at about 750-1500 kPa and 20-125°C. A permeate of reduced conradson carbon content and reduced vanadium and nickel content is recovered. The retentate can be fed to a deasphalt- ing process. The permeate of reduced metal and conradson carbon residue content has the characteristics of gas oil and may be used as cat cracker feed with or without further hydrotreatmen . The process can be run on raw or reduced crudes, heavy atmospheric and heavy vacuum residual oils, hydrorefined oils and hydrorefined atmospheric residual oils, shale oil, tar sands products, and coal liquefaction products.

US 4,816,140 combines conventional deasphalting with membrane ultrafiltration. The solvent used to perform a conventional solvent deasphalting step is recovered from the deasphalted oil as filtrate by ultrafiltration through inorganic membrane.

The Present Invention

It has been discovered that asphalts having a penetration of less than 100 @ 25°C and commensurate low temperature properties preferably the penetration and low temperature characteristic of an 85/100 asphalt cement can be made from vacuum residua which ordinarily cannot be used to produce such asphalt under normal vacuum tower

operating conditions, preferably vacuum residua derived from Arab light or similar crudes or feeds substantially comprising Arab light or Arab light type crudes by ultrafiltering the vacuum residua through a membrane. As used hereafter in the specification and the appended claims the crude source of such vacuum residua which ordinarily cannot be used to produce such asphalts under normal vacuum tower operating conditions is characterized as being and described as a crude whose vacuum residua is an inappropriate hard asphalt source while such vacuum residua is designated an inappropriate residua. Acceptable asphalts of less than 100 penetration could not be made from such inappropriate residua by simple vacuum distillation directly but required the use of sophisticated vacuum distillation procedures, oxidizers, or propane deasphalters. The present invention offers an alternative to using oxidizers and propane deasphalting to produce acceptable asphalt from such crudes whose vacuum residua is an inappropriate hard asphalt source, preferably Arab light-type crude source vacuum residua.

Arab Light crude cannot be vacuum reduced under normal refinery conditions to 85/100 penetration, a common hard grade of paving asphalt in Canada and the United States. This is a function of crude composition. Arab Light 120/150 penetration vacuum residua has the following typical composition

Asphaltenes (NHI) 8 wtX

Saturates 11 wt% naphthene-aromatics 52 wt_ polar aromatics 29 wtX

Asphaltenes give hardness to asphalt. Saturates can also contribute to this property if wax is present. Arab Light crude produces vacuum reduced asphalts which have satisfactory high-temperature viscosity; however, their low temperature properties are mediocre because of the presence of wax. Pavements made with such asphalts can crack under severe winter conditions (i.e., low temperature). Ultrafiltration done on Arab Light residue indicates that the viscosity-penetration

relationship for the retentate has not been affected. There is some evidence that its low temperature properties may be improved.

Other crudes having similar quantities ^* of asphaltenes, saturates and aromatics of the same type as Arab Light (See Table 2) may behave similarly when processed to make asphalt, that is, they will not be able to be distilled to make the harder grades.

Arab light or Arab light type crudes (including crudes such as Isthmus and Basrah) can be characterized in the following way (see Table 1):

Table 1 CANDIDATE CRUDES FOR ULTRAFILTRATION

50% T.J. Tia Juana Lt. - 50%

Crude Arab Lt. Isthmus Lt. Isthmus Basrah

Vacuum Residue

Fraction, °C 566+

Yield, vol_ 15.9

Penetration, @25°C 175

Viscosity, @135°C 246

Penetration Index -1.8

Penetration Ratio 25.0

Pen-Vis No. -0.32

Vacuum residua obtained from these types of crudes cannot be simply distilled to produce useful, hard asphalts having penetration of less than 100, preferably 85/100 penetration grade asphalt cements. Such residua could not be vacuum reduced to 100 penetration or lower without carbonizing and degrading the pitch product. To produce useful asphalts from such inappropriate residua it has been necessary to resort to using oxidizers or propane deasphalters. Such units or processes are not available at all refineries and, therefore, limited

the refineries' ability to make quality asphalt when such inappropri¬ ate crudes.

Paving asphalt cements, or basestocks for roofing and industrial asphalts, have traditionally been manufactured by the distillation of certain selected crude oils. Crude oils that are unsuitable for asphalt products are mainly those with high wax contents. Their composition can give vacuum residues which have low viscosity at 135°C relative to their penetration and/or poor low temperature properties as measured by their penetration indices and penetration ratios.

Arab light crude (a readily available feedstock) and Arab light-type crudes having moderately high wax contents give vacuum residues which have satisfactory viscosity vs penetration but have poor low temperature properties.

These crudes cannot be vacuum reduced under normal plant vacuum tower conditions to much less than 100 penetration at 25°C. A penetration of 100 or greater is softer than that required by road builders in many parts of the world.

Table 2 gives the composition, by Corbett Analysis, of three vacuum resides considered waxy; one from Arab light and two from Arab light-type crudes. These residues have the same penetration at 25°C. Those made from Cano Limon and Redwater-Gulf crudes have poor viscosity vs penetration as well as poor low temperature properties, would be unacceptable for use as paving asphalt cement by most road builders, and cannot be used to make good hard asphalt having a penetration of less than 100, preferably an asphalt meeting the 85/100 specification.

Table 2 TYPICAL PHYSICAL INSPECTIONS FOR THREE CRUDE SOURCES

Samples Crude Fraction, ^β C

Penetration at 25 ^β C (100/5)

Viscosity at 135 ^β C, cSt

Composition, wt% Asphaltenes Saturates

Naphthene-Aromatics Polar Aromatics

Sats + Naphthene Collection Asphaltenes, wtX

DESIRABLE CRITICAL PROPERTIES FOR ASPHALT EASTERN CANADA 85/100 PENETRATION GRADE

Penetration at 25°C, mm/10 85-100

Viscosity at 135°C, cSt 280 - and higher

Flash Point, COC, °C 230 minimum

Ductility @4°C (lcm/min) 6 min.

25 ^β C (5cm/min) 100 min.

Solubility in TCE, mZ 99.5 min.

Thin Film Oven Test:

Change in Mass, % 0.85% max. Retained Penetration, % 47 Ductility of Residue @25 ^β C 75 min.

Penetration Index (*) -1.6 - and higher

(*) Not a government specification, but an internal guideline based on climatic conditions and competitive asphalt quality.

Resort to ultrafiltration will not result in the production of acceptable asphalt from vacuum residua that are otherwise and in other ways totally unacceptable for asphalt production.

Ultrafiltration permits production of acceptable asphalt from vacuum residua without resort to sophisticated vacuum distillation systems, high vacuum distillation systems, oxidizers, or propane deasphalters. In the case of poor totally unacceptable crudes for which resort to even these sophisticated systems cannot produce good asphalt, ultra¬ filtration will also be incapable of producing good asphalt. Thus, vacuum residua possessing totally unacceptable viscosity properties cannot be ultrafiltered into good asphalt because, while ultrafiltra¬ tion may improve penetration index and penetration ratio, ultrafiltra¬ tion will not improve the penetration-viscosity relationship (pen-vis no) .

Thus, inappropriate vacuum residua, preferably Arab Light or Arab Light-type crude vacuum residua which are candidates for ultra- filtering to produce hard asphalts would be characterized as possess¬ ing a penetration at 25 ^β C (100/5) of about 120 and greater, and a viscosity at 135 ^β C (in cSt) of about 310 and less.

Table 3 gives the typical physical properties of Arab Light asphalts made by vacuum distillation and shows their penetration indices (-1.8) and penetration ratios (25.0) to be much lower than acceptable in Canada. Also, it is not possible to make the 85/100 grade. The removal of wax from Arab Light minimum residue (562°C+, Table 1) could give harder residues having improved low temperature properties. However, resort to solvent dewaxing or catalytic dewaxing of vacuum residue is not an attractive alternative, nor something routinely carried out on crudes prior to, or in the course of, atmospheric/vacuum distillation.

Table 3 TO .TT ASSAY

Crue: Arabian. igfac p_vnτ_ χ--~- -r r_yr«rr_ Targec Specifications

Penecraεion Grada 85Λ00 150/200 200/300 300/400

Fraction 'C 566+ 557+ 542+

Yield on Crude, volt (Extrasolacad) 15.9 17.0 17.9

Prooβrriβ-;

Penecraεion ac 25*C (100/5) 90 175 250 350

Paneεrarion Index Penecraεxon Ratio (1)

VlxeosiCT ac 60*C. Poiae lOO'C. cSt

135*C. cSt

Duecility ac 4*C (1 eaain), ca 25'C (5 caaia), ca

Softening Polnc (D36), 'C Deosicy ac 15*C. lcga ^a Acid No.. α-g KQH/g

Flash Poinc (C0C , ^* C 362 357 351

T n -'A- Qve_ T_a_

Change in Bass. % +0.10 +0.11 +0.11 Residue:

Recained Penecrar±on ac 25'C. t

Viscosity Ratio ac 60*C

Duecility ac 25*C (5 eaain), ca

(1) LOO (4*C (200/60) 25'C (100/5)].

Ultrafiltration of both Arab light and Arab light-type crude vacuum residua has been found to produce retentates which possess acceptable asphalt properties.

Ultrafiltration can be carried out using membranes having a pore size from about 0.01 micron to 1.0 micron, preferably about 0.1 micron.

Useful membranes include both polymeric and ceramic membranes such as polyi ide, polysulfone, nylon, polyester imide or other high temperature stable polymeric membranes, alumina or other refractory metal oxide, sintered metal, or glass non-polymeric membranes. A preferred polyimide membrane is the polyimide ultra¬ filtration membrane disclosed and claimed in USP 4,963,303.

Ultrafiltration can be carried out at pressure differentials across the membrane ranging from about 30-400 psi, preferably about 30-100 psi and temperatures sufficiently high to keep the vacuum residue liquid. Typical temperatures will range from 150-200°C for high temperature stable polymeric membranes while much higher tempera¬ tures can be used for the ceramic, sintered metal or glass membranes.

If lower operating temperatures are desired, a diluent can be added to the vacuum residue. It is desirable to use just enough diluent to help keep the vacuum residue in the liquid state at lower temperatures. Diluents such as kerosene, aliphatic solvents (e.g., Varsol Exsol D60, etc.) diesel or other light liquid hydrocarbon solvents can be used.

The selection of a solvent to be used to reduce the visco¬ sity of vacuum residue is mostly going to depend on refinery economics. From an economic standpoint 0% dilution is most desirable as this would eliminate the necessity of solvent stripping the product in order to meet product specifications. From a unit operation standpoint the higher the dilution the better. For instance, work has been done using light vacuum gas oil (LVGO) at about the 20% level in blends with vacuum pipestill (VP) pitch. The LVGO normally goes to

cat feed; in the ultrafiltration process, much of the LVGO would become a part of the permeate which would also go to cat feed. Similarly, other refinery light streams could be used (e.g., HVGO or HAGO) . When dilution solvents are employed it is necessary to strip the recovered retentate to remove any residual solvent in order to produce an asphalt of the required specification hardness.

Although aromatic solvents may have better solvency for vacuum residue, paraffinic solvents can give greater rejection (of metals, MCR) . Here again, refinery economics will determine what stream may be used. A stream such as splitter-bottoms may have desirable properties based on its paraffinic nature.

The retentate from the ultrafiltration contains a large amount of the metals present in the vacuum residua feed. This retentate constitutes the hard asphalt product.

The permeate, of reduced metals content is useful as cat feed.

Depending on the crude source, ultrafiltration is conducted so as to secure a yield of about at least 75% retentate, preferably about 70% retentate, more preferably about 60% retentate, most prefer¬ ably about 35-40% retentate, based on feed. At the lower yield percentages it may be necessary to employ one of the previously mentioned diluents in order to insure continued fluidity of the feed at a manageable temperature.

Examples

A refinery sample of vacuum residue (90% Arab Light crude feed) having a penetration at 25°C of 341 mm/10 was ultrafiltered in a laboratory batch unit. Three runs were conducted on the vacuum residue as such. A fourth run was conducted using the vacuum residue diluted with Varsol, level of dilution, 17 vol%.

The retentate and permeate were stripped to remove the Varsol.

The ultrafiltration was performed using an Alcoa ceramic membrane having a pore size of lOOOA (0.1 micron) (Alcoa 1000A ceramic alumina membrane) . The membrane was in tubular form 7 mm ID X 720 mm long. Temperature was maintained at 170°F; flow rate was maintained at 6 gp ; inlet pressure was 120 psi/outlet pressure 80 psi.

The properties of the vacuum residua and the resulting retentate are presented in Table 4.

Table 4

PROPERTIES OF RES I DUE AND RETENTATE

fso . acock VflC mn Boιtd* o R.-cπ.itc. \ pf Fes . ARAB LIGUT ASSAT

.13 ^# C COT HIVBC 569*C+ 81.7 71.7 62.3 37.5 + 570* (1) (2) (3) (3) (3) (4) 545*C+ 558*C

Pen at 25'C (100/5) 3.1 220 245 206 168 38.2 329 242 124

10*C (100/5) 54.5 32.3 39.7 33.1 27 11 5. 39 20.5

. ^• C (100/5) 20.4 15.2 16 15.3 13.5 5.7 22 16 8.5

4*C (200/60) 78.5 .8.1 58.3 5..5 42.5 17.3 81 60 31

Penetration Index -2.00 -2.05 -1.90 -i.βl -1.74 +0..8 -1.85 -1.93 -1.8 Penetration Ratio 23.0 21.8 23.8 26.4 25.3 .5.3 24.3 24.9 25.2 Pen-Vis No. -0.23 -0.35 -0.35 -0.39 -0.48 -0.49 -0.09 -0.15 -0.4

Viscosity, 60*C, Ps. 233 404 348 428 554 6748 297 465 1009 100'C. cSt 867 1269 1136 1256 1324 6793 1042 1331 2363 135*C, cSt 155 203 187 208 231 682 171 211 301

(1) Vacuum residue ( 1030°F AET) from 90% Arab Light crude.

(2) Hlvac distillation, 92.2 LVΪ of residue.

(3) Retentate from laboratory ultrafiltration unit.

(4) Feed diluted with Varsol; permeate and retentate then stripped