Hydrotreatment catalyst

Abstract

A catalyst for use in the conversion of heavy hydrocarbons to light ones, the catalyst being prepared from a naturally occurring material characterized by an elemental composition comprising aluminum, iron, silicon, magnesium and titanium by the thermal and chemical treatment of the naturally occurring material with steam/H.sub.2 +H.sub.2 S so as to change the physical properties and surface chemical properties of the starting material.

Description

BACKGROUND OF THE INVENTION

The present invention resides in a catalyst characterized by a surface composition of sulphide, oxides and/or hydroxides of aluminum, iron, silicon, magnesium, titanium and nickel for use in the conversion of heavy hydrocarbons to light ones and, more particularly, a method for the preparation of the catalyst from naturally occuring materials by thermal and chemical reaction of same and a process for the treatment of heavy hydrocarbons with the catalyst so produced.

Until now, catalysts of the type set forth above have never been used for converting heavy hydrocarbons containing a high level of metals and asphaltenes into light ones in the presence of hydrogen. The catalyst of the present invention provides a great advantage with respect to conventional ones due to its low cost, its high selectivity for vanadium removal, and its high stability.

SUMMARY OF THE INVENTION

According to the present invention, a catalyst is provided which contains sulphur, oxides and/or hydroxides of aluminum, iron, silicon, magnesium, titanium and nickel in surface, wherein the aluminum and iron, as metals, are present between 0.1 and 50% by weight of the total catalyst, the silicon and magnesium, as metals, are present between 0.1 and 30% by weight of the total catalyst and the titanium and nickel, as metals, are present between 0.1 and 10% by weight of the total catalyst.

The catalyst composition may also contain sulphur, oxides and/or hydroxides of calcium, potassium, sulphur, zinc, zirconium, gallium, copper, chrome, manganese, cobalt and molybdenum, wherein the metal has a concentration of 1 to 10,000 parts per million by weight of the total catalyst.

The catalyst is activated by means of thermal and chemical treatments at a temperature between 100 and 1,000.degree. C. in the presence of various oxidizing agents followed by a reducing atmosphere of H.sub.2 +H.sub.2 S for periods of time varying between 1 and 36 hours. The resulting catalyst thus treated has a total surface area varying between 50 and 500 m.sup.2 /g and a total porous volume between 0.20 and 0.88 cc/g and special surface chemical composition.

DETAILED DESCRIPTION

In accordance with the hydrocarbon treatment process of the present invention a heavy hydrocarbon with a high metal and asphaltene content is placed in a hydrotreatment zone in contact with the catalyst of the present and hydrogen is introduced under controlled conditions so as to produce the greatest possible quantity of light hydrocarbons with no significant production of "pitch".

The hydrocracking catalyst of the present invention has the physical characteristics shown in Table 1. They have a special pore distribution with 30 to 70% of pore volume having a pore radius of greater than 100 .ANG..

TABLE I______________________________________PHYSICAL CHARACTERISTICS OF THE CATALYST More Full Range Preferred Preferred Min. Max. Min. Max. Min. Max.______________________________________Surface Area, m.sup.2 /g 50 500 55 200 60 150Porous Volume, cc/g 0.20 0.60 0.22 0.50 0.30 0.43Mean Pore Radius, .ANG. 20 200 30 150 35 145Distribution of Porous VolumePV with R 10 .ANG., % 0 100 1 80 1 50PV with 10 .ANG. R 0 100 5 50 10 45100 .ANG., %PV with R 100 .ANG., % 0 100 5 80 30 70______________________________________

The catalyst consists of one or more oxides and/or hydroxides of aluminum on the surface, wherein the aluminum is present in at least 0.1% by weight (as metal) of the total catalyst, preferably between 0.5% and 50% by weight of the total catalyst, and more preferably between 1 and 30% by weight of the total catalyst.

It also has one or more sulphides, oxides and/or hydroxides of iron on catalyst surface wherein the iron is present in at least 1% by weight (as metal) of the total catalyst, preferably between 3 and 50% by weight of the total catalyst, and more preferably between 5 and 48% by weight of the total catalyst.

It also contains one or more oxides and/or hydroxides of silicon on catalyst surface wherein the silicon is present in at least 0.1% by weight (as metal) of the total catalyst, preferably between 1 and 30% by weight of the total catalyst, and more preferably between 5 and 20% by weight of the total catalyst.

The catalyst likewise possesses one or more oxides and/or hydroxides of magnesium on the surface, wherein the magnesium is present in at least 0.1% by weight (as metal) of the total catalyst, preferably between 0.1 and 30% by weight of the total catalyst, and more preferably between 0.1 and 20% by weight of the total catalyst.

The catalyst also contains sulphides and/or oxides of nickel and titanium on surface wherein the nickel and titanium are present in at least 0.1% by weight (as metal) of the total catalyst, preferably between 1 and 10% by weight of the total catalyst, and more preferably between 2 and 5% by weight of the total catalyst.

Other metals which may be present include calcium, potassium, sulphur, zinc, zirconium, gallium, copper, chrome, manganese, cobalt and molybdenum, generally found in a concentration between 1 to 10,000 parts per million by weight of the catalyst.

All of the above metals are present in the natural occuring material with the exception of sulphur which is added during chemical treatment.

The catalyst is prepared by the chemical treatment of a natural occuring material such as bauxite, laterite iron mineral, laterite nickel mineral or the like having the appropriate elemental composition. The mineral is treated first in air +steam at 300.degree.-900.degree. C., preferably at 500.degree.-800.degree. C. for 1 to 36 hours, preferably for 12 to 24 hours. The partial pressure of steam used is varied from 20-700 mmHg. Then the sample is treated in H.sub.2 +H.sub.2 S steam at 200.degree.-500.degree. C., preferably at 250.degree.-450.degree. C. for 1 to 12 hours, preferably for 3 to 5 hours; the pressure of H.sub.2 S is varied from 20 to 450 mmHg. Total pressure used is 760 mmHg.

The foregoing treatment changes the physical properties of the starting material such as pore volume, pore volume distribution and surface area. It also changes the surface chemical properties of the material.

The final catalyst contains between 3 and 40% sulphur, preferably between 8 and 30%.

The following examples are presented to illustrate the invention.

EXAMPLE 1

An experiment was carried out using the BU catalyst, prepared from a natural bauxite mineral from Upata in the Bolivar State of Venezuela and treated in accordance with the present invention. The activation method and chemical treatment was as follows. Temperature: 600.degree. C., with steam for 7 hours (P.sub.H.sbsb.2.sub.O : 330 mmHg) followed by treatment with H.sub.2 +H.sub.2 S at 250.degree. C. for 2 hours. (P.sub.H.sbsb.2.sub.S : 350 mmHg). The characteristics of this BU catalyst are shown in Table 2.

TABLE 2______________________________________BU CATALYSTComposition of the Catalyst: Actual Range______________________________________% Al 23.40 18.5-34.3% Fe 16.22 3.3-23.1% Si 2.53 0.3-10.5% Ti 1.52 0.5-2.0% S 12.01 8.4-17.3Physical Properties:Surface Area BET, m.sup.2 /g 135Total Porous Volume, cc/g 0.36Distribution of Pore Size:Mean Pore Radius, .ANG. 53Distribution of Porous Volume:PV with R 10 .ANG., % 1PV with 10 .ANG. R 100 .ANG., % 43PV with R 100 .ANG., % 46______________________________________ In Table 2, the "Range" column indicates most useful variations within the composition of the BU catalyst.

The catalyst was placed in contact with a heavy hydrocarbon feedstock, (JOBO), the characteristics of which appear in Table 3.

TABLE 3______________________________________PROPERTIES OF THE FEEDSTOCK (JOBO)______________________________________Specific Gravity 60/60.degree. F. 0.986API Gravity 12Sulphur, % by weight 2.70Vanadium, ppm 332Nickel, ppm 86Conradson Carbon, % by weight 11.77Asphaltenes, % by weight 8.71-9.27Water, % by volume 1.2Salts, ppm 104Carbon, % by weight 83.82Hydrogen, % by weight 10.89Nitrogen, % by weight 0.57TBP Distillation, % by volume T in .degree.C.Initial Boiling Point 77Residue (72.5) 400+______________________________________

The conditions for the treatment of the feedstock were: flow rate of the feedstock of 0.1 barrels per day with a flow of hydrogen of 445 1ts per hour, in contact 0.5 kg of the catalyst under a temperature of 400.degree. C. and a pressure of 105 bars.

The results of the product obtained from this experiment with the BU catalyst appear in Table 4.

TABLE 4______________________________________TBP Distillation, % by Volume T in .degree.C.______________________________________Initial Boiling Point 29 5 5710 11320 23230 33840 400Residue (60) 400+______________________________________ Sulphur: 2.30% by weight, Vanadium: 285 ppm, Asphaltenes: 7.61%.

EXAMPLE 2

A similar experiment was carried out using the LF catalyst, prepared from a natural laterite iron mineral from the region of Los Guaicas in the Bolivar State of Venezuela, and treated in accordance with the present invention. The treatment and activation method were as follows. Temperature: 800.degree. C., with steam for 24 hours (P.sub.H.sbsb.2.sub.O : 330 mmHg) followed by treatment with H.sub.2 + H.sub.2 S at 300.degree. C. for 4 hours. (P.sub.H.sbsb.2.sub.S : 350 mmHg). The characteristics of this LF catalyst are given in Table 5.

TABLE 5______________________________________LF CATALYSTComposition of the Catalyst: Actual Range______________________________________% Al 20.00 12.3-30.0% Fe 40.73 24.7-48.4% Si 1.92 0.8-2.3% Ti 3.03 2.0-4.8% S 13.04 10.0-25.1Physical Properties:Surface Area BET, m.sup.2 /g 48Total Porous Volume, cc/g 0.34Distribution of Pore Size:Mean Pore Radius, .ANG. 142Distribution of Porous Volume:PV with R 10 .ANG., % 40PV with 10 .ANG. R 100 .ANG., % 14PV with R 100 .ANG., % 46______________________________________

In Table 5, the "Range" column indicates most useful variations within the composition of the LF catalyst.

The catalyst was placed in contact with a heavy hydrocarbon feedstock, (JOBO), with the same characteristics as used in Example 1 and which appear in Table 3. The treatment conditions used were the same as in Example 1, except for the temperature which was 410.degree. C. The results of the product obtained from this experiment with the LF catalyst appear in Table 6.

TABLE 6______________________________________ TBP Distillation, % by Volume T in .degree.C.______________________________________Initial Boiling Point 104 5 17110 22120 28830 32940 36850 400Residue (50) 400+______________________________________ Sulphur: 2.14% by weight, Vanadium: 200 ppm, Asphaltenes: 6.82%?

EXAMPLE 3

A similar experiment was carried out using the LN catalyst, prepared from a natural laterite nickel mineral from the region of Loma de Hierro in the Aragua State of Venezuela, and treated in accordance with the present invention. The treatment and activation method were as follows. Temperature: 500.degree. C., with steam for 24 hours (P.sub.H.sbsb.2.sub.O : 330 mmHg) followed by treatment with H.sub.2 +H.sub.2 S at 300.degree. C. for 4 hours. (P.sub.H.sbsb.2.sub.S : 350 mmHg). The characteristics of the LN catalyst can be seen in Table 7.

TABLE 7______________________________________ LN CATALYSTComposition of the Catalyst: Actual Range______________________________________% Al 0.39 0.2-3.4% Fe 7.26 6.8-60.4% Si 19.46 2.5-19.5% Mg 18.88 2.0-18.9% Ni 2.78 0.7-3.6% S 10.45 7.4-28.6Physical Properties:Surface Area BET, m.sup.2 /g 128Total Porous Volume, cc/g 0.37Distribution of Pore Size:Mean Pore Radius, .ANG. 38Distribution of Porous Volume:PV with R 10 .ANG., % 26PV with 10 .ANG. R 100 .ANG., % 23PV with R 100 .ANG., % 41______________________________________

In Table 7, the "Range" column indicates most useful variations within the composition of the LN catalyst.

The catalyst was placed in contact with a heavy hydrocarbon feedstock, (JOBO), with the same characteristics as used in Examples 1 and 2, and which appear in Table 3.

The results of this experiment with the LN catalyst, and under the same conditions example in Example 1 except for the pressure, which was 120 bars, appear in Table 8.

TABLE 8______________________________________TBP Distillation, % by Volume T in .degree.C.______________________________________Initial Boiling Point 43 5 13210 19120 27730 34640 400Residue (60) 400+______________________________________ Sulphur: 2.08% by weight, Vanadium: 195 ppm, Asphaltenes: 5.59%.

As stated hereinabove, the above catalysts used according to this invention are prepared from natural material having the required elemental composition.

Example 4

In order to prove the effect of chemical treatment the previously described materials (BU, LF and LN samples) were treated with steam alone and with steam and H.sub.2 +H.sub.2 S atmosphere. In Table 9 the chemical composition, physical properties, activation method and the activity results are presented for the three catalysts claimed.

TABLE 9__________________________________________________________________________ EFFECT OF CHEMICAL ACTIVATION LF Treated LN Treated BU Treated LF Treated With Steam/ LN Treated With Steam/ BU Treated With Steam/ With Steam H.sub.2 + H.sub.2 S With Steam H.sub.2 + H.sub.2 S With Steam H.sub.2 + H.sub.2 S__________________________________________________________________________(A) ChemicalComposition% Fe 40.07 40.07 13.84 13.84 20 20% Al 20.32 20.32 0.59 0.59 45 45% Si 0.80 0.80 15.04 15.04 5 5% Ti 3.44 3.44 -- -- 1 1% Mg -- -- 16.69 16.69 -- --% Ni -- -- 1.47 1.47 -- --% S -- 18.03 -- 6.08 -- 13.5(B) PhysicalPropertiesArea (m.sup.2 /g) 46 31 94 58 135 103.5VP (cm.sup.3 /g) 0.30 0.25 0.56 0.56 0.36 0.35Average Pore 131 166 119 138 53 70Radius (.ANG.)PoreDistribution, (% V)Pore Radius (.ANG.)15-30 4.29 4.25 2.86 2.90 7.5 1.530-45 2.86 2.70 1.43 1.40 9.50 4.545-75 4.29 4.31 1.43 1.35 19.10 22.2575-150 5.71 5.60 5.71 6.04 23.10 28.75150-500 5.71 6.01 12.85 12.44 20.00 15.30500 77.14 77.13 75.71 75.87 20.00 27.7Partice Size (mm) 0.1-0.5 0.1-0.5 0.1-0.5 0.1-0.5 0.1-0.5 0.1-0.5(C) Activation Steam Steam Steam Steam Steam SteamMethod 800.degree. C. - 800.degree. C. 2h 500.degree. C. 500.degree. C. 3h 500.degree. C. 4h 500.degree. C. 4h during 2h followed during 3h followed (P.sub.H.sbsb.2.sub.O :200 followed (P.sub.H.sbsb.2.sub.O :200 by H.sub.2 + H.sub.2 S (P.sub.H.sbsb.2.sub.O :300 by H.sub.2 + H.sub.2 S mmHg) by H.sub.2 + H.sub.2 S mmHg) 400.degree. C. mmHg) (P.sub.H.sbsb.2.sub.S :70 (P.sub.H.sbsb.2.sub.S :100 (P.sub.H.sbsb.2.sub.S :70 mmHg) mmHg) mmHg) during 4h during 4h during 4h(D) Activity*TBP (Distillation)(% V) T(.degree.C.) T(.degree.C.) T(.degree.C.) T(.degree.C.) T(.degree.C.) T(.degree.C.)IBP 104 84 43 40 110 50 5 171 150 132 120 181 13010 221 200 191 165 200 18020 288 260 277 240 270 25030 329 301 346 305 315 31540 368 340 375 335 350 34550 400 360 410 350 410 360Residue (50) 400+ 360+ 410+ 350+ 410+ 360+Sulphur (%) w 2.14 2.01 2.08 1.84 2.25 1.95Vanadium (ppm) 200 150 195 138 215 145Asphaltene (%) 6.82 5.10 5.59 5.04 6.92 5.1Gravity .degree.API 15.7 17.0 16.1 17.5 14.7 17.0__________________________________________________________________________ *Reactor Conditions: T = 410.degree. C.; P = 120 bars; 0.1 b/D; 0.5 kg of cat; H.sub.2 flow 455 lt/h; Jobo Crude Oil.

It can be seen that the chemical activation modified the pore size distribution, the surface area and the sulphur content. The activity of the samples are improved after the chemical treatment. Sulphur, vanadium and residue conversion were increased by the activation method used.

EXAMPLE 5

In order to prove the change in surface chemical composition by the activation method, analysis of the surface composition was performed by XPS (X-Ray photoelectron spectrospcopy). The apparatus used was an AEI-ES200B using a cathode of aluminum (h=1486'6 eV=300 V). The aluminum, iron, titanium, oxygen, sulphur, coal, silicon, intensity pics was recorded and the ratio intensities of metals other than aluminum to the aluminum were taken as a measure of surface concentration. In Table 10 the results for one BU sample activated by air treatment as was claimed in the previous art, and results of other BU samples treated with the present method (steam/H.sub.2 +H.sub.2 S) are presented.

TABLE 10______________________________________SURFACE CHEMICAL COMPOSITION (XPS)BU (Air) BU Steam (H.sub.2 + H.sub.2 S)Element BULK SURFACE* BULK SURFACE*______________________________________Fe/Al 0.44 0.55 0.40 0.09Ti/Al 0.023 0.005 0.015 0.015Si/Al 0.11 0.011 0.05 0.030O/Al 0.50 0.90 0.31 0.67S/Al -- -- 0.22 0.19______________________________________ Fe*(2p):711/724; Ti*(2p):458.5/463.2; Si*(2p):103.4; Al*(2p):74.6; Fe**(2p):707/712; Ti**(2p):458.5/463.2; Si**(2p):103.4; Al**(2p):74.6; O(2p):510/511; S**(2p):161; O**(2p):510/511;

It can be seen that the sample chemically activated present a different composition than the other activated by air. This unexpected change in composition are produced by metal migration during chemical treatment to the bulk or from the bulk of the catalyst. Since the relative species present in surface are changed, the modification is hopefully reasonable of the activity improvement.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

Claims

1. A method for producing a catalyst for use in the conversion of heavy hydrocarbons to light ones by the thermal and chemical treatment of a natural occuring material characterized by an element composition comprising aluminum, iron, silicon, magnesium and titanium comprising the steps of treating said natural occurring material with air and steam at a temperature of from about 300.degree. to 900.degree. C. for about 1 to 36 hours at a partial pressure of steam of from about 20 to 700 mmHg and further treating the heated and steamed natural occurring material with H.sub.2 +H.sub.2 S at a temperature of from about 200.degree. to 500.degree. C. for about 1 to 12 hours at a pressure of H.sub.2 S of from about 20 to 450 mmHg whereby elemental migration occurs between the surface and bulk of the material such that the chemical composition on the surface of the material is changed thereby improving catalytic activity.

2. A method according to claim 1 including the steps of treating the heated and steamed natural occuring material with H.sub.2 +H.sub.2 S so as to obtain a catalyst having a sulphur content of between 3 to 40 weight % sulphur.

3. A method according to claim 1 wherein said heated and steamed natural occurring material is treated at a temperature of from about 250.degree. to 400.degree. C. for about 3 to 5 hours.

4. A method according to claim 3 including the steps of treating the heated and steamed natural occurring material with H.sub.2 +H.sub.2 S so as to obtain a catalyst having a sulphur content of between 8 to 30 weight % sulphur.

5. A method according to claim 1 including the steps of treating said natural occurring material with air and steam and H.sub.2 +H.sub.2 S so as to obtain a catalyst having the following physical properties

______________________________________Surface area, m.sup.2 /g 60 to 150Porous Volume, cc/g 0.30 to 0.43Mean Pore Radius, .ANG. 35 to 145Porous volume distribution:PV with R 10 .ANG., % 1 to 50PV with 10 .ANG. R 100 .ANG., % 10 to 45PV with R 100 .ANG., % 30 to 70______________________________________

and a surface chemical composition of from about

0.1 to 50 wt. % Al

1 to 50 wt. % Fe

0.1 to 30 wt. % Si

0.1 to 30 wt. % Mg

0.1 to 10 wt. % Ti 3 to 40 wt. % S.

6. A catalyst for use in the conversion of heavy hydrocarbons to light ones, said catalyst being prepared from a natural occurring material characterized by an elemental composition comprising aluminum, iron, silicon, magnesium and titanium by the thermal and chemical treatment of said natural occurring material with air and steam and H.sub.2 +H.sub.2 S, said catalyst having the following physical properties

______________________________________Surface Area, m.sup.2 /g 50 to 500Porous Volume, cc/g 0.20 to 0.60Mean Pore Radius, .ANG. 20 to 200Porous Volume Distribution:PV with R 10 .ANG., % 0 to 100PV with 10 .ANG. R 100 .ANG., % 0 to 100PV with R 100 .ANG., % 0 to 100______________________________________

and a surface chemical composition of from about

0.1 to 50 wt. % Al

1 to 50 wt. % Fe

0.1 to 30 wt. % Si

0.1 to 30 wt. % Mg

0.1 to 10 wt. % Ti

3 to 40 wt. % S

such that said catalytic activity is improved so as to produce the greatest possible quantity of light hydrocarbons from said heavy hydrocarbons upon treatment in a hydrotreatment zone with no significant production of pitch.

7. A catalyst according to claim 6 wherein said catalyst has a

______________________________________Surface Area, m.sup.2 /g 55 to 200Porous Volume, cc/g 0.22 to 0.50Mean Pore Radius, .ANG. 30 to 150Porous Volume Distribution:PV with R 10 .ANG., % 1 to 80PV with 10 .ANG. R 100 .ANG., % 5 to 50PV with R 100 .ANG., % 5 to 80______________________________________

and a surface chemical composition of from about

1 to 30 wt. % Al

5 to 48 wt. % Fe

5 to 20 wt. % Si

0.1 to 20 wt. % Mg

2 to 5 wt. % Ti

8 to 30 wt. % S.

8. A catalyst according to claim 6 wherein said catalyst has a

______________________________________Surface area, m.sup.2 /g 60 to 150Porous Volume, cc/g 0.30 to 0.43Mean Pore Radius, .ANG. 35 to 145Porous volume distribution:PV with R 10 .ANG., % 1 to 50PV with 10 .ANG. R 100 .ANG., % 10 to 45PV with R 100 .ANG., % 30 to 70______________________________________

and a surface chemical composition of from about

1 to 30 wt. % Al

5 to 48 wt. % Fe

5 to 20 wt. % Si 0.1 to 20 wt. % Mg 2 to 5 wt. % Ti

8 to 30 wt. % S.

9. A catalyst according to claim 6 wherein said natural occurring material is selected from the group consisting of bauxite, laterite iron mineral and laterite nickel-iron mineral.

10. A catalyst according to claim 6 wherein said natural occurring material is a bauxite type iron mineral wherein said catalyst has the following physical properties

______________________________________Surface Area, m.sup.2 /g 45 to 150Porous Volume, cc/g 0.30 to 0.45Mean Pore Radius, .ANG. 35 to 145Porous Volume Distribution:PV with R 10 .ANG., % 1 to 50PV with 10 .ANG. R 100 .ANG., % 10 to 45PV with R 100 .ANG., % 30 to 70______________________________________

and a surface chemical composition of from about

18.5-34.5 wt. % Al

3.3-23.1 wt. % Fe

0.3-10.5 wt. % Si

0.5-2.0 wt. % Ti

8.4-17.3 wt. % S.

11. A catalyst according to claim 6 wherein said natural occurring material is a laterite iron mineral wherein said catalyst has the following physical properties

______________________________________Surface Area, m.sup.2 /g 45 to 150Porous Volume, cc/g 0.30 to 0.45Mean Pore Radius, .ANG. 35 to 145Porous Volume Distribution:PV with R 10 .ANG., % 1 to 50PV with 10 .ANG. R 100 .ANG., % 10 to 45PV with R 100 .ANG., % 30 to 70______________________________________

and a surface chemical composition of from about

12.3-30.0 wt. % Al

24.7-48.4 wt. % Fe

0.8-2.3 wt. % Si

2.0-4.8 wt. % Ti

10.0-25.1 wt. % S.

12. A catalyst according to claim 6 wherein said natural occurring material is a laterite nickel-iron mineral wherein said catalyst has the following physical properties

______________________________________Surface Area, m.sup.2 /g 45 to 150Porous Volume, cc/g 0.30 to 0.45Mean Pore Radius, .ANG. 35 to 145Porous Volume Distribution:PV with R 10 .ANG., % 1 to 50PV with 10 .ANG. R 100 .ANG., % 10 to 45PV with R 100 .ANG., % 30 to 70______________________________________

and a surface chemical composition of from about

0.2-3.4 wt. % Al

6.8-60.4 wt. % Fe

2.5-19.5 wt. % Si

2.0-18.9 wt. % Mg

0.7-3.6 wt. % Ni

7.4-28.6 wt. % S.