Molten salt hydrofining process

BACKGROUND OF THE INVENTION

Field of the invention

This invention relates to a process for hydrofining heavy petroleum oils using a molten salt catalyst mixture 25 comprising cadmium halide, an alkali metal halide and optionally other metal salts as diluents and/or co-catalysts.

Description of the prior art

A steadily increasing demand for distillate petroleum products and decreasing supply of crude oils of low residue content provides increasing incentive for processes which upgrade high-boiling residual polynuclear hydrocarbon stocks. There are available large quantities of naphthenic, aromatic or mixed based crudes from which some distillate products are recoverably by traditional means. However, the residual fraction, in which is concentrated relatively large quantities of materials containing sulfur, oxygen, nitrogen, and organo-metallic compounds must be disposed of. In the past, low-value stocks have been used for industrial and marine fuels but the supply exceeds demand. Moreover, air pollution restrictions imposed on many industrial areas prevent the use of these high sulfur and nitrogen fuels.

Current technology for upgrading these fuels, such as thermal cracking, catalytic cracking, and catalytic hydrogenation are less than satisfactory. Cracking or hydrogenation is relatively costly when applied to residual stocks due to rapid catalyst deactivation by the high _5Qcontent of contaminants and catalyst poisons found in residues.

The use of molten salt catalytic systems has long been recognized as a method to obviate many of the difficulties encountered in more conventional refining techniques. In -the main, previous work has concentrated on the use of molten caustics, such as sodium hydroxide, for example U.S. 3,051,645, issued August 1962. More recently, acidic molten salt systems, such as zinc chloride, have been proposed for hydrocarcking (Gorin et al., U.S. ₆θ 3,355,376, issued November 1967). Use of a molten salt catalyst offers many advantages over conventional heterogeneous catalyst systems as, for example, continual renewal of catalyst surface, close temperature control by better and more uniform heat transfer and the possibility gg of continuous removal and relatively easy handling of contaminants, such as metals, which seriously interfere with catalyst performance in conventional heterogeneous phase catalytic systems.

The use of acidic salt systems also presents a number γθ of problems. The salt must have reasonably high catalytic activity and the ability to retain activity without sub- stantial decline over a period of use. The hydrocarbons and salt should be easily separated and the salt should be easily regenerated or otherwise restored for reuse after contamination or deactivation.

Th solubility of heavy hydrocarbons in some molten salt systems makes separation difficult. This feature alone is a serious economic deterrent to proposed molten salt hydroconversion processes and represents a major drawback of such systems.

We have now invented a process for hydrofining and/ or cracking heavy petroleum oils using a molten salt mixture possessing the required characteristics and advantages enumerated above. By hydrofining is meant, within the context of the present invention, hydrogenation, desulfurization, denitrification, and metals removal.

SUMMARY OF THE INVENTION

The process of the invention in broad aspect comprises contacting heavy petroleum fractions with a molten salt mixture or solution comprising cadmium halide and other metal halides as later specified, in the presence of hydrogen at elevated temperature and pressure.

The heavy petroleum fraction feed to the present process may be any high boiling hydrocarbon oil at least about 50% by volume of which boils above about 450° F. Though lighter hydrocarbons can, in principle, be processed, the present process is most advantageous for treatment of oils containing materials which cannot be distilled in commercial equipment without extensive cracking, e.g., residual materials and hydrocarbon oils, containing asphaltenes, resins and the like. The process finds its greatest utility in the treatment of stocks containing appreciable amounts of hetero-atoms and/or metals. It is, therefore, particularly useful for the treat35 ment of reduced crudes, pitch, vacuum residues, cracked gas oils, residues, and the like which cannot otherwise be deeply flashed without excessive carryover of metal contaminants. Tn addition, certain crude petroleum oils . which contain only small amounts of gasoline and kerosene ⁴⁸ boiling-range hydrocarbons and which have been topped to remove lighter components may also be processed.

Certain petroleum crude oils from tar sands and oils from shale or coal thus may be processed.

._ The metal salt catalyst of the invention comprises cadmium halide (chloride, bromide or iodide) which is mixed with and dissolved in alkali metal halides. Examples of suitable alkali metal halides are halides (chlorides, bromides, or iodides) of lithium, sodium, and potassium, additional metal salts as diluents or co-catalysts as, for example, any mineral acid salt of metals of Group I, Π, ΠΙ, IV-B, VI-B, VH-B, and VIII of the Periodic Table of Elements. The preferred co-catalytic additional salt is zinc halide. In general, at least about 5% w. alkali metal salt should be contained in the mixture. The alkali metal halide functions to reduce markedly the solubility of hydrocarbon in the salt melt, thus providing a mixture which can easily be separated from the hydrocarbon feed and products, as for example, by phase separation. The present process requires the use of an amount of molten salt mixture in excess of that required for stoichiometric reaction with the non-hydrocarbon elements of the heteroatom components in the feed, i.e., greatly in excess of that required for reaction with nitrogen, oxygen and sulfur in the feed. The invention lies in the catalytic effect of the salt and not in the stoichiometric reactions which concurrently occur. The use of a relatively large excess of salt, relative to feed, characterizes one of the distinctions of the present process over previously known process for hydrogenation of hydrocarbonaceous material, such as coal, by impregnation of the material to be hydrogenated with a small quantity of metallic salt.

3,679,577

The process is carried out in the presence of hydrogen at elevated temperatures and pressures and is characterized by very short reaction contact time.

Temperatures in the range of about 650-850° F. are used and preferably in the range from about 750-810° F. 5 Hydrogen pressures of between about 500-5,000 p.s.i.g. should be used—the total pressure depending, inter alia, upon the purity of the hydrogen used. It is an especially noteworthy characteristic of the present invention that reaction contact time is very short. In general, a contact 10 shown in Table I. From these data it can be seen that the salt mixtures containing cadmium halides effectively increase API gravity (indicating lower molecular weight), reduce the sulfur and nitrogen content of the feed, remove vanadium, and increase hydrogen content of the products. Run number N-l 1 illustrates that the absence of cadmium halide leads to thermal cracking only (note the negative hydrogen consumption denoting a positive hydrogen production) with little or no removal of sulfur, nitrogen or metals.

TABLE I.—MOLTEN SALT REACTIONS

Run Number

<td></td><td> Feed</td><td> N-7</td><td> N-8</td><td></td><td> N-9</td><td> N-10</td><td> N-ll</td>

<td> Salt (percent w.)_____________ Temp., ° F......-____________ Pressure, p.s.i.g.............. WHSV (gm. feed/gm. salt/hr ..................</td><td></td><td> CdL (31.2) LiCl (31.3) KOI (37.5).. 800 2,000 0.31</td><td> CdCli (80.0) KC1 (20.0) 800 2,000 0.19</td><td> CdL KI</td><td> (71.3) (28.7) 800 2,000 o.ir</td><td colspan="2"> CdBn (65.4) LiCl (45.5) NaBr (34.6) K€1 (54.5) 800 800 2,000 2,000 0.22 0.22</td>

<td> Hz/oil (mole)................. Conversion, percent w. (100-450+° F.)............. Hi consumption, s.e.f./bbl. — API at 60° F________________ Sulfur, percent w___________ Total N, p.p.m............. Metals, (p.p.m.)____________</td><td> 22.9 1.82 1,600 V (15)</td><td> 16.6 39.6 667 . 34.4 1.09 950 V (1 &lt;5)</td><td> 16.6 19.0 28.0 1.31 1,400 V (i &lt;5)</td><td colspan="2"> 16.6 24.9 254 31.5 1.02 900 V (1 &lt;5)</td><td> 16.6 33.7 519 32.7 0.95 1,200 V (1 &lt;5)</td><td> 16.6 23.7 —428 28.4 1.44 1,500 V(il)</td>

6 p.p.m. is the analytical senstivity.

time of between about 1.0 to 10 seconds is sufficient to obtain the desired results. By contact time is meant the time in which the feed and molten salt catalyst are in contact in the reaction zone. Longer contact time may, of course, be used depending, inter alia, upon the specific nature of the feed (i.e., boiling range, hetero-atom and metallic impurities), the degree of conversion desired and the temperature and contact efficiency of the specific reactor system employed.

As in other hydroconversion processes, excess hydrogen is usually recovered, at least in part, from the reaction zone effluent and recycled to the reaction zone together with additional makeup hydrogen. Pure hydrogen is not required and any suitable hydrogen-containing gas which is predominantly hydrogen can be used. For example, hydrogen-rich gas containing on the order of about 70% v. or more hydrogen which is obtained from a catalytic reforming process can be used.

Various methods of contacting the hydrocarbon feed with the molten salt catalyst may be employed. One simple method comprises merely passing the hydrocarbon into a molten salt bath. Various types of reactors may be used as will readily occur to those skilled in the art. Reactors employing a dispersed gas/liquid system have been found suitable. Reactors employing concurrent plugflow of the fluid (molten salt, hydrogen and hydrocarbon feed) with a high degree of gas-liquid and liquid-liquid contacting are especially useful. The process may be operated continuously or batchwise but is most efficiently and desirably conducted continuously in a short contact time plug-flow reactor system.

The following examples serve to further illustrate the practice and advantage of the invention and are not to be construed as limitations thereof.

EXAMPLE I

A series of experiments was made which illustrates the process of the invention. A straight run residue feed (properties given in Table I) was contacted with various molten salt mixtures in a tubular reactor packed with ceramic Berl saddles to aid hydrocarbon-salt contacting. The molten salt mixtures were transferred to the reactor and the reactor pressured with hydrogen. Preheated hydrocarbon feed and hydrogen gas was introduced into the bottom of the reactor and the products collected at an outlet located at the top of the reactor. Hydrocarbon was easily phase-separated from the salt since the alkali metal halide efficiently reduces hydrocarbon solubility. Salt composition, operating conditions and results are

EXAMPLE Π

The following experiments illustrate the hydrocracking 30 potential of a molten salt system containing cadmium halide and zinc halide as co-catalysts. A Straight Run Residue (properties shown in Table Π) was hydrocracked using a molten salt mixture containing cadmium bromide, zinc bromide and sodium bromide. For comparison, a run 35 was made on a zinc bromide/sodium bromide mixture.

The reaction was carried out in a tubular reactor as described in Example I, and the salt composition, operating conditions, and results are shown in Table Π.

TABLE 11

Run

Feed N-22 N-23

Salt composition, (percent w.)____________

Operating conditions: Temperature, °F _____________________

Pressure, p.s.i.g......................

WHSV (gm. feed/gm. salt/hr.).._______

Hs/oil mole ratio______________________

Yields, percent w.: CI±4-CsH,2--------------------------0,-450° F........ 2.3

450-615° F 17.7

615-900° F_____ 35.5

900° F.+_____________ 44.5

Liquid product properties: Sulfur, percent w 1.82

Nitrogen, p.p.m.w_ - 1,500

Vanadium, p.p.m__________15

ZnBrj (80.0)

CdBr₂ (15.0)

NaBr (5.0)

ZnBr (80.0)

NaBr (20.6)

750 1,500 0.15 16.0

44.9

30.2

15.6

7.7

1.6

0.14 &lt;7

0.42 &lt;5

As these data show, the salt melt containing cadmium bromide produced significantly better sulfur and nitrogen 60 removal and was more effective in reducing heavy (900°

F. plus) boiling-range material—at these conditions down to 1.6% w. basis feed.

These examples illustrate the potential of the process of the invention. Many ways of utilizing this process in 65 the conversion of heavy petroleum stocks both for removing sulfur, nitrogen and metal impurities, increasing hydrogen content of products, and reducing molecular weight within the scope of the invention will be obvious to those skilled in the art. The useful conversion of here70 tofore uneconomic feed stocks containing large quantities of sulfur, nitrogen, and metal impurities (which poison conversion catalysts), and large amounts of heavy fractions boiling above 900° F. is an increasing economic necessity. The process of the invention is a process useful ⁷⁵ for that purpose. The process may be employed, for ex3,679,577 ample, under mild conditions to remove metals and hetero-atom impurities making a product suitable for further more conventional processing. On the other hand, the process is capable of extensive cracking directly (as shown in Example Π) and may be so employed. Various combinations of such operation may be chosen depending on individual requirements.