NO774325L - PROCEDURE FOR REMOVING ALKYL LEAD POLLUTIONS FROM LIQUID HYDROCARBONES - Google Patents

Description

"Procedure for the Removal of Alkyl Lead Contaminants

from liquid hydrocarbons".

The invention relates to a method for removal

of alkyl lead contaminants from liquid hydrocarbons.

Lead and its compounds, especially alkyl lead, R4Pb, are recognized as naturally occurring in crude oil. However, lead is found in crude oils and their distillate fractions and is usually traced back to lead contamination in gasoline.

It is known to use copper (II) chloride that is impregnated on non-graphitic carbon or on silica gel for the removal of lead contamination from unleaded petrol, cf. A-. A. Zimmerman, G.S. Musser et al., SAE Fuels and Lubricants Meeting.

(Houston 6/3-5/75) Technical Paper; Chemical Abstracts, Volume 85-1976, 49026 G. It is also known to remove lead from motor fuels for internal combustion engines by contacting the fuel with a strongly acidic cation exchanger (German Patent No. 2,361,025), and to remove dissolved organic lead compounds from various liquid hydrocarbons by pretreatment with SiCl^, CuCl2, CuBr2, I2 or I2 combined with an acid followed by the pretreated hydrocarbon being brought into contact with activated carbon and an acid-treated clay or silica gel (US patent no. 3 893 912). However, significant amounts of lead contamination remain after such treatments. Additional lead contamination can occur during shipping, e.g. when a naphtha reformer feed is purchased at one location and shipped to another for reforming.

The present invention is therefore directed to a new. method where practically all the lead contaminants contained in a particular liquid hydrocarbon solution are removed. For example must. raw material for reformer units in refineries must be practically free of lead contamination in order to guarantee reasonable economy in operation. Contamination of raw material for the reformer in the form of lead contaminants puts the reformer plant out of balance and causes unnecessary poisoning of the reformer caralyser. Using the method described here, lead pollution is reduced in e.g. naphtha reformer raw material of 75 ppm to less than 5 parts per billion. Accordingly, the invention is more particularly directed to a method of carrying out the removal of alkyl lead contaminants from liquid hydrocarbon media containing said contaminant, comprising bringing the hydrocarbon at a temperature below its boiling point into contact with a solid absorbent having an amount of anhydrous HCl - gas adsorbed in it which is sufficient to effect a substantial reduction in the concentration of the contaminant and to maintain contact until practically all of the said contaminant has been removed.

The new process in accordance with the invention is generally useful for the removal of alkyl lead contaminants from any liquid hydrocarbon media. It is suitable for treating petroleum oils with lubricating viscosity, distillate fuel oils, gasoline and other light liquid hydrocarbon products including both mineral oil and synthetic hydrocarbon products. The preferred embodiment is the removal of lead contaminants from reformer feedstocks.

A large selection of solid adsorbents can be used with advantage. These adsorbents (carriers) can be crystalline or amorphous. However, amorphous adsorbents have been found to be more advantageous. In any case, the adsorbents must have sufficient surface area and porosity to adsorb an effective amount of the anhydrous HC1. The surface area of the adsorbents useful in connection with

the invention, is, from approx. 5 to approx. 1000 m 2/g. The surface area of crystalline zeolite adsorbents is usually from approx. 10.0 to approx. 1000 m<2>/g and more preferably from 100 to approx. 750 m<2>/g. The surface area of the amorphous adsorbents is usually

from approx. 5 to approx. 750 m 2/g and preferably from approx. 150 to 600 m 2/g. The average pore diameter of the adsorbent should be from approx. 3 to approx. 200Å. The average pore diameter of crystalline zeolite adsorbents used in connection with the invention is usually less than about 10Å, i.e. from approx. 3-9Å. For amorphous adsorbents it is usually from approx. 10-20 to approx. 200 Å and preferably from approx. 20-100Å.

Suitable adsorbents include, synthetic or naturally occurring materials - e.g., faujasite (zeolite X, zeolite Y), mordenite, and various other zeolites which may be suitable, e.g. zeolite ZK-4, zeolite ZSM-5, as well as such inorganic materials as bauxite, clay, silicon dioxide and/or metal oxides and naturally occurring clay species which may be compounded with the zeolites, which include montmorillonite

and the kaolin families, which include the sub-bentonites and kaolins commonly known as Dixie-McNamme-Georgia and Florida clays, or others in which the main mineral constituents are halloysite, kaolinite, dickite, nacrite or anauxite and activated carbon. Such clay species can be used in their raw state as they are extracted from the mines or initially subjected to calcination, acid treatment or chemical modification.

In addition to the above-mentioned materials, zeolites used in connection with the invention can also be composed of such material as bauxite, aluminum oxide, silicon oxide/aluminum oxide, silicon oxide/magnesium oxide, silicon oxide/zirconium oxide, silicon oxide/thorium oxide, silicon oxide, beryllium oxide, silicon oxide/titanium oxide as well as ternary mixtures, e.g. silicon oxide/alumina/thorium oxide, silicon oxide/alumina/zirconium oxide, silicon oxide/alumina/magnesium oxide and silicon oxide/magnesium oxide/zirconium oxide. Adsorbents selected from the group consisting of various forms of . silica, bauxite, mordenite, natural and synthetic clays, amorphous and crystalline aminosilicates, alumina and silica/alumina mixtures. Silicon oxide/alumina mixtures

can contain approx. 5-95% silicon oxide or preferably approx. 5-25% by weight or approx. 7^-95% by weight silicon oxide to aluminum oxide. Thermophoric cracking catalysts (TCC), e.g. newly made, used or regenerated bead types of TCC catalysts can be used in connection with the invention as adsorbents.

The effective amount of adsorbed anhydrous HCl gas will vary, depending on the type of adsorbent, adsorption conditions with regard to temperature and pressure as well as reaction parameters. Usually, the adsorbent described here will contain from approx. 0.001 to approx. 20% by weight adsorbed HC1 and preferably from approx. 0.1 to approx. 17.5% by weight, based on the total weight of the adsorbent.

IN

The procedure for removing lead contamination, e.g. tetraethyl or tetramethyl lead, from liquid hydrocarbons

is conveniently performed in a simple flow or batch process. A solution of the lead-contaminated hydrocarbon is passed over the adsorbent, e.g. NaX zeolite, amorphous silica, etc., lead compounds in the solution undergo a displacement hinge reaction giving an insoluble alkyl salt ie R^PbCl and a gaseous product ie RH. The gas escapes through the solution, and the insoluble salt remains on the adsorbent. The process is carried out at room temperature or at any temperature below the boiling point of the liquid hydrocarbons. Preferred operating conditions are a temperature of from approx. 25 to 60°C, LHSV of from approx. 5-20 and atmospheric or slightly higher pressure. A suitable adsorbent,. i.e. silica, alumina, mixtures thereof and calcined X and Y zeolites, e.g., calcined NaX, may be included

after the lead removal step to remove (ie adsorb) any HC1 that is desorbed during the lead removal step in the process. For a "wet" (ie with more than about 100 ppm water) hydrocarbon feedstock, a dryer using the above operating conditions and also using calcined NaX or another suitable dewatering agent may precede the lead removal step, e.g. commercial desiccants consisting of silica, alumina, mixtures thereof, and X and Y zeolites are suitable.

EXAMPLE 1

100 grams of NaX 1.6 mm extrudate was calcined in a glass reactor at .350°C in argon for approx. 16 hours and cooled at room temperature. A stream of anhydrous hydrogen chloride gas was brought into contact with the zeolite (pore diameter approx. 7-9Å; surface area.l approx. 750 m<2>/g), downstream until the loading was complete, i.e. approx. 15.6-17.5% by weight HC1 at equilibrium at room temperature. When anhydrous HC1 comes into contact with the adsorbent, an exothermic reaction zone develops at the top of the reactor. This zone moves down the layer. After the bottom section of the reactor had cooled, in an atmosphere of HCl gas, the reactor was flushed with dry argon for approx.

1 minute to remove any slightly desorbed HC1.

EXAMPLE 2

80 grams of a NaX molecular sieve, 1.6 mm extrudate, was placed in a glass reactor, calcined at 4.00°C in argon for approx. 16 hours and cooled to room temperature. Anhydrous HCl gas was then passed downstream (as in Example 1) over the calcined adsorbent until the HCl loading was complete. The NaX extrudate adsorbed approx. 12.5 g HC1, or approx. 15.6% by weight, and was otherwise prepared in the same way as in example 1.

EXAMPLE 3

32.1 grams of a commercially obtained amorphous silica/aluminum adsorbent ("Durabead"-1) with the following general. properties: .pore diameter approx. 80Å; surface area approx. 200 m /g and a silicon oxide:alumina ratio of approx. 9:1, was calcined in argon at 350°C for approx. 16 hours and cooled to room temperature. Dry HCl gas was then passed downstream over the catalyst until equilibrium at. room temperature had been reached. 0.345 grams of HC1 (about 1% by weight) was adsorbed by the adsorbent.

EXAMPLE 4

A regular gasoline containing 1.8 g/3.785 L of Pb was used as a 10% contaminant in a Pb-free naphtha reformer feedstock. A suitable reactor containing the NaX adsorbent.

with adsorbed anhydrous HC1 as described in example 1, was connected with a feed pump. Naphtha was introduced at the bottom of the reactor at 0.6 LHSV and at a temperature of approx. 5°C below the boiling point of the naphtha by means of a metering pump and moves upstream through the bed until it reaches the outlet at the top of the reactor. The naphtha is then collected as a product. Reformer naphtha properties are, as shown in Table 1, <5 ppb (parts per billion) lead before contamination and 75,000 ppb after contamination. The properties of the naphtha product are shown in table 2, after treatment with the adsorbent from example 2, the lead contamination was reduced to <5.

EXAMPLE 5 3.785 L of a hexane/toluene brine (70/30 vol) containing 174 ppm Pb was pumped upstream, 0.5 LHSV and at room temperature, through an adsorption system as described in Example 3, followed by another 3.785 L containing 340 ppm Pb. Finally, 1500 ml containing 450 ppm lead was used. 10 ml samples of product were taken for diagnostic Pb analyzes by Test Method A (described below) at 24 hour intervals. In addition, 500 mi samples were taken at approx. 25%, 65% and 75% HCl depletion points for ppb Pb analyzes by Test Method B (described below). Table 3 summarizes data obtained for samples of Pb-contaminated light hydrocarbon mixtures treated with the silica/alumina/HCl adsorption system from Example 3 at room temperature. Data in Table 3 show that the stoichiometry of the reaction is 1 mol HCl to 1 mol R^Pb. Thus, for that amount of HCl adsorbed, 0.345 g (9.45 mmol), a maximum of 1.958 g of Pb would be expected to react,

where R^Pb is .'a commercial mixture of tetraalkyl lead, . i.e. tetraethyl, tetramethyl, trimethylethyl, diethyldimethyl etc.

Table 3 further shows that with the 99.2% HCl that was used, the contact mass reduces the 450 ppm Pb in the feed to 38 ppm and a point of approx. 100% to >300 ppm and that alkyl lead compounds react with available HCl in the catalysts until all HCl is depleted.

Test method A is used for the determination of lead in reformer naphtha and similar light hydrocarbon raw materials at concentrations below 100 ppb, i.e. trace amounts of lead. Lead present as alkyl lead impurity and as naphthenates and other compounds decomposed by bromine is determined. Other metals do not interfere..

OVERVIEW OF METHOD A

A 500 ml sample is reacted in a suitable test bottle with 454 g (5N) of bromine diluted in carbonite tetrachloride to 1 liter, for 2 minutes at room temperature, and extracted, then with water. The extract is transferred to a test tube and aspirated into

in the burner of an atomic absorption spectrometer. The absorption at the 2170Å line is measured and converted to lead content using a calibration curve.

Test method B (ASTM D3237) is used for the analysis of materials to which no lead has been added, e.g. fuels containing 0.5 ppm or more of lead.

OVERVIEW OF METHOD B

The atomic absorption spectrophotometer is calibrated using commercially available standardizing solutions. The sample material is then aspirated directly into the instrument, and the absorption is measured.

As is clear from the data in the above tables, the adsorption system and the application method for this is a significant improvement from the state of the art.

EXAMPLE 6

Samples of naphtha (see Table 1) were contaminated by adding 0.2 ral of a 5 g Pb/3.785 L gasoline to 3.785 L Kuwait naphtha so that 88 ppb lead contamination was obtained. One went forward

as described above, using the adsorbent from example 3, see tables 4 and 5.

The data in Tables 4 and 4 illustrate that reformer feedstock containing as little as 88 ppb of contamination can be reduced even further to safe reformer levels, i.e., <5 ppm by the process of the invention.

Although preferred embodiments are exemplified,

one can resort to variations that are within the scope of the invention, which the person skilled in the art will easily understand.

Claims (19)

1. Method for removing alkyl lead contaminants from liquid hydrocarbons, characterized in that such a hydrocarbon is brought into contact with a solid adsorbent comprising 0.001 to 20% by weight of anhydrous hydrogen chloride adsorbed thereon. 2. Method as stated in claim 1, characterized in that an adsorbent is used which has an average pore diameter of 3-200Å and an average surface area of 5-1000 m 2 /g.' 3. Method as stated in claim 1 or 2, characterized in that an adsorbent is used which comprises 'silicon oxide, bauxite, mordenite, a natural or synthetic clay, an amorphous or crystalline aluminosilicate, aluminum oxide or silicon oxide/aluminum oxide. 4. Method as stated in claim 3, characterized in that a newly made, used or regenerated spherical thermophoretic cracking catalyst is used as adsorbent. 5. Procedure as stated in claim 3 or. 4, characterized in that an amorphous silicon oxide/alumina, silicon oxide/clay or another type of gel matrix is used as adsorbent which contains a smaller proportion of crystalline aluminosilicate zeolite. 6. Method as stated in any of claims 3-5, characterized in that zeolite X or zeolite Y is used as crystalline aluminosilicate. 7. Method as stated in Xrav 6, characterized in that a crystalline aluminosilicate is used which has an average pore diameter of 8-9Å and a surface area of 200-1000 m2/g. 8. Method as stated in any of the preceding claims, characterized in that it is used an amount of adsorbed hydrogen chloride of from 0.1 to 17.5% by weight. 9. Method as stated in any of the preceding claims, characterized in that the amount of adsorbed hydrogen chloride is from 1.0 to 17.5 V ect%. 10. Method as stated in any of claims 1-3 and 7-9, characterized in that silicon oxide/alumina oxide is used as adsorbent: with an average pore diameter of from 20-100Å and an average surface area of from 150 to 600 m 2/g. 11. Method as stated in claim 10, characterized • in that silicon oxide/alumina comprising from 5 to 95% by weight of silicon dioxide is used. 12. Method as stated in any one of the preceding claims, characterized in that the contaminant is tetraalkyl lead. 13. Method as stated in any of the preceding claims, characterized in that the said hydrocarbons are included in a naphtha suitable as reforming raw material. 14. Method as stated in any of claims 1-12, characterized in that the hydrocarbons are included in a motor fuel. 15. Method as stated in claim ^^ characterized in that the motor fuel is a petrol to which no lead has been added. 16. Method as stated in any of the preceding claims, characterized in that it continues to less than 5 parts per billion of said alkyl lead contamination remains in said hydrocarbons. 17. Method as stated in any one of the preceding claims, characterized in that it is carried out at a temperature of 25-60°C and a LHSV of 5-20. 18. Method as stated in any one of the preceding claims, characterized in that the liquid hydrocarbons are brought into contact with a desiccant before. contact with the adsorbent mentioned. 19. Method as stated in any of the preceding claims, characterized in that hydrogen chloride present in the hydrocarbons from which the contamination has been removed is adsorbed therefrom by contact with a hydrogen chloride.