WO2014202594A1

WO2014202594A1 - Process for removing metals from high-boiling hydrocarbon fractions

Info

Publication number: WO2014202594A1
Application number: PCT/EP2014/062704
Authority: WO
Inventors: Giuseppe CUSATI; Roberta Olindo; Gerhard Birke
Original assignee: L'Air Liquide, Société Anonyme pour l'Etude et l'Exploitation des Procédés Georges Claude
Priority date: 2013-06-20
Filing date: 2014-06-17
Publication date: 2014-12-24
Also published as: DE102013106441A1

Abstract

Process for Removing Metals from High-Boiling Hydrocarbon Fractions Subject-matter of the invention is a process for removing metal impurities from hydrocarbon fractions, as they are obtained for example as product of the Fischer-Tropsch synthesis by using a suspended catalyst. According to the invention, the hydrocarbon fraction to be treated therefore is mixed in the molten condition with an aqueous phase under stirring at a temperature of at least 100 ° C, which aqueous phase has a pH value of not more than 5 and furthermore contains a complexing agent. The metals to be removed are separated in a separate phase and can be removed from the process for example by means of filtration.

Description

Process for Removing Metals from High-Boiling Hydrocarbon Fractions

Field of the Invention

This invention relates to a process for removing metals from high-boiling hydrocarbon fractions, in particular for separating catalyst-induced nickel, cobalt and aluminum impurities from the primary products of a hydrocarbon synthesis, for example by the Fischer- Tropsch process.

Prior art

Hydrocarbons can be obtained as synthesis products from chemico-catalytical processes, such as for example the Fischer-Tropsch process, the fundamentals of which have been described in detail in the literature, e.g. in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 1998 Electronic Release, keyword "Coal Liquefaction", chapter 2.2 "Fischer-Tropsch Synthesis". A modern process variant is the conversion of synthesis gas in a suspension of the solid, fine-grained catalyst into the liquid product hydrocarbons (so-called slurry process). There are used highly active catalysts, which as active components contain metals, for example cobalt, on a carrier material, for example alumina, as it is described in the US patent specification US 4,801 ,573. The International Patent Application WO 98/27181 A1 - beside numerous other publications - proposes a process for separating the catalyst suspension from the hydrocarbon product. The product hydrocarbons obtained often contain significant amounts of heavy metals. A possible cause of this undesired heavy metal contamination are abrasion and corrosion processes on the catalysts and/or the container material used in the synthesis process. These methods based on mechanical separation methods, however, only are suitable for the separation of particulate metal impurities, but not for separating metals chemically bound in the hydrocarbon phase or dissolved in finely dispersed or colloidal form.

In addition to the heavy metal contamination, impurities with the metal of the catalyst carrier matrix (e.g. aluminum) also are observed. The described metal contamination can be disturbing in a further chemico-catalytical conversion of the product hydrocarbons, since the same can become active as catalyst poison. In addition, heavy metal contaminations, independent of the substance in which they are contained, represent a potential environmental and health hazard. Particular reference should be made to nickel and cobalt, which are classified as carcinogenic. On the other hand, both heavy met- als represent valuable catalyst components, which should be supplied to a recycling process, in order to avoid losses.

The German patent specification DE 1212662 describes a method for the treatment of hydrocarbon oils for the purpose of removing metallic impurities, which are detrimental for the catalysts used in their conversions. It is proposed to treat the contaminated hydrocarbon oils with a solution of hydrogen fluoride in an organic solvent, whereby the metals are transferred into a hardly soluble precipitate which subsequently can be separated with a mechanical separation method. The above-described problems in the treatment of a two-phase mixture of hydrocarbon phase and aqueous phase thereby are avoided. What is disadvantageous, however, is the use of the highly reactive, gaseous hydrogen fluoride for preparing the treatment solution for reasons of occupational safety and handling.

The US patent specification US 4,518,484 indicates a method for the treatment of metal- containing hydrocarbon feed streams, which comprises the following steps: (a) contacting the hydrocarbon feed streams in an extraction zone with at least one hydrocarbon solvent with 2 to 10 carbon atoms per molecule under supercritical conditions in the presence of an organophosphorus-based demetalizing agent, (b) discharging a top product from the extraction zone, which contains the hydrocarbons largely liberated from metals, and a bottom product which contains the solvent loaded with the metals. What is to be regarded as disadvantageous is the expensive procedure, in particular the adjust- ment of supercritical conditions.

Subject-matter of the patent application DE 10201 1013470 A1 is a process and means for removing metal impurities from hydrocarbon fractions, as they are obtained for example as product of the Fischer-Tropsch synthesis by using a suspended catalyst. The treatment of the feed hydrocarbon fractions is effected with a demetalizing agent, comprising at least one sulfur source and at least one basic compound, under anhydrous conditions. The metals to be removed are obtained as precipitate which can easily be separated with a mechanical separation method, for example the filtration. The International Patent Application WO 2006/053350 A1 discloses a method for separating metal impurities such as aluminum or cobalt from hydrocarbon fractions, in which the hydrocarbon fraction is treated with an aqueous phase at temperatures of at least 160 °C, typically about 170 °C, wherein the aqueous phase optionally can comprise an acid, for example an organic acid such as maleic acid. Detailed conditions of this meth- od, such as the set pH value, however are not disclosed there.

Description of the Invention

Therefore, it is the object underlying the present invention to indicate a simple process for removing metal impurities from high-boiling hydrocarbon fractions, which is charac- terized by a simple procedure and which can be carried out without the use of substances with a high hazard potential.

The solution of the object according to the invention substantially results from the features of claim 1 by a process for producing a hydrocarbon fraction poor in metals, wherein the metals are chemically bound in the hydrocarbon fraction or are dispersed in the hydrocarbon fraction in colloidal or finely dispersed form, comprising the following steps: (a) providing the metal-containing hydrocarbon fraction in liquid form,

(b) contacting the liquid, metal-containing hydrocarbon fraction with a water-containing liquid phase having a pH value of not more than 5, preferably not more than 3, at temperatures of at least 100 °C, preferably at least 200 °C under stirring, wherein the aque- ous liquid phase furthermore contains a complexing agent,

(c) terminating stirring, cooling and carrying out a phase separation, wherein a light, hydrocarbonaceous liquid phase, a heavy, water-containing liquid phase and a third phase is obtained, which is arranged between the light, hydrocarbonaceous liquid phase and the heavy, water-containing liquid phase and which comprises hydrocarbon, water and metal particles,

(d) separating the metal particles as metal-containing precipitate from the third phase with a mechanical separation method,

(e) separating the third phase liberated from metals into a light, hydrocarbonaceous liquid phase and a heavy, water-containing liquid phase, combining the separated liquid phases with the corresponding liquid phases obtained in method step (c),

(f) discharging the hydrocarbonaceous liquid phase as hydrocarbon fraction depleted of metals.

Further advantageous aspects of the process according to the invention can be found in the sub-claims.

For the treatment by the method according to the invention, the feed hydrocarbon fraction must be present in liquid form. Wax-like hydrocarbons, as they are obtained for example as products of the Fischer-Tropsch process, possibly must be molten before the treatment.

From the prior art, for example WO 2006/053350 A1 , it is known that an aqueous acid solution effects an agglomeration of the metallic impurities in a hydrocarbon fraction. These agglomerated metallic particles then can be separated from the hydrocarbon frac- tion by mechanical separation methods, for example the filtration or decantation. Detailed method conditions, however, are not mentioned in WO 2006/053350 A1 . Surprisingly, it was found in connection with the invention that after use of an aqueous EDTA solution having a pH value of 3, the metals were removed completely at 100 °C within the measurement accuracy. By increasing the pH value to 5, under otherwise identical conditions, a still far-reaching, but no longer complete metal removal was ob- served. The optimum pH range therefore lies between 3 and 5, particularly preferably at pH 3. Even smaller pH values are not preferred, since then the corrosiveness of the aqueous phase will rise and thus more corrosion-resistant and therefore more expensive materials will have to be used for the respective plant sections. The temperature also is an important influencing variable for the effectiveness of the method according to the invention. At a temperature of 150 °C a complete removal of the metal impurities within the measurement accuracy has been achieved already after 10 minutes, and in addition a smaller amount of EDTA was used. By further increasing the temperature, the required EDTA quantities could be reduced even further. There was each formed a third phase in which the metals are accumulated and which optically is distinctly visible. This third phase was removed by mechanical separation, preferably by filtration. The hydrocarbon fraction liberated from metal impurities then can be separated from the water by a simple phase separation. Further preferred aspects of the invention

In a preferred aspect of the invention the filtration is used in the process step according to claim 1 , item (d). The use of the centrifugation or decantation also is possible; however, the filtration offers an optimum with regard to expenditure and separation efficiency achieved.

In a further aspect of the invention, the water-containing liquid phase is recirculated after an optional treatment by the process step according to claim 1 , item (b). For certain applications of the invention in connection with integrated plant concepts it is advantageous that water can be obtained as reaction product of a preceding or downstream stage and thus already is present in the process, for example during the production of synthesis gas or the subsequent Fischer-Tropsch synthesis, so that here only a minimum or possibly even no fresh-water feed stream at all is required. It appears to be possible in principle to again and again circulate the used water, possibly after treatment.

It is advantageous when the complexing agent forms complexes of the chelate type with the metals to be removed. In this way, particularly stable metal complexes are formed and the metals are removed from the hydrocarbon fraction in a particularly efficient way. Particularly preferably, ethylenediaminetetraacetic acid and/or ethylenediaminetetraace- tate (EDTA) are used as complexing agents. Exemplary embodiments and numerical examples

Further developments, advantages and possible applications of the invention can also be taken from the following description of non-limiting exemplary embodiments and numerical examples. All features described form the invention per se or in any combination, independent of their inclusion in the claims or their back-reference.

General procedure in the experiments

For the described experiments a weight ratio between hydrocarbon mixture and water of approximately 1 :1 was used. The water quantity probably might be reduced, however, so that all metals might be concentrated in a smaller volume. This would lead to further advantages with regard to the process economy, since the quantity of the recirculated and possibly treated water would be reduced further. The stirring speed was the same in all experiments and constantly was 350 revolutions per minute. The mixture was stirred constantly from beginning to end. There can also be used other, preferably higher stirring speeds, as long as the same provide an intensive intermixing of the liquid mixture. The required duration of treatment then must possibly be adapted, in order to achieve the desired degree of metal separation. Suitable time periods can be determined by routine experiments. Some experiments with elevated pressure were carried out in an autoclave with an internal volume of 300 ml.

Example 1 : Invention

100 g of a hydrocarbon mixture (wax fraction from the Fischer-Tropsch synthesis with a metal content of about 351 wt-ppm (aluminum 220 wt-ppm, nickel 109 wt-ppm, cobalt 22 wt-ppm)) were molten at 85 °C and presented in a glass flask under reflux cooling. The determination of the metal content was effected by X-ray fluorescence analysis (RFA) with the method Uniquant 2. To the molten wax 100 g of an aqueous EDTA solution with a pH value of 5 were added. The amount of EDTA in the water corresponded to 5 g. The mixture was heated to 100 °C under vigorous stirring. The experimental arrangement was under atmospheric pressure. This temperature was maintained for 4 hours.

After terminating stirring, a grey-green phase was formed, which contained most of the metals and could be separated by a fluted filter. The filtrate was separated into two liquid phases (water and hydrocarbon).

The analysis of the hydrocarbon fraction still revealed a metal concentration of 61 wt- ppm. Hence, about 81 % of the metal impurities were removed. Example 2: Invention

100 g of a hydrocarbon mixture (wax fraction from the Fischer-Tropsch synthesis with a metal content of about 351 wt-ppm (aluminum 220 wt-ppm, nickel 109 wt-ppm, cobalt 22 wt-ppm)) were molten at 85 °C and presented in a glass flask under reflux cooling. The determination of the metal content was effected by X-ray fluorescence analysis (RFA) with the method Uniquant 2. To the molten wax 100 g of an aqueous EDTA solution with a pH value of 3 were added. The amount of EDTA in the water corresponded to 5 g. The mixture was heated to 100 °C under vigorous stirring. The experimental arrangement was under atmospheric pressure. This temperature was maintained for 4 hours. After terminating stirring, a grey-green phase was formed, which contained most of the metals and could be separated by a fluted filter. The filtrate was separated into two liquid phases (water and hydrocarbon).

The analysis of the hydrocarbon fraction revealed no detectable metal concentration. Within the detection limit, the metals thus were removed completely. Example 3: Invention

100 g of a hydrocarbon mixture (wax fraction from the Fischer-Tropsch synthesis with a metal content of about 351 wt-ppm (aluminum 220 wt-ppm, nickel 109 wt-ppm, cobalt 22 wt-ppm)) were molten at 85 °C and presented in an autoclave. The determination of the metal content was effected by X-ray fluorescence analysis (RFA) with the method Uniquant 2. To the molten wax 100 g of an aqueous EDTA solution with a pH value of 3 were added. The amount of EDTA in the water corresponded to 0.25 g. The mixture was heated to 150 °C under vigorous stirring. The autoclave was under a pressure of 4.7 bar, absolute. This temperature was maintained for 10 minutes.

After terminating stirring, a grey-green phase was formed, which contained most of the metals and could be separated by a fluted filter. The filtrate was separated into two liquid phases (water and hydrocarbon). The analysis of the hydrocarbon fraction revealed no detectable metal concentration. Within the detection limit, the metals thus were removed completely.

Example 4: Invention

100 g of a hydrocarbon mixture (wax fraction from the Fischer-Tropsch synthesis with a metal content of about 351 wt-ppm (aluminum 220 wt-ppm, nickel 109 wt-ppm, cobalt 22 wt-ppm)) were molten at 85 °C and presented in an autoclave. The determination of the metal content was effected by X-ray fluorescence analysis (RFA) with the method Uniquant 2. To the molten wax 100 g of an aqueous EDTA solution with a pH value of 3 were added. The amount of EDTA in the water corresponded to 0.10 g. The mixture was heated to 200 °C under vigorous stirring. The autoclave was under a pressure of 16 bar, absolute. This temperature was maintained for 10 minutes.

Comparative example

100 g of a hydrocarbon mixture (wax fraction from the Fischer-Tropsch synthesis with a metal content of about 351 wt-ppm (aluminum 220 wt-ppm, nickel 109 wt-ppm, cobalt 22 wt-ppm)) were molten at 85 °C and presented in an autoclave. The determination of the metal content was effected by X-ray fluorescence analysis (RFA) with the method Uniquant 2. To the molten wax 100 g of water were added and the mixture was heated to 150 °C under vigorous stirring. The autoclave was under a pressure of 4.7 bar, absolute. This temperature was maintained for one hour and the mixture was then cooled to 90 °C.

The analysis of the wax revealed that only 50 % of the metals were removed from the hydrocarbon fraction. In the hydrocarbon fraction, 120 wt-ppm of aluminum, 7 wt-ppm of cobalt and 54 wt-ppm of nickel were found in the wax.

Industrial Applicability

The invention provides a process for removing metal impurities from hydrocarbon fractions, which as compared to the processes known from the prior art is characterized by its technical simplicity and by the absence of additional extracting agents, in particular those foreign to the process. Furthermore, it is advantageous that only substances with low to medium hazard potential are used, and the use of substances with high hazard potential, such as hydrogen fluoride, is avoided.

Claims

Claims:

1. A process for producing a hydrocarbon fraction poor in metals, wherein the metals in the hydrocarbon fraction are chemically bound or dispersed in the hydrocarbon frac- tion in colloidal or finely dispersed form, comprising the following steps:

(a) providing the metal-containing hydrocarbon fraction in liquid form,

(b) contacting the liquid, metal-containing hydrocarbon fraction with a water- containing liquid phase having a pH value of not more than 5, preferably not more than 3, at temperatures of at least 100 °C, preferably at least 200 °C under stirring, wherein the water-containing liquid phase furthermore contains a complexing agent,

(c) terminating stirring, cooling and carrying out a phase separation, wherein a light, hydrocarbonaceous liquid phase, a heavy, water-containing liquid phase and a third phase is obtained, which is arranged between the light, hydrocarbonaceous liquid phase and the heavy, water-containing liquid phase, and which comprises hydrocar- bon, water and metal particles,

(e) separating the third phase liberated from metals into a light, hydrocarbonaceous liquid phase and a heavy, water-containing liquid phase, combining the separated liquid phases with the corresponding liquid phases obtained in process step (c),

2. The process according to claim 1 , characterized in that in process step (d) the filtration is used.

3. The process according to claim 1 or 2, characterized in that the water-containing liquid phase is recirculated after an optional treatment by process step (b).

4. The process according to any of the preceding claims, characterized in that the complexing agent forms complexes of the chelate type with the metals to be removed.

5. The method according to any of the preceding claims, characterized in that the complexing agent contains ethylenediaminetetraacetic acid and/or ethylenedia- minetetraacetate (EDTA).