Mercury capture from hydrocarbon fluids using deep eutectic solvents

Abstract

The present invention relates to a method for the extraction of mercury from a mercury-containing hydrocarbon feed, and to the use of a hydrophilic deep eutectic solvent for the extraction of a mercury source from a hydrocarbon feed.

Claims

1. A method for the extraction of mercury from a mercury-containing hydrocarbon feed, comprising the steps: providing a hydrocarbon feed, wherein the hydrocarbon feed comprises a mercury source at an initial concentration C.sub.Hg,i; providing a hydrophilic deep eutectic solvent; contacting the hydrophilic deep eutectic solvent with the hydrocarbon feed to form an extraction mixture; and separating a hydrocarbon product from the extraction mixture, wherein the hydrocarbon product comprises the mercury source at a final concentration C.sub.Hg,f, wherein C.sub.Hg,f, is smaller than C.sub.Hg,i; wherein the hydrophilic deep eutectic solvent comprises at least one hydrogen bond acceptor and at least one hydrogen bond donor, wherein the at least one hydrogen bond donor is an amine, an amide, a carboxylic acid or an alcohol, wherein the at least one hydrogen bond acceptor is a zwitterionic compound selected from the group consisting of proline, glycine, and N,N,N-trimethylglycine, and wherein the at least one hydrogen bond acceptor and the at least one hydrogen bond donor are included in the hydrophilic deep eutectic solvent in a molar ratio of about 1:2.

2. The method of claim 1, wherein the mercury source is elemental mercury, an ionic mercury compound, and/or an organic mercury compound.

3. The method of claim 1, wherein the at least one hydrogen bond donor is selected from the group consisting of urea, acetamide, thiourea, amino acids, malic acid, maleic acid, citric acid, lactic acid, pyruvic acid, fumaric acid, glycolic acid, succinic acid, acetic acid, aconitic acid, tartaric acid, malonic acid, ascorbic acid, glucuronic acid, oxalic acid, neuraminic acid, sialic acids, levulinic acid, trichloroacetic acid, phenylacetic acid, sucrose, glucose, fructose, lactose, maltose, arabinose, ribose, ribulose, galactose, rhamnose, raffinose, xylose, mannose, trehalose, mannitol, sorbitol, inositol, ribitol, galactitol, erythritol, xyletol, adonitol, cresol, phenol, ethylene glycol.

4. The method of claim 1, wherein the zwitterionic compound includes an amine group, a quaternary ammonium group or a phosphonium group.

5. The method of claim 1, wherein the hydrophilic deep eutectic solvent comprises choline chloride and urea; and/or choline chloride and ethylene glycol; and/or choline chloride and levulinic acid; and/or betaine and levulinic acid.

6. The method of claim 1, wherein the hydrocarbon feed is a liquid.

7. The method of claim 1, wherein the hydrophilic deep eutectic solvent and the hydrocarbon feed are provided in a mass ratio of between 1:1 and 2:1.

8. The method of claim 1, wherein the contacting is conducted at a temperature of at least 20° C.

9. The method of claim 1, wherein the contacting is conducted at a temperature of at most 50° C.

10. The method of claim 1, wherein the contacting is conducted at atmospheric pressure.

11. The method of claim 1, wherein the contacting is conducted for at least 1 hour.

12. The method of claim 1, wherein the hydrocarbon product is separated from the extraction mixture by means of gravity separation.

13. The method of claim 1, wherein C.sub.Hg,f, is at most 0.3 C.sub.Hg,i.

14. The method of claim 1, wherein the method has an extraction efficiency E, defined as (C.sub.Hg,i−C.sub.Hg,f)/C.sub.Hg,i of at least 0.85.

15. The method of claim 1, wherein after separating the hydrocarbon product, the hydrophilic deep eutectic solvent is recovered from the remaining extraction mixture.

Description

4. BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 illustrates a routine for the extraction of mercury according to the invention.

5. DETAILED DESCRIPTION OF THE INVENTION

(2) Preferred embodiments of the invention will be described in the following detailed description. It is emphasized, however, that the present invention is not limited to these embodiments.

(3) In 2003, Abbott et al. (Abbott et al. 2003) introduced a novel class of solvents, the so-called deep eutectic solvents (DESs). DESs comprise at least one predominantly hydrogen bond donor (HBD) compound and at least one predominantly hydrogen bond acceptor (HBA) compound that form a mixture exhibiting a significantly lower freezing point than both of the pure compounds. DESs have a low vapor pressure, a wide liquid range, and low flammability, and, importantly, are simple to prepare. In particular, low-cost HBD and HBA ingredients that are mostly biodegradable can be used.

(4) The present invention describes for the first time the use of DESs as extracting agents for removal mercury from Hg-containing hydrocarbons, such as crude oil or natural gas. The inventors found that DESs are highly efficient for the extraction of mercury, relating to their strong affinity for solvating various mercury species, their low mutual solubility with hydrocarbons, and their thermal stability. Compared to ionic liquids, which are formed from discrete anions and cations, deep eutectic solvents are generally less expensive, in particular because of their easier synthesis. No purification step is required during/after synthesis of the deep eutectic solvent, making a large-scale use of DESs feasible. Moreover, DESs are mostly biodegradable and non-toxic. Also, DESs might be recovered, e.g. by anti-solvent precipitation.

(5) As described in FIG. 1, the method according to the invention comprises the steps of providing a deep eutectic solvent and a mercury containing hydrocarbon feed. The method can be integrated into refining processes of natural gas or crude oil. The deep eutectic solvent and the hydrocarbon feed are contacted to form an extraction mixture. For example, in case the hydrocarbon feed is liquid, the feed and the solvent can be combined in a container to form the extraction mixture. Further, the extraction mixture can be constantly agitated during extraction to improve the overall extraction efficiency. The hydrocarbon product, which contains a lower concentration of mercury source than the feed, is then separated from the extraction mixture, e.g. via gravity separation or centrifugation. After separation, the deep eutectic solvent is enriched with the mercury source. It is also suggested to separate the mercury from the deep eutectic solvent by means of anti-solvent precipitation.

(6) The deep eutectic solvent can be regenerated to be used again in the method according to the invention. Alternatively, the deep eutectic solvent may be used for other applications, such as battery production or other electrochemical products or processes.

Example 1: Preparation of Deep Eutectic Solvents

(7) Several DESs for extracting mercury were tested:

(8) “DES-1”: choline chloride:urea

(9) “DES-2”: choline chloride:ethylene glycol

(10) “DES-3”: choline chloride:levulinic acid

(11) “DES-4”: betaine:levulinic acid

(12) In all cases the molar ratio was 1:2. DES-4 was chosen to test the influence of replacing a salt-based HBA with a zwitterionic HBA, i.e. with betaine.

(13) The chemical compounds, along with their sources and purities are reported in Table 1. The choline chloride was dried under vacuum prior to use. The other chemicals were used as obtained.

(14) TABLE-US-00001 TABLE 1 Chemicals for the preparation of DESs. Chemical Purity (wt %) Source Choline chloride ≥98 Sigma-Aldrich Urea ≥98 Sigma-Aldrich Ethylene glycol ≥99.8 Sigma-Aldrich Levulinic acid ≥98 Sigma-Aldrich Betaine ≥98 Sigma-Aldrich Dodecane ≥99 Merck Mercury Extra pure Merck

(15) The molecular structures of the constituents for the four DESs are provided in Table 2. The DESs (DES1 to DES4) were prepared in 50 g batches using a 1:2 molar ratio for HBA:HBD. The constituents were accurately weighed using a Sartorius ED 224S analytical balance with a precision of ±0.1 mg, then added together in closed 100 mL glass bottles and mixed thoroughly using a Vortex mixer (VWR). The mixtures were stirred at 323.15 K in a temperature controlled oil bath with a temperature controller (IKA ETS-D5, uncertainty=±0.1 K), until a homogeneous clear liquid was formed.

(16) TABLE-US-00002 TABLE 2 Molecular structure of the constituents for the DESs investigated. HBA HBD choline chloride urea betaine ethylene glycol levulinic acid

Example 2: Mercury Extraction from Hydrocarbon Feed

(17) N-dodecane was used as a model system for aliphatic hydrocarbons in petroleum. 25 mL of n-Dodecane (>99% purity) was saturated with elemental mercury (extra pure) at ambient conditions to a concentration of approximately 4000 μg kg.sup.−1. The saturated n-dodecane solution was added to the DESs using a 1:1 or a 2:1 solvent-to-feed mass ratio. The mixtures were initially mixed for a short time using a Vortex mixer followed by shaking the solutions for 2 h using an incubating shaker (IKA KS 4000 i) at temperatures of 303.15 K or 333.15 K. The mixtures were left to settle for 30 min until liquid-liquid coexistence was visually observed with the n-dodecane and DES being the upper and lower phases, respectively. A sample from the n-dodecane phase was taken using a syringe without disturbing the equilibrium interface. The n-dodecane sample was then analyzed for its mercury content using a Milestone Direct Mercury Analyzer DMA-80 pyrolysis/AA analyzer. A sample of the n-dodecane phase (20-30 mg) was introduced in the DMA-80, in which the sample is initially dried at T=573 K and then thermally decomposed at T=1123 K in an oxygen flow (200 mL min.sup.−1) and a gas pressure of 4 bar. The combustion products were carried off and further decomposed in a hot catalyst bed at T=873 K. The mercury vapors are trapped on a gold amalgamator and subsequently desorbed at T=1173 K. Finally, the mercury content was determined using atomic absorption spectrophotometry at 254 nm.

(18) The extraction performance for the system [n-dodecane+Hg.sub.o+DES] was evaluated for solvent: feed ratios of 1:1 and 2:1 (mass ratio), wherein the solvent and feed were incubated at temperatures T=303.15 and T=333.15 K and atmospheric pressure, as described above. No color change was noticed when the DESs were mixed with the n-dodecane solution and the mercury was transferred from the non-polar alkane phase to the polar DES phase. The initial and final mercury concentrations in the n-dodecane solution, C.sub.Hg,i and C.sub.Hg,f, respectively, were measured in triplicate for each sample, and each extraction experiment was done in duplicate. The results are reported in Table 3 The extraction efficiencies, E, were calculated as follows:
E=(C.sub.Hg,i−C.sub.Hg,f)/C.sub.Hg,i

(19) TABLE-US-00003 TABLE 3 Concentrations obtained for two extraction experiments (labeled by superscripts A and B), and derived efficiencies. The standard deviations are estimated from replicate measurements and error propagation. T Mass ratio C.sub.Hg, i.sup.A C.sub.Hg, f.sup.A C.sub.Hg, i.sup.B C.sub.Hg, f.sup.B E DES # [K] (solvent:feed) [μg kg.sup.−1] [μg kg.sup.−1] [μg kg.sup.−1] [μg kg.sup.−1] [%] DES-1 303.15 1:1 3670 ± 90 260 ± 10 3670 ± 90  280 ± 10 93 ± 3 DES-1 303.15 2:1 3420 ± 30 200 ± 10 4120 ± 140 600 ± 10 90 ± 7 DES-1 333.15 1:1 3950 ± 80 830 ± 20 3950 ± 80  520 ± 20 83 ± 6 DES-1 333.15 2:1 3950 ± 80 460 ± 20 3950 ± 80  790 ± 10 84 ± 7 DES-2 303.15 1:1 3670 ± 90 570 ± 20 3670 ± 90  590 ± 10 84 ± 3 DES-2 303.15 2:1 3420 ± 30 240 ± 10 4120 ± 140 480 ± 10 91 ± 5 DES-2 333.15 1:1  3990 ± 150 370 ± 10 3990 ± 150 330 ± 10 91 ± 4 DES-2 333.15 2:1  3990 ± 150 210 ± 10 3990 ± 150 170 ± 10 95 ± 5 DES-3 303.15 1:1 3680 ± 90 380 ± 10 3670 ± 90  460 ± 20 88 ± 4 DES-3 303.15 2:1 3420 ± 30 270 ± 10 4120 ± 140 270 ± 10 93 ± 4 DES-3 333.15 1:1 4970 ± 40 140 ± 10 4970 ± 40  110 ± 10 97 ± 6 DES-3 333.15 2:1 4970 ± 40 30 ± 2 4970 ± 40  24 ± 2 99 ± 6 DES-4 303.15 1:1 4160 ± 60 550 ± 10 4160 ± 60  480 ± 20 88 ± 3 DES-4 303.15 2:1 4160 ± 60 460 ± 20 4120 ± 140 220 ± 10 92 ± 6 DES-4 333.15 1:1  3710 ± 110 400 ± 10 3710 ± 110 450 ± 10 88 ± 3 DES-4 333.15 2:1  3710 ± 110 490 ± 20 3710 ± 110 490 ± 20 87 ± 4

(20) All tested DESs exhibited extraction efficiencies above 80%. The zwitterion containing DES-4 performed as well as the other DESs comprising choline chloride as HBA.