Sorbent design for improved glycerol adsorption

Abstract

Mesoporous organosilica sorbents are effective to remove contaminants (such as glycerol or detergent) from biodiesel. Contacting biodiesel with various a mesoporous organosilica sorbents comprising phenyl and sulfonate moieties resulted in the contaminants being absorbed by the sorbent and thus removed from the biodiesel.

Claims

1. A method of removing a contaminant from biodiesel, comprising: contacting a mesoporous organosilica sorbent comprising phenyl and sulfonate moieties with a biodiesel containing a contaminant; then separating the biodiesel from the sorbent, whereby a fraction of the contaminant in the biodiesel is absorbed by the sorbent and thus removed from the biodiesel.

2. The method of claim 1, wherein said contaminant is glycerol.

3. The method of claim 2, wherein the sorbent is effective to absorb at least 50% of the glycerol.

4. The method of claim 1, wherein said contaminant is a detergent.

5. The method of claim 4, wherein the sorbent is effective to absorb at least 50% of the detergent.

6. The method of claim 1, wherein the sorbent is selected from the group consisting of ED11-Ph1, D13b, and D13-Ph2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows various structures related to sorbent compositions. The material variants are presented here showing both the sorbent scaffold (boxed area) and the groups added during post-synthesis processing.

(2) FIG. 2A shows nitrogen sorption analysis for several sulfonated sorbents and FIG. 2B shows pore size distributions for the same sorbents. In each FIG. 2A, the curves appear in the following order from bottom to top: S65-Ph, S85-Ph, E25-Ph, and E50-Ph. In FIG. 2B, S65-Ph is represented by a line with two long dashes and a short dash, S85-Ph is represented by a line with one long dash and two short dashes, E25-Ph is represented by a line with widely-spaced medium dashes, and E50-Ph is represented by a line with closely-spaced smaller dashes.

(3) FIG. 3A shows nitrogen sorption analysis for additional sulfonated sorbents: top panel ED11-Ph1; lower panel top curve ED11 and lower curve ED11-Ph2. FIG. 3B shows pore size distributions for the same sorbents, labeled as follows: ED11 (two long dashes and a short dash), ED11-Ph1 (two short dashes and a long dash), and ED11-Ph2 (medium dashes).

(4) FIGS. 4A, 4B, 4C, and 4D show nitrogen sorption analysis (A and B) and pore size distribution (C and D), for further sulfonated sorbents. In FIGS. 4A and 4C, the curves represent, from top to bottom, D13a, D13c, and D13-Ph. In FIG. 4B the top curve is D13-Ph2 and the lower curve is D13-Ph. In FIG. 4D, D13-Ph2 has two long dashes and a short dash (heavier weight) while D13-Ph has two long dashes and a short dash (lighter weight).

(5) FIGS. 5A and 5B show nitrogen sorption analysis and pore size distribution, respectively, for sulfonated resins. In each of these, the top curve is PDVB-2 and the lower curve is PDVB-3.

(6) FIG. 6 shows glycerol binding by sorbents. Experiment used a solution consisting of 271 μM glycerol in water (10 mL) with 30 mg sorbent.

(7) FIGS. 7A and 7B show glycerol binding isotherms for E25-Ph (closely-spaced short dashes), S85-Ph (two long dashes and a short dash), ED11-Ph1 (widely-spaced medium dashes), D13-Ph (triplets of a long dash between two shorter dashes with spaces between), PDVB-2 (alternating long and short dashes) presented for use of equivalent sorbent mass (A) and calculated for equivalent sorbent surface area (B).

(8) FIG. 8 shows binding of glycerol from spiked biodiesel by the sorbents. Experiment used a solution consisting of 250 μM glycerol in biodiesel (10 mL) with 30 mg sorbent.

(9) FIG. 9 shows binding of Triton X-100 (250 μM) from water (dotted bars) and spiked biodiesel (gridded bars) by ED11-Ph1 (varied sorbent mass).

(10) Regarding the above identification of lines and curves by relative position, this relates to their relative position at the mid-point of the X axis.

DETAILED DESCRIPTION

(11) Definitions

(12) Before describing the present invention in detail, it is to be understood that the terminology used in the specification is for the purpose of describing particular embodiments, and is not necessarily intended to be limiting. Although many methods, structures and materials similar, modified, or equivalent to those described herein can be used in the practice of the present invention without undue experimentation, the preferred methods, structures and materials are described herein. In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below.

(13) As used in this specification and the appended claims, the singular forms “a”, “an,” and “the” do not preclude plural referents, unless the content clearly dictates otherwise.

(14) As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

(15) As used herein, the term “about” when used in conjunction with a stated numerical value or range denotes somewhat more or somewhat less than the stated value or range, to within a range of ±10% of that stated.

(16) Overview

(17) The sorbents developed under this effort are intended for use in the removal of glycerol and surfactants from fuel preparations. Their application may be (for example) (1) as dry wash polishing media, (2) for purification processes, or (3) as part of an analytical process for evaluation of fuel quality.

(18) Hierarchical nanoporous scaffolds offer an alternative to currently available commercial dry wash media. The materials under consideration are hybrid inorganic-organic materials.sup.7-17 in which inorganic and organic moieties are mixed on the molecular scale through the use of bridged polysilsesquioxane precursors..sup.18 The materials offer large macropores with a templated mesopore structure..sup.7,12,17,19 While a number of applications have been reported for mesoporous sorbents, additional applications can be facilitated through the use of these hierarchical structures; the macroscale features reduce diffusion limitations and increase access to the mesopore volumes..sup.20,21 Materials of this type have been used for the capture of nitroenergetic and organophosphate targets..sup.20,21 The materials of the current study were developed for adsorption of glycerol, which can result in fuel tank deposits, injector corrosion, and higher emissions of aldehydes. The materials are synthesized with varying composition of the pore walls then sulfonated to promote hydrogen bonding interactions with glycerol. While this sulfonation of the material provides a similar functionality to that present in several of the dry wash media mentioned above, incorporation of the sulfonate groups on and within the scaffold and adjacent to varying structures provides an avenue for significant improvements in performance through scaffold tailoring.

(19) Description and Operation

(20) Synthesis of Sorbent Materials

(21) E25-Ph and E50-Ph: Scaffold materials were synthesized as described in previous reports..sup.21,23 Pluronic P123 (3.8 g) and 0.5 g of mesitylene (E25) or 1.0 g of mesitylene (E50) were dissolved in 12.14 g of 0.1 M HNO.sub.3 with heat (˜65° C.) and magnetic stirring. The stirring mixture was allowed to cool to room temperature before drop-wise addition of 4.24 g of 1,2-bis(trimethoxysilyl)ethane. The mixture was stirred to homogenize (˜1 min) and transferred to culture tubes. Tubes were tightly sealed and incubated in an oven at 60° C. overnight. The tubes were unsealed, and the white monolithic gels were heated for 2 d at 60° C. followed by 2 d at 80° C. The block copolymer (Pluronic P123) was extracted from the dried materials by refluxing over-night in 1 M HCl in ethanol. The solid was collected by vacuum filtration; this process was repeated 2 more times. The collected solid was washed thoroughly with ethanol and water and dried at 110° C.

(22) Grafting with phenyl groups followed a simple published procedure, beginning with an additional drying step at >100° C. in a vacuum..sup.24 Sorbent (1.0 g) was refluxed with 5 mL of phenyltriethoxysilane in 50 mL of toluene for 24 h. Grafted material was collected by gravity filtration, washed thoroughly with ethanol, and dried at 110° C. Sulfonation was accomplished as described previously by magnetically stirring the phenyl-grafted material in 25 mL of H.sub.2SO.sub.4 at 75° C. for 1 d..sup.25 The acidic mixture was then added to ≧200 mL of H.sub.2O. Solid was collected by gravity filtration, washed with H.sub.2O, and dried at 110° C. Sulfonated material was magnetically stirred in 50 mL of 1 M NaCl solution at RT for 1 d followed by collection by gravity filtration, washing with H.sub.2O, and drying at 110° C.

(23) ED11-Ph1, ED11-Ph2, and ED11: The base scaffold was synthesized as described previously..sup.26 Pluronic P123 (3.8 g) and mesitylene (1.0 g) were dissolved in 15.0 g of 0.1 M HNO.sub.3 with heat (˜65° C.) and magnetic stirring. The stirring mixture was then allowed to cool to room temperature. A silane mixture of 1,2-bis(trimethoxysilyl)ethane (2.12 g) and bis(trimethoxysilylethyl)benzene (2.94 g) was added drop-wise, and the mixture was stirred to homogenize (˜1 min). The mixture was transferred to culture tubes that were tightly sealed and incubated in an oven at 60° C. overnight. The tubes were unsealed, and the white monolithic gels were heated for 2 d at 60° C. followed by 2 d at 80° C. The block copolymer was extracted from the dried materials by refluxing overnight in 1 M HCl in ethanol; the solid was collected by vacuum filtration. This process was repeated 2 more times. The collected solid was washed thoroughly with ethanol and water, then dried at 110° C. Grafting, sulfonation, and sodium exchange for ED11-Ph1 and ED11-Ph2 were completed using the protocols described above; ED11-Ph1 and ED11-Ph2 refer to similarly but separately synthesized materials. The sulfonation step produces the variation in materials characteristics. ED11 was not grafted with phenyl groups prior to sulfonation and sodium exchange.

(24) S65-Ph and S85-Ph:Scaffold materials were synthesized based on a previously published procedure..sup.27,28 Pluronic P123 (4.0 g) and 0.65 g (S65) or 0.85 g (S85) mesitylene were dissolved in 12.0 g of 1.0 M HNO.sub.3 with heat (˜65° C.) and magnetic stirring. The mixture was allowed to cool to room temperature before drop-wise addition of 5.15 g tetramethyl orthosilicate, and the mixture was stirred to homogenize (˜1 min). The mixture was transferred to culture tubes that were tightly sealed and incubated at 60° C. overnight. The tubes were unsealed, and the white monolithic gels were heated at 60° C. for 6 d. The material was calcined under ambient atmosphere: temperature was ramped 1° C/min to 650° C. and held for 5 h. Material was refluxed in 1 M HCl for 1 d, similar to the solvent extraction process for other materials, to condition the surface similarly for grafting. It was then collected by vacuum filtration, washed with ethanol and H.sub.2O, and dried at 110° C. Grafting, sulfonation, and sodium exchange for these sorbents were completed using the protocols described above.

(25) D13-Ph, D13a, D13b, D13c, and D13-Ph2: Scaffold materials were synthesized by dissolving Pluronic P123 (3.8 g) and mesitylene (1.8 g) in 16.0 g of 0.1 M HNO.sub.3 with heat (˜65° C.) and magnetic stirring. The mixture was allowed to cool to room temperature prior to drop-wise addition of bis(trimethoxysilylethyl)benzene (5.87 g), and the mixture was stirred to homogenize it (˜1 min). The mixture was transferred to culture tubes that were tightly sealed and incubated in an oven at 60° C. overnight. The tubes were unsealed, and the white monolithic gels were heated for 2 d at 60° C. and 2 d at 80° C. Block copolymer was extracted from the dried materials by refluxing overnight in 1 M HCl in ethanol; the solid was collected by vacuum filtration. This process was repeated 2 more times. The collected solid was washed thoroughly with ethanol and water, then dried at 110° C. Grafting, sulfonation, and sodium exchange for D13-Ph were completed using the protocols described above. D13a, D13b, and D13c were not grafted with phenyl groups prior to sulfonation and sodium exchange; the designations a, b, and c refer to similarly but separately synthesized materials. D13b in particular was sulfonated using 50% H.sub.2SO.sub.4 rather than undiluted acid. D13-pH2 is the same type of material as D13-Ph but was sulfonated with 50% H.sub.2SO.sub.4 in the way that D13b was treated.

(26) PDVB-2 and PDVB-3: Divinylbenzene (DVB) resins were synthesized in a Teflon-lined autoclave reactor (23 mL capacity) using a procedure adapted from Libu{hacek over (s)}e Hanková et al. “Role of Water as a Coporogen in the Synthesis of Mesoporous Poly(divinylbenzene),” Journal of Applied Polymer Science, 2014, DOI:10.1002/app.41198, incorporated herein by reference for this teaching. For PDVB-2, DVB (1.5 g; Aldrich technical grade, 80%) was added to tetrahydrofuran (15 mL) with water (0.75 mL) and 2,-2′-azobis(2-methylpropionitrile) (0.0375 g; Aldrich, 98%). The reactor was heated at 100° C. for 48 h. Following cooling to room temperature, the reactor was opened and the resin was allowed to dry overnight at room temperature followed by complete drying at 100° C. PDVB-3 was synthesized identically with the exception of the water coporogen used in the PDVB-2 synthesis which was omitted. Ground resin was added to hexane (20 mL) to produce a wet slurry, and sulfuric acid was added (25 mL) for the suflonation step. The mixture was heated at 75° C. for 1 d before addition of water (300 mL). Sulfonated material was collected by vacuum filtration and washed thoroughly with water before drying at 100° C. Sodium exchange was completed by stirring the material in 1 M NaCl (50 mL) at room temperature for 1 d. The resin was then washed with water, collected by vacuum filtration, and dried at 100° C.

(27) Sorbent Characteristics

(28) Sulfonation of poly-(styrene-co-divinylbenzene) resin has been described for increasing hydrogen bonding with and, therefore, removal of glycerol by resin material..sup.29 The previous work in this area did not consider the impact of the scaffold or the morphology of the resin on target adsorption. Because the chemical structures in close proximity to the sulfonate groups are likely to impact the interaction of those groups with glycerol, a series of porous organosilicate materials in which the pore wall composition has been varied was synthesized. Many cases were considered; S65/S85 and E25/E50 offer no sites for sulfonation on the base sorbent. ED11 and D13 offer phenyl rings that comprise at least a portion of the bridging groups. Sulfonation of the materials directly (ED11 and D13) or sulfonation following grafting of additional phenyl groups were completed for this range of materials. The schematic provided in FIG. 1 illustrates the variations in the resulting materials.

(29) Table 1 provides a summary of morphological characteristics for these materials.

(30) TABLE-US-00001 TABLE 1 Morphological characteristics for the sulfonated sorbents. Surface Pore Pore Area Volume Diameter Material Type (m.sup.2/g) (cm.sup.3/g) (Å) S65-Ph 1 515 0.548 56 S85-Ph 1 578 0.626 64 E25-Ph 2 803 0.740 64 E50-Ph 2 883 0.664  51* ED11-Ph1 3 147 0.151 48 ED11-Ph2 3 27 0.047 50 ED11 4 87 0.111 55 D13-Ph 5 4.0 0.010 —* D13-Ph2 5 310 0.510 67 D13a 6 3.1 0.007 —* D13b 6 337 0.536 75 D13c 6 3.2 0.013 —* ED13 — 478 0.527 56 PDVB-2 — 405 0.564 126  PDVB-3 — 336 0.375 65 *Broad; no well-defined peak in the pore size distribution

(31) FIG. 1 illustrates chemical structures of various types of sorbents described here, by type number 1 through 6. The Type 1 materials (FIG. 1) provide a sodium-exchanged, sulfonated phenyl group pendant on a silicate scaffold. Nitrogen sorption analysis indicates type IV isotherms characteristic of mesoporous materials (FIG. 2A). The silicate scaffolds are ordered mesostructures with 2D hexagonally packed cylindrical mesopores. The pore sizes in the two materials are influenced by the amounts of mesitylene swelling agent included in the syntheses..sup.27,28 The Type 2 materials provide the same pendant functional group on an ethane-bridged organosilicate sorbent. The base E50 scaffold offers a combination of disordered micropores and mesopores (FIG. 2B). The type IV nitrogen sorption isotherm of the E25 sorbent is similar to those of S65-Ph and S85-Ph.

(32) Type 3 materials, based on ED11, have 50% of the ethane bridging groups of the E50 and E25 scaffolds replaced with diethylbenzene groups. This provided the potential for direct sulfonation of phenylene groups within the pore walls in addition to the grafted phenyl groups. Type 4 sorbents are sodium-exchanged sulfonated ED11 with no grafted phenyl moieties. Most products sulfonated with undiluted H.sub.2SO.sub.4 display type II nitrogen sorption isotherms indicative of relatively non-porous materials (e.g. ED11-Ph2 in FIG. 3).

(33) Type 5 and 6 sorbents, based on D13, have the highest concentration of diethylbenzene bridging groups in their scaffold walls; Type 5 sorbents also include grafted pendant phenyl moieties. Functionalization using undiluted H.sub.2SO.sub.4 leads to collapse of the mesostructure (FIG. 4). D13b was treated with 50% H.sub.2SO.sub.4, preserving the mesostructure (FIG. 4). The nitrogen isotherm shows considerable hysteresis between its adsorption and desorption branches, indicative of “bottle-necks” in the mesopore structure. Nitrogen adsorption isotherms for porous sulfonated polydivinylbenzene resins PDVB-2 and PDVB-3 are provided for comparison (FIG. 5).

(34) Glycerol Bindingfrom Aqueous Solutions. Batch type experiments were used to generate isotherms for the binding of glycerol from water by the sorbent variants. Analysis was completed by determination of the glycerol remaining in solution following overnight incubation of varying sorbent masses with glycerol solutions of varied concentration. Analysis of glycerol was based on the method described by ASTM D6584-13..sup.30 Samples and control solutions were all water-based; water was removed from a 5 mL aliquot using a KD Scientific Centrifan PE-T (Model 78-0070). A stock solution of N-methyl-n-(trimethylsilyl)trifluoroacetamide (MSTFA; 1.2 mL) in pyridine (2 mL) was prepared. This solution (160 μL) was added to the dried sample followed by incubation for 20 min. Heptane (1.6 mL) was then added, and the sample was transferred to an autosampler vial for GC analysis. GC-MS analysis was performed using a Shimadzu GCMS-QP2010 with AOC-20 autoinjector equipped with a Restex Rtx-5 (30 m×0.25 mm ID×0.25 μm df) cross bond 5% diphenyl 95% dimethyl polysiloxane column. A GC injection temperature of 200° C. was used with a 1:1 split ratio at a flow rate of 3.6 mL/min at 69.4 kPa. The oven gradient ramped from 50° C. (1 min hold time) to 180° C. at 15 C/min and then to 300° C. at 20° C/min where it was held for 5 min.

(35) FIG. 7 provides some examples of binding isotherms. Target binding by these types of sorbents has previously been described by phenomenological models such as those represented by the Langmuir and Langmuir-Freundlich formulations..sup.20,26,31 For the glycerol binding data, the Langmuir-Freundlich equation was used:

(36) $q=\frac{q_s{\mathrm{Ak}\left[L\right]}^n}{1+{k\left[L\right]}^n}$

(37) Here, q is the amount of target bound per unit sorbent surface area, L is the free ligand, k is the affinity coefficient, n is the homogeneity factor, and A is the total surface area. The typically used saturation capacity is q.sub.s. FIGS. 7A and 7B show exemplary glycerol binding isotherms, and Table 2 provides a summary of the calculated parameters for the various materials.

(38) TABLE-US-00002 TABLE 2 Parameters generated from application of the Langmuir- Freundlich equation to glycerol binding data. Material q.sub.s (μg/m.sup.2) k (1/mg) n S65-Ph 72.4 2.78 1 S85-Ph 42.4 1.92 1 E25-Ph 14.9 4.78 1 E50-Ph 5.87 10.8 1 ED11-Ph1 145 13.5 1 ED11-Ph2 450 24.0 1 ED11 207 0.920 1 D13-Ph 2689 3.95 1 D13-Ph2 1780 4.15 1 D13a 5290 4.56 1 D13b 811 1.96 1 D13c 5190 4.45 1 ED13 81.2 0.461 1 PDVB-2 1059 0.019 1 PDVB-3 1620 0.029 1

(39) Glycerol Capture from Biodiesel. Several of the materials used for capture of glycerol from aqueous solution were also evaluated in a solution based on in-house prepared biodiesel. The solution was prepared through adaptation of a widely available small batch production protocol. Food grade canola oil (1 L) was warmed to 50° C. on a hotplate. In a separate container, methanol (355 mL) and sodium hydroxide (3.5 g) were mixed. This mixture was slowly added to the warmed oil and the result was stirred for 2 h (50° C.). The reacted solution was moved to a reparatory funnel and allowed to settle so that bottom glycerol could be drained. Rotary evaporation was used to remove residual methanol from the final solution and the pH was verified to be neutral. A known concentration of glycerol was added to this preparation for sorbent evaluation and controls were analyzed using a modification of the protocol described above for glycerol binding from aqueous solutions. For sample preparation, the sorbent containing solution was filtered to remove the sorbent (as necessary). A 100 μL aliquot was added to 100 μL MSTFA. This solution was mixed well and incubated at room temperature for 20 min before addition of heptane (8 mL). The result was transferred to an auto sample vial for analysis by the GC-MS protocol described above for glycerol binding from aqueous solutions.

(40) FIG. 8 presents data for capture of glycerol from the biodiesel preparation by several of the developed sorbents as well as by the commercial products BD ZorbX Dry Wash Media and DudaLite Dry Wash Resin DW-R10. The figure also shows data for sodium exchanged versions of the commercial media. A Type 6 sorbent dramatically out performs the commercial sorbents as does the Type 3 sorbent.

(41) Capture of Other Targets. In addition to providing removal of glycerol, the sorbents described here offer capture of other targets of potential interest to biodiesel production and analysis. Triton X-100 was used as a model for detergents. Table 3 provides parameters from Langmuir-Freundlich fits of data sets resulting from batch experiments in aqueous solution. Binding of Triton X-100 from spiked biodiesel samples was also evaluated. As shown in FIG. 9, capture of the target from biodiesel was similar to that from aqueous solution.

(42) TABLE-US-00003 TABLE 3 Parameters generated from application of the Langmuir- Freundlich equation to Triton X-100 binding data. Material q.sub.s (μg/m.sup.2) k (1/mg) n S65-Ph 5960 0.17 1 S85-Ph 860 8.99 1 E50-Ph 310 0.02 1 ED11-Ph1 2200 0.15 1 ED11-Ph2 12200 0.03 1 ED11 2180 0.08 1 D13-Ph 48200 0.44 1 D13-Ph2 Binds 100% from all experiments D13a 5500 11.6 1 D13b Binds 100% from all experiments D13c 31800 0.10 1 ED13 Binds 100% from all experiments PDVB-2 220 0.60 1 PDVB-3 200 0.60 1

(43) Prophetic Applications. The sorbents could be contacted with biodiesel or other liquids for various lengths of time ranging from minutes to hours to days or even longer, for example by introducing a biodiesel to a vessel containing the sorbent and removing a cleaned biodiesel from the vessel. The contacting could occur in various formats allowing continuous, column, or batch type applications. The contacting in these formats could occur as a gravity driven process, with added pressure, or be driven through application of a vacuum. The contacting could be with or without agitation including mechanical agitation such as stirring and/or sonication. The contacting can be at ambient or other temperature, for example at an elevated temperature between ambient and a flash point of the liquid. One or more different types of sorbent can be used. Following contacting, the sorbent(s) can be separated by filtration, centrifugation, or other techniques known in the art. In other embodiments, separation can be aided by passing a liquid (such as biodiesel) over immobilized sorbent, for example in a column. The used be washed (e.g., with alcohol and/or a aqueous solution) and reused, with glycerol optionally recovered.

(44) Concluding Remarks

(45) Reagents of the type described here provide the potential for improved dry wash media in biodiesel purification processes. The approach, controlling the distribution and concentration of sulfonate groups within the sorbent structure, provides a significant advantage over previous approaches utilized for development of these types of sorbents. The materials offer additional potential in analysis of biodiesel. Similar sorbents have been applied for solid phase extraction, resulting in concentration and purification of targets.

(46) Current efforts in reducing the water necessary for purification of biodiesel are focused on inexpensive and, often, disposable media. The advantages described here offer the potential for media with improved performance characteristics as well as a method for reuse of the material. These characteristics also lead to the potential for enhancing analytical methods applied to biodiesel analysis through their use as a solid-phase extraction sorbent.

(47) All documents mentioned herein are hereby incorporated by reference for the purpose of disclosing and describing the particular materials and methodologies for which the document was cited.

(48) Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention. Terminology used herein should not be construed as being “means-plus-function” language unless the term “means” is expressly used in association therewith.

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