Smoking article with mercaptopropyl functionalized sorbent and method

Abstract

Mercaptopropyl functionalized molecular sieves such as mesoporous SBA-15 silica molecular sieves can be prepared via incipient-wetness impregnation of (3-mercaptopropyl)triethoxysilane of up to a loading of about 15 mole %. The functionalized materials are more hydrophobic than parent material, and can be used as adsorbents to reduce the concentration of heavy metal (mercury and/or cadmium-containing) constituents in mainstream smoke. For example, SBA-15 silica comprising a 1% molar loading of mercaptopropyl groups has an adsorption capacity for mercury that is approximately seven to eight times that of un-functionalized parent SBA-15 silica.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/613,513 filed on Sep. 28, 2004, the entire content of which is incorporated herein by reference.

BACKGROUND

In the description that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art.

SUMMARY

Cigarette filters and smoking articles such as cigarettes, pipes, cigars or non-traditional cigarettes comprise a sorbent having mercaptopropyl groups bound to an inorganic molecular sieve substrate, wherein the sorbent is capable of reducing the concentration of at least one heavy metal constituent in mainstream smoke. Preferably, the sorbent is incorporated in an amount effective to reduce levels of mercury and/or cadmium in mainstream smoke.

The inorganic molecular sieve substrate can comprise mesoporous or microporous molecular sieves. Exemplary molecular sieve substrate materials include zeolites, silicates such as mesoporous silicates, aluminophosphates, mesoporous aluminosilicates, and mixtures thereof. Zeolites can include zeolite ZSM-5, zeolite A, zeolite X, zeolite Y, zeolite K-G, zeolite ZK-5, zeolite Beta, zeolite ZK-4, and mixtures thereof. When incorporated in a smoking article or in a cigarette filter, the sorbent preferably has a particle size from about 20 mesh to about 60 mesh.

One preferred sorbent comprises (3-mercaptopropyl) silane covalently bound to a zeolite. A further preferred sorbent comprises (3-mercaptopropyl) silane covalently bound to a mesoporous silicate. SBA-15 silica, for example, is a mesoporous molecular sieve that can have incorporated therein up to about 15 mole percent of (3-mercaptopropyl) trialkoxysilane with respect to silicon in the SBA-15.

Preferably, the mercaptopropyl groups are covalently bound to exterior and interior surfaces of the inorganic molecular sieve substrate. Smoking articles and filters can comprise from about 10 mg to about 300 mg or from about 100 mg to about 200 mg of the sorbent, and the sorbent is preferably in granular form having a particle size from about 20 mesh to about 60 mesh.

Preferred cigarette filters comprise mono filters, dual filters, triple filters, cavity filters, recessed filters and free-flow filters. Further, the cigarette filter can comprise cellulose acetate tow, cellulose paper, mono cellulose, mono acetate, and combinations thereof. The sorbent can be incorporated into one or more cigarette filter parts such as a shaped paper insert, a plug, a space, cigarette filter paper, and a free-flow sleeve. As an example, the sorbent can be incorporated with cellulose acetate fibers or polypropylene fibers forming a plug or a free-flow filter element.

In an embodiment, the sorbent can be incorporated in at least one of a mouthpiece filter plug, a first tubular filter element adjacent to the mouthpiece filter plug, and a second tubular filter element adjacent to the first tubular element. In a further embodiment, the sorbent can be incorporated in at least one part of a three-piece filter including a mouthpiece filter plug, a first filter plug adjacent to the mouthpiece filter plug, and a second filter plug adjacent to the first filter plug.

A method of making a cigarette filter comprises incorporating a sorbent into a cigarette filter, wherein the sorbent comprises mercaptopropyl groups bound to an inorganic molecular sieve substrate. As used herein, “MTP” denotes the mercaptopropyl group, and unless otherwise stated the percent loading of mercaptopropyl groups on a substrate is given in mole percent.

A method of making a cigarette comprises (i) providing a cut filler to a cigarette making machine to form a tobacco column; (ii) placing a paper wrapper around the tobacco column to form a tobacco rod; and (iii) attaching a cigarette filter comprising the sorbent to the tobacco rod using tipping paper.

A method of treating tobacco smoke comprises contacting mainstream tobacco smoke with a sorbent having at least one mercaptopropyl group bound to an inorganic molecular sieve substrate while drawing mainstream tobacco smoke through a smoking article, wherein the sorbent reduces the concentration of at least one heavy metal constituent in mainstream smoke.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an adsorption-desorption isotherm of argon at about 87 K from SBA-15 (8% MTP), where 8% denotes the molar loading of mercaptopropyl groups on a molecular sieve substrate comprising SBA-15 mesoporous silica. The inset shows the corresponding pore size distribution of the sorbent material.

FIG. 2(a) shows a TEM image in the direction of a pore axis and FIG. 2(b) shows EELS imaging of sulfur in SBA-15 (8% MTP).

FIG. 3 shows FTIR spectra in the hydroxyl stretching range of (a) parent SBA-15 silica, (b) SBA-15 (1% MTP), (c) SBA-15 (2% MTP), (d) SBA-15 (4% MTP), (e) SBA-15 (8% MTP) and (f) SBA-15 (16% MTP).

FIG. 4 shows single-pulse ²⁹Si MAS NMR spectra of (curve a1) parent SBA-15 silica and (curve b1) SBA-15 (16% MTP). Curves (a2) and (b2) are the corresponding ²⁹Si MAS NMR spectra with ¹H cross polarization of the same materials.

FIG. 5 is a ¹³C MAS NMR spectrum of SBA-15 (16% MTP).

FIG. 6 shows ¹H MAS NMR spectra of (a) parent SBA-15 silica and (b) SBA-15 (16% MTP).

FIG. 7 shows TGA and DTG curves of (a) parent SBA-15 silica, (b) SBA-15 (1% MTP), (c) SBA-15 (2% MTP), (d) SBA-15 (4% MTP), (e) SBA-15 (8% MTP), (f) and (f′) SBA-15 (16% MTP).

FIG. 8 shows mercury breakthrough of each mercury vapor pulse flowing through (●) cellulose acetate fibers only, (▾) parent SBA-15 silica, (♦) SBA-15 (1% MTP), (⋄) SBA-15 (2% MTP), (▴) SBA-15 (4% MTP) and (∘) SBA-15 (8% MTP).

FIGS. 9-11 show various cigarette embodiments in which a sorbent comprising at least one mercaptopropyl group bound to an inorganic molecular sieve substrate can be incorporated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Smoking articles, cigarette filters and methods for making cigarette filters comprise a sorbent that is adapted to reduce the concentration of at least one heavy metal constituent from the mainstream smoke of a cigarette. The sorbent comprises an inorganic molecular sieve substrate having mercaptopropyl (MTP) groups bound thereto.

The molecular sieve substrate can comprise a microporous or a mesoporous substrate. Microporous substrates have an average pore size of less than about 2 nm (20 Å), and mesoporous substrates have an average pore size of from about 2 nm to 50 nm (20 to 500 Å). The substrate can be a natural or a synthetic material. Exemplary substrates include zeolites, aluminophosphates, mesoporous silicates, mesoporous aluminosilicates, and mixtures thereof. Mesoporous silica molecular sieves, for example, can have an internal surface area of around 1000 m²/g and uniform mesopore channels. The sorbent can be used to adsorb molecules at temperatures up to about 700° C. or more.

Mercaptopropyl groups can be incorporated into a molecular sieve substrate via a direct synthesis route involving the co-condensation of tetraethoxysilane and (3-mercaptopropyl)triethoxysilane followed by post-synthesis acid or alcohol extraction of the structure-directing agent used in the synthesis. As an alternative, mercaptopropyl groups can be incorporated into molecular sieve substrates by refluxing a substrate material such as freshly calcined particles of mesoporous silica in dry toluene containing (3-mercaptopropyl)triethoxysilane. The mercaptopropyl groups can be transformed to alkylsulfonic acid groups via mild oxidation with hydrogen peroxide solution and further acidification.

A preferred substrate material is a SBA-15 silica molecular sieve. SBA-15 silica molecular sieve is a mesoporous molecular sieve having a uniform pore size of between about 5 to 20 nm and a mean surface area of about 200-230 m²/g.

As described herein, the mesoporous SBA-15 silica molecular sieves can be functionalized with mercaptopropyl functional groups in an effective amount, preferably in an amount of up to 15 mole % compared to the parent SBA-15. The incorporated mercaptopropyl groups are uniformly dispersed, and chemically bonded to surface silicon associated with the silanol groups in the parent SBA-15. The functionalized materials retain the well-defined mesoporosity of the SBA-15 silica, and can adsorb trace amounts of heavy metal vapor.

The incipient-wetness method is a preferred method of incorporating mercaptopropyl groups in a molecular sieve substrate material. SBA-15 silica molecular sieve (hereinafter SBA-15) can be functionalized with mercaptopropyl groups via incipient-wetness impregnation of (3-mercaptopropyl)triethoxysilane at elevated temperature using dry toluene. According to a preferred method, the SBA-15 is pre-calcined in air at 550° C. for 24 hours and then added to a dry toluene solution containing dissolved (3-mercaptopropyl)triethoxysilane followed by vigorous shaking at room temperature. The (3-mercaptopropyl)triethoxysilane concentration in the solution can vary from about 0.017-0.267 M, and the amount of SBA-15 and/or the amount of the toluene solution can be selected depending on the desired loading of mercaptopropyl groups. The mixture of SBA-15 and (3-mercaptopropyl)triethoxysilane can be heated (e.g., at 100° C. for 24 h), filtered, and washed with dry toluene followed by dichloromethane, and then dried at 120° C. for 12 h. The sorbent materials made using this method are designated SBA-15 (MTP-X), where MTP denotes the mercaptopropyl group and X is the molar percent of (3-mercaptopropyl)trialkoxysilane added to the toluene solution with respect to silicon in the parent SBA-15 material.

Characterization data for the SBA-15 (MTP-X) material are shown in FIGS. 1-8. Powder x-ray diffraction (XRD) patterns from 0-15° (2θ) were taken by IC Laboratories, Amawalk, N.Y. Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) measurements were conducted with an FEI Technai F20 field emission electron microscope operating at an accelerating voltage of 200 kV. EELS spectra and images were collected with a Gatan Imaging Filter and analyzed with Gatan Digital Micrograph software. Fast Fourier Transforms (FFT) of the images were also calculated with the Gatan Digital Micrograph software. EELS images of sulfur were collected by measuring the intensity from a window spanning the S_L edge and subtracting the intensity extrapolated from two pre-edge windows. A similar process using the C_K edge was used for carbon imaging.

Argon adsorption isotherms were measured at 87.29 K using a Micromeritics ASAP 2010 analyzer. The specific surface area, A_BET, was determined from the linear part of the Brunauer, Emmett, and Teller (BET) equation (P/P₀=0.05-0.31). The calculation of pore size distribution was performed using the desorption branch of an argon adsorption isotherm and the Barrett-Joyner-Halenda (BJH) formula. The cumulative mesopore surface area, A_BJH, and volume, V_BJH, were obtained from the pore size distribution curves. The average mesoporous pore diameter, D_BJH, was calculated as 4V_BJH/A_BJH.

Thermogravimetric analysis (TGA) was carried out on a TA Instruments 2950 Thermogravimetric Analyzer in helium at a heating rate of 10° C./min. The weight loss was normalized to the sample weight at 100° C. and plotted versus temperature as thermogravimetric (TG) and differential thermogravimetric (DTG) curves.

Fourier-transform infrared spectroscopy (FTIR) spectra were recorded on a MIDAC Corporation 2100 spectrophotometer, with a resolution of 0.5 cm⁻¹ equipped with a mercury-cadmium-telluride (MCT) detector. Measurements were conducted in reflectance mode using a Spectral-Tech Temperature/Vacuum chamber with potassium bromide (KBr) windows, which was mounted to a Spectral-Tech collector in the infrared beam.

Solid-state magic-angle-spinning (MAS) NMR spectra were recorded at 4.7 Tesla using a Varian Unity-200 spectrometer equipped with a Doty Scientific high-speed multinuclear MAS probe. ²⁹Si MAS spectra were measured at 39.7 MHz, with 30° pulses and 90 sec recycle delays using 7 mm silicon nitride rotors spinning at 8.2 kHz. ¹H-²⁹Si cross-polarization (CP) MAS NMR spectra were also recorded utilizing 7 mm silicon nitride rotors spinning at 8.2 kHz. The cross-polarization contact time was 3 ms, and the pulse repetition rate was 3 sec. The 50.3 MHz ¹³C CP MAS NMR spectra were obtained with a 750 μsec contact time and a 2.5 sec pulse repetition rate using silicon nitride rotors at the same spinning speed. The 200 MHz ¹H MAS NMR spectra were also obtained at a spinning speed of 8.2 kHz with a 2 sec pulse repetition rate. The chemical shifts are reported in ppm relative to external tetramethylsilane (TMS) for ¹H, ¹³C, and ²⁹Si.

To evaluate the adsorption efficiency of the sorbent material, a granular sample of the sorbent material was loaded into a sample tube. The granular sample was prepared by first pressing a pellet of the sorbent material (1000 kg force in a 31 mm inner diameter die) and then crushing and sieving the pellet to recover particles having an average size in the range of about 0.3-0.8 mm. In a typical experiment, about 50 mg of sorbent particles were placed into a polypropylene sample tube of 6 mm inner diameter and both ends of the tube were blocked with cellulose acetate fibers. A blank (i.e., reference) sample tube was similarly prepared but without adding any sorbent material.

Mercury uptake (mercury adsorption) measurements were carried out by injecting 7 ng pulses of elemental mercury vapor in a nitrogen carrier gas flowing through the sample tube at a constant flow rate of 70 cc/min. The breakthrough mercury (i.e., un-adsorbed mercury that passed through the tube) was collected by a gold trap and analyzed by cold vapor atomic absorption spectrometry (CVAAS) using a Perkin Elmer FIAS equipped with an amalgam system accessory and interfaced to a Perkin Elmer 4100ZL spectrometer. Multiple pulses of mercury vapor were dosed in sequence and analyzed individually for mercury breakthrough.

Both the parent and the mercaptopropyl-functionalized SBA-15 have well-resolved XRD patterns with a prominent peak at 0.8°, and two weak peaks at 1.6° and 1.7°, which match well with those reported for SBA-15. The SBA-15 can be indexed to a hexagonal lattice with a d(100)-spacing of 99.1 Å, which corresponds to a unit cell parameter, a₀˜114 Å, where a₀=2d(100)/√3).

FIG. 1 shows a typical argon adsorption-desorption isotherm of the mercaptopropyl-functionalized SBA-15. The functionalized material (8% MTP) exhibits an irreversible type IV adsorption isotherm with an H1 sorption hysteresis loop as defined by the International Union of Pure and Applied Chemistry (IUPAC) classification scheme and is substantially identical in its overall adsorption-desorption profile to the parent SBA-15. A corresponding BJH plot based on the isotherm is shown in the inset for FIG. 1. From the BJH plot, the sorbent material has a narrow pore size distribution with a predominant mesopore size of about 55 Å.

With an increase in the loading of mercaptopropyl groups, a shift in hysteresis toward low relative pressure and a slight decrease in overall argon adsorption volume are observed. The calculated pore structure parameters, summarized in Table 1, show a trend of slightly decreasing surface area, pore volume and pore diameter with increased loading of mercaptopropyl groups.

TABLE 1
Pore structure parameters of MTP-functionalized SBA-15
	ABET
Material	(m2/g)	ABJH (m2/g)	VBJH (cm3/g)	DBJH (nm)
SBA-15	704	685	1.12	6.53
SBA-15 (1% MTP)	589	676	0.97	5.74
SBA-15 (2% MTP)	640	733	1.10	5.98
SBA-15 (4% MTP)	578	665	0.97	5.82
SBA-15 (8% MTP)	467	542	0.71	5.27
SBA-15 (16% MTP)	374	447	0.56	5.03

TEM images of parent SBA-15 material and mercaptopropyl group functionalized SBA-15 (8% MTP) reveal hexagonal arrays of uniform channels of about 6 nm in diameter (FIG. 2a). Line spacing from the FFT show d-spacings ranging from 8-10 nm, indicating that slightly less than half of this spacing is wall material with the remainder being void space. The TEM image of the functionalized material also illustrates a tightly packed hexagonal silica grain, which mimics individual pore channels of the SBA-15.

As revealed by XRD, TEM, and argon adsorption measurements, the mercaptopropyl group functionalized SBA-15 has a uniform mesoporous structure with a narrow pore size distribution and a high surface area inherited from the parent SBA-15 silica. The average pore dimension shrinks slightly due to occupation of the incorporated mercaptopropyl groups. It is apparent that the inorganic wall structure of the SBA-15 silica remains intact during the modification process.

EELS imaging of sulfur in the mercaptopropyl group functionalized SBA-15 show a uniform distribution of the functional groups within the SBA-15 matrix (FIG. 2b). This suggests that the functional groups penetrated the entire depth of the channels. Sulfur is substantially absent from the channel walls.

The FTIR spectrum in the hydroxyl stretching range of the parent SBA-15 shows a narrow and intense band at 3740 cm⁻¹ and a broad low-frequency band centered at 3400 cm⁻¹ (FIG. 3a). The narrow band at 3740 cm⁻¹ is due to the stretching vibration mode of isolated terminal silanol (Si—OH) groups, while the broad low-frequency band at 3400 cm⁻¹ corresponds to adsorbed water, silanol groups and the hydrogen-bonding interaction there between.

For the mercaptopropyl group functionalized SBA-15, both bands at 3740 cm⁻¹ and 3400 cm⁻¹ decrease in intensity with increasing mercaptopropyl group loading (FIG. 3(b)-(f). The presence of mercaptopropyl groups is identified by the appearance of the C—H stretching bands at 2927 cm⁻¹ and 2857 cm⁻¹.

The ²⁹Si MAS NMR spectrum of the parent SBA-15 is broad and dominated by an intense line at −107 ppm along with two shoulders at −98 and −89 ppm (FIG. 4, curve a1). The latter two shoulders at −98 and −89 ppm appear in increased intensity in the spectrum with ¹H cross-polarization (FIG. 4, curve a2), which may indicate a close location of these silicon atoms to protons. By analogy, the chemical shift at −107 ppm for zeolites and amorphous silica materials can be assigned to Si(OSi)₄ (Q4, Q_n=Si(OSi)_n(OH)_4-n, n=2−4) structural units, and the lines at −98 and −89 ppm can be assigned to Si(OSi)₃OH (Q3) and Si(OSi)₂(OH)₂ (Q2) structural units, respectively. The Q4 structural units represent regularly interlinked SiO₄ tetrahedra in the interior of the mesopore walls, while Q3 and Q2 structural units are present on the wall surface, i.e., associated with silanol groups.

In contrast to the parent SBA-15 silica, the ²⁹Si MAS NMR spectra of the mercaptopropyl group functionalized SBA-15 show only a broad line centered at −107 ppm due to Q4 structural units. The lines at −98 and −89 ppm, which are due to Q3 and Q2 structural units, are missing even in the spectrum with ¹H cross-polarization (FIG. 4, curves b1 and b2). Three additional lines at −47, −57 and −66 ppm appear and their intensity is enhanced by ¹H cross-polarization (FIG. 4, curves b1 and b2). This indicates formation of new siloxane linkages (Si—O—Si) of mercaptopropylsilane silicon to the surface silicons of the SBA-15 silica. The line at −66 ppm is associated with silicon of mercaptopropylsilane attached via three siloxane bonds, (—O—)₃SiCH₂CH₂CH₂SH (T3, T_m=RSi(OSi)_m(OR′)_3-m, m≦3, where R and R′=H or a hydrocarbon chain), while the lines at −57 ppm and −47 ppm are associated with silicon attached via two siloxane bonds (—O—)₂SiCH₂CH₂CH₂SH (T2), and one siloxane bond, (—O—)SiCH₂CH₂CH₂SH (T1), respectively.

The ¹³C MAS NMR spectra of the mercaptopropyl group functionalized SBA-15 reveal three well-resolved lines at 49, 27 and 10 ppm (FIG. 5). These lines can be assigned to the C3, C2, and C1 carbons of the incorporated mercaptopropyl groups, (—O—)₃SiCH₂(1)CH₂(2)CH₂(3)SH, respectively. No lines at 59 ppm and 16 ppm due to residual ethoxy carbon are observed.

The ¹H MAS NMR spectrum of the parent SBA-15 silica (FIG. 6a) shows a narrow line at 1 ppm embedded in the central part of an extremely broad line spanning the entire range of chemical shifts due to various second order nuclear spin interactions. Because of the siliceous nature of the material, these lines are likely associated with the protons of the silanol groups on the internal surface of the SBA-15 silica.

By contrast, ¹H MAS NMR spectra of the mercaptopropyl group functionalized SBA-15 show a wider range of chemical shifts with a number of resolved lines at 0, −1, −4 ppm (FIG. 6b), but not at 1 ppm. These lines are apparently due to the protons in the side chains of the incorporated mercaptopropyl groups.

The parent SBA-15 silica shows a constant but slight weight loss with increasing temperature (FIG. 7a, Table 2), which can be due to surface dehydration and/or dehydroxylation. In contrast, the mercaptopropyl group functionalized SBA-15 shows a progressive weight loss (FIG. 7b-7f), apparently due to decomposition of the mercaptopropyl groups. The decomposition temperature, identified in the DTG curve (FIG. 7f′), is approximately 300° C., which is well above the boiling point of the source liquid (3-mercaptopropyl)triethoxysilane. The molar weight loss calculated from the total weight loss (Table 2) agrees well with the amount of mercaptopropyl groups added to the impregnation solution over the range of 1-8 molar % (calculated with respect to silicon in the parent SBA-15 silica). However, the total molar weight loss for the sample with the highest molar loading (16%) was 14.8%. The mercaptopropyl group functionalized SBA-15 samples were observed to be more hydrophobic showing less weight loss upon thermal treatment from room temperature to 100° C. as compared with the parent SBA-15 silica, indicating improved hydrophobicity.

As evidenced by EELS imaging of sulfur, FTIR, and ¹H, ¹³C and ²⁹Si MAS NMR spectra, the incorporated mercaptopropyl groups are uniformly dispersed over the SBA-15 silica particles and chemically bonded to the internal surface of the channels of the SBA-15. This may account for the increasing immobility and thermal stability of the incorporated mercaptopropyl groups in comparison with the neat (3-mercaptopropyl)triethoxysilane liquid. The observed improved hydrophobicity of the mercaptopropyl group functionalized SBA-15 suggests that the sorbent material can be used in a high humidity environment.

Spectra from FTIR, ¹H and ²⁹Si MAS NMR measurements provide information regarding the nature of the attachment and bonding patterns of the mercaptopropyl groups to the internal surface of the SBA-15 silica. The parent SBA-15 silica possesses abundant silanol groups which line the tubular channels, as evidenced by the intensive hydroxyl stretching bands in the FTIR spectra as well as by the well-resolved resonance lines of Q3 and Q2 structural units in the ²⁹Si CP MAS NMR spectra. The silanol groups are apparently located in a relatively uniform chemical environment with some mobility, as indicated by the well-resolved and narrow line in the ¹H MAS NMR spectrum. These spectral features become less predominant and disappear upon incorporation of the mercaptopropyl groups, suggesting that the surface silanol groups serve as sites for anchoring the mercaptopropyl groups and are consumed. The most probable mechanism for the attachment of the mercaptopropyl groups to the internal surface of the parent SBA-15 silica is through one, two, or three siloxane linkages (Si—O—Si) connecting a mercaptopropylsilane silicon to the surface silicon atoms of the SBA-15 material. Such a siloxane linkage may also occur between neighboring mercaptopropylsilane silicon atoms. A wider range of chemical shifts or the broad line shape of the ¹H MAS NMR spectra of the mercaptopropyl group functionalized SBA-15 silica suggest that mercaptopropyl groups are present in a variety of configurations, which restricts their free mobility or rotation.

In addition, ¹³C MAS NMR confirmed that the structure of the mercaptopropyl groups remain intact during the incorporation process. The lack of resonance lines of any residual ethoxy groups indicate a complete hydrolysis and/or condensation of the mercaptopropylsilane. This suggests that the synthesis method is effective in incorporating mercaptopropyl groups into the SBA-15 silica.

SBA-15 silica functionalized with mercaptopropyl groups can be used as an adsorbent to reduce the concentration of heavy metals (e.g., heavy metal vapors). The adsorbent properties of the functionalized mesoporous SBA-15 silica molecular sieves are inherited from both the inorganic support and the organic moieties. The mesoporous silica framework provides uniform and controlled mesoporosity, whereas the incorporated mercaptopropyl groups define interfacial and bulk characteristics, such as the environment of adsorption sites and the hydrophobicity associated with the alkyl chains.

FIG. 8 shows mercury breakthrough for a sequence of 7 ng pulses of elemental mercury vapor entrained in nitrogen and flowed over samples of (●) cellulose acetate fibers only, (▾) parent SBA-15 silica, (♦) SBA-15 (1% MTP), (⋄) SBA-15 (2% MTP), (▴) SBA-15 (4% MTP) and (∘) SBA-15 (8% MTP). The corresponding total mercury uptake in the first four pulses are integrated and summarized in Table 2. The blank sample tube filled only with cellulose acetate fibers did not show any notable reduction in mercury breakthrough, suggesting that the uptake of mercury vapor by the cellulose acetate fibers is negligible.

For the parent SBA-15, a small reduction in mercury breakthrough was observed only in the first pulse, but not in subsequent pulses. By contrast, the functionalized SBA-15 (1% MTP) shows a substantial reduction in mercury breakthrough of about 24% in the first pulse with decreasing, yet significant levels in the subsequent pulses. The calculated total mercury uptake for the SBA-15 (1% MTP) sorbent is between about seven to eight times greater than the uptake for the parent SBA-15 silica (Table 2). However, as the molar percentage loading of mercaptopropyl groups in the functionalized SBA-15 increases, the data in FIG. 8 show a trend of declining levels of the reduction in mercury breakthrough versus increasing loading of mercaptopropyl groups.

The data from TGA measurements indicate that the mercaptopropyl groups can be incorporated into the SBA-15 silica via incipient-wetness impregnation up to a molar percentage loading of about 15% verses the parent SBA-15 silica. The incorporated mercaptopropyl silane groups are chemically bonded to surface silicons associated with the silanol groups of the parent SBA-15 silica and remain intact during various stages of the preparation. Specifically, the channels of the SBA-15 silica can be uniformly lined with mercaptopropyl groups up to a molar percentage loading of about 15% while retaining the original mesoporosity.

Because the pore dimension of the SBA-15 silica is only slightly narrowed after functionalization with the mercaptopropyl groups (Table 1), and because most heavy metal elements such as mercury have a small atomic size (e.g., about 1.5 Å diameter), such a decrease in mercury breakthrough at higher loadings is not likely caused by steric effects. Without wishing to be bound by theory, it is anticipated that at higher loadings the incorporated mercaptopropyl groups align into a configuration with significant hydrogen bonding interaction among the tails of the functional groups, which may cause a reduction in their adsorption capacity. Such an alignment mechanism suggests that isolated mercaptopropyl groups on the internal surface of the SBA-15 silica may serve as preferred adsorption sites for heavy metal (e.g., mercury) vapor.

TABLE 2
Mercaptopropyl group content and total mercury uptake
of MTP-functionalized SBA-15
	Weight loss	MTP molar content	Mercury uptake
Material	(wt. %)	(wt. %)	(ng/g)
SBA-15	0	n/a	11.0
SBA-15 (1% MTP)	1.0	0.8	80.6
SBA-15 (2% MTP)	2.1	1.7	66
SBA-15 (4% MTP)	4.6	4.0	59.2
SBA-15 (8% MTP)	10.1	9.9	25.4
SBA-15 (16% MTP)	13.9	14.8	n/a

In Table 2, the total weight loss is determined from TGA measurements at 800° C. and normalized to the weight loss for SBA-15. The total weight loss, assuming complete decomposition of MTP at 800° C., is used to determine the MTP content in each sample. The measured value for mercury uptake was based on the total mass of the material.

As shown in Table 2, mercaptopropyl group functionalized SBA-15 can be an effective adsorbent for elemental mercury vapor from a gas stream as compared with the parent SBA-15. However, the decreased adsorption efficiency and capacity at the higher loading levels of mercaptopropyl groups implies that not only the mercaptopropyl groups, but also the interfacial properties on the internal surface of the functionalized SBA-15 can influence adsorption performance.

In a separate test, a cigarette tobacco smoke stream containing both particulate matter and volatile constituents was injected in eight 2 second 35 ml pulses at intervals of 60 seconds into an 8 mm sample tube containing 0.037 g of SBA-15 (8% MTP) material. The tobacco smoke stream comprised 5.3 ng arsenic, 61.8 ng cadmium, 4.9 ng mercury, about 10 ng nickel, 36.1 ng lead, and 1.86 ng selenium. The result showed a 44% reduction in cadmium breakthrough.

FIG. 9 depicts a traditional lit end cigarette comprising a filter 10, tobacco rod 12, and tipping paper 14. See, for example, the filter constructions in FIGS. 1-7 of commonly-owned U.S. Pat. No. 6,595,218, the disclosure of which is hereby incorporated by reference. The filter 10 can have any desired construction wherein the sorbent is incorporated therein.

FIG. 10 depicts an electrically heated smoking system 20 comprising a specially constructed cigarette 22 and an electrical lighter 24, the cigarette 22 including a filter portion 26 and a tobacco rod portion 28. When inserted in lighter 24, the cigarette releases tobacco flavor and aroma as a result of heater blades heating the cigarette along char lines 29. See, for example, commonly-owned U.S. Pat. No. 5,692,529, the disclosure of which is hereby incorporated by reference. The filter portion 26 can have any desired construction wherein the sorbent is incorporated therein.

FIG. 11 depicts a smoking article 30 having a filter 32, tobacco bed 34 and heating element 36 at the end of bed 34. See, for example, commonly-owned U.S. Pat. No. 4,966,171, the disclosure of which is hereby incorporated by reference. When drawn upon, heat from the heating element 36 heats the bed of tobacco to release tobacco flavors and aromas. The filter 32 can have any desired construction wherein the sorbent is incorporated therein.

In preferred embodiments, the sorbent can be incorporated in a smoking article such as traditional or non-traditional cigarettes, or in cigarette filters. Smoking articles and cigarette filters comprising sorbent media and methods of incorporating sorbent media in cigarettes and in cigarette filters are disclosed in commonly-owned U.S. Pat. No. 6,814,786 and in commonly-owned U.S. Patent Publication No. 2003/0159703, the contents of which are herein incorporated by reference.

All of the above-mentioned references are herein incorporated by reference in their entirety to the same extent as if each individual reference was specifically and individually indicated to be incorporated herein by reference in its entirety.

While the invention has been described with reference to preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the invention as defined by the claims appended hereto.

Claims

1. A smoking article comprising a sorbent having mercaptopropyl groups bound to an inorganic molecular sieve substrate, wherein the sorbent is capable of reducing the concentration of at least one heavy metal constituent in mainstream smoke.

2. The smoking article of claim 1, wherein the smoking article is selected from the group consisting of a cigarette, a pipe, a cigar and a non-traditional cigarette.

3. The smoking article of claim 1, wherein the sorbent is located in a filter selected from the group consisting of a mono filter, a dual filter, a triple filter, a cavity filter, a recessed filter, and a free-flow filter.

4. The smoking article of claim 1, wherein the heavy metal constituent comprises mercury and/or cadmium.

5. The smoking article of claim 1, wherein the inorganic molecular sieve substrate (a) comprises mesoporous or microporous molecular sieves; (b) is selected from the group consisting of a zeolite, silicate, aluminophosphate, mesoporous silicate, mesoporous aluminosilicate, and mixtures thereof; or (c) comprises a zeolite selected from the group consisting of zeolite ZSM-5, zeolite A, zeolite X, zeolite Y, zeolite K-G, zeolite ZK-5, zeolite Beta, zeolite ZK-4, and mixtures thereof.

6. The smoking article of claim 1, wherein the sorbent comprises (a) (3-mercaptopropyl)silane covalently bound to a zeolite; (b) SBA-15 silica having incorporated therein up to about 15 mole percent of (3-mercaptopropyl)trialkoxysilane with respect to silicon in the SBA-15; or (c) (3-mercaptopropyl)silane covalently bound to a mesoporous silicate.

7. The smoking article of claim 1, wherein the mercaptopropyl group is covalently bound to exterior and interior surfaces of the inorganic molecular sieve substrate and wherein the inorganic molecular sieve substrate is a mesoporous molecular sieve.

8. The smoking article of claim 1, wherein the sorbent is in granular form having a particle size from about 20 mesh to about 60 mesh and/or the smoking article comprises from about 10 mg to about 300 mg or from about 100 mg to about 200 mg of the sorbent.

9. A cigarette filter comprising a sorbent having mercaptopropyl groups bound to an inorganic molecular sieve substrate, wherein the sorbent is capable of reducing the concentration of at least one heavy metal constituent such as mercury and/or cadmium in mainstream smoke.

10. The cigarette filter of claim 9, wherein the inorganic molecular sieve substrate (a) comprises mesoporous or microporous molecular sieves; (b) is selected from the group consisting of a zeolite, silicate, aluminophosphate, mesoporous silicate, mesoporous aluminosilicate, and mixtures thereof, or (c) comprises a zeolite selected from the group consisting of zeolite ZSM-5, zeolite A, zeolite X, zeolite Y, zeolite K-G, zeolite ZK-5, zeolite Beta, zeolite ZK-4, and mixtures thereof.

11. The cigarette filter of claim 9, wherein the sorbent comprises (a) (3-mercaptopropyl)silane covalently bound to a zeolite; (b) SBA-15 silica having incorporated therein up to about 15 mole percent of (3-mercaptopropyl)trialkoxysilane with respect to silicon in the SBA-15; or (c) (3-mercaptopropyl)silane covalently bound to a mesoporous silicate.

12. The cigarette filter of claim 9, wherein the mercaptopropyl group is covalently bound to exterior and interior surfaces of the inorganic molecular sieve substrate and wherein the molecular sieve is a mesoporous molecular sieve.

13. The cigarette filter of claim 9, wherein the sorbent is in granular form having a particle size from about 20 mesh to about 60 mesh and/or the cigarette filter comprises from about 10 mg to about 300 mg or from about 100 mg to about 200 mg of the sorbent.

14. The cigarette filter of claim 9, wherein the filter is selected from the group consisting of a mono filter, a dual filter, a triple filter, a cavity filter, a recessed filter, and a free-flow filter.

15. The cigarette filter of claim 9, wherein the filter comprises cellulose acetate tow, cellulose paper, mono cellulose, mono acetate, and combinations thereof.

16. The cigarette filter of claim 9, wherein the sorbent is incorporated into one or more cigarette filter parts selected from the group consisting of shaped paper insert, a plug, a space, cigarette filter paper, and a free-flow sleeve.

17. The cigarette filter of claim 9, wherein the sorbent is incorporated with cellulose acetate fibers forming a plug or a free-flow filter element.

18. The cigarette filter of claim 9, wherein the sorbent is incorporated with polypropylene fibers forming a plug or free-flow filter element.

19. The cigarette filter of claim 9, wherein the sorbent is incorporated in at least one of a mouthpiece filter plug, a first tubular filter element adjacent to the mouthpiece filter plug, and a second tubular filter element adjacent to the first tubular element.

20. The cigarette filter of claim 9, wherein the sorbent is incorporated in at least one part of a three-piece filter including a mouthpiece filter plug, a first filter plug adjacent to the mouthpiece filter plug, and a second filter plug adjacent to the first filter plug.

21. A method of making a cigarette filter, the method comprising incorporating a sorbent into a cigarette filter, wherein the sorbent comprises mercaptopropyl groups bound to inorganic molecular sieve substrate, and wherein the filter is a mono filter, a dual filter, a triple filter, a cavity filter, a recessed filter, or a free-flow filter.

22. A method of making a cigarette, the method comprising:

(i) providing a cut filler to a cigarette making machine to form a tobacco column;

(ii) placing a paper wrapper around the tobacco column to form a tobacco rod; and

(iii) attaching the cigarette filter of claim 9 to the tobacco rod using tipping paper to form the cigarette.

23. A method of treating mainstream smoke comprising contacting mainstream tobacco smoke with a sorbent having at least one mercaptopropyl group bound to an inorganic molecular sieve substrate while drawing the smoke through a smoking article, wherein the sorbent reduces the concentration of at least one heavy metal constituent such as mercury and/or cadmium in mainstream smoke.