Classifications

• • A—HUMAN NECESSITIES
  • A24—TOBACCO; CIGARS; CIGARETTES; SIMULATED SMOKING DEVICES; SMOKERS' REQUISITES
  • A24D—CIGARS; CIGARETTES; TOBACCO SMOKE FILTERS; MOUTHPIECES FOR CIGARS OR CIGARETTES; MANUFACTURE OF TOBACCO SMOKE FILTERS OR MOUTHPIECES
  • A24D3/00—Tobacco smoke filters, e.g. filter-tips, filtering inserts; Filters specially adapted for simulated smoking devices; Mouthpieces for cigars or cigarettes
  • A24D3/06—Use of materials for tobacco smoke filters
  • A24D3/16—Use of materials for tobacco smoke filters of inorganic materials
  • A24D3/163—Carbon
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/30—Active carbon
  • C01B32/312—Preparation
  • C01B32/318—Preparation characterised by the starting materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
  • B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/30—Active carbon
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/30—Active carbon
  • C01B32/312—Preparation

Definitions

• the present invention relates to methods for preparing porous carbon material, and in particular to methods designed to produce porous carbon which exhibits selectivity for low molecular weight aldehydes, such as formaldehyde, and for hydrogen cyanide.
• the selective porous carbon is particularly useful for smoke filtration in smoking articles, as the porous structure provides improved adsorption of these smoke vapour phase constituents which are generally poorly adsorbed by conventional activated carbon.
• Filtration is used to reduce certain particulates and/ or vapour phase constituents of tobacco smoke inhaled during smoking. It is important that this is achieved without removing significant levels of other components, such as organoleptic components, thereby degrading the quality or taste of the product.
• Smoking article filters may include porous carbon materials to adsorb certain smoke constituents, typically by physisorption.
• porous carbon materials can be made from the carbonized form of many different organic materials, most commonly plant-based materials such as coconut shell.
• synthetic carbons are used, such as resins prepared by polycondensation reactions.
• Activated carbon materials have become widely used as versatile adsorbents owing to their large surface area, microporous structure, and high degree of surface reactivity. In particular, these materials are especially effective in the adsorption of organic and inorganic pollutants due to the high capacity of organic molecules to bind to carbon.
• Activated carbons are commonly produced from materials including coconut shell, wood powder, peat, bone, coal tar, resins and related polymers. Coconut shell is particularly attractive as a raw material for the production of activated carbon because it is cheap and readily available, and is also environmentally sustainable. Furthermore, it is possible to produce from coconut shell activated carbon material which is highly pure and has a high surface area.
• microporous carbon is synthetic carbons, such as those formed by a polymerisation reaction, such as resin-based synthetic carbons.
• Such carbons may, for example, be prepared by polycondensation of an aldehyde and a phenol.
• the performance and suitability of porous carbon material as an adsorbent in different environments is determined by various physical properties of the material, including the shape and size of the particles, the pore size, the surface area of the material, and so on. These various parameters may be controlled by manipulating the process and conditions by which the porous carbon is produced. Generally, the larger the surface area of a porous material, the greater is the adsorption capacity of the material. However, as the surface area of the material is increased, the density and the structural integrity are reduced. Furthermore, while the surface area of a material may be increased by increasing the number of pores and making the pores smaller, as the size of the pores approaches the size of the target molecule, it is less likely that the target molecules will enter the pores and adsorb to the material.
• porous carbon material has a strong influence on its properties. It is therefore possible to produce carbon particles having a wide range of shapes, sizes, size distributions, pore sizes, pore volumes, pore size distributions and surface areas, each of which influences their effectiveness as adsorbents.
• the attrition rate is also an important variable; low attrition rates are desirable to avoid the generation of dust during high speed filter manufacturing.
• micropores pores in an adsorbent material that are less than 2 nm in diameter are called “micropores”, and pores having diameters of between 2 nm and 50 nm are called “mesopores”. Pores are referred to as “macropores” if their diameter exceeds 50 nm. Pores having diameters greater than 500 nm do not usually contribute significantly to the adsorbency of porous materials.
• activated carbon material exhibits excellent general filtration of unwanted substances from the vapour phase of tobacco smoke, there are some smoke vapour constituents that are poorly adsorbed and these include low molecular weight aldehydes (such as formaldehyde) and hydrogen cyanide (HCN).
• aldehydes such as formaldehyde
• HCN hydrogen cyanide
• the present invention seeks to provide a method for preparing porous carbon materials which have nitrogen-containing groups on the surface of the carbon, to enhance selective adsorption of low molecular weight aldehydes and HCN.
• the present invention seeks to provide porous carbon materials having nitrogen- containing groups on their surfaces.
• a method of preparing porous carbon with adsorbent properties for use in smoke filtration comprising preparing the porous carbon in the presence of a nitrogen- donating agent.
• a porous carbon is provided which is obtained or obtainable by a method according to the first aspect of the invention.
• a filter element for a smoking article is provided, comprising a porous carbon according to the second aspect of the invention.
• a smoking article comprising a porous carbon according to the second aspect of the invention.
• the present invention relates to a method involving the addition of nitrogen- containing groups to the surface of porous carbon by preparing the carbon in the presence of a nitrogen-donating agent.
• a nitrogen-donating agent Preferably the porous surface structure of the carbon is formed in the presence of the nitrogen-donating agent, so that the nitrogen groups are present within the porous structure
• the porous carbon is a resin-based synthetic carbon, such as the carbon prepared by polycondensation of an aldehyde and a phenol. If available, commercially available polycondensates may be used.
• the starting material may be a phenolic compound such as phenol, resorcinol, catechin, hydrochinon and phloroglucinol, and an aldehyde such as formaldehyde, glyoxal, glutaraldehyde or furfural.
• a commonly used and preferred reaction mixture comprises resorcinol (1,3-dihydroxybenzol) and formaldehyde, which react with one another under alkaline conditions to form a gel- like polycondensate.
• the polycondensation process will usually be conducted under aqueous conditions.
• the reaction mixture may be warmed.
• the polycondensation reaction will be carried out at a temperature above room temperature and preferably between 40 and 90 °C.
• the polycondensation reaction is carried out in the presence of a nitrogen-donating agent so that the resultant resin has an increased nitrogen content and increased presence of nitrogen-containing groups on its surface.
• a nitrogen-donating agent for example, an aqueous solution containing the nitrogen-donating agent is added to an aqueous solution of resorcinol and formaldehyde under vigorous stirring to yield a homogeneous solution. This solution is then incubated to provide the polycondensate. The incubation period may be between 5 minutes and 24 hours.
• the rate of the polycondensation reaction as well as the degree of crosslinking of the resultant gel can, for example, be influenced by the relative amounts of the alcohol and catalyst. The skilled person would know how to adjust the amounts of these components used to achieve the desired outcome.
• the size reduction of the polycondensate may be carried out using conventional mechanical size reduction techniques or grinding. It is preferred that the size reduction step results in the formation of granules with the desired size distribution, whereby the formation of a powder portion is substantially avoided.
• the polycondensate (which has optionally been reduced in particle size) then undergoes pyrolysis.
• the pyrolysis may also be described as carbonisation.
• the surface properties of the resultant carbon are changed by treating the polycondensate before, during or after pyrolysis with a nitrogen-donating agent, optionally as well as with other more conventional means, such as steam, air, C0 2 , oxygen or a mixture of gases, which may be diluted with nitrogen or another inert gas. It is particularly preferred to use a mixture of nitrogen and steam.
• the activation stage preferably takes place in a gaseous atmosphere comprising nitrogen, water and/ or carbon dioxide.
• the dried gels used in the present invention may be non-activated or, in some embodiments, activated, for example steam activated or activated with carbon dioxide. Activation is preferred in order to provide an improved pore structure.
• the carbon precursor is preferably pyrolysed before then being activated.
• Conventional methods of pyrolysis may be used.
• the nitrogen-donating agent may be added to the material before or after the pyrolysis step, but it is preferably added before any pyrolysis step and before the activation step.
• Pyrolysis is a chemical process of incomplete combustion of a solid when subjected to high heat. By the action of heat, pyrolysis removes hydrogen and oxygen from the solid, so that the remaining product, the char, is composed primarily of carbon. Suitable pyrolysis or carbonisation methods that may be used include those that will be familiar to the skilled person, such as the pit method, the drum method, and destructive distillation.
• the incubation temperature and time may be between 300°C and 1000°C, and between 30 minutes and 4 hours, respectively.
• the pyrolysis step may involve heating the pre-treated carbon to a temperature of at least 500°C and maintaining the carbon at that temperature for a number of hours.
• the pyrolysis step involves heating the pre-treated carbon at a rate of 5-10°C/minute to 600°C under N 2 flowing at a rate of 10-200 cm 3 /min. In one embodiment, the pyrolysis step is carried out at a temperature of no more than 600°C, more preferably at a temperature of no more than 550°C, or of about 500°C. Pyrolysis at these temperatures is preferred as they provide a high nitrogen content and good surface area. Pyrolysis at higher temperatures may lead to a reduction in nitrogen content and can result in a lower surface area due to structural shrinkage.
• the carbon After pyrolysis, the carbon is cooled and the carbon surface is preferably deactivated, for example by exposure to a humid N 2 flow. This deactivation is necessary because of the high risk of exothermic 0 2 adsorption causing red-heat.
• the pyrolysed carbon is activated. This may be done by either physical or chemical means, and conventional activation techniques can be used.
• the material is activated by physical means, and most preferably the material is activated using nitrogen and steam, or alternatively, co 2 .
• the material is activated by reaction with steam under controlled nitrogen atmosphere in a kiln such as a rotary kiln.
• the temperature is important during the activation process. If the temperature is too low, the reaction becomes slow and is uneconomical. On the other hand, if the temperature is too high, the reaction becomes diffusion controlled and results in loss of the material.
• Activation of the material using nitrogen and steam may be performed at a temperature of between 600°C and 1100°C, and preferably activation is performed at a temperature of between 700°C and 900°C. Most preferably, the material is activated at about 850°C. The activation process is preferably carried out for between 30 minutes and 4 hours. Most preferably, the material is activated for 1 hour. As the temperature is increased, the nitrogen content is decreased.
• the material is activated by reaction with carbon dioxide.
• activation of the material may be performed at a temperature of between 400°C and 1000°C, and preferably activation is performed at a temperature of between 600°C and 800°C.
• the activation process is preferably carried out for between 30 minutes and 4 hours.
• the donating agent is able to add nitrogen-containing groups to the carbon's surface and these groups act as preferential sites for aldehyde and HCN adsorption. This hypothesis is supported by the experimental data provided and discussed below, and in particular by the XPS (X-ray photoelectron spectroscopy) results.
• porous carbon produced according to the methods of the present invention exhibit significantly increased selectivity for formaldehyde and HCN.
• the nitrogen-donating agent may be an amino acid or amino acid derivative, an amine, including an aromatic amine, or an imidazole, an imidazole derivative or a compound including the pyridine-like nitrogen of imidazole, such as 1 -methylimidazole.
• the nitrogen-donating agent is lysine, L-hydroxylysine, L-arginine, L-histidine, L- aspartic acid, 1 -methylimidazole (MIM), ethylenediamine (EDA), propylamine, dimethy amine, 2-propylamine, trimethylamine or aniline.
• Particularly preferred agents are lysine, MIM and EDA.
• the nitrogen-donating agent is preferably added to the constituent reagents of the polycondensate in the form of an aqueous solution. This solution may be added to the mixture of phenolic compound and aldehyde prior to polymerisation.
• the amount of nitrogen-donating agent used as a molar ratio to the amount of the phenolic compound may be between 30:1 and 3:1 (phenolic compound: nitrogen donating agent).
• the molar ratio of phenolic compound to water is preferably in the range of between 1 :3 and 1 :50 (phenolic compound: water).
• the surface areas of activated carbon materials are estimated by measuring the variation of the volume of nitrogen adsorbed by the material in relation to the partial pressure of nitrogen at a constant temperature. Analysis of the results by mathematical models originated by Brunauer, Emmett and Teller results in a value known as the BET surface area.
• the BET surface area of the activated carbon materials produced by the method is still important for the adsorption of smoke constituents other than low molecular weight aldehydes and HCN.
• the activation step may be controlled to ensure that the resultant product contains the desired volume of micropores.
• the porous carbon materials produced according to the present invention preferably have a BET surface area of at least 400, 450, 500, 550, 600, 650, 700, 750, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800 or at least 1900 m 2 /g.
• Porous carbon materials with BET surface areas of between 500 m 2 /g and 1300 m 2 /g are preferred, and material with surface areas of between 600 m 2 /g and 1200 m 2 /g are most preferred.
• the porous carbon materials of the invention preferably have a pore volume (as estimated by nitrogen adsorption) of at least 0.3 cm 3 /g, and desirably at least 0.5 cm 3 /g.
• Carbon materials with pore volumes of at least 0.5 cm 3 /g are particularly useful as an adsorbent for tobacco smoke.
• Carbon materials according to the invention with pore volumes significantly higher than 1 cm 3 /g are low in density and are therefore less easy to handle in cigarette production equipment. Such carbon materials are less favourable for use in cigarettes or smoke filters for that reason.
• the activated carbon produced by the methods of the present invention may be provided in monolithic or particulate form.
• Particles will preferably have a particle size in the range of between 10 ⁇ and 1500 ⁇ .
• the mean particle size is between 100 ⁇ and 1000 ⁇ , and more preferably between 150 ⁇ and 800 ⁇ .
• the particles of activated carbon material have a mean size of between 250 ⁇ and 750 ⁇ . The smaller the particles are, the larger is the combined surface area, however, if the size of the particles used is too small, the particles can interfere with manufacturing processes, especially high speed processes as used to manufacture cigarette filters.
• the mass percentage of (resorcinol+formaldehyde) and lysine in solution was approximately 30 weight % and molar ratio of resorcinohlysine was 6.6 with thermal curing (1 day at 50°C and 1 day at 90°C).
• the obtained bulk polymer was dried at 50°C for 1 day and pyrolysed at 700°C for 2 hours under nitrogen atmosphere.
• the resultant carbon had a BET surface area of 460 m 2 /g, a total pore volume of 0.23 cm 3 /g, and a micropore volume of 0.22 cm 3 /g.
• the surface nitrogen was detected using IR but the surface groups were not identified.
• sample 08-12-05 The process used to synthesise sample 08-12-05 was repeated, except that the surface area and porosity were slightly increased, so that the sample had a BET surface area of 580 m 2 /g, a total pore volume of 0.27 cm 3 /g and a micropore volume of 0.24 cm 3 / g.
• Performance of both of these carbon samples in a cigarette was measured by placing 60 mg into the cavity filter of a reference cigarette.
• the filter construction was a triple filter in the form of cellulose acetate - carbon granules - cellulose acetate. Filters having an empty cavity, or an equal weight of sorbite (coal based carbon) were used as controls. Sorbite was chosen as a control carbon because it has similar physical properties to sample 08-12-05 (460 m 2 /g surface area, 0.26 cm 3 /g total pore volume and 0.25 cm 3 /g micropore volume).
• XPS measurements (Axis Ultra, Kratos Analytical) on N I s signal are enabled to reveal the changes occurring in nitrogen species present on carbon surfaces after pyrolysis.
• the fitting of the N I s peaks gave the following binding energies: 399.8 ⁇ 0.3 eV (amide and/or pyrrolic nitrogen), 401.4 ⁇ 0.3 eV (quaternary nitrogen), and 402.8 eV (pyridine-N-oxide).
• the nitrogen content of samples are accordingly of 1.3, 1.9, 1.3, 0.8 and 0.5 wt%.
• the polycondensation of resorcinol with formaldehyde in the presence of MIM was conducted at 50°C for 4 hours and an ambient pressure drying followed by incubation at 800°C.
• thermal curing was carried out at 90°C for 4 hours and, after drying, the sample was thermally treated at 800°C under N 2 .
• micropore volumes of the samples were lower than that of coconut carbon currently typically used in cigarette filters (which is generally 0.4-0.5 cm 3 /g). This was expected to have an effect on the adsorption characteristics of the samples compared to the reference cigarette.
• the filter construction was a triple filter in the form of cellulose acetate - carbon granules - cellulose acetate.
• a filter having an empty cavity of similar dimensions was used as a control.

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• Solid-Sorbent Or Filter-Aiding Compositions (AREA)
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• 2011
  • 2011-01-20 CN CN2011100227952A patent/CN102600798A/zh active Pending
• 2012
  • 2012-01-19 WO PCT/GB2012/050117 patent/WO2012098405A1/en active Application Filing
  • 2012-01-19 CA CA2821581A patent/CA2821581A1/en not_active Abandoned
  • 2012-01-19 KR KR1020137021618A patent/KR20140005245A/ko not_active Application Discontinuation
  • 2012-01-19 EP EP12702612.8A patent/EP2665681A1/en not_active Withdrawn
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