Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
  • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
  • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
  • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
  • D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
  • D01F9/21—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D01F9/22—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyacrylonitriles

Definitions

• the invention relates to activated porous carbon fibers, in particular for the adsorption or separation of gaseous substances, and also to methods for the use and production thereof and of making protective clothing and a filter module.
• the production of activated carbon fibers by surface treatment of carbon fibers has been known for a relatively long time.
• precursor materials of polyacrylonitrile (PAN) or pitch are preferably used because of the good mechanical and adsorption properties of the carbon fibers that can be obtained therefrom.
• PAN polyacrylonitrile
• the production of activated carbon fibers based on polyacrylonitrile precursors begins with the stabilization in air at approximately 230-300° C. that is standard for carbon fibers. Chemical transformation of the polyacrylonitrile forms an infusible fiber.
• the resultant oxidized fiber can be activated directly or, more frequently, first processed further to form a textile structure. Heating the fibers to temperatures above approximately 1200° C. activates them. However, in contrast with the process for conventional carbon fibers, the activation is not carried out in an inert atmosphere, but in an oxidizing one. Typical oxidizing agents of this process step are H 2 O or CO 2 . The reaction of the oxidizing agents results in a strong attack on the surface of the fiber, whereby a porous surface is formed. The size of the specific surface area and the configuration of the carbon atoms within the surface pores substantially determine the selectivity and strength of adsorption of chemical substances by the activated carbon fiber. The activation of the carbon fibers that are produced based on pitch precursors is effected in a similar manner by surface oxidation of the carbonized fiber.
• the production of membranes with a particularly high specific surface area using porous fibers is described in European Patent Application EP 0 394 449 A1, which corresponds to U.S. Pat. No. 5,089,135.
• the membranes are formed by porous hollow carbon fibers.
• the production method provides for spinning polymer mixtures of PAN-based polymer A and (pyrolyzable) polymer B (i.e. a polymer that can be decomposed by heat), if applicable with a solvent and solubilizer, to form hollow polymer fibers.
• the hollow form is achieved, for example, by the use of slotted nozzles, with the inside diameter of the fibers being a few 100 ⁇ m.
• the porosity of the hollow fibers is established by the decomposition of the polymer B.
• the polymer B is decomposed at temperatures below 600° C.
• vinyl and methacrylate polymers are listed as the polymers.
• Their specific viscosity is specified as being preferably in the range of 0.1 to 0.4.
• U.S. Pat. No. 6,364,936 B1 to Rood, et al. describes the set-up of an adsorption/desorption module of activated carbon fibers.
• One or more hollow elements of activated carbon fiber fabric is/are configured lengthwise. The fiber elements are heated directly by electric current in order to be able to carry out selective adsorption of constituents from the gas stream and the subsequent desorption thereof.
• activated carbon fibers including pores of carbon fibers filled at least in part, that is, to at least 30% by volume, by active substances.
• the active substances are formed by carbon, metals and/or metal carbides originating from the carbonization of organic or metallo-organic polymers that are already present in a finely distributed manner in the precursor fiber for the production of carbon fibers.
• the carbon fibers are activated by producing pores that are partly filled with carbon, metal, and/or metal carbide.
• These active centers are formed by the carbonization of particles of an organic or metallo-organic polymer that are distributed in the carbon precursor fiber formed by polyacrylonitrile polymer.
• the production method for carbon fibers described at the beginning does not need to be changed substantially for this.
• the carbon fibers in accordance with the invention are suitable in particular for the adsorption or separation of gases.
• a method that provides for mixed polymers from a polyacrylonitrile-based (PAN-based) precursor for carbon fibers (polymer A) and a carbonizable polymer (polymer B) to be spun to form mixed fibers.
• PAN-based polyacrylonitrile-based
• polymer B carbonizable polymer
• the mixed fibers are stabilized.
• the fibers are carbonized to form the finished activated carbon fibers.
• the polymer B is selected with regard to its solubility and particle size so that it is present in the PAN-based fiber in a finely distributed or microdispersed manner.
• the framework of the carbon fiber is established from the PAN-based portion, while the decomposition product of the polymer B remains (behind) as a highly porous and active material and forms pores that are filled at least in part in and on the carbon fiber.
• the initial composition of the polymer B different carbon residues, metals or metal carbides that have differing selectivities with respect to different adsorbates can also be obtained in this way.
• the polymer B is only partly decomposed so that its solid and non-volatile residue remains as an active substance in the fiber.
• the active centers of the activated carbon fibers are thus substantially formed by the solid decomposition products of the polymer B.
• the method in accordance with the invention provides the following steps:
• PAN-based polymers that are usual in the market for the production of carbon fibers, also called precursors, are used as the polymer A. Typically, they are synthesized as copolymers from over 90 mol % acrylonitrile units and further comonomer units.
• a carbonizable organic or metallo-organic polymer whose carbonization residue is at least 22 wt % and preferably over 30 wt %, is used as the polymer B.
• the carbonization residue is that residue of the polymer B in wt % that results under the conditions of carbonization treatment of the corresponding mixed fiber. These are temperatures above 500° C. under non-oxidizing conditions.
• the carbonization residue of the polymer B preferably is below that of the PAN-based polymer. If the more intensive pyrolysis in the case of polymer B results in a greater volume shrinkage than in the case of the precursor material of polymer A, then opened pores are formed as a result. Particularly preferably, however, polymers B are used that show a comparatively small shrinkage in volume in the case of carbonization. As a result, the regions of carbonized polymer B remain microporous and increase the specific surface area of the fiber in an advantageous manner.
• the pores in the carrier fiber are at least in part filled by the generally microporous decomposition products of the polymer B. The pores are preferably filled to at least 30% by volume and particularly preferably to at least 50% by volume with the decomposition products that are, if applicable, microporous.
• the polymer B content typically lies below 50 wt % of the polymer mixture of A and B and preferably in the range of 3 to 40 wt %.
• the precondition for the formation of discrete regions of residues of the carbonization of polymer B is that the polymer B is already present in the mixed fiber in a finely dispersed or microdispersed manner.
• the particle size of the polymer B should not exceed 50% of the fiber diameter of the resulting mixed fiber.
• the average diameter of the individual particles of the polymer B preferably lies below 1500 nm and particularly preferably below 800 nm.
• the partly filled pores formed after the carbonization of the fibers should not have less than an average minimum diameter. This minimum diameter is approximately 30 nm.
• a microdispersed distribution is guaranteed in particular if the polymer B has a low level of solubility or no solubility at all in the PAN spinning solution.
• Usual PAN spinning solutions for the wet or dry spinning process contain solvents. In accordance with the invention, polymers B that are insoluble in the solvent used are therefore preferred.
• the polymers B are to have a melting point above the process temperature of the oxidization of the mixed fiber. Resins or polymers that cross-link to form infusible compounds are preferred. Examples of suitable organic polymers B are inter alia polyesters, phenolic resins, polyamides, polyaramides, copolyaramides, para-aramides, or cellulose.
• metallo-organic polymers such compounds in which metallic atoms are incorporated directly into the polymer chain and also those in which the metallic atoms are bound in a complex manner, in particular to heteroatoms, such as O or N.
• heteroatoms such as O or N.
• carboxyl, carbonyl, and imine groups crop up in the latter case.
• complex organic metal salts that are present in an aggregated and high-molecular form also can number among the metallo-organic polymers.
• Polyacetates, polymeric cyclopentadienyls or polymeric alcoholates, or acetylacetonates inter alia number among the metallo-organic polymers in accordance with the invention.
• Preferred metal constituents of the metallo-organic polymers are the transition metals, in particular of the first series, and the platinum metals. These are distinguished by high chemical activity in atomic form or as a carbide compound and establish a high and in part very selective adsorption capacity.
• Metallo-organic compounds or complex organic compounds of the elements Ti, Cr, W, Fe, Co, Ni, Pd, and Pt are particularly preferred.
• the metallo-organic polymer B also can contain further metal in elementary form, whereby the active region content of the fiber can be further increased.
• Resin-bonded metal micropowders of the elements Ti, Cr, Fe, or Pt are preferably used in this connection.
• the carbonization residue of the metallo-organic compounds typically includes a mixture of carbon, metal, and metal carbide in a varying composition.
• the carbonization residue of the compound used is preferably over 25 wt %, particularly preferably above 35 wt %.
• the fiber diameter of the mixed fibers in accordance with the invention after the spinning process is below 200 ⁇ m, with the range between 10 to 30 ⁇ m, which is usual for PAN fibers as precursor material for conventional carbon fibers, being preferred. Thick fibers above approximately 60 ⁇ m are, if applicable, also to be constructed as profiled fibers, since in this way their surface area is further enlarged.
• the mixed fibers are rendered infusible. This occurs by oxidation at temperatures of preferably 230 to 300° C. In a known way, as a result of dehydration and cyclization at a molecular level, stabilization of the polyacrylonitrile takes place that renders the polymer infusible and carbonizable.
• the polymers B are also present in an infusible form. If applicable, the cross-linkage of the polymer B that leads to the stabilization likewise first takes place in this method step. Subsequent cross-linkage is observed, for example, in the case of polyesters or phenolic resins.
• a preferred form of heat treatment for the stabilization provides for heating in air to 230° C. with a holding time of approximately 140 minutes at a heating rate of approximately 5° C./minute. Shorter process times can be rendered possible by higher temperature levels, for example approximately 60 minutes at approximately 270° C.
• metallo-organic compounds are used as the polymer B, an isothermal temperature profile at the lowest possible temperature is to be preferred, because overheating of the fiber under oxidizing conditions is to be avoided, since there is a risk of oxidation of the metallo-organic compounds to form metal oxides that are generally undesired.
• Partly carbonized fibers have inter alia reduced thermal conductivity, as a result of which, they have an advantage in applications that demand good thermal insulation compared with the carbon fibers.
• Such partly carbonized fibers are also referred to collectively as carbon fibers in the following.
• a further aspect of the invention is the use of the activated fibers to separate gas mixtures and to adsorb gaseous substances.
• the separation of CO 2 is considered in this connection.
• a typical configuration for separating gaseous substances, and in particular CO 2 as well, is set up out of two modules that alternately perform the function of adsorption, followed by desorption. The modules can then be heated in an advantageous manner by utilizing the electrical conductivity of the carbon fibers.
• the set-up of filter modules for example in the chemical industry, is designated as a further application.
• the fiber material can also be used as a component part of activated and, if applicable, thermally insulating protective clothing.
• the protective clothing can perform the additional function of adsorption of harmful substances.
• the partly carbonized fibers have the advantage over the carbon fibers, since the textile processibility and the wear comfort of the clothing are clearly better.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Inorganic Fibers (AREA)
• Carbon And Carbon Compounds (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)

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Citations (11)

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• 2002
  • 2002-06-17 DE DE10226969A patent/DE10226969B4/de not_active Expired - Fee Related
• 2003
  • 2003-06-13 JP JP2003168936A patent/JP4460232B2/ja not_active Expired - Fee Related
  • 2003-06-16 AT AT03013625T patent/ATE441747T1/de active
  • 2003-06-16 ES ES03013625T patent/ES2333113T3/es not_active Expired - Lifetime
  • 2003-06-16 DE DE50311860T patent/DE50311860D1/de not_active Expired - Fee Related
  • 2003-06-16 EP EP03013625A patent/EP1375707B1/de not_active Expired - Lifetime
  • 2003-06-16 PT PT03013625T patent/PT1375707E/pt unknown
  • 2003-06-17 US US10/463,018 patent/US20030230194A1/en not_active Abandoned
• 2007
  • 2007-01-22 US US11/656,259 patent/US7708805B2/en not_active Expired - Fee Related

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