Technical field

Invention covers production method for exfoliated graphite, equipment for production of exfoliated graphite from expandable intercalation graphite compounds. Furthermore, the invention describes exfoliated graphite with very high adsorption properties and means of its use.

Background art

Known are intercalation graphite compounds, in which graphite is a bearer of positive charges and anions are intercalated between planar layers of graphite crystal lattice. Graphite intercalation compounds are produced by many methods, the main principle of which consists in acting of different oxidants and hosting compounds, which are supposed to be intercalated, on dispersed graphite particles. Nitric acid, hydrogen peroxide, potassium chlorate, ammonium nitrate, potassium dichromate, potassium permanganate and similar compounds (U.S. Pat. No. 4,091,083, U.S. Pat. No. 3,404,061) are mainly used as oxidants. Concentrated sulphuric acid is used as a mixture element with substance, which is to be intercalated, whereas the reaction runs at 600C till 13O0C for several hours, many times in the presence of chlorine gas (E. Stumpp., Physics, 1981, 9-16). Expandable intercalated graphite compounds, also called the expandable graphite, when heated to temperatures over 1500C are accompanied by a major volume expansion as the intercalated substances are transformed to a gas state. Industrial production of exfoliated graphite is usually done by feeding of expandable graphite to the burner flame, resulting in creation of a "black snow". Expansion factor based on conditions varies from 80 till 300 times of original volume, as the result of expansion of graphene layers perpendicular to the surface (EP-B-008512). This property is used for sealing of cables, sealing of gaps for preventing fire propagation in buildings, extinguishing burning metals (mainly sodium, magnesium, aluminum, uranium and titanium) or for protection of melted metals against air in furnaces. Known is also the use for production of gaskets and electrodes in electro technical industry. Known is also the industrial production of carbon mixture of the high reaction ability by method of a cold destruction, and equipment for its production (patent RU2163883). Disadvantage of this apparatus is necessity of photochemical, electrochemical, mechanical, thermochemical, sonochemical or chemical initialization to start explosive decomposition, whereas resulting degree of conversion is insufficient thus the product when further heated reacts, changing its properties and its form (fine dust or ash) is not suitable for practical use as well. Known is also production method for mixture of high reaction ability produced by impedance heating (patent R.U2128624). This method requires use of special materials for reactor and is extremely high in electricity consumption.

Disclosure of the invention

The above mentioned disadvantages can be eliminated by the method according to this invention, the keystone of which is, that expandable graphite is fed on a plane surface, heated underneath to a temperatures between 2000C till 33000C, resulting in very rapid heating of expandable graphite with the temperature rate increase of at least 150°C/s, followed by its rapid volume expansion and reduction of its pouring mass from 2200 kg/m3 to a value in a range of 30 kg/m3 till 10 kg/m3. After passing though the heating part, the product is cooled down in a cooling chamber. Favorable is arrangement, in which at expandable graphite at least during expansion reaction in the heater, catalyst selected from metals of 8thB group (especially compounds of iron) is acting, resulting in clumps of tubular like nanoparticles generation, especially clumps of nanotubes. Drift of expandable graphite along the heater plane can be provided mechanically, for example by rotating scoops. It is more of advantage if the expandable graphite along with produced exfoliated graphite moves along the heater plane by means of gravity, so that it moves from input to the output section of inclined heater plane. Produced exfoliated graphite continuously falls down at inclined plane with a slope of 5 till 60 degrees. By changing inclination angle of the heater plane, the delay time in the reaction zone and the rate of conversion of the feedstock to exfoliated graphite is controlled. From the point of view of desired properties of resulting exfoliated graphite and to reach the lowest rate of non reacted expandable graphite, it is desirable that the heater plane temperature is between 10500C and 125O0C and the heater surface inclination angle is between 25 till 30 degrees. As advantage, the expanding reaction may be performed in the presence of helium and/or argon. After the exfoliated graphite is cooled down in the aftercooler chamber, the exfoliated graphite including gaseous products of expansion reaction is fed into a separator, where the exfoliated graphite is separated from the gaseous products. Exfoliated graphite is retrieved from separator and gaseous products are further cleaned in washers and/or are exhausted to the atmosphere. To achieve suitable structure of graphene layers, exfoliated graphite may be cooled down in a cooling chamber on the outlet section of heater to less than -2O0C by a liquefied gas. The equipment for production of exfoliated graphite according to this invention contains above all a heater, temperature controllers, storage tank, feeder and a cooling chamber. The heater is inclined having adjustable inclination within a range of 5 till 60 degrees, in the upper part a storage tank including feeder is located and in the lower part on the heater outlet is a cooling chamber. The feeder gas tight seals and separates the heater chamber from the storage tank to prevent the gas flow in the inclined heater to rise by a chimney draft, which could heat up expandable graphite in the storage tank, thus decreasing temperature gradient, which expandable graphite is exposed to at falling to input section of the heater. Heating the expandable graphite while still in the storage tank would result in an uncompleted, therefore undesired expansion reaction. To increase the temperature gradient it is of advantage that the feeder and/or the storage tank are equipped by a cooler. It is of advantage that the equipment for production of exfoliated graphite according this invention has a separator and gas washers, where the separator is attached to the cooling chamber. The cooling chamber in this arrangement has a feeding input for the surrounding air, by which the cooling chamber is cooled down and enables the suction of exfoliated graphite into the separator. Exfoliated graphite is sucked from the cooling chamber into the separators by means of a common fan or an exhauster. After separation of exfoliated graphite apart from gaseous products of expansion reaction, gas products are cleaned and neutralized in the washers and are exhausted to the atmosphere. For using device according to this invention near the application area of exfoliated graphite, it is of advantage that the equipment is placed in a mobile container. Raw material (expandable graphite) has a much higher density and is therefore more suitable for transportation. Mobile container with the device according to this invention with autonomy energy source (motor generator), enables production of exfoliated graphite for elimination of consequences caused by accidents of transportation means or elimination of hydrocarbon and crude oil spills in the mining area or in the other desired location. Exfoliated graphite produced according to this invention dominates by extraordinary adsorption properties, caused mainly by vacancies in graphene layers with sizes of 0,245 nm till 500 nm and violations of bonds between particular parallel graphene layers, so that the distance of graphene layers in the places of violated bonds is bigger than 0,335 nm. It is of advantage, if exfoliated graphite contains clamps of tubular nanostructures, of which ratio of length to diameter is at least 5: 1 and the diameter of tubular nanoparticles is maximum 500nm. Tubular nanoparticles are connected to the supporting material of exfoliated graphite. Exfoliated graphite produced according to this invention is featured by a low pouring density and by low heat conductivity, will not catch fire or inflame till the temperature of minimum 6500C. It has a form of flakes and extrudates mostly with diameter of 0.1 mm till 0.7 mm of dark grey, almost black color, containing 90 till 99.6% of carbon (aside a rest of oxygen), it is hydrophobic, does not contain water nor is easily mixed with water. Exfoliated graphite represents a special physically treated form of graphite and as so, it is ecologically clean and is harmless for health. Graphite is characterized by strong covalent bindings inside the horizontal graphene layer; build by hexagons of carbon atoms 0,142nm from each to the other. Each layer thus creates a giant stable macromolecule, while the bond between individual horizontal layers is O,335nm apart and is of a weak Van der Waals type of forces. In the covalent bounded layer, each carbon atom is bound to the three other atoms lying in the same layer, while the bond to the fourth atom laying in a parallel surface is much weaker. Exactly this bound is target of creation of intercalated compounds and is expansion area in the production method of exfoliated graphite according to this invention. On the attached pictures made by Ultra-High Resolution Field Emission SEM microscope JEOL JSM-7400F notice randomly distributed defects - vacancies of the graphitic structure sized from 0,245nm till 500 nm, we named nanoholes. These nanoholes along with earlier discovered fullerenes and nanotubes make-up kaleidoscope of nano-structures and significantly participate in the extraordinary adsorption properties of exfoliated graphite according to this invention. Size of the nanohole depends on a number of missing carbon atoms in a given graphene macromolecule. Exfoliated graphite produced by the method according to this invention reaches the following values of adsorption of particular substances expressed by grams of adsorbed material per gram of product according to this invention: Nitric acid 45 g/g Diesel oil 41 g/g Gasoline 95 30 g/g Sunflower oil 69 g/g Motor oil 78 g/g During measurements according to the ASTM F 726-81 method, the following values of adsorption of substances per gram of the product have been achieved: H3PO4 98 g/g Hydraulic oil HN 46 52 g/g Crude oil 53 g/g Demineralized water 0.3 g/g Adsorption materials used up till now on a base of pearlite, turf, polypropylene and similar substances, achieve much smaller levels of adsorption in a range of 1 till 5 grams per gram of adsorbent. This fact clearly shows the extraordinary adsorption properties of the exfoliated graphite produced according to this invention. The exfoliated graphite produced according to this invention can be implemented for adsorption of oils, crude oils, acids, alcohols, cyclic, aromatic hydrocarbons as well as other toxic and chemical substances, for eliminatipn of combat gasses from contaminated areas, to skim anions and cations including heavy metals and radionuclides, as a filling of filters and filtering equipment for drinking water cleaning, for pool water, waste industrial and rain waters, for cleaning of leaks and drains of gas stations, harbors, industrial equipments, industrial and communal waste dumps, as a medium for air filters, cleaning of flue gases and disposal of hazardous substances, as well as a neutron moderator, capturing and storing of radioactive materials. The exfoliated graphite produced according to this invention may also be used as a thermal, electromagnetic and sound insulating material, as a filter for capturing off-gasses and vents from tanks, from automobile tanks in particular, as well as a filter for elimination of odors and bad smells from wines and of alcoholic beverages. Exfoliated graphite is put into a direct contact with oils and/or crude oil products and/or with acids and/or with alcohols and/or with cyclic aromatic hydrocarbons and/or toxic substances where after their adsorption by exfoliated graphite these substances are recuperated by applying of pressure and/or centrifugal force and/or by extraction. Exfoliated graphite is mildly pressed to a specific weight of over 30kg/m3, followed by flowing water solutions and/or waste water where adsorbed anions and/or cations and/or heavy metals and/or radionuclides and these afterwards can be recuperated from the exfoliated graphite. Exfoliated graphite is put into cartridges of through-flow drinking water filters and/or swimming pool filters and/or filtering devices for industrial waste water and/or rain water filters. Exfoliated graphite can be put as background underneath gas stations and/or harbors and/or industrial equipment and/or industrial and municipal waste dumps and is compressed by the weight of a layer. In case of leakage of harmful substances, these are caught in the background layer of exfoliated graphite. Exfoliated graphite will be used as filter filling for fresh air and/or flue gases filters. Exfoliated graphite will be used as a neutron moderator. Exfoliated graphite will be used for collection, solidification, concentration, and storage of radioactive materials. Exfoliated graphite will be used for production of non flammable thermo- insulating panels. It is mixed with binding material and is expanded in a proper form to create plates for thermal, electromagnetic, sound and fire insulation. Exfoliated graphite will be used to improve soil structure. It is put on the soil then covered by a sand layer, which prevents exfoliated graphite to fade away by wind due to its low specific weight. Exfoliated graphite prevents soil to dehydrate, which is very important at fertilization of soil/sand areas.

Pictures and drawings overview

The invention is closely described at the pictures 1 through 6. Picture 1 shows the equipment for execution of method according to this invention with adjustable angle of inclination. Picture 2 shows equipment according to picture 1 including separator and a gas washers. Picture 3 is exfoliated graphite scanned by an electron microscope with visible nanoholes. Picture 4 is exfoliated graphite scanned by an electron microscope so that the graphene layers can be seen. Pictures 5 and 6 are exfoliated graphite scanned by an electron microscope, so that the clumps of tubular nanosized particles can be seen.

Examples of invention execution

Example 1 Picture 1 shows equipment for production of exfoliated graphite containing heater I, storage tank 3, feeder 2 and a cooling chamber 4. Heater I is of a pit shape with rectangular cross-section with detachable lid for cleaning purposes. The heater 1 is inclined by an angle X = 27 degrees from horizontal, this angle is adjustable from 5 till 60 degrees. Heater i is heated electrically, where the temperature controller 6 is computer controlled system with a feed-back. Storage tank 3 with feeder 2 is situated in the upper part of the heater I. Cooling chamber 4 is in the lower part on the exit. Feeder 2 consists of a roller with a longitudinal groove through the whole roller length dosing expandable graphite feedstock from the storage tank 3_ while rotating. Lubrication between rolling body and outer surface of feeder 2 is performed by expandable graphite itself. Feeding is not continuous and is regulated by rotation frequency of the roller. Length dimension of the roller of feeder 2 corresponds with width of an input section S of the heater L Feeder 2 hermetically seals and separates pit area of the heater 1 and feeder 3_ and is concealed with a cooler 5.. Cooler 5. is equipped by an air cooled metal ribs. Cooling chamber 4 is of a barrel shape and acts as a collecting area for the produced exfoliated graphite.

Example 2 Picture 2 shows equipment for production of exfoliated graphite according to picture 1 amended with a separator 9 and gas washers JJ), LL Separator 9 is a common cyclone separator and is connected to the cooling chamber 4 by a pipe. Cooling chamber 4 has suck-in opening for surrounding air input. In the bottom part of separator 9 is a space for short-term storage of produced exfoliated graphite and the separator is equipped with components for holding and filling of sacks by the produced exfoliated graphite 12. To the upper part of separator 9, the water washer ϋ_is connected, followed by the caustic gas washer K), and the cleaned gasses are exhausted H to the atmosphere.

Example 3 Picture 3 shows exfoliated graphite scanned by an electron microscope with visible nanoholes .14. On picture 4 is exfoliated graphite scanned by an electron microscope where graphene layers 15., \6_ can be seen as well as a captured molecule of foreign substance 17.

Example 4 By catalytic activity of iron compound at reaction of expansion, clamps of tubular nanoparticles 18, has been created. The tubular nanoparticles 18 can be seen on pictures 5 and 6.

Example 5 In order to get rid-off unwanted metals Mn, Cd, Cu, Cr, Zn, Pb and Ni from solution, exfoliated graphite is used as medium in a through-flow filter. The ability to adsorb the metals was monitored. Following values were measured in mg/kg:

Manganese (Mn) 130 - 160 mg/kg Zinc (Zn) 230 - 250 mg/kg Copper (Cu) 260 - 290 mg/kg Chromium (Cr) 200 - 230 mg/kg Cadmium (Cd) 280 - 320 mg/kg Lead (Pb) 910 - 950 mg/kg Nickel (Ni) 160 - 190 mg/kg Example 6 In order to extract oil from water surface, none weaved textile pillows (size lOcmxlOcm) filled with exfoliated graphite were dropped upon the oil spill. After 30 seconds oil has been adsorbed by the pillows. By applying pressure on the pillows the oil was recuperated back.

Industrial use Industrial use is obvious. According to this invention, it is possible to produced industrially exfoliated graphite with the high adsorption properties. In the same time it is possible to produce and to assemble equipments for exfoliated graphite production according to this protected method and is possible to industrially use exfoliated graphite for a wide range of use. List of relational marks used:

1- Heater 2 — Feeder 3- Storage tank 4- Cooling chamber 5- Cooler 6- Temperature controller 7- Output section 8- Input section 9- Separator 10,11- Gas washers 12- Output of exfoliated graphite 13- Gas exhaust 14- Vacancies 15,16- Graphene layers 17- Foreign material 18- Tubular nanoparticles X- Inclination