METHOD FOR THE PRODUCTION OF ACTIVATED CARBON

Description

[0001] The present invention relates to a process for producing activated carbon.

[0002] KUPRYIANCHYK DARYA ET AL: "Sorption of hydrophobic organic compounds to a diverse suite of carbonaceous materials with emphasis on biochar", CHEMOSPHERE, PERGAMON PRESS, OXFORD, UK, Vol. 144, 28 September 2015 (2015-09-28), pages 879-887, ISSN: 0045-6535, DOI: 10.1016 / J.CHEMOSPHERE.2015.09.055 deals with the sorption of hydrophobic organic compounds to various carbonaceous materials with special emphasis on biochar.

[0003] The object of the present invention was to provide an alternative process for producing biochar. In particular, one object was to provide a process for producing biochar with very low pollutant levels, in particular to produce biochar in a form that facilitates further processing into high-quality activated carbon.

[0004] This object is achieved according to the invention by the process according to claim 1. The process according to the invention is a process for producing activated carbon. The process comprises the steps Provision of the starting material in the form of natural wood, crushing of the starting material into pieces with a maximum edge length of 45 mm, drying of the starting material to a water content of a maximum of 20 percent by weight, pyrolysis of the dried pieces of the starting material in a reactor under oxygen exclusion to produce biochar, extinguishing the biochar after pyrolysis by adding water.

[0005] Pyrolysis is carried out at temperatures between 720°C and 800°C. The residence time of the wood pieces, or biochar pieces, in the reactor is at least 60 minutes. In particular, the residence time in the reactor is between 60 and 80 minutes.

[0006] The step of crushing the starting material can, for example, be carried out mechanically and before the drying of the starting material, since drying is possible efficiently with a maximum size of 45 mm.

[0007] The inventors recognized that the biochar produced in this way is particularly well-suited as raw activated carbon. A surface area of ​​390 m2 / g and more can be achieved in the biochar produced in this way. This surface area can be determined, for example, using a measurement based on the BET method. In this analytical method, named after the developers of the BET model (Brunauer, Emmett, and Teller), the surface area of ​​porous solids, in this case biochar, is determined using gas adsorption.

[0008] Furthermore, this process can produce biochar with a carbon content of greater than 85 percent by weight. A bulk density of the biochar of greater than 380 kg / m3 can be achieved.

[0009] Variants of the process result from the features of the dependent patent claims 2 to 6.

[0010] In one variant of the process, the starting material is pure natural wood residue from forestry and / or landscape management.

[0011] The composition of the raw material includes 35-45% softwood and 55-65% hardwood by weight. For example, the raw material can be 40% softwood and 60% hardwood by weight.

[0012] In one variant of the process, the drying step is performed thermally, utilizing the waste heat from the pyrolysis step. This variant results in a particularly energy-efficient process.

[0013] In one variant, the drying process is designed so that the water content of the starting material after drying and before pyrolysis is in the range of 12 to 20 percent by weight.

[0014] In one variant of the process, quenching takes place directly after pyrolysis. The quenching is carried out in such a way that the water content of the biochar is limited to a maximum of 30 percent by weight. Specifically, the quenching is carried out in such a way that the water content of the biochar is in the range of 10 to 30 percent by weight.

[0015] In the final step, the biochar is ground to a maximum grain size of 3 mm. The biochar can be ground to a grain size of less than 1 mm.

[0016] Grinding to a fine particle size, down to biochar dust, is a suitable preparatory step for the production of activated carbon. The resulting product can therefore be referred to as raw activated carbon.

[0017] Optionally, the biochar can be conditioned with an activator, a substance that promotes activation when the biochar is further processed into activated carbon. Demineralized water (Aqua PH5) is suitable for this. The distilled water must be sprayed onto the activated carbon during the annealing phase. During evaporation, the pores divide, resulting in a larger surface area.

[0018] To produce activated carbon, the ground biochar is oxidically activated in a fluidized bed reactor in a further step.

[0019] During the activation step, the pores already present in the biochar are enlarged, and the total surface area is further increased. The inventors have recognized that activation in a fluidized-bed reactor is particularly suitable for processing raw activated carbon produced according to the inventive method for producing biochar.

[0020] After the activation step, activated carbon is obtained with a surface area of ​​over 780 m² / g, with the proportion of micropores in the surface exceeding 440 m² / g. The surface area can be determined, for example, using the BET method.

[0021] Embodiments of the present invention are explained in more detail below with reference to figures. Fig. 1 a flow chart with an overview of process steps and products.

[0022] In Figure 1Process steps 11, 12, 13, 14, and 15 of the inventive method 1 for producing biochar are shown schematically. The product after step 15 of quenching by adding water is biochar 20 with the desired water content. The optional further step of grinding, according to a variant of the method, results in biochar dust 21. This can be followed by the activation step, which leads to the product activated carbon 22.

Claims

1. Method (2) for preparing activated carbon (22), the method comprising the steps of - providing (11) the starting material in the form of pure natural wood, wherein the composition of the starting material comprises 35-45% by weight of coniferous wood and 55-65% by weight of hardwood, - comminution (12) of the starting material into pieces of maximum edge length of 45 mm, - drying (13) of the starting material to a water content of maximum 20% by weight, - pyrolysis (14) of the dried pieces of the starting material in a reactor under exclusion of oxygen to produce biochar, - quenching (15) of the biochar after the pyrolysis by addition of water, wherein the pyrolysis is carried out in the temperature range of 720°C to 800°C and wherein the residence time in the reactor is at least 60 minutes, in particular wherein the residence time in the reactor is between 60 and 80 minutes, wherein, as last step (16), the biochar is grinded to a particle size of at most 3 mm, in particular less than 1 mm, wherein, in a further step (17), the ground biochar is oxidically activated in a fluidized bed reactor.

2. Method according to claim 1, wherein the starting material is pure natural wood residue from forestry and / or landscape maintenance.

3. Method according to one of claims 1 or 2, wherein the starting material comprises 40% by weight of coniferous wood and 60% by weight of hardwood.

4. Method according to one of claims 1 to 3, wherein the step of drying is carried out as thermal drying by utilizing the waste heat from the step of pyrolysis.

5. Method according to one of claims 1 to 4, wherein the water content of the starting material after the drying and before the pyrolysis is in the range of 12 to 20% by weight.

6. Method according to one of claims 1 to 5, wherein the quenching is carried out directly after the pyrolysis and such that a water content of the biochar is limited to a maximum of 30% by weight, in particular wherein the water content of the biochar is in the range of 10 to 30% by weight.