WO2018063125A2

WO2018063125A2 - Method for producing activated carbon and silica powder

Info

Publication number: WO2018063125A2
Application number: PCT/TR2017/050345
Authority: WO
Inventors: Orçun YÜCEL; Zeynep ERPOLAT; Nisa SIYIN; Sefa Yasin UZEN
Original assignee: Arçeli̇k Anoni̇m Şi̇rketi̇
Priority date: 2016-08-08
Filing date: 2017-07-26
Publication date: 2018-04-05
Also published as: WO2018063125A3

Abstract

The present invention relates to a method for producing activated carbon with high surface area, and silica powder of high-purity by pyrolysis of rice hull.

Description

METHOD FOR PRODUCING ACTIVATED CARBON AND SILICA

POWDER

Technical Field

The present invention relates to a method for producing activated carbon with high surface area, and silica powder of high-purity using rice hull.

Prior Art

Activated carbon is a processed material with advanced porous structure and high specific internal surface area. It has the ability to adsorb many materials from gas or liquid phase thanks to these properties. Adsorption properties of the products can be modified for various applications by selection of the initial material, the activation method and controlling production conditions.

Main characteristics of activated carbons depend on the type and properties of the raw material. Almost all materials with carbon content can be used for production of activated carbon. It is economically advantageous that these materials are abundant in nature or as industrial waste, and that they are inexpensive. The materials used for this purpose are, wood, charcoal, lignite, coal, agricultural bi- products and waste such as fruit seeds and shells of hazelnuts, coconuts, etc., and polymer waste.

Activated carbon is obtained by carbonization followed by activation. The product of carbonization is inactive in terms of adsorption. Activation is required for transforming such products to an adsorbent with large surface area and high porosity.

Pore structure is an important property since activated carbons are preferred which are capable of high adsorption levels and which have high surface area and porosity. Generally, porosity type depends on the raw material used. In addition, activation method is another parameter influencing the distribution of pore size and surface area. The two most preferred methods are physical and chemical activation. The activated carbon obtained by chemical activation has a larger surface area compared to activated carbon obtained by physical activation.

Rice hull is the most significant bi-product of rice production industry. In the recent years, activated carbon production method using rice hull is preferred as a result of low raw material prices. In addition to utilizing waste rice hull, another advantage of the invention is highly efficient adsorption of the obtained activated carbon.

Methods for producing activated carbon and producing silica powder can be performed simultaneously. During burning process, parameters such as burning temperature and burning duration are significantly effective in terms of the structure of silica content in rice hull ash.

Application no. CN102515156 relates to simultaneous production of activated carbon and sodium silicate by pyrolysis of rice hull ash. Rice hull as raw material, is pyrolyzed and consequently a high C/Si02 proportion is obtained. Sodium hydroxide raw material is used for hydrolysis of pyrolyzed ash under heat and pressure. Thus, sodium silicate is separated and carbon surface is activated. Pyrolysis process is performed in a single step.

In application no. CN 1229057, sodium silicate and, as bi-product, activated carbon are obtained from rice hull ash. The method comprises the steps of burning rice hull, mixing the obtained ash with caustic soda in a high-pressure reactor by a proportion of 10:3, adding water to soak the carbonized product, adding vapor for pressurizing and boiling when the solution is brought to 20 degrees. Subsequently, filtering and separation is performed and the precipitate formed during boiling is also filtered and separated. Obtained filtrate is collected to concentrate sodium silicate recovery.

Methods used in the prior art relate to use of chemical and physical activation and such methods comprise a single pyrolysis step. However, in the present invention, unlike the prior art, a successive two step pyrolysis method is used in the method of using rice hull as raw material.

Brief Description of the Invention

The present invention relates to a method of obtaining activated carbon having high surface area, and silica powder using rice hull, to eliminate above disadvantages and to bring new advantages to the related technical field.

The aim of the present invention is to obtain activated carbon with high surface area using the steps of: a) Subjecting the raw material, rice hull, to one or more of the processes: prewashing, treating with acid or base, and using it as milled or as pulp, b) Drying of the washed pulp, c) Pyrolyzing the same using an inert tube furnace and/or atmospheric electric oven (1st Pyrolysis step), d) Subjecting the pyrolyzed ash to process with one or both of KOH and NaOH (in various proportions), Performing this process by the effect of only heat, pressure or mixture, or together with each one of those or separately, e) Re-cooling of the ash, Using KOH in this process step enables the ash to better contact with the chemicals during boiling the ash with KOH or NaOH, and to increase its activation, The evaporated structure is again kept in the solution by means of re-cooling, f) Filtering the obtained product and drying the filtrate at a temperature range of 80-150°C, g) Second pyrolysis of the dried product in an inert environment at a temperature range of 500-900°C, h) Washing the final ash with one or more of pure water, deionized ultra-pure water, HC1, and ¾S0₄, and filtering thereof, i) Drying the final filtrate under vacuum or atmospheric conditions and obtaining activated carbon.

Another aim of the present invention is to obtain silica powder simultaneously with activated carbon, using the steps of: · Subsequent to subjecting the pyrolyzed ash with KOH and/or NaOH (step d), subjecting the obtained product to silica precipitation process by feeding carbon dioxide. The carbon-silica solution is precipitated as silica by adjusting the pH value thanks to the acidic effect formed by dissolving of gaseous C0₂ in water. · Filtering and drying.

Figures

Figure 1: Process of activated carbon production

Figure 2: Process of simultaneous production of activated carbon and silica powder Detailed Description of the Invention Activated Carbon Production:

Rice hull pulp washed with pure water is dried for 24 hours at approximately 60°C. An atmospheric oven can be used for drying.

First Carbonization (Pyrolysis) This step is very important as the porous structure is formed during carbonization. Mechanical strength and carbon enrichment are obtained in this step. The aim of carbonization process is to obtain desired porosity and to arrange the structure.

In the method of the invention, carbonization is performed for a duration range of 0,5-2 hours at 300-500°C in inert environment under nitrogen atmosphere. Activation

The underdeveloped porous structure gains adsorbent property by activation. During activation, the surface area and pore volume of the product increase by burning of carbon and separation of pyrolysis products. By activation, the mass of the material with carbon content decreases and porosity increases.

Chemical activation is used in the method of the invention for the reasons of short activation duration, high activated carbon yield, product exhibiting good adsorption properties, completion of the process in lower temperatures, and a greater overall yield.

In the method of the invention, chemical activation is performed with one of KOH and NaOH, or both (in various proportions). The process is applied for 1-3 hours at 100°C to increase effectiveness of the process by means of heat. After filtering the obtained product, the filtrate is dried for 12-24 hours at a temperature range of 80-150°C in atmospheric furnace.

Second Carbonization (Pyrolysis)

After drying, the product is subjected to pyrolysis for a second time. The second pyrolysis is performed at a higher temperature than the first one, at a range of 600- 900°C for a duration of 0,5- 1 hours.

The aim of the second pyrolysis is to increase the surface area of activated carbon and consequently the adsorption activity. A higher amount of pores is formed by subjecting the product activated by KOH or NaOH to a second pyrolysis, compared to the prior art method comprising a single pyrolysis process. This increases the surface area.

The first pyrolysis is pre-carbonization and eliminates organic impurities on rice hull. Reaching high temperatures in second pyrolysis can only be achieved in inert atmospheres and increasing the activation area is aimed in this step by forming on rice hull of complex and amorphous structure more regular pores. The reason high temperatures are used in second pyrolysis process is that reactions for formation of the functional groups on the surface of activated carbon which directly influence adsorption performance, appear only in these temperatures.

The product obtained after second pyrolysis is filtered and dried for 24-36 hours at 60°C to obtain activated carbon. Inert environment is utilized in the first and the second pyrolysis process. Burning/pyrolysis process in inert environment is used to obtain highly active carbon quality and high surface area (Figure 1).

Simultaneous production of activated carbon and powder silica: Rice hull pulp washed with pure water is dried for 24 hours at approximately 60°C.

In the method of the invention, the first carbonization is performed for a duration range of 0,5-2 hours at 300-500°C in atmospheric (oxygenated) environment.

The first boiling is performed with HCl acid and the aim is to increase the yield of obtained silica. Boiling with HCl acid is performed for eliminating organic impurities (if any is left) in the product obtained after the 1st burning/pyrolysis process.

In the second boiling process performed after filtering and drying of the obtained product, sodium carbonate is used in pulverized form to have a more active function thereof in the suspension. Sodium carbonate (Na₂C0₃), binds the silisium (Si) in the solution to itself forming sodium silicate (Na₂Si0₃).

During subjecting the obtained product to silica precipitation process by feeding carbon dioxide, the carbon-silica solution is precipitated as silica by adjusting the pH value thanks to the acidic effect formed by dissolving of gaseous C0₂ in water.

Oxygenated environment is used in the first pyrolysis since the quality of sodium silicate solution is the priority in the method applied for obtaining silica powder (Figure 2).

Subsequent to sodium carbonate treatment, the filtered and dried byproduct is activated using one of KOH and NaOH, or both.

The dried product is pyrolyzed for a second time at a temperature range of 600- 900°C in inert environment.

Activated carbon is obtained after filtering and drying. Including but not limited to, tube oven can be used in the methods described above, and the concentration of the activation agent is in the range of 0,3-3 M. In addition, the inert environment used during pyrolysis can be Nitrogen, Argon or Ar/Hydrogen.

Claims

1. Method for producing activated carbon, characterized in that, it comprises the steps of, i. Washing rice hull pulp and drying thereof for 24 hours at 60°C ii. Pyrolysis thereof for 0,5-2 hours at a temperature range of 300-

500°C in inert environment iii. Activation of the pyrolyzed ash for 1-3 hours at 100°C by either of KOH and NaOH, or by both iv. Filtering the obtained product and drying the filtrate at a temperature range of 80- 150°C v. Second pyrolysis of the dried product for 1 hour at a temperature range of 600-900°C in inert environment vi. Washing, filtering and drying of the final ash.

2. Method according to claim 1, characterized in that, after washing of the rice hull pulp, atmospheric oven is used for drying.

3. Method according to claim 1, characterized in that, tube furnace is used for the first and the second pyrolysis.

4. Method according to claim 1, characterized in that, the activation agents are 0,3-3 M.

5. Method according to claim 1, characterized in that, the drying in the step

(iv) of filtering the obtained product and drying the filtrate in the temperature range of 80-150°C is performed for 24-36 hours at 60°C.

6. Method according to claim 1, characterized in that, the inert environment used during pyrolysis is nitrogen, argon or ar/hydrogen.

7. Method for simultaneously producing activated carbon and powder silica, comprising the steps of, i. Washing rice hull pulp and drying thereof for 24 hours at around 60°C ii. Pyrolysis thereof at a temperature range of 300-500°C in inert environment iii. Boiling thereof with hydrochloric acid iv. Boiling with sodium carbonate after filtering and drying v. Subjecting the obtained product to silica precipitation process by feeding carbon dioxide and obtaining powder silica vi. After the step (iv) of filtering the obtained product and drying the filtrate in the temperature range of 80-150°C, activating the filtered and dried byproduct with either one of KOH and NaOH, or both vii. Second pyrolysis of the dried product for 1 hour at a temperature range of 600-900°C in inert environment viii. Washing, filtering and drying of the final ash

8. Method according to claim 7, characterized in that, after washing of the rice hull pulp, atmospheric oven is used for drying.

9. Method according to claim 7, characterized in that, tube furnace is used for the first and the second pyrolysis.

10. Method according to claim 7, characterized in that, the activation agents are 0,3-3 M.

11. Method according to claim 7, characterized in that, the drying in the step (vii) washing, filtering and drying of the final ash, is performed for 24-36 hours at 60°C.