WO2013100751A1

WO2013100751A1 - A process for producing activated carbon fibres

Info

Publication number: WO2013100751A1
Application number: PCT/MY2012/000112
Authority: WO
Inventors: Fei Yee YEOH; Wan Cheng TAN
Original assignee: Universiti Sains Malaysia
Priority date: 2011-12-30
Filing date: 2012-05-28
Publication date: 2013-07-04

Abstract

The present invention relates to a process for producing activated carbon fibres (ACF) from empty fruit brunch (EFB) fibres. The process includes the steps of: (i) washing EFB fibres with nitric acid (HNO₃) and followed by washing of the EFB fibres with deionized (DI) water and drying of the EFB fibres. This step is essential for removal of any adsorbed inorganic materials; (ii) mixing the EFB fibres obtained from step (i) with sulphuric acid (H₂S₄4); (iii) subjecting the EFB fibres obtained from step (ii) to a carbonization process; (iv) heating chars obtained from step (iii) in nitrogen gas environment up to temperature between 600 to 1200 °C and holding chars obtained from step (iv) at a temperature between 600 to 1200°C in carbon dioxide gas (CO₂) environment for a period between 1 to 24 hours and followed by cooling step in nitrogen gas environment.

Description

A PROCESS FOR PRODUCING ACTIVATED CARBON FIBRES

FIELD OF INVENTION

The present invention relates to a process for producing activated carbon fibres from empty fruit bunch (EFB) fibres.

BACKGROUND ART OF THE INVENTION

Activated carbon fibres (ACF) are advanced nonporous materials with fibrous shape and well-defined porous structure. Applications of ACF include antibacterial wound dressings, disposable gas masks, water filtration and treatment, metal adsorbent and catalyst. ACF are practical to be used for safe natural gas and biogas storage through Adsorbed Natural Gas (ANG) technology, which can be used as an energy storage technology for alternative fuel source to supply energy for natural gas vehicles, cooking stoves and generator in factories. Due to its excellent pores characteristics, ACF can achieve an outstanding storage capacity of methane gas which is a clean fuel and the main component in biogas and natural gas. ACF also have enormous potential in the field of metal removal and recovery especially for heavy metals and precious metals. In general, ACF have high specific surface area, high pore volume and narrow pore size distribution. Its characteristics depend on raw materials, preparation conditions and post treatment of fibres. High specific area, density, micro pore volume, short diffusion length, and narrow pore size distribution in micro range are desirable for high methane storage application.

Compared to conventional activated carbon, ACF have higher commercial value due to its better pore characteristics and larger surface area. Thus, it is more expensive than normal activated carbon. ACF are usually produced from polymeric materials such as rayon, polyacrylnitrile (PAN) and pitch which mainly derived from petroleum products, which makes it less environmental friendly product. Commercial chemicals are needed to produce these polymeric precursors. It has been limited by economical aspect due to it high burn-off percentages at high temperature. Therefore, there is a need for a simple and cost effective process for producing activated carbon fibres from natural, abundant, cheap and carbon neutral raw materials which solves the problem above.

SUMMARY OF INVENTION

The present invention relates to a process for producing activated carbon fibres.

The process includes steps of:

i) removing inorganic materials from empty fruit bunch (EFB) fibres;

ii) mixing the EFB fibres obtained from step (i) with sulphuric acid;

iii) subjecting the EFB fibres obtained from step (ii) to a carbonization process; iv) heating the dried chars in nitrogen gas environment up to temperature range of

600 to 1200°C;

v) holding the chars obtained from step (iv) at a temperature between 600 to 1200°C in carbon dioxide gas (C0₂) environment for a period between 1 to 24 hours; and

vi) cooling of the chars obtained from step (v).

The carbonization process can be done by heating the EFB fibres at a temperature range of 80 to 600 °C in air for a period between 1 to 24 hours or by heating the EFB fibres at a temperature range of 70 to 1000 °C in nitrogen gas environment for a period between 1 to 24 hours. The EFB fibres and the sulphuric acid in step (ii) having a weight ratio of 4:3. The activated carbon fibres having porous structure of micropores with size range 5-10 A. The chars obtained from step (iii) is washed with deionized (DI) water and then followed by drying. This step is to remove remnant of sulphuric acid. This step is an optional step.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be fully understood from the detailed description given herein below and the accompanying preferred drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein:

Figure 1 shows a flow chart of the process for producing activated carbon fibres. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for producing activated carbon fibres (ACF) from empty fruit brunch (EFB) fibres. This invention helps in solving disposable problems of agricultural wastes. There are abundant of agricultural commodity in Malaysia. Malaysia is the world's largest producer and exporter of palm oil which leaves behind substantial amount of lignocellulosic biomass in the form of empty fruit bunches (EFB), palm kernel shell (PKS) and palm mesocarp fiber (PMF). It is estimated that amount of solid waste produced could reach 39 million tonnes by the year 2020. These natural agricultural wastes consist mainly of celluloses, hemicelluloses and lignin which can be converted into carbon fibres after carbonization. Thus, they are potential candidates for ACF's preparation. Instead of using those agricultural wastes in low value conventional activity, as biomass for energy generation, the present invention converts the agricultural wastes to advanced materials with excellent adsorption properties which includes high methane adsorption capacity, micropores volume and specific surface area for highly value added applications such as gas storage, filtration and water treatment. A detailed description of preferred embodiments of the invention is disclosed herein. It should be understood, however, that the disclosed preferred embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and for teaching one skilled in the art of the invention.

Porous structure of ACF consists mainly of almost uniform micro pores in slit type. Kinetic diameter of carbon dioxide gas (C0₂) molecules is 3.3 A. C0₂ can act as an effective activating agent to develop more micropores without changing macropore structure of the fibres significantly. High flexibility, lightness and malleability of ACF offer additional advantages during its preparation. ACF's structure consists of aromatic sheets condensed ring system stacked in non-polar layers. In location of defects, dislocations and discontinuities, carbon atoms of aromatic sheets contain impaired electrons and residual valences. These carbon atoms are highly reactive and constitute active sites which are responsible for liquid and gases adsorption. Adsorption capacity of ACF is further improved with the presence of insignificant sulphur group in peripheral carbon atoms after acid treatment.

The process for producing ACF from empty fruit brunch (EFB) fibres is described herein. The process includes the steps of:

i) washing EFB fibres with nitric acid (HNO₃) and followed by washing of the EFB fibres with deionized (DI) water and drying of the EFB fibres. This step is essential for removal of any adsorbed inorganic materials and to obtain good porosity;

ii) mixing the EFB fibres obtained from step (i) with sulphuric acid (H2SO4) wherein the EFB fibres and sulphuric acid having a weight ratio of 4:3;

iii) subjecting the EFB fibres obtained from step (ii) to a carbonization process; iv) heating the chars obtained from step (iii) in nitrogen gas environment up to temperature range of 600 to 1200 °C and then holding the chars at a temperature between 600 to 1200°C in carbon dioxide gas (C0₂) environment for a period between 1 to 24 hours and followed by natural cooling to room temperature in nitrogen gas environment.

The carbonization process can be done by heating the EFB fibres at a temperature range of 80 to 600 °C in air for a period between 1 to 24 hours or by heating the EFB fibres at a temperature range of 70 to 1000 °C in nitrogen gas environment for a period between 1 to 24 hours. Besides sulphuric acid, other acids such as phosphoric acid, citric acid, hydrochloric acid, nitric acid and acetic acid can be also used for mixing with the EFB fibres. The chars obtained from step (iii) is washed with deionized (DI) water and then followed by drying. This step is to remove remnant of sulphuric acid. This step is an optional step.

The present invention involves low cost precursor, i.e. EFB fibres which favors economical concern in conjunction with solving wastes disposal issues. In the present invention, instead of using polymeric materials, natural materials from agricultural waste are further processed into ACF. The present invention creates a whole new class of ACF which are more environmental friendly and cost effective. The ACF are known as green product which enables users to claim carbon credit due to their nature obtained from agricultural waste rather than petrochemical activities. Although EFB fibres have been used by a few researchers to synthesize powdered activated carbon via thermal, physical and chemical activation respectively with KOH & H3PO4, none of them produces ACF from EFB fibres activated by both H2SO4 and C0₂. A variety of chemicals are used as activating agents in conventional process to produce ACF. The activating agents are such as H3PO4, ZnCl₂, KOH, NaOH and K₂C0₃. Alkali hydroxides such as KOH and NaOH are hazardous, expensive and corrosive and could remain in the ACF even after carbonization which affects the ACF's performance. ZnCl₂ is unfriendly to the environment and create waste disposal problem. In the present invention, only sulfuric acid is needed in ACF preparation. Almost all of sulfuric acid will be removed after chars heating above 337°C because boiling temperature of sulfuric acid is 337°C. Only small remnant of sulphur groups will remain in ACF to improve its methane storage capacity without blocking pores of ACF. In the present invention, ACF mainly consist of micro pores with a range of 5-10 A which are synthesized via C0₂ activation. This pore range has advantages in the methane storage application as compared to ACF in mesopores size. This is due to kinetic diameter of methane is 3.8 A (in micro- range).

Claims

1. A process for producing activated carbon fibres, the process includes steps of: i) removing inorganic materials from empty fruit bunch (EFB) fibres;

ii) mixing the EFB fibres obtained from step (i) with sulphuric acid;

iii) subjecting the EFB fibres obtained from step (ii) to a carbonization process;

iv) heating chars obtained from step (iii) in nitrogen gas environment up to temperature between 600 to 1200°C;

vi) cooling the chars obtained from step (v).

2. The process for producing activated carbon fibres as claimed in claim 1 wherein the carbonization process includes heating the EFB fibres at a temperature range of 80 to 600 °C in air for a period between 1 to 24 hours.

3. The process for producing activated carbon fibres as claimed in claim 1 wherein the carbonization process includes heating the EFB fibres at a temperature range of 70 to 1000 °C in nitrogen gas environment for a period between 1 to 24 hours.

4. The process for producing activated carbon fibres as claimed in claim 1 wherein the EFB fibres obtained and the sulphuric acid having a weight ratio of 4:3.

5. The process for producing activated carbon fibres as claimed in claim 1 wherein chars obtained after the carbonization process is subjected to removal of sulphuric acid. The process for producing activated carbon fibres as claimed in claim 1 wherein the activated carbon fibres having porous structure of micropores with size range 5-10 A.