Precipitated Silica from Sodium Silicate by CO2 on Fixed Bed Column

Abstract

The precipitated silica prepared by reaction of sodium silicate and gas CO2 on fixed bed column have been production successfully. In this study, silica from bagasse was extraction by sodium hydroxide 2N solution to produce sodium silicate solution. The sodium silicate solution was dilute by demineralize water to produce some concentration in the range of 0.33-0.98 %SiO2. Fixed bed column has a diameter of 7.5 cm with a height of 50 cm and a pH control apparatus. CO2 gas and sodium silicate liquid are both flowed from under of the column with a specified flow rate. The precipitate process was carried out on a fixed bed column with high of bed in the range of 10-30 cm. The effect of silica concentration and the high of the bed on the characterize of the precipitated silica product have been studied. The precipitated silica product characterized by XRF, XRD, SEM-EDX and BET. The quality of precipitated silica produced in the range concentration of 95-98 w% SiO2, surface area (BET) in the range of 46.1 – 58.8 m²/g.

Full text

Precipitated Silica from Sodium Silicate by CO2 on Fixed Bed Column
Retno Dewatia, Suprihatinb, Ketut Sumadac, and Srie Muljanid*
Chemical Engineering Department, Engineering Faculty, Universitas Pembangunan Nasional
“Veteran” Jawa Timur, Surabaya, Indonesia
adewati.r@gmail.com, bsuprihatinupnjatim@gmail.com, csumadaketut@gmail.com,
d*sriemuljani.tk@upnjatim.ac.id
Keywords: bagasse ash, carbon dioxide, fixed bed, sodium silicate, precipitated silica
Abstract. The precipitated silica prepared by reaction of sodium silicate and gas CO2 on fixed bed
column have been production successfully. In this study, silica from bagasse was extraction by
sodium hydroxide 2N solution to produce sodium silicate solution. The sodium silicate solution was
dilute by demineralize water to produce some concentration in the range of 0.33-0.98 %SiO2. Fixed
bed column has a diameter of 7.5 cm with a height of 50 cm and a pH control apparatus. CO2 gas
and sodium silicate liquid are both flowed from under of the column with a specified flow rate. The
precipitate process was carried out on a fixed bed column with high of bed in the range of 10-30 cm.
The effect of silica concentration and the high of the bed on the characterize of the precipitated
silica product have been studied. The precipitated silica product characterized by XRF, XRD, SEM-
EDX and BET. The quality of precipitated silica produced in the range concentration of 95-98 w%
SiO2, surface area (BET) in the range of 46.1 – 58.8 m2/g.
Introduction
The precipitated silica is required to support various types of industrial operations such as
vehicle, rubber, cosmetics, electronics, agriculture and other industries. The grade quality of
precipitate silica products depends on the type of industrial users. The production of precipitated
silica starts with the reaction of an alkaline silicate solution, usually but not necessarily sodium
silicate solution, with various types of acids such as hydrochloric, sulfuric, acetate and carbon
dioxide [1,2]. Preparation of sodium silicate by alkali extraction has been successfully used to
recover silica from bagasse ash, geothermal sludge and rice hull ash to produce porous silica powder
[3,4,5,6]. Sodium silicate was used in foundries to bind sand grains using carbon dioxide (CO2)
directly where the hardening of the sand immediately occurs as a result of the chemical reaction
between sodium silicate and carbon dioxide[7]. Cai et al [8] was reported a method for preparation
of silica powders using sodium silicate and carbon dioxide by pressured carbonation as a
precipitating agent. The reaction time, temperature and concentration of sodium silicate were
influential on silica powder characterize. Combination of a microreactor and a stirred reactor for
production of a large-pore-volume and narrow-pore-diameter distribution of silica materials was
reported [9] while the gelatine time was controlled by improing the mixing performance.
In the previous study reaction of sodium silicate from bagasse ash with CO2 was provide in the
bubble column. The duration of precipitation, the addition rate of reactants, sodium silicate
concentration, and pH can vary the properties of the silica [10]. The residence time and the rate of
CO2 gas was an obstacle in the formation of precipitated silica. This study developed the formation
of precipitated silica from reaction of sodium silicate and CO2 on fixed bed column in order to
increase the contact time in the column. The existence of bed material in the column was necessary
to be studied considering the formation of precipitated silica will be able to inhibit the subsequent
precipitation process and inhibit the performance of the fixed bed column itself too. By studying the
residence time with the rate of gas controller in a column it is expected that the precipitated material
can flow with liquid before deposited in the bed column. The precipitation silica product prepared
by acidification proses was followed a two-step process, namely the formation of primary particles
followed by flocculation which expand exponentially with an increase in acid concentration and
Materials Science Forum Submitted: 2018-12-05
ISSN: 1662-9752, Vol. 966, pp 14-18 Revised: 2019-04-01
doi:10.4028/www.scientific.net/MSF.966.14 Accepted: 2019-05-07
© 2019 Trans Tech Publications Ltd, Switzerland Online: 2019-08-06
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans
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with salt accelerates the process [7,11]. The reaction of sodium silicate solution with carbon dioxide
besides producing precipitated silica would also cause sodium carbonate salt. The presence of salt
trapped in precipitated silica particle can affect the purity and the surface area of the silica product.
In addition to investigate the fixed bed column performance for the formation of precipitated silica
at various height bed, this study also analyzed the morphology of the precipitated silica product
characteristic.
Materials and Methods
Silica source from bagasse ash obtained from the sugar industry. Sodium hydroxide (NaOH) as
solvent on silica extraction obtained from CV. Bratachem Surabaya and carbon dioxide (CO2) gas
as precipitator obtained from CV Medica Vanjaya Surabaya. The bagasse that obtained from the
sugar industry waste is black in color indicate that bagasse still contains a lot of carbon
The production precipitated silica from sodium silicate in this research was follow the two steps
process namely 1) preparation of sodium silicate solution from bagasse ash 2) preparation of
precipitated silica from sodium silicate and CO2 gas in fixed bed column.
The Bagasse ash from sugar industry burned on furnace at 700 C for 2 h. After burning in the
furnace bagasse ash was then cooled and grinded to a size about 80-100 mesh and analyzed for its
silica content. The chemical composition of bagasse ash by XRF analyze was SiO2: 73%, CaO:
8.63%, K2O 5.01%. The extraction of silica prepared by extraction of 80g bagasse ash using 1000ml
of sodium hydroxide (NaOH) 2 N solution at 95 °C for 2 h to produce the sodium silicate solution.
The sodium silicate solution was analyzed for the content of sodium oxide (Na2O) with AAS
method and silica content (SiO2) by Spectrophotometry method. The result showed that sodium
silicate solution was has a silica concentration of 4.85 % and sodium oxide concentration of 4.57 %.
Sodium silicate solution was then dilution by demineralized water in the range ratio of 1:1; 1:2; 1:3;
1:4; and 1:5 obtained the concentrations of 0.33; 0.39; 0.49; 0.65 and 0.98% SiO2 by stoichiometry
calculation method.
The Sodium silicate solution is pumped by dosage pump with a flow rate of 60 ml/min into the
fixed bed column (diameter column of 7.5 cm and height of 50 cm) and followed by injection of
carbon dioxide (CO2) gas with a rate of 4 l /min. The sodium silicate solution will react with carbon
dioxide gas, pH of sodium silicate solution decrease from value of 12 to 7. The precipitated silica
formed in the column will also flow with the liquid to the top of the column and then flow into the
settling tank until reached a volume of 2 liters and value of pH adjusted 7. From the settling tank,
precipitated silica was filtered using whatman 41 paper filter then washed and dried in an oven at
100 °C for 18h. Precipitated silica from oven was pounded to a size about 100 mesh for analysis
purpose.
In this study the reaction of sodium silicate solution with carbon dioxide (CO2) gas was followed
the reaction:
Na2SiO3 + CO2 + H2O → SiO2 + Na2CO3 + H2O (1)
The precipitated silica product was characterize by the X-ray fluorescence (XRF), X-ray
diffraction (XRD), surface area Brunauer-Emmet-Teller (BET) and Scanning electron microscopy
with energy diffraction x-ray (SEM-EDX ).
Result and Discussion
Fig. 1 showed the diffraction pattern of precipitated silica product prepared by sodium silicate
concentration of a) 0.49, 0.65 and 0.98 %SiO2 before washing, and b) 0.33-0.98 % SiO2 after
washing. Based on the XRD results for three samples (0.49, 0.68, and 0.98%) which have high
silica concentrations, they indicated the presence of salt (Na2CO3) impurities as shown in Fig. 1a,
then all samples (0.33-0.98 % SiO2) were washed in order to remove the impurities (Fig. 1b). It can
be stated that after the washing process in these samples the product's purity level also increases.
Materials Science Forum Vol. 966 15

The subsequent analysis of BET, SEM-EDX and XRF was based on precipitated silica after
washing.
20 30 40 50 60 70
0
100
200
300
400
500
600
0.98%SiO
2
0.49%SiO
2
0.65%SiO
2
Intensities (A.U)
2θ(deg)
20 30 40 50 60 70
-100
0
100
200
300
400
500
600
700
Intensities (A.U)
2θ(deg)
0.49 %
0.39 %
0.33%
0.98%
0.65%
Fig. 2 showed the effect of the height of bed on a) concentration of precipitated silica and b)
amount of precipitated silica. Silica concentration increases with bed height. The higher the bed
height is from 10 to 30 cm in a fixed bed column, the contact time between gas and liquid will be
longer, as a result the greater the amount of precipitated silica formed. However, if the bed is too
high, the residence time that is too long will cause sedimentation from precipitated silica so that it
can inhibit the reaction rate and inhibit the performance of fixed bed columns. The amount of silica
precipitation product produced at bed height from 10 to 30 cm and silica concentration from 0.33 to
0.98 % is shown in Fig. 2b. The amount of silica precipitation obtained depends on the silica
concentration in sodium silicate used. The greater the concentration of sodium silicate from 0.33 to
0.98 %, the greater the amount of silica obtained from about 10 to 33 g. However, the use of low
sodium silicate concentration (0.33%) can produced the least amount of precipitated silica (about
10-17g) but its purity is highest (up to 99%). However, in obtaining a large amount of silica
precipitation it is obtained a lower concentration of silica.
10 15 20 25 30
86
88
90
92
94
96
98
100
Concentration of precipitated silica (%SiO2)
Bed height (cm)
0.33%
0.39%
0.98%
0.65%
0.49%
(a)
10 15 20 25 30
12
16
20
24
28
32
(b)
0.33%
0.39%
0.49%
0.65%
0.98%
precipitated silica (g)
Bed height (cm)
Fig. 2. The effect of height of bed on (a) concentration of precipitated silica and (b) amount of
precipitated silica.
(a)
(b)
Fig. 1. Diffraction pattern of precipitated silica prepared (a) before washing and (b) after washing.
16 Functional Properties of Modern Materials II

Fig. 3 showed the typically isotherm of adsorption-desorption of precipitated product prepared by
sodium silicate concentration of 0.98% and 0.33% SiO2. The isotherms can be identified as type V
isotherms according to the IUPAC classification, which are correspond to micro porous solids. The
hysteresis can be classified as a type H2, in which the hysteresis loops of the desorption branch are
steeper than those of the adsorption branch. T the hysteresis loops was characterize of bottleneck
pores and small particles. The precipitated silica prepared by sodium silicate 0.33% SiO2 have a
surface area (BET) of 58.811 m2/g, pore volume of 0.263 cc/g and pore diameter of 3.781 nm, while
the precipitated silica prepared by sodium silicate 0.98% have a surface area (BET) of 46.089 m2/g,
pore volume of 0.160 cc/g and pore diameter of 4.261 nm.
0.0 0.2 0.4 0.6 0.8 1.0
-20
0
20
40
60
80
100
120
140
160
180
Volume (cc/g)
P/Po
0.33 %SiO
2
0.98 %SiO
2
Fig. 3. Adsorption-desorption isotherm of precipitated silica.
Fig. 4 showed the SEM images of precipitated silica prepared by sodium silicate 0.49% SiO2 by
height of bed in column was a) 10 cm b) 20 cm and c) 30 cm. Particles of precipitated silica
preparation on a bed height of 10 cm have a random shape of particle, while precipitated silica
preparation on a bed height of 30 cm obtained the particles with the shape almost spherical and
uniform in size.
Fig. 4. SEM images of precipitated silica prepared by sodium silicate 0.49% SiO2 with height of
bed on column of a) 10 cm b)20 cm and c) 30 cm.
The microanalysis by EDX showed that precipitated silica prepared by sodium silicate 0.49 %
the magnification particle size in the range of 1-20µ the component of silica was increased from
28.58 to 42.53 %. Meanwhile, precipitated silica prepared by sodium silicate 0.39 % and 0.33 % in
the range of particle size of 1-20 µm the component of silica decrease from 44.29 to 37.32%, and
47.67 to 43.88% respectively.
Materials Science Forum Vol. 966 17

Summary
Precipitated silica particles were successfully produced from sodium silicate using precipitator
CO2 on fixed bed column. The concentration of silica in product tended to increase with the
increasing of bed height. The morphology of precipitated silica prepared on bed height of 30cm was
more uniform and almost spherical in shape. The surface area of precipitated silica was reached
58.811m2/g on fixed bed column with a diameter of 7.5 cm, height of 15 cm and bed height of
30 cm.
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