Introduction, Literature review and Objectives
1.6. State of the art
1.6.1. Preparation of ceramic membrane
The manufacturing cost of ceramic membranes is much higher when compared to polymeric membranes (Yang et al., 2017). Though ceramic membranes can be applied even in a harsh environment owing to their excellent mechanical, thermal, and chemical stability when compared with their polymeric counterparts, their use in various fields is way too costly. In general, the cost of raw materials and energy involved in the sintering process are the two
components primarily responsible for the high price of ceramic membranes (Kumar et al., 2015b). Hence, in order to keep the membrane cost low, it has been suggested to use cheaply available raw materials, viz. natural clays (Workneh and Shukla, 2008), feldspar (Bose and Das, 2013), and kaolin (Vasanth et al., 2011) for the production of low-cost ceramic membranes. In comparison to the conventionally used raw materials, including silica (SiO2), zirconia (ZrO2), titania (TiO2), and alumina (Al2O3), the afore-mentioned starting materials are inexpensive, abundantly available and require a low sintering temperature for membrane fabrication. It is well reported that the inclusion of natural raw materials lowered the manufacturing cost of ceramic membranes (Malik et al., 2020). Kaolin clay was used to prepare a low-cost disc-shaped microfiltration membrane and the estimated cost was found to be 130 USD/m2 based on the cost of raw materials used (Nandi et al., 2009). In another study, a low cost tubular ceramic membrane was fabricated using kaolin, feldspar and sawdust. Based on selection of raw materials, preparation and energy consumption, support membrane cost was estimated to be around 250 USD/m2 (Bose and Das, 2013). Recently, Goswami and Pugazhenthi, (2022) developed a tubular ceramic membrane using fly ash as a key precursor and the estimated membrane cost was 250 USD/m2. Majouli et al. (2011) developed a flat ceramic membrane with an average pore size of 6.64 μm from Moroccan perlite using extrusion technique and the membrane was tested for the clarification of baking powder suspension. A low-cost ceramic membrane was prepared by Achiou et al. (2017) with an average pore size of 0.36 µm using natural pozzolan clay as a starting material for the pre-treatment of seawater.
Tunisian clay-based tubular configuration ceramic membrane was coated by the slip-cast technique and the average pore diameter of the coated layer was calculated to be 0.18 µm (Khemakhem et al., 2011). Majouli et al. (2012) developed tubular ceramic membranes with a mean pore size of 0.27 µm from Moroccan clay as a precursor for microfiltration (MF) of industrial wastewater. Circular-shaped flat ceramic membrane derived from kaolin clay
exhibited excellent water permeability, porosity and good corrosive resistance and was used for the treatment of chromium containing wastewater (Vasanth et al., 2012). As evident from Table 1.3, among the many materials investigated for the production of ceramic membranes, kaolin has delighted many researchers owing to its low cost and unique properties such as high strength, good hydrophilicity and low sintering temperature than alumina (Hedfi et al., 2014;
Hubadillah et al., 2018; Bose and Das, 2013; Vasanth et al., 2012). Moreover, the particle size and chemical composition of kaolin aid in manufacturing excellent porous ceramic membranes compared to other expensive raw materials (Bousbih et al., 2020). Besides, the membranes prepared with kaolin as a precursor offered low pore size (Chakraborty et al., 2018; Nandi et al., 2008; Hedfi et al., 2014; Bose and Das, 2013).
In addition to the raw materials used in the manufacture of ceramic membranes, binders play a vital role by enhancing the plasticity of the ceramic paste and improving the flow characteristics, which are very much required for extrusion. It also helps in reducing crack formation induced by changes in volume during thermal treatment (Elbadawi et al., 2017).
Besides, binders considerably alter the membrane characteristics, such as porosity, mechanical strength, chemical stability and morphology. Both organic and inorganic binders are generally used in the fabrication of porous ceramic membranes (Bose and Das, 2013; Elbadawi et al., 2017; Cai et al., 2015; Benito et al., 2005). Organic binders include polyvinyl alcohol (PVA), polyethylene glycol (PEG), carboxymethyl cellulose (CMC), etc., whereas inorganic binders are sodium metasilicate, boric acid, etc. Wang et al. (2006) developed circular shaped α- alumina membranes with 2 wt% methylcellulose as a binder and 2 wt% corn starch as a pore forming agent. It was reported that the fabricated membranes possess an average pore diameter of 0.8 µm and porosity of 40 %. In another study, Amin et al. (2020) prepared a flat ceramic membrane by adding 15 wt% of PVA to the raw material, and the membrane showed an apparent porosity and an average pore diameter of 49 % and 0.091 µm, respectively. Two
tubular ceramic supports made from α-alumina and cordierite through the extrusion method were fabricated by Benito et al. (2005). In this study, CMC and PEG were used as binder and plasticizer, respectively in order to get a smooth texture of the green supports. In another work, two different configurations (tubular and flat) of ceramic membranes were fabricated using kaolin and doloma mixture along with 4 wt% methocel (obtained from methylcellulose) as a plasticizer and 4 wt% amijel (derived from starch) as a binder (Bouzerara et al., 2006). The tubular membranes prepared via the extrusion method resulted in a lower porosity than flat membranes. Bose and Das (2014) prepared a tubular ceramic membrane using sodium metasilicate and boric acid as binders and the membrane showed porosity and average pore diameter values of 20 % and 0.21 µm, respectively.
As evident from the afore-mentioned literature (Table 1.3), ceramic membranes fabricated with organic binders have better mechanical strength, chemical stability and lower pore size than membranes prepared using other types of binders (Amin et al., 2020; Bose and Das, 2013;
Benito et al., 2005). Notably, organic binders with long chains and polar groups adhere easily to ceramic particles and improve rheological properties (Amin et al., 2020). Table 1.3 displays available literature on the fabrication of ceramic membranes using different raw materials and fabrication techniques.
Table 1.3 Available literature on fabrication of ceramic membranes Membrane material Method of
membrane fabrication
Sintering temperature
(oC)
Membrane Configuration
Porosity (%)
Pore size (µm)
Mechanical strength
(MPa)
Chemical stability
(interms of weight loss %)
References
α- alumina, titania, starch and methylcellulose
Pressing 1400 Flat 40 0.8 50 Acid: 0.55
Base: 0.2
Wang et al., (2006) α- alumina, kaolin,
methocel, PVA and Dolapix CE 64
Extrusion 1350 Tubular 48 0.75 37 - Oun et al.,
(2017) Grind waste from kiln
rollers and PVA
Pressing 1250 Flat 49 0.091 - - Amin et al.
(2019)
Pozzolan and phosphate Pressing 1050 Flat 32.07 1.33 15.69 Acid: 7.1
Base: 0.18
Beqqour et al., (2019)
Pozzolan Pressing 950 Flat 33 2.36 19.16 Acid: 3.14
Base: 0.7
Achiou et al., (2016) Pozzolan, starch, amijel
and methocel
Extrusion 950 Tubular 41.2 0.36 15.36 - Achiou et al.,
(2017) Perlite, methocel,
amijel and starch
Extrusion 1000 Flat 41.8 6.64 1.2 Acid: 0.2
Base: 6
Majouli et al., (2011) Perlite, methocel,
amijel and starch
Extrusion 1000 Tubular 42 6.6 - - Majouli et
al., (2012) Cordierite and
magnesium carbonate
Extrusion 1380 Tubular 36.2 8.66 31 Acid: 4.5
Base: 0.2
Dong et al., (2007) Moroccan clay,
zirconia, Amidon, Amijel, PVA, PEG, Methocel, and Dolapix
Extrusion 1225 Tubular 43 11 10 - Saffaj et al.,
(2006)
Moroccan clay and phosphate
Pressing 1100 Flat 28.11 2.5 17.5 Acid: 7.1
Base: 0.24
Mouiya et al., (2018) Fly ash, amijel,
methocel, and starch
Extrusion 1125 Tubular 51 4.5 18 Acid: 2 Jedidi et al.,
(2009) Kaolin, feldspar,
sodium metasilicate and boric acid
Pressing 850 Flat 29.98 0.93 8.75 - Chakraborty
et al., (2018) Kaolin, quartz, calcium
carbonate, sodium carbonate, boric acid and sodium metasilicate
Casting 850-1000 Flat 33-42 0.55- 0.81 3-8 Acid: < 4
Base: < 4
Nandi et al., (2008) Kaolin, quartz and
calcium carbonate
Pressing 900 Flat 30 1.3 34 Acid: < 6
Base: 0
Vasanth et al., (2011) Kaolin, quartz, calcium
carbonate, sodium carbonate, boric acid and sodium metasilicate
Pressing 900 Flat 37.4 2.16 73 - Emani et
al., (2014)
Kaolin Pressing 950 Flat 30 0.1 60 - Hedfi et al.,
(2014) Kaolin, Feldspar,
Quartz, and Saw dust
Pressing 850 Flat 36 0.19 2 - Bose and
Das, (2014) Kaolin, Feldspar, Saw
dust, Sodium metasilicate, and Boric
acid
Pressing 850 Tubular 21 0.21 11.68 Acid: < 6
Base: < 6
Bose and Das, (2014)