Study of the influence of the aluminum source (acetate or sulfate) on the synthesis of the ceramic membrane and applications of emulsion oil water: use and reuse

Antonielly dos Santos Barbosa ORCID: https://orcid.org/0000-0002-5739-8772 Universidade Federal de Campina Grande, Brazil E-mail: antoniellybarbosa@yahoo.com.br Antusia dos Santos Barbosa ORCID: https://orcid.org/0000-0002-8998-1727 Universidade Federal de Campina Grande, Brazil E-mail: antusiasb@hotmail.com Meiry Gláucia Freire Rodrigues ORCID: https://orcid.org/0000-0003-2258-4230 Universidade Federal de Campina Grande, Brazil E-mail: meiry.rodrigues@ufcg.edu.br


Introduction
Water is an essential resource in the world used for economic, social and cultural development. This feature is considered to be abundant. With the industrial revolution and the increase in population, its demand has increased and scarcity is now an irrefutable result (Singh, 2015).
The biggest energy problem is the limited supply of fossil energy, in addition it generates environmental impacts throughout the energy life cycle, from mining and processing to emissions, waste disposal and recycling (Evans et al., 2009).
Energy sustainability will be achieved through the development of sustainable technologies to replace non-renewable fossil fuels. Membranes technologies play an important role in water and energy sustainability.
The biggest waste generated in the oil industries is the water produced (Lodungi et al., 2016). One of the biggest challenges faced is the management of water produced by the oil and gas industries and the protection of human health and the environment is the management of produced water. This water is problematic to treat due to its complex physicochemical composition. Membrane technology plays an increasingly important role in produced water treatment (Ebrahimi et al., 2018).
Membrane technology has become a high-effectiveness separation technology for industrial processes (Burggraaf, & Cot, 1996;Samaei et al., 2018). Inorganic membranes exhibit excellent thermal, chemical and mechanical stability suitable for separation applications. These processes are operated under severe conditions, such as, high temperatures, high pressures and aggressive chemical environments that polymer membranes cannot handle (Li et al., 2006). In the last few years, inorganic membrane separation technology has knowledge an accelerate growth and innovation. Various membrane separation processes have been developed and new processes are continually being studied in both the academic and industrial research areas.
Membrane separation processes are alternative methods for the oil-water separation (Padaki et al., 2015;Madaeni et al., 2012;Barbosa et al., 2019;Barbosa et al., 2020). The present study is part of this line of research and represents another contribution to the field, presenting the preparation of the ceramic membrane (γ-alumina) from the decomposition of aluminum sulphate and aluminum acetate, which were used as an alternative source of matter for the production of alumina. The effect of experimental parameters such as the type of raw material used in the manufacture of the ceramic membranes and the mechanical stability of the membranes was investigated. As an application to evaluate its performance, the ceramic membranes were used for the separation of oil-water emulsion.

Starting materials
Inorganic membranes with two raw materials (aluminum sulfate or aluminum acetate) was produced by uniaxial dry compaction method on a laboratory scale. The results obtained in this research are quantitative, contributing to the literature.

Thermal decomposition of aluminum sulfate and aluminum acetate
Research, Society andDevelopment, v. 10, n. 13, e75101321023, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i13.21023 3 The aluminum sulfate was submitted to the following heat treatment: heating from room temperature until 1000 ºC with a controlled heating rate of 5 °C/min and then 2 h to obtain gamma-alumina (powder) (Pelovski et al., 1992). The aluminum acetate was submitted to the following heat treatment: heating from room temperature until 850 ºC with a controlled heating rate of 5 °C / min and then 2 h to obtain gamma-alumina (powder) (Sato et al., 1984). Thermal decomposition of aluminum sulphate and aluminum acetate was carried out using a muffle furnace.
The steps to be followed in the thermal decomposition of aluminum sulfate and aluminum acetate are shown in the diagram in Figure 1. Source: Authors.

Production of ceramic membrane (γ-alumina)
Inorganic membranes with two raw materials (aluminum sulfate or aluminum acetate) was produced by uniaxial dry compaction method.
There was a mixture of γ-alumina with additives in a total of 200 ml of dispersion in the following composition: 40 % of alumina obtained above; 0.2 % of para-aminobenzoic acid (dissolved in ethyl alcohol), 0.5 % oleic acid (lubricant), and 59.3 % ethyl alcohol. The mixture was milled in a ball mill for 1 h and then dried in an oven for 24 hours at 60 °C.
3.0 g of the undersieved powders were uniaxially pressed using a 5-ton hydraulic press to produce a disk-shaped ceramic membrane. Subsequently, the green compacts were submitted to the following heat treatment: heating from room temperature until 700 ºC for 2 h. After cooling, flat cylindrical ceramic membranes with final diameter of 26 mm and thickness of 3.0 mm were produced. The steps to be followed in the Production of the ceramic membrane (γ-alumina) from aluminum sulfate or aluminum acetate are shown in the diagram in Figure 2.

X-ray Diffraction (XRD)
X-ray diffraction analysis of samples was performed using a diffractometer Shimadzu XRD 6000m, Kyoto, Japan) with Copper Kα radiation, operated at 30 mA and 40 KV, with a goniometer velocity of 2 °/min and a step of 0.02 ° in the range of 2θ scanning from 2 º to 50 º.

Scanning Electron Microscopy (SEM)
Powders and membranes morphology was determined by scanning electron microscopy (Philips XL 30, Amsterdam, Netherlands

Bubble point
The bubble point method used is standardized by ASTM F316-03. It consists of filling the porous structure of the membrane with a liquid and measuring the air pressure needed to displace the liquid inside the pores. The mathematical relationship between pressure and pore size is given by Washburn equation 1: Eq. (1) Where ΔP is the pressure drop (bar), dp is the pore size (μm), φ is the contact angle between the fluid and pore walls, and γ is the surface tension of the liquid (isopropyl alcohol).

Water flux measurements
The performance of the ceramic membranes with regard to permeate flow was analyzed in a laboratory-scale continuous-flow separation system.
The permeate samples were run at 5 min intervals for a total period of 60 min for each membrane. The flow was calculated according to equation 2.
Eq. (2) where J is the water flux (L/m 2 .h), V is the permeate volume (L), A is the membrane area (m 2 ) and Δt is the permeation time (h).
The system permeation / separation is shown schematically in Figure 4.
The permeation/separation unit consists of a feed tank (glass beaker) (I) with a capacity of 2L; a peristaltic pump (II) Cole Parmer; and a stainless steel module for ceramic supports (ceramic membranes) and ceramic membranes (III).
In figure 4 it can be seen that the fluid pumped into the module is divided into two streams, the permeate and the concentrate. The system operates with constant removal of permeate (to analyze the flow and concentration of the remaining oil) and/or concentrate. The system features two gauge pressure indicators with a scale up to 10 bar, one installed before the module inlet (5-1) and another installed at the concentrate line outlet (5-2), they are accessories for regulating the fluid pressure through of the membrane, whose adjustment is made through the regulating valve (6)  Research, Society and Development, v. 10, n. 13, e75101321023, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i13.21023 7 500 mL of distilled water under stirring (high-speed stirrer) for 20 min to produce stable emulsion. The membrane filtration was carried out at a pressure of 2 bar for ceramic membranes. The oil concentrations of the feed and permeate streams were analyzed. The concentration of oil present in the aqueous phase was determined by analysis of absorbance using a UV-visible spectrophotometer (Zhong 2003). The oil rejection coefficient R was calculated as a percentage according to the following expression 3.

%
where C0 is the oil concentration in the feed, and Cf is the oil concentration in the permeate.

Evaluation of reused membranes
Membranes were reused in cycles of pure water flux and oil/water emulsion separation. The membranes were flushed with distilled water in a continuous flux system for 60 min to remove residual material from the membrane. Then, they were oven dried at 60 ° C for 24 h. The materials were reused for one more cycle (60 min permeation cycle) in pure water flux and separation of oil/water emulsion.

Results and Discussion
Among the various applications of porous ceramic materials, porous ceramic membranes (Wegmann et al., 2008;Qi et al., 2013;Busca, 2014) are the most viable. In the preparation of porous ceramic membranes, it is important to maintain a precise control of the average pore size, mechanical resistance and permeability, reducing material processing costs.
Metastable forms of aluminum oxide called "transition alumina" are used in manufacturing ceramic membranes.
The results obtained from Scanning Electron Microscopy for the membranesA1 and A2 can be observed by means of Figures 6a and 6b. According to the micrographs shown in Figure 6, the A1 membrane and A2 membrane, it is possible to observe a homogeneous microstructure, where it was not possible to observe cracks in the surface of the membranes.
The values of average pore diameter and tensile strength of the membranes are shown in Table 1. According to the average diameter of the pores presented in Table 1, for the membranes, we can classify it as ultrafiltration membranes, according to (Santos et al., 2015). And because of its narrow range of pore size distribution, the carrier is likely to have high selectivity. According to the International Union of Pure and Applied Chemistry (IUPAC), the ceramic membrane can be classified as mesoporous because it has a pore diameter in the region of (2nm < dp < 50nm) (Sikdar et al., 2017).
Characterization by diametric compression test results is shown in Table 1. The tensile strength of the A1 membrane was of 1.3 MPa and 6.7 MPa for A2 membrane. It can be noted that an increase of 500 % in the mechanical strength is observed at the different natures of precursors. Because of its porosity being higher when compared to the A2 membrane, a lower resistance was obtained.
Values of the pore diameter of the ceramic membranes calculated from Eq. 1 are shown in Table 2.  Table 2 shows that the ceramic membrane with the largest pore diameter, according to the bubble point method, was the A1 membrane, presenting 1.11 μm pore diameter. When comparing the A1 membrane with the A2 membrane, a decrease in the pore diameter is observed, considering that the A2 membrane has much smaller pores.

Water flux measurements
The pure water flux may be modified due to membrane structure and subsequently by the preparation conditions (Burggraaf, & Cot, 1996). Figure 7 presents pure water flux of the A1 membrane and A2 membrane as a function of time. The efficiency of the water flow measurements using membranes showed that two ceramic membranes were effective.
It is detected for the A1 membrane, that flow decreases slightly over time whereas for A2 membrane it was verified a more stable behavior over time. This behavior shows that the water flux of the ceramic membrane was influenced mainly for various reasons, such as pore diameter, according to results presented previously.
The characteristics of the membranes are different and were presented previously. Highlighting, the pore diameter and the mechanical strength. Therefore, it was to be expected that the results would be different. The A2 membrane showed lower the pure water flux compared to the A1 membrane. This result can be attributed to pore diameter.

Treatment of oil-in-water emulsion
Membranes were used for the treatment of oil/water emulsions because of their antifouling properties and excellent chemical stability (Barbosa et al., 2019;Barbosa et al., 2020;Gallucci et al., 2011;Barbosa et al., 2018;Bayat et al., 2016;Suresh et al., 2016;Zhong et al., 2013). Research, Society and Development, v. 10, n. 13, e75101321023, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i13.21023 From the results presented in Figure 8 (a), it can be seen that the membranes were efficient in the water-oil emulsion removal process. A removal of 90.80 % for the A1 membrane is evident while a removal of 93.48 % for the A2 membrane.
The maximum rejection of 93.48% is obtained for the A2 membrane due lowest pore size. The research findings precisely evidence the better performance of the A2 membrane for oil rejection.
The Table 3 presents characteristics of two membranes prepared in this work and results of the process. It was found that the oil concentration for the A1 membrane is 9.2 mg/mL. And it was found that the oil concentration for the A2 membrane is 6.52 mg/mL. The tests performed in this work showed that oil concentration of the membranes is within the limit stipulated for oil used as reference (CONAMA, Conselho Nacional do Meio Ambiente, 2011).

Evaluation of reused membranes
The reused membranes were investigated for their performances as a function of the oil rejection capacity. Figure 9 shows the percentage values of oil rejection. The best result presented for oil rejection for the A1 membrane and A2 membrane according to Figure 6 was 90.73 % and 92.74 %, respectively. According to the results we can observe that after the second cycle of ceramic membranes, they continue to present a satisfactory oil rejection potential.

Conclusion
It is possible to synthesize membranes through alternatives routes as the proposed procedure: thermal decomposition aluminum sulfate or aluminum acetate, producing high purity alumina, making the process of synthesis of these materials viable.
The values found for the permeate for the A1 membrane were 9.20 mg/L due to characteristics such as porosity and mechanical strength (44.63 % and 1.3 MPa), while the values A2 membrane was 6.52 mg/L, 18.86 % and 6.7 MPa.
The present study represents the development of suitable strategies to prepare ceramic membranes used in oil/water separation, as well as future applications in dye removal.