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Performance Evaluation of Fly Ash-based Tubular Ceramic Membrane in Liquid Phase Separation Processes

4.3 Separation of glycerol from biodiesel .1 Chemicals

4.3.2 Experimental methodology and investigations

The microfiltration experiment regarding the separation of glycerol from biodiesel was carried out by preparing a synthetic solution of biodiesel mixture using biodiesel, glycerol and methanol. Prior to the preparation of synthetic solution, the procured biodiesel was characterized for its free glycerol as well as the soap content, and all the properties of the biodiesel along with these two have been mentioned in Table 4.6.

Table 4.6 Properties of procured biodiesel

Parameter Value

Free glycerol# 0.015 wt.%

Soap# (612.15±7.95) ppm

Water content 0.13 wt.%

Methanol 0.01 wt.%

Calorific value 40,794 J/kg Kinematic viscosity (40 ˚C) 6 cSt

# Properties evaluated in our laboratory, while rest are reported as obtained from the supplier

It has been observed that the residual glycerol present in the biodiesel is very less, amounting to only 0.015 wt.%. However, the soap content in the biodiesel was found to be very high (612.15±7.95 ppm), which needs to be reduced before filtration so as to reduce the membrane fouling. This issue has been addressed later in this section.

It has been revealed in the literature that for the production of biodiesel using vegetable oil and methanol via transesterification in the presence of an alkaline catalyst, 1:6 molar ratio of oil and alcohol produced the highest yield (Freedman et al., 1985). Keeping this in mind, a stoichiometric calculation was carried out using the below-mentioned reaction scheme (equation 4.3) to evaluate the final composition of biodiesel emulsion produced via methanol transesterification process for the above-mentioned feed ratio. It was found that the final product was a mixture of 80% biodiesel, 10% glycerol and 10% methanol; all percentages are being weight percentage. Hence, an emulsion with the above-mentioned composition was

prepared using a probe ultrasonicator (IKA T10 basic, ULTRA-TURRAX) for the experiment purpose.

Once the solution was prepared, acidified water (0.5% HCl) was added to the emulsion in such an amount that the water weight corresponds to 20% of the total weight of the emulsion (Gomes et al., 2013). Addition of acidified water significantly reduced the excessive soap content of the emulsion to 168.54±4.45 ppm by converting the soap present in biodiesel into soluble salts.

Fig. 4.17 Cross flow filtration setup for separation of glycerol from biodiesel (1: Magnetic stirrer with heater, 2: Feed tank, 3: Reflux condenser (Used only during microfiltration of biodiesel), 4: Pump; 5, 10: ball valve, 6: pressure gauge, 7: membrane module, 8: permeate

tank, 9: Weighing balance, 11: Rotameter)

For the microfiltration of biodiesel emulsion, the experiments were conducted at 60 ˚C using cross-flow filtration setup (Fig. 4.17), as the solution viscosity at this temperature is

comparatively lower, which helps in reducing the load on the pump (Gomes et al., 2010). The possible evaporation losses of solvent from the emulsion at higher temperature were prevented by the use of reflux condenser during the experiment (Bell, 1925; Gerpen et al., 2004). The permeation experiments were conducted at a cross flow rate of 8.33×10-6 m3/s, using five different pressures within the range of 207 to 483 kPa. The permeate collected after each run was tested for free glycerol and soap content after evaporating the residual water and methanol in a rotary evaporator (Rotavapor R-300, Buchi, Switzerland) for a duration of 30 minutes at 90 ˚C bath temperature.

The soap content of feed as well as permeate samples was determined by dissolving 10 g of biodiesel in isopropyl alcohol, which was followed by the addition of 12-15 drops of bromophenyl blue indicator until the solution acquires a blue tint. The resultant mixture was then titrated against 0.01N HCl until the solution turns yellow. The amount of HCl required to achieve this colour change was used to calculate the soap content in biodiesel using equation (4.4):

𝑆𝑜𝑎𝑝 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 (𝑝𝑝𝑚) = 𝑊×0.01×𝐶

1000×𝐵 × 106 (4.4) where, W, C and B represent the amount of HCl (in mL), concentration factor (318 for biodiesel produced using sodium methoxide as a catalyst) and weight of the biodiesel sample (in grams), respectively (Atadashi et al., 2015).

The free glycerol content in biodiesel as well as permeate sample was analyzed using UV-vis spectrophotometer (UV-2600, Shimadzu, Singapore). For the analysis, formaldehyde structure was first formed by the reaction between biodiesel and sodium periodate, which on further reaction with acetylacetone produced a yellow-coloured complex, 3,5-diacetyl-1,4- dihydrolutidine having a very high specific absorption band at 410 nm wavelength (Bondioli and Bella, 2005; Nogueira, 2019). This method of determining free glycerol content in

biodiesel is quite simple, fast and cost effective than the conventional method like Gas Chromatography technique (Nogueira et al., 2019).

A microscope with 20X magnification (Model No.: Zeiss Axio Scope.A1, Make: Carl Zeiss Microscopy GmbH Germany) was used to capture the images of droplets of biodiesel emulsion prepared at 60 oC. The droplet size distribution and average size of the biodiesel emulsion were evaluated by analysing three different microscope images using ImageJ software (Open-source software, https://imagej.nih.gov/ij/).

On completion of each experiment, the setup was initially flushed with methanol for 30 minutes as the emulsion easily solubilises in methanol, which makes the cleaning easy. This was followed by cleaning the setup with 1 g/L surf excel solution for 30 minutes. An aqueous NaOH solution (1 wt.%) was allowed to pass through the setup for another 30 minutes to remove the traces of emulsion that may be present in the setup (Atadashi et al., 2015). Finally, flushing with Millipore water was carried out and the water permeability of the cleaned membrane was measured again. It was found that the hydraulic permeability of the cleaned membrane was within ±4% of its original value, which signifies the reusability of the membrane for further experiments.