MATERIALS AND METHODS

3.1 Introduction

This chapter describes those materials and methods common to all investigations carried out. Specific information related to each experiment is reported in the appropriate chapters following.

3.2 Materials 3.2.1 Lactalbumin

Lactalbumin is an insoluble powder prepared by washing and drying the proteins precipitated from heat-treated whey (Robinson et at. 1 976). A typical production

process includes: ( 1 ) denaturation, coagulation and precipitation of proteins by heat treatment and pH adjustment; (2) separation of the lactalbumin from the whey by decantation, centrifugation or filtration; (3) spray, roller, ring or tunnel drying; and (4) grinding, blending and bagging.

Remilled lactalbumin powder was obtained in 1 kg packs with multi-layer packing (paper-polyethylene-foil) from the New Zealand Dairy Board.

3.2.2 Water

RO (reverse osmosis) water at room temperature was used to prepare the lactalbumin suspensions, to set the operating conditions, to measure the pure water flux, to rinse the membrane, and to prepare cleaning solution. RO water was obtained from the RO plant (Millipore, Milli-RO 30 plus, model 8000-791-246, USA).

3.2.3 Cleaning agent

The cleaning agent used for cleaning the membranes during this project was Ultrasil 2500 -a chlorinated alkali, supplied by Ecolab., Hamilton, New Zealand.

3.2

3.3 Equipment

3.3.1 Malvern Mastersizer

A Malvern Mastersizer (model E version 1 . 1 , Malvern Instruments, UK) with a reading range of 0. 1 -80 jlm, located at the New Zealand Dairy Research Institute, Palmerston North, was used to determine the particle size distribution (PSD) of lactalbumin. This works on the principle of light scattering, a laser bulb is used as a source of light. Based on the light scattered by a lactalbumin particle in the suspension, the size of the particle is calculated. This is expressed in volume percent. It requires operation at least at 70 % laser power and feed at obscuration of about 20 %.

3.3.2 Membrane modules

Two different types of tubular alumina membrane module were used in this project. The first module (Ceraflow, Millipore COPL, Belford, USA) was 2 1 cm long, multi­ channel type with 1 9 lumen, each of 2.5 mm inner diameter. Membranes with pore sizes- 0.2 !lm and 1 .0 !lm were used in this module. The second module was 25 cm long, single-channel type with 6.8 mm inner diameter (Membralox, ITI-70, S.c.!.,

Bazet, France), obtained from the New Zealand Dairy Research Instit).lte. Membranes with pore sizes 0.2 �lm and 0 . 13 Jlm were used in this module.

3.3.3 Experimental set-up

The schematic diagram of the experimental set-up for constant TMP operation under permeate recycle mode is shown in the Fig. 3. 1 . The actual set-up is shown in Fig. 3.2.

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Fig. 3. 1 Schematic of the experimental set-up for constant TMP operation - ( 1 ) jacketed feed tank, (2) heat exchanger, (3) rotary type positive displacement pump, (4) frequency inverter, (5) magnetic flowmeter, (6) pressure transducers each on inlet side, outlet side and permeate side of the membrane module, (7) membrane module, (8) weighing scale (9) electro-pneumatic valve and (10) control panel.

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3.4

The feed tank was a 60 litre capacity stainless steel tank with a three compartment jacket. The bottom surface of the feed tank had a slope towards the central outlet to help avoid settling of the lactalbumin particles in the tank during operation and to facilitate complete draining at the end. A tubular heat exchanger was provided in the line. A twin lobe rotary positive displacement pump (model 55S, Flow Pump Ltd., UK) was used to pump the lactalbumin suspension. Selection of the pump was based on the results of the study on the effect of pumping on the lactalbumin particles (Chapter 4.3.2.2). The control panel comprised an automatic loop controller (Toshiba, model EC320, Japan) with two loops one each for controlling feed velocity through a frequency inverter (Zener, model MSC-M3, Australia) and for controlling TMP through an electro­ pneumatic valve (Keyston, model IP61 00, Australia). The control panel also housed a safety controller (Honeywell, model UDC200 Mini-Pro, USA) to protect the pump and rest of the system against high pressure by switching off the pump motor at a preset pressure. The frequency inverter was connected between the automatic loop controller and the rotary pump. Diaphragm type pressure transducers (Wika, Alexander Wiegand GmbH & Co., reading range 0-250 kPa, Germany) were placed at the inlet, at the outlet,

and on the permeate side of the membrane. A magnetic flowmeter (Yokogawa, model AM202A, Japan) on the feed flow line and the three pressure transducers were connected to the controller. The membrane module was vertically placed in the line. The electro-pneumatic valve was placed on the exit side of the membrane module (Fig. 3 . 1 ). A weighing scale was provided to measure the permeate flux.

3.4 Methods

3.4.1 Setting the operating conditions

Operating conditions - TMP and CFV - were set by circulating RO water in the rig with a clean membrane in place. This was done prior to addition of the feed suspension. The required level of TMP was obtained by adjusting the electro-pneumatic valve position through the loop controller based on the readings from different pressure transducers. The required level of CFV was obtained by adjusting the pump speed with help of the frequency inverter through the loop controller based on the reading from the magnetic flowmeter. TMP was held constant by maintaining the permeate side pressure constant through keeping the permeate side open to the atmosphere.

3.4.2 Cleaning of the membrane

At the end of each run, after recovering the cake and measuring the pure water flux, the membrane was cleaned to re-establish the same initial clean water permeation rates. Thus all the experiments were conducted with a similar membrane condition.

The following cleaning procedure was found to give satisfactory results: ( 1 ) Drain the suspension from the system by gravity.

(2) Replace the module after recovering the cake and circulate RO water at room temperature (about 1 8 QC) for 5 minutes.

(3) Circulation of hot RO water (50 °C) at 5.0 mls CFV and no applied pressure for 1 0 minutes.

(4) Circulation of 1 % Ultrasil 2500 solution at 50 °C at 5.0 mls crossflow velocity and no applied pressure for 20 minutes.

(5) Circulation of hot RO water (50 °C) at 5.0 mls crossflow velocity and no applied pressure for 1 0 minutes.