Development of a continuous process to produce the 1:1 [beta]/[alpha] mixed lactose crystal : a thesis in partial fulfilment of the requirements for the degree of Master of Engineering at Massey University
A new lactose crystal was formed at Massey University in 1997 while studying the effects of superheated steam on the production of β-lactose. The crystal typically had 50-52% β-lactose content and an X-ray diffraction pattern that did not match with either β-lactose or β-lactose monohydrate, and so it was thought to be an entirely new lactose crystal. Preliminary work was then done at Massey University to determine the conditions under which the crystal could be produced. The new crystal was produced in a batch process in a superheated steam environment between the temperatures of 125°C to l55°C and at very fast drying rates. The present work attempts to develop a continuous process to produce this new lactose crystal. During the late stages of the project it was found that a similar crystal was already documented in the literature and its crystal structure defined. So the crystal found at Massey University could not be termed as a new crystal. The crystal found in the literature was formed by a high thermal treatment to solid-state β-lactose monohydrate and amorphous lactose and had a β/α anomeric ratio of 1:1. The present work attempts to develop a continuous process to produce the 1:1 β/α mixed lactose crystal from a liquid state and in a superheated steam environment. A roller drier was thought to be the best option to produce the new crystal in a continuous process. Different arrangements were developed to create the required conditions under which it was expected that the 1:1 β/α mixed lactose crystal would be produced. Lactose solution sprayed on the roller drier using spray nozzles at temperatures of 125°C to 155°C and flow rates in the range of 1lOml/min to 40ml/min with varying drum speeds consistently produced 85% β-lactose. Lactose solution was smeared on the drum surface which also produced about 80% β-lactose. Lactose solution that was sprayed over a tray which was designed to allow only small amount of the solution (about 3ml/min) to pass through produced about 58% β-lactose. X-ray diffraction showed that the crystal was a mixture of 1:1 β/α mixed lactose crystal and β-lactose crystal. This confirmed that, to produce the 1:1 β/α mixed lactose crystal very low flow rates were required (1.5ml to 3ml/min flow rate). It was observed that the 1:1 β/α mixed lactose crystal was formed when the lactose solution formed a rubbery amorphous lactose solution and then quickly crystallized in the superheated steam environment. To confirm this hypothesis, spray dried amorphous lactose was crystallised over the roller dried inside the superheated steam environment at 125°C, 135°C and 145°C. The resulting product was a mixture of the 1:1 β/α mixed lactose crystal and β-lactose crystal. To produce an amorphous phase from the solution, the solution was injected in air for a few seconds before introducing it into the superheated steam environment. Lactose solution at 90 °C injected onto the roller with a temperature of 145°C for 10 sec in air and 15 minutes in superheated steam produced a crystal having a structure different to that of a β-lactose crystal or α-lactose crystal and it had a similar X-ray diffraction pattern to that of the 1:1 β/α mixed lactose crystal documented in the literature and the crystal formed at Massey in 1997. It was also shown that in the absence of superheated steam, β-lactose crystals were formed. It was clearly shown that a noticeable amount of the 1:1 β/α mixed lactose crystals are formed in products having β-lactose contents below 60%. The formation of 1:1 β/α mixed lactose crystal was found to be very problematic and thus the results were not repeatable. Further investigation should be carried out with better control of all the parameters. Moisture content (mc) was thought to be a
contributing factor that needs to be investigated further.