Part V : Reactor Design
Part 5 :Design the reactor that will be used in the proposed technology
a) What is the type of reactor to be used?
The operation of this technology for cellulose hydrolysis can be performed using several different configurations. The membrane reactor is the central feature of every set-up; in some instances there is a stirred reactor (STR) which provides an auxiliary mixing unit, additional volume for reaction, and/or a possibility to discharge the unconverted material. For this technology we suggest to use a jacketed mixing vessel 1 from Ghose and Kostick (1970) and special tubular membrane bioreactor (with adsorption of substrate and enzymes from Bélafi-Bakó et al., 2006).
A membrane bioreactor is a multifunction reactor that combines the reaction with a separation, namely in this case product removal by membrane separation. In practice, the used membrane bioreactor in enzyme technology have mainly employed ultrafiltration for the separation (Drioli, 2004; Pinelo et al., 2009). Ultrafiltration membrane reactors were first used in conjunction with development of novel enzyme immobilization techniques. However, immobilized enzymes are not suitable for insoluble, polymeric substrates, and this will include lignocellulose, due to the necessary enzyme adsorption on the macromolecular substrate particles that becomes severely mass transfer limited with immobilized enzymes (Alfani et al., 1983). The use of free, un-immobilized, enzymes confined in membrane reactors avoids some of these problems, and still allows continuous product removal (HahnHägerdal et al., 1981).
The membrane reactor is integrated in a system together with a jacketed mixing vessel. The mixing vessel is used mixed the cellulose with pre-treated substance and buffer. To keep the volume constant in the tubular reactor, all remaining buffer was recycled back from the membrane reactor to the mixing vessels (Yang et al., 2006). To improve the efficiency of the batch hydrolysis, Henley et al. (1980) incorporated a tubular membrane reactor with a jacketed mixing vessel. (Henley et al., 1980)
b) What is the size of the reactor?
The height of the tubular membrane bioreactor itself is considered to be approximately 10 m with the internal diameter is 1 m. The internal structure of the tubular membrane reactor consists of a porous stainless steel tube with inner diameter 10 cm, length 5 m, porous size 0.1 m and it is covered by a non-woven textile layer with thickness of 3 cm. The layer of textile provides a fine, hairy surface for adsorption of both the particles and the biocatalysts and, in addition, improves the selectivity of the tubular membrane. The membrane surface area is 580 cm2. In the primary side of the membrane, substrate solution containing the enzyme can be recirculated using the inlet and outlet ports, while permeate can be collected from inside of the tube. Pressure in the primary side can be adjusted by the air inlet valve. The layered tube’s house is made of glass, equipped with manometers and stubs, and the module is jacketed to keep temperature constant. The total height of the membrane reactor
c) Operating temperature and pressure?
The reaction involved in the reactors is an enzymatic reaction so it will be most effective with operating temperature around the body temperature. Based on the research done the most suitable operating temperature will be from 45oc to 55oc as can be observed from the graph below.
The pressure will not affect the enzymatic reaction. But to keep it at a certain level it will be maintained at atmospheric pressure.
d) Does it require any heating/cooling? How do you provide that?
To increase the productivity the operating process the inlet to the membrane reactor need to be heated to a temperature of approximately 50oc. This heat is given to the system from the jacketed mixing vessel. The jacketed vessel is a container that is designed for controlling the temperature of its contents, by using a cooling or heating "jacket" around the vessel through which a cooling or heating fluid is circulated.
e) Produce a mechanical drawing of the reactor
e) Cost of the reactor
The reactor used in this reaction is a special type of tubular membrane reactor. So that’s why it will be hard to use the conventional formula for cost estimation of tubular reactors. By using the method investigated by Young et al., 2006 we can assume the cost of the reactor. The total price estimated for the membrane bioreactor is said to be at USD 10 000. The cost of operating and maintenance cost for the membrane bio reactor is assumed to be USD 200 per month. The membrane of the reactor will face wear and tear that will reduce the efficiency. Therefore to maintain the efficiency of the system the membrane needs to be replaced every 6 months and the cost of replacement is assumed to be USD 300. The bioreactor uses a certain amount of power to produce a certain amount of product. This power is measured in the unit USD per gallon. For the bioreactor the energy cost is put at USD 0.05 per gallon.
So if the reactor runs for one year and produces one million gallon per year so the total cost FOR the first year will be calculated as
USD (10 000) + (200 X 12 months) + (300 X 2 times a year) + (0.05 per gallon X 1 000 000 gallon per year)
= USD 63 000 per year