Enzymes continuous stirred tank reactor

Cooking extmders have been studied for the Uquefaction of starch, but the high temperature inactivation of the enzymes in the extmder demands doses 5—10 times higher than under conditions in a jet cooker (69). Eor example, continuous nonpressure cooking of wheat for the production of ethanol is carried out at 85°C in two continuous stirred tank reactors (CSTR) connected in series plug-fiow tube reactors may be included if only one CSTR is used (70). 

A continuous stirred tank reactor has been reported for the hydrolysis of the triglycerides existing in vegetable oil in the presence of the aqueous phase and for synthesis reactions (Table 5). A microfilter can be used to prevent the immobilized enzyme from leaving the reactor. Kawano et al. [115] investigated the hydrolysis of olive oil in octane with Candida cylindracea lipase in aqueous solution in a Vibro Mixer reactor containing vibration plates connected to the crankshaft of a motor and oscillated with fixed rates. 

An excellent production figure for (R)-mandelonitrile (2400 g/1 per day) was achieved by Kragl et al. [105] using a continuously stirred tank reactor in which an ultrafiltration membrane enables continuous homogenous catalysis to occur from an enzyme (PaHnl) which is retained within the reaction vessel. In order to quench the reaction the outlet of this vessel was fed into a vessel containing a mixture of chloroform and hydrochloric acid, which allowed for accurate product analysis. 

A solution to this problem is the enzyme membrane reactor (Figure 10.8). This is a kind of CSTR (continuous stirred tank reactor), with retains the enzyme and the cofactor using an ultrafiltration membrane. This membrane has a cut-off of about 10000. Enzymes usually have a molecular mass of 25000-250000, but the molecular mass of NAD(H) is much too low for retention. Therefore it is first derivatized with polyethylene glycol (PEG 20000). The reactivity of NAD(H) is hardly affected by the derivatization with this soluble polymer. Alanine can now be produced continuously by high concentrations of both enzymes and of NAD (H) in this reactor. 

Figure 11.9 Different arrangements and modes of operation for membrane bioreactors Continuous Stirred Tank Reactor (CSTR) with recirculation arrangement (a), dead-end cell (b), tubular with entrapped enzyme (c).

Starch Liquefaction. Starch in its natural state is only degraded slowly by CC-amylases. To make the starch susceptible to enzymatic breakdown, it is necessary to gelatinize and liquefy a slurry with a 30—40% dry matter content. Gelatinization temperature depends on the type of starch (67) com is the most common source of industrial starches followed by wheat, tapioca, and potatoes. Liquefaction is achieved by adding a heat-stable a-amylase to the starch slurry. The equipment used for liquefaction may be stirred tank reactors, continuous stirred tank reactors (CSTR), or a jet cooker. Most starch processing plants liquefy the starch with a single enzyme dose in a process using a jet cooker (Fig. 9). 

A continuous stirred-tank reactor (CSTR) is an ideal reactor which is based on the assumption that the reactor contents are well mixed. Therefore, the concentrations of the various components of the outlet stream are assumed to be the same as the concentrations of these components in the reactor. Continuous operation of the enzyme reactor can increase the productivity of the reactor significantly by eliminating the downtime. It is also easy to automate in order to reduce labor costs. 

In the following we attempt to describe the acetylcholinesterase/choline acetyltransferase enzyme system inside the neural synaptic cleft in a simple fashion see Figure 4.49. The complete neurocycle of the acetylcholine as a neurotransmitter is simulated in our model as a simple two-enzymes/two-compartments model. Each compartment is described as a constant-flow, constant-volume, isothermal, continuous stirred tank reactor (CSTR). The two compartments (I) and (II) are separated by a nonselective permeable membrane as shown in Figure 4.50. 

The relevant parameter for studies of operating stability of enzymes is the product of active enzyme concentration [E]active and residence time T, [E]active T. In a continuously stirred tank reactor (CSTR) the quantities [E]active and T are linked by Eq. (2.28), where [S0] denotes the initial substrate concentration, x the degree of conversion and r(x) the conversion-dependent reaction rate (Wandrey, 1977 Bommarius, 1992). 

Enzyme Membrane Reactor (Continuous Stirred Tank Reactor, CSTR)... 

A recent development at laboratory scale is the application of an enzyme (lipase) to catalyze the hydrolysis Water and fat are mixed at low temperature (300 K) in a continuous stirred-tank reactor (CSTR). The water phase contains the enzyme. A much purer glycerol solution is obtained than in the conventional process. The disadvantage is that the equilibrium is not favorable. 

In general, the fixed D-glucose isomerase systems have many advantages with respect to enzyme use, efficiency, ease of handling, and adaptability to continuous-reactor operation. Methods have been described that employ a continuously stirred tank-reactor provided with a semipermeable membrane through which the isomerized liquor, having the steady-state composition, is removed from the reaction medium at the same rate as fresh substrate is introduced into the reactor.47 The soluble enzyme is retained in the reaction zone, because it is held back by the semipermeable membrane, and fresh enzyme may be added as needed, to compensate for enzyme inactivation, to the reaction zone with the fresh substrate. 

Enzymatic reactions were then performed in both free and immobilized catalyst reactors. Knez and Habulin [38] studied sunflower oil hydrolysis in a continuous stirred tank reactor acting as a free catalyst reactor. Enzyme was retained in the reactor... 

With respect to benzaldehyde, (R)-oxynitrilase exhibits saturation kinetics (Michaelis Menten kinetics, see Sect. 7.4.2.1) and a maximum reaction rate is reached above a concentration of about 5 mmol L 1. The chemical reaction presents a linear increase of the reaction rate with increasing benzaldehyde concentration, representing first order kinetics, when the concentration of HCN is kept constant (see Fig. 7-13). As a consequence the enzymatic reaction becomes more dominating at lower concentrations of the substrate benzaldehyde (for HCN as substrate the same kinetic behavior occurs, data not shown). Accordingly an enzyme reactor would be suitable that works under minimum average substrate concentrations. These requirements are satisfied by the continuous stirred tank reactor (CSTR). In Sect. 7.5.2.1 this aspect of enzyme reaction engineering will be discussed further. 

The ideal reactor to overcome substrate inhibition (Fig. 7-24A) is the continuous stirred tank reactor (possible in form of an Enzyme Membrane Reactor, see below). In spite of a high feed concentration of substrate a high reaction rate occurs, as the steady state substrate concentration within the reactor is low. 

Compared to batch processes, continuous processes often show a higher space-time yield. Reaction conditions may be kept within certain limits more easily. For easier scale-up of some enzyme-catalyzed reactions, the Enzyme Membrane Reactor (EMR) has been developed. The principle is shown in Fig. 7-26 A. The difference in size between a biocatalyst and the reactants enables continuous homogeneous catalysis to be achieved while retaining the catalyst in the vessel. For this purpose, commercially available ultrafiltration membranes are used. When continuously operated, the EMR behaves as a continuous stirred tank reactor (CSTR) with complete backmixing. For large-scale membrane reactors, hollow-fiber membranes or stacked flat membranes are used 129. To prevent concentration polarization on the membrane, the reaction mixture is circulated along the membrane surface by a low-shear recirculation pump (Fig. 7-26 B). 

Assume that you obtained the Cg versus t curve you calculated in part (a) experimentally. Estimate K/ and by plotting the (Cg - Cs)/ln(Cg /Cg) versus f/ln(Cgj,/Cg) curve according to Eq. (2.38). Is tnis approach reliable Chemostat (continuously stirred-tank reactor) runs with various flow rates were carried out. If the inlet substrate concentration is 300 mol/m and the flow rate is 100 cm / min, what is the steady-state substrate concentration of the outlet The reactor volume is 300 cm. Assume that the enzyme concentration in the reactor is constant so that the same kinetic parameters can be used. 

Effect of Diffusional Restrictions on Enzyme Reactor Design and Performance in Heterogeneous Systems. Determination of Effectiveness Factors. Batch Reactor Continuous Stirred Tank Reactor Under Complete Mixing Continuous Packed-Bed Reactor Under Plug Flow Regime... 

The degradation of the dye Orange n was carried out in an enzyme reactor consisting of a continuous stirred tank reactor (CSTR) coupled with a membrane to recover the enzyme (Fig. 6.6.2.B). From an economic point of view, a compromise... 

The work-up of batch processes, run in stirred vessels, had often faced the challenge to efficiently separate and recover the enzyme used. Meanwhile, there is abundant know-how available to immobilise enzymes on different carriers, though some issues need always to be considered maintained activity of the enzyme, its stability towards solvents and the operating temperature used in a reaction. Enzyme immobilisation allows for continuous reactions carried out in columns or in a sequence of continuous stirred-tank reactors. Certain advantages are offered by Degussa s enzyme-membrane-reactor (EMR), where the enzyme is surrounded by a hoUow-fibre membrane, that is permeable to substrate and product. 

Performance characteristics of multi-enzyme reactions in a continuous stirred tank reactor, in fixed-bed reactors, in fluid-bed reactors, ... 

The continuous production of aliphatic chiral alcohols was demonstrated by Leuchs et al. as shown in Scheme 6.20 by using continuous stirred tank reactor (CSTR). The CRED from Lactobacillus brevis was used in a biphasic system with MTBE as cosolvent to reduce aliphatic ketones with the general structure 53. It was shown that inaeasing the chain length resulted in a decreased yield due to less available substrate in the aqueous phase. The continuous process was run with a ketone concentration of 100 mmol/L and IPA was used as the reductant (1 mol/L). It was also demonstrated that 200 rpm was ideal for longevity of the enzyme. Doubling the residence time did not lead to a sigttificant increase in the space-time yield [30]. 

Biocatalysts in nature tend to be optimized to perform best in aqueous environments, at neutral pH, temperatures below 40 °C, and at low osmotic pressure. These conditions are sometimes in conflict with the need of the chemist or process engineer to optimize a reaction with respect to space-time yield or high product concentration in order to facilitate downstream processing. Furthermore, enzymes and whole cells are often inhibited by products or substrates. This might be overcome by the use of continuously operated stirred tank reactors, fed-batch reactors, or reactors with in situ product removal [14, 15]. The addition of organic solvents to increase the solubility of substrates and/or products is a common practice [16]. 

Enzymatic degradation was tested with commercial LAC from M. thermophila (2,000 U L ). E2 and EE2 were completely degraded even in the absence of mediators after 3 and 5 h, respectively, and after 1 h in the presence of some mediators. For El total removal was achieved in 8 h in the presence of VA and >70% for the other mediators after 24 h, whereas elimination reached 65% in the absence of mediators [8]. The immobilization of this enzyme by encapsulation in a sol-gel matrix [58] was employed for the treatment of a mixture of El, E2, and EE2 both in a batch stirred tank reactor (BSTR) operating in cycles and a continuous PBR. Removal of estrogens was >85% in the BSTR and 55%, 75%, and 60% for El, E2, and EE2, respectively, in the PBR. Both systems were able to reduce the estrogenic activity of the mixture in 63%. Likewise, the immobilization of VP in the form of CLEAs completely removed E2 and EE2 within 10 min from batch experiments, with a concomitant reduction of estrogenic activity, higher than 60% for both compounds [44]. 

---