Biocatalytic reaction, aqueous

Many interesting biocatalytic reactions involve organic components that are poorly water-soluble. When using organic-aqueous biphasic bioreactor, availability of poorly water-soluble reactants to cells and enzymes is improved, and product extraction can be coupled to the bioreaction. Many applications in two-phase media can use the existing standard-type bioreactors, such as stirred-tank, fluidized-bed, and column reactors with minor adjustments. 

The highly selective biocatalytic reactions afford a substantial reduction in waste. The overall isolated yield is greater than 90%, and the product is more than 98% chemically pure with an enantiomeric excess of >99.9%. All three evolved enzymes are highly active and are used at such low loadings that counter-current extraction can be used to minimize solvent volumes. Moreover, the butyl acetate solvent is recycled with an efficiency of 85%.The E factor (kgs waste per kg product) for the overall process is 5.8 if process water is excluded (2.3 for the reduction and 3.5 for the cyanation) [47]. If process water is included, the E factor for the whole process is 18 (6.6 for the reduction and 11.4 for the cyanation). The main contributors to the E factor are solvent losses which accounted for 51% of the waste, sodium gluconate (25%), NaCl and Na2SO4 (combined circa. 22%). The three enzymes and the NADP cofactor account for <1% of the waste. The main waste streams are aqueous and directly biodegradable. 

Multi-phase reactors are of interest in biocatalytic reactions if one or several components of the reaction are insoluble or insufficiently soluble in aqueous phases but if an aqueous phase has to be kept, if only for the biocatalyst. However, a two-phase system can be utilized advantageously for the shifting of an equilibrium this is demonstrated below. We analyze the simple reaction A <=> B in an organic-aqueous two-phase system with the assumption that reactant A and product B partition between the two phases. The partition coefficients Pw and Porg are de-... 

Enzymes as nature s catalysts are able to perform an outstanding array of regio- and stereoselective reactions. Therefore, as water is nature s solvent, it is not surprising that many biocatalytic reactions have been performed in the aqueous phase.However, in typical reactions, the substrates are limited to hydrophilic compounds because of a desire for reaction homogeneity. It should also be noted that, in most cases, the aqueous medium is a buffer solution of an ideal pH for the enzyme to function effectively. 

In an aqueous two-phase system, if the biocatalytic reaction takes place in one of the phases, while the products are either evenly distributed, or preferentially partitioned to the other... 

GDEs, however, have been poorly explored for integrating biocatalytic reactions, such as oxygen reduction as catalyzed by MCO. Integration of enzymes in GDE presents an additional materials challenge as the GDE must contain a catalytic layer that is hydrophilic enough for enzyme immobilization from aqueous solution. Yet, the material should be adaptable to treatments that yield transition to the superhydro-phobicity required in the GDL. To date, only a handful of enzyme-based GDEs have been reported. For example, in 1995 Iliev et al. demonstrated an amperometric... 

Aono et reported the oxidative bioconversion of cholesterol as a model biocatalytic reaction using a solvent-tolerant Pseudomonas species. Cholesterol and its products are insoluble in an aqueous solution but dissolve in some organic solvents. The attempt was successful. The conversion of cholesterol was more than 98% and the yield of oxidative products was 80%. 

Biocatalytic reaction in aqueous-supercritical fluids biphasic systems have also been investigated and some examples are shown further. 

Biocatalytic processes are often intrinsically "green" and therefore contribute to waste reduction. Many biocatalytic reactions are performed in aqueous media imder mild temperature and pressure using enzymes that are sustainably produced from renewable raw materials [8]. 

An important problem in emulsified organic-aqueous systems is that of scale-up, which is concerned with the realization of stable emulsions and the separation of phases after the reaction. The use of biphasic membrane systems that contain the enzyme and keep the two phases separated is likely to solve this problem. In the case of 5-naproxen an ee of 92% has been demonstrated without any decay in activity over a period of two weeks of continuous operation. A number of examples of biocatalytic membrane reactors have been provided by Giorno and Drioli (2000) and include the conversion of fumaric acid to L-aspartic acid, L-aspartic acid to L-alanine, and cortexolone to hydrocortisone and prednisolone. 

Considering only the aqueous phase of the biocatalytic system, the equilibrium constant for the reaction is given as a function of thermodynamic activities of the components shown ... 

The above mixture is incubated. The water-soluble salt contaminants would transfer from the fossil fuel into the aqueous phase during the procedure. Secondly, the biocatalytic agent would selectively break C—S bonds in the sulfur-bearing molecules to form water-soluble inorganic sulfur molecules. Both of these reactions occur without depleting the fossil fuel of combustible organic molecules and... 

A BDS method in which the feed has been emulsified with the aqueous solution of the biocatalytic agent and subjected to incubation for carrying out the reaction. 

A BDS method in which the feed has been emulsified with the aqueous solution of the biocatalytic agent and subjected to incubation for carrying out the reaction. The biocatalytic agent is a cell-free enzyme preparation from Rhodococcus sp. ATCC 53969, B. sphaericus ATCC 53969, or any of their mutant derivations. 

The selected biocatalyst is any of the already described alternatives based on R. rhodochrous bacteria ATCC No. 53968. Its concentration or proportion to the fossil fuel feedstock was neither reported nor claimed only a slight comment is made on the proportion between the crude oil and the biocatalytic aqueous solution, which states that it will not exceed one half the total incubation volumes. In addition, an additional amount of water, enough for desalting, is simultaneously added with the biocatalytic solution. The process is carried out by feeding the crude oil and water into a CSTR reaction vessel and stirred until an emulsion is formed. The mixture is incubated under stirring at temperature and pressure conditions, for a period of time adequate for both to occur, desalting and desulfurization. 

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