Seed stage

Seed stage medium, 77 28 Seed trains, in fermentation, 7 7 42 Segmented-arc nozzle design, 76 8 Segmented elastomeric polyurethane fibers, 25 476-477... 

The process usually starts with the polymerization of a small proportion of the reagents at a very low monomer to water ratio (the seed stage), followed by the feeding of the remaining monomer (which may take several hours) and of other materials (if needed) once the conversion in the reactor has reached 70% or more. The in-reactor conversion will then depend upon the rate of polymerization compared to the rate of feed. If the reaction is continued under the so-called monomer-starved conditions, the in-reactor conversion is kept at a high 80-90%, which reduces the polymerization rate. To compensate, temperature is raised however, then the initiator depletes faster and more has to be added during the reaction. 

Seed preparation The primary seed fermentation is performed using shaking-flask culture techniques. Once grown, the suspension is then transferred to further seed stages. The purpose of the seed preparation is to generate enough inoculums for the production of a fermenter. 

If growth in the fermenter proceeds unchecked at the rate prevailing in the seed stages, the culture would become very dense and the available aeration would no longer be sufficient to maintain penicillin production. Should oxygen availability fall... 

The seed stage, in which the diluent, a portion of the monomer, a portion of dispersant and the initiator (azo or peroxy type) are heated to form an initial low-concentration fine dispersion. 

In addition to the physical parameters discussed above, a number of other factors related to the culture and to the medium should be considered for both transfer of a process from shake flasks to fermenters and for scale-up to larger vessels. These include the provision of a culture stock giving reproducible growth after regeneration, the method of inoculum build-up that may require a number of shake flask and fermenter seed stages, an assessment of the variability within the process, the cost and availability of the medium components, and the method of sterilization within the fermenter. 

Warr SR, Gershater CJ, Box SJ (1996) Seed stage development for improved fermentation performance increased milbemycin production by Streptomyces hygroscopicus. J Ind Microbiol 16 295-300... 

The choice of method for introducing the monomer to the reaction vessel can have significant effects upon the particle size and panicle size distribution of the latex produced [e.g. 56]. Consider the effects of monomer addition and emulsion addition processes when used vdth the same formulation. The surfactant concentration in the seed stage will be higher fw the monomer addition process because all of the surfactant is used in the seed stage, whoeas only pan can be used for the emulsion addition process since some surfactant is required to prepare... 

The simplest way to establish the value of Rm below which monomer-starved conditions can be achieved, is to perform an experiment in which the chosen seed stage is carried out as planned for the semi-batch process, and to then add the remaining monomer over a short period of time to ensure that monomer-flooded conditions are attained. Measurement of the rate of polymerization (which should be i p ) after the initial period required for swelling of the seed particles, gives the limiting value of R ) below which monomer-starved conditions can be expected. 

The first stage of the preparations involves fomiation of the seed latex. After complete conversion of the seed-stage monomers, the monomer mixture and additional surfactant for the first growtii stage are added at controlled rates and the monomer completely converted before Hoceeding to add the monomer mixture and additional surfactant for the next growth sta. The preparation proceeds in this maiuier until the desired toughening [larticles are formed, both in terms... 

Gu et al studied the effects of the seeding procedures and the conditions of hydrothermal treatment on the FAU membranes quality. For the seeding stage, they used rubbing and dip-coating. They found that dip-coating combined with... 

There are two stages involved in a typical emulsion polymerization. In the seed stage, a mixture of water, surfactant, and colloid is first heated to the reaction temperature (85-90°C). Next, 5-10% of the monomer mixture with a portion of the initiator is added. At this point the reaction mixture contains monomer droplets stabilized by surfactant, some dissolved monomei the initiator, and surfactant (in solution and in micelles). The initiator breaks down to produce radicals, when heated and these initiate the polymerization of the dissolved monomers. Growing polymer chains eventually enter a micelle, initiating reaction of the monomer inside. If a second growing polymer enters the micelle, termination can occur. 

During the seed stage, micelles of monomer are converted to latex particles, which are stabilized by surfactant. Most of the particles present in the final latex are formed in the seed stage and polymerization will have proceeded to 10% or 15% completion. 

In addition, the presence of seeding stage in the semi-continuous process (by 10 wt % monomer), the increasing of the feeding time and better control of the initiator feed increased the monomer conversion, the average particle size, and the stabilities of the pol3rmerization and latex of VAc/DOM monomer system. The effect of these reaction variables on the conversion and the particle size of the VAC/DOM latex are given in Table 3 [99]. 

Monomer content in initial reactor charge (%, w/w) Seeding stage Feeding stage Completion stage Initiator feed Conversion (%) Particle size (nm)... 

Both the seed and main tank fermentations are very similar the former can be regarded as a smaller-scale version of the main fermentation tank. The main purpose of the seed stage is to start the fermentation process on a small scale and get more efficient utilization of the large fermentation tank. The size of the seed tank is dependant on the main tank, but usually the volume is in the range of 10% of the main tank. 

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