Pelletization concentrate product processing

Many studies investigating one or more of these potential rate-determining steps have been carried out over the years. These studies have shown that the rate of reaction depends upon many factors such as temperature [15, 27-29], pellet size [27-29], crystallinity [28], additive types and concentrations [30], process gas type and quantity [31, 32], molecular weight [22, 31] and end group concentrations [16, 33] - all of which will be addressed individually later in this section. Various models have also been proposed involving kinetics [33] and/or by-product diffusion [11, 16, 21, 27-29, 34, 35] through to empirical Equations [15]. The variety of models used and the wide range of kinetic and physical data published demonstrate the complexity of the mechanisms involved. 

Companies will custom formulate colorant and additive products designed to be used by plastic molders, who will, in turn, produce the final consumer products. The raw materials for colorant and additive products may be in powder, liquid, or solid form. The products formulated from them may also be in powder, liquid, or solid form. Dry color formulations (powder form) currently comprise less than 5% of the total colorant and additive products being produced today. Liquid formulations account for another 5% however, this form of product is increasing in popularity and is expected to capture a larger share of the colorant and additives market in the near future. The solid form, known as concentrates or masterbatch products, are concentrated ingredients encapsulated in a carrier resin that is usually in pellet form. This type of product comprises the overwhelming majority of the formulated products used by molders and compounders today. A discussion of the basic production processes associated with the production of the various colorant and additive product types is presented below. 

In the manufacture of color master batches, the current industry practice is to perform eritieal color measurements off-line. Typically, a sample of the pelletized color concentrate is diluted with natural resin at a standard ratio and milled, extruded or injection molded into a physieal form suitable for visual and instrumental evaluation. These methods are slow and labor intensive. Furthermore, they do not lend themselves well to statistical process eontrol strategies because of the time lag between production and testing. Since relatively few samples can be examined, laboratory measurements may not give a true indication of the consistency of the concentrate product over the entire manufacturing process. 

The concentrated (dressed) iron ore is formed into sintered pellets at the mine, which are then reduced to iron in a blast furnace by carbon (coke). A modern integrated steel production process based on ore is shown in Figure 8.23. 

Antimicrobials for plastics are usually supplied as a biocide concentrate rather than the pure active ingredient because the safe handling of many of the pure antimicrobial agents requires special precautions for which the typical plastic processor is not equipped. The use of concentrates also helps insure that the relatively low level of the additive is accurately dosed and well dispersed into the plastic during processing. Several products are offered as both liquid solutions or polymer pellet concentrates. 

Solid biocide concentrates have several advantages. They are easier to handle safely and clean up of any spilled material is safer and easier than with liquid products. Also, there are fewer problems with the disposal of empty containers. Some disadvantages to solid biocide pellet concentrates can be incompatibility with some customer formulations and processes. It is more difficult to meter small quantities of solid pellets than liquids and solid biocide pellets tend to be more expensive to use. 

Bacterium seeds, water, and methanol are fed into an inoculation tank. Sterilized air and nutrients are then injected into the fermenter along with an inoculum of cultivated bacteria. Ammonia is added as a nitrogen source and for pH control Continuous fermentation produces a steady stream of bacteria, which are sent into a flocculation tank after filtration and centrifu l separation. The concentrated effluent from the flocculation tank is further dewatered by a series of decanter centrifuges. SCP destined for human consumption must under an additional step to remove the nucleic acids contained in the cells by one of the following techniques [4] (1) acid hydrolysis, (2) cell disruption, (3) chemical extraction, (4) alkaline hydrolysis, or (5) enzymatic treatment. Finalfy, the concentrated product stream is dried and processed into granules, pellets, or powder and then packed for sale. The overall yield is 1 ton protein for every 1.8 ton methanol consumed in the process. 

A common form of dispersion used with antimony trioxide is that of small (1x3 mm) virtually dustless extruded strands, typically at an active level of 85-90 percent in a lubricant binder that promotes incorporation and may improve processing, possibly offsetting increased cost. This type of product is available from Chemtura it should be considered in cases where less than major quantities are used in high intensive mixers. An alternate is to use pelletized concentrates, usually of about 80 percent activity in an EVA binder. An appropriate use is via a proportioning meter in pellet extrusion, particularly in cases where a standard base compound is sometimes adjusted with antimony trioxide for a specific application. Such products are available, for example, from Rhein Chemie. 

Workplace safety has been taken care of by the reworking of some classes of additives into more environmentally acceptable forms. Some trends are the increased use of additive concentrates or masterbatches and the replacement of powder versions by uniform pellets or pastilles which release less dust and flow more easily. Moreover, the current move to multicomponent formulations of stabilisers and processing aids in a low- or nondusting product also takes away the risk of operator error, aids quality control, ISO protocols and good housekeeping. An additional benefit is more homogeneous incorporation of the additives in the polymeric matrix. 

Two of the most widely used and detected UV filters in the environment and WWTPs are BP3 and 4-MBC. Thus, they were the selected compounds to study individually their degradation by fungi [44, 49]. Studies with BP1, not only a BP3 metabolite but also an industrial UV filter (but its use in cosmetics is not allowed) itself have also been performed. Studies in liquid media allow a better analysis and monitoring of many parameters, both the contaminant concentration and the fungal metabolic state such as glucose consumption and enzyme production. In these studies, the degradation process was performed with the fungus in form of pellets. 

This process is of special interest if a product has to be frozen more quickly than is possible on belts or in trays A pellet of 2 mm diameter is cooled from 0 °C to -50 °C in approx. 10 s, or at a rate of approx. 300 °C/min. The advantages are minimum freeze concentration, free-flow product, small ice crystals (which are acceptable in this case of small transport distances for energy and water vapor). It is likely that some pellets (those too large or too small) will need to be removed by sieving. 

Diffusion Rate Controlled Process If the rate of chemical reaction is much faster than the diffusion of water and EG through the solid amorphous phase, then the reaction can be considered to be at equilibrium throughout the pellet [21], The reaction rate is dependent upon the pellet size, the diffusivity of both water and EG, the starting molecular weight, and the equilibrium constants Ki and K5. In addition, the pellet can be expected to have a radial viscosity profile due to a by-product concentration profile through the pellet with the molecular weight increasing as the by-product concentrations decreases in the direction of the pellet surface [22-24],... 

Some simulation results for trilobic particles (citral hydrogenation) are provided by Fig. 2. As the figure reveals, the process is heavily diffusion-limited, not only by hydrogen diffusion but also that of the organic educts and products. The effectiviness factor is typically within the range 0.03-1. In case of lower stirrer rates, the role of external diffusion limitation becomes more profound. Furthermore, the quasi-stationary concentration fronts move inside the catalyst pellet, as the catalyst deactivation proceeds. 

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