Concentrate processing pellet products

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. 

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. 

The mixing process for concentrate pellet product production via Leistritz-type extrusion equipment is essentially identical to that of dry color product mixing. Once weigh-out has been completed, the formula is usually transported to a mixer where the ingredients must be mixed to uniformity. The ingredients are usually manually dumped into the mixer, after which the lid is sealed and the mixer is operated until the formula reaches the desired uniformity. After mixing, the formula is manually removed from the mixer and placed into a hopper or container with a controlled outlet and is ready for the next operation. 

In the dry process, introduced by Allied Chemical Corp., the uranium concentrate is pelletized and directly reduced with hydrogen to uranium(IV) oxide at temperatures between 540 and 650°C in a fluidized bed reactor. Hydrofluorination to uranium(IV) fluoride proceeds in two fluidized bed reactors connected in series. After fluorinating the uranium(IV) fluoride formed in a production unit consisting of a flame-reactor and a fluidized bed reactor, the uranium(Vl) fluoride produced is purified in a two stage pressure distillation process. This distillative purification process is necessary, because, in contrast with the wet process, no purification is carried out in earlier stages. 

Wang et al. " compared the model predictions to experimental data on the desulfurization of simulated coal gas from a laboratory-scale fixed-bed reactor and from a process development reactor operated on actual coal gas. The solid reactant was formed from cylindrical pellets of zinc and titanium oxides. Data from six experiments using different temperatures, pressures, feed gas flow rates, and feed gas H2S concentrations were available. Product gas concentrations were measured as a function of time, and the axial distribution of sulfur within the reactor was determined at the conclusion of the test. 

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. 

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. 

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],... 

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. 

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