Split Feed Process

In the split feed process, the additives are fed into the polymer melt via a side feeder downstream of the plastification zone. Here, gravimetric feeding is always used (see Fig. 4.32). 

This process is particularly suitable for large batch sizes and has the following advantages 

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Figure 432 Schematic representation of the production of a masterbatch using the split feed process...

The most frequent application of phase-equilibrium calculations in chemical process design and analysis is probably in treatment of equilibrium separations. In these operations, often called flash processes, a feed stream (or several feed streams) enters a separation stage where it is split into two streams of different composition that are in equilibrium with each other. 

If a vapor from the phase split is either predominantly product or predominantly byproduct, then it is removed from the process. If the vapor contains predominantly unconverted feed material, it is normally recycled to the reactor. In these cases, there is no need to carry out any separation on the vapor. 

Separation Processes that split a feed into simpier or narrower fractions. 

All refining operations may be classed as either conversion processes or separation processes. In the former, the feed undergoes a chemical reaction such as cracking, polymerization, or desulfurization. Separation processes take advantage of differences in physical properties to split the feed into two or more different products. Distillation, the most common of all refinery separation processes, uses differences in boiling points to separate hydrocarbon mixtures. 

The fat oil is fed to a splitter or stripping tower, where the absorbed tight constituents are separated from the oil by distillation. Usually the lean oil is the same material as the heavier part of the absorber feed, so that the bottoms from the stripper are split into lean oil, which is recycled to the absorber, and a stabilized gasoline product, which is passed on to subsequent processing operations. 

The fresh feeds will be known from the process specification so if the split-fraction coefficients can be estimated, the equations can be solved to determine the flows of each component to each unit. Where the split-fractions are strongly dependent on the inlet flows, the values can be adjusted and the calculation repeated until a satisfactory convergence between the estimated values and those required by the calculated inlet flows is reached. 

Table 4.3 shows the feed of each component and the total flow to each unit. The composition of any other stream of interest can be calculated from these values and the split-fraction coefficients. The compositions and flows should be checked for compliance with the process constraints, the split-fraction values adjusted, and the calculation repeated, as necessary, until a satisfactory fit is obtained. Some of the constraints to check in this example are discussed below. 

A distillation column divides the feed stream components between the top and bottom streams, and any side streams. The product compositions are often known they may be specified, or fixed by process constraints, such as product specifications, effluent limits or an azeotropic composition. For a particular stream, 5 , the split-fraction coefficient is given by ... 

If the vapor from the phase split is either predominantly product or predominantly byproduct, then it can be removed from the process. If the vapor contains predominantly unconverted feed material, it is normally recycled to the reactor. If the vapor stream consists of a mixture of unconverted feed material, products and byproducts, then some separation of the vapor may be needed. The vapor from the phase split will be difficult to condense if the feed to the phase split has been cooled to cooling water temperature. If separation of the vapor is needed in such circumstances, one of the following methods can be used ... 

If the liquid from the phase split requires separation, then this can normally be accomplished by distillation, except under special circumstances. A distillation sequence is most often required with products and byproducts removed from the process and unreacted feed material recycled. In some situations, byproducts might be recycled for reasons discussed in the previous section. 

In the processing of petroleum the first step is the removal of salt water. The presence of salt water in any processing steps would mean that expensive corrosion-resistant materials are required for those steps. This would greatly increase the price of the equipment (see Chapter 9). After removing the salt water, the next major separation is the crude still where the feed is split into six or more large-volume streams to reduce the size of future processing equipment. 

SOFT [Split-olefin feed technology] An improved version of Phillips HF alkylation process. 

Example 1.3. Our third example illustrates a typical control scheme for an entire simple chemical plant. Figure 1.5 gives a simple schematic sketch of the process configuration and its control system. Two liquid feeds are pumped into a reactor in which they react to form products. The reaction is exothermic, and therefore heat must be removed from the reactor. This is accomplished by adding cooling water to a jacket surrounding the reactor. Reactor elHuent is pumped through a preheater into a distillation column that splits it into two product streams. 

We have evaluated and developed new process modifications using the model. The concept of staggering the reactor inlet temperatures to equalize the aging rates in all three reactors (15) was evaluated with the model. Model simulations, to quantify the benefits of this modification, could be carried out in a day. Corresponding experiments showing similar effects would have required months to complete. With minimal modifications to the model, the benefits for splitting the reformer feed among the three reactors (16) were also determined. 

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