Liquid raw materials

The early 1980s saw considerable interest in a new form of silicone materials, namely the liquid silicone mbbers. These may be considered as a development from the addition-cured RTV silicone rubbers but with a better pot life and improved physical properties, including heat stability similar to that of conventional peroxide-cured elastomers. The ability to process such liquid raw materials leads to a number of economic benefits such as lower production costs, increased ouput and reduced capital investment compared with more conventional rubbers. Liquid silicone rubbers are low-viscosity materials which range from a flow consistency to a paste consistency. They are usually supplied as a two-pack system which requires simple blending before use. The materials cure rapidly above 110°C and when injection moulded at high temperatures (200-250°C) cure times as low as a few seconds are possible for small parts. Because of the rapid mould filling, scorch is rarely a problem and, furthermore, post-curing is usually unnecessary. 

Liquid raw materials such as polymer emulsions, defoamers, pigment dispersions, dye solutions, dispersing aids and emulsifiers are all products that can themselves become infected with micro-organisms if not produced from non-contaminated ingredients, under good manufacturing conditions and with an effective preservative. 

A process is described [224] in which an exothermic reaction takes place in a semi-batch reactor at elevated temperatures and under pressure. The solid and liquid raw materials are both toxic and flammable. Spontaneous ignition is possible when the reaction mass is exposed to air. Therefore, the system must be totally enclosed and confined in order to contain safely any emissions arising from the loss of reactor control, and to prevent secondary combustion reactions upon discharge of the materials to the atmosphere. Further, procedures and equipment are necessary for the safe collection and disposal of solid, liquid, and gaseous emission products. 

Fig. 9.6 Comparison of the ratio between bio-liquid cost (plant-gate) and the theoretical H2 yield for different bio-liquid raw materials to be used in H2 production. (Adapted from [32]).

Reactive processing of polymers is based on the use of low-melting-point solid or liquid raw materials or premixes to form articles of the required by the usual polymerization process shape simultaneous transformation into linear, branched or network polymers and/or solidification at moderate temperatures (as a rule, up to 200°C) and pressure. 

The chemical systems for RIM all have one characteristic in common they require a RIM machine to convert liquid raw materials into quality plastic products. Assuming a properly formulated chemical system, the quality of the end product results from the ability to measure, control (Chapter 3), and adjust temperature, ratio, pressure, and other essential process parameters of the RIM dispensing machine. Such exacting control leads to a reduction in start-up time, minimal rejects and touch-up work, reproducible product quality, and the ability to pinpoint changes in product properties. 

Liquid colorant and additive product formulation may involve both powdered and liquid ingredients. All dry constituents are generally manually weighed out in the same manner as for the products described above. However, proportioning of liquid raw materials requires the use of volumetric measurement methods. 

Figure E5.8 is a hypothetical process used for demonstration by Diamond Shamrock Co. of their flowsheeting code PROVES. Makeup gas is compressed, combined with recycle gas, and fed, together with liquid raw material, into a three-phase, suspended bed catalytic reactor. The reactor is cooled by recirculating liquid through a heat reclamation steam generator. Reaction products are condensed and the pressure of the exit stream reduced in two stages. The gas from the first-stage separator is recirculated, whereas the liquid from the second-stage separator is fed into a distillation column. Pure product is withdrawn from the bottom of the column. The distillate is a by-product that is pumped to another plant.

Results. Column extraction offers a new method of sample preparation and can be applied to liquid raw materials and solids that are solvent soluble. The column extraction method is promising and offers an efficient alternative for a range of materials. Excellent extractions of Cu, Fe, Co and Ni are obtained with the PL-Thiourea, while only Cu and Fe are extracted with the PL-Thiol column for this monomer (Table 6.9). 

Dimethyl phthalate, a very convenient liquid raw material, is a by-product in the fabrication of dimethylterephthalate. The amidic polyols can be used to replace the Mannich polyols. The self catalytic effect in PU formation is much less important in the case of amidic polyols, as compared with Mannich polyols. The rigid PU foams derived from amidic polyols are much more thermoresistant than the rigid PU foams derived from Mannich polyols [2]. 

Liquid raw materials are mixed in a specific sequence in slow- to high-speed stirrers or mixers to give a homogeneous, streak-free mixture (see Section 7.3.3). In larger mixers and tanks (up to 50000 L capacity) the mixing device is permanently installed in the vessels. Precondensates and wax solutions are prepared in heatable and coolable vessels equipped with stirrers. 

All estimates (mid-1995 US ) are based on a grassroots production facility in a developing or transition economy country with an existir industrial infrastructure where the investment cost is assumed to be similar to that of a U.S. Gulf Coast location. Conveniait access to an ocean or inland port is assumed and the cost of land is not included. All raw materials are assumed to be purchased from international sources at the indicated free-on-board (f.o.b.) prices which, of course, can vary quite widely. The f.o.b. raw material prices were increased by US 30/tonne for solid materials and US 40/tonne for liquid materials to arrive at an assumed delivered cost at the plant site. Storage facilities (capacity) for dry and liquid raw materials are based on the receipt of raw materials in 3,000- to 5,000-tonne lots and an apj>rcKimate.2 rnonth inventory at the plant ate. 

Isoelectric heating Form of heating by means of electrical energy, in which a special form of element is employed, and which is submerged in liquid raw materials. In practice a series of such elements is employed. 

Because instruments and tools, etc., contaminated by the patients industrial chemicals are difficult to clean perfectly, it is handy to use disposable containers, syringes, stirrers or sticks to prepare test substances or dose them onto test chambers. Polypropylene is chemically inert and contains very few additional chemicals besides the polymer. If a liquid raw material dissolves plastic materials, glass containers should be used. Wooden stirrers and sticks may also be used. If the product is solid (in crystal or powder form), it can be pulverized using a mortar. 

BAT is to use pigging systems in multiproduct plants with liquid raw materials and products (see Section 12.1.16)... 

Liquid raw materials such as defoamers, surfactants, starch solutions and hydroxyethyl cellulose solutions may themselves be susceptible to microbial attack and, unless carefully manufactured and protected with biocides, can also introduce contamination into the product. 

Paint plants are characterised by storage tanks for liquid raw materials and products connected to the production units by pipes, they have silos for powdered raw material and filling units for the final packaging into buckets and pails. 

TABLE 11.2 Yield of the Products of Oxidation of Hydrocarbons with Air or Oxygen by Means of the Technology Developed hy Celanese Company (kg/1 of Liquid Raw Material) [263 ... 

Viscosities of raw materials are very important because they can influence not only the properties of final adhesive products, but also the production process. Methods for measuring viscosities of liquid raw materials are included in the following standards ISO 2555, ISO 3219, JIS K 7117, and ASTM D1084. 

Liquid products can, of course, also be processed with this extraction technique in this case the liquid raw material is fed into a distillation column and slowly falls to the bottom in countercurrent against the rising supercritical gas. At the bottom of the column, the residue is discharged from the sump by a level regulation system, and the extracted components are once again precipitated in the separator. With this procedure, the extractor in Fig. 16 must be replaced by a countercurrent extraction column. This process can be run continuously because liquid can be metered into the high-pressure area without difficulty. 

Number and Type of Building Blocks Used in the Polymerization Process. In some cases, the polymerization may involve the use of a single building block that is caused to repeatedly link to itself and form long chains, as is the case of e-caprolactam to form nylon 6. This type of reaction is referred to as addition polymerization. In other situations, two building blocks are combined to form a polymer, such as the polymerization of hexamethylenediame (HMDA) and adipic acid to form nylon 6/6. This type of reaction is called condensation polymerization. When liquid raw material constituents are used, it may be possible to directly convert them to parts, but this may be prevented if other factors are involved. 

Some processes produce parts by physically pushing liquid raw materials into a closed mold. Processes that use this strategy can be generally classified as injection-type processes, and they all involve pushing (inducing shear flow upon) the... 

Advantages. The RTM process was conceived to overcome some of the limitations of traditional compression molding. The use of liquid raw materials greatly enhances flow and allows for much more complex shapes to be produced. It also favors the production of smaller, more complex parts and allows for a multiple cavity strategy to be employed where appropriate. Encapsulation, particularly in electrical applications, is feasible and much easier to accomplish than with traditional compression techniques. 

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