Sulfur-Containing Additives

The effect of the addition of neutral donor ligands to the catalyst system was investigated by adding sulfur-containing compounds such as thioxanthene or thiols. 

Like oxygen, bonded sulfur has lone-pair electrons that provide it with donor properties, but dn orbitals are also available for use in ji-bonding [this bonding seems to be even more prominent with sulfur than with phosphorus compounds (27)]. Both properties appear to predispose sulfur compounds to form ligands of transition-metal ions. 

The addition of sulfur compounds to a solution of TiCl4 in 1,2-di-chloroethane or toluene causes a color change from yellow to brown, indicative of complex formation. The addition of aluminum alkyl produces a further deepening of the color but the solution remains transparent no Ti(IlI) is formed. Although the structure of the active catalyst species is not yet known, it is reasonable to assume that all three components form part of it 

The sulfur-containing additive may be expected to have a dual influence, both electronic and steric. The increase in electron density at the transition-metal center may prevent coordination of the a-olefins this effect must necessarily have a bearing on the coordination of the ethylene itself, decreasing the rate of ethylene consumption. On the other hand, very bulky sulfur ligands may block the coordination site effectively enough to make it accessible only for the small ethylene molecule, but not for the higher a-olefins. 

As expected, the overall rate is decreased in the presence of the additive, whereas the molecular weight does not appear to be greatly influenced. The addition of more than 2 moles of sulfur compound per mole trf Ti-compound does not further improve the result 

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Sulfur-containing additives include organic mono- and polysulfides, elemental sulfur as well as a wide variety of sulfurized fats and hydrocarbons. Phosphorus containing additives include esters of phosphoric acids, derivatives of thiophosphoric acids and phosphites (Davey, 1950 Sakurai and Sato, 1970). 

Clean Kentucky Coal and Clean Kentucky Coal with Sulfur-Containing Additives. In Figure 14 are presented values tor the clean Kentucky coal with synthesis gas, and clean Kentucky coal with additives containing sulfur. The additives were present in amounts calculated to contain the same relative amount of sulfur. All of the autoclave times were one hour. The point for clean Kentucky coal (which still contains some pyrite and some magnetite (as an artifact of the cleaning process) in about a 2 1 mole ratio) and the point for thiophene lie on the pyrite-pyrrhotite equilbrium line. The... 

Figure 14. Pyrrhotites from autoclaves (Clean Kentucky coal plus sulfur-containing additives) Clean Kentucky coal with synthesis gas, with additive noted (B).

Binder and/or lubricant selection depends on many considerations which are specific for the particular application. The additives must be compatible with the material to be agglomerated and the proposed uses of the product. For example, for pharmaceutical or food applications no toxic materials can be selected and for agglomeration of metal-bearing dusts intended for use in steel making sulfur-containing additives are normally prohibited. Many such limitations may be defined for specific materials and applications. 

Figure 9-6. Friction with sulfur-containing additives in the lubricant. Steel on steel. Load 29.9 N. From data by Sakurai, Okabe and Takahashi [18],...

This instrument [33] can provide analysis of nitrogen- and sulfur-containing additives in polyolefins. 

Quantitative analytical schemes (using calibration curves, internal standardisation) have been devised for selected (copolymeric) systems [540]. An example is the determination of the composition of styrene-methacrylate by PyGC [603]. Qther applications include the quantification of rubber components [604,605], cellulose esters [606], isocyanate components of polyurethanes [607], nylon [608], plasticisers [609], aliphatic sulfur-containing additives [4]. Standardisation for quantitative analysis based on PyGC data requires careful choice of reference polymers. Use of an internal standard may improve the precision when the concentration of a single polymeric component of a blend or copolymer is calculated on the basis of PyGC data [610]. 

It has a good extraction resistance. In the presence of sulfur-containing additives (e.g., thiodipropionic acid esters or cadmium sulphide pigments) it may cause discoloration at high processing temperatures. 

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