Viscose process Viscosity

Carbon disulfide s most important industrial use, however, has been in the manufacture of regenerated cellulose rayon by the viscose process (viscose rayon) and of cellophane (Davidson and Feinleib 1972 EPA 1978a NIOSH 1977 Timmerman 1978 WHO 1981). In 1974, over 80% of the carbon disulfide manufactured was used to make viscose rayon and cellophane (Austin 1974). This proportion fell to 50% in 1984, but the rayon and cellophane uses still accounted for the greatest fraction of carbon disulfide production (Mannsville Chemical Products Corp. 1985). Since 1989, the consumption of carbon disulfide in the production of carbon tetrachloride has increased to 38%, while the rayon industry s consumption has dropped to 34% (HSDB 1995). 

This property should also be within precise limits. In fact, a too-viscous fuel increases pressure drop in the pump and injectors which then tends to diminish the injection pressure and the degree of atomization as well as affecting the process of combustion. Inversely, insufficient viscosity can cause seizing of the Injection pump. 

This form of limited-conversion hydrocracking is a process that selectively prepares high quality residues for the special manufacture of base oils of high viscosity index or treating residues having low BMCl for the conversion of heavy fractions to ethylene, propylene, butadiene and aromatics. 

Hennico, A., A. Billon, P.-H. Bigeard and J.-P. Peries (1993), IFP s new flexible hydrocracking process combines maximum conversion with production of high viscosity, high VI lube stocks . Rev. Inst. Fran. du Petrole, Vol. 48, No. 2, p. 127. 

Kouzel, B. (1965), How pressure affects liquid viscosity . Hydrocarbon Process. Petrol. Refiner, Vol. 44, No. 3, p. 120. 

This section will firstly consider the properties of oils in the reservoir (compressibility, viscosity and density), and secondly the relationship of subsurface to surface volume of oil during the production process (formation volume factor and gas oil ratio). 

Viscosity and Density - which help determine how easily the fluids will move through the process facility. 

Steam is injected into a reservoir to reduce oil viscosity and make it flow more easily. This technique is used in reservoirs containing high viscosity crudes where conventional methods only yield very low recoveries. Steam can be injected in a cyclic process in which the same well is used for injection and production, and the steam is allowed to soak prior to back production (sometimes known as Huff and Puff). Alternatively steam is injected to create a steam flood, sweeping oil from injectors to producers much as in a conventional waterflood. In such cases it is still found beneficial to increase the residence (or relaxation) time of the steam to heat treat a greater volume of reservoir. 

Like steam injection, in-situ combustion is a thermal process designed to reduce oil viscosity and hence improve flow performance. Combustion of the lighter fractions of the oil in the reservoir is sustained by continuous air injection. Though there have been some economic successes claimed using this method, it has not been widely employed. Under the right conditions, combustion can be initiated spontaneously by injecting air into an oil reservoir. However a number of projects have also experienced explosions in surface compressors and injection wells. 

To conclude this section it should be pointed out again that the friction coefficient has been considered to be frequency independent as implied in assuming a Markov process, and that zero-frequency friction as represented by solvent viscosity is an adequate parameter to describe the effect of friction on observed reaction rates. 

As a multidimensional PES for the reaction from quantum chemical calculations is not available at present, one does not know the reason for the surprismg barrier effect in excited tran.s-stilbene. One could suspect diat tran.s-stilbene possesses already a significant amount of zwitterionic character in the confomiation at the barrier top, implying a fairly Tate barrier along the reaction path towards the twisted perpendicular structure. On the other hand, it could also be possible that die effective barrier changes with viscosity as a result of a multidimensional barrier crossing process along a curved reaction path. 

From stochastic molecnlar dynamics calcnlations on the same system, in the viscosity regime covered by the experiment, it appears that intra- and intennolecnlar energy flow occur on comparable time scales, which leads to the conclnsion that cyclohexane isomerization in liquid CS2 is an activated process [99]. Classical molecnlar dynamics calcnlations [104] also reprodnce the observed non-monotonic viscosity dependence of ic. Furthennore, they also yield a solvent contribntion to the free energy of activation for tlie isomerization reaction which in liquid CS, increases by abont 0.4 kJ moC when the solvent density is increased from 1.3 to 1.5 g cm T Tims the molecnlar dynamics calcnlations support the conclnsion that the high-pressure limit of this unimolecular reaction is not attained in liquid solntion at ambient pressure. It has to be remembered, though, that the analysis of the measnred isomerization rates depends critically on the estimated valne of... 

Nikowa L, Schwarzer D, Troe J and Schroeder J 1992 Viscosity and solvent dependence of low barrier processes photoisomerization of c/s-stilbene in compressed liquid solvents J. Chem. Phys. 97 4827... 

Most properties of linear polymers are controlled by two different factors. The chemical constitution of tire monomers detennines tire interaction strengtli between tire chains, tire interactions of tire polymer witli host molecules or witli interfaces. The monomer stmcture also detennines tire possible local confonnations of tire polymer chain. This relationship between the molecular stmcture and any interaction witli surrounding molecules is similar to tliat found for low-molecular-weight compounds. The second important parameter tliat controls polymer properties is tire molecular weight. Contrary to tire situation for low-molecular-weight compounds, it plays a fimdamental role in polymer behaviour. It detennines tire slow-mode dynamics and tire viscosity of polymers in solutions and in tire melt. These properties are of utmost importance in polymer rheology and condition tlieir processability. The mechanical properties, solubility and miscibility of different polymers also depend on tlieir molecular weights. 

In amoriDhous poiymers, tiiis reiation is vaiid for processes tiiat extend over very different iengtii scaies. Modes which invoived a few monomer units as weii as tenninai reiaxation processes, in which tire chains move as a whoie, obey tire superjDosition reiaxation. On tire basis of tiiis finding an empiricai expression for tire temperature dependence of viscosity at a zero shear rate and tiiat of tire mean reiaxation time of a. modes were derived ... 

Polymers owe much of their attractiveness to their ease of processing. In many important teclmiques, such as injection moulding, fibre spinning and film fonnation, polymers are processed in the melt, so that their flow behaviour is of paramount importance. Because of the viscoelastic properties of polymers, their flow behaviour is much more complex than that of Newtonian liquids for which the viscosity is the only essential parameter. In polymer melts, the recoverable shear compliance, which relates to the elastic forces, is used in addition to the viscosity in the description of flow [48]. 

Equation (2.14) has the advantage of simplicity its drawback is that we learn nothing about either the nature of viscosity or the nature of the sample from the result. In the next few sections we shall propose and develop a molecular model for the flow process. The goals of that development will be not only to describe the data, but also to do so in terms of parameters which have some significance at the molecular level. Before turning to this, it will be helpful if we consider a bit further the form of Eq. (2.14). 

Newtonian behavior the rate of shear is small compared to the rate constant for the flow process. When molecular displacements occur very much faster than the rate of shear (7 < kj ), the molecules show maximum efficiency in dissipating the applied forces. When the molecules cannot move fast enough to keep pace with the external forces, they couple with and dissipate those forces to a lesser extent. Thus there is a decrease in viscosity from its upper, Newtonian limit with increasing 7/kj. The rate constant for the flow process is therefore seen to define a standard against which the rate of shear is to be judged large or small. In the next section we shall consider a molecular model in terms of which this rate constant can be analyzed. 

This produces even greater increases in viscosity, with the attendant increase in the difficulty of heat removal and processing. 

Shaving products Shaw process Shear breeding Shear energy Shearlings Shearometer Shear plane Shear rate Shear stresses Shear test Shear thinning behavior Shear viscosity Sheath-core fiber... 

Eactors that could potentiaHy affect microbial retention include filter type, eg, stmcture, base polymer, surface modification chemistry, pore size distribution, and thickness fluid components, eg, formulation, surfactants, and additives sterilization conditions, eg, temperature, pressure, and time fluid properties, eg, pH, viscosity, osmolarity, and ionic strength and process conditions, eg, temperature, pressure differential, flow rate, and time. 

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