Cold Flow Temperatures

Gonz lez G6mez, M. E., Howard-Hildige, R., Leahy, J. J., and Rice, B. 2002. Winterization of Waste Cooking Oil Methyl Ester to Improve Cold Flow Temperature Fuel Properties. Fuel, 81,33-39. 

Fatty acid stmcture (composition and imsaturation degree) of vegetable oils used as feedstocks considerably affect the physical properties of biodiesel such as viscosity, cold flow properties, oxidation stability and exhaust emission profile (Knothe 2008). Even, there are many successful attempts to predict the biodiesel properties from the fatty acid composition of the plant oils. Fatty acid distribution of some common vegetable oils is given in Table 2. Higher saturated fatty acid based biodiesel has higher viscosity, cold flow temperatures, oxidation stability and calorific value while higher imsaturated fatty acid based biodiesel shows a combination of improved fuel properties as a whole (Knothe 2005 Ramos 2009 Kumar 2013). 

The typical mechanical properties that qualify PCTFE as a unique engineering thermoplastic are provided ia Table 1 the cryogenic mechanical properties are recorded ia Table 2. Other unique aspects of PCTFE are resistance to cold flow due to high compressive strength, and low coefficient of thermal expansion over a wide temperature range. 

Membrane Limitations Chemical attack, fouling, and compaction are prominent problems with RO and NF membranes. Compaction is the most straightforward. It is the result of creep, slow cold flow of the polymer resulting in a loss of water permeability. It is measured by the slope of log flux versus log time in seconds. It is independent of the flux units used and is reported as a slope, sometimes with the minus sign omitted. A slope of—0.001, typical for noncelhilosic membranes, means that for every threefold increase in log(time), 10 seconds, a membrane looses 10 percent of its flux. Since membranes are rated assuming that the dramatic early decline in permeability has already occurred, the further decline after the first few weeks is veiy slow. Compaction is specific to pressure, temperature, and envi-... 

It has been common practice to blend plasticisers with certain polymers since the early days of the plastics industry when Alexander Parkes introduced Parkesine. When they were first used their function was primarily to act as spacers between the polymer molecules. Less energy was therefore required for molecular bond rotation and polymers became capable of flow at temperatures below their decomposition temperature. It was subsequently found that plasticisers could serve two additional purposes, to lower the melt viscosity and to change physical properties of the product such as to increase softness and flexibility and decrease the cold flex temperature (a measure of the temperature below which the polymer compound loses its flexibility). 

Poly(vinyl acetate) is too soft and shows excessive cold flow for use in moulded plastics. This is no doubt associated with the fact that the glass transition temperature of 28°C is little above the usual ambient temperatures and in fact in many places at various times the glass temperature may be the lower. It has a density of 1.19 g/cm and a refractive index of 1.47. Commercial polymers are atactic and, since they do not crystallise, transparent (if free from emulsifier). They are successfully used in emulsion paints, as adhesives for textiles, paper and wood, as a sizing material and as a permanent starch . A number of grades are supplied by manufacturers which differ in molecular weight and in the nature of comonomers (e.g. vinyl maleate) which are commonly used (see Section 14.4.4)... 

Plasticizers soften the film and increase the adhesion and the setting speed. The most common are phthalates, adipates and benzoates. The amount added can be in a broad range of 10-50%. They affect the swelling and softening of the PVAc emulsion particles, ensure film formation at room temperature, and the tack of the still wet adhesive. They also provide improved moisture resistance of the bond. Disadvantages are the lower resistance of the bond line against heat, possible migration of the plasticizers and enhanced cold flow. 

The particle size of the dispersed phase depends upon the viscosity of the elastomer-monomer solution. Preferably the molecular weight of the polybutadiene elastomer should be around 2 x 10 and should have reasonable branching to reduce cold flow. Furthermore, the microstructure of the elastomer provides an important contribution toward the low-temperature impact behavior of the final product. It should also be emphasized that the use of EPDM rubber [136] or acrylate rubber [137] may provide improved weatherability. It has been observed that with an increase in agitator speed the mean diameter of the dispersed phase (D) decreases, which subsequently levels out at high shear [138-141]. However, reagglomeration may occur in the case of bulk... 

Product performance data Products subjected to a given load develop a corresponding predictable deformation. If it continues to increase without any increase in load or stress, the material is said to be experiencing creep or cold flow. Creep in any product is defined as increasing strain over time in the presence of a constant stress (Figs. 2-25 and 26). The rate of creep for any given plastic, steel, wood, etc. material depends on the basic applied stress, time, and temperature. 

When compared to TSs, they can have limitations of heat-distortion temperatures, cold flow and creep, and are more likely to be... 

Cold flow improvers (pour point depressants) These viscosity improvers are often specified in cold climates for unheated gas oil or where existing residual oil heaters are inadequate. The use of these paraffin crystal modifiers permits fuel to continue to flow at temperatures of 30 to 40 °F lower than the point at which wax crystallization would normally occur. 

Consider the scaleup of a small, tubular reactor in which diffusion of both mass and heat is important. As a practical matter, the same fluid, the same inlet temperature, and the same mean residence time will be used in the small and large reactors. Substitute fluids and cold-flow models are sometimes used to study the fluid mechanics of a reactor, but not the kinetics of the reaction. 

As mentioned in Section 11.3, fluidized-bed reactors are difficult to scale. One approach is to build a cold-flow model of the process. This is a unit in which the solids are fluidized to simulate the proposed plant, but at ambient temperature and with plain air as the fluidizing gas. The objective is to determine the gas and solid flow patterns. Experiments using both adsorbed and nonadsorbed tracers can be used in this determination. The nonadsorbed tracer determines the gas-phase residence time using the methods of Chapter 15. The adsorbed tracer also measures time spent on the solid surface, from which the contact time distribution can be estimated. See Section 15.4.2. 

Cold flow studies have several advantages. Operation at ambient temperature allows construction of the experimental units with transparent plastic material that provides full visibility of the unit during operation. In addition, the experimental unit is much easier to instrument because of operating conditions less severe than those of a hot model. The cold model can also be constructed at a lower cost in a shorter time and requires less manpower to operate. Larger experimental units, closer to commercial size, can thus be constructed at a reasonable cost and within an affordable time frame. If the simulation criteria are known, the results of cold flow model studies can then be combined with the kinetic models and the intrinsic rate equations generated from the bench-scale hot models to construct a realistic mathematical model for scale-up. 

Carnot efficiency is one of the cornerstones of thermodynamics. This concept was derived by Carnot from the impossibility of a perpetuum mobile of the second kind [ 1]. It was used by Clausius to define the most basic state function of thermodynamics, namely the entropy [2]. The Carnot cycle deals with the extraction, during one full cycle, of an amount of work W from an amount of heat Q, flowing from a hot reservoir (temperature Ti) into a cold reservoir (temperature T2 < T ). The efficiency r] for doing so obeys the following inequality ... 

Test method IP 309 is used to determine the low-temperature filterability of distillate fuels including those treated with a cold flow improver. The cold filter plugging point (CFPP) is defined as the highest temperature at which the fuel, when cooled under the prescribed conditions, will not flow through the filter or requires more than 60 seconds for 20 mL to pass through or fails to return completely to the test jar. This method is part of a series of standardized tests developed by the Institute of Petroleum. Test method IP 309 is summarized as follows ... 

The Tg of elastomers must be below the use temperature. The high degree of cold flow which is characteristic of polymers at temperatures above the Tg is reduced by the incorporation of a few crosslinks to produce a network polymer with a low crosslink density. 

---