Physical Properties (More)

Median Oil Droplet Size and Droplet Size Distribution
A small oil droplet size is critical to the stability of an emulsified vegetable oil (EVO). Oil-in-water emulsions produced by field processing normally have median droplet sizes ranging from 2 to 10 microns. Oil droplets in coarse emulsions may remain dispersed in water for a few hours to a few days, but physical separation by “creaming” results if such emulsions are allowed to stand for longer periods of time. As predicted by Stokes law, an emulsion with smaller droplets will separate more slowly than an emulsion with larger droplets at a rate proportional to the square of the ratio of the droplet size. An emulsion with a median droplet size of 1 micron will take 100 times longer to separate than an oil/water emulsion with a median droplet size of 10 microns. As a general rule, oil-in-water emulsions will be kinetically stable if the oil droplets are smaller than 1 micron. Such an emulsion will not separate until the surfactants used to create it are destroyed by bacteria or other environmental factors. Field processed emulsions and some commercial products contain oil droplets larger than one micron and therefore are not kinetically stable. Oil droplets larger than one micron can coalesce into even larger droplets, leading to clogged pore throats or oil/water separation.

By using an optimal blend of stabilizing agents and a sophisticated factory production method RNAS produces a very fine oil-in-water emulsions. Median droplet size is less than 0.3 microns. A tight droplet size distribution is also critical since a few large droplets may block soil pores. In the typical factory product 95% of the material consists of droplets between 0.15 microns and 0.6 microns. In most cases no droplets larger than 0.5 microns are detected with a laser diffraction particle size analysis (detection at less than 0.1% by mass). By making the droplets smaller than half a micron the emulsion remains stable for long periods of time and does not block soil pore throats even in fine grained soils. The tiny droplets do adsorb onto soils surfaces by interception allowing them coat soil surfaces without significantly reducing water flow through soils.

Droplet size data based on droplet counts or log-transformed data can be misleading. The only meaningful way to describe droplet size is by volume or mass distribution. If droplet count is used, most of the mass or oil volume can be contained in a few large droplets and the numerous small droplets, which represent a smaller proportion of the total mass. Hence, statistics based on count will skew the data and suggest a deceptively small mean droplet size. Using droplet count, an emulsion could contain a great majority of droplets under 1 micron while having 90% or more of the oil mass contained in droplets 10 microns or larger that will clog soil pore throats and lead to oil/water separation by creaming. Droplet size and distribution statistics used to describe our products is always based on a volume distribution as determined by laser diffraction analytical methods.

Droplet Size and Droplet Transport
Droplet size is critical for transport of oil/water emulsions through porous media. According to the model described by Soo and Radke (1986), oil droplets must be less than 0.30 times the soil pore throat size to ensure that oil droplets do not block soil pore throats. Xu, et al., (2006) determined that the effects of straining should be considered if oil droplets are larger than 0.008 times the size of soil grain diameter. Newman Zone® has a very small median droplet size and a very tight distribution of droplet size; typically the median droplet size is 0.28 microns with 90% of the material contained in droplets smaller than 0.41 microns. The narrow range of small droplet sizes allows injection of Newman Zone® into most soil and bedrock formations as the emulsion will pass through material retained on a #275 sieve without straining of the oil droplets and the associated decrease in permeability.

The oil droplets in Newman Zone® have a negative zeta potential of -45 to -55 milivolts, which results in good mobility of the droplets as soil particles also have a generally negative surface charge. The uniformly negative zeta potential contributes to the stability of the emulsion and reduces strong absorption on soil particles. The standard formulation of Newman Zone® contains lecithin which results in stronger absorption of the oil droplets onto sandy soils.

Viscosity
Unlike pure vegetable oil, dilute oil-in-water emulsions have a viscosity much closer to water than to oil. The viscosity of pure soybean oil is about 80 centipoise. The viscosity of Newman Zone®, containing 50% soybean oil by volume, is approximately 22 centipoise. After dilution with water by a factor of 10 to 100 for injection the viscosity is essentially the same as water (1 centipoise). Newman Zone® can be injected into any soil or bedrock formation that will receive water at an acceptable flow rate.

In contrast, many other slow-release electron donor amendments such as polylactate (a viscous fluid to semisolid) or pure vegetable oil are often not effectively distributed in the subsurface because of their high viscosity and can reduce soil permeability by blocking soil pore throats. The injection radius of these viscous products is commonly very small. Injection of diluted Newman Zone® can result in a large injection radius as large fluid injection volumes disperse the oil farther away from the injection well. Newman Zone® has been detected in monitoring wells as far as 100 feet away from the injection well.

Specific Gravity
The specific gravity of soybean oil is approximately 0.925. The kinetic stability of Newman Zone® prevents separation of the drops into a simple oil phase. Hence, undiluted Newman Zone® behaves like a single-phase fluid with a specific gravity of about 0.99 at 70°F (8.25 pounds per gallon at 70°F, 8.31 pounds per gallon at 40°F). The specific gravity of the emulsion is essentially 1.0 when diluted by 10 to 100 times with water as typically occurs for injection.

Newman Zone® Concentration vs. Turbidity
The very small and uniform droplets in Newman Zone® efficiently scatter light, resulting in an opaque white color even when diluted to 0.5% (5,000 mg/l) oil. (The standard formulation has a light yellow-cream color because of the lecithin). The emulsion becomes slightly translucent at about 500 mg/l of oil. The emulsion will cause a distinct discoloration of water at concentrations as low as 25 to 50 mg/L of oil or even lower.

One may be able to identify the presence of Newman Zone® in monitoring wells during and after injection by analyzing samples with a portable turbidimeter. One could similarly monitor nearby surface water for short circuiting of injection fluid that can happen during any injection. To assist in this endeavor, we have related Newman Zone® concentration to (NTU). One curve was generated by a simple serial dilution of Newman Zone® in deionized water to the lower accuracy limit of the turbidimeter. The second curve was generated by weighing each sample of Newman Zone® down to the accuracy limits of our balance and then serially diluting to the accuracy of the turbidimeter.