Project Progress  


Production of emulsions at laboratory scale

Two different Pyrolysis Oils were studied during the first 18 months of the project. The first one was a saw dust (spruce) flash pyrolysis oil produced by FORTUM (presently Neste Oil), while the second one was a Forestry Residue (spruce, pine, birch, bark, needles) Oil produced by VTT.
Both the oils were characterized in terms of their composition and physical-chemical properties. Similar analyses were already performed by VTT and FORTUM (presently Neste Oil), but they were repeated in order to check if changes occurred during the transportation from the production facility to our laboratories.
Composition and physical-chemical properties of oils are extremely important in the formulation of a stable emulsion.

Forestry Residue (VTT)

Spruce Saw Dust (FORTUM-presently Neste Oil)

H2O content (% w/w)a 25.8 26.1
Viscosity at 40C 17 cSt 25 cSt
Insoluble Solid Contentb (%w/w) 0.17 0.20
Ash Weigth (%w/w) 0.099 0.035
Density at 20C 1.12 kg/dm3 1.22 kg/dm3
pH 2.5-3 2.5-3

Elemental Analysis
Carbon content (% w/w) 45.07 49.55
Nitrogen content (% w/w) 0.41 0.06
Hydrogen content (% w/w) 6.41 7.03
Oxygen content (% w/w)c 48.11 43.36

Alkali/Ash (mg g1)
Na 4.59 0.55
K 16.44 3.94
Mg 11.44 1.67
Ca 31.87 4.1
Pb 0.003 0.048

Spruce oil (FORTUM-presently Neste Oil) showed higher values for viscosity and density, while the ash content is about a third with respect to the forestry residue oil (VTT). It is well known that these oils change their composition upon ageing, forming big aggregates that after long storage times (1 or 2 years) eventually settle down.
The higher viscosity value of spruce oil (FORTUM-presently Neste Oil) agrees with the higher stability experienced. While the forestry residue oil (VTT) showed a higher tendency to separate in a lighter top phase and a darker bottom phase, that can be hardly dispersed by vigorous agitation during the first storage months and can’t be dispersed anymore at about 6 months.
The low ash content of the spruce oil (FORTUM-presently Neste Oil) is due to the fact that they filter the oil as fresh.
Elemental analysis results reflected the difference in the feedstocks used by VTT and FORTUM (presently Neste Oil) and it was interesting to note a big difference in terms of alkali content.
No final conclusions on the quality of spruce and forestry residue oils can be made due to the limited number of samples.

Six different PO/Diesel oil emulsions were prepared: 30/70, 25/75, 20/80, 15/85, 10/90, 5/95 expressed as % by weight. In this way we tried to clarify the role of PO for emulsion stability: in fact emulsions constituted by a higher amount of oil are more stable than low oil content ones.
In order to finally formulate a stable emulsion, several trial and error tests were performed. For structures as complex as PO made of a mixture of several organic products and water, the choice of the proper surfactant was not an easy task, being dependent on the molecular structure (especially the hydrophilic and lipophilic tendency). Approximately one hundred different surfactants, cationic, anionic, zwitterionic, polymeric and non-ionic, with different values of HLB (Hydrophilic-Liphophilic Balance) were tested. Additives containing sulphur or nitrogen have been neglected in order to avoid an increase in NOx and SOx emissions during combustion.

The stability of emulsions was checked both leaving the emulsion at room temperature and in oven at 65°C in order to accelerate the aging process.
Preliminary tests were performed simply by dissolving the surfactant in the PO or in the Diesel oil, depending on its solubility. The amount of surfactant used at this stage was 1.5% wt/wt of emulsion. PO and Diesel were then mixed with a magnetic stirrer at room temperature. No stable emulsions were obtained.
Two methods were then tried: inverse phase emulsification and high energy dispersion. In the former case the surfactant was dissolved in PO. The Diesel oil was then added drop wise to this mixture, always mixing it gently with a magnetic stirrer. The PO phase initially represented the continuous phase. By increasing the Diesel amount, the emulsion went trough a bicontinuous emulsion (when PO and Diesel contents are similar) and finally formed an inverse phase emulsion, where Diesel represented the continuous phase and PO was dispersed as micro-dimensioned droplets. The effect of temperature on the stability of emulsions obtained by means of this methodology was investigated. A temperature of about 70ºC represented the optimal choice for stability. This effect was probably due to the presence of big aggregates in the PO that could be dissolved by increasing the temperature.
With regards to the high energy dispersion methodology a Ika Ultra-Turrax disperser was used. The high shear energy transferred by the disperser to the mixture was sufficient to produce droplets as small as a few micrometers.
The emulsion stability was strongly influenced by the methodology used to obtain it.
Also for high energy dispersion technology 70°C represented the optimal temperature to obtain stable emulsions.
The most stable emulsions were obtained by using the Ultra-Turrax disperser adding a non-ionic block copolymer surfactant.
From several experiments carried out, some of them also in oven at 65°C, the observed emulsion instability observed even just in few weeks was interpreted as a sedimentation phenomenon due to the highest density of PO with respect to the Diesel oil.

In order to investigate stability the variation of viscosity in time was measured and the droplet size distribution of the dispersed phase was studied by means of light scattering measurements and optical microscopy.

Measurements were performed both on freshly prepared samples and room temperature aged ones.

In the case of spruce oil (FORTUM-presently Neste Oil) the fresh emulsion and the shaken aged emulsion showed identical droplets size, confirming our hypothesis regarding the density depending sedimentation. While for emulsions prepared with forestry residue oil (VTT) two different destabilisation processes were identified: sedimentation due to density mismatching (effective also in the case of Fortum Oil) and growing of droplets (present only in the forestry residue oil case). However, these results have to be evaluated taking into account that the surfactant was developed for white wood oils and not for forestry residues oils.

A summary of the mean diameters as obtained by FOQELS (light scattering) and microscopy for both the oils is reported:

Average of diameters for emulsions with 30% PO, 70% Diesel oil, 1.0% surfactant wt respect to PO.

  FOQELS Microscopy
Spruce oil (FORTUM) fresh 1.87 [m] 3.90 [m]
Spruce oil (FORTUM) aged 2.26 [m] 3.15 [m]
Forestry residue oil (VTT) fresh 1.64 [m] 2.87 [m]
Forestry residue oil (VTT) aged 1.99 [m] 7.90 [m]

A summarizing conclusion is that emulsions containing forestry residue oil (VTT) are less stable than the ones prepared with spruce oil (FORTUM-presently Neste Oil), due to a higher tendency of forestry residue oil to separate in different phases.

In May 2005 further samples of pyrolysis oil were sent by VTT to CSGI:

1. Whole Forestry Residue (FR)
2. Fresh bottom phase of FR
3. Fresh top phase of FR
4. Emulsion 1 prepared by VTT using the whole FR + 2% ethanol
5. Emulsion 2 prepared by VTT using the bottom FR phase
6. Concentrated bottom phase

The emulsions produced were 30 wt% pyrolysis oil from samples 2, 3 and 6 and from samples 2 and 3 after aging process.
The aging process of samples 2 and 3 was obtained leaving the oils at 65° for 7 days.
All samples and the prepared emulsions were characterized by means of FOQELS and Optical Microscopy in the CSGI laboratories.
All the emulsions and the aged samples 2 and 3 were prepared and sent to IM for combustion tests.

Due to differences in composition the three oils showed different results for the emulsification process. Huge differences in viscosity between the emulsion prepared with the concentrated bottom phase and the fresh one were observed. These differences were found also in the droplets dimension, as it is shown by the results of FOQELS measurements.

The most important difference is the droplet size between the emulsion obtained with concentrated bottom phase and the fresh bottom phase. By means of optical microscopy it was possible to notice that the sample prepared with aged oil presented bigger droplets.

The emulsification plant

The plant is divided into three different skids, in order to keep small and light every single part and allow for easy handling and transport to the VTT facility where the in-line pyrolysation test will be performed.

Fuel storage tanks and pumping system are installed in the first skid, the heat exchangers, the dispersing motor and all the regulations are in the second and at the exit of the dispersing device the separator is installed.

The plant is a continuous LFO/PO emulsification system, with a production capacity of at least 50 l/h and a range between 5 and 50% of PO (w/w).

PO Pump

Additive Pump

Heat Exchanger

Storage Tank

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