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March

2017

HYDROCARBON

ENGINEERING

86

technology as applied to biofeedstocks. In this article,

three cases will illustrate some of the pilot-scale process

development steps, and reveal the lessons learned and

benefits that were achieved.

Algae oil processing

Algal oil is a promising feedstock, due to its renewable

nature and origin in a flowable biofarm slurry medium for

extraction and processing of the algal oil product. Algae

has limitations of high oxygen content in the fatty acids

cleaved from the triglycerides that make up the oil.

Furthermore, the subsequent paraffins produced are in the

molecular weight range that freezes at temperatures above

many fuel specifications. In this example, the proposed

processing scheme used a commercial catalyst to

hydrodeoxygenate the oil, followed by hydroisomerisation

of the paraffins produced to lower the freezing point,

before distilling the product into the target flash point and

end point temperatures.

Preparing the catalyst with hydrogen to convert the

stable oxide catalyst to the active form, followed by

sulfiding, was easily accomplished. The processing

objective, which required production of a trial quantity of

the product, was well matched to an 8 l reactor pilot

plant that was not as efficient for exploring the operating

conditions needed for processing. For that work, a 0.1 l

pilot plant was used, which could quickly change

conditions and required much less feedstock to

determine space velocity, operating temperature, and

pressure for the production run. Thus, with less operating

time focused on the small unit, the optimal conditions

were selected.

When the processing in the larger pilot plant

commenced, there was a rapid increase in the gas-make

that was traced to a rapid drop in space velocity. After

mechanical causes were eliminated, a plugging of the

reactor bed in the preheat section, packed with inert

alumina, was found to be the cause. Switching to another

alumina slowed the plugging, but did not eliminate it.

Literature was discovered that suggested that alumina

alone was active for the fatty acid hydrogenation, hence

the reaction in the preheat zone. A high concentration of

phosphorus in the deposits were discovered, which

suggested that unfilterable extraneous cellular content

from the algae was participating in the plugging.

A dilution of the feedstock and a disruption to the

plugging was attempted by tapping the reactor to

dislodge or redistribute the alumina at the top of the bed.

Thus, through a combination of approaches, the

sequential processing required to make a trial batch of oil

that met specification was completed. However, the best

means to ensure that commercial production would be

free of the plugging problem was left unresolved.

Ethanol oligomerisation

Ethanol produced from the fermentation or hydrolysis of

cellulose is a sustainable feedstock, one that is quite

versatile as a component of gasoline or as a synthetic

starting point for other products. As a reactive green

feedstock, it is attractive. However, it is hygroscopic,

Figure 1.

The 8 l reactor fixed-bed pilot plant.

Figure 2.

The 0.1 l reactor pilot plant.