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  • Neal Williams and Jacob Misuraca

Perlite for Renewable Diesel Feedstock Filtration

How to prevent costly plant shutdowns from logistics bottlenecks delaying filter-aid deliveries.

Demand for renewable energy is surging, and biofuel companies are meeting this need by rapidly investing in new renewable diesel and sustainable aviation fuel (SAF) capacity. To supply these plants and hit carbon-intensity targets, producers are drawn towards a variety of feedstocks that contain more impurities than virgin oils. Consequently, the refining process typically requires significant solids removal, and improved filtration techniques mean even the most heavily contaminated fats, oils or greases can be used to run engines. Whatever the source, the feedstock needs to be refined, either filtered or water-washed with a centrifuge. The latter process effectively scrubs away the contaminants but has a few drawbacks, namely heavy water demand and highly contaminated wastewater. For that reason, more biofuel suppliers are moving towards filtration.

The filtration process for waste-based biofuels needs to work with different feedstocks from different sources that contain different types of contamination. Mineral filter aids have this flexibility due to the wide range of permeability available. Although diatomaceous earth (DE) filter aids are more widely known, perlite filter aids are used in almost every industry that separates solids from liquids. Expanded perlite particles are precisely milled to desired particle-size distribution to make various grades, able to filter a wide array of liquids. The high solids-holding capacity of perlite filter cakes is a function of the maze of microscopic pathways formed in the cake. Perlite filter aids can be used in both the precoat and bodyfeed in pressure-filter applications or on rotary vacuum filters, matching the performance of diatomite. Yet, when converting from a DE filter aid, it is important to note that these are two different minerals with different physical properties. Producers considering switching from a DE to a perlite filter aid should work with a filtration technical expert to understand all of the conversion considerations and to find the best filter aid for their filtration system.

Security of Supply

An abundant and reliable perlite product can assure quick and uninterrupted supply. This is not always the case with comparable minerals that have longer lead times and require significant inventories to supply variations in demand. Perlite filter aids are produced at numerous, small expansion plants located across North America. This national footprint places perlite filter-aid production within close vicinity of nearly every biofuel producer. In contrast, other filter aids rely on a supply chain to customers that may be long and vulnerable to logistic complications. Due to its distribution of production locations, perlite capacity is less constrained. At Imerys, our network of six expansion plants can readily manufacture any filter-aid grade to minimize order backlogs. With operations close to customers and serving only the domestic market, perlite is the most readily available filter aid for biofuel producers.

Density Advantage

The unique structure of perlite makes for a very light weight with 30 percent to 50 percent less bulk density compared to other filter aids. Therefore, users typically require 30 percent to 50 percent less additive. The high void volume and porosity of perlite form a thick, permeable filter cake improving permeability and flux rates.

“The main consideration when making a conversion to perlite is the impact of density,” explains Mike Boerner, manager of filtration technical services at Imerys. “Dosage is based on filter area, so producers switching to perlite are typically using the same volume at nearly half the mass.”

Successful Conversions

Experience in a variety of applications has shown that most filter-aid users can economically switch to perlite from other filter aids without sacrificing efficacy or efficiency.

“We have successfully converted a variety of producers to perlite while maintaining excellent filtration performance,” Boerner confirms. “Qualifying an alternative filter aid gives our customers options.”

Cost Savings of Perlite Precoat

Perlite filter aids also provide significant savings due to density and supply advantages. The value proposition shown in Figure 4 was modeled using data from a successful customer conversion. Due to the lower density of perlite, the customer realized a 44 percent reduction in filter-aid usage by mass. The closer proximity to the customer also provided substantial shipping savings. In total, the savings are about $78,000 per year by switching to perlite filter aid for precoat.

Broad Portfolio Backed by Technical Expertise

With more than a century of production experience and technical expertise, Imerys has developed a portfolio of filter aids and filterable absorbents that offers unparalleled flexibility and cost-effectiveness in a wide range of feedstock.

Harborlite 900 RE is our perlite filter aid formulated and quality-tested to meet the specifications required by the biofuel market. We work closely with plant operators and their engineering support teams to help identify new solutions to problems that have yet to happen. Imerys’ proven track record and commitment to sustainable innovation are core to our reputation. Producers looking to optimize their filtration-system performance should reach out to the Imerys filtration team.


Neal Williams

Research Engineer, Imerys

Jacob Misuraca

Research Engineer, Imerys

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