Renewable Diesel : Not Biodiesel !!
in this article, Amir focuses on the hydrotreated renewable diesel and its promising market significance compared to common biodiesel.
Although Renewable Diesel and Biodiesel are derived from triglycerides contained in vegetable oil and animal fat, differences can be found in production process and product performance.
Biodiesel is composed of fatty acid methyl esters, which is produced by alkali-catalyzed transesterification using excess methanol. The reaction is carried out inside agitator-stirred tanks. Optimum temperature range (45 ºC – 60 ºC) and pressure in the atmospheric range. Therefore, the process requires lower economy of scale. Although a sustainable alternative to petroleum diesel, it must be blended, meaning the highest concentration allowed is 20% with petroleum diesel (ASTM D6751). beyond the blending ratio, there is high risk of damage to existing diesel engines and causing contaminant buildup. In addition, it has lower cetane number (45-52) compared to petroleum diesel (50-60).
Renewable Diesel or Hydrotreated Vegetable Oil is produced by hydro-deoxygenation through hydrogenating triglycerides to remove oxygen. Therefore, it can be substituted with petroleum diesel in existing vehicles (ASTM D975) because it is chemically identical, no blending limits as it runs efficiently in vehicles that use diesel fuel. Furthermore, it has higher cetane number (70-90) meaning it delivers more power to the engine compared to petroleum diesel.
Numerous technology vendors and producers are providing licensed processes for hydro-deoxygenation such as Green Diesel™ (Honeywell/UOP), NExBTL™ (Neste), SoladieselRD™ (Solazyme), Biofene™ (Amyris), HPR Diesel™ (Propel), and REG-9000™/RHD (REG). However, Green Diesel™ (Honeywell/UOP) is thought to be typical for illustration.
Renewable Diesel : Process Description
The feed -vegetable oil and animal fat waste- is pretreated including acid treatment to remove gums and greases using sulfuric or acetic acids, sedimentation to remove suspended particles, bleaching using bentonite clay to adsorb pigments and trace metals, neutralization using calcium hydroxide, and filtration.
The treated feed is heated and sent to hydro-deoxygenation reactor, in which hydrogen saturates the double bonds of the triglycerides producing hydrogenated triglyceride intermediates that is further hydrogenated to de-carboxylate, de-carbonylate , and de-oxygenate into linear paraffins. The reaction is carried inside packed bed reactor using heterogeneous catalyst composed of sulfided nickel and molybdenum fixed on alumina support. Optimum temperature range (270 ºC – 450 ºC) and pressure in the range of (13 bar – 50 bar). After leaving hydro-deoxygenation reactor, the effluent is further cooled and sent to phase separator, the vapor phase is sent to scrubber to capture carbon dioxide and water vapor, while excess hydrogen is recycled to the reactor.
The liquid phase is re-heated and sent to isomerization reactor, in which long chain paraffins are further hydrogenated and isomerized inside packed bed reactor over heterogeneous catalyst composed of platinum on chlorinated alumina support. Optimum temperature range (90 ºC – 200 ºC) and pressure in the range of (13 bar – 50 bar). After leaving isomerization reactor, the effluent is separated in fractionation column, not difficult because of the comparatively distinctive boiling points between diesel product and traces of kerosene, naphtha, and light fraction.
Renewable Diesel Market
Chemiprobe started “probing” on renewable diesel market since last week, and continuously networking with professionals in the trade. Therefore, renewable diesel business requires higher capital cost relative to biodiesel because it requires larger economy of scale, it is only considered as refinery expansion. On the other hand, renewable diesel market with global players in USA, Brazil, Italy, Finland, Netherlands, and Singapore is promising. Until now, there is no middle-eastern competitors.