Typical Feeds and USP 99.7 Product

Glycerin

A typical biodesel-derived glycerol feed containing sodium chloride capable of being purified to a glycerol product that meets USP grade 99.7 characteristics is shown in Table 1; characteristics of a sodium sulfate containing glycerol feed and purified product is provided in Table 2.. Given a fixed system based on the EET technology, refiners will be able to maintain product quality characteristics for varying feed chemistries. While product quality can be maintained, increased contaminant loading in the feed will only affect production rate and operating cost.

Table 1. Typical Sodium Chloride Containing Feed and USP Grade 99.7 Product Characteristics

Typical Characteristics
Parameter Range / Typical Product
Glycerol (wt%) 70-88 / 85 99.7
Water (wt%) 5-15 / 7 <1
Sodium Chloride (ppm) 50,000-100,000 / 80,000 <10
Sodium Sulfate (ppm) <1,000 <20
APHA Color NA <20
Methanol (wt%) <1 <0.01
FFA (wt%) <1-5 / 2 <0.002
MONG (wt%) <1-5 / 2 <0.002

Table 2. Typical Sodium Sulfate Containing Feed and USP Grade 99.7 Product Characteristics

Typical Characteristics
Parameter Range / Typical Product
Glycerol (wt%) 70-88 / 85 99.7
Water (wt%) 5-15 / 9 <1
Sodium Chloride (ppm) <1,000 <10
Sodium Sulfate (ppm) 30,000-80,000 / 50,000 <20
APHA Color NA <20
Methanol (wt%) <1 <0.01
FFA (wt%) <1-5 / 2 <0.002
MONG (wt%) <1-5 / 2 <0.002

In addition to chloride and sulfate containing streams, other biodiesel-derived glycerol feeds containing phosphates (potassium or sodium), mixtures of sulfates and chlorides, and mixtures of organic acids (e.g., acetic acid) and inorganic acids (chlorides) have been successfully purified to meet USP 99.7 specifications. Also, feeds with high FFAs and MONG content (>10%) have been successfully treated, as well as feeds with high methanol content (up to 20%) and high feed pH (>10). However, feed chemistry does impact both production rate and operating costs for a given system size, and the presence of some contaminants may require changes in processing conditions to allow optimum separations. In particular, crude glycerol streams with high FFA and MONG content (such as from biodiesel plants using feedstocks from rendering plants and grease traps) may prove more difficult to pretreat compared to those from plants processing soybean or rapeseed oil. Consequently, treatability studies with actual glycerol feed streams are usually necessary to establish preferred system sizes and operating conditions.

By-products of Glycerol Purification

  • Concentrated brine stream, typically dischargeable as sanitary wastes (check with your local regulators)
  • A dry solid waste (nonhazardous) passing the paint filter test (no free liquids). The amount of solid waste will depend on the amount of MONG and FFAs in the biodiesel-derived glycerol
  • Small amounts of hydrogen and oxygen gas, which are typically vented to atmosphere
By-products

Contact EET for more information.

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