Final Report: Commercialization of Solid Acid and Base Catalysts Derived from Biochar Optimized to Produce Biodiesel from Low Cost Oils
EPA Contract Number:
Commercialization of Solid Acid and Base Catalysts Derived from Biochar Optimized to Produce Biodiesel from Low Cost Oils
Keith, Lawrence H
Down to Earth Energy (formerly Mountain Creek Enterprises)
May 1, 2010 through
April 30, 2012
Small Business Innovation Research (SBIR) - Phase II (2010)
SBIR - Emission Reductions and Biofuels
Small Business Innovation Research (SBIR)
Researchers developed reusable and recoverable solid, porous acid and base catalysts for biodiesel production using pyrolyzed carbons generated from sustainable biomass. Various acid and base catalysts were prepared from biochars and biomass-based activated carbons and tested for their comparative catalytic activity. Peanut hulls, pine logging residues and wood chips were used as sources to generate biochar, while activated carbons were obtained from commercial sources (e.g., Norit-Americas, Carbochem, Calgon Carbon and MeadWestvaco). Acid catalysts were made by sulfonating the carbons with concentrated sulfuric acid or with sulfur trioxide. Ozonation as a pretreatment to functionalization was assessed and discontinued after it was found to provide no benefits. Base catalysts were made using the same carbon sources and attaching basic functional groups to the surface through various methods.
Laboratory results and economic analyses were presented to potential commercialization partners. Base catalyst development was largely unsuccessful and therefore not presented. For the acid catalyst, though, results demonstrated a cost savings to biodiesel producers utilizing the most efficient of the acid catalysts developed, on the order of more than $0.02/lb compared to a premium low-FFA oil feedstock. This, in conjunction with the biodiesel market analysis provided, however, was not enough to warrant an investment from any of the prospective partners.
Acid Catalyst Development
The efficiencies of the acid catalysts were measured using chemical conversion of palmitic acid and stearic acid (found in biodiesel feedstocks) to their methyl esters.
Catalysts made using gaseous sulfur trioxide at ambient temperatures were observed to be more effective than those made with sulfuric acid at elevated temperatures when compared side by side. The two primary analytical methods used to characterize the rates of acid catalyzed reactions were capillary gas chromatography (GC) and potentiometric titration. GC provided analysis of free fatty acids (FFAs) and their methyl esters and potentiometric titration provided a total acid number (TAN) expressed as mg of potassium hydroxide per gram of sample. In some cases, methyl hexadecanoate and methyl octadecanoate concentrations were determined using gas chromatography coupled with mass spectrometry (GC/MS). This served as an independent method that also verified that the GC peaks were identified correctly in the GC/FID method. Optimized reaction conditions were developed for multiple reuses of the best acid catalyst and commercialization plans were developed and presented to potential investors.
Key to industrial use of solid acid catalysts is their ease of recovery and reusability. Repeated reuse of biochar solid acid catalysts, without regeneration between steps, resulted in a decline in activity and this varied significantly among the many catalysts tested for reuse. Ultimately, the best acid catalyst was made from sustainable biomass (wood) by sulfonating C Gran activated carbon (a commercial Norit-Americas product) with concentrated sulfuric acid. Methyl ester production from palmitic and stearic acids ranged from 99 to 93% over 10 continuous uses. Other carbon sources used to prepare acid catalysts often also were very efficient in initial reactions, especially those sulfonated with gaseous sulfur trioxide. However, most reuse tests resulted in significant amounts of catalyst deactivation, but the Norit-Americas C Gran immobilized acid catalyst consistently performed the best with extended reuse trials.
The sulfonated C Gran acid catalyst has potential applications for converting free fatty acids in low-grade biodiesel feedstocks to their methyl esters, thus eliminating soap interferences. Current economic climate involving commercial biodiesel manufacturing has inhibited investors from entering into joint ventures or licensing the process and, until business conditions in this sector improve, commercialization is not likely to move forward. However, in addition to applications with biodiesel production, the immobilized acid catalyst also has potential in many of the thousands of commercial synthesis reactions where homogeneous liquid acid catalysts currently are used.
Base Catalyst Development
Base catalytic activities were measured using chemical conversion by transesterification of fats and oils to biodiesel. A variety of techniques were used to generate basic functional groups on the surface of pyrolyzed biomass. These techniques included treatment with urea, KNO3, KOH, ethylenediamine (EDA), and sodium 4-aminophenol (4-AP), with the latter being the most effective.
A highly efficient immobilized base catalyst for transesterification of oils to biodiesel was developed using several biochars reacted with 4-aminophenol. In these experiments, it was determined that the EDA and 4-AP functionalized biochars were active in the transesterification of glyceryl tridodecanoate. Both base catalysts functionalized with EDA converted essentially 100% of glyceryl tridodecanoate (a model compound) to dodecanoate methyl ester within 3 hours at 65oC. Researchers anticipated the formation of an amide bond (reaction of the amine group in 4-AP with carboxylic acid groups on the oxidized carbon surface) to attach 4-AP to the biochar surface (4-AP, Carbon Surface-CO-NH-C6H5-O- Na+). Infrared analysis of the base catalysts did indicate the formation of an amide bond and the presence of a primary amine group, but the bond was easily broken under reactions conditions, resulting in reduced catalytic activity. Low-temperature pyrolyzed biochars, which are ozonated, are highly conducive to functionalization by EDA and 4-AP, and had higher catalytic tranesterification activity than the other base catalysts. However, reuse studies resulted in rapidly diminishing catalytic activity of all base catalysts, thereby nullifying their potential commercial uses.
Our conclusions are that it is technically feasible to produce an immobilized acid catalyst from sustainable sources (specifically Norit C Gran activated carbon) that will enable a lower cost feedstock such as yellow grease (with high levels of free fatty acids) to be used for making biodiesel. There are hundreds of other commercial acid catalyzed reactions with which an acid catalyst such as this could be used. However, it was not technically feasible to produce an immobilized base catalyst from similar materials that could be used to make biodiesel by transesterification with methanol and that could be repeatedly reused in this process.
solid acid, base catalyst, biochar, biodiesel, low-cost oil, pyrolyzed carbon, sustainable biomass, methyl ester, transesterification
SBIR Phase I:
Feasibility Study to Produce Biodiesel from Low Cost Oils and New Catalysts Derived from Agricultural & Forestry Residues
| Final Report