G. Peter van Walsum

Production of jet and diesel fuel range alkanes from waste hemicellulose-derived aqueous solutions

In this paper we report a novel four-step process for the production of jet and diesel fuel range alkanes from hemicellulose extracts derived from northeastern hardwood trees. The extract is representative of a byproduct that could be produced by wood-processing industries such as biomass boilers or pulp mills in the northeastern U.S. The hemicellulose extract tested in this study contained mainly xylose oligomers (21.2 g/l xylose after the acid hydrolysis) as well as 0.31 g/l glucose, 0.91 g/l arabinose, 0.2 g/l lactic acid, 2.39 g/l acetic acid, 0.31 g/l formic acid, and other minor products. The first step in this process is an acid-catalyzed biphasic dehydration to produce furfural in yields up to 87%. The furfural is extracted from the aqueous solution into a tetrahydrofuran (THF) phase which is then fed into an aldol condensation step. The furfural-acetone-furfural (F-Ac-F) dimer is produced in this step by reaction of furfural with acetone in yields up to 96% for the F-Ac-F dimer. The F-Ac-F dimer is then subject to a low-temperature hydrogenation to form the hydrogenated dimer (H-FAF) at 110–130 °C and 800 psig with a 5 wt% Ru/C catalyst. Finally the H-FAF undergoes hydrodeoxygenation to make jet and diesel fuel range alkanes, primarily C13 and C12, in yields up to 91%. The theoretical yield for this process is 0.61 kg of alkane per kg of dry xylose derived from the hemicellulose extract. Experimentally we were able to obtain 76% of the theoretical yield for the overall process. We estimate that jet and diesel fuel range alkanes can be produced from between

Effect of varying feedstock-pretreatment chemistry combinations on the formation and accumulation of potentially inhibitory degradation products in biomass hydrolysates.

2.06/gal to

Conditioning hardwood-derived pre-pulping extracts for use in fermentation through removal and recovery of acetic acid using trioctylphosphine oxide (TOPO)

4.39/gal depending on the feed xylose concentration, the size of the biorefinery, and the overall yield. Sensitivity analysis shows that the prices of raw materials, the organic-to-aqueous mass ratio in the biphasic dehydration, and the feed xylose concentration in the hemicellulose extract significantly affect the product cost.

Mass balance on green liquor pre-pulping extraction of northeast mixed hardwood.

A variety of potentially inhibitory degradation products are produced during pretreatment of lignocellulosic biomass. Qualitative and quantitative interrogation of pretreatment hydrolysates is paramount to identifying potential correlations between pretreatment chemistries and microbial inhibition in downstream bioconversion processes. In the present study, corn stover, poplar, and pine feedstocks were pretreated under eight different chemical conditions, which are representative of leading pretreatment processes. Pretreatment processes included: 0.7% H2SO4, 0.07% H2SO4, liquid hot water, neutral buffer solution, aqueous ammonia, lime, lime with oxygen pressurization, and wet oxidation. Forty lignocellulosic degradation products resulting from pretreatment were analyzed using high performance liquid chromatography in combination with UV spectroscopy or tandem mass spectrometry detection (HPLC‐PDA‐MS/MS) and ion chromatography (IC). Of these compounds, several have been reported to be inhibitory, including furfural, hydroxymethyl furfural, ferulic acid, 3,4‐dihydroxybenzaldehyde, syringic acid among others. Formation and accumulation of monitored compounds in hydrolysates is demonstrated to be a function of both the feedstock and pretreatment conditions utilized. Biotechnol. Bioeng. 2010;107: 430–440.

Evaluation of Enzyme Mixtures in Releasing Fermentable Sugars from Pre-pulping Extracts of Mixed Northeast Hardwoods

Abstract Extraction characteristics are shown for trioctylphosphine oxide (TOPO) dissolved in alkane for recovery of acetic acid from dilute water solution and hardwood-derived hemicellulose extracts. The recovery of acetic acid with TOPO is significantly influenced by the pH in the aqueous phase and lightly affected by temperature. In a one-stage extraction, 76.0% of the acetic acid could be extracted below pH 3. The yield of fractional extractions increase with increasing TOPO concentration in alkane and with increasing acetic acid concentration in the aqueous phase. It was found that for dilute extractions carried out at 70°C and pH 1, the solvent extraction is effective at 37% TOPO in alkane (w/w) and that little improvement is realized by further increases in TOPO concentration. Partition coefficients for green liquor and hot water extracts ranged between 2.0 and 2.5 at the tested conditions. Fermentation of hemicellulose extracts that had been treated with TOPO for removal of acetic acid was tested to determine whether TOPO processing resulted in any positive or adverse affects on the microbial activity. Fermentation of TOPO-treated green liquor hemicellulose extract with Pichia stipitis resulted in improved ethanol production relative to untreated extract. Accordingly, placement of TOPO extraction after hydrolysis and prior to fermentation is optimal for acetic acid recovery and maintenance of fermentation rates.

Acidogenic Digestion of Pre-pulping Extracts for Production of Fuels and Bioproducts Via Carboxylate Platform Processing

A forest biorefinery configuration employing a hemicellulose pre-pulping extraction is being investigated that will retain pulp yields, reduce the organic and inorganic load for liquor recovery, and create a hemicellulose feed stream for the generation of biofuels and biomaterials. Current efforts are focused on developing extract production and conditioning processes that will result in fermentable sugars suitable for conversion to fuel alcohols or organic acid chemical products. As efforts move the process closer to commercial demonstration, it is apparent that a high level of confidence is needed in the analysis of the partitioning of fresh wood into its extracted wood and liquid extract fractions. Of particular interest is the partitioning of the carbohydrates, as these constitute the feedstock for bioconversion to fuels and chemicals. The extraction method employed utilizes green liquor derived from the kraft pulping process for pretreatment of the woodchips. To enable analysis, green liquor extraction was followed by 4% sulfuric acid hydrolysis to complete hydrolysis of the oligomers that were still present. High performance anion-exchange chromatography (HPAEC-PAD) and high performance liquid chromatography (HPLC) methods were used to analyze the carbohydrates in northern hardwood and its extract fractions. The Bio-Rad Aminex HPX-87H column did not separate mannose, xylose, and galactose, but the area of the collective peak corresponds well to the sum of these components as measured by HPAEC. In addition to sugars, standard methods were employed for quantification of the individual components (e.g., lignin, ash, nitrogen, carbon, extractives, uronic and acetic acid). The analytical mass balance closure was 102.2% and 103.6% for raw wood, 99.3% and 102.3% for extracted wood, and 94.7% and 95.6% for hemicellulose extract from the HPAEC and HPLC, respectively. The extraction mass balance was 96.9% and 98.2% for HPAEC and HPLC, respectively. The data generated by this analysis are important to further design work in commercializing the pulp and biorefinery processes.

Acetic Acid Removal from Pre-Pulping Wood Extract with Recovery and Recycling of Extraction Solvents

One near-term option to developing a forest product biorefinery is to derive pre-pulping extract from incoming wood chips before the main pulping step. The release of monomer sugars from a xylan-rich extract, creating a fermentable substrate is a prerequisite for utilization of pre-pulping extract for production of ethanol or other value-added products. This study examined the individual and mixture efficiencies of two hemicellulolytic microbial enzymes and two xylanase preparations in catalyzing degradation of green liquor (GL) and hot water (HW) pre-pulping extracts. The effects of four commercial enzyme preparations were determined by assessing yields of xylose + galactose + mannose (xmg) obtained under different reaction conditions. Of the individual enzyme preparations tested, a sample NS 50012 was superior to the other enzyme preparations in releasing xmg under conditions optimized for separate hydrolysis and fermentation and for simultaneous saccharification and fermentation. In comparison to pre-pulping extracts treated with HW, extract treated with GL was found to inhibit the action of all tested enzymes. This inhibition may be related to higher salt and lignin phenol in the GL extract. On both types of extracts, the mixture constituted by NS 50012 and NS 50030 provided the highest yield of hemicellulose conversion at 55 °C and pH 5.5. The generated digestibility thus signified that the synergistic effectiveness in xylan + galactan + mannan (XMG) hydrolysis between NS 50012 (from Aspergillus aculeatus) and NS 50030 (from Aspergillus oryzae) is the result of an interaction mechanism involving different XMG-degrading enzyme activities in the two enzyme preparations.

Production of lactic acid from hemicellulose extracts by Bacillus coagulans MXL-9

Hemicellulose extracted from wood prior to processing the wood into paper or composite materials can be a resource for the production of biofuels or bioproducts. Mixed microbial cultures are capable of converting biomass into mixed carboxylic acids, which can be purified as products or converted to biofuels or other biochemicals. Mixed cultures are robust conversion systems and do not require added enzymes to hydrolyze biomass to sugars. We produced mixed carboxylic acids using mesophilic and thermophilic fermentation of raw, unconditioned green liquor and hot water hardwood extracts, as well as baseline sugar solutions. Daily samples were taken from the fermentations and analyzed for composition, pH, and gas volume. The extract digestions were capable of hydrolyzing oligomeric hemicellulose without supplemental enzymes and converting all types of released sugars. Lactic acid was prominent in lower pH systems and acetic acid, the main product at more neutral pH. Compared to thermophilic systems, mesophilic fermentations had higher hydrolysis conversion, carbohydrate conversion, acid yields, and selectivity for C3–C7 acids. Carbon balances on the wood extracts closed to within ±9%. Methane production in all cases was essentially zero.

Acid Hydrolysis of Hemicellulose in Green Liquor Pre-Pulping Extract of Mixed Northern Hardwoods

Pre-pulping extraction is a means of deriving a hemicellulose-rich process stream from the front end of a kraft pulp mill. When the extraction is carried out using green liquor, pulp quality and quantity can be retained while still releasing hemicelluloses and acetic acid (HAc) for recovery as bioprocessing feedstock or chemical products. The HAc that is present in the wood extraction is inhibitory to microorganisms and can hinder fermentation. HAc is also a commodity chemical that may provide sufficient value to justify recovery and purification. In this study, a liquid–liquid extraction (LLE) method is applied to extract HAc from a green liquor pre-pulping hardwood extract (GLE). The HAc removal is carried out after acid hydrolysis and prior to fermentation. Two organic solutions: trioctylphosphine oxide (TOPO) diluted in undecane and trioctylamine (TOA) diluted in octanol were tested for their abilities to extract HAc from GLE and to be recycled back through the process. GLE was contacted with the organic solvents, phase separated by centrifugation, and the organic phase was then distilled to recover the acetic acid. The solvent was then recycled back for a subsequent extraction of fresh GLE. It was found that TOA was a superior extractant, but failed to easily release its HAc through distillation. It also quickly became contaminated with other compounds in the wood extracts and lost its extraction efficiency after only a few recycles. The TOPO solvent did release its HAc through distillation but also lost extraction capacity with recycling. Back extraction of the TOPO solvent with sodium hydroxide solution restored the performance of the TOPO solvent.