Mark Holtzapple

Debido a una amplia disponibilidad, el uso de recursos lignocelulosicos como materia prima para producir combustibles y otros productos quimicos es muy prometedor. Para hacer de esto una realidad, 18 anos de investigacion en la Universidad de Texas A&M han resultado en el desarrollo de un proceso novedoso denominado MixAlco. TM  Este articulo compara este proceso con otras tecnologias y provee algunos detalles del proceso. Por ultimo, se presenta un breve analisis economico.

This paper discusses the MixAlco Process which converts a wide variety of biomass materials (e.g. municipal solid waste, sewage sludge, agricultural residues) to mixed alcohols. First, the biomass is treated with lime to enhance its digestibility. Then, a mixed culture of acid-forming microorganisms converts the lime-treated biomass to volatile fatty acids (VFA) such as acetic, propionic, and butyric acids. To maintain fermentor pH, a neutralizing agent (e.g. calcium carbonate or lime) is added, so the fermentation actually produces VFA salts such as calcium acetate, propionate, and butyrate. The VFA salts are recovered and thermally converted to ketones (e.g. acetone, methylethyl ketone, diethyl ketone) which are subsequently hydrogenated to mixed alcohols (e.g. isopropanol, isobutanol, isopentanol). Processing costs are estimated at $0.72/gallon of mixed alcohols making it potentially attractive for transportation fuels.

The carboxylate platform employs a diverse microbial consortium of anaerobes in which the methanogens are inhibited. Nearly all biomass components are digested to a mixture of C1-C8 monocarboxylic acids and their corresponding salts. The methane-arrested anaerobic digestion proceeds readily without needing to sterilize biomass or equipment. It accepts a wide range of feedstocks (e.g., agricultural residues, municipal solid waste, sewage sludge, animal manure, food waste, algae, and energy crops), and produces high product yields. This review highlights several important aspects of the platform, including its thermodynamic underpinnings, influences of inoculum source and operating conditions on product formation, and downstream chemical processes that convert the carboxylates to hydrocarbon fuels and oxygenated chemicals. This review further establishes the carboxylate platform as a viable and economical route to industrial biomass utilization.

This research describes the production of hydrocarbons from acetone and isopropanol produced by the MixAlco process. The MixAlco process has two types of products: acetone and isopropanol. The effect of the temperature, weight hourly space velocity (WHSV), type of catalyst, feed composition, and pressure are studied. For the isopropanol reaction, the following conditions were used: HZSM-5 (280), 1 atm, 300–410°C, and 0.5–11.5 h–1, respectively. The temperature and WHSV affect the average carbon number of the reaction products. A product similar to commercial gasoline was obtained at T = 320 °C and WHSV= 1.3 to 2.7 h–1. Also, at these conditions, the amount of light hydrocarbons (C1–C4) is low. For the acetone reaction, the following conditions were used: HZSM-5 with silica alumina ratio (Si/Al) 80 and 280 mol silica/mol alumina, 1–7.8 atm, 305–415°C, 1.3–11.8 h–1, and hydrogen acetone ratio 0–1 mol H2 /mol acetone. The conversion on HZSM-5 (80) was higher than HZSM-5 (280); however,...

... 10. Priyadarsan, S., K. Annamalai, MT Holtzapple, S. Mukhtar. 2003b. Fixed bed gasification studies on chicken litter biomass under batch mode operation. In Proc 5th Annual Electric Power Conference and Exhibition, ASME, Houston, TX. 11. Scott, DH 1999. ...

Cellulosic biomass is the only resource from which liquid fuels so vital to transportation can be made at alarge scale sustainably and also minimize the conflict with food production [1]. Furthermore, cellulosic bio-mass costing about $60/dry ton is competitive with petroleum at about $20/barrel on an equivalent energycontent basis [2]. Therefore, the primary challenge to competitiveness is low-cost processing of cellulosicbiomass to fuels, and biological routes can take advantage of the rapidly evolving tools of biotechnology toradically reduce costs [1,3]. The economic challenge for biological options is to overcome the natural resist-ance of plants to release of sugars that are the building blocks of cellulose and hemicellulose and typicallycomprise two-thirds to three-quarters of cellulosic materials. Although modification of plants to facilitatesugar release and better enzyme/organism combinations that can attack cellulosic materials more effectivelyare often favored to improve performance [1], to date, biomass pretreatment has been essential to achievingthe high yields of sugars vital to economic success and is likely to remain an essential step in the overallconversion system [4]. At this point, we are faced with the conundrum that pretreatment is among the mostexpensive single steps in biological processing [5], but unit production costs are even higher if pretreatment iseliminated, due to the resulting low product yields [6]. It has therefore been stated that the “only step moreexpensive than pretreatment is no pretreatment” [4]. Full attention must be focused on developing lower-costpretreatment technologies that can integrate with advanced biological conversion systems and perhaps takeadvantage of plants that have been modified to facilitate sugar release.The Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI) was originally con-ceived in late 1999 in a meeting in Dallas, Texas among pretreatment leaders interested in working collabo-ratively. It was formally organized in early 2000 in a Chicago meeting among this team [7]. During theentire CAFI lifetime, the following goals were set: Develop data on leading pretreatments using common feedstocks, enzymes, analytical methods, materialand energy balance methods and costing methods. Seek to understand mechanisms that influence performance and differentiate pretreatments by providinga technology base to facilitate commercial use and identifying promising paths to advance pretreatmenttechnologies that achieve lower costs. Train and educate students in biomass conversion technologies.A key objective was to provide information to help industry select technologies fo r commercial applica-tions and not to “downselect” pretreatments. Rather, it was vital to provide extensive data on promisingoptions so that others could decide which technologies t o employ and avoid a lack of data clouding decisions.The CAFI team was fortunate to be selected for funding by a new United States Department of Agricul-ture (USDA) Program called the Initiative for Future Agricultural and Food Systems (IFAFS) through acompetitive solicitation released in the spring of 2000. Although the program unfortunately had a short life,the IFAFS approach was unique in that it funded large collaborative projects focused on advancing andapplying biomass conversion technologies, consistent with the CAFI spirit. In this inaugural CAFI projectthat ran from 2000 to 2004, now designated CAFI 1, the emphasis was on comparative data from applica-tion of leading pretreatments to a shared source of corn stover, with most of the work focused on perform-ance from just the pretreatment and enzymatic hydrolysis steps [7]. In 2004, the Office of the BiomassProgram (OBP) of the US Department of Energy selected the CAFI team for a second project as a result ofa competitive solicitation. This project, now known to our team as CAFI 2, applied most of the pretreatmenttechnologies employed in CAFI 1 to poplar wood but with more data developed on enzymatic hydrolysisand fermentation [8]. Following completion of the CAFI 2 work, OBP funded the team to apply the samestable of pretreatment technologies to switchgrass. This latter CAFI 3 project was somewhat broader inscope than prior projects in that, in addition to determining yields from pretreatment and enzymatic

Lime pretreatment has proven to be a useful method for selectively reducing the lignin content of lignocellulosic biomass without significant loss in carbohydrates, thus realizing an important increase in biodigestibility. In lime pretreatment, the biomass is pretreated with calcium hydroxide and water under different conditions of temperature and pressure. It can be accomplished in one of three fashions: (1) short-term pretreatment that lasts up to 6 h, requires temperatures of 100-160 degrees C, and can be applied with or without oxygen (pressure approximately 200 psig); (2) long-term pretreatment taking up to 8 weeks, requiring only 55-65 degrees C, and capable of running with or without air (atmospheric pressure); and (3) simple pretreatment requiring 1 h in boiling water, without air or oxygen. Nonoxidative conditions are effective at low lignin contents (below approximately 18% lignin), whereas oxidative conditions are required for high lignin contents (above approximately 18% lignin).

Oxidative lime pretreatment (OLP) is an effective pretreatment for highly recalcitrant lignocellulosic materials. This experiment was conducted to investigate the effect of short-term OLP on fermentative gas production kinetics of date palm prunings. Rachis and petiole were pretreated with excess lime (0.5 g Ca(OH)2 g(-1) dry matter) in a reactor charged with 10 bar pure oxygen pressure at different times and temperatures. Lignin removal was greatly affected by OLP, whereas cellulose was well preserved even after severe pretreatment. After 72 h fermentation, the cumulative gas production was 321.2 mL gas g(-1) organic matter (OM) for the most severe pretreatment, compared to 73.6 mL g(-1) OM for the untreated rachis. For the petiole pretreated at 120 °C for 280 min, 268 mL gas was produced compared to 59 mL gas g(-1) OM for the untreated petiole. Scanning electron microscope images showed the formation of pores (average diameter of 10-12 µm) and carbonate calcium deposits on the surface of treated biomass. An increase in biomass crystallinity was observed in pretreated samples resulting from cellulose enrichment. The results suggest that OLP improves the ruminal digestibility of date palm prunings, which may have potential for inclusion in the ruminant diet at low cost.

Moving bed biofilm reactor (MBBR) systems are increasingly used for municipal and industrial wastewater treatment, yet in contrast to activated sludge (AS) systems, little is known about their constituent microbial communities. This study investigated the community composition of two municipal MBBR wastewater treatment plants (WWTPs) in Wellington, New Zealand. Monthly samples comprising biofilm and suspended biomass were collected over a 12-month period. Bacterial and archaeal community composition was determined using a full-cycle community approach, including analysis of 16S rRNA gene libraries, fluorescence in situ hybridization (FISH) and automated ribosomal intergenic spacer analysis (ARISA). Differences in microbial community structure and abundance were observed between the two WWTPs and between biofilm and suspended biomass. Biofilms from both plants were dominated by Clostridia and sulfate-reducing members of the Deltaproteobacteria (SRBs). FISH analyses indicated morpholo...

Life support components are evaluated for application to an idealized closed life support system which includes an algal reactor for food production. Weight-based trade studies are reported as "break-even" time for replacing food stores with a regenerative bioreactor. It is concluded that closure of the life support gases (oxygen recovery) depends on the carbon dioxide reduction chemistry and that an algae-based food production can provide an attractive alternative to re-supply for longer duration missions.

A steady state chemical model and computer program have been developed for a life support system and applied to trade-off studies. The model is based on human demand for food and oxygen determined from crew metabolic needs. The model includes modules for water recycle, waste treatment, CO2 removal and treatment, and food production. The computer program calculates rates of use and material balance for food. O2, the recycle of human waste and trash, H2O, N2, and food production supply. A simple non-iterative solution for the model has been developed using the steady state rate equations for the chemical reactions. The model and program have been used in system sizing and subsystem trade-off studies of a partially closed life support system.

To feed a growing population, alternative sources of animal feed (e.g., lignocellulose) are needed to replace grains (e.g., corn). Oxidative lime pretreatment (OLP) increases lignocellulose digestibility by removing lignin and hemicellulose acetyl content. Adding a mechanical pretreatment (e.g., ball milling) further improves digestibility. This study determines the effectiveness of OLP and ball milling to enhance the ruminant digestibility of lignocellulose. For forage sorghum, the 48-h in vitro TDN were 40, 64, and 84 g nutrients digested/100 g organic matter (OM) for raw, short-term OLP, and short-term OLP + ball milling, respectively. In terms of compositional changes, OLP increases NDF and decreases non-fiber carbohydrate (NFC) and crude protein (CP), all of which would normally be associated with a decrease in digestibility. However, because OLP and ball milling beneficially change composition (lignin removal) and structural features (reduced crystallinity), digestibility actu...

Methane-arrested anaerobic digestion (MAAD) provides a sustainable route for cleaner production of carboxylic acids from renewable biomass. However, low acid productivity and high product recovery costs have restricted widespread industrial implementation of this technology. This study enhances carboxylic acid (C2 to C8) production from cellulosic biomass using a newly developed integrated digestion-separation system. Using a mixed culture of marine microorganisms grown under mesophilic conditions (40 • C), paper and chicken manure were co-digested to produce carboxylic acids through semi-continuous four-stage countercurrent MAAD. During digestion, multi-stage CO 2-sustained anion-exchange resin (Amberlite IRA-67) adsorption was applied for in-situ recovery of inhibitory acid products from the digestion medium. Efficiency was enhanced by supplying 1-atm CO 2 during the in-situ adsorption process. Compared with stand-alone digestion (control), biomass conversion and acid yield in the integrated MAAD system significantly increased by 2.28 and 2.09 times, respectively. The integrated system also increased the mass fractions of longer-chain carboxylic acids (C5 and C6) in liquid products. With various amounts of resin, the optimal normalized resin loadings for biomass conversion and acid yield were 10.9 and 14.6 g wet resin/(L liq ⋅d), respectively. This work demonstrates countercurrent digestion coupled with in-situ product separation via CO 2-sustained anion-exchange resin is highly effective at recovering carboxylic acids from cellulosic biomass.

There is a growing need to produce water and energy more sustainably by incorporating the following objectives: (1) enhanced solar utilization, (2) reduced fossil fuel usage, (3) increased desalination efficiency, and (4) decreased environmental emissions. This paper investigates the following hypotheses: (1) the aforementioned objectives require a novel systems-integration approach that identifies synergistic design and operational strategies, (2) the water-energy nexus must integrate power plants and desalination systems, and (3) optimal solutions must supplement existing infrastructure with emerging technologies. To reduce the carbon footprint, fossil-based power plants are augmented with solar energy. Because of seasonal variations in supply and demand for energy and water—and because of the diurnal nature of solar energy—a multi-period approach is utilized. As a result of complex water-energy interactions, a superstructure representation is created to embed potential configurations of interest. The optimization formulation incorporates multiple objectives and guides the design and operational decisions. This approach is applied to a case study on the Kuwait water-energy nexus, and considers the following: (1) seasonal variations in fuel availability, prices, power demand, and water needs; (2) multi-period optimization of fuel usage within the existing infrastructure; (3) the potential for solar retrofits; (4) the impact of several carbon-footprint constraints on the minimum cost; and (5) optimal design and operational strategies. In infrastructure renewal projects, the developed approach and targeted application can help decision-makers create simultaneous design and operational strategies that meet economic and environmental objectives.

Corn stover, an underutilized agricultural residue, is a promising lignocellulosic feedstock for producing biofuels. To fully utilize it, pretreatment is needed. Typically, pretreatments are rapidly assessed using extracellular enzymes that release sugars from cellulose and hemicellulose. In contrast, this study uses methane-arrested anaerobic

The United States is becoming more dependent on ethanol production as a renewable fuel source to decrease dependency on foreign oil. The increase in demand for renewable fuels, due in part to the Energy Policy Act of 2005, has led to increased research on alternative renewable fuels from biomass. One such avenue of research has been the conversion of biomass to renewable fuels, and specifically sweet sorghum, as an ethanol fuel stock.

Abstract Using methane-arrested mixed cultures, organic substrates can be fermented to mixed carboxylic acids (i.e., C2 to C8 volatile fatty acids) via the carboxylate platform. A commercial example, the MixAlco® process recovers the carboxylic acids and transforms them to chemicals and fuels. To reduce product inhibition, ion-exchange resin (IR) fermentors used weak-base anion-exchange resins (Amberlite IRA-67) to recover carboxylic acids from fermentation broth and thereby maintain near-neutral pH. Control fermentors used magnesium carbonate (MgCO3) to buffer to near-neutral pH. Compared to the control, the IR fermentors increased acid yields by 2.2, 1.54, and 1.55 times for α-cellulose substrate, paper substrate, and lime-pretreated corn stover, respectively. Furthermore, extraction increased yields of valuable long-chain carboxylic acids. These results suggest further improvements are possible in advanced MixAlco® process configurations, such as countercurrent continuous fermentations.