Impact of dual temperature profile in dilute acid hydrolysis of spruce for ethanol production

<p>Abstract</p> <p>Background</p> <p>The two-step dilute acid hydrolysis (DAH) of softwood is costly in energy demands and capital costs. However, it has the advantage that hydrolysis and subsequent removal of hemicellulose-derived sugars can be carried out under conditions of low severity, resulting in a reduction in the level of sugar degradation products during the more severe subsequent steps of cellulose hydrolysis. In this paper, we discuss a single-step DAH method that incorporates a temperature profile at two levels. This profile should simulate the two-step process while removing its major disadvantage, that is, the washing step between the runs, which leads to increased energy demand.</p> <p>Results</p> <p>The experiments were conducted in a reactor with a controlled temperature profile. The total dry matter content of the hydrolysate was up to 21.1% w/w, corresponding to a content of 15.5% w/w of water insoluble solids. The highest measured glucose yield, (18.3 g glucose per 100 g dry raw material), was obtained after DAH cycles of 3 min at 209°C and 6 min at 211°C with 1% H₂SO₄, which resulted in a total of 26.3 g solubilized C6 sugars per 100 g dry raw material. To estimate the remaining sugar potential, enzymatic hydrolysis (EH) of the solid fraction was also performed. EH of the solid residue increased the total level of solubilized C6 sugars to a maximum of 35.5 g per 100 g dry raw material when DAH was performed as described above (3 min at 210°C and 2 min at 211°C with 1% H₂SO₄).</p> <p>Conclusion</p> <p>The dual-temperature DAH method did not yield decisively better results than the single-temperature, one-step DAH. When we compared the results with those of earlier studies, the hydrolysis performance was better than with the one-step DAH but not as well as that of the two-step, single-temperature DAH. Additional enzymatic hydrolysis resulted in lower levels of solubilized sugars compared with other studies on one-step DAH and two-step DAH followed by enzymatic hydrolysis. A two-step steam pretreatment with EH gave rise to a considerably higher sugar yield in this study.</p

Greenhouse gas performance of biodiesel production from straw: Soil carbon changes and time-dependent climate impact

Background: Use of bio‑based diesel is increasing in Europe. It is currently produced from oilseed crops, but can also be generated from lignocellulosic biomass such as straw. However, removing straw affects soil organic carbon (SOC), with potential consequences for the climate impact of the biofuel. This study assessed the climate impacts and energy balance of biodiesel production from straw using oleaginous yeast, with subsequent biogas production from the residues, with particular emphasis on SOC changes over time. It also explored the impact of four different scenarios for returning the lignin fraction of the biomass to soil to mitigate SOC changes. Climate impact was assessed using two methods, global warming potential (GWP) and a time‑dependent temperature model (∆Ts) that describes changes in mean global surface temperature as a function of time or absolute temperature change potential (AGTP). Results: Straw‑derived biodiesel reduced GWP by 33–80% compared with fossil fuels and primary fossil energy use for biodiesel production was 0.33–0.80 MJprim/MJ, depending on the scenario studied. Simulations using the time‑dependent temperature model showed that a scenario where all straw fractions were converted to energy carriers and no lignin was returned to soil resulted in the highest avoided climate impact. The SOC changes due to straw removal had a large impact on the results, both when using GWP and the time‑dependent temperature model. Conclusions: In a climate perspective, it is preferable to combust straw lignin to produce electricity rather than returning it to the soil if the excess electricity replaces natural gas electricity, according to results from both GWP and time‑dependent temperature modelling. Using different methods to assess climate impact did not change the ranking between the scenarios, but the time‑dependent temperature model provided information about system behaviour over time that can be important for evaluation of biofuel systems, particularly in relation to climate target deadlines

Overcoming extended lag phase on optically pure lactic acid production from pretreated softwood solids

Optically pure lactic acid (LA) is needed in PLA (poly-lactic acid) production to build a crystalline structure with a higher melting point of the biopolymer than that of the racemic mixture. Lignocellulosic biomass can be used as raw material for LA production, in a non-food biorefinery concept. In the present study, genetically engineered P. acidilactici ZP26 was cultivated in a simultaneous saccharification and fermentation (SSF) process using steam pretreated softwood solids as a carbon source to produce optically pure D-LA. Given the low concentrations of identifiable inhibitory compounds from sugar and lignin degradation, the fermentation rate was expected to follow the rate of enzymatic hydrolysis. However, added pretreated solids (7% on weight (w/w) of water-insoluble solids [WIS]) significantly and immediately affected the process performance, which resulted in a long lag phase (more than 40 h) before the onset of the exponential phase of the fermentation. This unexpected delay was also observed without the addition of enzymes in the SSF and in a model fermentation with glucose and pretreated solids without added enzymes. Experiments showed that it was possible to overcome the extended lag phase in the presence of pretreated softwood solids by allowing the microorganism to initiate its exponential phase in synthetic medium, and subsequently adding the softwood solids and enzymatic blend to proceed to an SSF with D-LA production

Förbehandling av lignocellulosarika råvaror vid biogasproduktion - Nyckelaspekter vid jämförande utvärdering

I biogassektorn finns ett ökande behov av och en ökande konkurrens om råvaror, och intresset för användning av odlingsrester, vall, mellangrödor mm som biogasråvara ökar. Gemensamt för dessa råvaror är att de är fiberrika, dvs. har ett högt innehåll av lignocellulosa, vilket gör att det är osannolikt att de skulle användas för biogasproduktion utan förbehandling. Ett antal förbehandlingstekniker har introducerats på marknaden under senare år, och både företagsdrivna projekt och forskningsprojekt kring utvärdering av en eller flera förbehandlingstekniker pågår. Utvärderingarna läggs dock upp med olika utgångspunkter och metoder så att utkomster från olika projekt blir omöjliga att jämföra. Att utreda frågan om hur man utvärderar och jämför olika förbehandlingsmetoder ur teknik-, ekonomi-, energi- och miljöperspektiv är därför angeläget. Syftet med denna förstudie är att peka ut nyckelaspekter som är viktiga för att möjliggöra jämförande utvärdering av olika förbehandlingsmetoder samt att inspirera aktörer till att vilja medverka till att ta ett samlat grepp i frågan. Ett förslag till upplägg för vidare forskning, utveckling och demonstration presenteras. Arbetet med förstudien har finansierats genom Energimyndigheten

Improving inorganic composition and ash fusion behavior of spruce bark by leaching with water, acetic acid, and steam pre-treatment condensate

The present study evaluates the effect of water and acetic acid washing on the chemical composition of spruce bark in-depth. Also, washing with steam explosion condensate (SEC) was investigated which is a novel attempt. The leaching kinetics of troubling elements (TE) was studied to understand the leaching behavior of TEs and for upscaling the process. Furthermore, to study the ash transformation behavior of TEs in pre-treated and raw bark at high temperatures (500–1500 °C), thermodynamic equilibrium modeling (TEM) was also performed. The result of washing pre-treatment shows high removal of TEs: 22–97% Na, 46–82% Cl, 14–79% K, 14–65% Mg, 25–50% S, 3–22% Ca, 12–36% P, 3–43% Si, and 6–35% N. Continuous removal of TEs was seen with increasing washing duration where most of TEs followed a second-order leaching kinetics. Acid washing results in a much higher and quicker removal for all TEs than water washing. Due to the acidic nature of the SEC, it shows similar removal of TEs as the 0.1 M acetic acid solution. TEM reveals that the transformation behavior of TEs in bark changes considerably after pre-treatment. Pre-treated bark shows the formation of fewer problematic compounds responsible for fouling, slagging, and corrosion at typical gasification and combustion temperatures, such as KCl, K2SO4, K2CO3, KOH, Na2SO4, NaCl, and K-, Na-, P-, and Ca-slag. Though best washing efficiency was seen for longer washing durations, 10 min washing with 0.1 M acetic acid or SEC may be adequate for practical applications.publishedVersionPeer reviewe

Extraction of Lignin from Kraft Cooking Liquor by Ultrafiltration

Lignin is a potential biofuel which can be extracted from kraft cooking liquor. Lignin can also prove valuable as a speciality chemical. By extracting lignin potential economical revenue can be gained by pulp mills, as well as technical benefits such as easier delignification and bleaching. The subject of this work was the extraction of lignin from kraft cooking liquor using ceramic ultrafiltration membranes. Experiments have been performed in both the laboratory, at temperatures below 100°C, and in a pulp mill at temperatures between 90°C and 145°C. In order to operate membranes at high temperatures new methods which ensure safe and reliable operation were developed. Membranes with cut-offs of 5,000 Da and 15,000 Da have been used in the experimental studies. In the laboratory investigation the average flux at 90°C during concentration to 90% volume reduction of kraft cooking liquor was 55 l/m² h and 110 l/m² h using the 5,000 Da and 15,000 Da cut-off membranes, respectively. At the same time the lignin retention was 60% and 30%. Lignin purity with respect to total dry solids content was increased from 30% to 60% using the membrane with a cut-off of 5,000 Da. Reaching higher lignin purities by ultrafiltration alone proved difficult, and it is therefore suggested that diafiltration or acid precipitation be used on the ultrafiltration retentate to achieve higher lignin purities. It was shown that it is technically feasible to operate ceramic ultrafiltration membranes at temperatures above the normal boiling point when treating highly alkaline solutions. The flux was lower when treating kraft cooking liquor in a pulp mill than in the laboratory investigation. It was found that the lignin retention is temperature dependent, decreasing from 55% at 90°C to 30% at 145°C (at 400 kPa transmembrane pressure). Fouling and cleaning of the membranes were investigated both in laboratory and in mill trials. A successful cleaning method based on rinsing with cooking liquor permeate followed by alkaline cleaning was developed in the laboratory investigation. It was found in the mill trials that the membranes could be operated for up to 70 hours without the fouling becoming too severe and that the capacity of the membranes was restored after chemical cleaning

Pretreatment for biorefineries : A review of common methods for efficient utilisation of lignocellulosic materials

The implementation of biorefineries based on lignocellulosic materials as an alternative to fossil-based refineries calls for efficient methods for fractionation and recovery of the products. The focus for the biorefinery concept for utilisation of biomass has shifted, from design of more or less energy-driven biorefineries, to much more versatile facilities where chemicals and energy carriers can be produced. The sugar-based biorefinery platform requires pretreatment of lignocellulosic materials, which can be very recalcitrant, to improve further processing through enzymatic hydrolysis, and for other downstream unit operations. This review summarises the development in the field of pretreatment (and to some extent, of fractionation) of various lignocellulosic materials. The number of publications indicates that biomass pretreatment plays a very important role for the biorefinery concept to be realised in full scale. The traditional pretreatment methods, for example, steam pretreatment (explosion), organosolv and hydrothermal treatment are covered in the review. In addition, the rapidly increasing interest for chemical treatment employing ionic liquids and deep-eutectic solvents are discussed and reviewed. It can be concluded that the huge variation of lignocellulosic materials makes it difficult to find a general process design for a biorefinery. Therefore, it is difficult to define "the best pretreatment" method. In the end, this depends on the proposed application, and any recommendation of a suitable pretreatment method must be based on a thorough techno-economic evaluation