Ola Wallberg

Fractionation and concentration of kraft black liquor lignin with ultrafiltration

Kraft black liquor lignin is a biofuel that is separated from the cellulose during kraft pulping. Improved technology and energy integration in paper mills have led to an energy surplus at many mills. It is therefore of great interest to extract the lignin from the pulp mill and sell it as fuel to replace fossil fuel in other furnaces. The fractionation of kraft black liquor with a total dry matter content of about 15 wt% has been studied using ultrafiltration. The flux for three polymeric membranes with different cut-offs was investigated as well as their retention of lignin and other process specific substances. The retention of lignin for the three membranes with cut-offs of 4,8 and 20 kDa was 80%, 67% and 45%, respectively. The retention of sulphur and sodium was zero for all three membranes. The purity of the final lignin fuel is of importances as the ash content preferably should be as low as possible. The flux and retention during concentration and diafiltration of the black liquor were therefore studied. The dialfiltration operation was conducted in batch and semicontinuous mode. The lignin purity was 36% in the original kraft black liquor and 78% after semi-continuous dialfiltration.

Ultrafiltration of kraft black liquor with a ceramic membrane

Emissions from the combustion of fossil fuels contribute to the greenhouse effect around the globe. It is therefore of great interest to reduce the use of fossil fuels and revert to some form of biofuel. Lignin, extracted from kraft black liquor, has the potential to become a significant contributor to the biofuel market. A modern pulp mill has an energy surplus that can amount to 7 GJ per tonne of pulp. One way to reduce this surplus is to extract lignin, which is the main source of energy in a kraft pulp mill, and convert it to a usable biofuel, which can be sold on the market. If membrane technology is used to extract lignin from kraft black liquor additional benefits in the overall operation of the mill can be achieved, such as, an improved pulp quality. In this investigation a tubular ceramic membrane manufactured by Orelis, France, with a cut-off of 15,000 Da was used to fractionate kraft black liquor. The experiments were performed at 60, 75 and 90°C at various pressures. The flux and retention during concentration to a volume reduction of 0.9 were studied. The fluxes were 90, 110 and 130 l/m2h at 60, 75 and 90°C and TMP 100 kPa. The lignin retention was about 30%. The retention of monovalent ions was virtually zero, whereas multivalent ions were retained to a high degree, probably due to their association with the organic material. During concentration to a volume reduction of 0.9 at 100 kPa and 90°C, the dry substance increased from 16 wt% to 22 wt% and the lignin concentration from 55 g/1 to 158 g/I. The average flux during the concentration was 90 1/m2h. The flux was 20 l/m2h at the end of the concentration.

Effects of production and market factors on ethanol profitability for an integrated first and second generation ethanol plant using the whole sugarcane as feedstock.

BackgroundSugarcane is an attractive feedstock for ethanol production, especially if the lignocellulosic fraction can also be treated in second generation (2G) ethanol plants. However, the profitability of 2G ethanol is affected by the processing conditions, operating costs and market prices. This study focuses on the minimum ethanol selling price (MESP) and maximum profitability of ethanol production in an integrated first and second generation (1G + 2G) sugarcane-to-ethanol plant. The feedstock used was sugarcane juice, bagasse and leaves. The lignocellulosic fraction was hydrolysed with enzymes. Yields were assumed to be 95% of the theoretical for each of the critical steps in the process (steam pretreatment, enzymatic hydrolysis (EH), fermentation, solid/liquid separation, anaerobic digestion) in order to obtain the best conditions possible for ethanol production, to assess the lowest production costs. Techno-economic analysis was performed for various combinations of process options (for example use of pentoses, addition of leaves), EH conditions (water-insoluble solids (WIS) and residence time), operating cost (enzymes) and market factors (wholesale prices of electricity and ethanol, cost of the feedstock).ResultsThe greatest reduction in 2G MESP was achieved when using the pentoses for the production of ethanol rather than biogas. This was followed, in decreasing order, by higher enzymatic hydrolysis efficiency (EHE), by increasing the WIS to 30% and by a short residence time (48 hours) in the EH. The addition of leaves was found to have a slightly negative impact on 1G + 2G MESP, but the effect on 2G MESP was negligible. Sugarcane price significantly affected 1G + 2G MESP, while the price of leaves had a much lower impact. Net present value (NPV) analysis of the most interesting case showed that integrated 1G + 2G ethanol production including leaves could be more profitable than 1G ethanol, despite the fact that the MESP was higher than in 1G ethanol production.ConclusionsA combined 1G + 2G ethanol plant could potentially outperform a 1G plant in terms of NPV, depending on market wholesale prices of ethanol and electricity. Therefore, although it is more expensive than 1G ethanol production, 2G ethanol production can make the integrated 1G + 2G process more profitable.

Techno-economic comparison of a biological hydrogen process and a 2nd generation ethanol process using barley straw as feedstock

A process combining dark fermentation and photofermentation for production of hydrogen is interesting due to its potential of producing hydrogen at a high yields. In this study, the hydrogen process is compared to a 2nd generation ethanol process with respect to cost and with the aim of increasing our understanding of the pros and cons and giving a clear picture of the present status of the two processes. The hydrogen production cost was found to be about 20 times higher than the ethanol production cost, 421.7 €/GJ compared to 19.5 €/GJ. The main drawbacks of the hydrogen process are its low productivity, low energy efficiency, and the high cost of buffer and base required to control the pH.

Influence of the membrane cut-off during ultrafiltration of kraft black liquor with ceramic membranes

Fractionation of kraft black liquor by ultrafiltration is receiving a great deal of interest at the moment, mainly because the extracted lignin can be used as a biofuel, but also because there are indications that the pulp quality is improved when permeate is used instead of black liquor as the diluent in the cooking process. Fractionation of kraft black liquor calls for membranes that can withstand high temperatures at high pH. In this investigation the performance of two ceramic membranes manufactured by Orelis, France, with cut-offs of 5 and 15 kDa was studied. The temperature during the experiments was 90°C and no adjustment of the pH was made. The retention of cooking chemicals was almost zero for both membranes. The volume of black liquor was reduced by 80% with the 5 kDa membrane and by 90% with the 15 kDa membrane. The average flux during concentration with the 5 kDa membrane was 45 l m−2 h−1 (transmembrane pressure 400 kPa and circulation velocity 3.6 m s−1) while the flux of the 15 kDa membrane was 95 l m−2 h−1 (transmembrane pressure 100 kPa and circulation velocity 4.5 m s−1). The lignin recovery was 66% and 28% for the 5 and 15 kDa membranes, respectively. (Less)

Membrane cleaning - a case study in a sulphite pulp mill bleach plant

Abstract A study was performed to evaluate the cleaning and operation of the ultrafiltration plant at the Nymolla paper mill in southern Sweden Laboratory tests were carried out in order to find out what the fouling layer consists of and to find the most appropriate cleaning procedure Production data were analysed to establish if the membranes are cleaned unnecessarily often The fouling in the plant is mainly of organic origin and is seen as brown precipitation on the surface of the membranes Analysis of the membrane surface with energy dispersive X-rays (EDX) showed that there is also some inorganic fouling, mostly silicon, iron and magnesium Cleaning tests were carried out on a small laboratory test unit from PCI using fouled membranes from the mill Both acid and alkaline chemicals were used to clean the membranes It was shown that the current cleaning procedure was not optimal and some improvements are suggested Production data showed that the membranes are often cleaned when there is no decline in flux This leads to high wear on the membranes and shortens their operational lifetime Less frequent cleaning, especially during the first stages, of the UF plant is therefore recommended It was found that many of the membrane tubes were clogged with a clay-like precipitation consisting of fibres, organic material and precipitated magnesium hydroxide This clay completely stopped the flow through the tube, thereby reducing the active membrane area of the UF plant

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

BackgroundThe 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.ResultsThe 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).ConclusionThe 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.

Ethylene based on woody biomass-what are environmental key issues of a possible future Swedish production on industrial scale

PurposeIn order to reduce its environmental impact, the chemical industry no longer produces base chemicals such as ethylene, solely from fossil, but also from biomass-based feedstocks. However, a biomass option suitable for one region might not be as suitable for another region due to, e.g., long transport and the related environmental. Therefore, local biomass alternatives and the environmental impact related to the production of chemicals from these alternatives need to be investigated. This study assesses the environmental impact of producing ethylene from Swedish wood ethanol.MethodsThe study was conducted following the methodology of life cycle assessment. The life cycle was assessed using a cradle-to-gate perspective for the production of 50,000 tonnes ethylene/year for the impact categories global warming, acidification (ACP), photochemical ozone creation, and eutrophication (EP).Results and discussionThe production of enzymes used during the life cycle had a significant effect on all investigated impacts. However, reduced consumption of enzyme product, which could possibly be realized considering the rapid development of enzymes, lowered the overall environmental impact of the ethylene. Another approach could be to use alternative hydrolyzing agents. However, little information on their environmental impact is available. An additional key contributor, with regard to ACP, EP, and POCP, was the ethanol production. Therefore, further improvements with regard to the process’ design may have beneficial effects on its environmental impact.ConclusionsThe study assessed the environmental impact of wood ethylene and pointed to several directions for improvements, such as improved enzyme production and reduced consumption of enzyme products. Moreover, the analysis showed that further investigations into other process options and increase of ethylene production from biomass are worth continued research.

Influence of bark on fuel ethanol production from steam-pretreated spruce

BackgroundBark and bark-containing forest residues have the potential for utilization as raw material for lignocellulosic ethanol production due to their abundance and low cost. However, the different physical properties and chemical composition of bark compared to the conventionally used wood chips may influence the spruce-to-ethanol bioconversion process. This study assesses the impact of bark on the overall bioconversion in two process configurations, separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF), utilizing steam-pretreated spruce bark and wood mixtures.ResultsMixtures of different proportions of spruce bark and wood chips were subjected to SO2-catalyzed steam pretreatment at 210°C for five minutes, which has been shown to be effective for the pretreatment of spruce wood chips. The final ethanol concentration was the highest without bark and decreased significantly with increasing proportions of bark in both process configurations. However, this decrease cannot be attributed solely to the lower availability of the carbohydrates in mixtures containing bark, as the ethanol yield also decreased, from 85 to 59% in SSF and from 84 to 51% in SHF, as the mass fraction of bark was increased from 0 to 100%.ConclusionsThe results show that it was significantly more difficult to hydrolyse spruce bark to monomeric sugars than wood chips. Bark had an adverse effect on the whole bioconversion process due to its lower enzymatic hydrolyzability. On the other hand, bark inclusion had no detrimental effect on the fermentability of steam-pretreated spruce wood and bark mixtures. It was also observed that lower amounts of inhibitory degradation products were formed during the steam pretreatment of spruce bark than during the steam pretreatment of wood chips.

Integration potential, resource efficiency and cost of forest-fuel-based biorefineries

A multidisciplinary study of the implementation potential of a biorefinery, using forestry residues as feedstock, is performed by assessing techno-economic factors, system integration and feedstock supply. The process is based on biochemical conversion of logging residues to produce ethanol, biogas, pellets, heat and electricity. Nine models were designed in Aspen Plus based on the available feedstock and the required co-products. Focus was on the product ratio of pellets and heat. The net present value of the plants was calculated and thermal integration with district-heating systems in areas with regional feedstock availability was investigated. Also co-location with pulp and paper mills in Sweden was investigated to replace fossil fuels with pellets. Seven of the nine models showed a positive net present value assuming an 11% discount rate and 30% corporate tax. Five counties in Sweden were identified as potential feedstock suppliers to a biorefinery processing 200 kt dry feedstock/y