Magnus Härröd

Hydrogenation of oleochemicals at supercritical single-phase conditions : Influence of hydrogen and substrate concentrations on the process

Fatty alcohols can be produced by catalytic hydrogenation of fatty acid methyl esters. This heterogeneous catalytic reaction is normally performed in a multi-phase system. In such a system, with a low hydrogen solubility in the liquid substrate and a large mass transport resistance, the hydrogen concentration at the catalyst is low and limits the reaction rate. To overcome this limitation, we have used the unique properties of supercritical fluids, properties which are in between those of liquids and gases, making them a very suitable medium for reactions. By adding propane to the reaction mixture of hydrogen and fatty acid methyl esters (C18) we have created supercritical single-phase conditions. At these single-phase conditions the concentrations of all the reactants at the catalyst surface can be controlled, and an excess of hydrogen becomes possible. In this way, extremely rapid hydrogenation can be combined with a high product selectivity. In our lab-scale experiments the catalyst performance was studied as a function of hydrogen concentration, substrate concentration and temperature. Complete conversion of the liquid substrate was reached in a few seconds. As long as single-phase conditions remain, we have, in our experiments, tested up to 15 wt.% substrate, vapor-phase like reaction rates can be maintained. However, at these high substrate concentrations, mass transport becomes important again. Our results show that performing hydrogenation at supercritical single-phase conditions has a large potential for this and other catalytic processes where the hydrogen concentration at the catalyst is the limiting factor.

Comparison between methods using low-toxicity solvents for the extraction of lipids from herring (Clupea harengus)

Three alkane/alcohol/water-based lipid extraction systems were evaluated to determine which would be the best replacement for the frequently used chloroform/methanol/water system, nowadays known to be very toxic. All the methods were applied to samples of minced herring (Clupea harengus) differing in quality and composition. In addition to comparisons of total lipid yield, the extracted lipids were compared with respect to content of triglycerides, phospholipids, free fatty acids, α-tocopherol, lipid hydroperoxides and conjugated dienes. The content of phospholipids was found to differ most between the lipids extracted by the four methods. Here, the chloroform/methanol/water system was the most efficient, followed by heptane/ethanol/water/sodium dodecyl sulphate (SDS) and then iso-propanol/hexane. However, by decreasing the level of SDS, the efficiency of the heptane/ethanol/water/SDS system in extracting phospholipids was increased to the same level as that of the chloroform/methanol/water system. This decrease in SDS also resulted in a higher recovery of free fatty acids. The lack of correlation between yields of phospholipids and yields of lipid oxidation products throughout this study was surprising because of the often-described susceptibility of phospholipids to oxidation.

Partial hydrogenation of fatty acid methyl esters at supercritical conditions

Under supercritical or near-critical conditions propane is a very good solvent for both lipids and hydrogen. Thus, it is possible to generate an essentially homogeneous phase, in which the transport resistances for the hydrogen are eliminated. Therefore, the hydrogen concentration at the catalyst surface can be greatly increased, resulting in extremely high reaction rates and products having low trans fatty acid contents. In this study we present results from hydrogenation of rapeseed fatty acid methyl esters under near-critical and supercritical conditions. Temperature, residence time, hydrogen pressure, and catalyst life were varied systematically, using a statistical experimental design, in order to elucidate reaction rate and trans fatty acid formation as functions of the above variables. The experiments were carried out in a microscale fixed-bed reactor, using a 3% Pd-on-aminopolysiloxane catalyst. At 92 °C, a hydrogen pressure of 4 bar, and a residence time of 40 ms we obtained a trans content of 3.8 ± 1.7% at a iodine value of 70. Our results support the findings from traditional processes that at a constant iodine value (IV) the trans content decreases with decreasing temperature, increasing pH2, and increasing residence time. The reaction rate at our best conditions was roughly 500 times higher than in traditional batch hydrogenation. Partielle Hydrierung von Fettsauremethylestern bei uberkritischen Bedingungen.Im uberkritischen oder nahekritischen Zustand besitzt Propan sehr gute Losungseigenschaften fur sowohl Fette als auch Wasserstoff. Dies ermoglicht es, eine im wesentlichen homogene Reaktionsmischung zu erzeugen, in der die Transportwiderstande fur den Wasserstoff eliminiert sind. Dadurch kann die Wasserstoffkonzentration an der Katalysatoroberflache wesentlich erhoht werden, was zu extrem hohen Reaktionsgeschwindigkeiten fuhrt. Auserdem konnen auf diese Weise Produkte mit einem niedrigen Gehalt an trans-Fettsauren erzielt werden. In der vorliegenden Studie prasentieren wir die Ergebnisse der partiellen Hydrierung von Rapsol-Fettsauremethylestern bei nahekritischen und uberkritischen Bedingungen. Unter Verwendung eines statistischen Versuchsdesigns wurden Temperatur, Aufenthaltszeit, Wasserstoffpartialdruck und Katalysatorlebensdauer systematisch variiert, um die Reaktionsgeschwindigkeit und die Bildung von trans-Fettsauren als Funktionen dieser Variablen darzustellen. Die Versuche wurden in sehr kleinem Masstab in einem Festbettreaktor durchgefuhrt. Der verwendete Katalysator bestand aus 3% Pd auf einem Aminopolysiloxan-Trager. Bei 92 °C, einem Wasserstoffdruck von 4 bar und einer Aufenthaltszeit von 400 ms erreichten wir einen trans-Gehalt von 3,8 ± 1,7% bei einer Jodzahl von 70. Unsere Ergebnisse bestatigen die fur den traditionellen Prozes gefundenen Trends, das bei konstanter Jodzahl der trans-Gehalt abnimmt, wenn die Temperatur gesenkt, der Wasserstoffdruck erhoht, bzw. die Aufenthaltszeit verkurzt wird. Die hochsten von uns erzielten Reaktionsgeschwindigkeiten waren rund 500-fach hoher als in herkommlichen Batch-Prozessen.

Enzymatic Synthesis of Phosphatidylcholine with Fatty Acids, Isooctane, Carbon Dioxide, and Propane as Solvents

Phosphatidylcholine (PC) was synthesized from lyso-PC and long polyunsaturated fatty acids (PUFA) with phospholipase A2. In previous investigations, performed in small glass tubes, the enzymatic synthesis reaction was optimized. This paper presents results from experiments performed in a high-pressure reactor filled with an immobilized enzyme (Im.E.). Fatty acids were used as the main solvent while isooctane, CO2, or propane was used as an additional solvent. The water content was carefully controlled over wide ranges. The temperature was kept constant at 45°C for up to 50 h. The highest initial reaction rate was attained with pure fatty acids under relatively humid conditions (water=35% of dry Im.E.). The reaction rates were more than three times as high in the high-pressure reactor than in previous experiments in glass tubes. In all solvent systems, the best yield was attained after long times under dry conditions (water <15% of dry Im.E.). Addition of CO2 to the PUFA reduced the yield, while addition of isooctane or propane increased the yield. After 20 h at 45°C, the best yield (25%) was attained at a solvent composition of 91% PUFA and 9% propane.

Enzymatic and Non-Enzymatic Esterification of long Polyunsaturated Fatty Acids and Lysophosphatidylcholine in Isooctane

Phosphatidylcholine containing large amounts of long polyunsaturated fatty acid, eicosapentaenoic acid (C20:5) and docosahexaenoic acid (C22:6), was synthesized in isooctane. Immobilized phospholipase A2 was used as a catalyst. A parallel non-enzymatic esterification reaction was investigated in separate experiments.The concentrations of lyso-phosphatidylcholine, polyunsaturated fatty acids, water and the enzyme were varied over wide ranges as were the temperature and the reaction time. The type of enzyme, carrier and immobilization procedure were held constant.The yield of phosphatidylcholine was relatively high (about 21%) when the concentration of polyunsaturated fatty acids was high (300 mg/g of reaction mixture) and the water content was low (below 30% of the dry immobilized enzyme). The highest yield of phosphatidylcholine was found at 80 hours and 75°C. However, at this temperature an extensive non-enzymatic reaction between polyunsaturated fatty acids and lyso-phosphatidylcholine occurred. At 80°C...

Hydrogenation of fats and oils at supercritical conditions

Publisher Summary This chapter discusses the hydrogenation of fats and oils at supercritical conditions. For the hydrogenation, a solvent miscible with both oil and hydrogen is used that forms a substantially homogeneous phase to pass the catalyst surface. The solvent is near-critical or supercritical propane. The oil does not prevent the hydrogen from entering the pores of the catalyst anymore. With the addition of propane to the reaction mixture, extremely high reaction rates, up to 1000 times higher than with the traditional technique, are obtained. These reaction rates are very important for the process economy of both full and partial hydrogenation of triglycerides. The new supercritical hydrogenation technique increases the productivity that is attained using the traditional hydrogenation technique. The concentration of trans fatty acids is considerably reduced compared to conventional processes using the same catalyst and the same degree of hydrogenation. The consumption of catalyst is similar to the consumption using traditional techniques.

Hydrogenation under supercritical single-phase conditions

Supercritical fluids may combine gas- and liquid properties in a very favourable way. Using the new supercritical single-phase hydrogenation processes, extremely fast reactions can be achieved, and the time-scale for the reactions is seconds compared to hours in the traditional processes. This can be utilized to reduce investment- and production-costs and to improve product quality. In this chapter we put the new supercritical single-phase hydrogenation process into a general context. To create the basis for understanding the new technology, a short overview of the most important aspects of the traditional processes and the new technology are given. Finally, the impact of using the new technology will be described. To do this, concentration profiles and phase diagrams will be used.

Enzymatic Esterification of Long Polyunsaturated Fatty Acids and Lyso-Phosphatidylcholine in Isooctane and Ethanol

Phosphatidylcholine (PC) was synthesized from lyso-PC and long poly-unsaturated (n-3) fatty acids (PUFA) using immobilized phospholipase A2. The esterification was performed using the fatty acids as the main solvent and isooctane or ethanol (99.5%) at low concentrations (7–45%) as additional solvents. The temperature was kept constant at 45d`C and the water concentrations were carefully controlled.The best yield of PC (22%) was found in the isooctane system at a low water content (22% of the dry immobilized enzyme). In the ethanol system, the yield of PC was only half. The best yields were attained when the concentrations of both isooctane and ethanol were below 7% and the reaction time was very long (9 days). Improved contact between the enzyme and the substrates would probably increase the reaction rate.

Synthesis of Phosphatidylcholine with Polyunsaturated Fatty Acids by Phospholipase A2 in an Organic Solvent

Abstract Tailor-made phospholipids may have many important nutritional and medical applications. Enzymatic synthesis of phosphatidylcholine (PC) from lyso-PC and polyunsaturated fatty acids (PUFA) by phospholipase A 2 in microemulsion has recently been reported. However, the yield was low (below 7%). We have developed better reaction conditions and higher yields using immobilized enzyme and isooctane as a solvent. The concentrations of lyso-PC, PUFA, water, enzyme and the temperature were varied over wide ranges, while the enzyme, the carrier, the immobilization procedure and the reaction time were kept constant. The best yield, above 20%, was found when the concentration of lyso-PC was low, of PUFA was high, of water was low, and the temperature was about 60° C.

Production of fatty alcohols by heterogeneous catalysis at supercritical single-phase conditions

Fatty alcohols can be produced by catalytic hydrogenation of fatty acid methyl esters. This heterogeneous catalytic reaction, traditionally performed in a multi-phase system, is limited by the mass transport of hydrogen to the catalyst. To overcome this limitation we have used the unique properties of supercritical fluids, properties which are in between those of liquids and gases, making them a very suitable medium for reactions. By adding propane to the reaction mixture of hydrogen and fatty acid methyl esters we have created supercritical single-phase conditions. These single-phase conditions eliminate the transport resistance for hydrogen and create the possibility to control the concentration of all the reactants at the catalyst surface independently of the other process settings. In this way, extremely rapid hydrogenation can be combined with a high product selectivity. In our lab-scale experiments the catalyst activity was studied as a function of hydrogen pressure, substrate concentration and temperature. The catalyst activity was extremely high compared to the multi-phase hydrogenation. Complete conversion of the liquid substrate was reached in a few seconds. The high catalyst activity results in reaction rates which are comparable with similar gas-phase hydrogenation reactions of much smaller molecules (e.g. methylacetate). As long as single-phase conditions remain-in our experiments we have tested up to 15 wt.% substrate- the gas-phase-like activity can be maintained. Our results prove that performing hydrogenation at supercritical single-phase conditions is beneficial for this and other heterogeneous catalytic processes which are limited by mass transfer.