S. Lux

Synthesis of lactic acid from dihydroxyacetone: use of alkaline-earth metal hydroxides

By-products from bio-based processes show great potential as renewable feedstock sources. In this context, upgrading the biodiesel by-product glycerol is highly promising. This paper focuses on the production of lactic acid from dihydroxyacetone, which is a primary oxidation product of glycerol, under mild reaction conditions (ambient pressure and temperatures below 90 °C) with alkaline-earth metal hydroxides. Whereas both Ca(OH)2 and Ba(OH)2 effectively catalysed the formation of lactic acid in the liquid phase, lactic acid was not formed with Mg(OH)2 at 25 °C. The final yield was higher with Ca(OH)2 (59%) than with Ba(OH)2 (50%). With Ca(OH)2, increasing reaction temperatures resulted in higher reaction rates. At 85 °C, however, competing side and degradation reactions were dominating, limiting the yield of lactic acid to 36%. We demonstrated that the method can be directly applied to dihydroxyacetone in fermentation broths. This research opens up a new synthesis route for lactic acid from dihydroxyacetone and glycerol, respectively.

Lactic Acid Production as a New Approach for Exploitation of Glycerol

Electrochemical oxidation of glycerol, the principal by-product of biodiesel production, generally leads to multicomponent product mixtures. The aim of this project was to investigate the feasibility of a technical process for electrochemical oxidation of crude glycerol followed by catalytic conversion of the intermediates dihydroxyacetone and glyceraldehyde to lactic acid. Partial electrochemical oxidation of glycerol with diamond coated electrodes was assumed to provide a route for converting glycerol to dihydroxyacetone and glyceraldehyde. Through instant selective conversion of dihydroxyacetone and glyceraldehyde to lactic acid the major disadvantage of electrochemical conversion, cleavage of intermediates, may be limited. Continuous separation of lactic acid from the electrolyte enables acceptable current efficiency as well as yield of products. Reactive extraction with phosphoryl compounds has proven applicable for the isolation of lactic acid from the electrolyte. Based on the results of these investigations a complete process for lactic acid production from glycerol was designed.

Recovery of Formic Acid and Acetic Acid from Waste Water Using Reactive Distillation

Processing of biobased feedstock materials may lead to formation of multicomponent azeotropic mixtures. Reactive separations provide an opportunity to circumvent azeotropes by changing the substance properties through chemical reactions. Exemplarily several effluents from black liquor processing contain aqueous mixtures of low molecular weight fatty acids such as formic acid and acetic acid. These mixtures form inseparable azeotropes. Separation of the system formic acid–acetic acid–water by esterification with methanol was investigated. Reactive distillation experiments in batch and continuous mode confirmed complete removal of formic acid in a first step. Acetic acid may then be isolated by distillation or by reactive distillation.

Kinetic Study of the Heterogeneous Catalytic Esterification of Acetic Acid with Methanol Using Amberlyst®15

The bulk chemicals esters contribute to commodity chemicals in nearly unlimited variety. Common fields of application include their use as solvents, plasticizers, surfactants, flavours, inter mediates in preparative organic chemistry, and many more.1 Though well investigated, the technology of ester production offers some challenging characteristics regarding catalysis, operation conditions and downstream processing. The synthesis of methyl acetate (MeOAc) via liquid-phase esterification of acetic acid (HOAc) and methanol (MeOH) is a prominent example thereof. The reaction proceeds via the following reaction equation:

Sustainable iron production from mineral iron carbonate and hydrogen

The reduction of iron ores with hydrogen is considered a promising CO2 breakthrough technology to mitigate CO2 emissions from the iron and steel industry. The state-of-the-art production of iron and steel from mineral iron carbonates (FeCO3) is based on the thermal decomposition of FeCO3 in air to produce hematite (Fe2O3) suitable for iron production. Our approach is to directly reduce FeCO3 with hydrogen to elemental iron, avoiding Fe2O3 formation. As a consequence, CO2 emissions can be decreased by 60% and up to 33% less reducing agent is needed for iron production. The development of environmentally benign production pathways needs to be based on a fundamental understanding of the reaction kinetics and mechanism. Therefore, thermogravimetry was used to determine the kinetics of the formation of iron from mineral iron carbonate and the concomitant decomposition of the accessory matrix carbonates of calcium, magnesium, and manganese. The isoconversional kinetic analysis according to the Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose, and Friedman approach confirms the proposed parallel kinetic model. Multi-variate non-linear regression was used to determine the appropriate kinetic parameters. The conversion of iron carbonate to iron can be described with the two-dimensional Avrami-Erofeev model A2. Therefore, a temperature-controlled nucleation and diffusional growth mechanism is suggested for iron formation from mineral iron carbonate and hydrogen. The multi-parameter reaction models Cn-X and Bna can be used to describe the concomitant iron, calcium oxide, magnesium oxide, and manganese oxide formation without applying multi-step kinetics. The multi-parameter reaction models predict a conversion above 95% at 450 °C within less than 60 minutes reaction time. Unavoidably, 1 mole of carbon dioxide is always emitted when 1 mole of FeCO3 is converted into iron. Catalytic carbon dioxide hydrogenation (CCDH) can be applied to diminish inevitable CO2 emissions by chemical conversion into value-added carbon containing chemicals. Therefore, we propose a process that combines the improved iron production via direct FeCO3 reduction with CCDH as a follow-up reaction.

Catalytic Conversion of Dihydroxyacetone to Lactic Acid with Brønsted Acids and Multivalent Metal Ions

At present, a vast majority of products such as plastics, cosmetics or pharmaceuticals are still petroleum-based. A shift towards renewable bio-based feedstock will be inevitable in the future. However, the use of biomass for chemical production implicates the redesign of existing processes and involves new challenges. Handling of aqueous reaction systems and the need for adapted separation techniques from aqueous solutions come to the fore. Retrieval of biomass which does not compete with the food production draws attention to the exploitation of residual materials. Glycerol (propane-1,2,3-triol) is a versatile molecule obtained as a by-product in the biodiesel manufacturing process. Due to increasing biodiesel production over the last decades, it may be regarded as a potential renewable feedstock chemical. Exploitation of glycerol for the production of lactic acid is a promising approach. Lactic acid (2-hydroxypropionic acid) is emerging as a building block in a new generation of biobased materials. With both a hydroxyl and a carboxylic acid group, lactic acid may undergo many reactions. It therefore represents a central feedstock for the chemical industry, e.g., in the production of propylene glycol, acrylic acid or different condensation products. Besides applications in the food and cosmetics industries, growth in demand is expected due to expanding polymer markets (biodegradable synthetics) and elevated demand in the chemical sector due to ecologically friendly solvents and oxygenated chemicals.1,2 Nevertheless, commercial success depends on the development of an effective production method for highly pure lactic acid from abundant non-food biomass. Oxidation of one of the three alcoholic functions of glycerol gives access to the synthesis of the trioses dihydroxyacetone (1,3-dihydroxypropan-2-one, DHA) and glyceraldehyde (2,3-dihydroxypropanal, GLAH), which may further be catalytically converted to lactic acid. Dihydroxyacetone from glycerol is accessible via different synthesis routes. Chemical synthesis involves liquid phase self-condensation of formaldehyde with thiazolium catalysts.3 Much research has been done in the area of noble metal catalysed oxidation of glycerol.4–6 Partial electrochemical oxidation of glycerol to dihydroxyacetone is carried out with different electrode types in neutral7, alkaline8–11 and acidic media10,11. The first microbiological dehydration of glycerol to dihydroxyacetone was reported in 1898 by Bertrand.12 Since then, several routes for microbiological synthesis of dihydroxyacetone have been developed and patented. Mainly vinegar bacteria type Acetobacter and Gluconobacter are used.13,14 Catalytic Conversion of Dihydroxyacetone to Lactic Acid with Brønsted Acids and Multivalent Metal Ions

Pervaporative Separation of Methanol–Methyl Acetate Mixtures with Commercial PVA Membranes

Pervaporation may successfully be implemented for the separation of azeotropic mixtures which generally requires energy intensive separation procedures. Separation of methanol from methyl acetate by pervaporation is a representative application. In this study the commercial polyvinyl alcohol (PVA)-based membranes PERVAPTM 4155-30, PERVAPTM 4155-70, and PERVAPTM 4155-80 were used to recover methanol from binary methanol–methyl acetate mixtures. The separation performance was investigated for various operating parameters such as feed composition, feed temperature, and permeate pressure and discussed in terms of permeance and selectivity. An empirical model was developed to quantify the effect of membrane swelling on the permeate flux.

Solvent recovery via reactive distillation to intensify bio-based chemical production from waste effluents

ABSTRACT Biomass converting processes often struggle with downstream processing of dilute multicomponent mixtures. Liquid–liquid extraction is perfectly suited for removing carboxylic acids from aqueous streams, but solvent recovery is still energy intensive. Solvent recovery is simplified by reactive distillation, whereas the carboxylic acids are directly converted into their corresponding methyl esters. A process concept on the basis of formic acid and acetic acid isolation was evaluated and discussed for uncatalyzed and catalyzed batch reactive distillation with the acid laden solvent Cyanex® 923. 4-Dodecylbenzenesulfonic acid was used as catalyst. Catalytic conversion yielded 100% methyl formate and 88% methyl acetate formation.

Hydrogenation of Inorganic Metal Carbonates: A Review on Its Potential for Carbon Dioxide Utilization and Emission Reduction

Abstract Carbonaceous minerals represent a valuable and abundant resource. Their exploitation is based on decarboxylation at elevated temperature and under oxidizing conditions, which inevitably release carbon dioxide into the atmosphere. Hydrogenation of inorganic metal carbonates opens up a new pathway for processing several metal carbonates. Preliminary experimental studies revealed significant advantages over conventional isolation technologies. Under a reducing hydrogen atmosphere, the temperature of decarboxylation is significantly lower. Carbon dioxide is not directly released into the atmosphere, but may be reduced to carbon monoxide, methane, and higher hydrocarbons, which adds value to the overall process. Apart from metal oxides in different oxidation states, metals in their elemental form may also be obtained if transition‐metal carbonates are processed under a hydrogen atmosphere. This review summarizes the most important findings and fields of the application of metal carbonate hydrogenation to elucidate the need for a detailed investigation into optimized process conditions for large‐scale applications.