Total Conversion Yield Research Articles

Catalytic hydrocracking reactions of tetralin as aromatic biomass tar model compound to benzene/toluene/xylenes (BTX) over zeolites under ambient pressure conditions

The gas phase selective hydrocracking process of tetralin (biomass tar model chemical compound) into benzene, toluene and xylenes (BTX) was carried out over the H-Beta, H-Mordenite, H-USY, H-Y, and H-ZSM-5 zeolite catalysts in a packed bed reactor under applied atmospheric pressure. To the best of our scientific knowledge, this performed work presents the first systematic investigation, focused on tetralin, cracking to BTX under ambient 1bar. The highest catalytic activity and carbon deposition resistance were established over the H-ZSM-5 (SiO2/Al2O3=30) with the selectivity to the BTX of 52.2mol.% in intermediates’ liquid phase, 88.7mol.% of total conversion yield after the 4h time on stream, 370°C and gas hourly space velocity (GHSV)=530h–1, and limited site deactivation. The gas phase was analyzed and ethylene, propane, ethane and methane were identified as main gas products in the product mixture at different reaction conditions. All catalysts were characterized by BET, ICP-AES, XRD, HRSEM, NH3-TPD, and pyridine-DRIFT technique. This high catalytic performance of the H-ZSM-5 catalyst is attributed to the presence the high mesopore volume and mesopore surface area, the mild acidity and the highest Brönsted to Lewis acid sites ratio (BAS/LAS) comparing with other studied zeolite catalysts. Based on the experimental results, the reaction pathway of tetralin transformation into BTX was proposed. Hydrocracking, ring opening, ring contraction, dehydrogenation/hydrogenation, alkylation/dealkylation, isomerization, and overcracking reactions were involved. Results were consistent with the occurrence of the monomolecular reaction mechanism.

Optimization of simultaneously enzymatic fructo- and inulo-oligosaccharide production using co-substrates of sucrose and inulin from Jerusalem artichoke

ABSTRACTPrebiotic substances are extracted from various plant materials or enzymatic hydrolysis of different substrates. The production of fructo-oligosaccharide (FOS) and inulo-oligosaccharide (IOS) was performed by applying two substrates, sucrose and inulin; oligosaccharide yields were maximized using central composite design to evaluate the parameters influencing oligosaccharide production. Inulin from Jerusalem artichoke (5–15% w/v), sucrose (50–70% w/v), and inulinase from Aspergillus niger (2–7 U/g) were used as variable parameters for optimization. Based on our results, the application of sucrose and inulin as co-substrates for oligosaccharide production through inulinase hydrolysis and synthesis is viable in comparative to a method using a single substrate. Maximum yields (674.82 mg/g substrate) were obtained with 5.95% of inulin, 59.87% of sucrose, and 5.68 U/g of inulinase, with an incubation period of 9 hr. The use of sucrose and inulin as co-substrates in the reaction simultaneously produced FOS and IOS from sucrose and inulin. Total conversion yield was approximately 67%. Our results support the high value-added production of oligosaccharides using Jerusalem artichoke, which is generally used as a substrate in prebiotics and/or bioethanol production.

Biotransformation of acetoin to 2,3-butanediol: Assessment of plant and microbial biocatalysts

2,3-Butanediol (2,3-BD) is a valuable bulk chemical owing to its extensive application in chemical and pharmaceutical industry with diverse applications in drug, cosmetics and food products. In the present study, the biotransformation of acetoin to 2,3-BD by five plant species (Brassica oleracea, Brassica rapa, Daucuscarota, Pastinaca sativa, and Raphnussativus) and five microorganisms (Aspergillusfoetidus, Penicillumcitrinum, Saccharomyces carlbergensis, Pichiafermentans, and Rhodotrulaglutinis) was investigated as a method for the production of 2,3-BD, which can serve as an alternative to the common pentoses and hexoses fermentation by microorganisms. The produced 2,3-BD stereoisomers were characterized and their total conversion yields were determined. The results showed that the examined plants can be used as a green factory for the production of all 2,3-BD stereoisomers, except B. rapa. In microorganisms, P. fermentans and S. carlbergensis produced (–)-2R,3R and mesobutanediol, while P. citrinum produced (+)-2S,3S and mesobutanediol. R. glutinis and A. foetidus produced all three isomers. In conclusion, efficient whole-cell biocatalysts from plants and microorganisms were determined in the bioconversion of acetoin to 2,3-BD. The profile of produced stereoisomers demonstrated that microorganisms produce more specific stereoisomers.

Efficient photo-dissociation of CH4 and H2CO molecules with optimized ultra-short laser pulses

The fragmentation dynamics of CH4 and H2CO molecules have been studied with ultra-short pulses at laser intensityof up to 1015Wcm−2. Three dimensional molecular dynamics calculations for finding the optimized laser pulses are presented based on time-dependent density functional theory and quantum optimal control theory. A comparison of the results for orientation dependence in the ionization process shows that the electron distribution for CH4 is more isotropic than H2CO molecule. Total conversion yields of up to 70% at an orientation angle of 30o for CH4 and 65% at 900 for H2CO are achieved which lead to enhancement of dissociation probability.

Strong quantum interferences in frequency up-conversion towards short vacuum-ultraviolet radiation pulses

We present experimental data on quantum interferences in resonantly enhanced frequency up-conversion towards the vacuum-ultraviolet spectral regime. The process is driven in xenon atoms by ultrashort (picosecond) laser pulses. We use two simultaneous frequency conversion pathways via an excited intermediate state, i.e., fifth harmonicgenerationofthefundamentalwavelengthandfour-wavemixingofthefundamentalandtwophotonsof itssecondharmonicwavelength.Bothconversionpathwaysyieldradiationat102nm.Thetwopathwaysinterfere, depending on the relative phase of the fundamental and second harmonic. By appropriate choice of the phase we get constructive interference (resulting in increased conversion efficiency) or destructive interference (resulting in reduced conversion efficiency). The total conversion yield shows very pronounced constructive and destructive quantum interference with a visibility of roughly 90%. A stable and highly accurate phase control setup enables suchstrongquantuminterferencesformorethan260oscillationcycles.Inanextensionoftheexperiment,simultaneouslytofrequencyconversionwealsomonitorlaser-inducedfluorescenceasameasurefortheexcitationprobabilitytotheexcitedintermediatestate.Also,intheexcitationprobabilityweobservestrongquantuminterferences. As an interesting feature, a small phase lag occurs between the quantum interference patterns of frequency conversion and population transfer. This is due to an additional atomic phase acquired during frequency conversion.

Effect of particle size on enzymatic hydrolysis of pretreated Miscanthus

Particle size reduction is a crucial factor in transportation logistics as well as cellulosic conversion. The effect of particle size on enzymatic hydrolysis of pretreated Miscanthus x giganteus was determined. Miscanthus was ground using a hammer mill equipped with screens having 0.08, 2.0 or 6.0mm sieve openings. Particle size distribution and geometric mean diameters were determined for all samples. Ground samples were subjected to hot water, dilute acid or dilute ammonium hydroxide pretreatment. Enzyme hydrolysis was conducted on washed pretreated solids; sugar generation was used as a measure for pretreatment efficiency. Glucose and xylose concentrations were monitored using HPLC. Glucose and xylose profiles were generated and hydrolysis rates estimated. Glucose, xylose and total conversion yields were determined by comparing final sugar concentrations obtained to amounts present in pretreated biomass. Geometric mean diameters were the smallest from 0.08mm sieve screen (56μm) followed by 2.0mm (301μm) and 6.0mm (695μm) screens. An increasing trend in percent total conversion was observed with decreasing mean particle size. Across all pretreatments, biomass ground using 0.08mm screens resulted in highest total conversion. Enzyme hydrolysis of unpretreated biomass samples also resulted in increased total conversions as particle size decreased, although mean conversions (10–20%) were much lower than for pretreated biomass samples (53–94%), indicating the need for chemical pretreatments in biomass conversion.

Production of 2‐phenylethanol and 2‐phenylethylacetate from L‐phenylalanine by coupling whole‐cell biocatalysis with organophilic pervaporation

An integrated bioprocess for the production of the natural rose-like aroma compounds, 2-phenylethanol (2-PE) and 2-phenylethylacetate (2-PEAc), from L-phenylalanine (L-phe) with yeasts was investigated. The hydrophobicity of the products leads to product inhibition, which can be compensated by in situ product removal (ISPR). An organophilic pervaporation unit, equipped with a polyoctylmethylsiloxane (POMS) membrane, was coupled via a bypass to a bioreactor and proved to be a suitable technique for the in situ removal of high-boiling products from culture broth. With batch cultures of the thermotolerant yeast Kluyveromyces marxianus CBS 600 in a standard medium at 35 degrees C, the use of pervaporation resulted in a double 2-PE concentration (2.2 g/L) and 1.3 g/L 2-PEAc, which only accumulated transiently in low concentrations during cultivation without ISPR. Using a previously optimized medium, the variation of the temperature from 30 degrees C to 40 degrees C caused an increase in the total conversion yield from 63% to 79%, corresponding to total product concentrations of 5.23 and 5.85 g/L, respectively. In the 40 degrees C batch experiment, the volumetric productivity (2-PE + 2-PEAc) during the exponential phase was 5.2 mmol/L h. While for 2-PE, there is still potential for further optimization, the more hydrophobic 2-PEAc was nearly completely removed from the aqueous culture broth (enrichment factor >400), resulting in highly aroma-enriched permeates. Due to the temperature-correlated performance of the pervaporation, the bioconversion was still efficient even at 45 degrees C (conversion yield: 69%). Surprisingly, at 45 degrees C, the molar ratio of the two products inverted and 2-PEAc turned out to be the main product (4.0 g/L), which opens easy control of the reaction's selectivity by external means. Retrofitting the process with interim heating and cooling equipment to use different temperature levels for cultivation and pervaporation resulted in a decreased yield and product concentration caused by multiple stress factors. The medium composition affected the pervaporation efficiency with molasses acting detrimental.

Sequential two-step conversion of 4-oxoisophorone to 4-hydroxy-2,2,6-trimethylcyclohexanone by thermophilic bacteria

The sequential two-step conversion of 4-oxoisophorone (OIP) to 4-hydroxy-2,2,6-trimethylcyclohexanone (4-HTMCH) via diyhdrooxoisophorone (DOIP) was achieved using two kinds of thermophiles, Thermomonospora curvata and Bacillus stearothermophilus. In the first step, 83% OIP was converted to DOIP by T. curvata during 12 h incubation at 50° C. The resulting reaction mixture containing thermophile cells, DOIP (2.5 mg/ml), and OIP (0.5 mg/ml) was used directly in the second step after adjusting to pH 7 and adding glycerol. In the second step, DOIP in the reaction mixture was converted to 4-HTMCH by B. stearothermophilus. The final concentration of 4-HTMCH and DOIP after 24 h of incubation was 2.5 mg/ml and 0.5 mg/ml respectively; OIP was not detected. The total conversion yield of 4-HTMCH from OIP was 83% through the two-step conversion. The two-step conversion by a sequential culture system using T. curvata and B. stearothermophilus was found to be suitable for 4-HTMCH production.

Glycolate Formation and Excretion by Chlorella pyrenoidosa and Netrium digitus

Conditions are described whereby suspensions of Chlorella pyrenoidosa and Netrium digitus photosynthetically biosynthesize and excrete glycolate continuously in high yields. Aminooxyacetic acid, an inhibitor of pyridoxal phosphate-linked enzymes, increased the excretion of glycolate approximately 4-fold in 1 hour (8 millimolar) and 20-fold in 4 hours (40 millimolar) in the presence of 0.2% CO(2) in air. The amount of glycolate excreted in the presence of aminooxyacetate and an atmosphere of 0.2% CO(2) in air equaled or exceeded the amount excreted in 0.2% CO(2) in O(2) minus aminooxyacetate. CO(2) and light were required for glycolate excretion. Aminooxyacetate also stimulated photosynthetic glycolate excretion in an atmosphere of 0.2% CO(2) in nitrogen or helium, although the stimulation was not as great as when air or O(2) was present.The excreted glycolate was converted to H(2) and CO(2) by the combined action of glycolic oxidase and the formic hydrogenlyase complex found in Escherichia coli in total conversion yields of 80%.