Biofuels and renewable chemicals production by catalytic pyrolysis of cellulose: a review

Levoglucosenone production by catalytic fast pyrolysis of cellulose mixed with alkali metal-doped Keggin heterpolyacid salt

The transformation of acetone (a byproduct of phenol manufacturing or a bioderived chemical) into mesitylene is a very attractive reaction to prepare renewable fuels and chemicals. This reaction has been studied over both base and acid catalysts, with relevant limitations (side reactions over acid catalysts, oligomerization of isophorones over basic materials, etc.). We propose an alternative strategy to perform this reaction combining acid and basic catalysts either as separate beds or as mechanical mixtures. For this purpose, we first study the reaction over five representative materials (β-zeolite, Al-MCM-41, Mg–Al mixed oxide, MgO, and TiO2). These studies allow determining the rate-limiting steps and identifying the most relevant catalytic properties to enhance the selectivity toward mesitylene, minimizing the deactivation produced by the permanent adsorption and oligomerization as well as side reactions yielding undesired products (β-scissions). Once the combining strategies are studied, we propose using double beds of Al-MCM-41 and TiO2 as the optimum approach. The observed synergistic effects enhance the mesitylene productivity by more than 57% to the most active catalyst (Al-MCM-41), working at a low temperature (250 °C). This improvement is due to the activity of the base catalyst (TiO2), producing an optimum mixture of mesityl oxide and acetone that contacts with the acid catalyst (Al-MCM-41), where the second condensation and dehydration steps are so fast that the mesitylene production is stable, not being affected by any deactivation process.

Acetic acid conversion reactions on basic and acidic catalysts under biomass fast pyrolysis conditions

Mechanistic studies of the role of formaldehyde in the gas-phase methylation of phenol

The alkylation of phenol with methanol on HY and CsY/CsOH catalysts was studied in situ under static conditions by 13C NMR spectroscopy. Attention was largely given to the identification of intermediate compounds and mechanisms of anisole, cresol, and xylenol formation. The mechanisms of phenol methylation were found to be different on acid and basic catalysts. The primary process on acid catalysts was the dehydration of methanol to dimethyl ether and methoxy groups. This resulted in the formation of anisole and dimethyl ether, the ratio between which depended on the reagent ratio, which was evidence of similar mechanisms of their formation. Subsequent reactions with phenol gave cresols and anisoles. Cresols formed at higher temperatures both in the direct alkylation of phenol and in the rearrangement of anisole. The main alkylation product on basic catalysts was anisole formed in the interaction of phenolate anions with methanol; no cresol formation was observed. The deactivation of acid catalysts was caused by the formation of condensed aromatic hydrocarbons that blocked zeolite pores. The deactivation of basic catalysts resulted from the condensation of phenol and formaldehyde with the formation of phenol-formaldehyde resins.

Several techniques, in which different homogenous catalysts and procedures, that are in use for transesterification of a vegetable oil or an animal fat have been successful in synthesizing biodiesel, although with some certain limitations. For such a purpose, among the catalysts employed are acidic as well as basic catalysts. It has been found that acidic catalysts can be tolerant with a high content of free fatty acids found in those low value feedstock oils/fats to be transesterified, although some sort of pretreatment by means of esterification might be required in order to synthesize biodiesel. Moreover, with employing homogenous acidic catalysts, it seems that biodiesel purification procedures are simplified; thus, reducing synthesis cost. In fact, these features of homogenous acidic catalysts render them advantageous over basic ones. With basic homogenous catalysts this; however, has not been possible due to the development of saponification reaction. To effectively perform, such catalysts require that the content of free fatty acids in the feedstock oil/fat is minimal. This requirement is also applicable to the moisture level in the feedstock. In terms of corrosive effects; nevertheless, acidic catalysts are disadvantageous compared to basic ones.

Research in Thermochemical Biomass Conversion

The effect of acid and base catalysts on phase purity and dissolution behavior of sol–gel derived in situ silica coated apatite composite nanopowders

First pilot scale study of basic vs acidic catalysts in biomass pyrolysis: Deoxygenation mechanisms and catalyst deactivation

Low-density foam balls with a diameter of ~1 mm were produced from a density-matched emulsion consisting of a resorcinol-formaldehyde (RF) aqueous solution (W) and an exterior oil of carbontetrachloride/(mineral oil) (O). Phase-transfer catalysts such as an alkyl amine were dissolved in the exterior oil, following which the catalyst moved into the RF solution from the exterior oil. A gelation process was monitored by a complete gelation test. When the basic catalysts were used at room temperature as a phase-transfer catalyst, gelation occurred within 30 to 120 min, whereas when the acidic catalyst was used, gelation occurred within 20 to 30 min at room temperature. When ~0.39 wt% of triethylamine and tri(n-butyl)amine in the oil phase were used, complete gelation took place. A basic catalyst with a long alkyl chain such as dimethyl(n-hexyl)amine did not induce gelation. The gelated balls obtained using the basic catalyst with a short alkyl chain were dried by extraction using supercritical fluid CO2 and the solvent was replaced with 2-propanol to produce the foam structure. Except 0.39 wt% tri(n-butyl)amine, the basic catalysts yielded foam balls with higher densities of 173 to 184 mg/cm3 as compared to those obtained from a benzoic acid catalyst, namely, 158 mg/cm3. The density difference can be attributed to the inclusion of the basic catalyst in the RF solution. Scanning electron microscopy images revealed a surface membrane formation, which can be explained by local concentration at the W/O interface. The cell size of the bulk foam was observed to depend on the catalysts, and it was surmised that the cell sizes varied because of the different gelation rates. A smooth surface membrane tri(n-butyl)amine was used as a catalyst. The membrane obtained on using a basic phase-transfer catalyst was smoother than that obtained on using an acid catalyst. Such a smooth membrane is useful for coating the ablation layer of foam capsule targets.

Recent advances in pyrolysis of cellulose to value-added chemicals

Catalytic co-pyrolysis of cellulose and linear low-density polyethylene over MgO-impregnated catalysts with different acid-base properties

In situ performance of various metal doped catalysts in micro-pyrolysis and continuous fast pyrolysis

The management of municipal and industrial organic solid wastes has become one of the most critical environmental problems in modern societies. Nowadays, commonly used management techniques are incineration, composting, and landfilling, with the former one being the most common for hazardous organic wastes. An alternative eco-friendly method that offers a sustainable and economically viable solution for hazardous wastes management is fast pyrolysis, being one of the most important thermochemical processes in the petrochemical and biomass valorization industry. The objective of this work was to study the application of fast pyrolysis for the valorization of three types of wastes, i.e., petroleum-based sludges and sediments, residual paints left on used/scrap metal packaging, and creosote-treated wood waste, towards high-added-value fuels, chemicals, and (bio)char. Fast pyrolysis experiments were performed on a lab-scale fixed-bed reactor for the determination of product yields, i.e., pyrolysis (bio)oil, gases, and solids (char). In addition, the composition of (bio)oil was also determined by Py/GC-MS tests. The thermal pyrolysis oil from the petroleum sludge was only 15.8 wt.% due to the remarkably high content of ash (74 wt.%) of this type of waste, in contrast to the treated wood and the residual paints (also containing 30 wt.% inorganics), which provided 46.9 wt.% and 35 wt.% pyrolysis oil, respectively. The gaseous products ranged from ~7.9 wt.% (sludge) to 14.7 (wood) and 19.2 wt.% (paints), while the respective solids (ash, char, reaction coke) values were 75.1, 35, and 36.9 wt.%. The thermal (non-catalytic) pyrolysis of residual paint contained relatively high concentrations of short acrylic aliphatic ester (i.e., n-butyl methacrylate), being valuable monomers in the polymer industry. The use of an acidic zeolitic catalyst (ZSM-5) for the in situ upgrading of the pyrolysis vapors induced changes on the product yields (decreased oil due to cracking reactions and increased gases and char/coke), but mostly on the pyrolysis oil composition. The main effect of the ZSM-5 zeolite catalyst was that, for all three organic wastes, the catalytic pyrolysis oils were enriched in the value-added mono-aromatics (BTX), especially in the case of the treated wood waste and residual paints. The non-condensable gases were mostly consisting of CO, CO2, and different amounts of C1–C4 hydrocarbons, depending on initial feed and use or not of the catalyst that increased the production of ethylene and propylene.

Fuel Quality Assessment of Green Diesel Produced from Waste Cooking Oil