• Energy Research

The CO2 adsorption capacities (AC) of biochars obtained at 350, 550, and 750 °C from the main organic (cellulose, lignin, and protein) and inorganic (CaCO3) macro-components of biogenic waste, as well as from co-digested manure (CDM), have been determined for different CO2 concentrations (2–83 vol%) at 25 °C and atmospheric pressure. CO2 adsorption isotherms have been determined using two different experimental methodologies: thermogravimetric and fixed-bed dynamic adsorption tests, yielding similar results. The composition effect has been analyzed by comparing the adsorption performance of the chars derived from individual macro-components and the potential interactions occurring during their co-pyrolysis. Lignin and cellulose-derived chars showed higher CO2 retention (≈77 mg gbiochar−1) than those produced from protein (≈40 mg gbiochar−1). Pyrolyzed CaCO3 exhibited negligible CO2 adsorption. For surrogate_CDM chars, prepared at pyrolysis temperatures high enough to decompose CaCO3 in the organic matrix, experimental results showed a synergistic effect, with AC between 14 % and 47 % higher than theoretical predictions. This decomposition promoted the reverse Boudouard reaction and enhanced char microporosity. However, the improvement was insufficient to offset the dilution effect caused by the high CaCO3 content. AC results have been discussed based on the biochar textural and chemical properties, with ultramicroporosity being the key factor determining adsorption capacity. The AC of CDM-derived sorbents is similar to that of cellulose-derived, expressed per gram of waste (7–13 mg gwaste−1). Furthermore, the biochars retained at least 80 % of their initial AC after 3 adsorption-desorption cycles, indicating their potential for stable CO2 capture.

A selective online condensation system, including a scrubber and an electrostatic precipitator, has been tested in a lab-scale fluidized bed pyrolysis plant with the aim of reducing the water content of the pyrolysis liquid obtained from sewage sludge. Water and triethylene glycol at different temperatures were tested as washing liquids in the scrubber. The pyrolysis liquids collected with this liquid recovery system showed lower water contents (13−30 wt %) than those collected with a previous system (48 wt %) consisting of two condensers and an electrostatic precipitator. In spite of these significant reductions in the water contents, the liquids obtained still separated into three phases (light organic, heavy organic, and aqueous). The properties and yields of these phases were also affected by the operational conditions used in the scrubber. The aqueous phase was the most affected because the compounds present in this phase are those with greater affinity for the polar washing liquid used in the scrubber. The properties of the organic phases were less affected by the condensation system, although it is of interest that when using triethylene glycol at 80 °C as washing liquid, the yield to the light organic phase was increased by about 41% compared to the previous system without affecting its good properties as fuel.

Abstract This work examines the influence of sewage sludge pre-treatment by torrefaction on the distribution and properties of the products obtained from its pyrolysis followed by catalytic post-treatment of the hot pyrolysis vapors. Sewage sludge was first torrefied in an auger reactor under two different conditions: temperature of 250 °C and 275°C and average solid residence times of 13 min and 24 min, respectively. Pyrolysis was conducted at 530 °C in a fluidized bed reactor. The catalytic post-treatment of the hot pyrolysis vapors was carried out in a fixed bed reactor using gamma-alumina (γ-Al 2 O 3 ) as a catalyst. The experimental results showed that the combination of the torrefaction pre-treatment with the catalytic post-treatment of the hot pyrolysis vapors did not noticeably improved the properties of the liquid organic phases for use as a fuel, in terms of O/C molar ratio and nitrogen content, compared to pyrolysis of sewage sludge with the same catalytic post-treatment of the hot pyrolysis vapors but without the torrefaction pre-treatment. Generally, the torrefaction did not have effect on the type of chemical families identified in the liquid phases and had little effect on the proportion of these families. The advantages of the combination of treatments were, on the one hand, the catalyst saving resulting from the lower amount of vapors generated by the pyrolysis of torrefied sewage sludge and, on the other hand, the slight decrease in the coke yield.

This paper reviews the literature related to the complex chemical composition and multiphase nature of bio-oils and their practical implications. Over time, bio-oil forms separated phases due to purely physical phenomena (phase stability) or chemical composition changes in storage (aging reactions). Bio-oil multiphase behavior and the formation of separated phases are controlled by the complex chemical composition of these oils. Fast pyrolysis oils from woody biomass are typically observed in a single phase. However, feedstocks with high extractives content and/or high ash content commonly produce oils with more than one phase (an aqueous phase, an upper layer, and a decanted heavy oily phase). The first part of this Review focuses on the effects of feedstock composition, particle size, type of pyrolysis reactor, and condensation systems on bio-oil chemical composition and their impact on stable oils production. The second section reviews our current understanding of fresh bio-oil multiphase behavior and ...

Abstract The high output of sewage sludge, which is increasing during recent years, and the limitations of the existing means of disposing sewage sludge highlight the need to find alternative routes to manage this waste. Biomass and residues like sewage sludge are the only renewable energy sources that can provide C and H, thus it is interesting to process them by means of treatments that enable to obtain chemically valuable products like fuels and not only heat and power; pyrolysis can be one of these treatments. The main objective of this review is to provide an account of the state of the art of sewage sludge pyrolysis for liquid production, which is under study during recent years. This process yields around 50 wt% (daf) of liquid. Typically, this liquid is heterogeneous and it usually separates into two or three phases. Some of these organic phases have very high gross heating values, even similar to those of petroleum-based fuels. The only industrial sewage sludge pyrolysis plant operated to date is currently closed due to some technical challenges and problems of economic viability.

The hydrodeoxygenation (HDO) of bio-oil at 350 °C and 200 bar in a batch reactor over a Ru/C catalyst has been studied experimentally with the aim of contributing to the understanding of the HDO re...

Abstract The pyrolysis of dry and of torrefied sewage sludge in a lab-scale fluidized bed reactor has been studied in order to determine whether torrefaction pre-treatment could enhance the properties of the liquid product obtained after pyrolysis. The aim of this work is to evaluate the influence of the torrefaction temperature (220–320 °C) and average solid residence time (3.6–10.2 min) on the product distribution and the properties of the pyrolysis products. Pyrolysis was conducted at 530 °C with an average solid residence time of 5.7 min and a nitrogen volumetric flow per reactor area of 0.074 m 3 (STP) m −2 s −1 (measured at 0 °C and 1.01·10 5 Pa). The experimental results show that torrefaction pre-treatment affects the pyrolysis liquid product, although it does not improve the homogeneity of the liquid. Specifically, it reduces the yields of water and the liquid aqueous phase obtained in the pyrolysis step, especially after torrefaction under the most severe conditions, but it does not have a great effect on the properties of the liquid organic phases obtained. The cumulative yields of gas and organic compounds from the two-step process are not different from the yields obtained from one-step pyrolysis.

A three-stage thermochemical process comprising torrefaction, pyrolysis, and char activation is proposed for the treatment of dry sewage sludge or biomass materials. To assess the feasibility of the process, lab-scale experiments were carried out with dried sewage sludge as feedstock, and mass and energy balances were calculated. In the process, 19.3% of the sewage sludge initial weight was transformed into a bio-oil with three distinct phases and reduced water content (66.1% of water content in the aqueous phase compared to 73.8% in a single-step fast pyrolysis). The product gases had a high H2S content but also enough heating value to be combusted. After being activated by the torrefaction vapors, the solid fraction (48.2% of the initial sludge weight) showed certain pore development and might be suitable for adsorption applications. Regarding the energy balance, it was found that the combustion of part of the product gas would provide the necessary heat to drive the process (1019 kJ/kg of dry sewage sludge).

Bio-oil derived from fast pyrolysis of lignocellulosic materials is among the most complex and inexpensive raw oils that can be produced today. Although commercial or demonstration scale fast pyrolysis units can readily produce this oil, the pyrolysis industry has not grown to significant commercial impact due to the lack of bio-oil market pull. This paper is a review of the challenges and opportunities for bio-oil upgrading and refining. Pyrolysis oil consists of six major fractions (water 15-30 wt %, light oxygenates 8-26 wt %, monophenols 2-7 wt %, water insoluble oligomers derived from lignin 15-25 wt %, and water-soluble molecules 10-30 wt %). The composition of water-soluble oligomers is relatively poorly studied. In the 1880s, bio-oil refining (formally known as wood distillation) targeted the separation and commercialization of C1-C4 light oxygenated compounds to produce methanol, acetic acid, and acetone with the commercialization of the lignin derived water insoluble fraction for preserving wooden sailing vessels against rot. More recently, the company Ensyn extracted and commercialized condensed natural smoke as a food additive. Most research efforts in the last 20 years have focused on the two-step hydrotreatment concept for the production of transportation fuels. In spite of major progress, this concept remains at the demonstration scale. In this review, the opportunities and progress to separate bio-oil fractions and chemicals, mainly acetic acid (HAc), hydroxyacetaldehyde (HHA), acetol, and levoglucosan, and convert them into value added coproducts are thoroughly discussed. In spite of the large number of separation schemes and products tested, very few of them have been tested as part of fully integrated bio-oil refinery concepts. The synthesis and techno-economic and environmental evaluation of novel integrated bio-oil refinery concepts is likely to become a subject of intense research activity in the coming years.