Effects of Pressure and the Addition of a Rejected Material from Municipal Waste Composting on the Pyrolysis of Two-Phase Olive Mill Waste

Abstract

This work examines the effect of the absolute pressure (0.1 or 1.0 MPa) and the addition of a high-ash rejected material from municipal solid waste (MSW) composting (RC) on the slow pyrolysis of two-phase olive mill waste (OW). The experiments were conducted in a batch pyrolysis system using an initial mass of 750 g of feedstock. Three types of initial materials were tested: the OW alone, a mixture of OW and pure additives (5 % wt. of K 2 CO 3 and 5% wt. of CaO) and a mixture of OW and RC (10 % wt.). For the OW without any additive, an increased pressure led to a market increase in the carbonization efficiency (i.e., fixed-carbon yield). At atmospheric pressure, the addition of either additives (CaO + K 2 CO 3 ) or RC led to important changes in the pyrolysis behavior, due to the catalytic role of the alkali and alkaline Earth metals (AAEMs). However, this catalytic effect, which is translated into an enhancement of the decomposition of both the hemicellulose and cellulose fractions, was not observed at 1.0 MPa.The potential stability of all the produced biochars appeared to be very high, given the results obtained from both proximate and ultimate analysis. This high stability was confirmed by 13 C and 1 H solid-state NMR, which showed that the carbon contained in the biochars was composed mainly or entirely of highly condensed aromatic structures. However, the highest values of stable C (Edinburgh stability tool) and R 50,x (recalcitrance index) were obtained for biochars produced from the OW+RC mixtures at any pressure . In summary, the addition of the rejected material from MSW composting appears to be a very cost-effective measure to obtain a potentially highstable biochar, even at atmospheric pressure.

Evolution of the mass-loss rate during atmospheric and pressurized slow pyrolysis of wheat straw in a bench-scale reactor

“…In this sense and as already observed in previous studies [4,10], a low (but certain) extent of the steam gasification reaction cannot be discarded. In spite of the extremely low temperature and the related thermodynamic limitations, the AAEMs contained in the wheat straw pellets (especially K, with a relatively high content, as reported in Table 1) Concerning the gas release profiles (also shown in Fig.…”

“…A promising solution for such issues is biochar [2], a form of charred organic matter, which is possible to apply to soil in a deliberate manner as a means of potentially improving soil productivity and carbon sequestration [3]. In order to produce biochar, pyrolysis of agricultural wastes seems to be an interesting solution, due to its feasibility to manage biowaste and simultaneously generate environmental and agronomic benefits [4,5]. Among the wide range of pyrolysis processes, slow pyrolysis is a promising route to produce a relatively high yield of biochar, obtaining gas as co-product for cogeneration use.…”

“…Among all the process variables, the absolute pressure is probably one of the most interesting parameters to study in deep. Relatively few studies [4,[10][11][12][13][14][15][16] have been focused on the effect of the absolute pressure on the biomass pyrolysis behavior. Most of these earlier studies reported an increase in the char and gas yields, while the yield of the condensable fraction decreased, when both the pressure and the residence time of the vapor phase were increased [13,[15][16][17][18][19].…”

Biochar production through slow pyrolysis of different biomass materials: Seeking the best operating conditions

“…Slow pyrolysis is usually preferred to produce biochar, with gas as co-product. It is a relatively simple and robust process which can be applicable to small-scale and farm-based production of biochar [3,4].…”

Evolution of the Mass Loss Rate During Atmospheric and Pressurized Slow Pyrolysis of Wheat Straw in a Bench-Scale Reactor

“…The reactor was supported on a ceramic tube, which was placed on a weighing platform. More details regarding the configuration of the reactor is available in a previous publication [2]. The composition of the gas fraction (N 2 , CO 2, CH 4 , CO, C 2 H X and H 2 ) was determined using a dual channel micro-GC (Agilent 490).…”