Gasiﬁcation of Crude Glycerol after Salt Removal Ana Almeida, † Rosa Pilã o,* ,† Albina Ribeiro, † Elisa Ramalho, † and Carlos Pinho ‡ † CIETI, Instituto Superior de Engenharia do Porto (ISEP), Rua Dr. Antó nio Bernardino de Almeida 431, 4200-072 Porto, Portugal ‡ CEFT, Faculdade de Engenharia da Universidade do Porto (FEUP), Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal ABSTRACT: The increase in the amount of crude glycerol available on the market, as well as the decrease in its purity due to the use of waste materials in the production of biodiesel, has forced producers to look for alternative ways of valuing this byproduct. In this research work, crude glycerol of a Portuguese biodiesel producer was pretreated using an ion exchange process in order to reduce its salt content. The gasiﬁcation process was performed using steam as the oxidizing agent in a down- ﬂow ﬁxed-bed reactor using alumina particles as bed material. After the gasiﬁcation process, the producer gas ﬂowed through a condensing and cleaning system, in order to remove the condensable fraction. Dry gas samples were collected and analyzed by GC in order to quantify the CO, CO 2 , CH 4 , and H 2 content. Three diﬀerent feed mixtures were studied with 35%, 39%, and 59% (w/w) water, and the tests were performed at 850, 900, and 950 °C. The results showed that the increase of the water content in the feed mixture led to higher values of H 2 and CO 2 , and lower values for CO and CH 4 , on the producer gas composition. A slight increase of dry gas yield and hydrogen conversion eﬃciency with the increase of water content in the feed was observed, while the lower heating value of producer gas decreased. No signiﬁcant inﬂuence of water content was detected in the carbon conversion eﬃciency and cold gas eﬃciency. The increase of temperature resulted in the increase of four gasiﬁcation parameters with maximum mean values of 90% for carbon conversion eﬃciency, 100% for hydrogen conversion eﬃciency, 107% for cold gas eﬃciency, and 1.3 m 3 /kg raw material. The maximum lower heating value of 14.5 MJ/m 3 was obtained at 850 °C. 1. INTRODUCTION In Portugal, biodiesel is the biofuel with the greatest impact on the market. In 2017, the biodiesel sector registered the highest production ever in the country, at 355828 t, where 49% was obtained from virgin oils and 51% from residual matter such as waste cooking oils or animal fat. It was the ﬁrst time for the Portuguese biodiesel industry that the use of waste materials for biodiesel production exceeded that for virgin oils (Figure 1). 1 European directives have driven the dynamic of the biofuels sector and biodiesel in particular. However, in the past decade, the biodiesel industry has faced several sustainability and product problems. The use or incorporation of residual matter in biodiesel production is a key requirement for biodiesel producers, since it represents a predominant issue in sustainability criteria. However, the use of residues as part of raw material results in a lower quality of both biodiesel and crude glycerol, a byproduct which represents 10% (w/w) of the conventional process. For this reason, the crude glycerol market price has suﬀered a huge decrease. In Portugal, the crude glycerol market has become even less competitive, with an estimated decrease above 50% of its liquid value in the past ﬁve years. At this moment, it is imperative to ﬁnd energetic and economic alternatives for its valorization. Crude glycerol diﬀers from other glycerol nomenclatures since its composition is about 80% of glycerol (C 3 H 8 O 3 ), and the remaining 20% may be methanol, water, MONG (matter organic non-glycerol), and salts. Due to the low purity of crude glycerol, high-energy costs are required for its puriﬁcation, which leads to the need to ﬁnd new valorization alternatives. 2 Gasiﬁcation, a partial oxidation process performed at high temperatures, seems to be a feasible option for crude glycerol valorization. This thermochemical process allows for the conversion of residual raw materials into a combustible gas mixture, along with residual fractions of char (solid phase) and bio-oil/tars (liquid phase). The producer gas is mainly composed by hydrogen (H 2 ), carbon monoxide (CO), carbon dioxide (CO 2 ), and methane (CH 4 ). Residual amounts of light hydrocarbons could also be formed (C n H m ). There are several gasiﬁcation agents that can be used on the process, such as air, oxygen, steam, and carbon dioxide. 3 There has been remarkable growth in the experimental research of technical glycerol (product with glycerol content higher than 98%) gasiﬁcation, possibly in order to study the process feasibility and to extrapolate to the crude glycerol. However, there are few studies regarding the eﬀective use and valorization of crude glycerol, particularly related with noncatalyzed steam gasiﬁcation in ﬁxed-bed reactors. Suero et al. (2015) studied crude glycerol steam gasiﬁcation, reaching conclusions about the inﬂuence of the bed temper- ature (600-900 °C), feed ﬂow rate (0.5-3.0 mL/min), and water/glycerol ratio on the process performance and on the composition of the producer gas. The results showed that higher temperatures contribute for water-gas and water-gas shift reactions and H 2 concentration. Regarding the feed ﬂow rate, with a rate of 3.0 mL/min, an increase in gas production and a decrease in H 2 was obtained. 4 Sabio et al. (2011) studied the inﬂuence of bed temperature (682-1018 °C), water/glycerol ratio (0.7-3.3 w/w), and feed ﬂow rate 8.5-35.5 mL/min on the performance of non- catalyzed crude glycerol steam gasiﬁcation. The authors concluded that the bed temperature and water/glycerol ratio Received: July 22, 2019 Revised: September 17, 2019 Published: September 24, 2019 Article pubs.acs.org/EF Cite This: Energy Fuels 2019, 33, 9942-9948 © 2019 American Chemical Society 9942 DOI: 10.1021/acs.energyfuels.9b02390 Energy Fuels 2019, 33, 9942-9948 Downloaded via NORTHWESTERN UNIV on October 23, 2019 at 03:44:38 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.