Novel nickel ceramic filter for hot gas cleanup of tars from syngas

https://doi.org/10.1016/j.fuproc.2023.107708Get rights and content

Highlights

  • Novel Ni ceramic filter developed for hot gas cleanup of biomass syngas

  • Process intensification by integrating tar and particulate removal into one unit

  • Ceramic filter's surface area of over 90 m2/g, allows for excellent Ni dispersion

  • Naphthalene conversions as high as 79% using 15 wt% Ni ceramic filter

  • Presents an economically viable solution for biomass syngas cleanup

Abstract

Tars, defined as hydrocarbons having molecular weights above that of benzene, have been considered to be one of the major impurities in syngas preventing largescale commercialization of biomass gasification. Catalytic tar removal has shown the most promise in reforming/eliminating tars compared to physical and thermal techniques. Nickel based catalytic filter was developed using porous ceramic support, which acts both as a particulate filter and tar reformer, resulting in process intensification. The relatively high surface area of the ceramic filter (100 m2/g) makes it an ideal catalyst support. Nickel based ceramic catalysts were prepared using incipient wetness method and evaluated for tar removal effectiveness using naphthalene as a tar simulant. Influence of nickel loading, steam/carbon ratios, and temperatures on steam reforming activity of the catalyst was performed. Promising results were obtained with naphthalene conversions of 76% using a 15 wt% nickel filter over 2 h with very minimal pressure drop across the catalytic filter, offering a promising potential of using catalytic ceramic filters for integrated tar and particulate removal applications.

Introduction

Renewable energy and fuels have been a topic of particular interest recently with the growing awareness of climate change and the harmful effects that the use of fossil fuels has on the environment. Attention towards alternative energy production has also been spurred on by volatility of the fossil fuel market and the devastating impact it has brought on local and global economies that are reliant upon a single source for energy and jobs. In order to diversify the energy portfolio, the U.S. investment in alternative energies such as wind, solar, hydroelectric, and biomass has risen from $11.3 billion in 2005 to $45 billion in 2015 to a record $59 billion in 2019 [1]. Globally, investments in clean energy reached a record $301.7 billion in 2019 with the U.S. planning to invest additional $2 trillion over the next four years [2]. This comes at a time when energy demand is ever increasing as evidence by total U.S. energy consumption is at an all-time high of 100.1 quadrillion BTUs with renewable energy sources comprising 11%. Of these sources, energy from biomass leads the way totaling 43.5% with a variety of conversion routes including thermal, chemical, biochemical, and thermochemical [3].

A promising route within thermochemical conversion of biomass is gasification. There are 238 commercial gasification plants globally with 33 located in the U.S. Amongst these 33 facilities, eight use biomass/waste as a feedstock [4]. Traditionally coal has been used as the feedstock in the gasification process, however the source of energy has been expanded to natural gas, petroleum, petcoke, and even MSW (municipal solid waste)/plastics. Gasification has several advantages over combustion as the produced syngas can be used for a variety of applications including combined heat and power, generation of electricity, conversion into transportation fuels, production of general and specialty chemicals, and further separation to produce hydrogen. Gasification involves the partial oxidation of a carbonaceous feedstock to produce synthesis gas (syngas) composed mostly of carbon monoxide, hydrogen and carbon dioxide [5]. Syngas also contains several unwanted impurities including ammonia, H2S, tars and particulates. Downstream syngas applications require contaminants to be below certain levels in order for the process to be effective. For downstream usage of syngas in methanol synthesis, particulate and tar concentrations must be below 0.1 mg/m3 and 1 mg/m3, respectively [6]. While particulates, responsible for equipment damage, can be separated through high temperature filtration, tar formation is the most cost-inducing problem whereby their condensation clogs downstream equipment presenting a major hurdle limiting biomass gasification commercialization. Existing tar removal technologies include physical methods such as scrubbing or thermal cracking, however catalytic tar reforming is a cost-effective strategy for tar abatement whereby conversion of tars into syngas not only eliminates tars but improves the overall efficiency of the gasification process [7]. Further, integrating tar and particulate removal into one unit could be realized by using a ceramic filter as a catalyst support. This approach will result in process intensification and will improve the overall process economics of the gasification process. Ceramic catalyst supports come in a variety of geometries and compositions including candles, monoliths, and foams [[8], [9], [10], [11]]. Traditionally ceramic filters are made of SiC, however there have been studies using α-Al2O3, ZrO2, CeO2, and CaSiO3 for boosting material flexibility and decreasing the density [[12], [13], [14], [15], [16]]. The open cell high porosity format of the ceramic foams gives advantages including minimal external mass transfer limitations and low fluid flow resistance creating a lower pressure drop [17]. All of these characteristics in addition to the natural high temperature resistance of ceramics are advantageous for continuous filtration of particulate matter and as a catalyst support material in hot syngas cleanup.

Nickel (Ni) was chosen as a catalyst owing to its low cost, high effectiveness towards tar reforming, and ease in regeneration [[17], [18], [19], [20], [21]]. The relatively high activity of nickel compared to other less economic high activity transition metal catalysts such as Pt, Pd, Ru, Rh has made Ni-based catalysts the subject of many steam reforming studies [[21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31]]. It has also been theorized that the high activity towards tar compounds that nickel possesses may in part be due to its ability to use H2O and CO2 for the purpose of breaking Csingle bondH and Csingle bondC bonds [32]. Ni-based catalysts have been shown to reduce tar by >99%, however the challenge has been in maintaining this activity by overcoming challenges such as metal sintering and carbon deposition [31]. Coking of catalysts has been one of the challenges in tar reforming applications as it is a major contributor leading to the loss of catalytic activity over time due to its deposition on the nickel metal as well as support material. Deposition of coke on catalyst surface will lead to blocking active sites and blocking of pores thus restricting access to active sites present within the pores [33].

Limited number of studies have been performed investigating the use of ceramics as a catalyst support for the purposes of process intensification for simultaneous filtration and tar reforming [10,18,19,[34], [35], [36], [37]]. Zhao et al. [38] used nickel impregnated on a ceramic disc (surface area 0.33 m2/g) for preliminary studies on catalytic tar removal. At 1% nickel, the catalyst was able to achieve nearly 100% naphthalene (tar model compound) removal at 900°C, a gas hourly space velocity (GHSV) of 2088 h−1. They were able to achieve nearly complete naphthalene removal at a velocity of 2.5 cm/s where filtration velocity is typically 1–4 cm/s for candle filters [39]. A study by Straczewski et al. [40] compares ceramic filter discs impregnated with different catalysts including metals for their tar reforming capabilities. The Al2O3 (44)/SiO2 disc had a surface area of only 1.9 m2/g. The catalytic filter was able to achieve over 90% naphthalene conversion at a GHSV of 8400 h−1 and 20,700 h−1. In a review of studies using catalytic ceramic filters, the pressure drop was found to be in the range of 2.5–6.8 kPa when operating within the normal filtration velocity of 1–4 cm/s [41]. The tar conversion ranged from 57% to ∼100%.

These studies highlight the fact that in order to achieve high tar conversions it is necessary to provide certain compensation to make up for limitations in the material properties of the catalyst support. The surface area of the filters seen in these studies are extremely low and thus do not provide satisfactory support area for catalyst deposition. To compensate for this, the addition of noble metals such as platinum or ruthenium are added to boost catalytic activity. Furthermore, the catalysts are only able to achieve a high conversion by operating at a low GHSV. The ceramic filter used in this study boasts a surface area significantly higher than those found in previous studies so as to allow for easier access to a plethora of active sites for tar conversion. Additionally, the pressure drops observed are at an order of magnitude less than those seen in previous studies. This is achieved at a high GHSV using a filter with mesopores. These mesopores are able to reduce the internal diffusion limitations while also allowing a high porosity for low pressure drop. The material properties of the filter in question give several advantages that give way to high tar conversions at operating conditions necessary for high throughput steam reforming processing.

In this study, a Ni-based catalyst was prepared using incipient wetness method on a ceramic filter support. Additionally, proof of concept was tested by performing preliminary steam reforming experiments using naphthalene as a tar simulant molecule due to its high abundance in biomass syngas, high stability, and the ease of comparison due to the plethora of literature [21,31,[42], [43], [44], [45], [46], [47]].

Section snippets

Catalyst preparation methods

Porous ceramic high temperature filters were supplied by Borla Composites (Formerly CerX Filters) based out of Johnson City, Tennessee, USA. They specialize in the manufacture of ceramic filters for a wide range of high temperature applications. The filter materials have a thickness of 1.27 mm (0.05″) and were cut into 1.588 cm (0.625″) diameter discs for further testing. Incorporation of nickel into the ceramic discs was done using incipient wetness impregnation technique. The discs were

BET

Surface measurements were run on the ceramic filter used in this study and are displayed along with properties of ceramic filters used in other steam reforming studies in Table 1. The table shows that the filter used in this study has a much greater surface area compared to those used in other studies (< 2 m2/g). The primary composition of ceramic fiber filter is α-Al2O3, which was then wash coated with γ-Al2O3 and heat treated at 500 °C. γ-Al2O3 primarily contributes to the higher surface area

Conclusions

A novel ceramic filter support was impregnated with nickel for the purposes of catalytic tar reforming. Naphthalene was used as a simulant molecule for tar in order to evaluate the effectiveness of the catalytic filter in terms of tar conversion. Based on the results of the steam reforming experiments, several conclusions were made and are as follows:

  • The incipient wetness impregnation technique was effective at depositing nickel particles on the surface of an alumina ceramic filter support as

CRediT authorship contribution statement

Devin Peck: Methodology, Validation, Formal analysis, Investigation, Writing – original draft, Writing – review & editing, Visualization. William Holmes: Resources, Investigation. Mark Zappi: Resources, Writing – review & editing. Rafael Hernandez: Resources, Writing – review & editing. Daniel Gang: Resources, Writing – review & editing. Prashanth Buchireddy: Conceptualization, Methodology, Formal analysis, Resources, Supervision, Writing – review & editing, Visualization, Project

Declaration of Competing Interest

Prashanth Buchireddy reports equipment, drugs, or supplies was provided by CerX Filters.

References (93)

  • R. Balzarotti

    Ni/CeO2-thin ceramic layer depositions on ceramic monoliths for syngas production by Oxy Steam Reforming of biogas

    Fuel Process. Technol.

    (2016)
  • D. Świerczyński

    Steam reforming of tar from a biomass gasification process over Ni/olivine catalyst using toluene as a model compound

    Appl. Catal. B Environ.

    (2007)
  • T. Furusawa

    Steam reforming of naphthalene/benzene with various types of Pt- and Ni-based catalysts for hydrogen production

    Fuel

    (2013)
  • S.Y. Park

    Deactivation characteristics of Ni and Ru catalysts in tar steam reforming

    Renew. Energy

    (2017)
  • J. Pu

    Ru–Ni bimetallic catalysts for steam reforming of xylene: effects of active metals and calcination temperature of the support

    RSC Adv.

    (2021)
  • C.P.B. Quitete et al.

    Steam reforming of tar using toluene as a model compound with nickel catalysts supported on hexaaluminates

    Appl. Catal. A Gen.

    (2014)
  • M. Nacken

    New DeTar catalytic filter with integrated catalytic ceramic foam: catalytic activity under model and real bio syngas conditions

    Fuel Process. Technol.

    (2015)
  • F. García-Labiano

    Tar abatement in a fixed bed catalytic filter candle during biomass gasification in a dual fluidized bed

    Appl. Catal. B Environ.

    (2016)
  • N. Gao et al.

    Study on steam reforming of coal tar over Ni Co/ceramic foam catalyst for hydrogen production: effect of Ni/Co ratio

    Int. J. Hydrog. Energy

    (2018)
  • L. Devi

    Catalytic decomposition of biomass tars: use of dolomite and untreated olivine

    Renew. Energy

    (2005)
  • L.F. de Diego

    Tar abatement for clean syngas production during biomass gasification in a dual fluidized bed

    Fuel Process. Technol.

    (2016)
  • J. Pu

    Ceria-promoted Ni@Al 2 O 3 core-shell catalyst for steam reforming of acetic acid with enhanced activity and coke resistance

    Int. J. Hydrog. Energy

    (2018)
  • S.J. Hassani Rad

    Sol–gel vs. impregnation preparation of MgO and CeO2 doped Ni/Al2O3 nanocatalysts used in dry reforming of methane: effect of process conditions, synthesis method and support composition

    Int. J. Hydrog. Energy

    (2016)
  • G. Oh

    Ni/Ru–Mn/Al 2 O 3 catalysts for steam reforming of toluene as model biomass tar

    Renew. Energy

    (2016)
  • M. Mayerhofer

    Fluidized bed gasification of biomass – in bed investigation of gas and tar formation

    Fuel

    (2014)
  • U. Rhyner

    Experimental study on high temperature catalytic conversion of tars and organic sulfur compounds

    Int. J. Hydrog. Energy

    (2014)
  • J. Ashok

    Recent progress in the development of catalysts for steam reforming of biomass tar model reaction

    Fuel Process. Technol.

    (2020)
  • Z. Zhang

    Preparation, modification and development of Ni-based catalysts for catalytic reforming of tar produced from biomass gasification

    Renew. Sust. Energ. Rev.

    (2018)
  • D. Draelants et al.

    Catalytic conversion of tars in biomass gasification fuel gases with nickel-activated ceramic filters

    Studies in Surface Science and Catalysis - STUD SURF SCI CATAL

    (2000)
  • S. Karnjanakom

    Catalytic steam reforming of tar derived from steam gasification of sunflower stalk over ethylene glycol assisting prepared Ni/MCM-41

    Energy Convers. Manag.

    (2015)
  • S. Heidenreich

    Chapter Eleven - Hot Gas Filters

  • M. Artetxe

    Steam reforming of different biomass tar model compounds over Ni/Al2O3 catalysts

    Energy Convers. Manag.

    (2017)
  • Y. Yamamoto et al.

    Hydrotreating catalyst deactivation by coke from SRC-II oil

    Fuel Process. Technol.

    (1988)
  • K. Hou et al.

    The kinetics of methane steam reforming over a Ni/α-Al2O catalyst

    Chem. Eng. J.

    (2001)
  • N. Gao

    Steam reforming of biomass tar for hydrogen production over NiO/ceramic foam catalyst

    Int. J. Hydrog. Energy

    (2015)
  • R. Michel

    Steam reforming of α-methylnaphthalene as a model tar compound over olivine and olivine supported nickel

    Fuel

    (2013)
  • Y. Matsumura et al.

    Steam reforming of methane over nickel catalysts at low reaction temperature

    Appl. Catal. A Gen.

    (2004)
  • X. Gao

    A comprehensive review of anti-coking, anti-poisoning and anti-sintering catalysts for biomass tar reforming reaction

    Chemical Engineering Science: X

    (2020)
  • C.H. Bartholomew

    Mechanisms of catalyst deactivation

    Appl. Catal. A Gen.

    (2001)
  • H.S. Bengaard

    Steam Reforming and Graphite Formation on Ni Catalysts

    J. Catal.

    (2002)
  • J.R. Rostrup-Nielsen

    Industrial relevance of coking

    Catal. Today

    (1997)
  • B. Yue

    Catalytic reforming of model tar compounds from hot coke oven gas with low steam/carbon ratio over Ni/MgO–Al2O3 catalysts

    Fuel Process. Technol.

    (2010)
  • Energy, O.o.E.E.R
  • N. Cook et al.

    Biden Plans $2.25 Trilion Spending, Corporate Tax Hikes

    (2021)
  • E.I. Administration

    Annual Energy Outlook 2021, U.S.F.S. System

    (2021)
  • Council, G.S.T

    The Gasification Industry

  • Cited by (0)

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