Techno-economic analysis (TEA) for CO₂ reforming of methane in a membrane reactor for simultaneous CO₂ utilization and ultra-pure H₂ production

Highlights

• Techno-economic analysis was performed for CO₂ reforming of methane in a MR.

• Design guidelines for a H₂O sweep gas flow rate and a CO₂/CH₄ ratio were obtained.

• Useful economic indicators were identified from cumulative cash flow diagrams.

Abstract

Techno-economic analysis (TEA) for CO₂ reforming of methane in a membrane reactor (MR) was conducted by using process simulation and economic analysis. Parametric studies for key operating conditions like a H₂ permeance, a H₂O sweep gas flow rate, operating temperature, and a CO₂/CH₄ ratio were carried out for a conventional packed-bed reactor (PBR) and a MR using Aspen HYSYS^®, a commercial process simulator program and some critical design guidelines for a MR in terms of a H₂O sweep gas flow rate and a CO₂/CH₄ ratio were obtained. Further economic analysis based on process simulation results showed about 42% reduction in a unit H₂ production cost in a MR (6.48 $ kgH₂⁻¹) than a PBR (11.18 $ kgH₂⁻¹) mostly due to the elimination of a pressure swing adsorption (PSA) system in a MR. In addition, sensitivity analysis (SA) revealed that reactant price and labor were the most influential economic factors to determine a unit H₂ production cost for both a PBR and a MR. Lastly, profitability analysis (PA) from cumulative cash flow diagram (CCFD) in Korea provided positive net present value (NPV) of $443,760∼$240,980, discounted payback period (DPBP) of 3.03–3.18 y, and present value ratio (PVR) of 7.51–4.97 for discount rates from 2 to 10% showing economic feasibility of the use of a MR as simultaneous CO₂ utilization and ultra-pure H₂ production.

Introduction

A synthetic gas (syngas) consisting of mostly CO, CO₂, and H₂ has been successfully serving as useful precursors to produce important chemicals like methanol, dimethyl ether (DME), alkanes, polyethylene, etc. [1]. To obtain syngas, reforming reactions of hydrocarbons have been widely used and a new concept of a membrane reactor (MR) combining a reactor and a separator is of great interest as a means to improve product yields by Le Chatelier's principle [2], [3], [4]. With this MR concept, numerous experimental and theoretical studies were reported to show improved performance in a MR compared to a conventional packed-bed reactor (PBR) in methane dry reforming [5], [6], [7], [8], [9], [10], methane steam reforming [11], [12], [13], [14], methanol steam reforming [15], [16], [17], [18], ethanol steam reforming [19], [20], [21], and water gas shift reaction [22], [23], [24].

As a unique method to simultaneously reduce CH₄ and CO₂ which are greenhouse gases (GHGs), CO₂ reforming of methane has been attempted by numerous research groups [25], [26], [27], [28], [29], [30], [31], [32], [33] and the MR concept was also successfully applied to CO₂ reforming of methane with improved reactant conversion and H₂ production [5], [6], [7], [8], [9], [10], [34], [35], [36], [37], [38]. Gallucci et al. [8] carried out experimental MR studies employing a Pd-Ag tubular membranes for effective consumption of CO₂ via chemical reaction with methane, which are both greenhouse gases and suggested that a porous Pd-Ag membrane (some defect) works best for CO₂ consumption with a dense Pd-Ag membrane (defect-free) for H₂ production. Lee and Lim [10] proposed a 1-D reactor model for CO₂ reforming of methane in a MR to evaluate the feasibility of it as a new CO₂ utilization method. Improved CH₄ conversions and H₂ product yields were observed in a MR and these enhancements were successfully confirmed by profiles of H₂ partial pressure differences across membranes. Múnera et al. [36] investigated the use of Rh/CaO-SiO₂ catalysts for CO₂ reforming of methane in a MR fitted with a commercial Pd-Ag alloy membrane and reported various catalytic characteristics and favorable effect of Ar sweep gas flow rate on CH₄ conversion and H₂ recovery in a MR. In addition, two competing effects of increased pressure derived from both thermodynamic nature and H₂ permeation through membrane were identified. Sumrunronnasak et al. [38] also performed dry reforming of methane over Ni-based catalyst in a MR equipped with a PdAgCu membrane and showed significantly enhanced CH₄ and CO₂ conversions as well as H₂ yield enhancement in a MR confirming the benefit of the use of a MR. However, studies of the effect of key operating parameters including a H₂ permeance, a H₂O sweep gas flow rate, operating temperature, and a CO₂/CH₄ ratio on the performance in a MR have been rarely performed, to the best of knowledge. Therefore, we report in this paper the process simulation results using Aspen HYSYS^® (Aspen Technology, Inc.) for CO₂ reforming of methane in a MR compared to a conventional PBR particularly focusing on a wide range of a H₂ permeance of 1 × 10⁻⁵ ∼ 1 × 10⁻⁴ mol m⁻² s⁻¹ Pa⁻¹. In addition, techno-economic analysis (TEA) combining process simulation and economic analysis was carried out for CO₂ reforming of methane based on experimental data obtained from Korea Institute of Energy Research, where various Pd-alloy H₂ separation membranes are being actively developed, to evaluate techno-economic feasibility of employing a MR as simultaneous CO₂ utilization and ultra-pure H₂ production. As TEA, unit H₂ production cost calculations for both a PBR and a MR, sensitivity analysis (SA) to identify key economic factors, and profitability analysis (PA) based on cumulative cash flow diagram (CCFD) targeting from a small-to a medium-sized H₂ fueling stations in Korea were carried out in this study.