# Prospects and Technical Challenges in Hydrogen Production through Dry Reforming of Methane
## 4 Large-Scale Applications of DRM
The unreacted CO\({}_{2}\) is recycled to the reformer and the H\({}_{2}\) produced during the reaction is either burnt as fuel or sold as a separate product. Despite the toxicity, CO is an important chemical building block for the production of several carbon-based chemicals such as acetic acid and phospene [164; 167; 155]. The SPARG(tm) (sulfur passivated reforming) process, which was initially designed by Haldor-Topsoe and commercialized by Sterling Chemical Inc. in 1987, is another example of an industrial application of DRM for the production of syngas with lower H\({}_{2}\)/CO ratios. This process takes advantage of the already existing infrastructure for SRM, combining characteristics of both SRM and DRM, and it is able to deliver syngas with a H\({}_{2}\)/CO ratio ranging from 1.8 to 3.0 [158; 165; 168]. The process can operate with different CO\({}_{2}\) and H\({}_{2}\)O mixtures and can be considered a type of CSDRM [165]. In this process (Figure 8), sulfur is selectively used to poison the catalyst sites that are most active for coke formation in order to minimize it during the reaction, while keeping part of the reforming activity [168]. The SPARG(tm) process is operated between 915 \({}^{\circ}\)C and 945 \({}^{\circ}\)C, and the coke formation over the Ni catalyst is minimized by the sulfur pretreatment that passivates the main coke-active sites on the catalyst [165]. Figure 7: Simplified block diagram of the CALCOR(tm) process for CO production [155]. PSA—Pressure swing adsorption. Both the CALCOR(tm) and the SPARG(tm) processes are designed to prevent the formation of coke under DRM conditions. Unfortunately, these processes require specific conditions for their full applicability. Therefore, in order to reduce these barriers and increase the range of applicability of these processes, a better understanding of the mechanisms of cooking and measures related to the development of catalysts are necessary, as well as the choice of the reactor material [158]. The MIDREX(tm) process (Figure 9) was developed in the 1960s and remains, to this day, a leading process in the field of the direct reduction technology [169]. This process takes advantage of a combined DRM and SRM process to produce syngas which is later used as a reducing agent for the production of metallic iron [161]. In the MIDREX(tm) process, the reformer is fed with a mixture of CO\({}_{2}\):CH\({}_{4}\):H\({}_{2}\)O = 1:1:1. The MIDREX reforming process is performed over a Ni-based catalyst supported on \(\alpha\)-alumina, MgO or a combination thereof, and operated between 850 and 1000 \({}^{\circ}\)C at 1.9-3.0 bar. Basic promoters such as Zr, Ce and La are also frequently used on commercial catalysts for this process, which can increase the overall basicity of the catalysts, prevent carbon deposition and stabilize Ni particles [160; 161]. Although detailed information on the syngas produced via the MIDREX(tm) process is not available, since the syngas is not actually the final product, modeling has indicated that the H\({}_{2}\)/CO ratio of the syngas should be in the range between 2.0 and 2.5 [160]. The MIDREX(tm) process operates commercially since the 1970s and has currently over 100 plants installed in 21 countries, having decommissioned only the pilot- and demonstration-scale plants built pre-1975 [159]. Linde and BASF have recently collaborated to the advancement of DRM industrial implementation. The DRYREF(tm) technology (Figure 10) has been developed by Linde with the aims of not only contributing to the efforts towards anthropogenic CO\({}_{2}\) utilization, but also for reducing the capital (CAPEX) and operational (OPEX) costs of CH\({}_{4}\) reforming technologies [170]. The process is based on an innovative catalyst developed by BASF, the SYNSPIRE(tm) G1-110, which is a Ni-based oxide-supported catalyst, specially designed to prevent coke formation and to operate at pressurized reforming conditions (20-40 bar) [162].