May-2022

Repurposing existing process units to reduce CO2 emissions

Converting an existing hydrotreater or naphtha reformer to a Methaformer can reduce both CO2 emissions and energy costs

Stephen Sims New Gas Technologies Synthesis (NGTS)
Meritxell Vila MERYT Catalyst and Innovation

Article Summary

Methaforming is a lower-cost alternative for upgrading naphtha to gasoline blendstock in a one-step process that reduces energy costs and CO2 emissions. An existing hydrotreater or naphtha reformer can be converted to a Methaformer at a low cost and reduce CO2 emissions by 0.5t CO2/t naphtha. For a typical 20K BPD (860K tpa) process unit, the conversion cost will be <$20 million with CO2 emissions reductions of 430K tpa, worth $22 million/year at $50/t of CO2 or a whopping $62 million/year at the current $140/T in California (CA). The conversion may be of either the hydrotreater or the reformer. For the hydrotreater, the main cost is for two reactors (one on-stream while the other is regenerated), and for a semi-regen reformer, the main revisions are piping changes.

The CO2 emissions credits mentioned above are in addition to the underlying Methaformer yield advantage, which is worth $40 million/year compared to a semi-regen reformer (based on US Gulf Coast long-range prices). Methaformer yields are comparable to a semi-regen reformer with isomerisation but without the need for hydrotreating, while ensuring benzene in the product is <1%. Additionally, Methaforming reactively extracts ethylene from fluid catalytic cracker (FCC) dry gas, which from a companion 50K BPD FCC would be worth an additional $10 million/year in upgrading the ethylene from fuel gas to gasoline.

CO2 emissions reduction

The estimation of CO2 emissions savings is based on the California Low Carbon Fuel Standard (LCFS) methodology. Methaforming is inherently more energy efficient, as it does not require the reheat furnaces as in a reformer or any energy for a naphtha hydrotreater. This accounts for 20% of the emission credits, equivalent to 0.1t CO2/t naphtha. Then for ethanol co-feed, the hydrocarbon portion that becomes gasoline, the CO2 emissions due to combustion in the automobile are offset by the CO2 absorption in growing the crops for the ethanol. This is why blending ethanol into gasoline is attractive. In essence, using ethanol as the co-feed in the Methaformer enables the environmental benefit of blending more ethanol into gasoline without hitting the blend wall.

While still following the LCFS methodology, the mechanism for CO2 emissions reduction when ethylene is used as a co-feed is totally different. In a common refinery configuration, ethylene in the FCC dry gas is used as refinery fuel gas. When the ethylene is reactively extracted at the Methaformer, its heating value is replaced with natural gas. This has two benefits. First, the hydrogen/carbon ratio for natural gas is twice that for ethylene. More of the BTUs come from hydrogen than carbon. Second, the CO2 emissions allocated to the ethylene include a share of the emissions from the entire value chain from crude into refining through the FCC, allocated based on contained heating value. This is much more than the CO2 emissions from natural gas production. In this way, in essence, natural gas is converted directly into gasoline.

Methaforming economics vs conventional technology

Methaforming is a one-step process (see Figure 1). Naphtha and ethanol/methanol or FCC dry gas are upgraded in a unit similar to a hydrotreater at modest pressure and temperature. The product is similar to reformate: a gasoline blendstock with relatively low sulphur and, importantly, <1% benzene. The process flow resembles a hydrotreater in which ethanol/ethylene is used instead of hydrogen without a recycle compressor. The yields are comparable to a semi-regen reformer plus isomerisation, except that most of the benzene is converted to toluene, and half the ethanol becomes water. Byproducts include hydrogen, some light ends, and H2S in the overhead. The inexpensive zeolite catalyst does not contain precious metals.

The capital and operating costs are comparable to a single hydrotreater. The operating costs are much lower than conventional processes (see Figure 2) because the Methaformer replaces four units. The Methaformer can upgrade most naphthas and reduces sulphur by 90%, thereby avoiding the need for a hydrotreater and hydrogen supply to this unit. It replaces the reformer and, because of low benzene production, avoids the need for benzene reduction steps. Methaforming also effectively processes light naphtha, thereby eliminating the need for an isomerisation unit. In this way, capital and operating costs are reduced to about one-third.

 Table 1 shows the economics for converting a 20K BPD (860K tpa) semi-regen reformer into a Methaformer.

- The second column shows the economics for Methaforming. First, the yields including net fuel gas, then CO2 credits, followed by other operating expenses, and finally, the estimated Capex is $20 million. Then, the bottom row shows the total 20-year net present value (NPV) for a Methaformer

- The third column shows the same values for an existing naphtha hydrotreater plus a semi-regen reformer without isomerisation

- The last column shows the difference between Methaforming versus this alternative. The Methaformer has $31 million/year better yields plus an additional $22 million/year for a reduction in CO2 emissions (valued at $50/t) when using ethanol/ethylene as the co-feed

- The fixed and variable Opex is $10 million/year lower because of less equipment. The lower fuel gas requirements are incorporated into the yields. Finally, the Capex for the conversion to Methaforming is approximately $20 million. This gives an NPV difference of $400 million.

The CO2 emissions reductions occur to the extent ethanol or ethylene are used as a co-feed. When ethylene is used as the co-feed, the process is called Aroforming. For a Methaformer/Aroformer, the co-feed is 15-50% of the naphtha quantity and can be any mix of light alcohol or light olefins. To what extent ethylene is the co-feed, there are added economic benefits, as highlighted in Table 3. Aroforming a full-range naphtha with ethylene from FCC dry gas shows a large net margin at $247/t of naphtha based on US Gulf Coast long-range prices. The naphtha is co-processed with 0.27t of ethylene, priced at its fuel gas value. Aroformate yield is 92% at 90.3 RON, and LPG/C4 yield is 34%.

To what extent ethylene is the co-feed, the yield economics are improved by $100/t of naphtha. For a refinery with a 50K BPD FCC, this added benefit is worth $10 million/year.

The Methaforming catalyst and process were developed and operating parameters optimised in three pilot plants with over 7,000 hours of processing. A fourth pilot plant, started up in 2019, has a 9 litre, three-stage reactor and capacity of a 320 l/d (2 BPD). It has confirmed the yields from the 100ml pilot plant, which has been used for 300 pilot plant tests on 50 different naphthas.