Decarbonisation Technology May 2022 Issue

GC-1

To GFU

Fuel gas

AC-1

AC-2

S-1

LPG

S-1

P-3

Water

HE-1

F-1

Water

Naphtha

HE-4

P-1

P-4

HE-2

R-1

R-2

Steam

Ethanol

P-2

Condensate water

Air Nitrogen

HE-3

F-2

AC-3

Methaformate

To atmosphere

GC-2

AC-4

S-2

Water

Figure 3 Methaforming process flow

the Methaformer would be able to upgrade the ethylene from the FCC dry gas. Details of the process chemistry Naphthas from different sources vary greatly in their hydrocarbon composition and, therefore, in the ease of conversion in isomerisation and reforming, and Methaforming. Methaforming will convert most normal paraffins, naphthenes, and olefins to isoparaffins and aromatics. Numerous chemical reactions occur during the Methaforming process, some of which are highlighted here. Upon contact with the catalyst, alcohol converts to a corresponding alkyl radical in a highly exothermic reaction of alcohol dehydration. The heat of this reaction supports the subsequent endothermic dehydrogenation of naphthenes (see Figure 3 ; for simplicity, shown with methanol co-feed). The occurrence of the endo- and exothermic reactions in the same vessel translates into a significant economic and environmental advantage of Methaforming over the traditional methods of naphtha processing due to the reduced reheat duty. For example, with the full-range naphtha plus ethanol feed combination, the need for fuel gas in Methaforming is about one-fifth of the corresponding amount for traditional reforming. The water formed from alcohol dehydration becomes steam that reduces coke formation on

the catalyst, ensuring a longer catalyst cycle. The catalyst is a specially treated zeolite that is resistant to degradation from the steam. The typical run length between regeneration is one month, so two reactors are provided for continuous operation. The alkyl radical from alcohol dehydration can alkylate aromatic groups, for example converting most of the benzene to toluene, xylene, and C 9 aromatics, or react with itself to make longer-chain radicals, further converted to higher olefins and aromatics. The content of fused-ring aromatics (for example, naphthalene) in the product remains <0.5%. Olefins in the feedstock follow a conversion pathway similar to that for alcohol. Newly formed aromatics can be further alkylated; paraffins and naphthenes can be further converted to isoparaffins and aromatics. Every step in the pathways is an equilibrium reaction, and hence the products of the conversion process will depend on process parameters. Methaforming process flow Heating and vaporisation of naphtha and alcohol are performed sequentially in the heat exchanger HE-1 and furnace F-1. After heating to 360-430°C (680-806°F), the gaseous feed mixture is fed into reactor R-1 or R-2, which operate alternately (~800 hr on feed