Post-combustion CO 2 Capture with Amino-Acid Salts

Abstract

Conventional amine-based solvents used for post-combustion CO2 capture suffer from several common drawbacks. The most serious is the prohibitive energy consumed by solvent regeneration. Others include the additional process complexity needed to address solvent volatility, as well as dealing with oxidative and thermal degradation. Salts of amino acids have been used for acid gas removal since the 1930s, mostly in Europe and especially in Germany for applications including refinery, natural gas and coke oven gas. These early solvents used the potassium salts of N,N-dimethylaminoacetic acid and N-methylalanine, the so-called ALKAZID® solvents developed by I. G. Farbenindustrie in the early 1930s. Within the last five years, interest has developed in using the sodium or potassium salt of glycine (NaGly), the simplest primary amino acid, for CO2 capture. Another proposal (Wagner et al., 2009) is to use the potassium salt of a tertiary amino acid such as dimethylglycine (KDiMGly), promoted with a conventional alkanolamine such as monoethanolamine (MEA). Sufficient kinetic and equilibrium data have been recently published to permit the detailed simulation of a CO2 capture plant using sodium glycinate (NaGly). Public-domain data have been available for Alkazid DIK since at least 1979. NaGly and KDiMGly have recently been implemented within ProTreat™, a well-established mass transfer rate-based gas treating process simulator. This paper benchmarks the performance of a conventionally configured 3,000 tonne/day CO2 capture plant using NaGly, MEA-promoted KDiMGly and piperazine-promoted KDiMGly against the standard, 30 wt% MEA. Piperazine-promoted MDEA is also considered. The results are striking—the regeneration energy required with piperazine-promoted KDiMGly appears to be about 20% lower that for MEA in an identical plant. Furthermore, solvent rates are lower by about 20%. Combined with a neutralized amino acid’s complete lack of volatility and its natural resistance to oxidation and thermal degradation, this finding puts caustic- neutralized amino acids into a class of solvents of potential commercial interest. The paper provides a detailed explanation of how and why a process based on NaGly or piperazine- promoted KDiMGly is likely to perform well.