Biobutanol Recovery Using Dual Extraction Process

The purpose of this thesis was to present two novel processes for the recovery of butanol from dilute aqueous mixtures. One of these processes, the Dual Extraction (DE) method, enables the usage of non-biocompatible, but very effective solvents in extraction. Traditionally these slightly water soluble components have not been applicable as they would kill or strongly inhibit the production microbes. The DE process works by applying an additional extraction after the main extraction. The main function of this is to remove the non-biocompatible component from the broth, thus making it safe to recycle the fermentation broth back to the fermenter. It was found that alcohols are the best solvents for the main extraction, because of their high extraction capacities. These solvents are not biocompatible, but they can be very effective extractants for ABE, meaning that smaller amounts of solvent and thus smaller equipment can be used. This also means lowered energy consumption. With DE process, energy consumption of only 4 MJ kg-1 butanol was achieved, which is the lowest value reported in literature, and close to the acknowledged target which is 10% of the lower heating value of butanol (3.3 MJ kg-1 butanol). The best option for the second solvent was found to be alkanes. These have very limited extraction efficiency towards ABE, but they are very effective in the extraction of the first solvent and they are biocompatible. On the other hand, other extraction solvents can also be used in the DE process. For example gasoline oxygenates; MTBE, ETBE, TAME and TAEE could be used in conjunction with isooctane to extract biobutanol from the broth. When using these as extraction solvents, the product mixture could be used directly as a gasoline additive without any expensive and energy consuming unit operations. In addition to DE, also another process was developed for the same purpose. In this process all the extraction solvents are produced from the fermentation products, thus eliminating the need to purchase any make-up solvents. This was called the Reactive Distillation (RD) process, and the extraction solvent this process produces is a mixture of esters. When compared with DE, the preliminary cost estimations indicated that these processes would require practically identical investment cost. However, when compared with DE, the energy consumption of the RD process was found to be over two and a half times as large. When the cost of the needed make-up solvent in the DE process was taken into account, the operating costs of the RD process became twice as large. Also, the sales revenue and therefore the profitability of the DE process was found to be higher, making the DE process more economical option of these two. However, this does not mean that by using DE process, the ABE fermentation would automatically become profitable. This is just one step in the right direction.; Taman tyon tarkoituksena oli esitella kaksi uutta prosessia butanolin talteenottamiseksi laimeista liuoksista. Toinen naista oli kaksoisuutto- eli Dual…