267281 Production of Bio-Olefins: Tall-Oils and Waste Greases to Green Chemicals and Polymers

Monday, October 29, 2012: 1:50 PM
316 (Convention Center )
Kevin M. Van Geem1, Steven Pyl2, Thomas Dijkamns3, Jinto Anthonykutty4, Marie-Françoise Reyniers2, Ali Harlin5 and Guy Marin6, (1)Laboratory for Chemical Technology, Ghent University, Ghent, Belgium, (2)Univeristeit Gent, Zwijnaarde, Belgium, (3)Department of Chemical Technology, Ghent University, Ghent, Belgium, (4)VTT Technical Research Centre of Finland, Espoo, Finland, (5)VTT, Espoo, Finland, (6)Ghent university, Ghent, Belgium

There is an increasing trend of using bio-polyethylene and bio-polypropylene in Europe for making consumer goods. However there is currently very limited production capacity available for producing these base chemicals that are used in the polymerization processes. This contribution will give an overview of the presently available routes for the production of bio-ethylene and bio-propylene (bio-ethanol to olefins, methanol to olefins, hydrodeoxygenation of biomass followed by steam cracking, fast pyrolysis of biomass) and discuss advantages and disadvantages. The talk will be completed with results obtained from different pilot plant studies starting from tall-oil and waste fats and greases. In a first step these feedstocks are catalytically converted, in a second step  they are cracked towards olefins. The total light olefin yield (ethylene and propylene) that has been obtained is in all cases higher than with naphtha and is above 50 wt% depending on process conditions, pretreatment and the biomass origin. 

Crude tall oil is a viscous liquid obtained as a by-product of the Kraft process for wood pulp manufacture when pulping mainly coniferous trees. It can be fractionated into distilled tall oil (DTO) and tall oil fatty acids (TOFA). These fractions mainly contain long chain fatty acids. DTO also contains significant amounts of rosin acids, i.e. a mixture of organic acids such as abietic acid. Catalytic hydrodeoxygenation (HDO) of both DTO as well as TOFA removes the oxygen in these acids in the form of H2O, CO and CO2, producing highly paraffinic hydrocarbon liquids, i.e. HDO-TOFA and HDO-DTO respectively.

Similarly, catalytic hydrodeoxygenation of triglyceride based biomass (TGB), such as algae oils or low cost waste greases like poultry fat and yellow grease, also produces paraffinic liquids (HDO-TGB) that are attractive feedstocks for conventional steam crackers.

The detailed composition of the studied feedstocks was determined using GC×GC-FID/TOF-MS. In Figure 1 the group-type compositions of the hydrodexygenated oils are presented as well as the composition of a typical petroleum-derived naphtha, i.e. currently the main steam cracker feedstock. Compared to this naphtha, the HDO-TGB contains high amounts of n-paraffins in a significantly higher carbon range, i.e. C14-C24 for the HDO-TGB versus C3-C13 for the naphtha. Only small amounts of naphthenes and no more than traces of aromatics were detected in the HDO-TGB. Also the HDO-TOFA and HDO-DTO feeds are highly n-paraffinic mixtures (C14-C24). The rosin acids present in the untreated TOFA and DTO fractions result in significant amounts of tricyclic naphthenes, such as norabietane (C19), and aromatics, such as norabietatriene (C19). In both fractions also some fatty acids methyl esters (FAME) were measured.

Description: U:\conferenties\aiche\AIChE-2012\Production of bioethylene-alternatives for green chemicals and polymers_files\image001.pngDescription: U:\conferenties\aiche\AIChE-2012\Production of bioethylene-alternatives for green chemicals and polymers_files\image002.png

Description: U:\conferenties\aiche\AIChE-2012\Production of bioethylene-alternatives for green chemicals and polymers_files\image003.pngDescription: U:\conferenties\aiche\AIChE-2012\Production of bioethylene-alternatives for green chemicals and polymers_files\image004.png

Figure 1: Group-type composition of (a) reference petroleum naphtha (C3-C13), (b) HDO-TGB (C14-C24), (c) HDO-TOFA (C14-C24) and (d) HDO-DTO (C14-C24)

The combination of detailed feedstock analyses and pilot plant data allows validation of the mechanistic model describing the radical reactions of the feedstock molecules. Table 1 compares the measured and simulated yields of some important products.

Table 1: Comparison of experimental and simulated product yields [d = 0.45 kg/kg; τ = 0.3 s, COP = 1.7 bar, COT = 820 °C]

Feed

Naphtha

HDO-TGB

HDO-TOFA

 

Exp.

Sim.

Exp.

Sim.

Exp.

Sim.

Methane

12.7

12.4

9.81

9.48

10.4

9.42

Ethylene

25.9

25.7

36.0

35.5

35.4

33.6

Propylene

17.8

17.9

19.5

20.4

17.5

19.5

1-Butene

2.37

2.81

4.18

4.34

2.20

3.73

1.3-Butadiene

4.72

5.03

7.45

6.51

4.51

6.25

Benzene

4.48

3.32

4.16

5.35

4.45

6.54

Toluene

2.14

1.56

1.29

1.27

1.42

1.83

For the naphtha, the model performance is quite exceptional. Not surprisingly, since the model was optimized based on an extensive set of pilot plant data, mainly comprising experiments with gaseous and naphtha feedstocks. Nevertheless, the model performance is more than adequate for both HDO-TGB and HDO-TOFA. This, after inclusion of retro-ene decompositions for long-chain olefins which proved to be necessary to accurately model the measured product distribution of these highly paraffinic feeds.

As discussed above, the HDO-TOFA also contains a small amount of FAME. Since the SEMK model currently does not contain any esters, these components were represented by n-paraffins. This can explain the somewhat larger discrepancies between measured and simulated yields for this feedstock. However, including the decomposition of esters to the SEMK model should result in more accurate predictions.

 


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