Optimal design of an integrated macroalgal-based biorefinery

CLAUDIO A. DELPINO; VANINA G. ESTRADA; MARIA SOLEDAD DIAZ

Dalian

Congreso; 3rd International Conference on Sustainable Chemical Product and Process Engineering; 2013

Dalian Univ. of Tech., China; Wayne State Univ., USA

The feasibility of fuel production, using macroalgae biomass as a raw material has been extensively discussed and reviewed. Especially, the fermentation of sugars obtained from such biomass to ethanol has   been   assesed,  with   several   processing   options   being   proposed.  A   key  differentiating   aspect   of macroalgae   biomass   as   a   source   of   polysaccharides,   which   can   be   directly   fermented   by   special organisms   in   a   simultaneous   saccharification   and   fermentation,   or   hydrolized   into   simple   sugars fermentable   by   well   known   ethanol   producing   organisms   such   as  Saccharomyces   cerevisiae  or Zymomonas mobilis, is the absence of lignin. Macroalgae have distinct characteristics which allows clasification in three groups. Those known as "brown" algae, in which polysaccharides are represented by storage molecules  like laminarin and mannitol, and alginates and cellulose, which conform the amorphous and fibrillar part of their cell wall, respectively; The so called "red" algae, in which the fermentable polysaccharides involve galactans (which are nowadays used for agar production) and could amount to higher ethanol yields due to their presence, and also cellulose.  A  biorefinery  scheme  is proposed  and  mathematically  modeled  based  on  published  data   and  efforts   from  other  sources .   The   proposed   biorefinery   main   route   includes   cultivation,   harvesting   and processing of macroalgae. Cultivation is to be carried out in  terrestrial  installations, which offer an easier and more precise control of the cultivation (when compared with sea­farms), with higher yields, at the expense of higher capital and operating costs.   Processing of macroalgal biomass includes both succesive  acid  and  enzymatic  hydrolisis  of  polysaccharides  and  their  posterior  fermentation, and an innovative process involving a genetically modified strain mentioned in [4], which would perform said simultaneous saccharification and fermentation of the alginate of brown seaweed.  We also allow for the production of agar, as it is a current high value product obtained from some seaweeds, and its a reference  to have into  account,  in  order  to  have  an  integrated  biorefinery  or an  energetically self­ sufficient agar production process. We formulate a mathematical model allowing for cost, energy and water  need  calculations.  The  model  also  includes  the  possibility  to  allow   for  several  macroalgae species  and  origins,  diverse  processing  routes,  and  several  products  and  by­products.  This  allows comparison of the different alternatives, and optimization of the economical and energetic performance of the process using mathematical programming techniques. The optimization framework   is specially useful  for  the  macroalgae  context,  where  the  integration  with  current  algal  high­value  products production facilities, or even the production of this high­value byproducts (i. e. agar) in the integrated biorefinery,  is  vital  for  the  process  economic  sustainability.  Numerical  results  provide  quantitative information  and  give  useful  insights  on  macroalgal­based  biorefineries, allowing for adaptations to local conditions.