The invention relates to an integrated process for the production of 5-hydroxymethyl furfural (HMF), K2SO4, levulinic acid and formic acid from κ-carrageenan, the latter being obtained from fresh Kappaphycus alvarezii seaweed biomass after expelling the juice. Mg(HSO4)2 was used in HMF synthesis, with co-production of galactose. The aqueous stream after HMF extraction was treated with the seaweed juice which process facilitated recovery of K2SO4 in pure form. The galactose may be utilised for synthesis of levulinic acid and formic acid before or after K2SO4 recovery or, alternatively, utilised for other purposes. Catalysts required in the synthetic reactions are generated in the process itself while the process energy required is met out of additional supplies of the seaweed biomass which is subjected to combustion/gasification.